The paper introduces the DAS system based on advanced phase-sensitive optical time domain reflectometry (φ-OTDR) with fading noise suppressed. Besides, the DAS system based on time-gated digital optical frequency domain reflectometry (TGD-OFDR) and its improved systems are introduced. The application of DAS in railway perimeter security is introduced at the end of the paper.

Single mode (SM) optical fiber with multiple Brillouin scattering peaks can be used for simultaneous strain and temperature measurement based on Brillouin frequency shift (BFS), but the measurement uncertainties are high due to the low Brillouin gains of higher-order acoustic modes. A new SM fiber is designed and fabricated with enhanced Brillouin gain of higher-order acoustic modes so that the gains of the multiple Brillouin peaks are at a similar level. The temperature coefficients of the BFSs of the peaks are also made significantly different to improve the accuracy of the measured strain and temperature.

Taking the advantages of SOI rib waveguide, a compact and efficient SPR sensor based on SOI rib waveguide is proposed. Ribs and air trenches are formed by ICP deep etch on SOI wafer. Then, the metal film for SPR is sputtered on the sidewall of the air trench. A tunable laser and an optical power meter are used to test the sensor. The sensor with micron dimensions can be directly end face coupled with the single-mode fibers of the laser and the power meter. Resonance curves of water and milk are obtained. The sensitivity of the sensor can reach 1200nm/RIU.

This paper analyses several wavelength demodulation methods based on optical fiber Fabry-Perot tunable filter. In view of the shortcomings of these methods, we proposed a real-time data acquisition method and a simple and effective demodulation algorithm based on optical fiber Fabry-Perot tunable filter and set up a temperature sensing system. The sensing system consists of an FBG sensor part, a data acquisition part, a data demodulation part and a data display part, we introduce the operation of the data acquisition part by explaining how the hardware and software work. Then we introduce the method of data demodulation we proposed, and demonstrated the steps of data demodulation in detail. We test the performance of this data acquisition part by carrying out a temperature sensor experiment, and prove the effectiveness of the demodulation algorithm at the same time. In addition, most programming languages can implement this simple and effective algorithm.

Pipelines are used across multiple key industries and in a sense acts like a circulatory system for society by carrying vital fluids safely across large distances. A wide variety of tools have been developed to help monitor the health of pipelines. Among these tools, the fiber Bragg grating (FBG) hoop strain sensor has great potential to measure the hoop strain variation on a pressurized pipeline and thus help detect anomalies, such as leakages. In this work, the hoop strain sensor with enhanced sensitivity is developed and encapsulated for pipeline leakage monitoring. Its specially designed mechanism with pre-tension function is detailed. The other branch of this research is the application of hoop strain information for pipeline leakage detection and localization. Three hoop strain-based methods are proposed to localize pipeline leakages with higher accuracy and in wider variety of situations. Some simulation work and experimental study are conducted to verify these methods. The results demonstrate that the FBG hoop strain sensor shows great promise for pipeline leakage detection and localization.

It is well known that the sensitivity could be enhanced by modifying the structure of plastic optical fibers (POFs) in some ways, such as side-polishing, tapering, bending, and so on. Therefore, in this work we tried to a new approach to modify the structure of POFs for RI sensing purpose. The corrugated surface long period gratings (LPGs) were fabricated on the commercial POFs by a simple mechanical die press print method using a periodic V-grooved metal plate as the mould. The LPGs were fabricated on two kinds of commercial POFs with the diameters of 0.5 and 1.0mm, respectively. The results indicate that the LPGs on the POF with the thinner diameter exhibits better performance in term of RI sensitivity and SNR. By altering the LPG structural parameters, the RI sensing performances were studied. When the LPG with the tilted angle of 20°, the period of 100μm and the groove depth of 45μm, the highest sensitivity of 1058%/RIU with a resolution of 4.88x10^-4RIU in the RI range of 1.333-1.430 was obtained in our experiments. The RI sensor is a low cost solution, which has the features of simple structure, easy fabrication, compact size and intensity modulation at visible wavelengths.

This paper studies a humidity dual biconical fiber sensor coated with agarose gel. The sensor was fabricated by the taper drawing technique of using a LZM-100 fusion splicer from single mode fiber, forming a Mach-Zehnder interferometer. Humidity modifies the refractive index of the coating layer, which in turn alters the high order modes along the dual biconical fiber segment and causes a detectable shift to the interference pattern. Due to the strong light absorption of agarose at 2 μm, the sensitivity of sensor was greatly enhanced. It has been found that the sensor’s sensitivity operated at 2 μm is tens of times higher than that at 1.55 μm region.

In most experimental installations and prototypes of miniature (the largest size of the sensing element from hundreds of μm to 2 cm) optical gyros, the waveguide passive ring resonators are used as sensing elements. In this case, only singlemode waveguides are used, since the use of multimode waveguides is impossible due to the dispersion of modes. For the same reason, most nonplanar ring resonators cannot be used. Nevertheless, there are confocal configurations of the ring resonators with strongly degenerate and equidistant spectrum. The application of such configurations as sensing elements allows to avoid the negative effect of the mode dispersion. Replacing the waveguide ring resonator on the confocal one can give some advantages for some types of miniature optical gyros (for example, those using the phase characteristic of a passive ring resonator). This work is devoted to the analysis of these optical gyros types and the advantages that the use of ring confocal resonator can give.

A new type of refractive index (RI) sensor based on a side-polished fiber Bragg grating (FBG) has been experimentally demonstrated. At first, a FBG was inscribed in a single mode fiber by means of 267 nm fs laser irradiation through a uniform phase mask, which has an excellent spectral shape with a transmission loss of −9 dB (i.e., a high reflectivity of 87.41%), a 3dB bandwidth of 0.78 nm. Then, the portion of the fiber cladding enclosing the FBG was side-polished into a D-shaped configuration, and the D-shaped FBG was employed as an RI sensor. The removal of the fiber cladding via side-polishing technique ensures that the propagating core-mode of the FBG can interact with the external medium, and hence the Bragg wavelength of the D-shaped FBG will be sensitive to the RI change of the external medium. A conventional unpolished FBG demonstrated a linear relationship between the Bragg wavelength and the surrounding RI with a low sensitivity of ~1.8 pm/RIU at an RI of 1.45. For comparison, the side-polished FBG exhibited a considerably increased RI sensitivity of up to ~10 nm/RIU at an RI of 1.45. Hence, it may be attractive for biochemical sensing applications.

