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- Front Matter: Volume 10464
- AOPC 2017: Fiber Optic Sensing and Optical Communications
Front Matter: Volume 10464
Front Matter: Volume 10464
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This PDF file contains the front matter associated with SPIE Proceedings Volume 10464 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
AOPC 2017: Fiber Optic Sensing and Optical Communications
Influence of optical dome for airborne laser communication beam far-field divergence
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When the center of the dome inner and outer concentric spherical surfaces and the gimbal joint of the airborne laser communication antenna are not coincidence, the influence of asymmetry dome to communication beam far-field divergence angle for different transmitting angles is analyzed. The simulations shows that, at a maximum off-axis transmitting angle 54°, a K9 spherical dome with a 200mm diameter and 5mm thickness makes the communication beam far-field divergence angle expands to 5.27~6.46mrad from 126μrad. The divergence angle variation purely introduced by the dome manufacturing precision is very tiny, and can be ignored compared the variation introduced by the dome optical power. A lens with spherical surfaces is used to compensate the far-field divergence angle change, and after the compensation the far-field divergence angle of the beam on the whole range of transmitting angles is reduced to no more than 600μrad.
Research on the novel FBG detection system for temperature and strain field distribution
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In order to collect the information of temperature and strain field distribution information, the novel FBG detection system was designed. The system applied linear chirped FBG structure for large bandwidth. The structure of novel FBG cover was designed as a linear change in thickness, in order to have a different response at different locations. It can obtain the temperature and strain field distribution information by reflection spectrum simultaneously. The structure of novel FBG cover was designed, and its theoretical function is calculated. Its solution is derived for strain field distribution. By simulation analysis the change trend of temperature and strain field distribution were analyzed in the conditions of different strain strength and action position, the strain field distribution can be resolved. The FOB100 series equipment was used to test the temperature in experiment, and The JSM-A10 series equipment was used to test the strain field distribution in experiment. The average error of experimental results was better than 1.1% for temperature, and the average error of experimental results was better than 1.3% for strain. There were individual errors when the strain was small in test data. It is feasibility by theoretical analysis, simulation calculation and experiment, and it is very suitable for application practice.
A high spatial resolution distributed optical fiber grating sensing system based on OFDR
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A distributed optical fiber grating sensing system with large capacity and high spatial resolution is presented. Since highdensity identical weak grating array was utilized as sensing fiber, the multiplexing number was greatly increased, meanwhile, optical frequency domain reflectometry (OFDR) technology was used to implement high resolution distributed sensing system. In order to eliminate the nonlinear effect of tunable light source, a windowed FFT algorithm based on cubic spline interpolation was applied. The feasibility of the algorithm was experimentally testified, ultimately, the spatial resolution of system can reach mm-level. The influence of the crosstalk signal in the grating array on the OFDR system was analyzed. A method that a long enough delay fiber was added before the first FBG to remove crosstalk signal was proposed. The experiment was verified using an optical fiber with 113 uniform Bragg gratings at an interval of 10cm whose reflectivity are less than 1%. It demonstrates that crosstalk signal and measurement signal can be completely separated in the distance domain after adding a long enough delay fiber. Finally, the temperature experiment of distributed grating sensing system was carried out. The results display that each raster’s center wavelength in the fiber link is independent of each other and the center wavelength drift has a good linear relationship with the temperature. The sensitivity of linear fitting is equal to 11.1pm/°C.
Perturbation theory and the longitudinal relaxation time T1 measurement for spin exchange optical polarized 129Xe
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Spin exchange optical pumping is an efficient technique to obtain large quantities of hyperpolarized 129Xe nuclei. The spin oscillating perturbation theory for spin exchange optical polarized 129Xe nuclei is established in this paper. The theoretical framework relies on the perturbation method of the steady state solution to derive the rate equations and analytical solutions of 129Xe nuclear spin. This model gives rise to a novel fast determination of longitudinal relaxation time T1 for the hyperpolarized 129Xe nuclei. This direct measurement method is applied to the 129Xe in the gas phase and reduces the time consuming than the conventional inversion-recovery method. The method exhibits potential role in the development of the samples with long longitudinal relaxation time.
Three layers multi-granularity OCDM switching system based on learning-stateful PCE
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In the existing three layers multi-granularity OCDM switching system (TLMG-OCDMSS), F-LSP, L-LSP and OC-LSP can be bundled as switching granularity. For CPU-intensive network, the node not only needs to compute the path but also needs to bundle the switching granularity so that the load of single node is heavy. The node will paralyze when the traffic of the node is too heavy, which will impact the performance of the whole network seriously. The introduction of stateful PCE(S-PCE) will effectively solve these problems. PCE is composed of two parts, namely, the path computation element and the database (TED and LSPDB), and returns the result of path computation to PCC (path computation clients) after PCC sends the path computation request to it. In this way, the pressure of the distributed path computation in each node is reduced. In this paper, we propose the concept of Learning PCE (L-PCE), which uses the existing LSPDB as the data source of PCE’s learning. By this means, we can simplify the path computation and reduce the network delay, as a result, improving the performance of network.
Nonlinear optical response of a new Si-Ge waveguides with mid-infrared using femtosecond optical pulses
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We describe the nonlinear optical response of low-loss Si0.6Ge0.4/Si waveguides in the mid-IR between 3.3 μm and 4 μm using femtosecond long pulses. Furthermore, we estimate the three-photon and four-photon absorption coefficients together with the nonlinear refractive index of Si0.6Ge0.4/Si waveguides, which are found to be comparable to previous work on the same material but with different waveguide length and geometries, and with longer optical pulses. Therefore, this work corroborates the previous measurements and thus provides some guidelines for future nonlinear device work. Using the estimated coefficients, the nonlinear FOM of Si0.6Ge0.4/Si waveguides in the mid-infrared(mid-IR) is evaluated. An optimum FOM is observed around 4 μm due to the decrease of the three-photon absorption coefficient, together with a small four-photon absorption coefficient. We find that this optimum of the FOM also depends on the coupled peak intensity since the three and four-photon absorption scales differently with this parameter. Finally, we compare the impact of free carrier absorption at mid-infrared wavelengths versus near-infrared (near-IR) wavelengths for these femtosecond long pulses, and highlights the need to accurately account for free carrier effects even when using ultrashort optical pulses in the mid-IR. This work provides useful groundwork for the design of photonic devices such as supercontinuum sources based on this material platform.
Refractive index and curvature sensitivity of LPFG inscribed in few-modes fiber
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A novel long period fiber grating (LPFG) is inscribed in few-mode fibers(FMFs) by CO2 laser-irradiation method. The experiment results and theoretical calculation demonstrate that the LPFGs are originated from the strong coupling between the high-order core mode LP02 and the LP04 cladding mode. The resonant wavelengths of the LPFGs is found to shift toward the lower wavelength with refractive index(RI) of surrounding or curvature increasing. For comparision, LPFGs that coupling fundamental core mode to the same cladding mode are inscribed in single-mode fibers(SMFs) by the same method. The LPFGs inscribed in FMFs have higher RI sensitivity and slight lower curvature sensitivity comparing with LPFGs inscribed in SMFs.
Information hiding technology and application analysis based on decimal expansion of irrational numbers
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In this paper, an information hiding method using decimal expansion of irrational numbers to generate random phase mask is proposed. Firstly, the decimal expansion parts of irrational numbers generate pseudo-random sequences using a new coding schemed, the irrational number and start and end bit numbers were used as keys in image information hiding. Secondly, we apply the coding schemed to the double phase encoding system, the pseudo-random sequences are taken to generate random phase masks. The mean square error is used to calculate the quality of the recovered image information. Finally, two tests had been carried out to verify the security of our method; the experimental results demonstrate that the cipher image has such features, strong robustness, key sensitivity, and resistance to brute force attack.
Research on performance of three-layer MG-OXC system based on MLAG and OCDM
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At present, as traffic volume which optical transport networks convey and species of traffic grooming methods increase rapidly, optical switching techniques are faced with a series of issues, such as more requests for the number of wavelengths and complicated structure management and implementation. This work introduces optical code switching based on wavelength switching, constructs the three layers multi-granularity optical cross connection (MG-OXC) system on the basis of optical code division multiplexing (OCDM) and presents a new traffic grooming algorithm. The proposed architecture can improve the flexibility of traffic grooming, reduce the amount of used wavelengths and save the number of consumed ports, hence, it can simplify routing device and enhance the performance of the system significantly. Through analyzing the network model of switching structure on multicast layered auxiliary graph (MLAG) and the establishment of traffic grooming links, and the simulation of blocking probability and throughput, this paper shows the excellent performance of this mentioned architecture.
Deduction of HiBi-PCF-LM interference spectrum equation with a independent probe and the influence of sensor length size
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Fiber Loop Mirror(FLM) sensing system has been widely studied in recent years, and High Birefringence Photonic Crystal Fiber (HiBi-PCF) has high birefringence, which is always the best choice for FLM sensing system(HiBi-PCF-LM). Currently, PCF is generally embedded in the fiber loop in most HiBi-PCF-LM sensing systems, and the sensor size is large. This sensing system can not be used for distributed remote measurement, and it is limited in the practical application. Therefore, HiBi-PCF-LM sensing system with an independent probe is proposed, and it provides the direction for the practical application of the FLM sensing system. However, there is no specific theoretical analysis of this sensing system in the existing research results. In order to further clarify its sensing mechanism and improve the application value of the sensing system, the interference spectrum equation are specifically deduced and the relationship between the period of interference spectrum and the length size of HiBi-PCF is discussed in this paper. It provides the theoretical basis for the practical and miniaturization of the FLM sensor.
Instrument for all-fiber structure measurement of ultra-low turbidity by using single photon detection technique
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An all-fiber structure detection system based on single photon detection technique(SPDT) has been developed to measure the ultra-low turbidity ofliquids. To assure the measurement accuracy,the total intensity of transmission light has been detected and quantified as number of photons by avalanche photodiode (APD) which has the advantage of high sensitivity.A fresh all-fiber structure optical fiber probe based on SPDT is applied in the system to reduce the volume and fluctuation of traditional transmission-light measurement system,in which the all-fiber structure probe is used to delivery and collection of transmission light.On the basis of Beer-Lambert (B-L) transmission law,a test system has been established and carried out a series of experiments.By combining B-Llaw with the principle of SPDT,a novel model for detecting turbidity has been proposed to explain the experimental results.The results have shown a well exponential relationship over the range of 0.01–1NTU (Nephelometric Turbidity Units).It also has showna good linear relationship with a resolution as high as 0.01NTUin the range of 0.01-0.09 NTU.When it is 1 secondofthe sampling time,the mean error of measurement result can be controlled within 5% of full scale.In addition,the new detection structure proposed in this paper, which makes the system more compact and more suitable in the small special space.
