Study of the output characteristics of nonlinear optical loop mirror on an erbium-doped mode-locked fiber laser

We experimentally discussed the output characteristics of a passively mode-locked erbium-doped fiber laser using a single-mode fiber (SMF) structure as a saturable absorber (SA) based on nonlinear optic loop mirror (NOLM). The NOLM acting as an SA has properties of controllable pulse interval and pulse width. Four different types of NOLMs are experimentally discussed and the results show that fine adjustment to the coupler ratio together with optimization of the SMF length inside the NOLM can simultaneously implement high pulse energy and pulse internal tunability. The laser configuration provides a method to generate well-performing mode-locked lasing, and the investigations of the effects of changing some parameters of the laser also provide some help for the development of mode-locked fiber laser based on NOLM.     

Investigation on switchable operation states in a Tm/Ho co-doped fiber laser based on nonlinear optical loop mirror

The nonlinear pulse dynamics have been studied in a thulium/holmium co-doped passively mode-locked fiber laser based on nonlinear optical loop mirror (NOLM). By enhancing the nonlinear effect of the cavity and without changing the polarization state of the cavity, four types of operation states that switch between each other, including the basic mode-locking pulse, the two solitons pulse, the bright-dark pulse, and the harmonic mode-locking pulse, can be obtained. Compared with the laser of single mode-locking state, passively mode-locked fiber lasers (PMLFLs) with switchable operation states can be used in a wide range of applications, such as optical communication, material processing and optical fiber sensing technology.     

8字形腔锁模掺Yb3+光纤激光器

报道了利用非线性光纤环形镜（NOLM）锁模运行的掺Yb^3＋光纤激光器的实验研究。获得了脉冲宽度234ps。中心波长1053nm的锁模脉冲激光输出。光谱带宽6nm。输出功率2.05mW，重复频率3.842MHz。该锁模光纤激光器的工作中心波长可在1030～1081nm范围内调谐，锁模过程可以完全自启动，几乎不受外界环境变化的影响。可长时间稳定锁模工作，完全可以作为微焦耳级单脉冲能量光纤激光放大系统前端种子源使用，而且有望成为其他科学研究工作的中心波长可调谐的宽带锁模光纤激光光源。     

波长可调谐被动锁模光纤激光器

为在光纤激光器中获得特定中心波长的锁模激光,进行了采用非线性光纤环形镜锁模的掺Yb3+光纤激光器的波长可调谐实验研究。获得了自启动锁模、中心波长在1030nm~1081nm范围内连续调谐的锁模脉冲输出;在中心波长1053nm时,测得光谱带宽6nm、脉冲宽度234.375ps、输出功率2.05mW、重复频率3.842MHz。这种被动锁模光纤激光器的锁模过程可以完全自启动,几乎不受外界环境变化的影响,可以长时间稳定工作,不仅可以提供特定中心波长的锁模激光,而且有望成为其它科学研究工作的中心波长可调谐的宽带锁模光纤激光种子源。     

160-gb/s OTDM signal source with 3R function utilizing ultrafast mode-locked laser diodes and modified NOLM

High-quality 160-Gb/s optical time-division-multiplexing (OTDM) signal source with 3R functions was demonstrated using ultrafast mode-locked laser diodes (MLLDs) and a nonlinear optical fiber loop mirror (NOLM) modified with inline and external polarizers and an inline optical phase-bias compensator. Pulse quality for each OTDM channel was successfully improved and equalized owing to the clock extraction at the true data bit rate using a 160-GHz MLLD and also to the improvement of the switching performance of the NOLM.     

Simultaneous 4 × 10 Gb/s NRZ-to-RZ Modulation Format Conversion in Nonlinear Optical Loop Mirror With a Photonic Crystal Fiber

Orthogonal cross-phase-modulation (XPM) scheme in a nonlinear optical loop mirror (NOLM) is proposed to simultaneously convert four synchronized 10-Gb/s nonreturn-to-zero signals into return-to-zero (RZ) format. Modulation format conversion is achieved by using a synchronized optical control pulse train as the pulse carver in a NOLM. The control pulse train and the targeted signals are orthogonal in their states of polarization. This orthogonal nonlinear interaction substantially suppresses the undesirable four-wave mixing (FWM) induced crosstalk in the multichannel operation. Experimental demonstration of the proposed scheme shows that the suppression of the generated FWM idler is >26 dB. Error-free operation is achieved for the four converted 10-Gb/s RZ signals in a single NOLM by sharing the nonlinear XPM effect induced by the control pulse train.     

