Analyzing the Switching Characteristics of a NOLM Demultiplexer with on Analytic and Numrical Methods

1IntroduCtionAllopticalswitchesarekeycOrnpoentsinfuturehigh-speedOPticaltimediVisi0nmultiPleking(0TDM),yst.ms[i].Asasort0fall-OPticalsWtchingdevices,nonllnear0Pticalboharrors(NOLMs)areverysultablef0rall-0PticaldemultiplexinginultrahighsPeedOTDMsystemsbecause0ftheirsimPleconfiguratdri,stableandreliableperformance,andultrafastresP0ndingspeed['J.HOWever,asN0LMutilizestheinherentnonlinearity(crossphasemodulation:XPM)0ffibertoperf0rmswttching,weaknonlineareffects0ffibercausethatl0nger…     

Bit-error-rate analysis for a 100-Gbit/s nonlinear optical loop mirror demultiplexer employing soliton control and signal pulses

On the basis of a previously derived mathematical model, the power penalty associated with a nonlinear optical loop mirror (NOLM) demultiplexer was calculated, with timing jitter noise, bit-to-bit cross talk, and channel cross talk taken into consideration. Simulation results show that a 3-dBm improvement in the receiver sensitivity at a bit error rate of 10(-9) can be achieved by choice of the appropriate walk-off time between the control and the signal pulses within the NOLM demultiplexer.     

交叉相位调制对非线性光纤环镜中光脉冲传输的影响

基于耦合非线性薛定谔方程,采用分步傅里叶方法分析了在单波长信道和WDM（波分复用）4波长信道中XPM（交叉相位调制）对高速NOLM（非线性光纤环镜）光开关中脉冲传输的影响.数值计算表明：XPM造成NOLM中信号脉冲串扰与畸变,并造成NOLM开关性能的下降.WDM系统NOLM光纤环中的同向传播的各波长之间的XPM串扰比相向脉冲之间的XPM效应的影响更大,并且波长越短输出功率越低,中间信道受XPM的影响所导致的脉座现象和走离效应比两侧波长信道严重.     

Performances of Switching Window of Ultrafast Nonlinear Interferometer (UNI) Demultiplexer

In this paper, the theoretical model of the UNI is proposed in detail, which counts on the ultrafast nonlinearities and longitudinal effects of semiconductor optical amplifier (SOA). The transfer function of UNI is also obtained. The switching window, which is a key parameter for demultiplexer, is then analyzed. It's shown that the switching window properties are determined by the length of SOA, the length of the birefringence fiber (BRF), and the parameters of control pulses such as control pulse energy, pulsewidth, power.     

Nonlinear-optical loop mirror demultiplexer using a random birefringence fiber: comparisons between simulations and experiments

A numerical simulation of the switching characteristics of a polarization multiplexed nonlinear-optical loop mirror demultiplexer is presented and compared with experiment. The model assumes that the optical fiber that composes the loop has a randomly varying birefringence, that the signal and the control pulses have the same frequency, and that these pulses are nearly solitons. Factors that affect the shape and the width of the switching window curve are discussed. A phase-dependent modulation of the switching window curve, which is due to incomplete averaging of the light polarization state, is observed both experimentally and numerically. Models in which the randomness is neglected are not able to describe this modulation adequately.     

Periodicity Characteristic of TOAD's Switching Window

1 IntroductionThere are a variety of all-optical demultiplexing schemes for OPtical time divisionmultiplexing (OvuM) system, such as nonlinear optical loop horror (NOLM)[IJ,terahertz optical asyrnxnetric demultiplexer (TOAD)[2], four wave ndking (aaM) offiber or semiconductor optical amplifier (~)[3'4), etc. Axnong them, the terahertzoptical asymmetric demultiplexer (TOAD) has advantages of requirement for shorterlength of fiber and lOWer energy of control pulse, no dispersion and walk…     

Periodicity Characteristic of TOAD's Switching Window

The periodicity characteristic of switching window of a terahertz optical asymmetric demultiplexer (TOAD) using numerical simulation was investigated. The results show that the switching window width of TOAD changes periodically with the time asymmetry of TOAD and the period is one half of the period of control pulses. The theoretical results agree with the experimental results very well.     

Optimizing the performance of TOAD by changing the wavelength and power of control pulse

The performance of terahertz optical asymmetric demultiplexer (TOAD) has been studied by modelling the semiconductor optical amplifier (SOA) in which the intraband effects had been taken into account. Numerical results are coincident with the experiment results. We interpret why there are three peaks in the switching window, which has never been reported before. In addition, we put forward the definition of the flatness of the switching window of TOAD for the first time By analysing the different phase of clockwise and counter clockwise signal pulse changed by SOA, appropriate peak power of control pulse and wavelength of signal and control pulse have been calculated in order to obtain large output power and flat switching window of TOAD.     

