Linearly Polarized Polarization-Maintaining Er^(3+)-Doped Fluoride Fiber Laser in the Mid-Infrared

We demonstrated the~2.8-μm and~3.5-μm linearly polarized continuous wave(CW)laser outputs from a polarization-maintaining(PM)Er^(3+)-doped fluoride fiber laser.By introducing a film polarizer into the cavity to select the laser polarization orientation,the~2.8-μm linearly polarized CW laser with a high polarization extinction ratio(PER)of~23 dB and maximum output power of 2.37 W was achieved under double-end pumping at 976 nm.By adding another 1981-nm pump source simultaneously,the~3.5-μm linearly polarized CW laser was also obtained,giving higher PER of~27 dB and maximum output power of 307 mW which is only limited by the available power of 1981-nm pump.To the best of our knowledge,this is the first report on a mid-infrared linearly polarized CW PM fiber laser in the>2.5-μm mid-infrared region.This work not only opens up opportunities for some new mid-infrared applications,but also provides a promising platform for developing high-stability and versatile mid-infrared laser sources.

Low-noise compact fiber laser based on nonlinear polarization evolution in an all-polarization-maintaining figure-8 cavity

We demonstrate an all-polarization-maintaining(APM)fiber mode-locked laser based on nonlinear polarization evolution(NPE).A well-designed Sagnac fiber loop is employed to establish the nonlinear polarization evolution process in a polarization beam splitter(PBS)figure-8 fiber laser.Nonlinear loss curves are calculated to verify the saturable absorption characteristic of this NPE-based APM oscillator.Then,we simulate the pulse propagation process in the cavity to demonstrate the pulse mode-locked formation.Finally,we also design a realizable compact scheme to further reduce noise disturbances,achieving a 101-fs mode-locked pulse train with a 0.3-mrad integrated phase noise and a 0.006%integrated relative intensity noise(RIN).This figure-8 fiber laser provides a new scheme for compacting low-noise compact APM fiber lasers based on the NPE mode-locked mechanism.

Electro-Optical Effect Measurement of Thin-Film Material Using PM Fiber Mach-Zehnder Interferometer

A polarization-maintaining （PM） fiber Mach-Zehnder （MZ） interferometer has been established to measure the EO effect of very thin film materials with optical anisotropy. Unlike a common MZ interferometer, all the components are connected via polarization-maintaining fibers. At the same time, a polarized DFB laser with a maximum power output of 10mW is adopted as the light source to induce a large extinction ratio. Here,we take it to determine the electro-optical coefficients of a very thin superlattice structure with GaAs, KTP, and GaN as comparative samples. The measured EO coefficients show good comparability with the others.

Generation of cavity-birefringence-dependent multi-wavelength bright-dark pulse pair in a figure-eight thulium-doped fiber laser

We experimentally demonstrated a stable multi-wavelength bright-dark pulse pair in a mode-locked thulium-doped fiber laser(TDFL).The nonlinear polarization rotation(NPR)and nonlinear optical loop mirror(NOLM)were employed in a figure-eight cavity to allow for multi-wavelength mode-locking operation.By incorporating different lengths of high birefringence polarization-maintaining fiber(PMF),the fiber laser could operate stably in a multi-wavelength emission state.Compared with the absence of the PMF,the birefringence effect caused by PMF resulted in rich multi-wavelength optical spectra and better intensity symmetry and stability of the bright-dark pulse pair.

Self-starting all-fiber PM Er:laser mode locked by a biased nonlinear amplifying loop mirror

A compact all-fiber polarization-maintaining Er:laser using a nonlinear amplifying loop mirror is reported. Fundamental single-pulse mode-locking operation can always self start, with a cavity round-trip decreased from ~ 4.7 m to~ 1.7 m. When the pulse repetition rate is 121.0328 MHz, output pulse is measured to have a center wavelength/3-d B spectral bandwidth/radio frequency signal to noise ratio(SNR)/pulse width of 1571.65 nm/18.70 nm/80 d B/477 fs, respectively. Besides, three states including the exponential growth, damping state, and steady state are investigated through the build-up process both experimentally and numerically. Excellent stability of this compact Er:laser is further evaluated,demonstrating that it can be an easy-fabrication maintenance-free ultrafast candidate for the scientific area of this kind.

A kind of multiwavelength erbium-doped fiber laser based on Lyot filter

A multiwavelength tunable ring-cavity erbium-doped fiber laser(EDFL)based on a Lyot filter was presented.For the proposed Lyot filter,a comb filter consisting of an EDF-polarization-maintaining fiber(EDF-PMF),a polarization controller(PC),and a circulator with four ports was used to suppress the mode competition.The light transmission direction was guaranteed by the circulator.For the proposed fiber laser,tunable single,dual,triple,quadruple,quintuple,sextuple,and septuple wavelengths were realized.A single-wavelength laser output with an optical signal-to-noise ratio(SNR)of up to30.56 dB was realized,and a tuning range of 1590.54 nm to 1599.54 nm was achieved by tuning the PC.The stability of the single,dual,triple,and quadruple-wavelength center power fluctuations was less than 0.05 dB,0.98 dB,5.07 dB,and7.71 dB respectively.When the laser was operated in the multiwavelength condition,the SNR was more than 20.97 dB.The proposed erbium-doped fiber laser is suitable for fiber-sensing system applications.

