Counting signal processing and counting level normalization techniques of polarization-insensitive fiber-optic Michelson interferometric sensors

A counting signal processing technique of the fiber-optic interferometric sensor is proposed. The technique is capable of counting the numbers of the maximum and minimum of the output interferometric signal in a specific time duration, and it can be used as the basis to distinguish the sensing phase signal. It can also be used as a signal detector on applications such as intrusion detection. All sensors are subject to aging of the optical components and bending loss, and therefore the output signal of each sensor may vary with time. We propose a counting level normalization technique to compensate for these variations and to obtain the correct counting numbers.     

A base-band NDS electrode configuration for HACT devices

Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal     

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.     

In-line interferometric time-integrating acousto-optic correlator

A novel, efficient, stable, in-line interferometric, two Bragg cell, acousto-optic architecture is introduced for signal correlation and spectrum analysis. The processor employs an image-inversion technique to produce a correlation output that does not have to be generated on a fast spatial carrier, thus reducing the burden on the required space-bandwidth product on the output time-integrating detector array. The system is particularly suited for wide-instantaneous-bandwidth signal processing and is demonstrated as an autocorrelator for dc-to-10-MHz AM signals on a 100-MHz carrier. A fixed-spatial-carrier outputbased correlator and spectrum-analyzer architecture that is particularly limited in the wideband mode is demonstrated for comparison purposes with the proposed flexible-spatial-carrier-design-based in-line acousto-optic correlator.     

Multiplexed interferometric fiber-optic sensors with digital signal processing

A microcontroller-based digital signal processing system developed for use with fiber-optic sensors for measuring pressure in internal combustion engines is described. A single distributed feedback laser source provides optical power for four interferometric sensors. The laser current is repetitively modulated so that its optical frequency is nearly a linear function of time over most of a cycle. The interferometer phase shift is proportional to the elapsed time from the initiation of a sawtooth until the sensor output signal level crosses a threshold value proportional to the laser output power. This elapsed time, assumed to vary linearly with the combustion chamber pressure, is determined by the use of a digital timer-counter. The system has been used with fiber Fabry-Perot interferometer transducers for in-cylinder pressure measurement on a four-cylinder gasoline-powered engine.     

基于单片机的数字式热电偶传感器设计

针对热电偶传感器存在的输出热电势信号小、不便于远距离传输,需要进行冷端温度补偿、不便于使用,输出的是模拟信号、不便于实现数字式测量等问题,提出一种基于单片机的测量电路,该电路可对热电偶输出的信号进行测量,并能够自动进行冷端温度补偿,测量结果转换为RS232串行信号向外输出。热电偶传感器配备上该测量电路,便可实现所测温度的数字输出,具有较高的实用性。     

一种针对频率扫描测量系统的信号处理方法

设计了一种针对频率扫描绝对距离测量系统的信号处理算法。该系统采用基于电流调制式的频率扫描方法,利用一个比对干涉光路与一个测量干涉光路进行同步测量。两路扫描干涉信号分别由两个光电探测器进行光电转换,作为绝对距离计算处理的输入信号。分析了测量系统的原理与扫描干涉信号的特点,应用两步差分卷积算法进行信号处理,提取的比对光路与测量光路的周期或频率信息进行绝对距离测量。分析了该算法的周期计算误差。实验验证这种方法具有较大的计算优势。     

基于干涉解调技术的光纤激光器水声传感系统

分析了基于Michelson干涉解调技术的光纤激光器水声传感的原理,在一段掺铒光纤中写入具有π相移的光纤光栅构成光纤激光器,水声压力作用在激光器上引起激光工作波长的变化;采用基于3×3耦合器的偏振无关的非平衡光纤Michelson干涉仪将激光波长变化转化为干涉仪的相位变化;干涉仪的输出由光电探测器转换后使用DSP进行信号解调.针对3×3耦合器分光比不对称的问题,本文提出利用实时调整幅度的2路干涉信号进行解调的方案,该方案不需要3×3耦合器有严格的分光比,消除了外界环境对解调输出的非线性影响.水声探测实验表明,光纤激光器水声传感系统的声压灵敏度为-166.5 dB(参考值1 rad/μPa),解调结果与水声信号具有良好的线性关系.     

