The influence of the spin rate profiles on the stability of polarization transformations of all-fiber polarization transformers (AFPTs), which behave as a broad-band all-fiber quarter-wave plate, is analyzed by the super-mode theory. Huang firstly proposed and demonstrated these AFPTs, and suggested qualitatively that to perform a stable polarization transformation, the variation of the spin rate from zero to fast of the AFPT should be slow. However a compact fiber structure is desirable for an optical current transformers (OCT) system, and bending or wrapping AFPTs will weaken their abilities to hold the output SOPs. A first-order analytical approximation describing the coupling between the two local eigen-modes in the AFPT is derived, and two more detail suggestions for the spin rate profiles design of AFPTs are proposed. A random orthogonal axial gradient method (ROAGM) is developed to optimize the spin rate profiles. Numerical simulations show that for an AFPT with a shorter length, the stable transformation can also be obtained by a carefully designed spin rate profile according the two suggestions.

The deformation of machine tool base is one of main error elements of heavy-duty CNC machine tool. A new deformation measurement method for heavy-duty machine tool base by multipoint distributed FBG sensors is developed in this study. Experiment is implemented on a real moving beam gantry machine tool. 16 FBG strain sensors are installed on the side-surface of the machine tool base. Moving the machine tool column to different positions, varying strain signals are collected. The testing results show that this distributed measurement method based on FBG sensors can effectively detect the deformation of the machine tool base. The largest deflection in vertical direction (axis Z) can be 75μm. This work is of great significance to the structure optimizing of machine tool base and real-time error compensation of heavy-duty CNC machine tool.

Spatial resolution determines the minimum space unit that a distributed temperature sensor system can distinguish along the fiber thus it is an important parameter to evaluate the performance of the distributed temperature sensor system. A typical distributed temperature sensor system with a spatial resolution of 5m is built and an algorithm of linear fitting correction is proposed to realize temperature measurement of fiber length shorter than 5m accurately. With the method of linear fitting correction, the spatial resolution of the distributed temperature sensor system has been improved from 5m to 1m. The measured temperature of the DTS system is well calibrated by using linear fitting correction algorithm with a fiber length of 4m, 3m, 2m and 1m respectively. The maximum error of the corrective temperature is 2℃ for long term measurement.

Microwave photonic links (MPLs) can provide many advantages over traditional coaxial and waveguide solutions due to its low loss, small size, lightweight, large bandwidth, superior stability and immunity to external interference. It has been considered in various applications such as: the transmission of radio frequency (RF) signal over optical carriers, video television transmission, radar and communication systems. Stability of phase of the microwave photonic links is a critical issue in several realistic applications. The delay line technique for phase noise measurement of phase modulation microwave photonic links is measured for the first time. Using this approach, the input signal noise and power supply noise can be effectively cancelled, and it does not require phase locking. The phase noise of a microwave photonic links with a 10 GHz sinusoidal signal is experimentally demonstrated.

The resonant fiber optic gyro (RFOG) is a high accuracy inertial rotation sensor based on the Sagnac effect. The existence of various noises, including the nonreciprocal noises such as the polarization noise and the Kerr noise as well as the reciprocal circuit noise, limits the performance improvement of the RFOG. An improved scheme by inserting two in-line polarizers in the polarization maintaining fiber transmission-type resonator has been proposed to suppress the polarization-fluctuation induced drift. Furthermore, the adoption of the air-core photonic bandgap fibers (PBFs) offers a novel solution to reduce the optical Kerr effect. In addition, A digital signal processor is designed to reduce the reciprocal noises and detect the rotation information. A minimum actual rotation of 0.001°/s is achieved. The dynamic range is improved by a factor of 7 and the scale factor nonlinearity is decreased by a factor of 60.

It is known theoretically that the long wavelength infrared has better performance when transmitting in atmospheric turbulence. In order to evaluate the influence of the atmospheric turbulence quantificationally, the characteristics of different infrareds transmission in atmospheric turbulence are simulated and studied. A series of time relevant phase screens of atmospheric turbulence are simulated based on Fourier transform method proposed by McGlamery. Wind speed and direction are introduced in the meantime. Wavefront distortion, image spot dancing and spreading, receive loss of different wavelengths (0.85μm, 3.6μm, 10.6μm) are simulated respectively and compared to each other. The results show that the performances of long wavelength infrared (10.6μm) are the best, mid wavelength infrared (3.6μm) takes the second place and short wavelength infrared (0.85μm) is the worst.

A 20Gb/s polarization-insensitive all-optical wavelength switching system for high-speed free-space optical communication (FSO) network is experimentally demonstrated All-optical wavelength conversion (AOWC) is implemented using four-wave mixing (FWM) by highly-nonlinear fiber (HNLF). In the experimental setup, a simple actively mode-locked fiber ring laser (AML-FRL) with repetition frequency from 1 to 15 GHz is used to generate eight 2.5Gb/s tributary signals, which are multiplexed into one 20Gb/s optical data stream. At the receiver, the 20 Gb/s OTDM data stream is demultiplexed down to 2.5 Gb/s via a polarization-insensitive FWM scheme. The whole space communication distance is over 10 meters in building hallway. The experimental results show that this system can stably run over 24 hours at 10^-9 BER level, thus the proposed architecture can work at higher rate with wavelength-division multiplexing (WDM) and high order modulation schemes.