A compact optical alignment structure and a novel beam-tracing method were proposed for tunable laser absorption spectroscopy (TLAS) based gas measurements, in order to minimize sensor size and ease beam alignment procedure. A near-infrared carbon dioxide (CO₂) sensor system was developed based on the alignment structure. A distributed feedback (DFB) laser centered at 6361.3 cm^-1 and a multi-pass gas cell (MPGC) with an effective optical path length of 29.8 m were employed. The sensor system was integrated as standalone equipment by customizing an aluminum baseplate for a stable field operation. A series of experiments were carried out to assess the performance of the sensor system. A limit of detection (LoD) of ~ 7.1 parts-per-million in volume (ppmv) at a 0.4 s averaging time was obtained, and the LoD was reduced to ~ 277 parts-per-billion in volume (ppbv) at an optimum averaging time of 153.6 s. Considering gas mixing times, the rise and fall time were measured to be ~ 290 s and ~ 200 s, respectively.

The measurement of plant growth's luminous environment is the basis of urban agriculture, such as LED plant factory. The PAR quantum sensors, which measure the photon flux of radiation in the spectral interval 400nm-700nm, can't measure the several intervals which are used in plant lighting simultaneously, but the LED plant factory needs these data and their ratios by far, a type of multi-channel quantum sensor is designed to solve this problem. Firstly, the paper expounds the design principle, circuit and structure of the sensor, and calibrate the unregulated sensors by the PQS-1 sensor under the calibration device constructed by controller based on DMX512 protocol. The test results show that the sensor has good linear response, whose average R² is 0.9956. The article finally designs a set of light environment control system, which can auto control the photon fluxes and light quality ratios, based on the sensors.

The Low level light sensor has evolved from early ICCD device to EMCCD that appeared at the beginning of this century. With the continuous progress of CMOS technology, the scientific CMOS sensors were developed, which have been used for industrial cameras in high sensitivity imaging. This article described a low level light CMOS detector and its associated camera, which were developed by Beijing Institute of Space Mechanics and Electricity (BISME) in cooperation with a domestic detector manufacturer. We had an in-depth discussion of the chip's high sensitivity design techniques and analyze the weak charge transfer optimization mechanism. Then both the CMOS and EMCCD detector were combined with lens and video processing circuits to conduct a laboratorial test, finally low light detection performance of them were compared and analyzed. The SNR of CMOS imaging circuits was basically equal to the EMCCD imaging circuits when the camera's entrance pupil radiance was less than 0.5E-05 W/m² /sr, when the radiance was up to 2E-05 W/m² /sr, the SNR of CMOS circuits was about 2dB better than the EMCCD circuits.

Aiming at being carried on various underwater vehicles for the detection of plankton, a miniaturized in-situ digital inline holographic system named OUC-HoloCam²⁰⁰ is designed and developed. Although the structure of OUC-HoloCam²⁰⁰ is simple and compact, the system performance is still excellent. Tests have been carried out and the result shows that the optical resolution of OUC-HoloCam²⁰⁰ is 8.77 μm, the depth of field is up to 30 cm, the field of view is 8.44×6.75 mm² , which means theoretically with each exposure, about 300 mL of seawater can be investigated. OUC-HoloCam²⁰⁰ have been deployed in the nearshore area of the South China Sea and have worked continuously over 48 hours, after holographic reproduction and image processing the data is able to show the trends of changing in number and species of plankton over time in the same location.

The readout chain circuits for time delay integration charge coupled device camera imaging system include CCD focal plane driving circuit, analog-to-digital conversion circuit, high-speed digital data transmission circuit and other parts together. The parasitic factors such as the quality of high frequency clock, high speed data transmission error rate and the aging of printed circuit board will induce more noise to image data of camera. As the longer time circuits working, the noise of readout chain becomes bigger and bigger, then the signal-to-noise becomes worse. This paper proposed a method to make circuit system check its noise as the circuit is working, which is based on pseudo CCD-signal to check the Signal-to-Noise of readout chain of TDICCD, and sends the result to control core of the system. The paper combines the theory calculation and actual measurement as the method for testing. High precision pseudo CCD signal source is used to test the onboard circuit and circuit SNR results of readout chain, harmonic frequency, noise floor and other related parameters are automatic processed.

Fiber optic sensors represent an attractive alternative in chemical, bio-chemical and medical applications. Their success can be retrieved in their peculiar properties such as: electromagnetic interference immunity, fast response, high sensitivity, and small size. In this context, Fiber Bragg Gratings (FBGs) play a key role in applications like measurements of temperature and strain. The mechanism of FBGs is related to the dependence between the characteristic wavelength reflected by the FBG and the effective index of the modes propagating inside the fibers. This property can be exploited to engineer a new and inexpensive class of FBG devices for measuring refractive index of solutions. By reducing the cladding thickness of the single mode fiber, where the FBG is inscribed, the structure becomes three layers and the modes guidance properties become more and more dependent on the external environment, including the refractive index of the solution to measure. In this work, an FBG has been etched by a solution of HF acid and immersed in different solutions of water and sucrose. Results show a strong multi-modal behavior induced by the guidance properties of the three-layer system. The reflected spectra, characterized by a large band whose width, are strictly dependent on the sucrose concentration in solution. As the sucrose increases, the refractive index of the solution increases. The bandwidth reduces, showing a wavelength shift toward longer wavelength. While the wavelength shift is not so relevant the variation of the bandwidth is significant, suggesting an effective interrogation method based on wavelet signal processing.

It is demonstrated that the constitution of complex Faraday rotation in presence of intrinsic birefringence. We analyze the relationships between incident azimuth of linearly polarized light and birefringence and the influence of different orders birefringence on the measurement of magneto-optical effect. We proposed a relatively simple technique to accurately measure Faraday rotation of fiber. The order of birefringence in optical fiber and the high sensitivity magnetooptical characteristics can be determined by the measurement system.