Generation of a 4 /spl times/ 100 GHz pulse-train from a single-wavelength 10-GHz mode-locked laser using superimposed fiber Bragg gratings and nonlinear conversion

In this paper, the design of a simple and practical repetition-rate multiplier based on superimposed-chirped fiber Bragg gratings (FBGs) is presented. A tenfold increase in the repetition rate of a mode-locked fiber source, by generating a 100-GHz optical pulse train from a 10-GHz train, is demonstrated experimentally. As compared with previous demonstrations, the superimposed FBG filter was specifically designed to decrease the duty cycle of the generated pulse train or, in other words, decrease the pulsewidth. In addition, a fiber nonlinear optical loop mirror (NOLM) is used to eliminate the pulse-to-pulse phase fluctuations in the output high-repetition-rate train and to achieve a wavelength-tunable transform-limited pulse sequence. Moreover, it is shown that nonlinear conversion using the NOLM can be used to simultaneously generate multiwavelength high-repetition-rate optical pulse trains (4 /spl times/ 100 GHz in the example shown here).     

哑铃形高功率全保偏大模场掺镱锁模光纤激光器

采用基于非线性光纤环形镜的哑铃形结构搭建了全光纤全保偏掺镱锁模激光器。通过使用全保偏大模场光纤、高功率光纤器件和优化的腔结构,实现了脉冲宽度在156 ps到8.1 ns范围内可调的高功率、大能量矩形耗散孤子共振脉冲输出,在最大泵浦功率22.7 W下激光器直接输出功率达到5.5 W,脉冲能量达到0.68μJ,峰值功率为84 W。得益于全保偏光纤结构,所设计的激光器具有出色的抗干扰性和稳定性。     

A grating-based OCDMA coding-decoding system incorporating anonlinear optical loop mirror for improved code recognition and noisereduction

We demonstrate an elementary grating-based optical code division multiple access (OCDMA) code generation and recognition system incorporating a nonlinear optical loop mirror (NOLM) within the receiver. We show that the NOLM can act as a nonlinear processing element capable of reducing both the pedestal associated with conventional matched filtering and the width of the associated code-recognition pulse. The pedestal rejection allows for an improved code recognition signal-to-noise ratio (SNR) relative to simple matched filtering alone, and reduced intra- and interchannel interference noise due to code overlap. The system benefits of using the NOLM are experimentally demonstrated under both single- and multiuser operation within a variety of seven- and 63-chip 160-Gchip/s code generation, recognition, and transmission experiments based on the use of bipolar superstructure fiber Bragg grating (SSFBG) coding-decoding pairs. Incorporation of the NOLM is shown to allow error-free penalty-free operation at data rates as high as 2.5 Gb/s under single-user operation, and to provide error-free performance with reduced power penalty in two-user experiments. The narrowed pulse recognition signature offers major advantages in terms of the further all-optical processing of decoded signals, such as code regeneration and recoding     

长腔被动锁模掺镱光纤激光器的方波脉冲产生

报道了一种基于非线性光纤环形镜(NOLM)、工作在耗散孤子共振(DSR)区的长腔被动锁模掺镱光纤激光器,该激光器谐振腔的总长度约为1502 m,可以输出重复频率为133.18 kHz的高能量方波脉冲,且输出脉冲的宽度和单脉冲能量均随泵浦功率的增大而呈线性增大。当泵浦功率增大到414.47 mW时,输出的方波脉冲具有最大宽度(761.6 ns),同时单脉冲能量达到了最大值(60.2 nJ)。通过改变NOLM中单模光纤的长度,进一步研究了谐振腔长度对输出方波脉冲特性的影响,结果表明:谐振腔越长,所得DSR方波脉冲越宽,脉冲峰值功率越低。     

光纤通信非线性补偿中的非线性光环路镜

介绍了用于光纤通信非线性补偿中的几种非线性光环路镜(NOLM,包括ANOLM、DALM、NALM、DILM、RA-NOLM、NBLM及DANLM)的构成和功能,给出了部分传输补偿实例,指出NOLM的发展趋势是小型化和集成化。     

All-optical TDM data demultiplexing at 80 Gb/s with significant timing jitter tolerance using a fiber Bragg grating based rectangular pulse switching technology

We demonstrate the use of fiber Bragg grating based pulse-shaping technology to provide timing jitter tolerant data demultiplexing in an 80 Gb/s all-optical time division multiplexing (OTDM) system. Error-free demultiplexing operation is achieved with /spl sim/6 ps timing jitter tolerance using superstructured fiber Bragg grating based 1.7 ps soliton to 10 ps rectangular pulse conversion at the switching pulse input to a nonlinear optical loop mirror (NOLM) demultiplexer comprising highly nonlinear dispersion shifted fiber (HNLF). A 2-dB power-penalty improvement is obtained compared to demultiplexing without the pulse-shaping grating.     