Selected cladding mode recoupling between a long period grating (LPG) and a tilted fiber Bragg grating (TFBG) is demonstrated for satellites vibration environment monitoring. The mode recoupling characteristic between LPGs with different resonance wavelengths and TFBGs with different tilt angles are investigated. Strong coupling occurs between the two associated cladding modes of the same order over the overlapped resonance bands of the two gratings. Suppression ratio of over 20 dB between the recoupled cladding mode and the core reflection mode is achieved when the resonance wavelength of the LPG matches the Bragg wavelength of the TFBG. The present sensor has the features of cost-effective power detection and tip-reflection sensing ability, and give a remarkably simple and elegant approach to dynamic vibration monitoring.

A new kind of power frequency current mutual inductance device based on the optical fiber measurement technology was proposed in this paper. The new device was made up of excitation current source, sensing system and magnetic circuit. The bus-bar was selected as excitation current source. The giant magnetostrictive material and fiber Bragg Grating (GMM-FBG) were combined as the sensing system. The magnetic circuit was consisting of the magnetic materials and permanent magnet materials. The numerical analysis of the magnetic field which generated in the sensors was achieved through the finite element analysis. In the simulation, the quiescent operating point of GMM-FBG sensor was confirmed; the size of the material in the magnetic circuit system was optimized to ensure the good output performance of sensing system. Finally, the numerical relationship between excitation current and the internal magnetic field of the Terfenol-D rods was established. Meanwhile, the calibration of sensor was achieved through the experiment system of the GMM-FBG current transformer sensor.

In this contribution, optic fibers of a serial of doping proportions were prepared and tested. It’s found that B could decrease the sensitivity of refractive index to the temperature, and the sensitivity decreased 2% as the B’s molar percentage increased 1%. By comparing fiber samples’ test results, the proportion of Si: B: Ge to achieve the lowest Δn/ΔT was 0.75: 0.15: 0.1. After balancing the Δn/ΔT and loss, the recommended proportion of Si: B: Ge was given as 0.77: 0.15: 0.08. With this method, the optic fiber delay lines’ time delay could be reduced to 30 ps/km/°C, and their loss is lower than 0.5dB/km at 1550nm wavelength. Besides B and Ge, other kinds of elements are now being used to add into the fiber to improve the property of delay, and decay lines will make the photonic sensing more reliable and stable.

Fiber optical gyro (FOG) is a kind of solid-state optical gyroscope with good environmental adaptability, which has been widely used in national defense, aviation, aerospace and other civilian areas. In some applications, FOG will experience environmental conditions such as vacuum, radiation, vibration and so on, and the scale-factor performance is concerned as an important accuracy indicator. However, the scale-factor performance of FOG under these environmental conditions is difficult to test using conventional methods, as the turntable can't work under these environmental conditions. According to the phenomenon that the physical effects of FOG produced by the sawtooth voltage signal under static conditions is consistent with the physical effects of FOG produced by a turntable in uniform rotation, a new method for the scale-factor performance test of FOG without turntable is proposed in this paper. In this method, the test system of the scale-factor performance is constituted by an external operational amplifier circuit and a FOG which the modulation signal and Y waveguied are disconnected. The external operational amplifier circuit is used to superimpose the externally generated sawtooth voltage signal and the modulation signal of FOG, and to exert the superimposed signal on the Y waveguide of the FOG. The test system can produce different equivalent angular velocities by changing the cycle of the sawtooth signal in the scale-factor performance test. In this paper, the system model of FOG superimposed with an externally generated sawtooth is analyzed, and a conclusion that the effect of the equivalent input angular velocity produced by the sawtooth voltage signal is consistent with the effect of input angular velocity produced by the turntable is obtained. The relationship between the equivalent angular velocity and the parameters such as sawtooth cycle and so on is presented, and the correction method for the equivalent angular velocity is also presented by analyzing the influence of each parameter error on the equivalent angular velocity. A comparative experiment of the method proposed in this paper and the method of turntable calibration was conducted, and the scale-factor performance test results of the same FOG using the two methods were consistent. Using the method proposed in this paper to test the scale-factor performance of FOG, the input angular velocity is the equivalent effect produced by a sawtooth voltage signal, and there is no need to use a turntable to produce mechanical rotation, so this method can be used to test the performance of FOG at the ambient conditions which turntable can not work.

The five of FBG were embedded in the PE sheath of a tether optical cable, which has about 18mm diameter and 7000mm length. The temperature and tension characteristics of the FBGs embedded in the polythene (PE) sheath had been demonstrated quantitatively. The Bragg wavelength of the embedded FBG shift linearly with the change of pulling force loaded on the tether optical cable and its tension sensitivity is about 3.75 pm/kg. The results of temperature experiment suggest the embedded FBG have been sensitized by PE material, so that its temperature sensitivity increase from 9.37pm/°C to about 12.51pm/°C.