A compact fiber sensor based on the high birefringence polarization maintaining fiber for simultaneous strain and temperature measurement
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A compact high birefringence polarization maintaining fiber (PMF) sensor for simultaneous strain and temperature measurement is proposed. This sensor is a modal interferometer (MI) sensor which is composed of a segment of high birefringence polarization maintaining fiber. One side of the fiber is spliced to the pigtail of a polarization beam splitter (PBS) with core-offset and axes alignment, the other end is spliced to the standard single-mode fiber (SMF) with core alignment and forms a fiber bubble. In experiments, an optical switch and the PBS are used to generate two orthogonal linear polarized lights. When the two orthogonal linear polarized lights enter the sensing fiber respectively, two different interference spectra will be achieved and own different response to the strain and temperature. Using these properties, the sensor realizes the simultaneous strain and temperature measurement. For 0.01 nm wavelength resolution, the strain and temperature resolution of the sensor are 10 uε and 0.285°C, respectively.
Temperature sensitivity of LPFG inscribed in few modes fiber
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A LPFG with a period of 145μm has been successfully inscribed in the few modes fiber (FMF) by CO2 laser-irradition method. The mode coupling theory indicates that the first two resonant wavelengths of the LPFG attribute to the mode coupling between the core mode LP01 and the cladding modes LP0,21 and LP0,22. The third one is the result of the coupling between the higher-order core mode LP02 and cladding mode LP0,29 or LP0,30. These resonant wavelengths shift in different direction with the increasing temperature, and the experimental results show their temperature sensitivity are 66.54pm/°C,90.36pm/°,115.1pm/°, respectively
Three-tier multi-granularity switching system based on PCE
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With the growing demand for business communications, electrical signal processing optical path switching can’t meet the demand. The multi-granularity switch system that can improve node routing and switching capabilities came into being. In the traditional network, each node is responsible for calculating the path; synchronize the whole network state, which will increase the burden on the network, so the concept of path calculation element (PCE) is proposed. The PCE is responsible for routing and allocating resources in the network1. In the traditional band-switched optical network, the wavelength is used as the basic routing unit, resulting in relatively low wavelength utilization. Due to the limitation of wavelength continuity, the routing design of the band technology becomes complicated, which directly affects the utilization of the system. In this paper, optical code granularity is adopted. There is no continuity of the optical code, and the number of optical codes is more flexible than the wavelength. For the introduction of optical code switching, we propose a Code Group Routing Entity (CGRE) algorithm. In short, the combination of three-tier multi-granularity optical switching system and PCE can simplify the network structure, reduce the node load, and enhance the network scalability and survivability. Realize the intelligentization of optical network.
Changes of quantum state of polarization in coexistence scheme of quantum-classical signal
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State of polarization(SOP) of single photon is the information carrier of polarization encoding BB84 protocol. SOP of quantum must be interrupted when quantum key distribution(QKD) propagates with classical signal in the same fiber. Coexistence schemes of quantum-classical signal based on two-channel and four-channel have been built respectively on Optisystem in this paper. The influence on SOP of quantum signal in BB84 protocol from different classical optical signal channel has been analyzed and compared by Stokes vector method and Poincare sphere method. SOP of 100 photons in QKD have been simulated. The results show that more channels will increase the bit error rate of QKD, and this paper has described the SOP changes well in coexistence scheme of quantum-classical signal based on wavelength division multiplexing.
Study on the performance of quantum key distribution scheme with the single photon frequency up-conversion detector
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In order to improve the detection efficiency in QKD system, this paper has put forward a new quantum key distribution scheme based on the single photon frequency up-conversion detection technology and decoy-state BB84 protocol. A long wavelength pump light is adopted in single photon detector (SPD) to avoid the noise caused by spontaneous parametric down conversion (SPDC), thus an overall 28% detection efficiency is achieved which is five times of 4.5% in conventional InGaAs-based detectors. Moreover, the propagating distances has reached 90km and 150km with weak coherent pulse (WCP) and decoy weak coherent pulse (DWCP) respectively, which is 1.3 times and 1.05 times of the conventional InGaAs-based detectors of 70km and 140km.
Applications in bridge structure health monitoring using distributed fiber sensing
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In this paper, Brillouin Optical Time Domain Analysis (BOTDA) is proposed to solve the problem that the traditional point sensor is difficult to realize the comprehensive safety monitoring of bridges and so on. This technology not only breaks through the bottleneck of traditional monitoring point sensor, realize the distributed measurement of temperature and strain on a transmission path; can also be used for bridge and other structures of the damage identification, fracture positioning, settlement monitoring. The effectiveness and frontier of the technology are proved by comparing the test of the indoor model beam and the external field bridge, and the significance of the distributed optical fiber sensing technology to the monitoring of the important structure of the bridge is fully explained.
The design of a signal processing system for CCD star sensor
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The CCD star sensor is a kind of higher accuracy and more advanced technology of attitude sensitive equipment which observes fixed star as benchmark, and it is widely used on satellite attitude control system. It has many advantages which includes high precision, high sensitivity, no attitude accumulative error and so on. This paper describes how to design and develop a signal processing system (SPS) based on FPGA (Field Programmable Gate Array) for CCD star sensor. Above all, an integrated solution to a signal processing system is put forward briefly, which contains the design of system architecture and system function. Secondly, Some Key technologies of design and implementation are described in detail, which contain these designs of data stream, instructions stream, multi-clock data processing and triple modular redundancy (TMR). In practice, hardware and system tests have been carried out, and the results prove that the SPS is reliable and stable, and it has been used successfully in CCD start sensor.
Health monitoring of unmanned aerial vehicle based on optical fiber sensor array
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The unmanned aerial vehicle (UAV) in flight needs to face the complicated environment, especially to withstand harsh weather conditions, such as the temperature and pressure. Compared with conventional sensors, fiber Bragg grating (FBG) sensor has the advantages of small size, light weight, high reliability, high precision, anti-electromagnetic interference, long lift-span, moistureproof and good resistance to causticity. It’s easy to be embedded in composite structural components of UAVs. In the paper, over 1000 FBG sensors distribute regularly on a wide range of UAVs body, combining wavelength division multiplexing (WDM), time division multiplexing (TDM) and multichannel parallel architecture. WDM has the advantage of high spatial resolution. TDM has the advantage of large capacity and wide range. It is worthful to constitute a sensor network by different technologies. For the signal demodulation of FBG sensor array, WDM works by means of wavelength scanning light sources and F-P etalon. TDM adopts the technology of optical time-domain reflectometry. In order to demodulate efficiently, the most proper sensor multiplex number with some reflectivity is given by the curves fitting. Due to the regular array arrangement of FBG sensors on the UAVs, we can acquire the health state of UAVs in the form of 3D visualization. It is helpful to master the information of health status rapidly and give a real-time health evaluation.
A frequency-doubling microwave photonic phase shifter based on dual-polarization MZM
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A new microwave photonic phase shifter based on polarization modulation with capability of frequency doubling is proposed and analyzed in this paper. A +1st order sideband signal with a carrier signal and a -1st order sideband signal with a carrier signal are producted by a dual-polarization Mach-Zehnder modulator (DPol-MZM) instead of the conventional polarization modulator, which are then sent to a fiber Bragg grating (FBG) used as an optical filter to filter out 1st orthogonal sidebands signals. By adjusting the polarization direction of the polarizer and beating 1st orthogonal sidebands signals at a photodetector, a frequency-doubled microwave signal is generated and its phase is continuously tunable by tuning the polarization controller (PC2). Taking advantages of the ability of frequency doubling and using PC tune, the frequency tuning range can be wider and fully tuned over 360°. By theoretical analyses and simulated verifications, a wideband frequency-doubling microwave signal with full range phase shift is achieved.
A new quantum private comparison protocol
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For two participants to compare the equality of their private information without revealing them, a new quantum private protocol with the help of semi-honest third party TP is proposed. Different from previous protocols, the four particle |Wf⟩ state and the |χ+⟩ state are utilized in this protocol as the carriers of quantum information and form the entanglement swapping as basic principle. The simple measurement of quantum states and exclusive-or operation are only required to conduct in this protocol. What’s more, this protocol can compare two bits of two participants’ private information in every comparison time. Meanwhile, it needs no unitary operation to fulfill this protocol. This protocol is feasible and efficient to execute through these aspects. In the end, the security of this protocol is analyzed at great length from two kinds of attacks including the outside attack and the participant attack. And the analysis result shows that this protocol can withstand various kinds of attacks and be secure to perform efficiently.
Fiber optic refractive index sensor using optofluidic anti-resonant reflecting guidance
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An optofluidic anti-resonant reflecting guidance has been proposed and experimental demonstrated for the measurement of liquid refractive index. Two micro-channels were fabricated for the delivery of the liquid sample in the hollow core photonic crystal fiber by using femtosecond laser micromachining, serving as an inlet and outlet. The refractive index can be detected by using the resonant condition of the Fabry-Perot resonator, which is interrogated through the wavelength shift and of the lossy dip in the transmission spectrum. The experimental results show that the sensitivity of up to 1328 nm/RIU is achieved for the refractive index in the range from 1.345 to 1.363 RIU, respectively. The proposed sensor appears to have potential applications of precise measurement in chemistry, medicine, and biology.
Research of hydroelectric generating set low-frequency vibration monitoring system based on optical fiber sensing
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In order to satisfy hydroelectric generating set low-frequency vibration monitoring, the design of Passive low-frequency vibration monitoring system based on Optical fiber sensing in this paper. The hardware of the system adopts the passive optical fiber grating sensor and unbalanced-Michelson interferometer. The software system is used to programming by Labview software and finishing the control of system. The experiment show that this system has good performance on the standard vibration testing-platform and it meets system requirements. The frequency of the monitoring system can be as low as 0.2Hz and the resolution is 0.01Hz.
Performance analysis of spin-oscillator system based on Simulink
Xubo Liao,
Zhiguo Wang,
Shaomin Hu,
et al.
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The spin oscillator has been widely used in the field of frontier science, and it is of great significance to research its properties. The purpose of this paper is to analyze the noise performance of the spin oscillator system and discover the influence of the filter on the self-excited closed-loop system. We consider to set three noise points at My, Bz, Bx respectively. When SNRMy =104; SNRBz =107; SNRBx =104, we can meet the standard deviation accuracy at 0.1μHz. On this condition. The effect of the filter is discussed that the bandwidth is linearly related to the frequency offset. Besides, a scheme has been proposed to guarantee a high precision phase compensation tracking when the center frequency is changed.
