All-fiber narrowband polarization controller based on coherent acousto-optic mode coupling in single-mode fiber

An all-fiber, narrowband, tunable polarization controller is proposed and demonstrated. The device is based on coherent acousto-optic mode coupling induced by two orthogonal acoustic waves on a dispersion-compensating fiber. The cooperative coupling between the two polarizations of the core mode and the TE01 cladding mode through the two gratings permits indirect coupling between the two polarizations of the core mode with nearly 100% efficiency, which makes the polarization-controlling function possible. Experimental results verify the operation of the polarization controller with an insertion loss of <1 dB.     

All-fiber polarization switch

We report an all-fiber polarization switch made out of silica-based microstructured fiber suitable for Q-switching all-fiber lasers. Nanosecond high-voltage pulses are used to heat and expand an internal electrode to cause lambda/2-polarization rotation in less than 10 ns for 1.5 microm light. The 10 cm long component has an experimentally measured optical insertion loss of 0.2 dB and a 0-10 kHz repetition frequency capacity and has been durability tested for more than 10(9) pulses.     

All-fiber acousto-optic tunable notch filter with electronically controllable spectral profile

We demonstrate a novel all-fiber acousto-optic tunable notch filter based on coupling to cladding modes in a single-mode fiber. The device has the advantage of low loss (<0.1 dB) and low polarization dependence. By coupling input light to multiple cladding modes by use of multiple acoustic waves, we achieved an electronically controllable variable spectral profile without a significant coherent cross-talk problem.     

All-fiber controller of radial polarization using a periodic stress

Our aim is to transpose the polarization control by mechanical stress, usually applied to single-mode fibers, to the (TM(01), TE(01), HE(21)(ev), HE(21)(od)) annular mode family. Nevertheless, the quasi-degeneracy of these four modes makes the situation more complex than with the fundamental mode HE(11). We propose a simple device based on periodic perturbation and mode coupling to produce the radially polarized TM(01) mode or at least one of the four modes at the extremity of an arbitrarily long fiber, the conversion to TM(01) mode being achievable by classical crystalline plates.     

Rotation of laser beam polarization in acousto-optic devices

When a linear, polarized laser beam is passed through an acousto-optic device, the polarization direction of the outgoing beam is often different from that of the entering beam, and thus a rotation of the polarization angle takes place. This paper shows how the polarization rotation and the intensity can be calculated for different polarization angles. Experimental results obtained with a single crystal germanium frequency shifter in the 10.6 μm region agreed well with theory.     

All-fiber polarization locked vector soliton laser using carbon nanotubes

We report an all-fiber mode-locked erbium-doped fiber laser (EDFL) employing carbon nanotube (CNT) polymer composite film. By using only standard telecom grade components, without any complex polarization control elements in the laser cavity, we have demonstrated polarization locked vector solitons generation with duration of ~583 fs, average power of ~3 mW (pulse energy of 118 pJ) at the repetition rate of ~25.7 MHz.     

声光调制器偏振特性的实验研究

声光调制器利用声光晶体的声光效应对输入信号进行外调制。另外,实验结果也表明:由声光调制器出射的衍射光存在偏振态的改变。旋转起偏器的透振方向,拉曼—纳斯衍射的一级衍射光的偏振态发生变化;且各级衍射光的偏振度随着透振方向的改变而发生周期性的变化。     

All-fiber acousto-optic tunable notch filter with a fiber winding driven by a cuneal acoustic transducer

We report a type of all-fiber acousto-optic tunable notch filter consisting of a cuneal acoustic transducer and a fiber winding of four unjacketed single-mode fibers. With -32 dB peak rejection efficiency and 178 nm tunable range of the central wavelength, all of the tunable characteristics of the all-fiber acousto-optic tunable filter are kept. In addition, the structure is versatile and convenient for use in building other complicated filters. As an example, a coarse comblike filter has been built by adjusting the axial strains of the unjacketed fibers.     