The high power consumption and the speed improvement hindrance of the electrical Serializer / Deserializer (SerDes) in current optical interconnection are in the way of the optical interconnection development. Depending on the breakthrough of single-chip opto-electrical integration, high-speed transceiver with optical SerDes is proposed in this paper. The proposal employs time-interleaving multiplexing to realize direct conversion between parallel electrical signal and serial optical signal without an intermediary of serial electrical signal. The absence of the electrical SerDes dramatically decreases the power consumption in the data transmission channel. A transceiver working between 20 parallel digital paths at the data rate of 2GHz and one 40GHz serial optical channel is simulated, and the power consumption is only about 13.5pJ/b. The proposal is compatible with various kinds of optical multiplexing technologies, such as wavelength division multiplexing (WDM), pulse amplitude modulation (PAM), and quadrature phase-shift keying (QPSM), so the bandwidth can be further improved.

Underwater wireless optical communication is a communication technology which uses laser as an information carrier and transmits data through water. Underwater wireless optical communication has some good features such as broader bandwidth, high transmission rate, better security, anti—interference performance. Therefore, it is promising to be widely used in the civil and military communication domains. It is also suitable for high-speed, short-range communication between underwater mobile vehicles. This paper presents a design approach of omni-directional light source used in underwater wireless optical communication, using TRACEPRO simulation tool to help design a combination solid composed of the lens, conical reflector and parabolic reflector, and using the modulated DPSS green laser in the transmitter module to output the laser beam in small divergence angles, after expanded by the combination refraction-reflection solid, the angle turns into a space divergence angle of 2π, achieving the omni-directional light source of hemisphere space, and test in the air and underwater, the result shows that the effect is fine. This paper analyzes the experimental test in the air and water, in order to make further improvement of the uniformity of light distribution, we optimize the reflector surface parameters of combination refraction-reflection solid and test in the air and water. The result shows that omni-directional light source used in underwater wireless optical communication optimized could achieve the uniformity of light distribution of underwater space divergence angle of 2π. Omni-directional light source used in underwater wireless optical communication designed in this paper has the characteristics of small size and uniformity of light distribution, it is suitable for application between UUVs, AUVs, Swimmer Delivery Vehicles (SDVs) and other underwater vehicle fleet, it realizes point-to-multipoint communications.

There are varies modulation formats such as ASK, OOK, BPSK, QPSK, DP-QPSK. The DP-QPSK modulation format appears as the best performing 50 Gbit/s modulation format solution with higher transmission efficiency and stronger anti-interference ability. Therefore, this topic has great significance for the study of a test system of DP-QPSK optical transmission. There is hardware and software design of the test system. Hardware design is the basis and prerequisite for the design of the test system, requiring further understanding of the composition of the test system. The software which completes the work of data processing is a crucial part of the whole test system.

Adaptive optics (AO) technology is an effective way to alleviate the effect of turbulence on free space optical communication (FSO). A new adaptive compensation method can be used without a wave-front sensor. Artificial bee colony algorithm (ABC) is a population-based heuristic evolutionary algorithm inspired by the intelligent foraging behaviour of the honeybee swarm with the advantage of simple, good convergence rate, robust and less parameter setting. In this paper, we simulate the application of the improved ABC to correct the distorted wavefront and proved its effectiveness. Then we simulate the application of ABC algorithm, differential evolution (DE) algorithm and stochastic parallel gradient descent (SPGD) algorithm to the FSO system and analyze the wavefront correction capabilities by comparison of the coupling efficiency, the error rate and the intensity fluctuation in different turbulence before and after the correction. The results show that the ABC algorithm has much faster correction speed than DE algorithm and better correct ability for strong turbulence than SPGD algorithm. Intensity fluctuation can be effectively reduced in strong turbulence, but not so effective in week turbulence.

Multipath transmission features the indoor visible light communication (VLC), which will lead to non-uniformity distribution of the power received by receivers. In this paper, a genetic algorithm is proposed to optimize the refraction indexes of the concentrators on receivers to achieve a uniform distribution of the received power, without decreasing the illuminance quality. Simulation results show that the proposed method can effectively reduce the RPDP (the Ratio of Power Deviation from Peak) from 88% to 52%, comparing with those methods on optimization of the transmitted power.

Fiber optic gyro (FOG) is an optical gyroscope which is based on the Sagnac effect and uses the optical fiber coil as light propagation channel. Gyro drift consists of two components: systemic drift and random drift. Systemic drift can be compensated by testing and calibrating. Random drift changes with time, so it becomes an important indicator to measure the precision of gyroscope, which has a great impact on the inertial navigation system. It can’t be compensated by the simple method. Random drift is a main error of fiber optic gyro (FOG). The static output of FOG is a random project and it has more random noise when as the inertial navigation sensor, which will affect the measurement accuracy. It is an efficient method to reduce the random drift and improve the accuracy by modeling and compensation from the output of FOG. According to the characteristic of fiber optic gyro, the random drift model is studied. Using the time series method, the constant component of the random noise original data is extracted. After stationarity and normality tests, a normal random process is acquired. Based on this, the model is established using the recursive least squares, and then the model is applied to the normal Kalman and adaptive Kalman, finally the data is process with the filter. After experimental verification, the noise variance was reduced after filtering, and the effect is obvious.