The laser wavelength in self-sweeping laser is linearly changing in time from start to stop wavelength without use of optical elements and electrical drivers for frequency tuning. Absolute difference between the start and stop wavelength values (sweeping span) characterizing the sweeping process is one of the key characteristics of any tunable source. Owing to broad sweeping span (more than 10 nm) and simplicity, self-sweeping fiber lasers are attractive sources for applications demanding tunable radiation such as sensors interrogation, spectral analysis, optical frequency domain reflectometry and so on. Self-induced nature of the sweeping process leads to fluctuations of the sweeping span borders. We demonstrate in this talk implementation of fiber Bragg gratings (FBG) for control and stabilization of start and stop wavelengths in the self-sweeping laser. We showed that the short-wavelength FBG helps to initialize the sweeping process and long-wavelength FBG blocks the laser line sweeping in long-wavelength region. The last effect is associated with mismatch of longitudinal mode structures of the laser and FBG-based selector. As a result, fluctuations of the sweeping span borders decreased by one or two orders of magnitude down to several picometers. In addition, we studied influence of the parameters for FBG-based selectors such as reflections and mode structure on quality of sweeping range stabilization. The results allow to improve the characteristics of self-sweeping fiber laser which can be used for different sensing applications such as atmospheric remote sensing and interrogation of the sensors based on fiber Bragg gratings.

In this paper, we theoretically and experimentally demonstrate a dynamic strain sensor system utilizing a semiconductor optical amplifier (SOA)-based fiber-ring laser(FRL).The outside of the laser cavity consisting of a fiber FabryPerot(FFP) filter as an intensity demodulator. The SOA-based FRL is incorporating the fiber Bragg gratings(FBGs) as wavelength selective components for fiber lasers.The optical signals reflected from the FBGs are detected by photodetectors (PDs) after filtering by the FFP filter and band-pass filter (BPF). The change of the external dynamic strain will cause the spectral-shift of the reflected light of the FBG which can be dynamically monitored by the change of the output light intensity from the filter.The experimental results show that the sensing system we proposed here has a good response to the dynamic strain signal.In the meantime,we also simulated the spectra of the FFP filter and the FBG,and then we obtained the optimal response range near the peak of the spectrum of the FFP filter.The system demonstrated here has a simple structure and low cost,which make it attractive for dynamic strain detection in structure health monitoring.

An innovative demodulation system for multilongitudinal mode fiber laser sensor has been proposed. By using a bandpass filter and a low-speed analog-to-digital converter (ADC), the high-frequency sensing signal can be downconverted and sampled simultaneously when the unaliasing condition is satisfied. Since the MLM fiber laser sensor could generate a wideband electrical signal after optical-to-electrical conversion, it is convenient to filter the signal to meet the unaliasing condition by a tunable bandpass filter while keeping the sample rate unchanged. Moreover, each tone of the beating frequency signal has the full information for demodulation of measurand. The demodulation system only needs a bandpass filter and a low-speed ADC which reduces the cost of the system and make the system more stable. A proof-of-concept experiment is conducted to verify the proposed scheme. Eventually by demodulating a beat frequency in 1.625GHz, a sensitivity of -5.87kHz/°C is achieved in a fiber laser sensing system with a sample rate of 500MHz.

In this study, we developed a kind of gold-silver alloy film based SPR (AuAg-SPR) sensors with wavelength interrogation to detect Cancer antigen 125 (CA125) by sandwich immunoassay. The experiment shows that the changes in resonance wavelength (Δλ_𝑅) of AuAg-SPR sensors are higher than that of the gold film based SPR (Au-SPR) sensors when the final sandwich structures were formed. We have applied the Fresnel reflection equations and Bruggeman approximation formula to calculate the volume fractions of adsorbates in different adlayers, and the dispersion curves of the effective refractive index (RI) of adsorbates with different volume fractions of adlayers were obtained. Moreover, we simulated the sensitivity of RI of two kinds of sensors by using the waveguide equations, when the initial resonance wavelength (λ_𝑅) was fixed at 628nm, changing RI from 1.333 to 1.335, the Δλ_𝑅 of AuAg-SPR sensor is 2.25-fold compared with that of Au-SPR sensor. Finally, the effect of the size of antigen on the detection result and effective RI were analyzed. In conclusion, the AuAgSPR sensors with a higher sensitivity than the conventional Au-SPR sensors in detecting CA125, owing to the advantages of low-cost, stability, highly efficient for the clinical determination of CA125 levels

A dynamic acceleration measurement system based on a high sensitivity compliant cylinder fiber optic probe and an all-fiber configuration Distributed Bragg Reflector (DBR) fiber laser with self-mixing technique is presented. The compliant cylinder fiber optic probe consists of a mass-block and an elastic cylinder twined with single mode fiber and can be regarded as being close to that of a simple mass spring system. Experimental results show that the signal to noise ratio (SNR) can achieve 50dB at 800 Hz under 1.5 mg acceleration stimulation, voltage sensitivity is 6.04 V/g and minimum detectable acceleration of the measuring system is 4.7μg/sqrt Hz at 800Hz. Moreover, the material of elastic cylinder is polyurethane (PU) which has better temperature stability and can be applied widely in the field of vibration measurements.

In this paper, a multi-parameter optical fiber system is developed and demonstrated by using a single polarimetric fiber ring laser sensor and beat frequency demodulation technique. The polarimetric fiber ring laser is formed by a fiber Bragg grating, a piece of Erbium doped fiber and a 3 dB fiber coupler. Since the fiber laser cavity is long enough, there are many longitudinal modes in the laser cavity. For each order longitudinal mode, two orthogonal polarization modes will experience slightly mode splitting due to the intrinsic fiber birefringence. As a result, in this polarimetric fiber ring laser, there exists two kinds of beat frequency signals, i.e. longitudinal mode beat frequency and polarization mode beat frequency signals. When the fiber laser cavity suffers from external perturbations, such as temperature change, strain change, and the fiber birefringence change, these two kinds of beat frequency signals will experience different response and can be used to measure multiple parameters simultaneously. We have theoretically analyzed the principle of measurement temperature, strain and fiber birefringence and experimentally measured these parameters in the test. The proposed multi-parameter sensing system just uses a single polarimetric fiber ring laser sensor and one beat frequency demodulation equipment. It will be promising in many application fields due to its advantages of simple structure, portability, high sensitivity, and low cost.