High-energy pulses from a figure 8 fiber laser with normal net dispersion

In this paper we show numerically that high-energy pulses can be obtained with a figure-eight Erbium-doped fiber laser with large normal net dispersion, and in which an anomalous-dispersion Nonlinear Optical Loop Mirror (NOLM) is used as the effective saturable absorber. One advantage of this configuration over the ring cavity is the possibility to adjust the length of the NOLM loop to avoid overdriving the saturable absorber. The ring section of the laser includes a bandpass filter to balance the combined effects of Kerr nonlinearity and normal dispersion. Strict polarization control is performed in the NOLM as well as in the ring section of the laser. The NOLM is a power-symmetric scheme whose switching relies on nonlinear polarization rotation. This architecture allows a precise control of the low-power NOLM transmission through the orientation of a quarter-wave retarder, whose adjustment is shown to be critical for stable pulsed operation. Pulse formation appears to depend critically on the filter width. If it is wide enough, ps pulses with a large positive linear chirp are produced. After dechirping outside the laser, nearly transform-limited pulses with durations down to 240 fs, energies up to 10 nJ and peak powers beyond 40 kW are predicted.     

光时分复用(OTDM)系统中基于电吸收调制器(EAM)的短脉冲光源及解复用器的设计考虑

研究了电吸收调制器(EAM)的衰减随外加反向电压增加而指数增加的情形下,短脉冲光源的脉冲输出和解复用器的开关窗口对EAM的消光效率、反向DC偏置电压以及正弦RF驱动信号的幅度等参量的依赖关系.在基于EAM的短脉冲光源中,输出脉冲的消光比等于EAM消光效率η与正弦驱动电压峰峰值V_pp的乘积,输出光脉冲的消光比和脉宽均与EAM的反向偏置电压无关,但输出脉冲的峰值功率与η、V_pp和V_b都有关系.在基于EAM的解复用器中,为了使解复用器的开关窗口近似为矩形,可利用EAM的削波效应,使V_pp/2>V_b.在EAM的消光效率η已知时,通过仔细设计反向DC偏置电压V_b和正弦驱动电压的峰峰值V_pp,达到OTDM解复用器所需要的开关窗口形状、宽度和消光比.     

Analysis of optical time domain demultiplexer using microring resonators

A time domain optical demultiplexer using electrooptic microring resonator is proposed. The switching window with pico-second order width is generated by using a sinusoidal electrical control voltage to shift the refractive index of the material. The modulation characteristics and switching window of the microring resonator are studied. The dependences of the width and extinction ratio of the switching window on the control voltage are analyzed. The demultiplexing performance of a 40–10 Gbps system is evaluated by numerical simulation technology. Results show that switching windows with required width and extinction ratio can be generated.     

光时分复用(OTDM)系统中基于电吸收调制器(EAM)的短脉冲光源及解复用器的设计考虑

研究了电吸收调制器（ＥＡＭ） 的衰减随外加反向电压增加而指数增加的情形下,短脉冲光源的脉冲输出和解复用器的开关窗口对ＥＡＭ 的消光效率、反向ＤＣ 偏置电压以及正弦ＲＦ 驱动信号的幅度等参量的依赖关系－ 在基于ＥＡＭ 的短脉冲光源中,输出脉冲的消光比等于ＥＡＭ 消光效率η与正弦驱动电压峰峰值Ｖｐｐ 的乘积,输出光脉冲的消光比和脉宽均与ＥＡＭ 的反向偏置电压无关,但输出脉冲的峰值功率与η、Ｖｐｐ 和Ｖｂ 都有关系－ 在基于ＥＡＭ的解复用器中,为了使解复用器的开关窗口近似为矩形,可利用ＥＡＭ 的削波效应,使Ｖｐｐ／２＞ Ｖｂ－ 在ＥＡＭ 的消光效率η已知时,通过仔细设计反向ＤＣ 偏置电压Ｖｂ 和正弦驱动电压的峰峰值Ｖｐｐ ,达到ＯＴＤＭ 解复用器所需要的开关窗口形状、宽度和消光比－     

输入光特性对超快非线性干涉仪开关窗口的影响

就超快非线性干涉仪(UNI)的输入光特性对其开关窗口的影响进行了数值模拟和实验研究,输入光包括控制光脉冲和探测光脉冲。在数值模拟中,调节控制光脉冲和探测光脉冲的功率及脉宽,功率越高和脉宽越窄,窗口的形状越好。在调节过程中发现控制光脉冲和探测光脉冲都存在一个最佳的功率点使窗口的形状达到最优。如果继续增大控制光脉冲功率,会使窗口的顶部倾斜,窗口形状恶化;而继续增大探测光脉冲功率,窗口的消光比开始下降。在数值模拟的基础上进行了10Gb／s的超快非线性干涉仪全光开关实验,在实验中用连续光代替探测光脉冲以观察窗口形状。通过改变控制光脉冲和连续光功率来验证它们对超快非线性干涉仪开关窗口的影响。实验表明,应选用短而强的控制光脉冲和最优功率点的连续光,这与模拟结果吻合。     

非线性光环路镜去复用理论研究

本文从非线性光环路镜(NOLM)的一般原理出发,研究了NOLM的一般特性,发现利用光纤的双折射李效应并通过合理地选择波长能减小群色散的影响,降低开关光功率.在忽略群色散条件下,研究了光开关功率、消光比与控制脉冲抖动大小和文中定义的参数d的变化关系.     