Optical orthogonal frequency division multiplexing (OFDM) system combines the advantages of both wireless OFDM and optical fiber technology, thus has high spectral efficiency and can effectively resist polarization mode dispersion and chromatic dispersion in fiber link. However, high peak-to-average power ratio (PAPR) is one of the important shortcomings of optical OFDM system, which requires not only amplifiers with a greater dynamic range, but also leads to serious fiber nonlinear effect. So how to reduce PAPR of optical OFDM system is a crucial issue. This work, aiming to reduce PAPR and improving system BER, analyzes suppression technology of PAPR based on optical OFDM system. Firstly, to improve BER, we utilize Partial Transmit Sequence (PTS) algorithm which introduces phase factors b^(v) multiplying IFFT converted signals and searches a b^(v) which will make PAPR minimum. But this method needs much calculation. Then we exploit companding which can compress amplitude of big OFDM signals and expand small signals. Secondly, simulating the two algorithms respectively and finding two algorithms can suppress PAPR, but the effect has room for improvement. Therefore, an implementation of PTS and companding joint algorithm is proposed, then simulating this method and adding it into optical OFDM system. A system was set up, fiber length setting as 10km, utilizing a MZM modulator and a distributed feedback laser, taking 4QAM and 512points IFFT. The results show that, joint algorithm can reduce PAPR from about 12dB to 8dB, improving the problem of high PAPR, constellation convergence, enhances optical OFDM system transmission performance.

Fibers with different depths of hermetically coated carbon are hydrogen loaded and radiated, and it’s found that too thick of carbon layer around fiber can’t bring best radiation-resistant properties, because the thick carbon layer would make the entering of hydrogen difficult although it can help to stop the hydrogen escaping. We also research the duration of saturated hydrogen loading under the temperature of 30°C, 50°C and 80°C respectively, and it’s found that after 150h, 100h and 48h, the fibers’ photo sensitivities tend to be flat. Besides, in order to research the period of validity of hydrogen, some hydrogen loaded fibers are idle for from 1 day to 1 months before etched. The additional loss of these fibers are tested and compared.

Differential phase-shift keying (DPSK) has been widely implemented and developed in high-speed optical communication systems. The low error rate detection at high access rate is one of the considerable issues in practical engineering application. Balanced detection based on fiber Mach-Zehnder delay interferometer (MZDI) is the typical optical DPSK signal detecting method. It requires that the free spectrum range (FSR) of the MZDI equals the reciprocal of symbol period of the DPSK signal. For the reasons of ambient temperature variation and nonlinear phase noise, a dynamic frequency offset always exists between the FSR and the reciprocal of symbol period. That may introduce some optical signal-to-noise ratio (OSNR) costs and fault detections. Therefore, it is significant to inhibit the frequency offset on DPSK detection. In this paper, firstly, we discuss the effects of frequency offset on DPSK detection, and realize the conclusion that frequency offset is virtually equivalent to an additional phase difference between adjacent symbols. Secondly, through simulation, we analyze the feasibility of DPSK detection in the presence of a definite range of frequency offset, and present the quantitative computation of effective coverage, duty cycle, and optimal sampling time of symbol interference. Some issues which should be considered in practical implementation are also discussed. Finally, according to the relationship among phase difference, temperature and voltage, we propose a phase difference compensation scheme which can automatically adjust the voltage for optimal detections, and dynamically track the changing of ambient temperature and nonlinear phase noise. Furthermore, we ascertain the performance of the voltage requested for implementing the scheme. The scheme can be also developed to quadrature phase-shift keying (QPSK) and differential QPSK (DQPSK) modulation situations.

A feasible program of single-polarization active resonator using hollow-core photonic crystal fiber is proposed in this paper. The basic structure of HCPCF active resonator is designed, and the influence of polarization mode dispersion on the detection accuracy is analyzed with a solution being put forward using single-polarization HCPCF. Then the cross structure of photonic crystal fiber is designed, modeled and simulated by finite element method (FEM) at the wavelength of 632.8nm, and the mode field distribution in the cross-section is obtained. By designing the core size of photonic crystal fiber properly, a polarization extinction ratio of 8.4dB is achieved; therefore single-polarization propagation can be realized in the HCPCF, resulting in suppression of polarization mode dispersion of resonator and improving the theoretical gyroscope detection limit. This research is of great guiding significance to the development of HCPCF RLG.

A novel kind of terahertz (THz) photonic crystal fibers (PCFs) based on the material-filled structure is proposed in this paper. Different materials can be selectively filled into parts of air-holes in the designed THz PCFs, and then perfect features such as single-mode transmission and ultra-flattened dispersion are obtained easily in large frequency ranges near 1THz. Employing full-vectorial finite element method (FEM) and plane wave expansion method (PWE), confinement losses and modal dispersion with different structural parameters and diverse refractive indices of the filled materials are investigated respectively. Numerical results show that the proposed PCFs have acceptable confinement losses, low and flattened dispersions whose absolute values are lower than 1ps/nm*km. Moreover, its structure is simple and its feature is insensitive to variations of parameters. It is helpful for PCFs design and real fabrication in the potential THz applications.

Secure optical communication technologies are important means to solve the physical layer security for optical network. We present a scheme of secure optical communication system by all-optical signal processing technique. The scheme consists of three parts, as all-optical signal processing unit, optical key sequence generator, and synchronous control unit. In the paper, all-optical signal processing method is key technology using all-optical exclusive disjunction (XOR) gate based on optical cross-gain modulation effect, has advantages of wide dynamic range of input optical signal, simple structure and so on. All-optical XOR gate composed of two semiconductor optical amplifiers (SOA) is a symmetrical structure. By controlling injection current, input signal power, delay and filter bandwidth, the extinction ratio of XOR can be greater than 8dB. Finally, some performance parameters are calculated and the results are analyzed. The simulation and experimental results show that the proposed method can be achieved over 10Gbps optical signal encryption and decryption, which is simple, easy to implement, and error-free diffusion.