A fiber optic refractive index (RI) sensor that consists of cascaded single mode fiber-no core fiber-single mode fiber (SNS) structure followed by a fiber Bragg grating (FBG) was proposed and demonstrated. Because the SNS structure and FBG have similar temperature characteristics and the FBG is not sensitivity to the RI, temperature self-compensation during the RI measurement can be realized by calculating the difference between the characteristic wavelengths of the SNS and FBG. Three SNS-FBG-based sensors with different lengths of the NCF and different Bragg wavelengths were cascaded to achieve wavelength division multiplexing (WDM) in the range of 1510nm-1590nm. Experimental results show that three-point independent RI measurement can be accomplished with the maximum sensitivity of 211.088, 243.429 and 242.511nm/RIU (RI unit) in the RI range from 1.333 to 1.405, respectively. The RI errors caused by temperature are only 4.548×10-5RIU/°C, 3.779×10-5RIU/°C and 4.458×10-5RIU/°C respectively. These sensors feature the advantages of good reproducibility, small size, low cost, high sensitivity and very low temperature cross-sensitivity, which have a good practical prospect in the simultaneous multi-point RI measurement application area.

A fiber Bragg grating (FBG) textile-based pulse wave sensor is proposed and demonstrated based on multi-layers compound fabrics structure which can convert the fabric tension to the pressure of FBG sensing unit needed by pulse measurement and improve its sensitivity. On the basis of material mechanics theory, the sensing model is established and the theoretical formulas are deduced. A prototype of cuff-type FBG textile-based pulse sensor is achieved by the knitted way of compound fabrics. The test results show that the sensor can effectively obtain pulse wave which has higher signal-to-noise ratio and contains more detail features than the photoplethysmography (PPG) sensor. This sensor has potential applications in smart textile and a good practical prospect for the wearable human pulse measurement during the magnetic resonance imaging (MRI) scan.

Coherent Doppler lidars (CDL) and coherent differential absorption lidars are widely applied in the measurements of atmospheric wind and constituents respectively. To improve the detection range of heterodyne lidars, the demands for laser linewidth are studied based on the statistical theory and Monte Carlo simulations. The signal to noise ratio (SNR) and the spectrum of intermediate frequency (IF) signal are analyzed under different laser power and linewidth. When the detection range is beyond the coherent length, the IF signal can still be measured, and the power spectrum of IF signal will be broadened, which results in the peak value decrease in the power spectrum. In heterodyne Doppler lidars, the frequency extraction errors of IF signal fluctuate with SNR. To realize the velocity measurement performance for wind and other moving targets, detection performances with various laser linewidth are analyzed according to the 3σ criterion. The calculations indicate that better results can be obtained with larger powers when the laser linewidth is relatively wider and that the effective detection range of lidar can be longer than the coherent length for lasers with certain linewidth. To verify the analysis, heterodyne experiments are carried out based on the fiber delay lines and fiber lasers with different linewidths, and the SNR is controlled by a variable optical attenuator. The results show that measurements with large laser power can reduce the errors caused by the power spectrum broadening of IF signal. The analysis may aid the determination of laser power and linewidth in heterodyne lidars.

Dynamic stress sensing interrogation has become into a potential research for its wide applications. In order to test and monitor the dynamic stress in real-time, new types of fiber Bragg gratings (FBGs) sensing interrogation systems have been gradually developed. In this paper, a high interrogation rate dynamic stress sensing interrogation system by using a wavelength-swept laser with high sweeping rate and flexible-controlled sweeping step is proposed and demonstrated. In this system, a single sideband (SSB) modulator driven by radio-frequency (RF) signal is used to realize the abovementioned parameters of the wavelength-swept laser, which overcomes the limitation of traditional mechanical sweeping devices. The interrogation rate of the whole system is decided by the sweeping rate of the source, which is significantly improved and tunable with a broad range. Owing to the advantages of the sweeping source, our sensing interrogation system is effective to deal with different vibration sensing interrogations. Experimentally, the sweeping rate of the wavelength-swept laser can be tuned from 40 kHz to 200 kHz as sweeping step tuned from 5 GHz to 15 GHz. The highspeed vibration generated by a piezoelectric transducer (PZT) on the FBGs is sensed and interrogated in real-time. The interrogation of frequency vibration sensing from 5 Hz to 11 kHz are obtained. A 25 μs transient vibration mutation is also successfully interrogated by this system.

In this paper, a multi-wavelength parallel swept light source (MWPSS) is proposed for fiber Bragg grating (FBG) interrogation. The MWPSS has two main parts: a multi-wavelength light source used as a seed source and a synchronous lightwave synthesized frequency sweeper (SLSFS). The multi-wavelength of the seed source is shifted with a constant frequency sweeping step synchronously every circulation in the SLSFS. There is a one-to-one correspondence between the swept range of the seed source and the central reflection wavelength of each FBG sensor. By interrogating the data of reflection intensity in time-domain to calculate the difference between the center wavelength of each sensing FBG and the reference FBG, 10.055±0.005pm/°C temperature sensitivity and 1.614±0.002pm/με static strain sensitivity were obtained synchronously without cross-talk.