Apodization of elliptical-core two-mode fiber acousto-optic filter based on acoustic polarization control

We propose and demonstrate a novel apodization technique for an elliptical-core two-mode fiber acousto-optic filter by twisting the fiber and adjusting the acoustic polarization. The sidelobe suppression in the filter spectrum was improved from -9.7 to -15.5 dB. A theoretical analysis that includes acoustic birefringence explains the experimental results with good agreement.     

All-fiber Kerr cell

An all-fiber nanosecond Kerr light gate is described that was constructed using microstructured fibers. The switching voltage for a 20?cm long device is as low as Vπ～85 V at a 1.06?μm wavelength. The device is fully spliced. The active element is a three-hole fiber provided with internal electrodes in the side-holes and a liquid core of nitrobenzene, which is fully enclosed. This work allows the exploiting of electrically driven liquid-core fibers and demonstrated the removal of the major limitations of Kerr cells in the past, allowing for integration, safe use, and relatively low switching voltage.     

All-fiber micromachined microcell

This Letter presents an open-path, all-fiber microcell and a micromachining method for its production. The proposed micromachining method utilizes the selective etching of a purposely designed phosphorus-doped fiber that is spliced in between two standard lead-in fibers. Microcells with various open optical-path lengths were successfully demonstrated. The proposed microcell can be used as a transmission cell or as a miniature Fabry-Perot resonator. The transmission losses and fringe contrast were experimentally investigated over a range of prototype microcells with different lengths. For example, the insertion losses below 1 dB were demonstrated for 50 μm or shorter open path prototype microcells, when immersed in dematerialized water.     

All-fiber,octave-spanning supercontinuum

We present an all-fiber supercontinuum source based on a passively mode-locked erbium fiber laser and a small-effective-area, germanium-doped silica fiber. The parallels between this system and the continuum generated in microstructured fibers with 800-nm pulses are discussed, and the role of dispersion is investigated experimentally. We construct a hybrid fiber by fusion splicing lengths of different-dispersion fiber together, generating more than an octave of bandwidth.     

All-fiber Raman supercontinuum generator

The results on an all-fiber supercontinuum generator that exhibits a continuous wide spectrum in the range 1060–1640 nm predominantly owing to the cascade stimulated Raman scattering in a single-mode quartz fiber at a relatively high power of the combined femtosecond-picosecond pumping with a central wavelength of 1080 nm are presented for the first time. The mean power of the supercontinuum is 2.1 W.     

70 W全光纤超连续谱光源

超连续谱光源在很多领域具有广泛而重要的应用,过去40多年一直是国际研究热点之一。但一方面由于普通双包层光纤与光子晶体光纤模场不匹配会导致较高的熔接损耗和耦合损耗;另一方面受高质量超快光纤脉冲激光器输出平均功率的限制,目前超连续谱光源的最高输出平均功率只有50 W。报道了一种全光纤结构的超连续谱光源,输出平均功率为 70 W。由于整个装置采用一种新的超连续谱形成机制,较好解决了普通双包层光纤与光子晶体光纤由于模场不匹配导致的较高熔接损耗和耦合损耗;降低了对脉冲泵浦源光谱质量的要求。     

70 W全光纤超连续谱光源

 超连续谱光源在很多领域具有广泛而重要的应用,过去40多年一直是国际研究热点之一。但一方面由于普通双包层光纤与光子晶体光纤模场不匹配会导致较高的熔接损耗和耦合损耗;另一方面受高质量超快光纤脉冲激光器输出平均功率的限制,目前超连续谱光源的最高输出平均功率只有50 W。报道了一种全光纤结构的超连续谱光源,输出平均功率为 70 W。由于整个装置采用一种新的超连续谱形成机制,较好解决了普通双包层光纤与光子晶体光纤由于模场不匹配导致的较高熔接损耗和耦合损耗;降低了对脉冲泵浦源光谱质量的要求。     

All-fiber mode-locked fiber laser

An environmentally stable mode-locked fiber laser based on nonlinear polarization rotation is experimentally demonstrated. The laser is based on a novel laser configuration that has negligible low-power steady-state reflectivity from one side and, consequently, no CW gain. The laser is self starting and the configuration is implementable as an all-fiber laser with standard polarization-maintaining fiber-pigtailed components. A pulse duration of 5.6 ps is obtained at a repetition rate of 5.96 MHz and at an average power of 8 mW. As an application of the proposed laser configuration, 213 mW of supercontinuum (600-1750 nm) was demonstrated from a fiber laser system with no sections of free-space optics.     