A low-flattened index-guiding photonic crystal fiber (PCF) with high birefringence and low effective mode area is proposed. Elliptical air-holes with different diameters are distributed on the squeezed lattice. With the supercell lattice method, we simulate numerically the dispersion property and the birefringence property of the fundamental modes in this PCF. Simulation results show that the proposed PCF has a total dispersion as low as 0 ±1(ps/nm/ km) over ultra-broad wavelength band from1.3μm to1.6μm . Meanwhile, the birefringence can be reached the order of 10⁻³ and the low effective mode area is also obtained. Moreover, the influences on the birefringence and dispersion by geometrical parameters have also been discussed in detail.

A three-dimensional magnetic field generator has been constructed taking advantage of three groups of square Helmholtz coils in order to do research on the magnetic susceptibility of optical sensors. Whether the uniformity in the center of the magnetic field is standard has to be analyzed to ensure the accuracy of test data from the optical sensor. Regarding square Helmholtz coil as four current-carrying conductor, three-dimensional space magnetic intensity and its uniformity of square Helmholtz coil were analyzed, and the result of simulating data were given. Due to that two coils may partly produce magnetic-field component possibly cancelling each other out, B_x, B_y, which can have an effect on the uniformity of the magnetic field, so that we need to evaluate the effects. First, we build a mathematical model of the magnetic field intensity of the square Helmholtz coil in the three-dimensional space. Then, some related analysis data and structural models of the three-dimensional uniform magnetic field of the square Helmholtz coil are given by Using the computer software MATLAB and LABVIEW. Finally, that square Helmholtz coils can be applied to study the magnetic susceptibility of optical sensors is proven to be feasible with the standardized testing environments of the magnetic susceptibility and evaluation methods proposed.

In this paper, we demonstrate a distributed fence-perimeter intrusion detection system using a phase-sensitive optical time domain reflectometer (Φ-OTDR) with several advantages, such as high spatial resolution, large detection range, single-end measurement and immunity from electromagnetic interference. By the effort of generating a high-extinction-ratio optical pulse, optimizing the incident optical power and utilizing a differential algorithm, a home-made Φ-OTDR system, as a distributed vibration sensor, is implemented with a spatial resolution of 10 meter. Nowadays, a fence-perimeter intrusion detection system is desired for the security monitor. We set up a fence perimeter using a fiber cable containing only one fiber and a field experiment is carried out based on our Φ-OTDR system. Various vibration events are recorded and analyzed, including wind blowing, personal climbing and knocking. The experiment results reveal unique vibration characteristics of different events in the frequency domain and confirm the effectiveness of the homemade Φ-OTDR system in the application of the distributed fence-perimeter intrusion detection.

The single-channel blind source separation (SCBSS) technique makes great significance in many fields, such as optical fiber communication, sensor detection, image processing and so on. It is a wide range application to realize blind source separation (BSS) from a single optical fiber sensor received data. The performance of many BSS algorithms and signal process methods will be worsened with inaccurate source number estimation. Many excellent algorithms have been proposed to deal with the source number estimation in array signal process which consists of multiple sensors, but they can not be applied directly to the single sensor condition. This paper presents a source number estimation method dealing with the single optical fiber sensor received data. By delay process, this paper converts the single sensor received data to multi-dimension form. And the data covariance matrix is constructed. Then the estimation algorithms used in array signal processing can be utilized. The information theoretic criteria (ITC) based methods, presented by AIC and MDL, Gerschgorin’s disk estimation (GDE) are introduced to estimate the source number of the single optical fiber sensor’s received signal. To improve the performance of these estimation methods at low signal noise ratio (SNR), this paper make a smooth process to the data covariance matrix. By the smooth process, the fluctuation and uncertainty of the eigenvalues of the covariance matrix are reduced. Simulation results prove that ITC base methods can not estimate the source number effectively under colored noise. The GDE method, although gets a poor performance at low SNR, but it is able to accurately estimate the number of sources with colored noise. The experiments also show that the proposed method can be applied to estimate the source number of single sensor received data.

A refractive index insensitive curvature sensor based on cladding-mode resonance of specialty triple-clad fiber (STCF) is proposed. The corresponding mode properties of STCF are investigated theoretically based on the coupled mode theory. The different mode dispersion curves are calculated and a resonance wavelength is obtained. A straightforward experiment is performed to prove the curvature sensitivity. Experimental results shows that the curvature sensitivity can be achieve -11.03374nm/m^-1 in the range of 0~1.17m^-1, and it also has good linearity. This curvature sensor has the advantages of simple structure, easy manufacturing, highly sensitivity and has no cross-sensitivity when it compared to the other sensors. Thus it can be used for curvature monitoring in time.

Tilt sensor is becoming more and more popular in many engineering fields. With the development of the sensor, tilt sensor with high sensitivity and directional is required in these fields. A simple, compact and high sensitivity fiber-optic directional tilt angle sensor is proposed and experimentally demonstrated in this paper. This novel structure is based on an asymmetrical in-line M-Z inclinometer, as a result, the structure is very compact. At the same time, the structure is easy to fabricate. Because of the asymmetrical structure, different changes happened to the sensor and the sensor can recognize the tilt direction. The tilt angle is obtained by monitoring the resonant wavelength shift and the tilt direction can be obtained from the redshift or blueshift. This structure got a very high sensitivity of 0.935nm/° in a range from -3° to 3°.

