Nanosecond thermal fiber switch using a Sagnac interferometer

We demonstrate a new, fast, and stable all-optical fiber switch based on the TOAD principle. It utilizes a transient thermal phase shift induced by a short pump pulse to cause switching in a cobalt (Co)-doped fiber placed in a Sagnac fiber loop. Switched pulses as short as 7-ns were observed in a 2-m loop containing a 2.55-cm length of Co-doped fiber pumped with 12-ns pulses. Compared to other all-optical switches using doped fibers, this switch offers a dramatic increase in speed and stability, and a sizable reduction in fiber length requirement     

Nonlinear switching behaviours in a compact all-semiconductoroptical-amplifier Sagnac interferometer device

Nonlinear switching effects in a GaAs-AlGaAs all-semiconductor optical-amplifier loop device with a multimode interference waveguide amplifier (MMIWA) for closing the loop was investigated experimentally and numerically. The miniaturized device, designed to imitate a nonlinear optical loop mirror (NOLM), has a latency more than one hundred times smaller than that of a NOLM. Also, because it used an MMIWA for replacing a coupler in a conventional NOLM, its operation was quite different from that previously reported. In CW signal operation, the nonlinear switching behaviour resulted from the combined effect of nonlinear coupling in the MMIWA and the amplification and lateral field redistribution of the signal through the loop structure. Efficient self-switching and cross-polarized switching were observed. Numerical simulations showed consistent trends in varying device parameters     

Effects of crosstalk and timing jitter on all-optical time-divisiondemultiplexing using a nonlinear fiber Sagnac interferometer switch

All-optical time-division demultiplexing using a nonlinear fiber Sagnac interferometer switch (NSIS) is studied with respect to the two main causes that degrade the bit-error-rate (BER) performance: crosstalk and timing jitter. It is shown that unwanted cross-phase-modulation in the reference signal which counter-propagates to the control pulse, as well as the poor extinction of the switch itself, seriously degrades the extinction ratio of the switch, thus increasing the crosstalk from other channels. Numerical calculations clarify the effect of the switching window width, window shape, and the multiplexed channel number on the power penalty in terms of BER performance. Timing jitter between the signal and control pulses is investigated as another degradation factor that causes an error floor in BER performance. It is found that the minimum BER is obtained when the window width is set to the time slot width and the rms value of the jitter must be less than 1/14.1 times the time slot width to ensure that BER<10^-12. To confirm this analysis, precise measurements of BER performance with NSIS-based demultiplexing are performed using amplified gain-switched laser diode pulses, as the relative timing jitter, switching window width, and multiplexed channel number are varied. Good agreement with the analysis is shown. Finally, optimum system design based on a small power penalty and low error floor is described. It is shown that the NSIS has the potential of demultiplexing a 160-Gb/s or 320-Gb/s optical data stream into its 40-Gb/s constituents with only a 4-dB or 7-dB power penalty     

All optical signal regularizing/regeneration using a nonlinearfiber Sagnac interferometer switch with signal-clock walk-off

All-optical signal regularizing/regeneration using a nonlinear fiber Sagnac interferometer switch (NSIS) that employs signal-clock walk-off is investigated. The NSIS realizes all-optical signal regeneration, including timing and amplitude regularizing, by switching clock pulses with amplified input signals using a walk-off-induced, wide, square switching window and intensity-dependent transmittance of the device. First, characteristics (in both the temporal and spectral domains) of the all-optical signal regeneration achieved with the NSIS are investigated theoretically and experimentally. They certify that if clock pulses are within the square switching window obtained with signal-clock walk-off, the clock pulses can be modulated according to the data that the input signals carry and retain their temporal and spectral profiles. This means that if clock pulses can be prepared that meet the system requirements, the NSIS can convert input signals that may not satisfy system requirements into high-quality output signals. Limitations on the switching contrast due to the cross-phase modulation of counterpropagating reference pulses is also discussed. Second, two possible applications of NSIS-based all-optical signal regularizing/regeneration, 1) an all-optical multiplexer with an optical clock and 2) an all-optical regenerative repeater, are discussed. Preliminary experiments with ~10-ps pulses at bit rates of ~5 Gb/s that use locally prepared optical clock pulses, show that the NSIS provides an error-free regeneration function with a certain tolerance for pulse-period irregularity if a proper optical clock is obtained     

Effects of group velocity dispersion on self/cross phase modulationin a nonlinear Sagnac interferometer switch