With the development of military industry and intelligence, accelerometer with high-performance will be demanded imminently. The resonant graphene accelerometer combines excellent mechanics and mechanism properties of graphene with the technique of MEMS accelerometer, with the advantages of high-performance, low-energy consumption, lowcost and mass production. An optically driven resonant graphene accelerometer is resonated by a laser beam with periodically varying intensity. A single-layer graphene fixed on its substrate is heated by the laser beam to make the graphene film resonate. When there is external acceleration, a proof mass fixed on the single-layer graphene film can change the resonant frequency by adding a force on the film. The acceleration can be calculated through the variation of the resonant frequency. However, the deadly drawback of the optically driven resonant graphene accelerometer is its low quality factor, which is large dissipation. In this paper, the mechanism of the squeeze-film air damping of a resonant graphene accelerometer is theoretically modeled. The influential parameters are optimized to decrease the damping. The results show that the effect of squeezefilm damping on quality factor can be significant, while that on resonant frequency can be negligible. Meanwhile, the squeeze-film damping will increase as the pressure, free and fixed edges of the single-layer graphene grow. The influence on the quality factor by changing the size of the free edges is more remarkable, compared to that of fixed edges. Therefore, decreasing the pressure and geometrical size of the single-layer graphene, especially the free edges, is an effectively method to reduce the damping of the resonant graphene accelerometer.

Aiming at the problem of incomplete scanning map information and poor anti-interference ability when the robot uses a single sensor for fast simultaneous locating and mapping (FastSLAM), a novel method based on multiple sensor information fusion is proposed. At the first, the RGB-D vision sensor, laser range finder and odometer are preprocessed by noise reduction, and the depth image of RGB-D vision sensor is converted into the simulated laser data. The feature information is acquired by the simulated laser data and laser sensor data. The simulate laser and the real-time laser can be fused by introduced information fusion rule in this paper, this step expands the robot's vision and makes up for the visual blind spots of the robot single sensor, and obtaining a high-accurate map. Then, the unscented Kalman filter (UKF) algorithm is introduced in FastSLAM method, the new particles proposal distribution can be obtained. This step can not only avoids increasing the complexity of the algorithm when calculating the Jacobi matrix, but also improve the system's state estimation accuracy and the speed of algorithm convergence. Finally, the real scene experiments on the method of this paper are carried out on a Pioneer3-DX robot equipped with robot operating system (ROS), laser sensor and RGB-D camera. It is proved that this paper proposes a fast simultaneous locating and mapping method based on information fusion of RGB-D and laser sensor can not only improve the accuracy of the SLAM, but also enable the robot to construct a high-precision grid map in the environment.

Resonators with an equidistant spectrum are required in optics quite often. One of ways to obtain them is to use degeneracy of the frequencies of the resonator modes, which is observed, for example, in well-known confocal resonators. At the same time it is possible to find configuration of the ring resonator with a similar properties – confocal ring resonator. In the first approximation, the ring confocal resonator can be obtained using several (at least three) reflecting surfaces: flat and concave toroidal with the radii of curvature in the two main meridional sections ensuring the fulfillment of the confocality condition and the degeneration of the spectrum. Such resonators can be manufactured as a single monolithic element (prism) and used, in particular, as sensing elements of miniature optical gyroscopes. This work is devoted to the study of the properties of ring confocal resonator with the use of multiphysical modeling.

A multichannel all fiber current sensor that can be used to measure currents at different positions simultaneously is presented in the paper. Each sensor head uses single-polarization single-mode devices and loop scheme to realize current measurement. All the sensor heads are connected via a series structure and the measured results are received by only one photo-detector based on the principle of time-division multiplexing. Theory and experiment prove that the sensor is feasible.

In the coastal water quality monitoring, turbidity has vital effect on the optical method for the measurement of the concentration of the chemical oxygen demand (COD) using UV-Vis spectrum. The mixture absorption spectrum of turbidity and COD was studied using a 10mm optical path in this paper. The COD calculation band is from 200 to 300nm which is contained in the turbidity absorption spectrum (200-720nm), the intensity of absorption spectrum was enhanced with the increase of turbidity, The result shows that the absorption spectrum of COD increases with the increasing of concentration. The absorbance between 300nm and 720nm is almost unchanged, which is mainly caused by turbidity, turbidity compensation can be carried out by eliminating the absorbance between 300-720nm. In order to verify the feasibility of this method, the spectrum of COD and turbidity mixed solution with different concentration was measured. Error analysis is made between calculation results and laboratory measurements. The results show that mean absolute error, variance and standard deviation are 0.83, 0.92 and 0.96 respectively, which can be used for the on-line monitoring.

A printing method of quantum dots (QDs) optical fiber is presented in this paper. The printing ink with suitable viscosity is composed of the UV adhesive and the CdSe/ZnS quantum dot. By adjusting the pressure and waveform parameters of inkjet printer, a stable droplet is formed. A segment of QDs optical fiber is printed on the organic polymer material substrate subjected to viscous treatment by controlling the spacing between adjacent droplets. When the printed QDs optical fiber is aligned to multi-mode optical fiber which is used to transmit the excitation light, strong fluorescence of the QDs fiber is detected by the optical spectrum analyzer (OSA). Using the printed QDs optical fiber as the senor, the temperature measurement is realized. The sensitivity of the luminescent peak with the temperature is about 115.0pm/°C.

This paper presents a multi-class support vector machine (MCSVM) based high-efficiency events discrimination method for asymmetric dual Mach-Zehnder interferometers (ADMZI) distributed infrared fiber vibration sensor. This method combined empirical mode decomposition (EMD), kurtosis characteristics with MCSVM, which can improve the recognition rate effectively. Filed experimental results demonstrate that the proposed method can discriminate four common invasive events (climbing the fence, knocking the cable, cutting the fence, and waggling the fence) with an average recognition rate above 90.9%, which can satisfy actual application requirements.

Based on the principle of Solc interferometer, an optical fiber sensor which can realize torsional direction and torsion angle measurement simultaneously is proposed in this paper. The sensor is consisted of a segment of single mode fiber (SMF), polarization maintaining fiber (PMF) and two polarizers. When the light of the broad band source is transmitted in the sensor, the interference spectra can be observed at the output of the sensor. The interference spectra of the sensor can be changed when the sensor is twisted clockwise or counter-clockwise. Because the peaks position and dips position in interference spectra are reversed when clockwise and counter-clockwise torsions are applied, the torsional direction can be judged conveniently. With the increase of the torsion angle, the extinction ratio (ER) of interference spectra will change significantly. By measuring the changes of the ER, torsion angle can be calculated easily. The highest sensitivity can reach to 0.79dB/° in the range of [-50,52°].