We successfully fabricate and demonstrate a type of in-line M-Z interferometer by using single mode fiber and suspended dual-core hollow fiber. We fuse one section of dual-core hollow fiber (about 5-10cm length used as interferometer arms) with two part of single mode fiber by arc discharging on their cross sections. After this new M-Z interferometer’s fabrication and related experiments, we improved it by absorbing drops of alcohol in its dual-core hollow body which can do much of contributions to its sensitivity. With bunches of temperature experiments conducted, we find this new interferometer has a good temperature sensitivity highly as 1.751nm/°C (from 20 to 100 °C) and interferometer with alcohol inside has a better temperature sensitivity highly as 3.015nm/ °C (from 20 to 60 °C) respectively.

An improved optical pulse heterodyne demodulation scheme for fiber-optic interferometric sensors is demonstrated. This scheme uses two series-connected Acoustic-optic modulators (AOMs) as intensity modulator and frequency shifter respectively. Compared to the traditional optical heterodyne demodulation structure, this scheme eliminates the polarization-induced signal fading and the noise floor is lowered for using the Michelson-configuration delay structure and Faraday rotation mirrors (FRMs) in the optic architecture of system. At the same time, the architecture of this scheme is not complicated and can be used to complex a large sensor array. Experimental results show that the phase noise floor of this demodulation scheme is flat and reaches -99dB/sqrt(Hz) at frequencies above 300 Hz.

All-fiber interferometer sensor system is a new type of system, which could be used in long-distance, strong-EMI condition for monitoring and inspection. A fiber optic perimeter detection system based on all-fiber interferometric sensor is proposed, through the back-end analysis, processing and intelligent identification, which can distinguish effects of different intrusion activities. In this paper, the universal steps in triggering pattern recognition is introduced, which includes signal characteristics extracting by accurate endpoint detecting, templates establishing by training, and pattern matching. By training the samples acquired in the laboratory, this paper uses the wavelet transformation to decompose the detection signals of the intrusion activities into sub-signals in different frequency bands with multi-resolution analysis. Then extracts the features of the above mentioned intrusions signals by frequency band energy and wavelet information entropy and the system could recognize the intrusion activities occurred along the perimeter sensors. Experiment results show that the proposed method for the perimeter is able to differentiate intrusion signals from ambient noises such as windy and walk effectively. What’s more, the recognition rate of the system is improved while deduced the false alarm rate, the approach is proved by large practical experiment and project.

In this paper we present the field test of the fiber optic ocean bottom cable (FOOBC). The FOOBC are several ocean bottom seismic stations connected by optical fiber cables. In the ocean bottom seismic station, there are three orthogonal fiber optic accelerometers and one fiber optic hydrophone. The design of the sensors and stations are introduced. The field demonstration of an ocean bottom seismic station is carried out in Yunnan Province, China. The test results show that the three accelerometers has similar response to the seismic signal with traditional MEMS accelerometers. We believe that the fiber optic seismic cable is promising in the field of oil and gas exploration and earthquake monitoring.

Long period fiber gratings (LPFGs), which can couple the core mode to the forward propagating cladding modes of a fiber and have the advantage of small additional loss, no backward reflection, small size, which is widely used in optical fiber sensors and optical communication systems. LPFG has different fabricating methods, in order to write gratings on the twin-core at the same time effectively, we specially choose electric heating fused taper system to fabricate asymmetric dual-core long period fiber grating, because this kind of method can guarantee the similarity of gratings on the twin cores and obtain good geometric parameters of LPFG, such as cycle, cone waist. Then we use bending test platform to conduct bending test for each of the core of twin-core asymmetric long period fiber grating. Experiments show that: the sensitivity of asymmetrical twin-core long period fiber grating’s central core under bending is -5.47nm·m, while the sensitivity of asymmetric twin-core long period fiber grating partial core changed with the relative position of screw micrometer. The sensitivity at 0°, 30°, 90° direction is -4.22nm·m, -9.84nm·m, -11.44nm·m respectively. The experiment results strongly demonstrate the properties of rim sensing of asymmetrical twin-core fiber gratings which provides the possibility of simultaneously measuring the bending magnitude and direction and solving the problem of cross sensing when multi-parameter measuring. In other words, we can detect temperature and bend at the same time by this sensor. As our knowledge, it is the first time simultaneously measuring bend and temperature using this structure of fiber sensors.

In most distributed Brillouin sensing systems, it is crucial to keep the long-term stability of the electro-optic modulator (EOM) operating point. The dither-tone based bias control methods are widely adopted in this kind of systems for its robustness and reliability, but the low frequency dither tone (a few kilohertz) added into the dc bias port of the EOM may have a detrimental impact on the sensing performance of the Brillouin sensing system. Experimental results show that the dither frequency should not be set around quarter of the pulse repetition rate or its multiples, and the employed dither amplitude should be in the range of 0.003V_π to 0.015V_π (V_π is the RF half-wave voltage of the EOM), in order to overcome the limitation of dither tone based bias control techniques in BOTDA systems. These results will provide guidelines to improve the performance of the Brillouin sensing systems using dither-based EOM bias control method.

