Generation of bright and dark soliton trains from continuous-wavelight using cross-phase modulation in a nonlinear-optical loop mirror

A simple technique for the simultaneous generation of bright and dark soliton trains from continuous-wave (CW) light is proposed and demonstrated theoretically. It is based on the optical switching characteristics of a nonlinear-optical loop mirror (NOLM) through which the CW signal is switched by a pump pulse train at another wavelength by the creation of cross-phase modulation-induced phase bias between the counter-propagating CW components. The transmitted and reflected signals exiting from the NOLM can then evolve, respectively, into bright and dark soliton trains in fibers with the appropriate group-velocity dispersion at the signal wavelength. Numerical simulations indicate that the generated solitons can be narrower than the pump pulses and that the scheme permits the conversion of nearly all of the CW energy into the soliton train energy without generating pulse pedestals     

40 Gbit/s pulsewidth-maintained wavelength conversion based on ahigh-nonlinearity DSF-NOLM

The authors present results showing that walkoff and dispersion effects are reduced when only 1 km HNL-DSF fibre is used in a nonlinear optical loop mirror (NOLM). Broadband and pulsewidth-maintained wavelength conversion at 40 Gbit/s based on a high-nonlinearity DSF-NOLM is obtained     

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。     

An Efficient Wavelength Converter Exploiting a Grating-Based Saw-Tooth Pulse Shaper

We experimentally demonstrate the generation of picosecond triangular optical pulses using a superstructured fiber Bragg grating and show experimentally that use of this pulse shape can provide a three-fold improvement in conversion efficiency relative to the use of Gaussian pulses with similar pulsewidths when used in a wavelength conversion scheme based on self-phase modulation and subsequent offset filtering.      

40-Gb/s all-optical wavelength conversion based on a nonlinearoptical loop mirror

All-optical wavelength conversion based on a nonlinear optical loop mirror (NOLM) at 40 Gb/s is demonstrated for the first time. The effect of walkoff time between control beam and signal beams is investigated when the NOLM is used as an all-optical wavelength converter or an all-optical demultiplexer     

Optimal loop length of a nonlinear optical loop mirror in switchingsolitons

The optimal loop length of a nonlinear optical loop mirror (NOLM) for switching solitons was investigated numerically for the case where the wavelengths of the control pulse and signal soliton straddle the dispersion zero. In our analysis, the Raman effect is also included because the wavelength difference between the control and signal pulses is within the Raman gainband. It was found that the control pulse not only imposes phase shift on the copropagating signal, but also transfers part of its energy to the signal. Furthermore, the broadening of the control pulse due to the combined effect of self-phase modulation and group velocity dispersion increases the switching power of the control pulse significantly. The broadening of the control pulse also introduces more uniform phase shift to the signal, thus resulting in a higher switching efficiency. Finally, our results show that the pulse distortion is minimal if a loop length equivalent to one soliton period is employed     

Wavelength and repetition rate tunable optical pulse source using a chirped fiber Bragg grating and a nonlinear optical loop mirror

We experimentally demonstrate a simple and novel scheme for tunable real-repetition-rate multiplication, based on the combined use of fractional Talbot effect in a linearly tunable chirped fiber Bragg grating (FBG) and cross-phase modulation (XPM) effect in a nonlinear optical loop mirror (NOLM). By tuning the group-velocity dispersion of the chirped FBG fabricated with the S-bending method using a uniform FBG, we obtain high quality pulses at pseudorepetition rates of 20/spl sim/50 GHz from an original 8.5-ps 10-GHz soliton pulse train. We subsequently convert this pseudorate multiplication into a real-rate multiplication using XPM effect in an NOLM. A wavelength tuning is also achieved over a /spl sim/15-nm range.     

基于微结构光纤中交叉相位调制效应的波长变换

利用光波在一段80 m长的微结构光纤(MSF)中的交叉相位调制效应实现了对10 GHz时钟信号的全光波长变换,变换带宽超过30 nm。该实验所使用的微结构光纤非线性系数约为11 W-1.km-1,其在1530~1570 nm波长范围内具有小的正常色散和平坦的色散曲线。实验结果表明,利用这种微结构光纤可以实现结构紧凑的宽带波长变换器。     

群速度色散对非线性光纤环镜型OTDM解复用器影响的理论与数值分析

本文就群速度色散对非线性光纤环镜型ＯＴＤＭ解复用器的影响进行了理论与数值分析．首先给出了描述群速度色散与非线性效应之间相互作用的耦合非线性薛定谔方程组,然后用分步傅立叶方法对该方程组进行了数值求解．经分析指出,要达到一定的开关性能,孤子阶数、色散的正负、脉冲宽度及控制和信号脉冲之间的走离时间应满足一定的条件．     

Simultaneous generation of wavelength tunable two-coloredfemtosecond soliton pulses using optical fibers

Wavelength tunable two-colored femtosecond (fs) soliton pulse generation is proposed and demonstrated for the first time, using passively mode-locked fs fiber laser and polarization maintaining fibers. The wavelengths of the two soliton pulses can be changed arbitrarily by varying the power and polarization direction of the fiber-input pulse. Ideal two colored soliton pulses in which the pulsewidths are about 200 fs are generated in the wavelength region of 1.56-1.70 μm for 110-m fiber. The generated pulses are almost transform-limited ones     

Design and Performance of an All-Optical Wavelength Converter Based on a Semiconductor Optical Amplifier and Delay Interferometer

The design and performance of an all-optical wavelength converter based on a semiconductor optical amplifier (SOA) and a delay interferometer (DI) are presented for 10-Gb/s return-to-zero (RZ) transmission systems with pulsewidths of 25-45 ps. The performance of the wavelength converter is investigated in terms of the operating conditions for the SOA and DI, and the properties of the input signal. The regenerative characteristics of the wavelength converter are also examined for input signals degraded by amplified spontaneous emission noise and residual dispersion. With proper design, the SOA-DI structure provides a high-performance all-optical wavelength converter for 10-Gb/s RZ transmission with practical pulsewidths.     