Time-resolved numerical analysis of a nonlinear Sagnac interferometer switch (NSIS) reveals that the combined effects of group velocity dispersion (GVD), self phase modulation, cross phase modulation, and pump-probe walk-off seriously degrade switching performance when the soliton number N of the pump pulse is under 5. This means that the peak power of short pump pulses cannot be reduced to less than the critical value at N>5 to prevent the effect of GVD. This restriction is more severe for pump pulses in the anomalous dispersion region than for those in the normal dispersion region because of higher-order soliton compression. System designs for time-division demultiplexers that use NSISs and picosecond pump pulses generated by a laser-diode coupled to erbium-doped fiber amplifiers are discussed. It is found that 1:32 demultiplexing from 160 to 5 Gb/s and 1:8 demultiplexing from 80 to 10 Gb/s with a switching contrast of more than 60 are possible using diode-laser-pumped 1- and 2-ps pump pulses, respectively     

Frequency modulated heterodyne optical fiber Sagnac interferometer

This paper describes a new approach to the detection of rotation rate using the optical fiber Sagnac interferometer. An inherently reciprocal heterodyne system gives the advantages in terms of signal-to-noise ratios (SNR's) of heterodyne detection, while independent electronic monitoring of each propagation path through the interferometer significantly enhances signal processing flexibility. The system may thus be used as a probe to evaluate fiber properties in a way compatible with other architectures, and these measurements should lead to advances in performance characteristics. A prototype system has exhibited noise levels in the region of 100°/h, and improvement to the signal processing will soon improve on this figure.     

The Sagnac interferometer as a two-parameter sensor

We show the Sagnac interferometer as a two-parameter sensing device where nonreciprocal and reciprocal effects can be independently and simultaneously monitored. Phase shifts induced by nonreciprocal effects affect differently the counterpropagating beams in the loop and are accurately detected by a phase sensitive detection scheme. A probe for reciprocal effects is built by introducing a birefringence modulator inside the polarization-maintaining loop with its axes rotated with respect to the axes of the loop fiber. The resulting quadrature component of the demodulated signal is proportional to the phase shift induced by reciprocal effects at the probe site, making the interferometer suitable for dual parameter sensing. Demonstration of a electric/magnetic field sensor is presented     

A variable-loop Sagnac interferometer for distributed impactsensing

A variable-loop fiber optic Sagnac interferometer is designed to locate a time-varying disturbance. Phase perturbation on a Sagnac loop produces a nonreciprocal phase signal which contains information of the perturbation location. Both location and amplitude of the perturbation can be determined by combining two phase signals from the variable-loop Sagnac interferometer. Spatial resolution better than 1 m has been demonstrated in a 180 m prototype system     

实时数字散斑干涉仪及其应用

介绍了一种用于工程的多功能数字散斑干涉仪的测量原理、系统结构和设计特点，并给出了测量结果。     

Temperature sensor based on PNR in Sagnac interferometer

A temperature sensor based on polarization non-reciprocity (PNR) in fiber-optic Sagnac interferometer (FSI) was proposed. The experimental study was made primarily and the results agree with theory well.Discussion shows that this kind of temperature sensor can achieve high precision and have great application potential.     

DEVELOPMENT OF PHOTOCONDUCTIVE SWITCH AND ITS APPLICATIONS

The picosecond photoconductive switches are developed and used to detect the pulse laser waveform. By using the photoconductive switches, an novel lab model of ultra-wide band(UWB) radar is also developed. The experimental results are given to show the performances of the switches and the UWB radar.     

Complete switching in a three-terminal Sagnac switch

A three-terminal all-optical fiber switch based on a fiber Sagnac interferometer is described. The use of polarization components allows the construction of a switch in which the control beam and signal beam are isolated (i.e. the device is three terminal) and which is cascadable (the device output can drive its inputs). The interaction length need not be limited by the walkoff length in the fiber, as cross-splices can be made in the birefringent fiber to permit multiple passes. Contrast ratios as high as 40:1 have been demonstrated in a switch driven by an amplified laser diode.<>     

采用萨格纳克干涉仪与螺旋相位片生成矢量光束

萨格纳克干涉仪中传播的两束光具有相同的光程,因而适合用于高稳定的合束系统,螺旋相位片作为无源、分离器件具有螺旋光束转化效率高、工作环境适用条件低等优点。研究将萨格纳克干涉仪和螺旋相位片结合起来生成矢量光束的方法具有重要的研究意义。通过分析光束的轨道角动量态和偏振态在萨格纳克干涉仪中的演化规律,优化设计出了等腰直角三角形的合束光路结构。合束装置可以不使用1/2波片进行光束偏振态调制,因此光路结构更紧凑和稳定。通过旋转检偏器方法测量了生成矢量光束的阶数。实验结果证实了合束方法的高稳定性和高效率。     

Position determination of an acoustic burst along a Sagnac interferometer

We report on a method to measure the longitudinal position of an acoustic burst, or spark, using an all-fiber Sagnac interferometer (SI). A focused pulsed /spl sim/10 ns laser is used to ionize air creating the spark. This ionization point is situated near a coil of test fiber connected to the SI but acoustically separated from the bulk of the SI. A fast Fourier transform (FFT) performed on the temporal signal of the SI shows a series of s from which the position of the acoustic signal is determined. Over an SI length of /spl sim/35 km, longitudinal positions are determined to within tens of meters, corresponding to a best run percent uncertainty of 0.07%.     

