Phase modulation spectroscopy using an all-fiber piezoelectric transducer modulator for a resonator fiber-optic gyroscope

The theoretical analysis and experimental demonstration of phase modulation spectroscopy employing an all-fiber piezoelectric transducer modulator for a fiber ring resonator fiber-optic gyroscope is presented for the first time as far as we know. The results support the feasibility of such a technique as a rotation detection scheme for a resonator fiber-optic gyroscope.     

Ringing phenomenon of the fiber ring resonator

A resonator fiber-optic gyro (R-FOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect. A fiber ring resonator is the core sensing element in the R-FOG. When the frequency of the fiber ring resonator input laser is swept linearly with time, ringing of the output resonance curve is observed. The output field of the fiber ring resonator is derived from the superposition of the light transmitted through the directional coupler directly and the multiple light components circulated in the fiber ring resonator when the frequency of the laser is swept. The amplitude and phase of the output field are analyzed, and it is found that the difference in time for different light components in the fiber ring resonator to reach a point of destructive interference causes the ringing phenomenon. Finally the ringing phenomenon is observed in experiments, and the experimental results agree with the theoretical analysis well.     

Y波导残余强度调制对IFOG性能的影响

本文首先通过正弦波调制下干涉信号光强分析解调出光纤陀螺的输出信号,进而得出残余强度调制存在的情况下陀螺输出信号的变化情况,同时,通过分析陀螺信号的变化说明残余强度调制对光纤陀螺性能的影响与陀螺精度要求有关,精度越高,其影响越明显.其次,具体分析了数字闭环光纤陀螺受残余强度调制影响的情况下,其解调输出电压变化引起的数字阶梯高度变化,并通过残余强度调制系数与数字阶梯高度的关系式,说明了残余强度调制对光纤陀螺零偏和标度因数的影响.最后,对所得出的残余强度调制系数与光纤陀螺标度因数稳定性的关系进行了Matlab仿真,通过仿真结果,更进一步说明残余强度调制对数字闭环光纤陀螺标度因数稳定性的影响.     

Multifrequency erbium-doped fiber laser operating at room temperature

A method to realize room-temperature operation of a multifrequency Er-doped fiber laser with low-frequency shift feedback placed within a linear laser cavity is theoretically proposed and experimentally demonstrated. Simultaneous multiwavelength lasing with 0.5 nm wavelength spacing is experimentally demonstrated by applying a sinusoidal signal of 10 kHz to a fiber phase modulator inserted within the linear cavity to prevent single wavelength steady-state oscillation. In the linear cavity, an all-polarization-maintaining fiber Sagnac loop is used as a periodic filter, and a single-mode fiber loop with a polarization controller is used as a partial reflector and also as an output port.     

Establishment of All Digital Closed-Loop Interferometric Fiber-Optic Gyroscope and Scale Factor Comparison for Open-Loop and All Digital Closed-Loop Configurations

This paper covers the design details of an all digital closed-loop interferometric fiber-optic gyroscope (ADCL-IFOG) prototype, constructed in TUBITAK UME, and scale factor comparison between open-loop and ADCL-IFOG prototypes with sine wave biasing modulation. The output of demodulation circuit, proportional to the applied rotation rate, was sampled by AD7714YN analog-to-digital converter (ADC), operated in 16 bit resolution. Error voltage, generated by microcomputer – controlled LTC 1667CG, 14 bit digital to analog converter (DAC), was sent to the phase modulator through a linear summing circuit to make Sagnac Phase Shift zero, depending on the rotation direction. For this implementation, the ultimate rotation rate of 1.84 ($^{circ}/{hbox{h}}$ ) was nullified. The averaged sensitivity of the proposed closed-loop IFOG in unit of error voltage applied to the phase modulator was determined as 132.65 $mu hbox{V}/(^{circ}/{hbox{h}}$ ). The scale factors of both the open-loop and ADCL-IFOG prototypes were compared in a range of 1–15270 ( $^{circ}/hbox{h}$) rotation rate, corresponding to Sagnac Phase Shifts varying from 0.00115 ( $^{circ}$) to 17.57448 ( $^{circ}$). The maximum peak to peak noise and the bias stability of ADCL-IFOG prototype were determined as 4.97 ($^{circ}/hbox{h}$ ) and 1.48 ($^{circ}/hbox{h}$ ) at 23.0$~^{circ}hbox{C}$ , respectively.      