A cost-effective and reliable method for Brillouin optical time domain analysis
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In this paper we propose a low-cost and stable configuration of Brillouin Optical Time Domain Analysis (BOTDA). Both pump and probe are generated by one single laser source for steady frequency beating. Polarization-maintaining modulators and amplifiers have been applied into the system in order to suppress the ground noise and to control the stability of the pump pulse. The probe is filtered and amplified to obtain the Stokes wave. The bias voltages of modulators are carefully controlled. We implement the prototype of interrogator by using this method and compare it with commercial products. The result shows that the long-term stability of the prototype is three times higher than that of commercial product.
Progress on single-frequency fiber lasers for sensing technology
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Single-frequency fiber lasers have been attracting extensive interest for the applications on fiber sensing over the past few years, because the high signal-to-noise ratio and narrow-linewidth facilitate the realization of long-distance and high-resolution sensing. In this paper, we reviewed the research progress on single-frequency fiber lasers for fiber sensing applications. Performance improvement in laser noise and linewidth has been addressed with the newly developed physical mechanisms.
Distributed FBG sensors apply in spacecraft health monitoring
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At present, Spacecraft manufacturing face with high adventure for its complicate structure, serious space environment and not maintained on orbit. When something wrong with spacecraft, monitoring its health state, supply health data in real time would assure quickly locate error and save more time to rescue it. For FBG sensor can distributed test several parameters such as temperature, strain, vibration and easily construct net. At same time, it has more advantages such as ant-radiate, anti-jamming, rodent-resistant and with long lifetime, which more fit for applying in space. In this paper, a spacecraft health monitor system based on FBG sensors is present, Firstly, spacecraft health monitor system and its development are introduced. Then a four channels FBG demodulator is design. At last, Temperature and strain detecting experiment is done. The result shows that the demodulator fully satisfied the need of spacecraft health monitor system.
Dual-wavelength single-frequency Erbium-doped ring fiber laser for high-resolution temperature and strain sensing
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We achieve a dual-wavelength single-frequency Erbium-doped ring fiber laser by using umpumped Erbium-doped fiber and polarization-maintained fiber Bragg grating. The maximum output power is 2.11 mW when the pump power is about 225 mW, corresponding to a slope efficiency of 1%. And the SNR is larger than 60 dB. The two lasing wavelengths of the dual-wavelength ring fiber laser are 1550.16 nm and 1550.54 nm, corresponding to the linewidths of 769 Hz and 673 Hz, respectively. Meanwhile, these two lasing wavelengths can be tuned from 1550.12 nm to 1550.52 nm and from 1550.49 nm to 1550.82 nm, respectively, when the temperature is verified from 15 °C to 55 °C. It can be used as a temperature sensor with a sensitivity about 0.01 nm/°C, which possesses a resolution about ∼4×10-6 °C through using optical heterodyne method. In addition, it can be used to realize high-resolution strain sensor by employing heterodyne method to measure the wavelength separation at the same time.
Ad hoc laser networks component technology for modular spacecraft
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Distributed reconfigurable satellite is a new kind of spacecraft system, which is based on a flexible platform of modularization and standardization. Based on the module data flow analysis of the spacecraft, this paper proposes a network component of ad hoc Laser networks architecture. Low speed control network with high speed load network of Microwave-Laser communication mode, no mesh network mode, to improve the flexibility of the network. Ad hoc Laser networks component technology was developed, and carried out the related performance testing and experiment. The results showed that ad hoc Laser networks components can meet the demand of future networking between the module of spacecraft.
Modeling and analysis of laser active interference optical path
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By using the geometrical optics and physical optics method, the models of wedge plate interference optical path, Michelson interferometer and Mach Zehnder interferometer thus three different active interference pattern are built. The optical path difference (OPD) launched by different interference patterns, fringe spacing and contrast expression have been derived. The results show that far field interference peak intensity of the wedge plate interference is small, so the detection distance is limited, Michelson interferometer with low contrast affects the performance of detection system, Mach Zehnder interferometer has greater advantages in peak intensity, the variable range of interference fringe spacing and contrast ratio. The results of this study are useful for the theoretical research and practical application of laser active interference detection.
A method for velocity signal reconstruction of AFDISAR/PDV based on crazy-climber algorithm
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The resolution of Continuous wavelet transformation (CWT) is different when the frequency is different. For this property, the time-frequency signal of coherent signal obtained by All Fiber Displacement Interferometer System for Any Reflector (AFDISAR) is extracted. Crazy-climber Algorithm is adopted to extract wavelet ridge while Velocity history curve of the measuring object is obtained. Numerical simulation is carried out. The reconstruction signal is completely consistent with the original signal, which verifies the accuracy of the algorithm. Vibration of loudspeaker and free end of Hopkinson incident bar under impact loading are measured by AFDISAR, and the measured coherent signals are processed. Velocity signals of loudspeaker and free end of Hopkinson incident bar are reconstructed respectively. Comparing with the theoretical calculation, the particle vibration arrival time difference error of the free end of Hopkinson incident bar is 2μs. It is indicated from the results that the algorithm is of high accuracy, and is of high adaptability to signals of different time-frequency feature. The algorithm overcomes the limitation of modulating the time window artificially according to the signal variation when adopting STFT, and is suitable for extracting signal measured by AFDISAR.
Long distance Φ-OTDR system based on Raman and EDFA synthetic amplification
Xiaozhong Tian,
Yuan Yu,
Meng Zhao M.D.,
et al.
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Comprehensive using of Raman amplifier and bi-directional Er-doped fiber amplifier (EDFA), a long distance (72.3 km) Φ-OTDR system is demonstrated. In this system, a LD laser (~500mw) with wavelength from 1420 nm to 1470 nm is used as both EDFA pump power and Raman pump power. Meanwhile, difference value of upper-envelope and lower-envelope of Rayleigh scattering trace is calculated to test the sensitivity of the system, the intrusion with SNR of 3.99 dB、8.59 dB at two test points of sensing fiber is extracted.
Off-resonance laser frequency stabilization method by Faraday rotation spectroscopy using acoustic-optic modulator
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We propose a far off-resonance laser frequency stabilization method that can accurately adjust the frequency lock points based on the Faraday rotation spectroscopy. The atomic magnetometer based on the spin-exchange relaxation-free (SERF) theory needs to stabilize the frequency of the probe laser on the detuning of several gigahertz (GHz) away from the resonance of the alkali metal atom, to reduce the absorption of the probe light by the alkali metal vapor cell. We propose a laser frequency stabilization method that can accurately adjust the frequency lock points using an acousto-optic modulator based on Faraday rotation spectroscopy. We reveal the principles of the method and simulate the new Faraday rotation spectra. Besides, we study the effect of the amount of frequency shift of the acousto - optic modulator and the temperature of the alkali metal vapor cell on the frequency lock points of the spectra, and give the formula for calculating the frequency point. Our proposed laser frequency stabilization method can stabilize the laser frequency on the detuning of several gigahertz (GHz) away from the resonance of the alkali metal atom and can adjust the frequency lock points quickly and accurately. This method can be used in atomic magnetometer, degenerate Raman sideband cooling (DRSC) and two photon excitation of Rydberg states.
Study of the technics of coating stripping and FBG writing on polyimide fiber
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Compared with ordinary optical fiber, polyimide fiber has the characteristics of high temperature resistance and high strength, which has important application in the field of optical fiber sensing. The common methods of polyimide coating stripping were introduced in this paper, including high temperature stripping, chemical stripping and arc ablation. In order to meet the requirements of FBG writing technology, a method using argon ion laser ablation coating was proposed. The method can precisely control the stripping length of the coating and completely does not affect the tensile strength of the optical fiber. According to the experiment, the fabrication process of polyimide FBG is stripping-hydrogen loadingwriting. Under the same conditions, 10 FBG samples were fabricated with good uniformity of wavelength bandwidth and reflectivity. UV laser ablation of polyimide coating has been proved to be a safe, reliable and efficient method.
A buried intrusion monitoring system based on high sensitivity optical fiber geophone
Shujuan Li,
Faxiang Zhang,
Xiaolei Zhang,
et al.
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A new intrusion monitoring system is designed, based on a high sensitivity fiber grating geophone and PGC interferometric demodulation. A kind of high sensitive fiber Bragg grating geophone is designed. The sensitivity of the geophone is analyzed by finite element software. The PGC interferometric demodulation algorithm is used to detect the wavelength of the geophone, to reduce the noise of the system and improve the signal-to-noise ratio. Invasive monitoring test was carried out, the personnel and vehicles invading signal were collected and analyzed. Test results show that the intrusion monitoring system based on fiber geophone can effectively identify remote intrusion, and has low false alarm rate.
The design of photoelectric signal processing system for a nuclear magnetic resonance gyroscope based on FPGA
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Navigation technology is crucial to the national defense and military, which can realize the measurement of orientation, positioning, attitude and speed for moving object. Inertial navigation is not only autonomous, real-time, continuous, hidden, undisturbed but also no time-limited and environment-limited. The gyroscope is the core component of the inertial navigation system, whose precision and size are the bottleneck of the performance. However, nuclear magnetic resonance gyroscope is characteristic of the advantage of high precision and small size. Nuclear magnetic resonance gyroscope can meet the urgent needs of high-tech weapons and equipment development of new generation. This paper mainly designs a set of photoelectric signal processing system for nuclear magnetic resonance gyroscope based on FPGA, which process and control the information of detecting laser .The photoelectric signal with high frequency carrier is demodulated by in-phase and quadrature demodulation method. Finally, the processing system of photoelectric signal can compensate the residual magnetism of the shielding barrel and provide the information of nuclear magnetic resonance gyroscope angular velocity.
Monitoring of bolt clamping force at high temperatures using metal-packaged regenerated fiber Bragg grating strain sensors
Yong-Kuo Huang,
Yun Tu,
Shan-Tung Tu
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Insufficient or excessive preload has been regarded as the main issue that may endanger the safety of bolted joints operated at high temperatures. A new technique for monitoring the bolt clamping force is thus proposed using metal-packaged regenerated fiber Bragg grating (RFBG) strain sensors spot-welded onto the bolt. The measurement of the clamping force in a bolted steel-steel joint subjected to thermal loading is conducted. The experimental results show that the bolt clamping force can be monitored by the metal-packaged RFBG strain sensor at high temperatures up to 500 °C. This technique provides a new possibility for structural health monitoring of bolted joints operated at high temperatures.
Orthogonal demodulation phase: shifting design of optical fiber hydrophone based on Hilbert transform
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Orthogonal demodulation, as an important part of the demodulation process of heterodyne interferometric optic fiber hydrophone signal, directly determines whether the demodulation system can demodulate the underwater acoustic signal without distortion. The phase shift operation of reference signal is the key step of orthogonal demodulation algorithm. In this paper, the influence of phase shift error on the distortion of underwater acoustic signal is introduced and analyzed by combining the interferometric optic fiber hydrophone demodulation system, the phase shift range of undistorted signal is obtained by simulation analysis. Hilbert algorithm is proposed and used for phase shift of reference signal, to improve the phase shift accuracy, and then enhance the performance of orthogonal demodulation. Using the actual system to verify, it is proved that the heterodyne demodulation of optic fiber hydrophone based on Hilbert algorithm can demodulate the characteristics of underwater acoustic signals without distortion.
