Polarization Jitters Caused by Fiber Nonlinearity in PM Optical Communication System

The phenomenon of polarization jitters caused by fiber nonlinearity is investigated. A general formula about the polarization jitter is concluded in polarization multiplexing (PM) system based on two orthogonal linear polarization states when the best polarization correction is used. A 100 Gb/s PM system based on NRZ code is investigated by simulation, and the Stocks parameter about polarization jitter and Poincare sphere diagrams are got for different power and phase difference of two orthogonal polarized light. The results show that the polarization jitters will be suppressed when the combined PM signal is the linear or circular polarization state.

Coupling Character of Polarization Maintaining Optical Fiber Under the Condition of Bend

In the field of optical fiber communication and sensing,polarization maintaining optical fiber with special polarization wave transmit character has been taken more and more attentions.It is more important of couple between polarization modes,with the help of microdisturbed and coupled mode theories,the coupled characters of high birefracting Bow-Tie optical fiber in the condition of pure bend are analysed,and power coupling relationships between transmit modes are also derivated.

Low-repetition-rate, all-polarization-maintaining Yb-doped fiber laser mode-locked by a semiconductor saturable absorber

A low-repetition-rate, all-polarization-maintaining（PM）-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standard PM fiber, and passively mode-locked by a fiber pigtailed semiconductor saturable absorber. Linearly polarized pulses with 1.66 MHz repetition rate and 22 dB polarization extinction ratio are generated at a wavelength of 1030 nm, which is determined by an intracavity filter. In addition, to demonstrate that the oscillator is a good seed for high energy pulse generation, an all-fiber master oscillator power amplifier is built and amplified pulses with energy about 2 μJ are obtained.

Microstructure and properties of novel polarization maintaining fiber

An improved type of elliptical jacket polarization maintaining fiber was developed by using a modified chemical vapor deposition method with special treatment. Different from conventional elliptical jacket, the shape of the stress jacket was transmuted. The cross-section of fiber consists of 5 layers: substrate, outer cladding, stress jacket, inner cladding and core. The cross sectional component distribution was investigated by electron probe microscopy and energy dispersive spectrum. The finite element method was used to calculate the stress birefringence. Based on the analyses of the microstructure, the technological process is improved. The temperature cycling test of the fiber wound into gyroscope coils was performed. The results show that the fiber possesses superior performance at high and low temperatures compared with other fibers. The high homogeneity is achieved by well-controlled modified chemical vapor deposition process. A homogeneous length of 8 km fiber is obtained. With advantages in homogeneity and length, the fiber has great potential in applications such as fiber gyroscopes, fiber hydrophone and other optical fiber sensors.

Measurement of Rotatory Optics Element in Tensor Dielectric Matrix for Rotatory Optical Fiber

The rotatory optics element in the tensor dielectric coefficient matrix is an important para-(meter) for analyzing and calculating a rotatory optical fiber by electromagnetic theory. But the mea-(surement) of rotatory optics element is difficult for the rotatory optical fiber. A simple principle and method for measuring rotatory optics element are put forward in this paper. Firstly by using electromagnetic theory it was demonstrated that the rotatory optics element has a simple linear relation with the rotatory angle, and then the rotatory optics element has a simple linear relation with the magnetic field strength (or bias current in the helix coil) . Secondly a measurement system for the rotatory optics element in the rotatory optical fiber was designed. Using the measurement system the rotatory element can be obtained by measuring the bias current simply.

A tunable comb filter using single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop

A novel tunable comb filter composed of a single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop is proposed and experimentally demonstrated. The filter tunability is achieved by rotating the polarization controller. The spectral shift is dependent on rotation direction and the position of the polarization controller. In addition, the adjustable range achieved by rotating the half-wave-plate polarization controller is twice higher than that of the quarter-wave-plate one.

Wide-Band Polarization-Independent Semiconductor Optical Amplifier Gate with Tensile-Strained Quasi-Bulk InGaAs

A semiconductor optical amplifier gate based on tensile strained quasi bulk InGaAs is developed.At injection current of 80mA,a 3dB optical bandwidth of more than 85nm is achieved due to dominant band filling effect.Moreover,the most important is that very low polarization dependence of gain (<0 7dB),fiber to fiber lossless operation current (70～90mA) and a high extinction ratio (>50dB) are simultaneously obtained over this wide 3dB optical bandwidth (1520～1609nm) which nearly covers the spectral region of the whole C band (1525～1565nm) and the whole L band (1570～1610nm).The gating time is also improved by decreasing carrier lifetime.The wide band polarization insensitive SOA gate is promising for use in future dense wavelength division multiplexing (DWDM) communication systems.