Experimental investigation of an optically amplified time-division-multiplexed polarization-insensitive fiber-optic michelson interferometric sensor system

We experimentally investigate optically amplified time-division-multiplexed polarization-insensitive fiber-optic Michelson interferometric (PIFOMI) sensor systems, using an erbium-doped fiber amplifier (EDFA) and a phase-generated carrier (PGC) demodulation technique. The influence of the EDFA on the extinction ratio (ER) of the light pulse and on the minimum phase-detection sensitivity (MPDS) is examined. We find that the EDFA acting as a preamplifier has limited usefulness because the highly amplified spontaneous emission (ASE) noise generated by the EDFA degrades the ER and the MPDS. However, both postamplifiers and in-line EDFA's can work successfully. The MPDS of the unamplified time-division-multiplexed PIFOMI system with an ER of 33 dB was 2.4 x 10(-5) rad/(Hz)(1/2) at ~1 kHz. For maintaining a MPDS of better than 3.4 x 10(-5) rad/(Hz)(1/2) at ~1 kHz, the worst ER's for the postamplified and in-line amplified systems were 20 and 17.8 dB, respectively. The corresponding input signal peak power should be larger than -20 and -25 dBm for the postamplifiers and in-line amplifiers, respectively. When two postamplifiers and two in-line amplifiers are used, an allowable sensor system loss of 47 dB and a link length of the input-output lead fiber of 108 km can be realized for this system with a 32-sensor array. Implementation of optically amplified time-division-multiplexed and wavelength-division multiplexed-time-division multiplexed PIFOMI subarray sensor systems are also addressed.     

Analysis of polarization properties of a mode-locked fiber laser gyroscope

We investigated the polarization characteristics of a mode-locked fiber laser gyroscope (MLPLG) formed with a Nd-doped fiber as an optical gain medium and a Sagnac loop mirror. The output pulse patterns and the polarization states were found to be determined by fiber birefringence in the different sections of the MLPLG. We describe the conditions for the MLPLG to operate with automatic reciprocity leading to the possibility of phase-error-free operation.     

Sagnac环形电流互感器的原理与发展研究

高压变电站中用于电力系统电流测量的全光纤电流传感器由于具有传统电流互感器无法比拟的优点,具有广阔的应用前景.Sagnac环形电流互感器是在干涉式光纤陀螺结构上发展起来的一种互感器结构.由于基于Sagnac干涉仪技术的光纤陀螺的实用化,用此技术来实现Sagnac环形电流互感器的实用化成为电流互感器的热点.本文首先介绍了S...     

Microwave generation with photonic frequency octupling using a DPMZM in a Sagnac loop

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated. The scheme is based on bi-directional use of a dual-parallel Mach–Zehnder modulator (DPMZM) in a Sagnac loop. The two sub-modulators in the DPMZM are driven by two low-frequency signals with a π/2 phase difference, and the dc biases of the modulator are all set at the maximum transmission points. Due to the velocity mismatch of the modulator, only the light wave along the clockwise direction is effectively modulated by the drive signals to generate an optical signal with a carrier and ±4th order sidebands, while the modulation of the light wave along the counterclockwise direction is far less effective and can be ignored. By properly adjusting the polarization of the light wave output from the Sagnac loop, the optical carrier can be significantly suppressed at a polarizer, and then an optical signal with only ±4th order sidebands is generated. In the experiment, a pure 24-GHz microwave signal without additional phase noise from the optical system is generated using a 3-GHz local oscillator signal. As no electrical or optical filter is used, the photonic frequency octupler is of good frequency tunability.     

Sagnac 干涉型水听器的信号解调技术

为了对Sagnac干涉型水听器的信号进行解调,在讨论了Sagnac干涉型水听器的原理,得到和Mach-Zehnder干涉型水听器的不同之处后,提出了相应的解调技术．并用软件实现了信号的解调．解调结果表明,输出信号与输出信号完全一致,并可以准确标定出干涉仪的相位调制．     

Fiber-optic gyroscope with suppression of excess noise from the radiation source

A new optical system is proposed and investigated experimentally for a Sagnac fiber interferometer in which the excess noise of the wide-band radiation source is suppressed. A tenfold improvement in the sensitivity of a fiber-optic gyroscope with an erbium/ytterbium fiber superfluorescent light source was achieved experimentally. It is shown that the identity of the polarization characteristics of the interferometer channels plays an important role. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (September 26, 1998)     

IFOG中相位调制器的残余强度调制及其测量

利用开环正弦波调制解调方法,推导了铌酸锂相位调制器的残余强度调制(简称RIM)对干涉型光纤陀螺(简称IFOG)信号的影响,指出在调制频率漂移或光纤环渡越时间变化时RIM可导致陀螺的零偏和噪声增大.对典型条件的计算表明,0.01°/h的IFOG容许的最大RIM为13ppm,0.1°/h的中低精度IFOG则为81ppm.提出利用锁相放大器精确测量相位调制器RIM的方法,并对国产器件进行测量,结果表明,器件RIM指标可在中低精度IFOG中应用.     