Convention of Optical Vortices in Two-Helix Long-Period Fiber Gratings

An effective method to fabricate two-helix long-period fiber gratings （TH-LFGs） is presented. Based on the coupling mode theory, the conversion of optical vortices （OVs） in TH-LFGs are analyzed in detail. The conversions of OVs with different topological charges： 0 → ±2 and 1 → 3 are simulated as three examples and the conversion efficiency higher than 98% can be realized.

Generation of a large orbital angular momentum beam via an optical fiber winding around a curved path and its application

Many papers have been published on the study of orbital angular momentum(OAM)of the laser modes based on the Laguerre-Gaussian(LG)beam and helical phase plate or rotating cylindrical lens,and the principal ray of the LG beam remains straight line.These ways are difficult to get a large OAM modes.In this paper,we propose a novel method to prepare a large OAM modes when the light propagates through a optical fiber winding around a curved path,and establish a theoretical framework based on the principal ray path changing.Firstly,we investigate three kinds of winding structure.Secondly,based on the analytical solutions and numerical calculations,we can find that the spiral body can achieve a large OAM temporal pulse.At the same time,based on the zero OAM diffraction diagram,we can obtain an improvement of resolving power beyond Rayleigh’s criterion.Finally,applying a large OAM diffraction pattern to realize 12-bitencodes,we can obtain a high-security optical information transfer system.

Polarization-maintaining few mode fiber composed of a central circular-hole and an elliptical-ring core

We propose a novel waveguide design of polarization-maintaining few mode fiber(PM-FMF) supporting ≥10non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes, including the fundamental polarization mode. Numerical simulations demonstrate that, by optimizing the air hole and elliptical-ring core,a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δn_(eff) between the adjacent guided modes could be kept larger than 1.32 × 10^(-4) over the whole C +L band. The proposed fiber structure can flexibly tailored to support an even larger number of modes in PM-FMF(14-mode PM-FMF has been demonstrated as an example), which can be readily applicable to a scalable mode division multiplexing system.

Design of PANDA ring-core fiber with 10 polarization-maintaining modes

We present a polarization-maintaining PANDA ring-core fiber(PM-PRCF) characterized by the combination of a ring-core structure with two stress-applying rods. This special fiber design separates the adjacent modes and avoids the cutoff of the higher-order modes, which is a common problem in elliptical core polarization-maintaining few-mode fibers. Using a high-contrast index ring and stress-induced birefringence, the PM-PRCF features support for 10 vector modes, with effective refractive index separations from their adjacent modes >10^(-4).Broadband performance is investigated subsequently over a wide wavelength range from 1500 to 1630 nm.The proposed fiber is targeted at applications in space-division multiplexing while eliminating the complex multiple-input multiple-output signal processing.

环形纤芯结构光纤设计与制备技术研究

为支持光子轨道角动量(OAM)模式大容量通信传输,文章探讨了新型OAM信号传输光纤的设计与制备技术,满足大幅度提高通信系统频谱效率和容量对特殊光纤的需求。文章模拟和评估了OAM模式在不同波导结构光纤中的模式特性和传播效果,研究结果表明,提高芯-包层折射率差有利于高阶OAM模式传输,降低了光纤内部的各种微扰。采用等离子体化学气相沉积工艺,高精度实现了设计的折射率剖面,并成功拉制了高质量的OAM光纤,其支持50 km传输28个有效OAM通道的渐变折射率;开发出了可支持96个有效OAM通道的三环芯层结构传输光纤。同时,针对新型传输需求,通过对精确制备技术进行模拟,研究开发出了保偏型OAM传输光纤和OAM掺铒光纤等支持更多OAM模式稳定传输的新型光纤。

Design of novel circular lattice photonic crystal fiber suitable for transporting 48 OAM modes

In this paper,we propose and numerically investigate a novel circular lattice photonic crystal fiber(CL-PCF)using controllable GeO_(2) doped silica,suitable for modes carrying quantized orbital angular momentum(OAM).Large effective index separations between 25 supported vector modes(≥10^(-4))are confirmed over large bandwidth(C+L bands)leading to 48 OAM modes bearing information.The simulations show that the modes in the proposed CLPCF have good features including low and flat dispersion(within 51.82 ps/km/nm),low confinement loss(lower than 0.002 d B/m),high effective mode area(88.5μm^(2))and low nonlinearity(1.22 W^(-1)·km^(-1)).These promising results show that the proposed CL-PCF could be an arguably candidate in fiber-based OAM multiplexing or other applications using OAM states.