We present three rotation symmetric planar metamaterials and consist of 3, 4 and 6 split resonant rings (SRRs) respectively, proved that they are polarization-insensitive. The modulation characters constructed by the three planar metamaterials are also studied and compared to demonstrate that the structure with more even rotation symmetry is much more beneficial to be polarization-independence. Furthermore, the influencing rules of the electrodes on the polarization character of metamaterials are obtained. The polarization character can be converted by tailoring the electrodes which provides a guide to construct and design novel terahertz polarimetirc devices for potential applications.

We present three rotation symmetric planar metamaterials and consist of 3, 4 and 6 split resonant rings (SRRs) respectively, proved that they are polarization-insensitive. The modulation characters constructed by the three planar metamaterials are also studied and compared to demonstrate that the structure with more even rotation symmetry is much more beneficial to be polarization-independence. Furthermore, the influencing rules of the electrodes on the polarization character of metamaterials are obtained. The polarization character can be converted by tailoring the electrodes which provides a guide to construct and design novel terahertz polarimetirc devices for potential applications.

The fiber optic gyroscope (FOG)based on Sagnac effect has became to one of the most important sensors in developing due to light in quality, high accuracy, compact in dimension and long life and has played a very important role in both military and civil use. It is the most difficult problem that the FOG has an obvious bias drift caused by temperature change and temperature grade, so its application is limited to a great extent. Fiber coil is one of the most critical components in FOG. Here, the characteristic of temperature error of the fiber optical coil was analyzed. At first, by studying the glass transition of coating adhesive in the fiber coil, the element model of the fiber coil with the glass transition of coating adhesive in FOG was built. Then the discrete mathematics model of SHUPE error with the glass transition of coating adhesive in FOG was built. Finally, based on the temperature models mentioned above, the effects caused by the glass transition of coating adhesive on temperature performance of fiber optic gyroscope were analyzed. Theoretical analysis and experimental results show that effect caused by the glass transition of coating adhesive had seriously affected the temperature performance of FOG. By optimizing the glass transition temperature of coating adhesive, the SHUPE error of fiber coils can be reduced. At the same time, the amplitude uniformity of the SHUPE error can be improved greatly to reduce the difficulty in temperature compensation.

Based on weak fluctuation theory, the expression of bit-error rate (BER) of Multiple Quadrature Amplitude Modulation (MQAM) with the consideration of detector noise in the downlink of space communication system is discussed in this paper. According to the expression, the performance of three typical modulation schemes, which are 4QAM, 16QAM, 64QAM, are specially analyzed. It is known that the higher the order of the modulation scheme is, the more bits of information per symbol can carry. However, when the transmission power is 1 W and the receiver diameter Dr is 1 m, the BER is 2.12×10^-13 for 4QAM, 5.98×10^-8 for 16QAM and 6.22×10^-5 for 64QAM, which means that a higher order modulation scheme shows a higher bit-error rate (BER). Thus considering bandwidth efficiency as well as bit error rate, 16QAM is highly recommended in the real space optical communication system. In addition, the relationships between BER and optimum divergence angle, transmitter beam radius, receiving aperture for downlink are also suggested respectively in this paper, which has important reference significance for the design of the ground-to-satellite laser communication system.

Orthogonal frequency division multiplexing (OFDM) technique applied to the atmospheric optical communication can improve data transmission rate, restrain pulse interference, and reduce effect of multipath caused by atmospheric scattering. Channel estimation, as one of the important modules in OFDM, has been investigated thoroughly and widely with great progress. In atmospheric optical communication system, channel estimation methods based on pilot are common approaches, such as traditional least-squares (LS) algorithm and minimum mean square error (MMSE) algorithm. However, sensitivity of the noise effects and high complexity of computation are shortcomings of LS algorithm and MMSE algorithm, respectively. Here, a new method based on compressive sensing is proposed to estimate the channel state information of atmospheric optical communication OFDM system, especially when the condition is closely associated with turbulence. Firstly, time-varying channel model is established under the condition of turbulence. Then, in consideration of multipath effect, sparse channel model is available for compressive sensing. And, the pilot signal is reconstructed with orthogonal matching tracking (OMP) algorithm, which is used for reconstruction. By contrast, the work of channel estimation is completed by LS algorithm as well. After that, simulations are conducted respectively in two different indexes -signal error rate (SER) and mean square error (MSE). Finally, result shows that compared with LS algorithm, the application of compressive sensing can improve the performance of SER and MSE. Theoretical analysis and simulation results show that the proposed method is reasonable and efficient.

With the improvement of people’s living standard, the requirement of network is higher and higher. The rate and capacity of network communication are rising all the time, it ’s outstanding on the backbone networks. The rate of backbone network had improved from 10G to 100G in recent years. This change also put forward new requirement for optical network equipment . The key technologies of lower order cross-connect equipment is discussing in this passage. This passage mainly discusses the following aspects: time division multiplexing of STM-1 lower-order pointer interpretation and lower -order pointer generation. By using the technologies discussed in this passage, the lower -order cross-connect devices has the higher cross-connect capacity under consuming the same logic resource, and the equipment will meet the requirement of the backbone network transmission capacity.

