Refractive-index dispersion measurement of bulk optical materials using a fiber raman laser widely tunable in the visible and near-infrared

We propose a simple, highly sensitive fiber-optic autocollimation method for refractive-index dispersion measurement of solid-state and liquid bulk optical materials using a double-pass fiber Raman laser with Littrow-prism-tuned emission. The optical fiber is a key element of the scheme and serves simultaneously as a point laser source for the test, as a highly sensitive point receiver (or spatial filter) of the autocollimation backreflectance signal and as a medium for nonlinear frequency conversion and generation of a broadband continuum spectrum. When the Raman medium is a graded-index multimode fiber with powerful pumping (over 100 kW) using the second harmonic of a Q-switched Nd:YAG laser (λ_p=532nm), we obtain widely tunable (0.54-1.01 μm) generation in both the visible and near-IR ranges. The results obtained in the refractive-index dispersion measurements are fitted to the Sellmeier dispersion equation and the standard deviation of the experimental data from the analytical curve does not exceed 5x10^-5.     

Controllable photoinduced optical attenuation in a single-mode optical fiber by irradiation of a femtosecond pulse laser

Novel optical attenuation fibers were fabricated by the irradiation of a focused infrared femtosecond pulsed laser onto the core of a silica glass single-mode optical fiber. Optical attenuation at a wavelength of 1.55 microm proportionally increased with increasing numbers of irradiation points and was controllable under laser irradiation conditions. The single-mode property of the waveguide and the mode-field diameter of the optical fiber were maintained after irradiation of the femtosecond laser. It is suggested that the attenuation results from optical scattering at photoinduced spots formed inside the fiber core.     

大功率激光单模光纤远距离传输的注入光纤光功率限值分析

对于大功率激光单模光纤远距离传输, 采用传统的受激拉曼散射(SRS)阈值作为注入光纤激光功率值取值过大。本文对单模光纤远距离传输过程中泵浦光和拉曼斯托克斯光(Stokes)光功率随注入光纤激光功率的变化进行仿真与理论分析。根据光纤中SRS产生的机理, 提出以拉曼Stokes光在单模光纤中传输的光功率变化曲线曲率极大值点对应的注入激光功率为限值, 对注入单模光纤光功率限值随着光纤长度变化进行仿真, 通过曲线拟合得出注入单模光纤激光功率限值公式, 并搭建实验系统进行验证。结果表明, 提出的注入单模光纤激光功率限值适用于大功率激光远距离单模光纤传输。     

Characterization of a fiber lens

A practical method for characterizing microstructure fiber lenses in the near field is described. By detecting the optical power of the light reflected by a mirror and coupled back into the single-mode fiber, one can accurately determine the focal point and the working distance of a fiber lens. The approach is relatively simple and easy to implement. The accuracy in determining the focal point and working distance is better than 2%.     

