Interferometric, modulation-free laser stabilization

We demonstrate novel modulation-free frequency locking of a diode laser, utilizing a simple Sagnac interferometer to create an error signal from saturated-absorption spectroscopy. The interference condition at the output of the Sagnac is strongly affected by the sharp dispersion feature near an atomic resonance. Slight misalignment of the interferometer and subsequent spatially selective, or tilt, detection allows this phase change to be converted into an error signal. Tilt locking has significant advantages over previously described methods, as it requires only a small number of low-cost optical components and a detector. In addition, the system has the potential to be constructed as a plug-and-play fiber-coupled monolithic device to provide submegahertz stability for lasers in the commercial market.     

Demonstration for a two-axis interferometric tilt sensor in KAGRA

Recently, a folded Mach–Zehnder interferometer with homodyne in- and quadrature-phase detection was proposed as a high-precision, wide-dynamic range tilt sensor. By way of a practical application and to validate actual performance, two-axis tilt sensors were developed and installed for one mirror of the input mode cleaner cavity in KAGRA, the large-scale cryogenic gravitational-wave telescope in Kamioka, Gifu, Japan. Building on previous work, we have demonstrated that the two-axis tilt sensor has properly sensed the tilt angle changes of the mirror motion with high precision and without calibration. Compared with our initial angular sensor, an optical lever, which is calibrated by using the interferometer tilt sensor, we found that both sensors showed actual tilt motions of the mirror at low frequencies, and the two-axis interferometer sensor has a better sensitivity at higher frequencies.     

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.     

An experimental investigation of the optical switching characteristics using an optical Sagnac interferometer incorporating one and two ring resonators

We present the use of a fiber optic Sagnac interferometer incorporating one and two fiber optic ring resonators to characterize experimentally the optical switching behaviors. These prototypes were formed by the Sagnac interferometer and serially connected to the ring resonators. The input optical signal was launched via one end of the interferometer, where the polarization control was employed to obtain the maximum optical transmission power. Results obtained have shown that the increasing in switching time (i.e. narrower spectral width) and power can be achieved.     

Soliton squeezing in a highly transmissive nonlinear optical loop mirror

A perturbation approach is used to study the quantum noise of optical solitons in an asymmetric fiber Sagnac interferometer (a highly transmissive nonlinear optical loop mirror). Analytical expressions for the three second-order quadrature correlators are derived and used to predict the amount of detectable amplitude squeezing along with the optimum power-splitting ratio of the Sagnac interferometer. We find that it is the number-phase correlation owing to the Kerr nonlinearity that is primarily responsible for the observable noise reduction. The group-velocity dispersion affecting the field in the nonsoliton arm of the fiber interferometer is shown to limit the minimum achievable Fano factor.     

Numerical study on a compact all-semiconductor-optical-amplifier Sagnac interferometer device

The nonlinear switching effect of an all-semiconductor-optical-amplifier Sagnac interferometer is numerically investigated. The device, stemming from the conventional nonlinear optical loop mirror made of fiber, has a much more compact size and a latency several hundred times smaller than the conventional ones. Numerical simulations are conducted for the case of cw signal operation. It is found that the nonlinear coupling in the MMIWA and the lateral field redistribution as well as the amplification of the signal through the loop structure contribute together to the nonlinear switching. Besides investigating the physical mechanism of the device, we vary relevant parameters to evaluate their influences on device performance. The numerical simulations show good agreement in trend with the experimental results.     

Features of the interference field in a diffraction interferometer for surface testing

The interference field in an interferometer with a zone plate set at the center of curvature of a tested mirror has been investigated. The conditions for testing spherical and parabolic surfaces have been determined. It has been shown that the zero-fringe tracing method allows imperfections in the mirror shape to be distinguished from the instrumental error of the interferometer. The results of testing a parabolic surface are compared with measurements by the Ritchey method. The deviations between the mean asphericity values did not exceed λ/20.     

Balanced heterodyne signal extraction in a postmodulated Sagnac interferometer at low frequency

We describe a balanced-heterodyne postmodulated Sagnac interferometer signal extraction method that is suitable for gravitational wave detection. The method is simple to implement by placement of a polarization-selective modulator after the beam splitter in the dark port of the interferometer. The postmodulated Sagnac interferometer retains its common path advantage and exhibits insensitivity to laser frequency noise below, at, and above the heterodyne frequency. Balanced detection reduces sensitivity to laser amplitude noise. In this scheme mirror displacement signals were rf demodulated and observed from 0.2 to 10kHz.     