Quantum access network can't guarantee the absolute security of multi-user detector and eavesdropper can get access to key information through time-shift attack and other ways. Measurement-device-independent quantum key distribution is immune from all the detection attacks, and accomplishes the safe sharing of quantum key. In this paper, that Measurement-device-independent quantum key distribution is used in the application of multi-user quantum access to the network is on the research. By adopting time-division multiplexing technology to achieve the sharing of multiuser detector, the system structure is simplified and the security of quantum key sharing is acquired.

Hollow-core photonic crystal fiber (HCPCF) resonator optic gyroscope is an important direction of high accuracy fiber optic gyroscope. The development and application of HCPCF has provided broad prospect for the research of resonator fiber optic gyroscope (RFOG). The HCPCF can restrict light to propagate in the fiber core filled with air/vacuum based on photonic band-gap effect. Compared with conventional polarization maintaining fiber based RFOG (PM-RFOG), the HCPCF based RFOG (HC-RFOG) has great potential to achieve lower nonreciprocal bias and better environment adaptability. The polarization noise, which is one of the main noise sources in the RFOG, is modeled and simulated in this paper. The resonance curves of RFOG with two polarization modes excited are presented, and the polarization noises caused by fiber parameters are calculated. The comparison of polarization noises between HCPCF resonator and polarization maintaining optical fiber (PMF) resonator are carried out by numerical simulation. The polarization features of the HCPCF resonator and conventional PMF resonator are experimentally characterized. The analysis result shows that the polarization stability of HCPCF resonator can be two orders of magnitude lower than that of the conventional PMF resonator. Therefore, the HCPCF resonator has evidently superiority in reducing polarization noise and improving gyro performance. The captive tests based on the HCPCF RFOG system are realized, and a bias stability in the range of 2.5°/s is successfully demonstrated.

An optical fiber sensor to accurately judge the level of a point is presented in this paper. Three fibers are used in the sensor, one as the source to emit infrared light, and the others as the differential inputs to absorb the scattering of light. Adopting a differential structure of dual signal fibers helps removing the interference of external environment and the change of the intensity of the light source. When the sensor contacts the liquid, the emitted light will be scatted by the liquid so that the output voltage will have significant difference from it when the sensor is above the liquid. A 45 degree oblique end-face of fibers is not just used to reduce the adhesion of liquid but also can increase discrepancy between differential inputs due to different scattered light intensity at different position, and then enhance the sensitivity. Base on this point, the optical fiber point liquid level sensor is designed and its working performance is investigated by experiments. The experimental results indicated stability, accuracy and excellent performance in the use of this sensor to measure the status of liquid level. And the safety will be ensured for the characteristic of fiber and excellent electrical isolation.

Fiber optic gyroscopes (FOG) are getting more and more attention in areas such as stabilization control systems as they are all solid state and have a wide bandwidth. In stabilization systems that require wide bandwidth control, motors are usually used as actuating mechanism for active disturbance restrain. Voice coil motors (VCMs) are usually used in compact stabilization systems that require large torque and fast response. However, AC magnetic field, which can affect the output of FOG due to Faraday effect, will be generated during operation of VCMs. The frequency range affected by the AC magnetic field to the FOG’s output is the same as VCMs drive signal frequency range, which is also exactly the stabilization system’s working range. Therefore the effect of the AC magnetic field to FOGs must be evaluated to verify the feasibility of a stable system design that uses both FOGs and VCMs. In this article, the basic structure and operating principle of stabilization system is introduced. The influence of AC magnetic field to FOG is theoretically analyzed. The magnetic field generated by VCMs is numerically simulated based on the theory deduction of the magnetic field near energized wires. To verify the influence of the VCM generated magnetic field to the FOGs in practical designs, a simplified random fiber coil model is built for it’s hard to accurately test the exact polarize axis’s twisting rate in a fiber coil. The influence to the FOG’s output of different random coil model is simulated and the result shows a same trend that the influence of the VCM’s magnetic field to the FOG is reduced as the distance between the VCM and the FOG increasing. The influence of a VCM to a FOG with the same parameters is experimentally tested. In the Fourier transformed FOG data the same frequency point as the VCM drive signal frequency can be read. The result fit simulated result that as the distance increases, the influence decreases. The amplitude of the frequency point is just above the average noise spectrum amplitude of the tested FOG and that indicates the influence of the particular VCM’s AC magnetic field to the FOG’s output is negligible in this design. The feasibility of the future design can also be tested in the same way as the article introduced.

An integrated RF photonic phase shifter that can achieve a tunable phase shift with little RF amplitude variation is presented. The beating between phase-modulated optical carrier and the first-order sideband can generate RF signal with desired phase shift. Results show the RF phase shifter can achieve a continuous 0° − 360° phase shift with low amplitude variation.

A novel power-interrogated sensor that allows for the simultaneous measurement of temperature and strain is proposed and experimentally demonstrated. The sensor is based on the use of a linearly chirped fiber Bragg grating (FBG) with a broad (~10 nm) as well as slant reflection spectrum. Unlike most of the previous FBG-based sensors, the FBG proposed here is simultaneously used as both the sensing and the interrogating element. The measurement accuracies for the temperature and the strain are estimated to be ±2 °C in the range of 12-197 °C and ±24in με the range of 0-1270 με, respectively.