分体式原向反射法水下武器速度测试技术研究

水下动态参数的测试是特种武器、两栖武器、水下专用武器性能考核的必备环节，而水下运动体的速度信息是评价水下武器性能的重要指标之一。针对现有的水下高速目标参数测试系统中存在的成本高、安装调试复杂、设备体积庞大等问题，提出一种以激光光幕为有效区域水上、水下分体式，实时、非接触的测速方法。通过分析Lambert-Beer定律和体散射函数等数学原理，确定了水下光谱传输规律综合考虑性价比获得最佳峰值波长；将1m的圆柱体作为散射体模拟光在水中的散射情况，追迹空间区域内的光线总数为1×105，获得位于传播方向上1，3，5和7 m处的接收面上辐照度的光能量分布，从而获取系统激光光源的最佳峰值功率。以此为依据，采用定距测时原理和一维原向反射技术，由峰值波长为532 nm的半导体光纤耦合绿光激光器、光纤耦合式鲍威尔棱镜防水扩束器、一维原向反射器等构建光学系统。激光光源、光电转换部分和信号调理部分位于水上，激光光幕和原向反射器位于水下，通过光纤束完成两路光信号的发射和反射光的回收。发射端光纤一端与光源耦合，另外一端与鲍威尔棱镜耦合置于水下形成扇形光幕。接收端光纤一端均布于鲍威尔棱镜出口，另一端与PIN型光电传感器耦合。设计齿形一维原向反射器并完成加工制造，光线将沿着入射光方向原向返回，另外一维方向则仍为镜面反射，将接收系统置于发射点垂直光面内附近即可接收大部分光能量，解决了现有原向发射器因水介质折射率不同于空气而导致原向反射特性消失的问题。实验采用波长为(532±5) nm绿光激光器，功率稳定性<1%，光学噪声< 0.5%，准直后耦合至长度为2 m的单模光纤再经过鲍威尔棱镜展宽为60°扇形一字线光幕，扩束模块封装采用尼龙防水材料，接收光纤均布于光源周围形成环形光纤束，光纤另外一端均匀排列与PIN光敏二极管直接耦合。光敏二极管前加中心波长为532 nm的光学滤光片，FWHM=(3±1) nm，透过率为70%。PIN型光敏二极管有效尺寸为5.0 mm×5.0 mm。采用多档可调的光电信号调理电路以适应不同尺寸的测试对象。该系统进行了不同目标速度参数测试实验，以钢弩为发射装置，信号经过光纤回收、信号调理，采集至计算机处理获得波形及区间内平均速度，两激光光幕之间的距离为定值300 mm，波形峰值作为计时时刻。成功获取了较高信噪比的波形信号和目标速度值。利用水下运动体模型与模拟结果进行比较得到其绝对误差。实验结果表明： 本方法结构简单、重复性好，可实现有效区域达到1 m×1 m，最小可测目标尺寸为5 mm，理论测速上限可达1 000 m·s-1，实验数据通过与理论经验公式结果比对表明，系统测试精度可达0.2%。     

复合材料界面力学的光纤测试方法

本文将单模先导纤维代替普通玻璃纤维埋设于聚脂之中,将He-Ne激光分光后接入这一信号光纤及另一同样长度的参考光纤中,利用这两根光纤输出的激光的干涉效应采测试埋设于聚脂之中光导纤维的各种应力情况(在复合材料受各种外力时),从而得到玻璃纤维同聚脂的界面微观力学的各种结果,开拓了一种新的复合材料的测试方法.     

A single-mode-fiber-based point diffraction interferometer

Based on the modification of a point diffraction interferometer, a method for measuring the optical fields from remote objects and external sources is developed. In this method, the reference beam is obtained from the studied beam by filtration of its spatial spectrum with a single-mode optical fiber. To eliminate the effect of phase errors caused by the nonideality of elements of the optical scheme on the measurement results, we developed a procedure of interferometer calibration that permits one to determine these errors with the aim of subtracting them from the measured field phase distributions.     

Characterization of a high-power tapered semiconductor amplifier system

We have characterized a semiconductor amplifier laser system which provides up to 200 mW output after a single-mode optical fiber at 780 nm wavelength. The system is based on a tapered semiconductor gain element, which amplifies the output of a narrow-linewidth diode laser. Gain and saturation are discussed as a function of operating temperature and injection current. The spectral properties of the amplifier are investigated with a grating spectrometer. Amplified spontaneous emission (ASE) causes a spectral background with a width of 4 nm FWHM. The ASE background was suppressed to below our detection limit by a proper choice of operating current and temperature and by sending the light through a single-mode optical fiber. The final ASE spectral density was less than 0.1 nW/MHz, i.e. less than 0.2% of the optical power. Related to an optical transition linewidth of Γ/2π=6 MHz for rubidium, this gives a background suppression of better than -82 dB. An indication of the beam quality is provided by the fiber coupling efficiency of up to 59%. The application of the amplifier system as a laser source for atom-optical experiments is discussed. Received: 8 May 2000 / Revised version: 21 September 2000 / Published online: 7 February 2001     

Fiber-optic dielectric multilayer temperature sensor: in situ measurement in vitreous during Er:YAG laser irradiation

A fiber-optic instrument for temperature measurement is presented. The sensing element consists of an optical dielectric multilayer system acting as a micro-interferometer which is deposited on a single-mode fiber tip. The sensitivity of the implemented system is theoretically derived and experimentally determined by a calibration measurement. The small size of the probe makes the system well-suited, for instance, for endoscopic in vitro and in vivo measurements in medical applications, especially in small samples. The sensor is used for the investigation of the transient thermal behavior of vitreous during Er:YAG laser irradiation in order to study the local thermal effects that are important to minimize the potential for unintentional injury in laser vitrectomy and laser vitreoretinal surgery.     