Polarization-maintained coupled optoelectronic oscillator incorporating an unpumped erbium-doped fiber

A polarization-maintained coupled optoelectronic oscillator（COEO） with its performance significantly improved by a short-length unpumped erbium-doped fiber（EDF） is reported and experimentally investigated.A 10 GHz optical pulse train with a supermode suppression ratio of 61.8 d B and a 10 GHz radio frequency signal with a sidemode suppression ratio of 94 d B and a phase noise of-121.9 d Bc∕Hz at 10 k Hz offset are simultaneously generated. Thanks to saturable absorption of the 1 m unpumped EDF, which introduces relatively large cavity loss to the undesired modes and noise, the supermode suppression ratio and the phase noise are improved by 9.4 and 7.9 d B, respectively.

光纤通信新型复用技术(本期优秀论文)

介绍了基于少模光纤(FMF)的MDM技术和基于涡旋光纤的OAM复用技术的研究背景与最新研究进展,并对其原理和理论模型进行概述,讨论了OAM模式的生成方式、OAM复用技术和模分复用的特点,并对这两种技术面临问题的解决方法和复用技术的发展方向提出了一些思路。

Study on the effect of ellipticity and misalignment on OAM modes in a ring fiber

Based on the optical fiber mode theory and employing the expertized software COMSOL,we study the effect of ellipticity and misalignment on the effective refractive indices,walk-off and intensity distribution of the even and odd eigenmodes that form the basis of the orbital angular momentum(OAM)modes in a ring fiber.Our results show that the effective refractive index difference and the walk-off increase with the ellipticity and misalignment,thus reducing the stability of the OAM modes.We find that the misalignment has a greater impact on the OAM modes than the ellipticity,and both the misalignment and ellipticity affect the lower-order OAM modes more significantly,suggesting that the higher-order OAM modes are more stable during propagation.

一种利用报文镜像的ONU远程设备管理调试方法

OAM/OMCI作为PON系统中的远程管理协议,对整个PON系统能否正常工作起着至关重要的作用。无论是对于开发中的还是已经部署的现场ONU设备,都能够比较方便地获取到OAM/OMCI交互数据,对于功能调试、对接测试和故障排除都具有重要的意义。提出了一种在ONU驱动层软件上利用报文镜像获取OAM/OMCI报文的调试方法,制定了报文封装格式并开发了对应的插件。最后,在实际环境中验证了该方法,证明了其有效性。

基于双芯光纤耦合器的高纯度涡旋光产生研究

为了实现全光纤化轨道角动量(orbital angular momentum,OAM)模式产生系统,设计了一种基于标准单模光纤和环芯光纤的双芯光纤耦合器结构。基于模式匹配法和相位匹配原理,仿真计算了双芯光纤耦合区中轨道角动量模式光场及相位的变化。结果表明:当单模光纤中的光场耦合到环芯光纤时,会在环芯光纤中激发出多种高阶矢量模式,引起模间串扰和降低产生的轨道角动量模式纯度,同时耦合产生的轨道角动量模式能量会在具有相反拓扑电荷数的同阶模式间震荡。通过调控波导间距,对耦合效应的强弱进行调控,实现了高纯度的一阶轨道角动量模式的产生,最大耦合效率可达99%,模间串扰<−20 dB。

Information Transferring between a Photon's Orbital Angular Momentum and Frequency

A photon's orbital angular momentum(OAM)offers a promising resource for the higher-dimensional quantum information process,which is due to the infinite values of OAM.One of the obstacles for its application is that it is difficult to transmit information encoded in OAM space in long distance quantum communication,e.g.,photons with different OAMs are unsupported in optical fiber transmitting.We propose an efficient scheme to transform the information from OAM to frequency.Then the information encoded in frequency freedom can be used in fiber transmission and finally be recovered to OAM from frequency.Our scheme can be easily extended to higher-dimensional quantum information transferring between OAM and frequency.

基于数字信号处理技术的模分复用通信系统研究

作为一种先进的数字信号处理技术,光纤环路在模分复用通信系统中具有较大的应用优势。基于此,文章对该技术的具体应用进行分析。首先对其主体技术与控制模块的具体设计方式进行探讨;随后对其进行实质性搭建,在系统梳理搭建过程与注意事项的基础上对其仿真结果进行判断。该系统在信息传输效能以及抗噪性上表现良好,具有较高的应用价值。

High pulse energy fiber/solid-slab hybrid picosecond pulse system for material processing on polycrystalline diamonds

We demonstrate an all polarization-maintaining(PM) fiber mode-locked laser seeded, hybrid fiber/solid-slab picosecond pulse laser system which outputs 40 μJ, 10 ps pulses at the central wavelength of 1064 nm. The beam quality factors M2 in the unstable and stable directions are 1.35 and 1.31, respectively. 15 μJ picosecond pulses at the central wavelength of 355 nm are generated through third harmonic generation(THG) by using two Li B3 O5(LBO) crystals, in order to get better processing efficiency on polycrystalline diamonds. The high pulse energy and beam quality of these ultraviolet(UV) picosecond pulses are confirmed by latter experiments of material processing on polycrystalline diamonds. This scheme which combines the advantages of the all PM fiber mode-locked laser and the solid-slab amplifier enables compact, robust and chirped pulse amplification-free amplification with high power picosecond pulses.