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.     

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。     

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.     

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.     

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 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.     

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。     

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.     

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-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.     

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.     

Efficient single-photon frequency conversion using a Sagnac interferometer

We propose a scheme for efficient optical frequency conversion at the single-photon power level. The scheme exploits the quantum interference of single-photon states at a three-level quantum emitter coupled to a Sagnac interferometer. We show that this device can achieve single-photon frequency up- or down-conversion with near unity efficiency.     

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.     

All-optical wavelength and pulse-width conversions with a Sagnac interferometer semiconductor-based switch

A Sagnac interferometer switch with a semiconductor optical amplifier is proposed for all-optical wavelength and pulse-width conversions. The configuration of this switch is simple, and the switching speed is not limited by the semiconductor carrier's recovery time. The pulse width of the input data, 1.5 ps, is converted to 2.4-18.1 ps. A wavelength conversion of input data at 1539 nm to a tunable-wavelength bandwidth of 15 nm (1550-1565 nm) is also demonstrated.     

Hybrid configuration of Sagnac and modal interferometer with high extinction ratio

A hybrid configuration of Sagnac and modal interferometer is proposed to obtain high extinction ratio (ER). Firstly, a modal interferometer based on core-offset splicing of three sections of single mode fiber is obtained through manually controlling the fusion parameters. Then the modal interferometer is inscribed into a Sagnac loop, which can obtain a higher ER by carefully adjusting the polarization controller (PC). There is about 10 dB extinction ratio higher than the modal interferometer. The higher the extinction ratio is, the sharper the bottom of waveform will be, so the wavelength shifts can be measured more accurately when sensing temperature, pressure or other parameters. The measured sensitivity of temperature is 48.67 pm/°C in the band of 1550 nm. It also can be applied in strain measurement, vibration measurement and so on.