Spectrum control and shaping of optical pulses in optical fibre interferometers

This paper discusses the use of single-mode fibre ring interferometers for injection laser line narrowing and for enhancement of optical emission power. The efficient launching into fibre ring interferometers of multi-frequency external cavity injection laser emission, in both the c.w. and mode-locking regime, has been achieved. Matching the optical lengths of the external cavity and fibre interferometer allowed the measurement of mode width of such a laser. A method is proposed for shaping optical pulses in fibre ring interferometers from constant intensity frequency modulated emission. The mode-locking regime of all-fibre external cavity injection lasers has been achieved.     

掺镱硼酸钙氧钇飞秒激光器及在拉锥光纤中产生跨倍频程超连续光

跨倍频程超连续光谱的产生是光学频率梳系统中测量载波包络相移频率的关键.本文采用拉锥单模光纤作为非线性光谱展宽介质, 将半导体激光(LD)抽运的掺镱硼酸钙氧钇(Yb:YCOB)振荡器输出的飞秒激光耦合到该拉锥光纤中, 通过飞秒激光在光纤中发生的相位调制、四波混频等非线性效应将光谱展宽至超过倍频程的范围.振荡器输出的飞秒激光脉冲宽度为130 fs, 中心波长为1052 nm, 重复频率为76.8 MHz, 平均功率为620 mW, 耦合进单模拉锥光纤后获得了光谱覆盖范围从550 nm至1350 nm的跨倍频程超连续光谱, 最大输出平均功率为323 mW, 耦合效率达到52%.为进一步实现全固态飞秒激光光学频率梳提供了重要基础.     

布里渊动态光栅原理及其在光纤传感中的应用

自从2007年布里渊动态光栅被首次提出用于实现光存储以来,该技术得到了国际上的广泛关注和研究.布里渊动态光栅本质上是由相干声波场激发的折射率光栅,一般情况下两束抽运光(频率差等于光纤的布里渊频移)以相同的偏振态从光纤两端注入到光纤中,通过受激布里渊散射效应激发出相干声波场,即形成布里渊动态光栅.光纤布里渊动态光栅因具有全光产生、参数灵活可控的优点,已被广泛研究应用于光纤传感、光纤特性表征、光存储、全光信号处理、微波光子学和高精度光谱分析等.本文分析布里渊动态光栅产生和探测原理,重点探讨在高性能分布式光纤传感上的应用,这些应用包括高灵敏度温度和应变分布式传感、温度和应变同时解调、分布式横向压力传感、分布式静压力(气压或液压)传感、高空间分辨率分布式传感和高精度光谱分析.     

Estimation of coupling efficiency of optical fiber by far-field method

Coupling efficiency to a single-mode optical fiber can be estimated with the field amplitudes at far-field of an incident beam and optical fiber mode. We call it the calculation by far-field method (FFM) in this paper. The coupling efficiency by FFM is formulated including effects of optical aberrations, vignetting of the incident beam, and misalignments of the optical fiber such as defocus, lateral displacements, and angle deviation in arrangement of the fiber. As the results, it is shown the coupling efficiency is proportional to the central intensity of the focused spot, i.e., Strehl intensity of a virtual beam determined by the incident beam and mode of the optical fiber. Using the FFM, a typical optics in which a laser beam is coupled to an optical fiber with a lens of finite numerical aperture (NA) is analyzed for several cases of amplitude distributions of the incident light.     