All-fiber linear polarization and orbital angular momentum modes amplifier based on few-mode erbium-doped fiber and long period fiber grating

A few-mode erbium-doped fiber(FM-EDF) is fabricated using modified chemical vapor deposition in combination with liquid solution. The core and cladding diameters of the fiber are approximately 19.44 and 124.12 μm,respectively. The refractive index difference is 0.98%, numerical aperture(NA) is 0.17, and normalized cut-off frequency at 1550 nm is 6.81. Therefore, it is a five-mode fiber, and can be used as a higher-order mode gain medium. Furthermore, a long period fiber grating(LPFG) is fabricated, which can convert LP01 mode to LP11 mode, and its conversion efficiency is up to 99%. The first-order orbital angular momentum(OAM) is also generated by combining the LPFG and polarization controller(PC). Then, an all-fiber amplification system based on the FM-EDF and LPFG, for LP11 mode and first-order OAM beams, is built up. Its on-off gain of the LP11 mode beam is 37.2 d B at 1521.2 nm. The variation, whose transverse mode field intensity of first-order OAM is increased with the increase of pumping power, is obvious. These show that both the LP11 mode and first-order OAM beams are amplified in the all-fiber amplification system. This is a novel all-fiber amplification scheme,which can be used in the optical communication fields.     

All-fiber anamorphic core-shape transitions

We demonstrate low-loss anamorphic transitions between circular and rectangular fiber cores with aspect ratios up to 5:1, and hence improved coupling from a diode laser by using only a spherical lens. Differential hole pressurization and localized heating of a stock photonic crystal fiber inflates the holes at different rates. Some holes are plugged in the fiber end face where pressure is applied, so they remain at ambient pressure. Alternatively, holes of different sizes expand at different rates because the effective pressure due to surface tension differs.     

基于声光滤光和液晶相位调谐的高光谱全偏振成像新技术

为了获取高光谱分辨率、高空间分辨率、高偏振精度、高信噪比和稳定性好的全部Stokes参量光谱图像, 考虑到声光可调谐滤光器(acousto-optical tunable filter, AOTF)的±1级衍射光的正交特性, 提出用一个AOTF滤光, 一个液晶可变延迟器(liquid crystal variable retarder, LCVR)进行相位调制和两个CCD相机分别对±1级衍射光成像的高光谱全偏振成像新技术. 从所采用的光学元件的穆勒矩阵出发, 阐述了该技术的基本工作原理; 理论分析表明, LCVR不但不会影响到第一个Stokes参量的探测精度, 而且后3个Stokes参量的相对误差分别优于0.064%, 0.31%和3.97%; 利用原理样机获取了450–700 nm、光谱带宽为10 nm的26个光谱通道的图像数据, 成像质量良好; 以工作波长为600 nm的入射光为例, 对其全部Stokes参量图像进行了具体分析讨论. 结果表明, 该新技术原理正确, 方案可行. 该研究可为光谱偏振成像技术提供新的理论和实现方案.     

An acousto-optic beamformer

There is a great variety of beamforming techniques that can be used for localization of sound sources. The differences among them usually lie in the array layout or in the specific signal processing algorithm used to compute the beamforming output. Any beamforming system consists of a finite number of transducers, which makes beamforming methods vulnerable to spatial aliasing above a certain frequency. The present work uses the acousto-optic effect, i.e., the interaction between sound and light, to localize sound sources in a plane. The use of a beam of light as the sensing element is equivalent to a continuous line aperture with an infinite number of microphones. This makes the proposed acousto-optic beamformer immune to spatial aliasing. This unique feature is illustrated by means of simulations and experimental results within the entire audible frequency range. For ease of comparison, the study is supplemented with measurements carried out with a line array of microphones.