A low noise photoelectric signal acquisition system applying in nuclear magnetic resonance gyroscope
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The nuclear magnetic resonance gyroscope serves as a new generation of strong support for the development of high-tech weapons, it solves the core problem that limits the development of the long-playing seamless navigation and positioning. In the NMR gyroscope, the output signal with atomic precession frequency is detected by the probe light, the final crucial photoelectric signal of the probe light directly decides the quality of the gyro signal. But the output signal has high sensitivity, resolution and measurement accuracy for the photoelectric detection system. In order to detect the measured signal better, this paper proposed a weak photoelectric signal rapid acquisition system, which has high SNR and the frequency of responded signal is up to 100 KHz to let the weak output signal with high frequency of the NMR gyroscope can be detected better.
An intrusion detection system based on fiber hydrophone
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This paper provides a new intrusion detection system based on fiber hydrophone, focusing beam forming figure positioning according to the near field and high precision sound source location algorithm which can accurately position the intrusion; obtaining its behavior path , obtaining the intrusion events related information such as speed form tracking intrusion trace; And analyze identification the detected intrusion behavior. If the monitor area is larger, the algorithm will take too much time once, and influence the system response time, for reduce the calculating time. This paper provides way that coarse location first, and then scanned for accuracy, so as to realize the intrusion events (such as car, etc.) the remote monitoring of positioning.
The system makes up the blank in process capture of the fiber optic intrusion detection technology, and improves the understanding of the invasion. Through the capture of the process of intrusion behavior, and the fusion detection of intrusion behavior itself, thus analysis, judgment, identification of the intrusion information can greatly reduce the rate of false positives, greatly improved the reliability and practicability of the perimeter security system.
Study of the characteristics about the digital holography with spherical and plane reference wave
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In order to design and optimize the optical system of digital holography, rebuild the object field with high quality, the characteristics of imaging system with spherical and plane reference wave are demonstrated respectively based on optical scalar diffraction theory. Based on the discrete Fresnel diffraction integral, recording and reconstruction of hologram with plane reference wave as well as the impact of CCD size and reconstructed distance on holographic imaging have been simulated with matlab. The simulation results show that: zero-order image and twin images are spatially separated when choosing the parameters of recording system properly; the quality of rebuild image suffers as CCD decreases in size and the reconstruction distance deviates from the recording distance.
Study of LED layout in indoor visible light communication and performance analysis
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Light emitting diodes(LED) could provide both illumination and data communication in indoor visible light communication(VLC) that owns the modulation bandwith from several from several MHz to seneral hundreds of MHz. The layout of LED plays an important role in maintaining a steady optical power distribution over the receiving plane. The existing rectangular LED layout does not provide a full coverage on the receiving plane leaving receiving optical power outage area, which in turn affects the best performance of the VLC system. This paper design a circular layout scheme of LED in 5mX5mX3m room based on the criterion of the illumination minimum mean square deviation. The influence of the distribution of the intensity of illumination with the radius of 1m and 1.5m,for including the wall reflection and not including the wall reflection, and make a comparison with rectangular LED layout of illumination distribution, when the number of LEDs with rectangular layout as same as circular layout. Including the number of LEDs are 4 and 16.For a specific simulation parameters as following:height of receiving plane is 0.85m,a single LEDs is composed of 60X60 LED chips, the parameters of a single chip is that transmitting power is 20mW,center luminous intensity is 0.73cd.semiangle at half power is 70deg.The parameters of concentrator is that photodiode area is 1cm2,photodiode responsivity is 0.4,field of view at the receiver is 85deg.Other parameters are that reflective index of concentrator is 1.5,reflectivity of wall is 0.8.Circular layout and rectangular layout are analyzed through simulation of the received optical power distribution, signal noise ratio distribution in non line of sight(including the wall reflection) and line of sight(not including the wall reflection),when the number of the LED is different. It is clear from the results that the received optical power distribution of non line of sight is better than line of sight, when the number of the LED are same, but the signal noise ratio distribution is decreased result of the reflection of the wall. It is found that the received optical power of circular layout is better than the received optical power distribution of rectangulr layout, and circular layout is a good solution that add the received optical power at the 4 corners of room, improve the system ability of communication, when making a contrast of rectangular lyout with circular layout,at the same time,the fluctuate of circular layout’s signal to noise ratio of is smller than rectangular layuot.The radius of circular layout or the location of rectangular layout is keeping, the received optical power of receiving plane is increased, by adding the number of LED,in the meantime, the interference between LED light source also increase. But the increase of the circular layout radius when the number of LED remain the same is helpful to reduce the inter symbol interference that work out between LED each other, enhance the system signal noise ratio. In this paper, the results of the reaearch provides a new idea for indoor visible light communication with non-standard room (Size of room is not 5mX5mX3m), at the same time, provides guiding significance for future setting up the indoor visible light communication links.
The variance of angle-of-arrival fluctuation of partially coherent Gaussian-Schell Model beam propagations in slant atmospheric turbulence
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The variance of angle-of-arrival fluctuation of the partially coherent Gaussian-Schell Model (GSM) beam propagations in the slant path, based on the extended Huygens-Fresnel principle and the model of atmospheric refraction index structural constant proposed by the international telecommunication union-radio (ITU-R), has been investigated under the modified Hill turbulence model. The expression of that has been obtained. Firstly, the effects of optical wavelength, the inner-and-outer scale of the turbulence and turbulence intensity on the variance of angle-of-arrival fluctuation have been analyzed by comparing with the partially coherent GSM beam and the completely coherent Gaussian beam. Secondly, the variance of angle-of-arrival fluctuation has been compared with the von Karman spectrum and the modified Hill spectrum under the partially coherent GSM beam. Finally, the effects of beam waist radius and partial coherence length on the variance of angle-of-arrival of the collimated (focused) beam have been analyzed under the modified Hill turbulence model. The results show that the influence of the variance of angle-of-arrival fluctuation for the inner scale effect is larger than that of the outer scale effect. The variance of angle-of-arrival fluctuation under the modified Hill spectrum is larger than that of the von Karman spectrum. The influence of the waist radius on the variance of angle-of-arrival for the collimated beam is less than focused the beam. This study will provide a necessary theoretical basis for the experiments of partially coherent GSM beam propagation through atmosphere turbulence.
Real time distributed temperature measurement of the gain fiber in all-fiber laser employing OFDR technology
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Thermal effect of the gain fiber is one of the main factors which limit the power improvement of high power fiber lasers. Using traditional temperature measurement methods, we can only obtain the surface temperature of fiber while the core temperature cannot be detected. In this paper, the temperature of the gain fiber core in all-fiber laser is measured by optical frequency domain reflectometry(OFDR). The fiber laser is operating at 1080nm and the wavelength of detecting light emitted by OFDR is approximately 1550nm. The different wavelength of the two lasers has ensured the proper operating of fiber laser without effecting the operating lasers at 1080nm. The maximum output power of the fiber laser is 58.95W and results show that OFDR is a practical way to monitor the temperature of fiber laser system.
Research on influence factors of flashing light source measurement
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The flashing light source is a kind of pulse light, has short duration. For the measurement of the light source, the response ability of the instrument to the light source parameters should be considered. Through experimental analysis of flashing light intensity and pulse width with the two instruments, the effect of stray light on the measurement of light intensity is studied. On the other hand, the effect of the response time of the detector on the measurement results is discussed. It has an important significance to accurately measure flashing light.
Effect of spherical nonuniform distribute magnetic field on FOG
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Using matrix optics and optical propagation theory, a model for bias errors of an optical fiber gyroscope (FOG) caused by the spherical nonuniform distribute magnetic field has been deduced. Based on the above model, the effect on the FOG caused by the nonuniform distribute magnetic field and common circuit board is also analyzed. Results indicate that, i) the nearer of distance between the center of magnetic field and the fiber loop, the bigger of the bias errors of FOG will be; ii) relationship between bias and magnetic field direction is a inclined sine; iii) outside of the loop, the bigger of the height H0, the smaller of the bias error will be; iv) inside of the loop, the bias error is independent on the height H0; v) the common circuit board which radiate intensity is very weak can also cause unstable and direction related of the FOG’s output. Abolve conclusions may be useful for understanding the effect of actual magnetic field.
Simultaneous measurement of temperature and strain based on all-fiber Fabry-Perot sensor
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An all-fiber Fabry-Perot (FP) interferometer (FPI) sensor which can simultaneously measure strain and temperature is proposed and experimentally demonstrated. The FPI sensor is composed of a cascaded-cavity structure with a hollow-core tube fiber cavity and a standard single-mode fiber (SMF) cavity. Different cross section areas and thermal-optic coefficients of the two cavities make them differently sensitive to temperature and strain. The individual interference spectrum based on the air cavity or silica cavity can be extracted by band-pass filtering the spectrum of the sensor in frequency domain. The temperature and strain sensitivity of each cavity are obtained by tracing the wavelength shifts of the interference spectra. Furthermore, the temperature-strain cross-talk is eliminated by solving a cofficient matrix equation composed by the temperature and strain sensitivities of the two FP cavities. The strain sensitivities of two FP cavities achieved are 1.173 nm/με and 1.86 nm/με. The temperature sensitivities of two FP cavities are 0.00574 nm/°C and 0.00549 nm/°C. The advantages of the proposed sensor including simultaneous measurement of temperature and strain, no temperature-strain cross-talk, simple fabrication, and all-fiber structure make it appropriate for the real sensing applications.
Adaptive elimination of optical fiber transmission noise in fiber ocean bottom seismic system
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In this paper, a pressure and acceleration insensitive reference Interferometer is used to obtain laser and public noise introduced by transmission fiber and laser. By using direct subtraction and adaptive filtering, this paper attempts to eliminate and estimation the transmission noise of sensing probe. This paper compares the noise suppression effect of four methods, including the direct subtraction (DS), the least mean square error adaptive elimination (LMS), the normalized least mean square error adaptive elimination (NLMS) and the least square (RLS) adaptive filtering. The experimental results show that the noise reduction effect of RLS and NLMS are almost the same, better than LMS and DS, which can reach 8dB (@100Hz). But considering the workload, RLS is not conducive to the real-time operating system. When it comes to the same treatment effect, the practicability of NLMS is higher than RLS. The noise reduction effect of LMS is slightly worse than that of RLS and NLMS, about 6dB (@100Hz), but its computational complexity is small, which is beneficial to the real time system implementation. It can also be seen that the DS method has the least amount of computational complexity, but the noise suppression effect is worse than that of the adaptive filter due to the difference of the noise amplitude between the RI and the SI, only 4dB (@100Hz) can be reached. The adaptive filter can basically eliminate the influence of the transmission noise, and the simulation signal of the sensor is kept intact.