Fiber-optic sensor array based on Sagnac interferometer with stablephase bias

We propose and experimentally demonstrate a novel fiber sensor array based on a Sagnac interferometer with very simple electronic signal processing. A stable quadrature phase bias was obtained using a phase modulator, and the polarization-induced signal fading was suppressed by using a depolarizer and a broad-band source. A phase sensitivity of about 4.0 μrad_rms/√Hz at 5 kHz was obtained using a two-sensor array     

Simulation model of magneto-optic fiber Bragg gratings and its applications in Sagnac interferometers

According to the symmetry of transmission matrix for non-uniform magneto-optic fiber Bragg gratings (MFBGs),the simulation model of the non-uniform MFBGs with bidirectional injection of light has been presented for the Optisystem software.The simulation model is verified by comparing with the Matlab numeric results using the piecewise-uniform MFBG model.As an example,the polarization-dependent loss (PDL) of an MFBG-based Sagnac interferometer (MSI) is analyzed in detail.Simulation results indicate that the magnetic field sensitivity of the MSI system can be improved by optimizing the coupling coefficient of the coupler,and the maximum of peak PDL is up to three times that of the single MFBG structure.The simulation model proposed in the paper is useful for the design of MFBG-based optical information devices.     

基于Sagnac干涉仪的多点局部放电检测系统

提出了一种基于光纤Sagnac干涉仪用于多点局部放电超声检测的光纤传感系统。该超声检测系统由光源、单模光纤延迟线、光纤耦合器、相位调制器、偏振控制器和对比度为1的光纤Sagnac干涉仪组成。首先介绍了传感系统的超声检测的原理,然后搭建了模拟局部放电超声实验平台,利用Nd∶YAG激光器照射钢板激发出的表面波和高频声源,针对局部放电超声在钢板和变压绝缘油中的传播情况进行了实验。实验结果证明了使用该系统用于局部放电超声检测的有效性,在100kHz～200kHz频率范围内,信噪比可达40dB以上,同时实验验证了该Sagnac传感器对局部放电超声的多点检测能力。该光纤超声检测系统结构简单,频率响应高,成本低廉在局部放电等领域有着巨大潜力。     

基于分体式Sagnac干涉仪的长波红外干涉成像光谱系统

介绍了基于分体式Sagnac 干涉仪的静态高通量干涉成像光谱技术的基本原理,设计并实现了长波红外宽波段等比消偏振分光膜系,给出了干涉仪尺寸的设计方法并利用TracePro 软件验证了设计的干涉光路。使用制冷型和非制冷型探测器对该红外干涉成像光谱仪方案进行了塑料薄膜透过率测试,实验结果与高精度Michelson 光谱仪测量值有较高的吻合度,证实了该方案的正确性。最后进行了推扫实验,给出了数据重排、基线校正和切趾等数据预处理方法,验证了该系统方案工作模式的可行性。     

Application of Sagnac interferometer for measuring chromaticdispersion of installed single-mode fibres

A novel method is described which is suitable for measuring the chromatic dispersion of installed single-mode fibres by using a modified σ-type Sagnac interferometer, which contains an off-centred phase modulator. Chromatic dispersion is measured with high resolution from the output interference fringe without requiring any fast diagnostic equipment. Measurement of the chromatic dispersion of a single-mode fibre in the wavelength range 1.5-1.58 μm is demonstrated     

An ultrasonic fiber-optic hydrophone incorporating a push-pulltransducer in a Sagnac interferometer

A theoretical and experimental analysis of a push-pull acoustic transducer incorporated in a Sagnac interferometer is presented. The transducer is optimized for detection of ultrasonic signals in the frequency range 0.4-1.5 MHz. Two different configurations are investigated. In one, the sensing fiber forming the transducer constitutes the total loop length, and in the second an additional delay coil is included in the middle section of the Sagnac loop. In the latter we demonstrate experimentally noise-equivalent pressures of 36-43 dB re. 1 μPa/Hz^1/2 in the frequency range 0.4-1.0 MHz. An approximate theoretical model is presented, and we obtain reasonable agreement between theory and experiment for both the frequency-dependent noise equivalent pressure and the directional responsivity of this push-pull acoustic fiber-optic sensor