干涉型光纤传感器的分集消偏振衰落技术的信号处理

对干涉型光纤传感器的分集检测消偏振衰落技术进行了理论分析，提出了将各路信号平方后相加的信号处理方式，使之能实现单元及阵列的实时消偏振衰落信号检测。通过理论计算，可以使干涉信号幅度波动小于4.7dB，并得出三路检偏是分集检测的最简取的结论，通过信号处理电路，能够在信噪比略有降低的情况下消除偏振衰落的影响，实现进一步光纤传感器的消偏振衰落，并设计了用于阵列的分集检测的实现方式。     

Interferometric antenna response for gravitational-wave detection

The interferometric antenna response to gravitational-wave excitation is studied with the Fermi Normal Coordinate (FNC) reference system, with the limit that the gravitational wavelength must be much larger than the interferometric arm length. An optical configuration of the antenna, quite similar to the one generally considered in the long-baseline antenna projects, has been studied, i.e., Fabry-Perot optical cavities in the interferometer arms and reflectors at the input and the output of the interferometer for the purpose of recycling both the laser power and the output signals. An exact computation of the antenna response is given in a form that is also suitable to provide directly the responses for simplier optical configurations without the power or the signal recycling. Furthermore the response of the antenna for the narrow-band detection mode is also calculated. The results obtained in the FNC gauge at rest with the antenna are consistent with the ones given in the literature that were computed in the transverse traceless gauge at rest with the gravitational radiation.     

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．     

Use of time-frequency distributions to estimate the parameters of motion of a tonal signal source

Algorithms for obtaining estimates of the trajectory parameters of a moving signal source for the case of one receiver and two spatially separated receivers are considered. The optimization algorithm is based on the method of coordinate descent using a combination of the golden-section method and subsequent parabolic interpolation. For the interferometric scheme and moderate signal/noise ratios a distance estimation error of ±(5–15%)%, a traverse time error of ±(1–2) sec and a velocity error of ±(2–4)% are attainable. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 48–52, March, 1997.     

Measurement of Distance and Medium Velocity Using Frequency-Modulated Sound/Ultrasound

The methods reported for the measurement of distance and medium velocity using ultrasound are based on the principles of pulse radar, pulse Doppler radar, and continuous- wave radar. In this paper, the use of frequency-modulated sonic/ultrasonic radiations for such measurements has been proposed. The required measurement setup has been described, and the mathematical model needed for extraction of distance/medium velocity from the electrical output signal has been developed. The proposed measurement setup has been implemented for distance measurement with commonly used ICs.     

MIMO线性系统输入输出信号统计特征的双谱评定方法

基于高阶统计量具备处理随机信号的特性,提出了一种利用三阶谱(双谱)评定MIMO线性系统时域输入输出信号统计特征的新方法。通过建立线性系统双谱数学模型,根据系统响应、所测得的频响函数以及离散信号的双谱数值估计算法,经逆运算获得系统的双谱驱动信号,随后利用高阶谱对高斯随机信号的盲性判定其输入信号的高斯性。将上述方法与采用传统相位随机化法(对功率谱添加随机相位)所获得的驱动信号分别应用于一悬臂梁模拟控制系统中,通过对输入信号的分析及控制结果的比较,发现基于双谱所生成的时域随机驱动信号呈现出较强的非高斯性且收敛速度更快。对于输出信号统计特征的评定,提出从输入信号与系统频带接近的程度入手,再次利用高阶统计量对高斯随机信号的盲性进行定性判定,对于无法判别满足何种非高斯统计分布特征的,不管是对于输入信号还是输出信号,一律采用绘制信号的概率分布特征曲线进行定量评定。     

Interferometric probe for near-field optical microscopy systems

We have studied the possibility of creating a new type of the interferometric near-field pinhole probe for near-field optical microscopy systems based on a Fabry-Perot fiber microresonator with a nanodimensional pinhole in one of its output mirrors. The dependence of the resonance wavelength shift in the Fabry-Perot interferometer on the distance from the output diaphragm to the object has been determined using the finite-difference method in the time domain. It is shown that the proposed technique ensures a spatial resolution of no worse than λ/15.     