All-fiber passive mode-locked laser to generate ps pulses based in a symmetrical NOLM

We experimentally investigate an all-fiber passively mode-locked laser generating ps pulses. The experimental setup is a figure eight fiber laser configuration, including a power-symmetric Nonlinear Optical Loop Mirror (NOLM) with highly twisted low-birefringence fiber in the loop. NOLM switching is achieved by polarization asymmetry between the counter-propagating beams in the loop. We used a Quarter-Wave Retarder in the loop to break the polarization symmetry. Using a polarizer beam-splitter cube as the NOLM output we got the best quality output pulses from the laser. At this output, we are monitoring the output pulse polarization component which is parallel to the input NOLM component. We achieved stable generation of ～25 ps pulses at the repetition frequency of 0.78 MHz with milliwatts average output power. The mode-locked laser ran in stable operation for hours.     

Wavelength-conversion type picosecond optical switching using a waveguide QPM-SHG/DFG device

We report picosecond all-optical switching in optical communication band using a LiNbO₃ waveguide quasi-phase matched second-harmonic generation/difference-frequency generation device. Analysis based on the beam propagation method showed that 1 ps switching with 3.1% efficiency is feasible with 10 W peak control pulse power. Switching efficiency of ?22 dB was demonstrated using control pulses of 10 ps width and 2 W peak power.     

自启动被动锁模掺铒光纤激光器的研究

在非线性光纤环形镜非线性开关效应和块状半导体波导饱和吸收效应的共同作用下，实现了掺铒光纤激光器的自启动被动锁模，获得了十分稳定的锁模脉冲序列，观察到高次谐频锁模脉冲输出。分析了非线性光纤环形镜的非线性开关反射特性。     

全光纤高功率被动锁模掺铥光纤激光器

利用非线性光环形镜(NOLM)的可饱和吸收特性实现了可自启动的2μm全光纤高能量被动锁模掺铥光纤激光器。当泵浦功率大于3W时,激光器工作在连续或不稳定脉冲运转状态;泵浦功率达到4.69W后,输出为自启动锁模脉冲,重复频率4.26MHz,中心波长2 061.5nm,光谱半极大宽度18.1nm,平均输出功率8.8mW;继续增加泵浦功率到最大值7.56W,可以得到中心波长2 062.2nm、光谱半极大宽度17.1nm、斜率效率为6.2%、脉冲宽度和能量分别为424fs和65.6nJ的稳定锁模脉冲。这是目前已报道的在未经放大情况下脉冲能量最高的2μm锁模脉冲光纤激光器。     

Optical pulse shaping at moderate power using a twisted-fibre NOLM with single output polarisation selection

We demonstrate theoretically and experimentally that efficient signal shaping operation can be obtained at moderate power by using the transmission characteristic of a power-symmetric nonlinear optical loop mirror (NOLM) including highly twisted fibre and operating through nonlinear polarisation rotation, when the circular polarisation state orthogonal to the input polarisation is selected at the NOLM output. By adjusting the angle of the quarter-wave retarder inserted in the loop, the phase bias of the transfer characteristic can be adjusted precisely to enable proper signal shaping for moderate values of input power, remaining well below switching power. The tolerance of the procedure to deviations of the input polarisation from the ideal circular case is investigated numerically. We demonstrate experimentally the capabilities of this setup for both power equalisation and extinction ratio enhancement. Finally, we show that this setup is also useful to shape ultrashort optical pulses from the relaxation oscillations of a DFB semiconductor laser. In comparison with other NOLM-based techniques, the proposed approach allows to reduce by a factor of 8-10 the peak power required for pulse shaping, for the same fibre length and Kerr coefficient.     

Analysis of the Switching Characteristics of TOAD

The dynamic gain responses of the semiconductor optical amplifier (SOA) in a terahertz optical asymmetric demultiplexer (TOAD) to intense control pulses with different input energies and pulse widths are investigated. The influences on the switching characteristics of TOAD for different control pulse energies, widths, loop time asymmetry, and time delays between the signal pulse and control pulse are studied and analyzed in detail. The theoretical analysis coincides well with the experimental result.