基于超长环形激光器泵浦的94 km布里渊分布式传感系统

首次将超长光纤环形激光器的光放大应用于布里渊光时域分析(BOTDA)传感系统,以延伸传感距离。 通过对布里渊泵浦消耗、 拉曼泵浦相对强度噪声(RIN)转移的抑制及拉曼泵浦功率分布的优化,基于对布里渊增益谱分析的原理在94 km的传感距离上实现了3 m空间分辨率,以及全程28 με/1.4 ℃应变/温度精度。     

Erbium-doped fiber ring laser sensor for high temperature measurements based on a regenerated fiber Bragg grating

This article presents an erbium-doped fiber ring laser for high temperature measurement with high accuracy. The proposed laser sensor employs a regenerated fiber Bragg grating (RFBG) as a sensor element. Through thermal treatments, the RFBG with enhanced thermal resistance was obtained. The laser emission optical spectrum presents good performance with a high optical signal-to-noise ratio of 58dB. Experimental results demonstrate a wavelength sensitivity to the temperature is 15.5 pm/ºC with the temperature range from 300ºC to 900ºC, and the correlation coefficient is 0.999. The results prove it is able to provide potential applications in high temperature measurement.     

Tunable single-mode fiber-VCSEL using an intracavity polymer microlens

We report a tunable, single-mode vertical cavity surface-emitting laser (VCSEL) format suitable for array operation, power scaling, fiber coupling, and operation in isolated environments such as those required by atom optics. The devices are fiber VCSELs, consisting of a semiconductor gain and mirror structure separated from a mirror-coated optical fiber by an air (or vacuum) gap. The gain structure has polymer microlenses fabricated on its surface, of characteristics suitable to focus the oscillating mode on both cavity mirrors, ensuring stable fundamental mode emission and high fiber coupling efficiency. We demonstrate such devices in continuous-wave operation at 1.03 microm at room temperature, with a single-mode tuning range of 13 nm, laser threshold as low as 2.5 mW, and a maximum fiber-coupled output power of 10 mW.     

Dispersion measurement technique based on the self-seeding laser oscillation of a Fabry-Perot laser diode

A simple dispersion measurement technique has been proposed and demonstrated by using the self-seeding laser oscillation of a Fabry-Perot laser diode through an optical closed-loop path. When the multi-mode optical pulses emitted from the laser are re-injected into the laser after traversing a fiber-under-test, a single mode laser oscillation occurs through the closed-loop path due to the group velocity difference between the pulses of different wavelengths. We measured the dispersion parameter of the fiber-under-test from the modulation frequency changes required to induce single-mode laser oscillations through the optical closed-loop path. The maximum measurement error was less than 1.5% for the optical fibers as compared with a commercial instrument.     

漂移量反馈控制式激光准直方法

提出一种集光纤准直与光束漂移量反馈控制准直技术于一体的激光光束准直方法 ,它是在单模光纤对激光器出射光束漂移量进行初级准直的基础上 ,进一步对光束的漂移量进行反馈控制 ,进而提高出射光束的方向稳定性。准直系统中利用漂移量分离光路和光电检测系统对光束的平漂量和角漂量进行了分离检测 ,并各自构成相应的光束空间平漂量反馈控制系统和光束空间角漂量反馈控制系统 ,减小了平漂量和角漂量反馈控制中的相互耦合。引入单模光纤使激光器与光束漂移量反馈控制准直系统相隔离 ,减小了激光管热源温度变化等因素对准直系统的影响 ,同时还便于准直系统使用中的安装布置。上述方法的应用 ,提高了准直精度及准直效率。实验表明目前该方法准直精度可达 0 .7× 10 -7rad。     

Innovative confocal laser method for exact dioptric power measurement of intraocular lens implants Invited Paper

We present a novel confocal laser method (CLM) for precise testing of the dioptric power of both positive and negative intraocular lens (IOL) implants. The CLM principle is based on a simple fiber-optic confocal laser design including a single-mode fiber coupler that serves simultaneously as a point light source used for formation of a collimated Gaussian laser beam, and as a highly sensitive confocal point receiver. The CLM approach provides an accurate, repeatable, objective, and fast method for IOL dioptric power measurement over the range from 0 D to greater than =t=30 D under both dry and in-situ simulated conditions.     

Twist sensor based on Sagnac single-mode optic fiber interferometer

An optical fiber twist sensor based on Sagnac single-mode optic fiber interferometer is proposed. The stress-induced birefringence of single-mode optical fiber is obtained by applying a transverse force against a short length of singlemode fiber. A high sensitivity and resolution of the twist angle measurement of 0.19 nm/° and 0.002° is achieved experimentally, respectively. The proposed sensor is more convenient and simple than that of standard polarization-maintaining fibers.