转镜式高灵敏度干涉光谱成像仪ROSI的设计方法

介绍了转镜式高灵敏度干涉光谱成像仪(ROSI)的设计计算方法,包括系统基本参量计算、光程差与干涉仪结构参量和转镜角度的关系以及转镜转速与探测器采样帧频的关系等,同时,分析了像点位移与探测器采样之间的失配问题,并给出了最小采样频率公式.     

Reduced minimum configuration fiber optic gyro for land navigation applications

Further cost reduction of the fiber optic gyroscope is necessary in order to meet the economic requirements of land navigation systems. We have previously concentrated on the reduction of the number of splices and component improvements in the open-loop, minimum configuration. Now we eliminate nonessential components and splices. The source-detector coupler is not part of the Sagnac interferometer and serves solely to provide isolation between the broadband optical source and the photodetector. Many commercial laser diodes incorporate a back-facet photodetector to monitor laser intensity. The signal returned from the Sagnac interferometer traverses the laser, is received at this photodetector, and can be distinguished from the laser signal by the bias modulation. Configuring a gyro in this manner eliminates a directional coupler and the separate photodetector as well as up to three fiber splices in an all-fiber gyroscope. A production, open-loop, fiber optic gyroscope has been modified to demonstrate this principal. The gyroscope can be constructed with only two fiber splices and exhibits performance comparable to the conventional minimum configuration.     

Comparisons of multi-wavelength oscillations using Sagnac loop mirror and Mach-Zehnder interferometer for ytterbium doped fiber lasers

A multiwavelength Ytterbium-doped fiber ring laser operating at 1030 nm region is demonstrated using a Sagnac loop mirror and a Mach-Zehnder interferometer. We report the Performance comparisons of multi-wavelength oscillations in Yb³⁺ doped fiber lasers (YDFL) with typical commercial ytterbium doped silica fibers. By adjusting the polarization controller (PC), a widely tunable laser range of 22 nm from 1030 nm to 1050 nm is obtained. The Mach-Zehnder interferometer (MZI) design has exhibited simplicity in the operation for controlling the smallest wavelength spacing compared to Sagnac loop mirror method. In our observations, the smallest achieved stable wavelength spacing in Sagnac loop mirror setup and MZI setup were 2.1 nm and 0.7 nm, respectively. In case of nine-wavelength operation with a MZI setup, the stability, Full Width at Half Maximum (FWHM) and side mode suppression ratio (SMSR) of laser lines are not affected by increasing pump power, While for above four wavelength operation, the laser stability with Sagnac loop mirror becomes worse specially for higher input pump power and the power fluctuation among the wave-lengths would be also slightly larger.     

环形光纤声发射传感器的相位调制特性研究

提出了一种基于光纤Sagnac干涉仪的环形传感器，用于固体表面传播的超声波的检测.这种传感器的特点是能够精确地检测由固体表面传播的超声波产生的微弱振动.当超声波信号通过光纤传感器的两个臂到达探测器时，干涉仪的输出光强度受到了超声信号的调制.通过检测干涉仪的输出光强度并利用Fourier变换，测得了超声信号的振幅和频率.而且对传感系统的位相调制特性进行了仿真，并对实验结果进行了分析，结果表明该系统可用于固体表面传播的超声波频率特征的识别.     

新型分布式光纤管道泄漏检测技术及定位方法研究

介绍了一种基于萨尼亚克(Sagnac)干涉仪的直线型分布式光纤管道泄漏监测系统,实时进行管道泄漏监测和定位。此系统有两条传感光纤,可有效提高管道监测距离。推导了泄漏信号引起的光信号相位变化表达式;分析了该干涉仪应用于泄漏检测的原理及其泄漏源定位方法,并在分别距两传感光纤末端的法拉第旋转镜为3.990km和4.024 km处进行了泄漏检测实验。管道泄漏实验结果表明,该系统较准确地确定了泄漏源位置且定位误差小于1.05%.     