Balloon-like singlemode-tapered multimode-singlemode fiber structure for refractive index sensing
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A novel high sensitivity refractive index sensor based on balloon-like singlemode-tapered multimode-singlemode (STMS) fiber structure has been proposed and experimentally demonstrated. Combining the tapering and bending endows the proposed sensor with large evanescent field, resulting in high sensitivity. Experimental results show that the proposed sensor has an average sensitivity of 1104.75 nm/RIU (RI Unit) in the range of 1.33-1.41 and a maximum sensitivity of 3374.50 nm/RIU at RI of 1.41.
Microwave photonic frequency downconverter based on single sideband modulation
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A microwave photonic frequency downconverter is proposed and experimentally demonstrated based on an integrated polarization division multiplexing dual-parallel Mach-Zehnder (PDM-DPMZM) modulator. The radio frequency (RF) and the local oscillator (LO) signals are feed to the modulator through two electrical 90° hybrid couplers, respectively. The carrier suppress single sideband (CS-SSB) modulation can be achieved by adjusting the DC biases of the modulator. Then an intermediate frequency (IF) signal can be obtained by beating. The microwave photonic frequency downconversion link based on PDM-DPMZM is built. The result shows that both optical carrier sideband suppression ratio and sideband suppression ratio are over 20dB, and the spurious-free dynamic range achieves 98.0 dB·Hz2/3. No extra mixing spurs interferes the interested IF signal owing to the CS-SSB modulation. Besides, the proposed method has good isolation between the RF signal and LO signal.
Field test investigation of high sensitivity fiber optic seismic geophone
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Seismic reflection, whose measured signal is the artificial seismic waves ,is the most effective method and widely used in the geophysical prospecting. And this method can be used for exploration of oil, gas and coal. When a seismic wave travelling through the Earth encounters an interface between two materials with different acoustic impedances, some of the wave energy will reflect off the interface and some will refract through the interface. At its most basic, the seismic reflection technique consists of generating seismic waves and measuring the time taken for the waves to travel from the source, reflect off an interface and be detected by an array of geophones at the surface. Compared to traditional geophones such as electric, magnetic, mechanical and gas geophone, optical fiber geophones have many advantages. Optical fiber geophones can achieve sensing and signal transmission simultaneously. With the development of fiber grating sensor technology, fiber bragg grating (FBG) is being applied in seismic exploration and draws more and more attention to its advantage of anti-electromagnetic interference, high sensitivity and insensitivity to meteorological conditions.
In this paper, we designed a high sensitivity geophone and tested its sensitivity, based on the theory of FBG sensing. The frequency response range is from 10 Hz to 100 Hz and the acceleration of the fiber optic seismic geophone is over 1000pm/g. sixteen-element fiber optic seismic geophone array system is presented and the field test is performed in Shengli oilfield of China. The field test shows that: (1) the fiber optic seismic geophone has a higher sensitivity than the traditional geophone between 1-100 Hz;(2) The low frequency reflection wave continuity of fiber Bragg grating geophone is better.
An interferometric fiber optic hydrophone with large upper limit of dynamic range
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Interferometric fiber optic hydrophone based on heterodyne detection is used to measure the missile dropping point in the sea. The signal caused by the missile dropping in the water will be too large to be detected, so it is necessary to boost the upper limit of dynamic range (ULODR) of fiber optic hydrophone. In this article we analysis the factors which influence the ULODR of fiber optic hydrophone based on heterodyne detection, the ULODR is decided by the sampling frequency fsam and the heterodyne frequency Δf. The sampling frequency and the heterodyne frequency should be satisfied with the Nyquist sampling theorem which fsam will be two times larger than Δf, in this condition the ULODR is depended on the heterodyne frequency. In order to enlarge the ULODR, the Nyquist sampling theorem was broken, and we proposed a fiber optic hydrophone which the heterodyne frequency is larger than the sampling frequency. Both the simulation and experiment were done in this paper, the consequences are similar: When the sampling frequency is 100kHz, the ULODR of large heterodyne frequency fiber optic hydrophone is 2.6 times larger than that of the small heterodyne frequency fiber optic hydrophone. As the heterodyne frequency is larger than the sampling frequency, the ULODR is depended on the sampling frequency. If the sampling frequency was set at 2MHz, the ULODR of fiber optic hydrophone based on heterodyne detection will be boosted to 1000rad at 1kHz, and this large heterodyne fiber optic hydrophone can be applied to locate the drop position of the missile in the sea.
Features extraction algorithm about typical railway perimeter intrusion event
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Research purposes: Optical fiber vibration sensing system has been widely used in the oil, gas, frontier defence, prison and power industries. But, there are few reports about the application in railway defence. That is because the surrounding environment is complicated and there are many challenges to be overcomed in the optical fiber vibration sensing system application. For example, how to eliminate the effects of vibration caused by train, the natural environments such as wind and rain and how to identify and classify the intrusion events. In order to solve these problems, the feature signals of these events should be extracted firstly. Research conclusions: (1) In optical fiber vibration sensing system based on Sagnac interferometer, the peak-to-peak value, peak-to-average ratio, standard deviation, zero-crossing rate, short-term energy and kurtosis may serve as feature signals. (2) The feature signals of resting state, climbing concrete fence, breaking barbed wire, knocking concrete fence and rainstorm have been extracted, which shows significant difference among each other. (3) The research conclusions can be used in the identification and classification of intrusion events.
A high sensitivity all-fiber temperature sensor based on SPS fiber structure-based Sagnac loop
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A high sensitivity and low cost all-fiber temperature sensor combined a single-mode-polarization maintaining-single-mode optical fiber (SPS) structure and a Sagnac loop is proposed and experimentally demonstrated. In this sensor, the SPS structure is reeled into a circle is inserted into a Sagnac loop. Experimental results show that the radius of the circle has significant influence on temperature sensitivity. The temperature sensitivity can reach up to 1.678nm/°C for the radius of 3cm.
Rayleigh scattering based distributed optical fiber sensing
Enbang Li
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Rayleigh scattering based distributed optical fiber sensing utilizes back-scattered light signals from the naturally existed impurities (scatters) in normal optical fibers, eliminating the need for introduction of other markers for achieving sensing purposes. Similar to fiber Bragg grating (FBG) sensing, the primary physical parameters which can be detected by Rayleigh scattering are strain and temperature with resolutions up to 1 με and 0.1°C respectively. Depending on the technique used for the signal processing, various spatial resolution and sensing distance can be achieved. Here we report a Rayleigh scattering based distributed optical fiber sensing system for strain and high temperature measurements. In the sensing system, optical time domain reflectometry is adopted for signal detection. The highest spatial resolution can be achieved is 20 microns with a sensing distance up to 30 meters, and the longest sensing distance can be 2 km. By using normal communications fibers as the sensing elements, continuously distributed strain sensing has been successfully demonstrated along three different planes of a balsa wood beam with different loading conditions. In the temperature sensing experiments, we have measured the temperature distributions in a tube furnace with the maximum temperature above 1000°C.
Research on temperature dependent mean wavelength stability of Erbium-doped fiber super fluorescent source for fiber optic gyroscopes
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Absorption and emission cross sections are the key parameters of the erbium-doped fiber super fluorescent source (EFSFS). They form the foundation of theoretical spectrum analysis including mean wavelength stability. In pervious works those parameters were usually determined by loss or gain spectra measurement with a broad band light source (BBS) and an optical spectrum analyzer (OSA). Though the absorption or emission cross sections all over the whole wavelength range can be acquired at the same time, the popular method suffers from low precision due to the crosstalk between different wavelengths transmitted in the fiber. As an improvement, in this paper the measurement was conducted based on a point-by-point wavelength sweep method with a tunable laser near 1550nm and a power meter. That provides the access to accurate simulation of the EFSFS spectrum, which reveals that the left peak around 1530nm of the single-pass backward (SPB) configuration has superior mean wavelength stability against temperature variation. Moreover, the performance can be further improved by a narrow optical filter. The mean wavelength shift range is suppressed to 1 part per million (ppm) when the bandwidth is under 2nm. Those conclusions are expected to be applied to design of EFSFS for the fiber optic gyroscope (FOG) in the future.
Design of fiber optic F-P cavity pressure sensor based on corrugated diaphragm
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To meet the need of the measurement in high temperature and high pressure in oil and gas well, an optical fiber extrinsic Fabry Perot(F-P) cavity pressure sensor based on corrugated diaphragm is developed. The measured medium is isolated from the fiber F-P cavity by corrugated diaphragm which can transmit pressure simultaneously. The probe of the sensor is fabricated by hydrogen and oxygen flame thermal bonding in high temperature technique, and the change of the senor’s cavity length is compensated in temperature changing with cascading fiber bragg grating, and the sensor has characteristics of large dynamic range, high resolution, high repeatability, long term operation stability and high temperature resistance. The pressure measuring range is 0~69MPa, the repeatability is 0.01% F·S, the hysteresis is less than 0.01% F·S, the long term stability is less than 0.02MPa/y, and the sensor can satisfy the requirement of the measurement in the oil and gas well.
Design of the flame detector based on pyroelectric infrared sensor
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As a fire detection device, flame detector has the advantages of short reaction time and long distance. Based on pyroelectric infrared sensor working principle, the passive pyroelectric infrared alarm system is designed, which is mainly used for safety of tunnel to detect whether fire occurred or not. Modelling and Simulation of the pyroelectric Detector Using Labview. An attempt was made to obtain a simple test platform of a pyroelectric detector which would make an excellent basis for the analysis of its dynamic behaviour. After many experiments, This system has sensitive response, high anti-interference ability and safe and reliable performance.
Towed solid fiber streamer research on acoustic property
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Towed seismic exploration is an important way to detect the geological structure of the seabed. The traditional application of the towing streamer in the marine seismic exploration is the liquid streamer. Because of the easy deformation of the cross section, the vibrations of the controller and mechanical towing equipment are transmitted to the hydrophone through the axial extensional wave. Solid streamer can reduce the flow noise and the influence of mechanical vibration, so it can greatly expand the operational weather window. In addition, compared with the present applied liquid fiber towed streamer, the solid fiber streamer does not have oil leakage problems, so its a more environmental friendly choice. Three kinds of fiber optic scalar hydrophone streamers have being made. They were filled with oil, gel and polyurethane. The sensitivity of fiber optic hydrophones were measured by standing wave tube method before and after filled. The acoustic properties of solid streamer are analyzed by means of comparison. The experimental results show that the solid fiber optic hydrophone streamer is feasible.