We investigate the quadrature crosstalk characteristics of three-dimensional optical fiber vector sensor in a time-divisionmultiplexing (TDM) array based on phase generated carrier (PGC) technology in theory and experiment. A theoretical model based on PGC demodulation technology is established. The numerical simulation based on the theoretical model is carried on and indicates that the quadrature crosstalk of the optical fiber vector sensor is governed by the path difference of the interferometer, the length of the delay fiber, the number of array channels and the extinction ratio of the acousto-optic modulator (AOM). A four channels TDM array based on four cascaded interferometers was set up to verify the theoretical analysis. The experimental results agree well with the theoretical analysis. This research provides insight into the quadrature crosstalk in a TDM optical fiber vector sensor array, and can be used to optimize the array design in specific applications.

With the development of laser technology, rectangular laser pulses can get narrower rising and falling edge, and the time scale of the rising or falling edge can reach nanosecond. When the falling edge of a rectangular laser pulse is incident to a Fabry-Perot interferometer and the time scale is less than the single round-trip time of light traveling in the Fabry-Perot cavity, the fast degradation of incident light intensity causes the change of the reflected light intensity and energy. The reflected light intensity and energy vary with the time scale of the rectangular laser pulse for an invariant phase difference of the light propagating through the Fabry-Perot cavity. For a fixed time scale of the rectangular laser pulse, the intensity and energy of reflected light vary with the phase difference. In this paper, the temporal response of the reflected light intensity and energy of the Fabry-Perot interferometer is studied, and a high precision sensing scheme can be achieved. To improve the sensitivity of the reflected light energy to phase difference by optimizing the parameters of the rectangular laser pulse and the Fabry-Perot interferometer, we calculate the signal-to-noise of the reflected light energy versus the response time, reflectivity and phase difference of Fabry-Perot interferometer. Furthermore, we analyze absorption property of the Fabry-Perot interferometer to expand the field of application of this sensing scheme.

High-speed wavelength interrogation technology for fiber Bragg grating (FBG) has attracted increasing attention in recent decades. Dynamic population gratings, formed in the rare-earth doped fibers, can be worked as adaptive beamsplitters in the adaptive interferometric detection configurations based on two-wave mixing (TWM). In combination the advantages of a semiconductor optical amplifier-based fiber ring laser (SOAFRL) sensors and fast response of dynamic population gratings demodulation in TWM system, in this work, we propose a demodulator for fiber Bragg grating (FBG) sensor using an interferometer based on transient two-wave mixing via dynamic population gratings in saturable Er-doped fiber (EDF). The proposed simple and robust configuration has an all-fiber design based on commercially available elements which makes it promising for applications in optical fiber ultrasonic sensors. Experimental results show that the SOAFRL is stable and can stably respond to dynamic signals with high frequencies.

The photodetection intensity noise to demodulated phase noise conversion process of fiber optic sensors using phase generated carrier (PGC) scheme is investigated through theoretical calculation and experimental verification. Several categories of intensity noise are calculated, according to their relation between intensity noise power spectral density and photodetection current. The results revealed that demodulated phase noise power level increases by several decibels over the relative intensity noise power level of detected light power signal. Phase noise power level could also fluctuate with demodulated phase signal. Increase of phase noise power level varies according to the noise type, as well as the fluctuation amplitude. For noises that intensity noise power level unrelated to detected light power, such as electronic noise of detector circuit, phase noise power level increases by about 3.7 dB and do not fluctuate with demodulated phase signal. For noises that intensity noise power level proportional to detected light power, such as signal-amplified spontaneous emission(ASE) beat noise of optical amplifiers, phase noise power level fluctuates with demodulated phase signal by about 5.7 decibels and averagely increases about 3.7 decibels over a 2π period of demodulated phase signal. For noises that intensity noise power level proportional to square of detected light power, such as light source relative intensity noise, phase noise power level fluctuates with demodulated phase signal by about 9.0 decibels and averagely increases about 4.8 decibels over a 2π period of demodulated phase signal. Verification experiments are demonstrated on electronic noise, ASE-signal beat noise and light source relative intensity noise separately.

We present a comparative assessment of several refractometric optical fiber platforms based on reflective long-period fiber gratings (RLPGs), which was fabricated by combining the long-period gratings with the different fiber optic reflectors such as fiber optic retroreflector, Faraday rotator mirror, and Sagnac fiber loop mirror. In the experiment the refractive index (RI) of liquid was measured with RLPGs. It was found that the reflection spectrum remained the resonant dip without interference in fringe and the resonant wavelength appeared obvious blue shift with the increase of external RI. The spectral depth was reduced about 20 dB after a fiber optic reflector was configured. The simulation result of the resonance wavelength change with the refractive index of the liquid was also given. Meanwhile, the sensitivity of surrounding temperature has been considered. During the temperature measurement process, the intensity hardly changed with temperature. The absolute error of LPG was 1.15dB, and the absolute error of RLPG was about 0.2. The refractometric optical fiber platforms with the configuration of RLPGs had several advantages such as longer sensing distance, RLPG operation mode and non-interference fringe. Combined with the advantages, the sensor structure can not only be applied to measure the RI of glycerol/water solutions, but also be widely used to the measurement of toxic chemical liquid based on the fiber characteristic of resistance to hostile environments, especially far away from the toxic source.

This article presents a novel multi-layer artifact for systematic error correction of a gap measuring system, consisting a 3D laser scanner and motorized linear stages. This artifact representation of five-layers gap shape with continuous free-form surface was designed, which include diverse form dimensions. Then, in order to improve the measurement accuracy of the range dimension of the gaps, a one-step calibration procedure based on an experimental process has been developed. The influence of the three parameters on width error, depth error and flush error, defining the relative position and the orientation between the scanner and the range gaps, is respectively considered. The results obtained in accuracy and repeatability tests performed on this multi-layer artifact primitives attest to the viability of this correction method for gap measuring system.