Nonlinear optical loop mirror based on standard communication fiber

We numerically analyze the effectiveness of a nonlinear optical loop mirror (NOLM) based on standard communication fiber with randomly varying birefringence for demultiplexing streams of picosecond pulses at 100 GHz. A broad switching window of about three pulse full-width at half maximum (FWHM) can be obtained. The device performance is defined by the pulse duration, the dispersion of the fiber, and the fiber length. We show that imperfect averaging of the randomly varying birefringence causes amplitude fluctuations on the NOLM transmission curve. We also show that the Raman self-frequency shift does not affect the NOLM switching characteristics at picosecond pulse durations     

非线性光环镜在光通信系统中的新应用

非线性光环镜(NOLM)以其独特的优点,被广泛应用于光通信系统中.文章阐述了非线性光环镜的基本原理,主要介绍了应用NOLM作为光判决单元、多波长可调谐掺铒光纤激光器的增益均衡器以及2R中继器等在高速光通信系统中的新应用,分别分析了它们特点和发展状况.     

Highly stable 68-fs pulse generation from a stretched-pulse Yb/sup 3+/-doped fiber laser with frequency shifted feedback

We report on the development of a passively mode-locked and highly-stable stretched pulse laser based on Yb/sup 3+/-doped silica fiber. Mode-locking is achieved by nonlinear polarization evolution coupled with the frequency-shifted feedback technique for ensuring robust self-starting. The Fabry-Perot (F-P) cavity incorporates also a diffraction grating pair to compensate for the normal dispersion of the fiber. The laser generates chirped pulses with energies of 100 pJ at a repetition rate of 23 MHz (2.3 mW average power) around 1055 nm which were subsequently compressed to near-bandwidth-limited pulses of 68 fs duration.     

基于非线性光纤环镜的全光波长变换器性能分析

非线性光纤环镜是一种很有前途的全光波长变换装置。介绍了利用光束传输法（ＢＰＭ） 对耦合非线性薛定谔方程组进行数值解析,详细讨论了对变换信号质量起作用的因素,包括泵浦光脉冲与信号光脉冲之间的走离和初始时延、光纤长度、向长波长变换和向短波长变换等。结果表明,适当的初始时延可以补偿走离的影响,适当增加光纤长度可以改善脉冲波形。     

Semiconductor all-optical modulator for synchronization of independent fiber laser oscillators and active mode-locking

Using an optically driven nonlinear semiconductor mirror, we have synchronized a 1.56-/spl mu/m mode-locked erbium fiber laser to the pulse train from a mode-locked ytterbium fiber laser operating at 1.05 /spl mu/m. We demonstrate that a robust active or passive mode-locked picosecond pulse operation and tight control of the repetition rate can be obtained resulting in a large value of the locking tolerance for the slave laser cavity mismatch exceeding 250 /spl mu/m.     

基于不平衡损耗非线性光纤环镜的双波长功率均衡实验研究

在波分复用（WDM）光纤网络中，存在很多因素会造成信道间的功率差异。针对波分复用光网络中功率均衡的需求，提出了利用带有不平衡放置的损耗结构的非线性光纤环镜（NOLM）来实现多信道功率均衡的技术方案。理论上分析了该方案利用自相位调制（SPM）效应产生均衡作用的基本原理，指出了该方案所能达到的最佳均衡指标。通过两波长10Gb／s幅度调制信道的实验，观察了不平衡损耗结构非线性光纤环镜（L-NOLM）的输出功率的变化过程，验证了它的均衡效果，当输入信道功率差异为7dB时，输出信道功率最大差异不超过2dB。该方案结构简单，无需解复用、复用，响应速度快，具有自适应均衡的特点。     

被动锁模光纤激光器的多模式输出

被动锁模光纤激光器腔体结构简单,可以实现全光纤集成,是产生超短脉冲的有效方法,而非线性偏振旋转又是其中最重要、最简单的被动锁模方法。为了研究基于非线性偏振旋转被动锁模光纤激光器存在的多种不同工作模式,采用实验方法,得到了包括正常孤子态,多脉冲束缚态,噪声像脉冲态等输出模式。结果表明,基于非线性偏振旋转被动锁模光纤激光器存在多种不同的工作模式。     

Pedestal suppression from compressed femtosecond pulses using anonlinear fiber loop mirror

The compression of higher order soliton pulses in dispersion decreasing fibers (DDF's) generates ultrashort fundamental soliton-like pulses accompanied by a broad low-intensity pedestal component. In this paper, we investigate the subsequent removal of the pedestal using a nonlinear optical fiber loop mirror (NOLM) to produce high-quality pulses. The influence of higher order effects such as stimulated Raman scattering and third-order fiber dispersion on the pedestal removal from ultrashort pulses are considered, and the effectiveness of using dispersion-flattened fiber within the loop is shown. The technique is experimentally demonstrated for 540-fs pulses generated by compression in DDF. In this case, high-quality pulses are produced by pedestal removal using a NOLM constructed from dispersion-shifted fiber