Degeneracy and splitting of defect modes in one-dimensional symmetric photonic crystal
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In this study, we focus on the analysis of one-dimensional photonic crystal with symmetric double defect. Using the transfer matrix method (TMM), the properties of defect modes including degeneracy and splitting, can be analyzed in detail. It is found that such properties are mainly depending on symmetry and spatial interval of defects. The results show that the degeneracy of defect modes occurs in two defects separate to each other. And defect modes split when two defects close to each other. The results have potential applications in photonic integration and fiber optic sensor.
An optical fiber expendable seawater temperature/depth profile sensor
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Marine expendable temperature/depth profiler (XBT) is a disposable measuring instrument which can obtain temperature/depth profile data quickly in large area waters and mainly used for marine surveys, scientific research, military application. The temperature measuring device is a thermistor in the conventional XBT probe (CXBT)and the depth data is only a calculated value by speed and time depth calculation formula which is not an accurate measurement result. Firstly, an optical fiber expendable temperature/depth sensor based on the FBG-LPG cascaded structure is proposed to solve the problems of the CXBT, namely the use of LPG and FBG were used to detect the water temperature and depth, respectively. Secondly, the fiber end reflective mirror is used to simplify optical cascade structure and optimize the system performance. Finally, the optical path is designed and optimized using the reflective optical fiber end mirror. The experimental results show that the sensitivity of temperature and depth sensing based on FBG-LPG cascade structure is about 0.0030C and 0.1%F.S. respectively, which can meet the requirements of the sea water temperature/depth observation. The reflectivity of reflection mirror is in the range from 48.8% to 72.5%, the resonant peak of FBG and LPG are reasonable and the whole spectrum are suitable for demodulation. Through research on the optical fiber XBT (FXBT), the direct measurement of deep-sea temperature/depth profile data can be obtained simultaneously, quickly and accurately. The FXBT is a new all-optical seawater temperature/depth sensor, which has important academic value and broad application prospect and is expected to replace the CXBT in the future.
The seam visual tracking method for large structures
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In this paper, a compact and flexible weld visual tracking method is proposed. Firstly, there was the interference between the visual device and the work-piece to be welded when visual tracking height cannot change. a kind of weld vision system with compact structure and tracking height is researched. Secondly, according to analyze the relative spatial pose between the camera, the laser and the work-piece to be welded and study with the theory of relative geometric imaging, The mathematical model between image feature parameters and three-dimensional trajectory of the assembly gap to be welded is established. Thirdly, the visual imaging parameters of line structured light are optimized by experiment of the weld structure of the weld. Fourth, the interference that line structure light will be scatters at the bright area of metal and the area of surface scratches will be bright is exited in the imaging. These disturbances seriously affect the computational efficiency. The algorithm based on the human eye visual attention mechanism is used to extract the weld characteristics efficiently and stably. Finally, in the experiment, It is verified that the compact and flexible weld tracking method has the tracking accuracy of 0.5mm in the tracking of large structural parts. It is a wide range of industrial application prospects.
Hybrid fiber optic interferometers for temperature and strain measurements
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The hybrid fiber optic interferometers are proposed and experimentally demonstrated. In our schemes, the hybrid fiber optic interferometers are constructed by single mode-multimode-polarization maintaining-single mode optical fiber (SMPS) structure and a Sagnac loop. The temperature and strain characteristics of the hybrid interferometers are studied in experiment, and the sensitivities depending on the length of polarization maintaining optical fiber (PMF) and multimode optical fiber (MMF) are detailedly investigated in experiment. The experimental results have demonstrated that the PMF and MMF lengths have low affect on the strain sensitivity but has great influence on the temperature sensitivity. The achieved strain sensitivity is 37.2pm/με for 10cm PMF and 12cm MMF. The achieved strain sensitivity is 38.0pm/με for 12cm PMF when the length of MMF is fixed at 15cm, and is 37.2 pm/με for 12cm MMF when the length of PMF is fixed at 10cm. The obtained temperature sensitivities is 1.723nm/°C when the length of MPF is 8cm with the fixed length of 15cm MMF, and the obtained temperature sensitivities reach 1.848nm/℃when the length of MMF is 12cm with the fixed length of 10cm PMF.
Fiber-optic dosimeters for radiation therapy
Enbang Li,
James Archer
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According to the figures provided by the World Health Organization, cancer is a leading cause of death worldwide, accounting for 8.8 million deaths in 2015. Radiation therapy, which uses x-rays to destroy or injure cancer cells, has become one of the most important modalities to treat the primary cancer or advanced cancer. The newly developed microbeam radiation therapy (MRT), which uses highly collimated, quasi-parallel arrays of x-ray microbeams (typically 50 μm wide and separated by 400 μm) produced by synchrotron sources, represents a new paradigm in radiotherapy and has shown great promise in pre-clinical studies on different animal models. Measurements of the absorbed dose distribution of microbeams are vitally important for clinical acceptance of MRT and for developing quality assurance systems for MRT, hence are a challenging and important task for radiation dosimetry. On the other hand, during the traditional LINAC based radiotherapy and breast cancer brachytherapy, skin dose measurements and treatment planning also require a high spatial resolution, tissue equivalent, on-line dosimeter that is both economical and highly reliable. Such a dosimeter currently does not exist and remains a challenge in the development of radiation dosimetry. High resolution, water equivalent, optical and passive x-ray dosimeters have been developed and constructed by using plastic scintillators and optical fibers. The dosimeters have peak edge-on spatial resolutions ranging from 50 to 500 microns in one dimension, with a 10 micron resolution dosimeter under development. The developed fiber-optic dosimeters have been test with both LINAC and synchrotron x-ray beams. This work demonstrates that water-equivalent and high spatial resolution radiation detection can be achieved with scintillators and optical fiber systems. Among other advantages, the developed fiber-optic probes are also passive, energy independent, and radiation hard.
Ultra-wideband microwave photonic link based on single-sideband modulation
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Comparing with the conventional double-sideband (DSB) modulation in communication system, single-sideband (SSB) modulation only demands half bandwidth of DSB in transmission. Two common ways are employed to implement SSB modulation by using optical filter (OF) or electrical 90° phase shift, respectively. However, the bandwidth of above methods is limited by characteristics of current OF and electrical phase shift. To overcome this problem, an ultra-wideband microwave photonic link based on SSB modulation is proposed and demonstrated. The radio frequency (RF) signal modulates a single-drive dual-parallel Mach-Zehnder modulator, and the SSB modulation is realized by combining an electrical 90° hybrid coupler and an optical bandpass filter. The experimental results indicate that the system can achieve SSB modulation for RF signal from 2 to 40 GHz. The proposed microwave photonic link provides an ultra-wideband approach based on SSB modulation for radio-over-fiber system.
Holding-time-aware asymmetric spectrum allocation in virtual optical networks
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Virtual optical networks (VONs) have been considered as a promising solution to support current high-capacity dynamic traffic and achieve rapid applications deployment. Since most of the network services (e.g., high-definition video service, cloud computing, distributed storage) in VONs are provisioned by dedicated data centers, needing different amount of bandwidth resources in both directions, the network traffic is mostly asymmetric. The common strategy, symmetric provisioning of traffic in optical networks, leads to a waste of spectrum resources in such traffic patterns. In this paper, we design a holding-time-aware asymmetric spectrum allocation module based on SDON architecture and an asymmetric spectrum allocation algorithm based on the module is proposed. For the purpose of reducing spectrum resources’ waste, the algorithm attempts to reallocate the idle unidirectional spectrum slots in VONs, which are generated due to the asymmetry of services’ bidirectional bandwidth. This part of resources can be exploited by other requests, such as short-time non-VON requests. We also introduce a two-dimensional asymmetric resource model for maintaining idle spectrum resources information of VON in spectrum and time domains. Moreover, a simulation is designed to evaluate the performance of the proposed algorithm, and results show that our proposed asymmetric spectrum allocation algorithm can improve the resource waste and reduce blocking probability.
A long distance voice transmission system based on the white light LED
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A long distance voice transmission system based on a visible light communication technology (VLCT) is proposed in the paper. Our proposed system includes transmitter, receiver and the voice signal processing of single chip microcomputer. In the compact-sized LED transmitter, we use on-off-keying and not-return-to-zero (OOK-NRZ) to easily realize high speed modulation, and then systematic complexity is reduced. A voice transmission system, which possesses the properties of the low-noise and wide modulation band, is achieved by the design of high efficiency receiving optical path and using filters to reduce noise from the surrounding light. To improve the speed of the signal processing, we use single chip microcomputer to code and decode voice signal. Furthermore, serial peripheral interface (SPI) is adopted to accurately transmit voice signal data. The test results of our proposed system show that the transmission distance of this system is more than100 meters with the maximum data rate of 1.5 Mbit/s and a SNR of 30dB. This system has many advantages, such as simple construction, low cost and strong practicality. Therefore, it has extensive application prospect in the fields of the emergency communication and indoor wireless communication, etc.
Research on propane leak detection system and device based on mid infrared laser
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Propane is a key component of liquefied petroleum gas (LPG) and crude oil volatile. This issue summarizes the recent progress of propane detection technology. Meanwhile, base on the development trend, our latest progress is also provided. We demonstrated a mid infrared propane sensor system, which is based on wavelength modulation spectroscopy (WMS) technique with a CW interband cascade laser (ICL) emitting at 3370.4nm. The ICL laser scanned over a sharp feature in the broader spectrum of propane, and harmonic signals are obtained by lock-in amplifier for gas concentration deduction. The surrounding gas is extracted into the fine optical absorption cell through the pump to realize online detection. The absorption cell is designed in mid infrared windows range. An example experimental setup is shown. The second harmonic signals 2f and first harmonic signals1f are obtained. We present the sensor performance test data including dynamic precision and temperature stability. The propane detection sensor system and device is portable can carried on the mobile inspection vehicle platforms or intelligent robot inspection platform to realize the leakage monitoring of whole oil gas tank area.
A temperature sensor based on Fresnel reflection on a collimator
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An optical sensor for temperature measurement with much higher reflected light power based on Fresnel reflection and a collimator is presented. The sensor includes only a light source, three couplers, two photodetectors and two sensing ends. One of the sensing ends is designed with a collimator which is covered by solidified epoxy resin with an oil-paper cover, and another is a fiber end with protective cladding. The measurement principle is based on relative Fresnel reflective intensity. Various ambient temperatures are measured in the experiment. The measured data is fitted to linear equation very well. Experiment is implemented by comparing the performances of the fiber-sensor and the collimator-sensor, and the latter shows a much higher reflected light power which means a high signal to noise ratio (SNR) and longer measurement distance may be gained. This is very important and useful for long distance measurement and the situation of many sensors working in parallel mode, which is sensitive to the reflected light power.