The antiresonance spectral characteristics based on a silica capillary sandwiched between two single-mode fibers are investigated on the aspects of both transmission and reflection. Basic theory of the antiresonance reflecting optical waveguide model is presented and analyzed for this structure. During the fabrication, suitable parameters are adopted in in the manual welding process to keep the cross section of the capillary fiber away from the discharge electrode, which ensures the smoothness between the welding surfaces. Subsequently, three experimental samples are fabricated with the same inner diameter and various lengths of 650 μm, 837 μm, and 1070 μm, respectively. It can be observed that devices with different lengths have the same resonance wavelength in the wavelength range of 1500-1700 nm. However, the transmission depth at the resonance wavelength increases with the increase of the capillary length. We also discuss the relationship between inner diameter and transmission spectra through three samples with inner diameters of 25 μm, 50 μm, and 75 μm. The experimental results show that the free spectral range is 22.9 nm, 29.8 nm, and 44.1 nm, respectively. It also exists antiresonance in the reflection, which shows a novel mechanism for possible sensing applications.

A fiber-optic hydrogen sensor based on tunable diode laser spectroscopy is designed. The fiber-optic hydrogen sensor is composed of a fiber-optic Fabry-Perot interferometer, where one mirror is made of a hydrogen sensitive Pd thin film. By optimizing the structure parameters of the fiber-optic hydrogen sensor, a reflectance spectrum with the similar curve to a gas absorption spectrum is obtained. The reflectance spectrum of the fiber-optic hydrogen sensor is calculated at different hydrogen concentrations and the relation between the intensity minimums of the spectrum and the hydrogen concentrations is explored. The wavelength modulation spectroscopy is used to analyze the reflectance spectra, the relation between the second harmonic component and hydrogen concentrations is obtained, and the feasibility of the application of TDLAS on the fiber-optic hydrogen sensor is verified. This hydrogen sensing method has great potential in industrial application due to the advantages of high sensitivity, low cost, system’s simplicity.

In order to improve the quality of greenhouse vegetable plug seedlings and realize rapid detection of growth information of greenhouse vegetable plug seedlings, a device for detecting the growth information was designed. The detection device contained a weighing unit, an image acquisition unit, a light source unit and a control processing unit, mainly realizing vegetable seedling morphological index of projection area, stem diameter and plant height detection and weight information collection. The light source unit was composed of high-power LEDs. The image acquisition unit was made up of two cameras, the first camera in the vertical downward orientation, was used to obtain projection area parameter of vegetable seedling, the second camera in the horizontal position, was employed to capture of vegetable seedling stem diameter and plant height parameters. The weighing unit adopted a high precision weight sensor to obtain the weight information of the vegetable seedlings. The control processing unit included a single chip microcomputer and a computer. The single chip microcomputer was introduced to control the background board opening and closing, and to control camera work. The computer was mainly used to process images and realize information fusion and the design of humancomputer interaction interface. The software system of the device was developed based on C++ language, including image processing algorithm and control programs. The detection error of the device was less than 5% for morphological indicators and weight information. The results showed that the greenhouse vegetable seedling growth information detection device had high detection accuracy.

In order to improve the integration of the detection system for underwater acoustic, temperature and pressure in the ocean, a novel fiber-optic combined underwater acoustic, temperature and pressure sensor is proposed. The fiber-optic combined sensor consists of a FBG temperature sensor, a FBG pressure sensor and a Michelson interferometric fiberoptic hydrophone, which are connected by a single optical fiber. The optical signals from the FBG sensors and the fiberoptic hydrophone are completely independent and do not affect each other, so they can be detected and demodulated simultaneously. The fiber-optic combined acoustic temperature and pressure sensor can also be used in combined sensor arrays by time division multiplexing and wavelength division multiplexing. The fiber-optic combined sensor is designed and fabricated, and the performance of the sensor is tested experimentally. The experimental results show that the fiberoptic combined sensor system can measure the underwater temperature and pressure, underwater acoustic signal accurately.

A fiber-optic temperature and pressure sensor array for ocean observation is built and studied experimentally. The sensor array consists of 4 subarrays. Each sensor subarray is composed of a certain number of FBG temperature sensors and FBG pressure sensors which are connected in a single optical fiber. The wavelength scanning and time division multiplexing techniques are combined to demodulate the FBG wavelengths of sensor array. The experimental results show that the wavelengths of FBGs in different subarrays can be demodulated and all the sensors can measure the temperature or pressure with high accuracy. The fiber-optic temperature and pressure sensor array and the demodulation method have great potential application in acquirement of the vertical profile of temperature in seawater.

The plastic optical fiber (POF) with a multi-notched structure was used for liquid level measurement. The multi-notched structure was fabricated on the POFs by a die-press-print method. When the notched structure was immerged by the liquid, the transmitted light power of the POF probe could be changed. So, this can be used as a liquid level sensor. The influence of the structure parameters on the sensor performances was investigated experimentally. Experimental results show that the sensitivity can reach to 0.0457/mm with a resolution of 1 mm, and the sensor resolution is flexible. The sensor is simple structure and easy fabrication, and it is a low cost solution for the liquid level measurement.

An image fiber-based miniature suspended solid sensor has been demonstrated. The diameter of the sensor is only a few millimeters. A superhydrophobic material is coated on the end of the image fiber to avoid the adsorption of suspended solids and bubbles. Multiple parameters, including mass concentration, morphology and particle sizes of suspended solids, can be visually measured in real time. Dynamic ranges of 0 ~ 100 kg/m3, full range accuracies of ±2‰ and a response time of 0.05 s were experimentally realized for the mass concentration measurements. Determinations of particle sizes of the suspended solids are also presented by means of digital image processing. This new technique will significantly advance ultralow-intrusion measurements in studies on the dynamics of suspended solids.

In this work, we proposed a dual-core fiber coupler. Identical long-period fiber grating is written in each core of the dual-core fiber by using point-by-point high-frequency CO₂ laser irradiation. The peak attenuations of the two similar LPGs are -19.8 dB and 13.2 dB, respectively. And the proposed coupler can achieve a peak coupling efficiency of 48%.

In this work, we analyze the classification, characteristics, and applications of photonic crystal fibers, and measure the sensing character of this device fabricated by lateral offset splicing a piece of grapefruit microstructure fiber with single mode fiber. The effective mode analysis software COMSOL is used to analyze the transmission modes in the grapefruit fiber, and the effective mode transmission index is measured. At the same time, the interference principle of the whole experiment is analyzed. With press and temperature changes, the sensitivity of the device was shown as 0.0078nm°C and 0.0021nm/με.

