Polarization Sagnac interferometer with postmodulation for gravitational-wave detection

We describe a polarization Sagnac interferometer with an in-loop half-wave plate that allows signal detection at the reciprocal port of the beam splitter while maintaining the ability to detect the signal at a dark fringe. Postmodulation and balanced heterodyne detection are used to recover the signal. This topology is simple to control because of its common-path characteristics and its collinear signal and local oscillator. The robustness of this scheme to amplitude and frequency fluctuations of the laser is demonstrated. Intraloop birefringence in this interferometer acts as a loss, reducing the power on the detector. The magnitude of this loss is discussed and experimentally verified.     

Compact phase-shifted Sagnac interferometer for ultrasound detection

A compact fibre, phase-shifted Sagnac interferometer for ultrasound detection has been developed. The interferometer is a truly path-matched device, and therefore requires no path stabilization or heterodyning. It is a less expensive and more robust alternative to the heterodyne or path-stabilized Michelson interferometer. The device provides high spatial resolution of ultrasonic detection. It has been used in conjunction with conventional piezoelectric transducers (PZT) to detect Rayleigh and Lamb waves and to image a crack in a thin plate, rivet cracks in riveted plates, and for ultrasonic beam profiling.     

Fiber laser mode locked by a Sagnac interferometer with nonlinear polarization rotation

We describe a new fiber laser configuration based on a nonlinear optical loop mirror with a symmetrical coupler, a quarter-wave retarder, and highly twisted, birefringent fiber in the loop. The nonlinear optical loop mirror configuration operates by nonlinear polarization rotation. We have achieved stable generation of subpicosecond pulses with milliwatts of average output power.     

A dual-loop Sagnac interferometer

A new type of all-fibre Sagnac interferometer composed of two loops is proposed and analysed in detail. It can be used with a very long transmission line while maintaining excellent performance characteristics due to the automatic compensation of any birefringence effects in the trunk fibre. Preliminary experiments at 1310~nm wavelength with a 70~km long trunk fibre demonstrated an interference visibility as high as 98%, indicating that this scheme has promising potential applications.     

Arrayed waveguide Sagnac interferometer

We present a novel device, an arrayed waveguide Sagnac interferometer, that combines the flexibility of arrayed waveguides and the wide application range of fiber or integrated optics Sagnac loops. We form the device by closing an array of wavelength-selective light paths provided by two arrayed waveguides with a single 2 x 2 coupler in a Sagnac configuration. The equations that describe the device's operation in general conditions are derived. A preliminary experimental demonstration is provided of a fiber prototype in passive operation that shows good agreement with the expected theoretical performance. Potential applications of the device in nonlinear operation are outlined and discussed.     

基于Sagnac光纤干涉仪的管道泄漏检测和定位技术

研制了一种基于Sagnac干涉仪的分布式光纤传感器,可实时进行管道泄漏检测与定位.阐述了该传感技术的工作原理和泄漏点定位方法,并推导了泄漏引起的光信号相位变化表达式。管道泄漏实验结果表明,水压为0.3MPa时,该技术能有效地检测到管道泄漏的发生并准确定位。     

Non-contact detection of laser-generated surface acoustic waves using fiber optic Sagnac interferometer

A high powered Q-switched Nd:YAG laser was used to excite the surface waves, and an optical fiber sensor was used to detect the out-of-plane displacements due to the propagating waves. This sensor is based on the fiber optic Sagnac interferometer, which has the path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence in an optical path using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. The performance of the fiber optic Sagnac interferometer was investigated, and laser-generated surface wave signals were detected using this fiber optic sensor. The developed fiber optic sensor configured in this study is very simple and is effective for non-contact detection of ultrasonic waves.     

用于光纤Sagnac干涉仪的全息耦合器

我们利用重铬酸明胶作为全息记录介质,制得了分光比接近1:1,总衍射效率超过60%的双重全息透镜.本文讨论了这种全息透镜作为Sagnac光纤干涉仪的耦合器的优点,并给出了初步的实验结果.本文还推导了倾斜光栅的Q因子,提出了全息光栅的等效Bragg定律,并通过它们设计出所需的全息透镜.     

Sagnac interferometer for photothermal deflection spectroscopy

Photothermal deflection spectroscopy is combined with a Sagnac interferometer to enhance the sensitivity of the absorption measurement by converting the photothermal beam deflection effect into the light intensity change by the interference effect. Because of stable light interference due to the common path, the signal intensity can be amplified without increasing the noise by extending the optical path length between a sample and a photodetector. The sensitivity is further improved by the use of focusing optics and double-pass geometry. This makes photothermal deflection spectroscopy applicable to any kind of material in the whole visible region with a xenon lamp for excitation and water or air as a deflection medium.     