Effective distance adaptation traffic dispatching in software defined IP over optical network
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The rapid growth of IP traffic has contributed to the wide deployment of optical devices (ROADM/OXC, etc.). Meanwhile, with the emergence and application of high-performance network services such as ultra-high video transmission, people are increasingly becoming more and more particular about the quality of service (QoS) of network. However, the pass-band shape of WSSs which is utilized in the ROADM/OXC is not ideal, causing narrowing of spectrum. Spectral narrowing can lead to signal impairment. Therefore, guard-bands need to be inserted between adjacent paths. In order to minimize the bandwidth waste due to guard bands, we propose an effective distance-adaptation traffic dispatching algorithm in IP over optical network based on SDON architecture. We use virtualization technology to set up virtual resources direct links by extracting part of the resources on paths which meet certain specific constraints. We also assign different bandwidth to each IP request based on path length. There is no need for guard-bands between the adjacent paths on the virtual link, which can effectively reduce the number of guard-bands and save the spectrum.
Multi-domain service dispatching scheme based on SDON virtualized network
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With the information flow in the network growing rapidly and the size of network extending gradually, it is essential that SDON networking supports multi-domain optical services. Since the type of network has moved toward complicated and converged, the disparate network resource has interlaced, an isomerized network situation is the trend in the future. Accordingly, end-to-end (E2E) services have shifted from a single service provider domain towards a multi-domain service provider. On this condition, the traditional isolated networking mode is so difficult to meet the current demand. E2E multi-domain services are the trend in the future. This paper proposes a multi-domain service dispatching scheme based on SDON virtualized network. By sending concurrent http requests to controller multiple single-domain controllers, web service management will manage optical devices and achieve E2E multi-domain service requests over this scheme. The management layer establishes E2E services dispatching system in multi-domain virtual optical network and it changes the present situation of disparate single service provider incompatibility. The experiment also indicates the reality possibility of the multi-domain dispatching scheme. This scheme will provide basis for the large scale multi-domain networking based on SDON in the future.
A fiber Bragg grating acceleration sensor for ground surveillance
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Ground surveillance system is a kind of intelligent monitoring equipment for detecting and tracking the ground target. This paper presents a fiber Bragg grating (FBG) acceleration sensor for ground surveillance, which has the characteristics of no power supply, anti-electromagnetic interference, easy large-scale networking, and small size. Which make it able to achieve the advantage of the ground surveillance system while avoiding the shortcoming of the electric sensing. The sensor has a double cantilever beam structure with a sensitivity of 1000 pm/g. Field experiment has been carried out on a flood beach to examine the sensor performance. The result shows that the detection distance on the walking of personnel reaches 70m, and the detection distance on the ordinary motor vehicle reaches 200m. The performance of the FBG sensor can satisfy the actual needs of the ground surveillance system.
A multi-function and high precision submarine optical fiber monitor
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In this paper we study a multi-function and high precision submarine optical fiber monitorsystem. This design is based on the core technology of coherent optical time-domain reflectometry (COTDR) which is used for submarine optical fiber monitor. The design provides multi-functionwhich including: undersea amplifier gain monitor, output power monitor; undersea fiber events monitor (such as fiber cut, attenuation as well as reflection) and also the fiber fault location which may identify the accurate location of the failurepoint (distance from failure point to its upstream amplifier). With these functions, the designcan facilitate the staff to inquiry and debug, and it also improves the maintainability and operability of the undersea equipment.
Multi-layer service function chaining scheduling based on auxiliary graph in IP over optical network
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Software Defined Optical Network (SDON) can be considered as extension of Software Defined Network (SDN) in optical networks. SDON offers a unified control plane and makes optical network an intelligent transport network with dynamic flexibility and service adaptability. For this reason, a comprehensive optical transmission service, able to achieve service differentiation all the way down to the optical transport layer, can be provided to service function chaining (SFC). IP over optical network, as a promising networking architecture to interconnect data centers, is the most widely used scenarios of SFC. In this paper, we offer a flexible and dynamic resource allocation method for diverse SFC service requests in the IP over optical network. To do so, we firstly propose the concept of optical service function (OSF) and a multi-layer SFC model. OSF represents the comprehensive optical transmission service (e.g., multicast, low latency, quality of service, etc.), which can be achieved in multi-layer SFC model. OSF can also be considered as a special SF. Secondly, we design a resource allocation algorithm, which we call OSF-oriented optical service scheduling algorithm. It is able to address multi-layer SFC optical service scheduling and provide comprehensive optical transmission service, while meeting multiple optical transmission requirements (e.g., bandwidth, latency, availability). Moreover, the algorithm exploits the concept of Auxiliary Graph. Finally, we compare our algorithm with the Baseline algorithm in simulation. And simulation results show that our algorithm achieves superior performance than Baseline algorithm in low traffic load condition.
The routing, modulation level, and spectrum allocation algorithm in the virtual optical network mapping
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With the development of large video services and cloud computing, the network is increasingly in the form of services. In SDON, the SDN controller holds the underlying physical resource information, thus allocating the appropriate resources and bandwidth to the VON service. However, for some services that require extremely strict QoT (quality of transmission), the shortest distance path algorithm is often unable to meet the requirements because it does not take the link spectrum resources into account. And in accordance with the choice of the most unoccupied links, there may be more spectrum fragments. So here we propose a new RMLSA (the routing, modulation Level, and spectrum allocation) algorithm to reduce the blocking probability. The results show about 40% less blocking probability than the shortest-distance algorithm and the minimum usage of the spectrum priority algorithm. This algorithm is used to satisfy strict request of QoT for demands.
High resolution 3C fiber laser micro-seismic geophone array for cross-well seismic
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A two level 3-component distributed feed-back (DFB) fiber laser micro-seismic geophone array based on wavelength/space division multiplexing is developed. High resolution dynamic wavelength demodulation was realized with a coherent detection technology. The geophone array was tested in laboratory and showed that the detection capability of the weak vibration signals between 5-500 Hz was better than conventional moving-coil geophone. A cross-well test of the array was performed in a 100 m depth well in Changqing Oil Field in northwest China. The two level 3-component fiber laser micro-seismic geophone array was compared with the traditional in-well seismic geophone and showed better signal noise ratio (SNR) in the cross-well seismic signal acquisition. This 3C fiber laser micro-seismic geophone array system is promising in the cross-well seismic monitoring.
Transmission properties of defect mode in one-dimensional symmetry photonic crystal under one-way stress
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Using 4×4 transfer matrix method, we investigated the transmission properties of defect mode in one-dimensional photonic crystal. The system can be transformed to be biaxial photonic crystal under one-way stress. It is found that the transmission properties of defect mode are critically depending on the numbers of dielectric layers and degree of asymmetry. For the system without stress, in the case of system with mirror symmetry, the defect mode is appearing gradually and its peak wavelength always keeps stable with the numbers of dielectric layers increasing, and its corresponding transmittance will be sharply decrease from a constant to zero at the same time. In the case of asymmetry, the defect mode is appearing gradually and its peak wavelength still keeps stable with the asymmetric degree continuously growth. Meanwhile, its transmittance exist an evolution from increase to decrease in this progress, and the maximum transmittance can be obtained at Δm=0 . After applying a fixed one-way stress on the system, the single defect mode will be split into Left-side defect mode (LDM) and Right-side defect mode (RDM). In the case of system with mirror symmetry, the two defect modes are appearing gradually and their peak wavelength always keep constant with the numbers of dielectric layers increasing, respectively, and their corresponding transmittance decrease asynchronously from a constant to zero. In the case of asymmetry, the peak wavelengths of LDM and RDM are being a constant with the changing of asymmetric degree and their corresponding transmittance are synchronously increasing or decreasing with the continuously increasing of asymmetric degree. Particularly, the maximum transmittance of defect mode also can be obtained at Δm=0 . This study provided a theoretical guidance for the best choice of numbers of dielectric layers to design a pressure sensor.
Environmental and reliability test of FBG based geophone as geophysical exploration instrument
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A fiber Bragg grating (FBG) based geophone is designed for low-frequency signal detection has high acceleration response of about 60 dB re pm/g in a low frequency range of 5 Hz ~60 Hz. To Guarantee normal operation in field test and practical application, an acceleration amplitude restriction is added in the mechanical design of the FBG geophone. Then a series of environmental and reliability test have been proceeded with online or offline monitoring of its working performance, including high and low temperature test, vibration test, shock test and free drop test. All the tests are planned according to National standard or Oil & Gas Industry Standard. And the experimental results indicate that our FBG geophone meet the criterion of oil and gas industry product and is capable of field application.
Nonuniform distribution of phase noise in distributed acoustic sensing based on phase-sensitive OTDR
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A phase-sensitive optical time-domain reflectometry (∅-OTDR) implements distributed acoustic sensing (DAS) due to its ability for high sensitivity vibration measurement. Phase information of acoustic vibration events can be acquired by interrogation of the vibration-induced phase change between coherent Rayleigh scattering light from two points of the sensing fiber. And DAS can be realized when applying phase generated carrier (PGC) algorithm to the whole sensing fiber while the sensing fiber is transformed into a series of virtual sensing channels. Minimum detectable vibration of a ∅-OTDR is limited by phase noise level. In this paper, nonuniform distribution of phase noise of virtual sensing channels in a ∅-OTDR is investigated theoretically and experimentally. Correspondence between the intensity of Rayleigh scattering light and interference fading as well as polarization fading is analyzed considering inner interference of coherent Rayleigh light scattered from a multitude of scatters within pulse duration, and intensity noise related to the intensity of Rayleigh scattering light can be converted to phase noise while measuring vibration-induced phase change. Experiments are performed and the results confirm the predictions of the theoretical analysis. This study is essential for acquiring insight into nonuniformity of phase noise in DAS based on a ∅-OTDR, and would put forward some feasible methods to eliminate the effect of interference fading and polarization fading and optimize the minimum detectable vibration of a ∅-OTDR.
Numerical simulation of the photon absorption cross-section of 87Rb D1 line
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For realizing optimal performance, knowing the photon absorption cross-section of alkali atoms is significant in a wide range of fields, such as atomic clock, atomic magnetometer and atomic spin gyroscope. By analyzing the pressure broadening and shift, natural broadening and Doppler broadening of the absorption line of 87Rb D1 line, the numerical simulation of photon absorption cross-section of 87Rb D1 line is conducted. Based on the results of numerical simulation, natural broadening is found to be much smaller than pressure broadening and Doppler broadening in general. The pressure broadening becomes the dominant factor of broadening for high pressure of buffer and quenching gases, while the Doppler broadening is dominant for low pressure of buffer and quenching gases. The results of numerical simulation demonstrate that, with the increasing broadening of absorption line, the number of peaks of the photon absorption cross-section decreases from four to one gradually, and the amplitudes of these peaks decline in the meantime.