Full investigation of the resonant frequency servo loop for resonator fiber-optic gyro

Resonator fiber-optic gyro (RFOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect. A high-accuracy resonant frequency servo loop is indispensable for a high-performance RFOG. It is composed of a frequency discriminator, a loop filter, and a laser actuator. Influences of the loop parameters are fully developed. Optimized loop parameters are obtained by considering the noise reduction and wide dynamic performance of the RFOG. As a result, with the integration time of 10?s, the accuracy of the resonant frequency loop is increased to 0.02?Hz (1σ). It is equivalent to a rotation rate of 0.067°/h, which is close to the shot noise limit for the RFOG, while a minimum rotation of ±0.05°/s has been carried out simultaneously. These are the best results reported to date, to the best of our knowledge, for an RFOG using the miniature semiconductor laser that benefits from the optimization of the resonant frequency servo-loop parameters.     

Orthogonal polarization fiber gyroscope with increased stability and resolution

The orthogonal polarization fiber gyroscope (OPFG) is an interferometric fiber gyroscope design that requires no phase bias in the fiber ring and is insensitive to light-source intensity noise. However, in the original OPFG [Hitachi Rev. 33, 215 (1984)], environmental changes caused first-order false rotation signals. We propose and experimentally verify modifications that eliminate the first-order sensitivity to environmental changes and that improve the gyroscope's resolution as well. We believe that this modified OPFG is the first interferometric fiber gyroscope capable of stable, high-sensitivity measurement that contains only reciprocal optical elements.     

Open-loop operation experiments in a resonator fiber-optic gyro using the phase modulation spectroscopy technique

A detection system in the resonator fiber-optic gyro is set up by the phase modulation (PM) spectroscopy technique. The slope of the demodulated curve near the resonant point is found to affect the ultimate sensitivity of the gyro. To maximize the demodulated signal slope, the modulation frequency and index are optimized by the expansion of the Bessel function and optical field overlapping method. Using different PM frequencies for the light waves, the open-loop gyro output signal is observed. The modulation frequency in this PM technique is limited only by the cutoff frequency of the LiNbO3 phase modulators, which can reach several gigahertz. This detection technique and system can be applied to the resonator micro-optic gyro with a less than 10 cm long integrated optical ring.     

Robust and environmental insensitive fiber optic Sagnac interferometer for microwave photonic applications

A technique that allows a fiber optic Sagnac interferometer based microwave photonic device to be implemented using non-polarization maintaining components inside the Sagnac loop while still obtaining an output that is insensitive to changes in environmental conditions is presented. It is based on inserting the non-polarization maintaining components in between a polarization beam combiner and a Faraday rotator mirror inside the loop. The technique also introduces a phase bias to the light propagating inside the loop. Experimental results demonstrate that the discretely and continuously tunable Sagnac loop based signal processors implemented using non-polarization maintaining components have an environmentally insensitive frequency response.     

Effective fiber-optic polarization modulator

A fiber-optic polarization modulator based on a piezoelectric ceramic transducer is considered. The device employs the phenomenon of photoelasticity, whereby the polarization of light in the fiber is modulated due to the birefringence variations induced by oscillating transverse pressure applied to the fiber. An analytical expression for the modulation efficiency is obtained. A high efficiency of the proposed modulator is confirmed by experimental data.     

Modified phase-generated carrier demodulation compensated for the propagation delay of the fiber

In general applications, the output signals of the fiber-optic interferometric sensor (FOIS) need some demodulation techniques to linearly demodulate the sensing phase signal. The common signal demodulation circuit of the FOIS is passive homodyne demodulation using phase-generated carrier [(PGC) demodulation]. Preliminary analysis of the research demonstrates that a variation in the output demodulated signal is related to the length of the fiber, and the output demodulated signal will approach zero at some certain lengths of the fiber. To improve the performance of the FOIS, it is necessary to develop the modified PGC demodulation to compensate for the propagation delay of the fiber.     

Real-time digital holographic beam-shaping system with a genetic feedback tuning loop

A novel implementation of a real-time digital holographic system with a genetic feedback tuning loop is proposed. The proposed genetic feedback tuning loop is effective in encoding optimal phase holograms on a liquid-crystal spatial light modulator in the system. Optimal calibration of the liquid-crystal spatial light modulator can be achieved via the genetic feedback tuning loop, and the optimal phase hologram can then overcome the aberration of the internal optics of the system.