A high-speed optical star network using TDMA and all-opticaldemultiplexing techniques

The authors demonstrate the use of time-division multiplexing (TDM) to realize a high capacity optical star network. The fundamental element of the demonstration network is a 10 ps, wavelength tunable, low jitter, pulse source. Electrical data is encoded onto three optical pulse trains, and the resultant low duty cycle optical data channels are multiplexed together using 25 ps fiber delay lines. This gives an overall network capacity of 40 Gb/s. A nonlinear optical loop mirror (NOLM) is used to carry out the demultiplexing at the station receiver. The channel to be switched out can be selected by adjusting the phase of the electrical signal used to generate the control pulses for the NOLM. By using external injection into a gain-switched distributed feedback (DFB) laser we are able to obtain very low jitter control pulses of 4-ps duration (RMS jitter <1 ps) after compression of the highly chirped gain switched pulses in a normal dispersive fiber. This enables us to achieve excellent eye openings for the three demultiplexed channels. The difficulty in obtaining complete switching of the signal pulses is presented. This is shown to be due to the deformation of the control pulse in the NOLM (caused by the soliton effect compression). The use of optical time-division multiplexing (OTDM) with all-optical switching devices is shown to be an excellent method to allow us to exploit as efficiently as possible the available fiber bandwidth, and to achieve very high bit-rate optical networks     

40 Gbit/s wavelength conversion in cascade of SOA and NOLM and demonstration of extinction ratio improvement

The authors demonstrate that the extinction ratio (ER) can be improved when a nonlinear optical loop mirror (NOLM) is used as a wavelength conversion medium. At 4O Gbit/s. An extinction ratio (ER) of 7 dB for a converted signal generated by cross-gain modulation in a semiconductor optical amplifier is improved to an ER of 10 dB after wavelength conversion in an NOLM.     

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     

NOLM全光波长变换输出脉冲波形特性研究

本文分析了在利用非线性光学环形镜的开关效应和光纤内交叉相位调制效应实现全光波长变换系统中,色散位移光纤长度、砂浦脉冲峰值功率、泵浦脉冲宽度以及泵浦脉冲和连续探测波之间群速度失配参量对输出脉冲波形特性的影响。通过优化系统各项参数,可以在实现最高转换效率的同时,降低波长变换脉冲扶真程度,使波长变换脉冲无展宽,从而适用于超高速率通信系统。     

Simple autocorrelation technique based on degree-of-polarization measurement

We demonstrate a simple optical-fiber-based autocorrelator for picosecond short pulses based on degree-of-polarization measurement while tuning the relative delay of the two orthogonal polarization states of the pulse. The pulsewidths of 20-, 40-, and 80-GHz pulse trains and 2-ps pulses generated by a mode-locked laser are measured. The <-10-dBm optical powers are used in the experiment. The measurement results agree well with the measurements using conventional techniques. Compared with conventional autocorrelators, this technique has the advantages of 1) wavelength independent, 2) significant less alignment, and 3) no high power required.     

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     

Multirate and Dual-Wavelength Semiconductor Fiber Laser

We demonstrate the successful operation of a multirate and dual-wavelength mode-locked semiconductor fiber laser that incorporates a multichannel nonlinear optical loop mirror (NOLM) functioning as a multichannel all-optical modulator. Each channel of the NOLM incorporates its own length of highly nonlinear fiber and can be driven by independent pump signals. Thus, the single NOLM is capable of processing multiple wavelength channels independently and simultaneously. We obtain mode-locked operation at different frequencies (5 and 10 GHz) for two wavelengths with spacing as narrow as 0.8 nm.      

Fundamental limits of all-optical NRZ-to-soliton conversion bynonlinear optical loop mirrors

All-optical NRZ-to-RZ conversion through nonlinear optical loop mirrors (NOLM) is analysed. By computing the time-bandwidth output characteristics, we investigate the dependence of the NOLM switching power and control envelope on the chirp of the switched RZ pulses. The effect of this chirp on further propagation in the soliton regime and related continuum generation is then analysed by an inverse-scattering transform     

OTDM add-drop multiplexer based on XPM-induced wavelength shifting in highly nonlinear fiber

In this paper, we study experimentally and numerically simultaneous time-domain add-drop multiplexing for high-speed optical time-division multiplexing (OTDM) networks based on cross-phase-modulation (XPM)-induced wavelength shifting in a 50-m highly nonlinear fiber. This scheme needs only a single-channel clock rate and does not alter the input signal wavelength. Simultaneous add and drop operations at 80 Gb/s have been demonstrated experimentally with less than 1-dB power penalty for the dropped channel and no distinct bit-error-rate (BER) degradation for the added channel. Numerical simulations show that the experimental results are only limited by the available signal pulsewidth, and simultaneous add-drop multiplexing at 160-Gb/s or higher bit rates is possible with this scheme by employing control and signal pulses with proper pulsewidths.