The star sensor is a high-precision attitude measurement device widely used in aerospace vehicles. One of the most significant influence on the accuracy of star sensor is the operating temperature. Experiments show that with the increase of temperature, the dark current noise of CMOS increases exponentially, which greatly reduces the Signal-to-Noise ratio(SNR) of the star map. A novel and efficient thermal control design is presented in this manuscript, for the purpose of keeping the temperature of CMOS and temperature fluctuation in a limited range. To validate the design, thermal analysis of the model of CMOS assemblies are built by utilizing finite element method. During orbital operation, the temperature of the optical system of the star sensor is unevenly distributed. The structural parameters such as the refractive index of the lens, the thickness of the lens, and the curvature radius will change, affecting the imaging position and energy distribution of the star point. Star point extraction and positioning accuracy will be greatly affected. These jobs could give some guidance and reference for the precise thermal control of CMOS assembly of other space optical camera.

We propose a real-time monitoring method for shield tunnel boring machine cutter wear based on chirped fiber Bragg grating (CFBG). We use the chirped fiber Bragg grating as the wear detection sensor. When the wear occurs at the end face of the wear detection sensor (the end face of chirped fiber Bragg grating), the grating area of the chirped fiber Bragg grating will shorten with the occurrence of wear, which causes the bandwidth of the grating reflection spectrum to be narrowed, and the correlation theory of the fiber Bragg grating is used to calculate the wear rate. Experimental data shows that the sensor can survive in the actual operating conditions of the shield tunnel boring machine. After calibration, measurement accuracy can less than 1mm, and it can be used for real time wear detection of large machinery, such as shield tunnel boring machine.

The use of nanoparticles is gaining large interest in modern photonic technology, mainly because nanoparticles can drastically change the properties of optical media. Here, a custom special fiber has been considered for investigation. The fiber presents a co-doped erbium and magnesium oxide nanoparticles core, and standard telecommunication size. Modified Chemical Vapor Deposition technique, together with the spontaneous phase separation, permits to grow inside the core a random distributed pattern of nanoparticles, whose size varies between 20 to 100 nm, considering the transversal section. The nanoparticle increases the scattering, which is, in general, an unwanted occurrence. Nevertheless, interesting applications can emerge in sensor field. In this work the focus has been concentrated on the distributed sensing applications offered by the enhanced backscattering. The fiber has been characterized by the use of an Optical Backscatter Reflectometer (OBR) Luna 4600. Results show that the intensity of backscattering, induced by the nanoparticles, is 50 dB larger than the one shown by standard single mode fiber. This results in an exponential decay of the reflected optical power, which vanish after 1.7 meter of propagation. Moreover, using the OBR, it has been possible to characterize the polarization properties of this special fiber. Because the nanoparticles are stretched during the drawing process, the fiber presents a well-defined polarization signature pattern, with a random alternation of polarization state every, roughly, 10 cm. These properties are promising for creating a distributed, high reflectivity, sensors, in application like OBR spatial multiplexing.

A microring resonator based sensor is proposed to detect different poisonous gases, such as carbon monoxide, phosphine, and nitrogen dioxide. These gases are very dangerous in environment if the leakage concentration is high. The single slot microring resonator sensor is used for detection of hazardous gases. The sensor has been analyzed through finite-difference-time-domain method by varying the radii of microring resonator from 1.4 μm to 2.2 μm and refractive index of the analytes. Transmission of microring resonator is observed and detected the different poisonous gases.

We propose an electrical I/Q demodulation scheme to decrease the sampling rate and computational cost in coherent phase-sensitive Optical Time-Domain Reflectometry systems. The IF signal from the photon detector and the local-oscillator from the acoustic-optic modulator driver are splited into two parts, respectively. One of local-oscillators is 90°shifted, then the signals and LOs are cross-mixed and the outputs are low-pass filtered to obtain the I/Q signal. Besides of the save of computational cost, the sampling rate and data storage is reduced at least 1.6 times. At last, a quantitative measurement of a 50 Hz vibration is successfully demonstrated in the experiment.

As a kind of distributed optical fiber sensor, Optical Frequency-Domain Reflectometry (OFDR) can realize high spatial resolution distributed strain/temperature measurement. A method of measuring Rayleigh backscatter spectrum shift by cross-correlation calculation is widely adopted in OFDR sensor system. The other approach is based on the phase shift induced by the strain/temperature variation. In this paper, we propose a digital demodulation method to achieve it. Firstly the output of the photon detector is Fourier transformed and the phase information is obtained. The cross-correlation method and phase demodulation method are compared based on the theoretical and numerical analysis. The result shows that the spatial resolution (SR) of strain/temperature sensing is decided by the sweep range of the tunable laser source, while this parameter is much larger in traditional scheme. However, better stability can be achieved in cross-correlation scheme for sharp varying strain/temperature.

Artificial incubation of chicken eggs is the economic procedure in the poultry farms. Eggs candling method is widely used to check for the embryo fertility among the incubated chicken eggs. At late incubation period, fertilized eggs appear darker than unfertilized eggs under dark-field illumination. However, the method cannot precisely differentiate between live eggs and non-viable eggs at the late incubation days since both types of eggs appear dark. Infertile eggs could be exploded in the hatcher baskets and cause infection to newborn chicks. In this work, we proposed a non-contact and noninvasive method that can precisely checked for live embryos by extracting the heart rate of multiple incubated eggs using a digital camera. System consisted of light emitting diode as light source and CMOS camera for recording video images. Digital processing techniques followed by fast Fourier transform algorithm were employed to extract embryonic HR information. A total of 30 chicken eggs including 24 fertile and 6 infertile eggs were examined from days 7-16 of incubation. The proposed technique may offer benefits to both poultry industry and animal science researchers. Poultry industry may use this system to confirm for chicken embryos’ fertility as well as sorting out dead eggs from live eggs whereas animal science researchers may use this system to further the study about the development of chicken embryos.