Signal extraction in a power-recycled michelson interferometer with fabry-perot arm cavities by use of a multiple-carrier frontal modulation scheme

We present a signal extraction scheme for longitudinal sensing and control of an interferometric gravitational-wave detector based on a multiple-frequency heterodyne detection technique. Gravitational-wave detectors use multiple-mirror resonant optical systems where resonance conditions must be satisfied for multiple degrees of freedom that are optically coupled. The multiple-carrier longitudinal-sensing technique provides sensitive signals for all interferometric lengths to be controlled and successfully decouples them. The feasibility of the technique is demonstrated on a tabletop-scale power-recycled Michelson interferometer with Fabry-Perot arm cavities, and the experimentally measured values of the length-sensing signals are in good agreement with theoretical calculations.     

A Doppler radar for multiple targets

A programmable instrument for the simultaneous measurement of velocities and acceleration or deceleration of different objects becomes possible through the use of spectral analysis of the Doppler signal. Programmable gain and frequency synthesis is under software control. Spectra for different segments of the Doppler time series are displayed versus time. When scaled, velocity versus time is displayed. By integration, velocity versus distance could also be displayed. Curve fitting is applied to chosen segments so that velocity and acceleration or retardation can be calculated. The raw digitized Doppler signals as well as calculated results are stored on disk for further off-line review and editing     

Influence of chromatic dispersion on a dual-wavelength passive-homodyne detection method for fiber-coupled interferometers

The passive-homodyne method is very attractive for demodulating optical signals available at the output of interferometric sensors by the use of coherence multiplexing. Phase measurement and the use of two broadband sources with different central wavelengths permit a resolution of λ/10(5) to be achieved with a 20-μ range-sensor optical path difference. However, dispersive birefringent elements are required in this technique, which has some disturbing effects on the correlation signal position, on its envelope form, and on the measured phase. An analytical treatment of the problem and a numerical validation are described. Experimental evidence of the effects predicted by theory is presented.     

Interferometric distributed optical-fiber sensor

An interferometric technique is described for detecting and locating perturbations along an optical fiber. This distributed sensor, based on a modified fiber-ring interferometer, has a position-dependent response to time-varying disturbances such as strain or temperature. These disturbances cause a phase shift that is detected and converted to spatial information. The sensor consists of two parts, namely, a reflecting-fiber-ring interferometer and a differentiating-ring interferometer. The reflecting ring consists of a fiber ring with one port of the coupler connected to a reflector. Consequently the output port of the reflecting-ring interferometer is the same as the input port. Because it is an inherent zero-path-imbalanced system, a short-coherence-length source such as a light-emitting diode can be used. Any time-varying perturbation on the fiber in the ring results in a detector signal proportional to the product of the rate-of-phase change caused by the perturbation and the distance of the perturbation relative to the center of the fiber ring. The second part of the system, a differentiating-ring interferometer, consists of the same fiber-ring interferometer modified only slightly. The output of this part of the sensor is proportional only to the rate of phase change as a result of the unknown perturbation and contains no distance information. By dividing the output of the reflecting-ring interferometer by the output of the differentiating-ring interferometer, we determine disturbance location. Results obtained with a 155-m distributed fiber sensor are discussed.     

Investigation of interferometric noise in fiber-optic gas sensors with use of wavelength modulation spectroscopy

We report on interferometric noise limitation of fiber-optic gas sensors with highly coherent lasers and wavelength modulation spectroscopy. Interference between signal wave and reflected waves causes signal fluctuation in the output, which limits the performance of the sensing system. Sensor resolution limited by interferometric noise is calculated for a fiber-optic gas sensor with the Q(6) absorption line of methane gas at approximately 1650 nm. The results are useful for system designers of this particular type of gas sensor.