Novel Polarization Control Approach to Long-Term Fiber-Optic Frequency Transfer

We demonstrate a novel polarization control system based on a gradient descent algorithm,applied to a 450-km optical frequency transfer link.The power of the out-loop beat note is retrieved by controlling the polarization state of the transferred signal,with a recovery time of 24 ms,thereby ensuring the long-term evaluation of the fiber link.As a result,data utilization is enhanced from 70%to 99%over a continuous measurement period of^12 h.A fractional transfer instability of 7.2×10^-20 is achieved at an integration time of 10000 s.This work lays the foundation for the comparison of a remote optical clock system via a long-haul optical fiber link.

Analysis of errors induced by λ/4 wave plate in fiber-optic current sensor system

1/4λ wave plate is a key element in the fiber-optic current sensor system. When a retardation error or an orientation error of birefringence axes of 1/4λ wave plate with respect to the hi-bi fiber axes occurs in the 1/4λ wave plate, the sensor system will output a wrong result of the measured current. The contributions of these two errors to the final result of the whole system were studied and the errors functions were deduced by establishing the measurement function of the current sensor system with Jones matrixes of the optical elements. The results show that that the greater the orientation error or the retardation error, the larger the final error, and that these two errors cannot be compensated each other.

Beyond 100 Gb/s Optical OFDM Transmitted in Optical Long-Haul System

100 G Ethernet is considered to become the next generation Ethernet standard for IP networks.Typical 100 Gb/s transmission systems and their performance are presented.Comparision and analysis for 100 Gb/s transmission systems have been discussed.It is demonstrated that optical OFDM can be used in future 100 Gb/s/ch and long-haul system.

Polarization Characteristics of the Deformed Low-Mode Fiber Waveguides with Polarization Conservation

In this work the results of polarization researches of low-optical fiber waveguides with conservation of polarization are presented. Obtained results quite convincingly testify regarding a high sensitivity low-mode regime of work of an optical fiber to anisotropic external influences, in comparison with one-mode regime of work of the same fibre. This result, can represent a big practical value at the realization of high-sensitivity fiber-optical devices of different physical values.

An all-optical buffer based on polarization rotation in an EAM

A theoretical model of the refractive index changes of the TE and TM modes in an electro-absorption modulator （EAM） is deduced. The photon absorption and refractive index changes are analyzed numerically. The influence of pump intensity on the phase difference between the TE and TM modes is studied. The polarization rotation effect is obtained in the EAM, and a novel all-optical fiber loop buffer is designed.

A Passive Optical Fiber Current Sensor Based on YIG

A research on passive optical fiber current sensor based on magneto-optical crystal and a new design of light path of the sensor head are presented. Both methods of dual-channel optical detection of the polarization state of the output light and signal processing are proposed. Signal processing can obtain the linear output of the current measurement of the wire more conveniently. Theoretical analysis on the magnetooptical fiber current sensor is given, followed by experiments. After that, further analysis is made according to the results, which leads to clarifying the exiting problems and their placements.

Retrieval of Aerosol Optical Properties over a Vegetation Surface Using Multi-angular, Multi-spectral, and Polarized Data

An algorithm to retrieve aerosol optical properties using multi-angular,multi-spectral,and polarized data without a priori knowledge of the land surface was developed.In the algorithm,the surface polarized reflectance was estimated by eliminating the atmospheric scattering from measured polarized reflectance at 1640 nm.A lookup table （LUT） and an iterative method were adopted in the algorithm to retrieve the aerosol optical thickness （AOT,at 665 nm） and the （A）ngstr（o）m exponent （computed between the AOTs at 665 and 865 nm）.Experiments were performed in Tianjin to verify the algorithm.Data were provided by a newly developed airborne instrument,the Advanced Atmosphere Multi-angle Polarization Radiometer （AMPR）.The AMPR measurements over the target field agreed well with the nearby ground-based sun photometer.An algorithm based on Research Scanning Polarimeter （RSP） measurements was introduced to validate the observational measurements along a flight path over Tianjin.The retrievals were consistent between the two algorithms.The AMPR algorithm shows potential in retrieving aerosol optical properties over a vegetation surface.