Dual-wavelength switchable erbium-doped fiber ring laser based on merged sagnac and intermodal interferences in sagnac loop mirror

A simple but novel concept of switchable dual-wavelength erbium-doped fiber ring laser is proposed and experimentally demonstrated. It is based on a Sagnac loop mirror incorporating a high birefringence few-mode fiber and polarization controller (PC). Since its transmission properties depend on the PC state, the proposed fiber ring laser can operate in the random combination of two wavelengths by adjusting only the PC settings. The potential lasing lines are determined by simultaneous occurrence of the Sagnac and intermodal interferences in the Sagnac loop mirror. All lasing emissions have the optical signal to noise extinction ratio higher than 45 dB and their power fluctuations lower than 0.5 dB.     

Harmonic and Intermodulation Performance of Sagnac Fiber-Optic Interferometer

Abstract

In this article, closed-form expressions are obtained for the amplitudes of the harmonic and intermodulation products generated when driving the fiber-optic Sagnac interferometer by a DC bias voltage plus an equal-amplitude two-tone signal. The results clearly show the strong dependence of the harmonic and intermodulation performance on the DC bias voltage and/or the phase bias of the fiber-optic Sagnac interferometer. The results obtained suggest that the DC bias voltage and/or the phase bias play an important role in deciding the linearity of the fiber-optic Sagnac interferometer and, hence, its suitability for analog applications.     

The effect of a laser beam displacement on parametric oscillatory instabilities for Advanced LIGO

The arm cavities of real gravitational wave detectors can show small deviations like a tilt or a spatial shift between the cavity mirrors. These deviations lead to a separation of the optical mode centres with respect to the mirror?s centre. In this Letter we perform the computation of parametric instable modes considering the described displacement. We further analyse the possibility of parametric oscillatory instability in the Advanced LIGO interferometer for the case of a displaced arm cavity. Our results reveal an additional number of optical and elastic mode combinations due to a displacement that can give rise to the undesirable effect of parametric oscillatory instability.     

基于Sagnac干涉仪的光纤非接触式瞬变信号测量技术

基于对Sagnac干涉仪在外界瞬变信号影响下响应特性的理论分析,提出了一种基于光纤Sagnac干涉仪的非接触式测量技术.针对陷波波形的特性,提出了相应的解调技术.实验结果表明,基于Sagnac干涉仪的非接触式测量技术不仅能识别瞬变信号,同时能实现对信号源的良好定位,相对定位准确度达到1.5%.     

Optical characteristics of transparent PMNT ceramic and its application at high speed electro-optic switch

The optical characteristics of transparent lead magnesium niobate titanate (PMNT) electro-optic ceramic, including the electro-optic phase modulation, electric hysteresis property and thermo-optic coefficient, are investigated in detail. Based on this novel ceramic, a polarization independent electro-optic switch by using fiber Sagnac interferometer (FSI) structure is realized. An initial π-shift is introduced into the Sagnac loop to eliminate the effect of the polarization orientation of the incident light on the switch performance. Then an electrically controllable PMNT phase retarder is used to switch the optical signal between the reflection and transmission ports. Some theoretical analyses are given and the switch performances are also discussed, including the thermal characteristic and different switching frequency response.     

Principle and analysis of a moving double-sided mirror interferometer

A moving double-sided mirror interferometer (MDSMI) is presented. It comprises one moving double-sided mirror (MDSM), one fixed corner-cube mirror, one fixed plane mirror, and one beam-splitter. The MDSM is a plane-parallel glass plate with both faces coated with high-reflectivity films. The optical path difference (OPD) is created by the straight reciprocating motion of the MDSM driven by a linear actuator, and the OPD value is four times the displacement of the MDSM without tilt. The effect of tilt of the MDSM is analyzed, and the tilt tolerance of the MDSM is systematically analyzed by means of modulation depth and phase error. The MDSMI is very suitable for high-resolution rapid-scan infrared spectrometers.     

一种紧凑结构型干涉仪的设计

设计了一种基于立体角镜与固定平面镜组合的紧凑结构型干涉仪系统,分析其光学系统,得到各器件的影响与设计指标。对动镜驱动系统进行设计与分析,并通过PID算法进行调速,确保动镜运动的准直、匀速与平稳。实验表明仪器的波数精度、分辨率、信噪比等关键指标能够满足实际应用的需要。