Walkaway-VSP survey using distributed optical fiber in China oilfield
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Distributed acoustic sensing (DAS) is a new type of replacement technology for geophysical geophone. DAS system is similar to high-density surface seismic geophone array. In the stage of acquisition, DAS can obtain the full well data with one shot. And it can provide enhanced vertical seismic profile (VSP) imaging and monitor fluids and pressures changes in the hydrocarbon production reservoir. Walkaway VSP data acquired over a former producing well in north eastern China provided a rich set of very high quality data. A standard VSP data pre-processing workflow was applied, followed by pre-stack Kirchhoff time migration. In the DAS pre-processing step we were faced with additional and special challenges: strong coherent noise due to cable slapping and ringing along the borehole casing. The single well DAS Walkaway VSP images provide a good result with higher vertical and lateral resolution than the surface seismic in the objective area. This paper reports on lessons learned in the handling of the wireline cable and subsequent special DAS data processing steps developed to remediate some of the practical wireline deployment issues. Optical wireline cable as a conveyance of fiber optic cables for VSP in vertical wells will open the use of the DAS system to much wider applications.
Fiber optic microphone with large dynamic range based on bi-fiber Fabry-Perot cavity
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In this paper, we report a fiber optic microphone with a large dynamic range. The probe of microphone consists of bi-fiber Fabry-Perot cavity architecture. The wavelength of the working laser is about 1552.05nm. At this wavelength, the interference spectroscopies of these two fiber Fabry-Perot cavities have a quadrature shift. So the outputs of these two fiber Fabry-Perot sensors are orthogonal signal. By using orthogonal signal demodulation method, this microphone can output a signal of acoustic wave. Due to no relationship between output signal and the linear region on interference spectroscopy, the microphones have a large maximum acoustic pressure above 125dB.
Fourier phase demodulation of interferometric fiber sensor
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A novel demodulation method for interferometric fiber sensor is proposed in this paper. The physical parameters to be measured by the sensor is obtained by calculating the phase variation of the interference components. The phase variation is computed with the assist of the fast Fourier analysis. For fiber interferometers, most of the energy is contained in the few spatial frequencies corresponding to the components that produce the interference. Therefore, the information of the interference fringe can be presented by the Fourier results at those intrinsic frequencies. Based on this assumption, we proposed a novel method to interrogate the fiber interferometer by calculating the Fourier phase at the spatial frequency. Theoretical derivation proves that the Fourier phase variation is equal to the phase change of the interferometer. Simulation results demonstrate the ability of noise resistance of the proposed method since the information of all wavelength sampling points are adopted for the demodulation process. A Sagnac interferometer based on a section of polarization-maintaining photonic crystal fiber is utilized to verify the feasibility of the phase demodulation technique by lateral pressure sensing. Experimental results of -0.069rad/kPa is acquired.
Wavelength-switched phase interrogator for EFPI sensors with polarization self-calibrated
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The stability of the demodulation system for extrinsic Fabry-Perot interferometric(EFPI) sensors is significant to dynamic signal recovery. In the wavelength-switched demodulation system, a phase interrogation with a wavelength-switched structure has been presented. Two reflected peaks were in perpendicular polarization direction and switched in the time-domain. However, the operation point of system affected output of the linearly-polarized beams seriously, and the stability of the system decreased and even failed to work. In order to solve this problem, a polarization control unit is added into the system in this paper. The modified demodulation system has been demonstrated to have a higher stability.
Simultaneous measurement for strain and temperature based on the twisted-tapering fiber structure
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A novel special fiber fabrication method based on a common single mode fiber (SMF) for dual-parameters measurement has been proposed and experimentally demonstrated. The fabrication setup is based on a three dimensional electric displacement platform which can realize the function of twisting and tapering at the same time. The proposed novel structure simultaneously undergoes the aforementioned two processes. Then a twisted-tapering fiber structure is formed. There are two dominant resonant wavelengths in the spectrum. Thus, simultaneous measurement for strain and temperature can be achieved. The following result shows that the strain measurement can be achieved by intensity demodulation, with the sensitivity of -0.01565 dB/με and 0.00705 dB/με corresponding to the dip1 and dip2, respectively. Therefore, the total sensitivity of the strain is 0.0227 dB/με. Moreover, the cross impacts of the wavelength shift are - 0.772 pm/με and 0.895 pm/με. Similarly, the wavelength demodulation is selected to temperature measurement. The temperature sensitivity of 50.53pm/°C and 45.12pm/°C are obtained. The cross sensitivity of the intensity variation are 0.04058dB/°C and 0.02031 dB/°C. As a result, the dual-parameters can be described to a cross matrix of the sensitivity value. The proposed sensor has a great potential for engineering applications due to its compact structure, simple manufacture and low cost.
A glucose concentration and temperature sensor based on long period fiber gratings induced by electric-arc discharge
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As one of the key parameters in biological and chemical reactions, glucose concentration objectively reflects the characteristics of reactions, so the real-time monitoring of glucose concentration is important in the field of biochemical. Meanwhile, the influence from temperature should be considered. The fiber sensors have been studied extensively for decades due to the advantages of small size, immunity to electromagnetic interference and high sensitivity, which are suitable for the application of biochemical sensing.
A long period fiber grating (LPFG) sensor induced by electric-arc discharge has been fabricated and demonstrated for simultaneous measurement of glucose concentration and temperature. The proposed sensor was fabricated by inscribing a sing mode fiber (SMF) with periodic electric-arc discharge technology. During the fabrication process, the electric-arc discharge technology was produced by a commercial fusion splicer, and the period of inscribed LPFG was determined by the movement of translation stages. A serials of periodic geometrical deformations would be formed in SMF after the fabrication, and the discharge intensity and discharge time can be adjusted though the fusion splicer settings screen. The core mode can be coupled into the cladding modes at certain wavelength when they satisfy the phase-matching conditions, and there will be several resonance dips in the transmission spectrum in LPFG. The resonance dips formed by the coupling between cladding modes and core mode have different sensitivity responses, so the simultaneous measurement for multi-parameter can be realized by monitoring the wavelength shifts of the resonance dips. Compared with the LPFG based on conventional SMF, the glucose concentration sensitivity has been obviously enhanced by etching the cladding with hydrofluoric acid solution. Based on the independent measured results, a dual-parameter measurement matrix has been built for signal demodulation. Because of the easy fabrication, low cost, small size and high sensitivity, the sensor is promising to be used for the biochemical sensing field where simultaneous measurement of glucose concentration and temperature is required.
φ-OTDR Sensing System with Bidirectional Pumped Fiber Raman Amplifier and Unbalanced MZ Interferometer
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In order to improve the detection distance and the sensitivity, we propose a novel distributed optical fiber sensing system. This system is composed of bidirectional pumping fiber Raman amplifier and unbalanced fiber Mach-Zehnder interferometer. Based on the interference mechanism of phase sensitive optical time domain reflectometer (φ-OTDR), the system can get the sensing information of the whole optical fiber by analyzing the backward scattered light. The interferometer is used as the demodulator of the sensing system, which consists of a 3×3 coupler and two faraday rotator mirrors. By means of the demodulator, the signal light is divided into three beams with fixed phase difference. To deal with these three signals, we can get the vibration information directly on the optical fiber. Through experimental study, this system has a high sensitivity. The maximum sensing length and the spatial resolution of the φ-OTDR system are 100 km and 10 m. The signal to noise ratio about 18 dB is achieved.
Research on calibration method of downhole optical fiber temperature measurement and its application in SAGD well
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With the development of oil and gas fields, the accuracy and quantity requirements of real-time dynamic monitoring data needed for well dynamic analysis and regulation are increasing. Permanent, distributed downhole optical fiber temperature and pressure monitoring and other online real-time continuous data monitoring has become an important data acquisition and transmission technology in digital oil field and intelligent oil field construction. Considering the requirement of dynamic analysis of steam chamber developing state in SAGD horizontal wells in F oil reservoir in Xinjiang oilfield, it is necessary to carry out real-time and continuous temperature monitoring in horizontal section. Based on the study of the principle of optical fiber temperature measurement, the factors that cause the deviation of optical fiber temperature sensing are analyzed, and the method of fiber temperature calibration is proposed to solve the problem of temperature deviation. Field application in three wells showed that it could attain accurate measurement of downhole temperature by temperature correction. The real-time and continuous downhole distributed fiber temperature sensing technology has higher application value in the reservoir management of SAGD horizontal wells. It also has a reference for similar dynamic monitoring in reservoir production.
Application of distributed optical fiber sensing technologies to the monitoring of leakage and abnormal disturbance of oil pipeline
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To improve the level of management and monitoring of leakage and abnormal disturbance of long distance oil pipeline, the distributed optical fiber temperature and vibration sensing system is employed to test the feasibility for the healthy monitoring of a domestic oil pipeline. The simulating leakage and abnormal disturbance affairs of oil pipeline are performed in the experiment. It is demonstrated that the leakage and abnormal disturbance affairs of oil pipeline can be monitored and located accurately with the distributed optical fiber sensing system, which exhibits good performance in the sensitivity, reliability, operation and maintenance etc., and shows good market application prospect.
Distributed acoustic sensing technique and its field trial in SAGD well
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Steam assisted gravity drainage (SAGD) is a very promising way for the development of heavy oil, extra heavy oil and tight oil reservoirs. Proper monitoring of the SAGD operations is essential to avoid operational issues and improve efficiency. Among all the monitoring techniques, micro-seismic monitoring and related interpretation method can give useful information about the steam chamber development and has been extensively studied. Distributed acoustic sensor (DAS) based on Rayleigh backscattering is a newly developed technique that can measure acoustic signal at all points along the sensing fiber. In this paper, we demonstrate a DAS system based on dual-pulse heterodyne demodulation technique and did field trial in SAGD well located in Xinjiang Oilfield, China. The field trail results validated the performance of the DAS system and indicated its applicability in steam-chamber monitoring and hydraulic monitoring.
Distributed optical fiber temperature sensor and its application in high-temperature well logging
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This paper analyzes the demand of temperature measurement for high temperature wells of oilfields and demonstrates the unique advantages of the distributed optical fiber temperature sensors in comparison with conventional means for temperature measurement. Through the actual test results of the heavy oil area, the feasibility and advantages of the distributed optical fiber temperature measurement are verified. A summary of development trend of the distributed optical fiber temperature measurement system as the core technology applied in the oilfield logging is also given.