Phase-difference amplification using a Sagnac interferometer

In this paper, we describe a new method for achieving phase-difference amplification, which is quick and convenient, operates in real time, and requires no photographic steps. Magnification factors of 2, 4 or 6 are achieved easily in one step. Because the system operates in real time, phase stepping may be applied to extract the amplified phase distributions. Our method is a variation on longitudinally reversed shearing interferometry, using first- or higher-order diffraction from a grating (hologram) which is in fact the interferogram of the wavefront under test. The grating is derived from a standard two-beam interferometer which is phase-stepped, and displayed in real time on a spatial light modulator in the phase-difference amplification setup. It is illuminated by the two output beams from a Sagnac interferometer, similar to the set up used by (Barnes et al. Barnes TH, Eiju T, Matsuda K. Appl Opt 1986; 25:1864). for spectral resolution enhancement, and a phase-amplified fringe pattern is obtained by spatial filtering using a Fourier transform lens. We demonstrate operation of the phase amplifier and show amplified phase maps retrieved by phase-stepping. We believe this is the first time that real-time phase amplification without photographic steps and with phase stepping has been demonstrated.     

Sagnac干涉仪与光纤环形激光器

依据相干光学理论,以现代激光干涉侧试技术中的光纤Ｓａｇｎａｃ干涉仪为例,分析和讨论了光纤环形激光器的基本工作原理,并结合其物理原理简要介绍了光纤环形激光器和光纤陀螺（ＦＯＧ）的应用的发展前景。     

Analysis of a Sagnac interferometer with low-birefringence twisted fiber

The fiber Sagnac interferometer of low birefringence and twist is analyzed numerically in the linear region. A novel method for measurement of the birefringence of the fiber and the angle of rotation of the axes inside the fiber loop of the interferometer is also presented.     

Polarization Sagnac interferometer with a reflective grating beam splitter

All-reflective interferometric gravitational-wave detector configurations with a diffraction grating as a power beam splitter have been proposed to reduce thermal lensing. We demonstrate the use of a diffraction grating as a polarization beam splitter in a zero-area polarization Sagnac interferometer.     

Polarization-based balanced heterodyne detection method in a Sagnac interferometer for precision phase measurement

We describe a balanced heterodyne detection method for a Sagnac interferometer that uses a polarization-dependent beam splitter. The signal and the local oscillator are orthogonally polarized components of a single laser beam, permitting the detection of the signal by subtraction of two photocurrents produced in appropriate polarization projections. Using this scheme, we experimentally demonstrate a phase measurement with a sensitivity of 9x10(-10) rad/ radicalHz. The measurement is robust in the presence of laser frequency noise, as a result of preserving the common-path nature of the Sagnac interferometer, and of laser-amplitude noise, as a result of balanced detection.     

Two-parameter estimation in a matter-wave Sagnac interferometer

We explore the general characteristics of a matter-wave Sagnac interferometer in a two-parameter estimation scheme. We find that the measurement precisions of both parameters cannot reach the Heisenberg limit (HL) simultaneously when the input state is maximally entangled. Only one of the parameters’ uncertainties can approach the HL while the other is scaled by the standard quantum limit. We provide the conditions with which the measurement precision of the specific parameter can reach the HL. We also discuss and figure out the concrete expressions of the constraint conditions for saturating the quantum Cramér–Rao bound. To satisfy these constraint conditions, the evolution time has to be a series of discrete values. Additionally, we calculate the variances of the parameters through some examples under these constraint conditions. The results provided in our work show some intrinsic features of the matter-wave Sagnac interferometer for the two-parameter estimation, which can be valuable in actual experiments.     

基于Sagnac干涉仪的紫外超短脉冲放大技术

 介绍了一种基于Sagnac干涉仪形式的超短脉冲多路放大技术，能够实现多个激光脉冲的自动复合，并且在理论上能够实现锁相输出。分析了调节偏差对于干涉仪性能的影响，在仔细调节好干涉仪的情况下，起主要限制作用的是放大器介质折射率的随机变化，同时给出了一种利用偏振分束片的多路放大方法及实验结果，将直径为50mm，能量为2~3mJ的脉冲激光放大为最大输出能量为120mJ，稳定运行在100mJ的脉冲。     

Electro-optical fiber modulation in a Sagnac interferometer

The linear electro-optical effect was induced in optical fibers by thermal poling. A Sagnac all-spliced fiber loop was constructed incorporating an electro-optical fiber used as a phase modulator at 1.5 microm and stable switching was obtained. A rise time of approximately 40 ns was obtained, and signals <2 V generated a measurable optical response.     

基于成像光谱仪的Sagnac干涉仪的优化设计

为了满足仪器的轻量化设计要求,研究了成像光谱仪系统中Sagnac干涉仪的优化设计方法,讨论仪器轻量化设计中干涉仪尺寸与系统前置望远镜倍率的制约关系,通过将Sagnac干涉仪展开为平板玻璃的方法对干涉仪的结构和光路进行分析,根据几何关系推导出Sagnac干涉仪几何尺寸与入射干涉仪的光束孔径和视场角的关系表达式,通过该关系式可以求出干涉仪的尺寸极值和对应的系统前置望远镜倍率大小。以某短波红外光谱仪为例,运用推导出的关系式,计算并给出了优化设计结果。