Harmful Intrusion Detection Algorithm of Optical Fiber Pre-Warning System Based on Correlation of Orthogonal Polarization Signals

At present, advanced researches of optical fiber intrusion measurement are based on the constant false alarm rate （CFAR） algorithm. Although these conventional methods overcome the interference of non-stationary random signals, there are still a large number of false alarms in practical applications. This is because there is no specific study on orthogonal polarization signals of false alarm and intrusion. In order to further reduce false alarms, we analyze the correlation of optical fiber signals using birefringence of single-mode fiber. This paper proposes the harmful intrusion detection algorithm based on the correlation of two orthogonal polarization signals. The proposed method uses correlation coefficient to distinguish false alarms and intrusions, which can decrease false alarms. Experiments on real data, which are collected from the practical environment, demonstrate that the difference in correlation is a robust feature. Furthermore, the results show that the proposed algorithm can reduce the false alarms and ensure the detection performance when it is used in optical fiber pre-warning system （OFPS）.

Radiation-induced effects in polarization-maintaining optical fibers for interferometric gyroscope

Radiation-induced attenuation （RIA） in four types of polarization-maintaining optical fibers for interfer-ometric fiberoptic gyroscope （IFOG） at 1310 nm is measured. The measurements are conducted during and after steady-state γ-ray irradiation using a 60 Co source in order to observe significantly different RIA behavior and recovery kinetics. Mechanisms involving dopants and manufacturing process are introduced to analyze the RIA discrepancy as well as to guide the choice and hardening of optical fibers during the design of IFOG. Medium-accuracy IFOG using Ge–F-codoped fiber and pure silica core fiber can survive in the space radiation environment.

Finite element analysis on stress-induced birefringence of polarization-maintaining optical fiber

Influence of thermal-mechanical properties on the features of the panda polarization-maintaining optical fiber (PMF-) in fabrication process is studied in detail by finite element method (FEM). The stress birefringence is 2.13443×10-4 obtained by the static analysis and 2.1269×10-4 by dynamic analysis. The difference in simulation by two methods is around 0.4%. The non-uniformity of stress birefringence in the fiber core is about 1.6%. Predicted results demonstrate that effect of the thermal conductive parameter on fiber thermal stress dominates. The high and uniform stress birefringence in the fiber core is obtained by appropriately selecting suitable stress region area and position.

Generation of a mid-infrared broadband polarized supercontinuum in As_2Se_3 photonic crystal fibers

A simplified structure of birefringent chalcogenide As 2 Se 3 photonic crystal fiber（PCF） is designed.Properties of birefringence,polarization extinction ratio,chromatic dispersion,nonlinear coefficient,and transmission are studied by using the multipole method,the finite-difference beam propagation method,and the adaptive split-step Fourier method.Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm,we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail,with femtosecond pulses at a wavelength of 4 μm as the pump pulses.Especially,mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm.Their spectral width at 20 dB reaches up to 12 μm.In the birefringent PCF,we find that the supercontinuum generation changes with the pump alignment angle.Research results show that no coupling between eigenpolarization modes are observed at the maximum average power（i.e.,37 mW）,which indicates that the polarization state is well maintained.

Optical sampling system using periodically-poled lithium niobate waveguide and nonlinear polarization rotation mode-locked fiber laser

A novel design of optical sampling system has been developed by using sum-frequency generation （SFG） in a periodically-poled lithium niobate （PPLN） waveguide and using passive mode-locked fiber laser pulses as optical sampling pulses. The system achieved high temporal resolution and high sensitivity using a 30 mm length PPLN with quasi phase match period of 19.3 μm and 151 fs sampling pulses which were generated by passive modelock fiber laser based on nonlinear polarization rotation （NPR）. Clear eye-diagram of 10 Gbit/s non-return-to-zeros （NRZ） pseudorandom binary sequence （PRBS） optical signal were successfully reconstructed by this system.

Self-starting all-fiber PM Er:laser mode locked by a biased nonlinear amplifying loop mirror

A compact all-fiber polarization-maintaining Er:laser using a nonlinear amplifying loop mirror is reported. Fundamental single-pulse mode-locking operation can always self start, with a cavity round-trip decreased from ~ 4.7 m to~ 1.7 m. When the pulse repetition rate is 121.0328 MHz, output pulse is measured to have a center wavelength/3-d B spectral bandwidth/radio frequency signal to noise ratio(SNR)/pulse width of 1571.65 nm/18.70 nm/80 d B/477 fs, respectively. Besides, three states including the exponential growth, damping state, and steady state are investigated through the build-up process both experimentally and numerically. Excellent stability of this compact Er:laser is further evaluated,demonstrating that it can be an easy-fabrication maintenance-free ultrafast candidate for the scientific area of this kind.