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.     

OTDM add-drop multiplexer based on time-frequency signal processing

A time-division add-drop multiplexer capable of high-extinction-ratio operation is presented both theoretically and experimentally. The approach used is based on time-to-frequency domain conversion of optical signals and relies upon the switching of linearly chirped optical pulses. By converting a 40-Gb/s optical time-division multiplexing (OTDM) signal to 4 /spl times/ 10-Gb/s wavelength-division multiplexing (WDM) channels and using fiber Bragg gratings for frequency-domain add-drop multiplexing, a timeslot suppression ratio in excess of 30 dB and error-free operation for the dropped, through, and added channels were achieved. A further stage of WDM-to-TDM signal conversion was used to map the resulting signal back into the time domain. Moreover, it is shown that it is straightforward to simultaneously operate on multiple channels by simply cascading gratings to make more complex filtering functions without the requirement for any further synchronization of the tributary channels.     

Correlated and uncorrelated timing jitter in gain-switched laserdiodes

The author describes correlated and uncorrelated timing jitter of gain-switched pulses generated from sinusoidally modulated laser diodes measured from photocurrent power spectra. It is found that if dc bias is decreased to obtain shorter pulses, then the root-mean-square (rms) value of uncorrelated timing jitter drastically increases to more than 2 ps, while correlated jitter remains constant at the drive circuit level of ~0.2 ps. By optimizing the bias condition and compression fiber length, total timing jitter of gain-switched pulses can be reduced to as low as ~0.5 ps, as their pulse width is kept less than 10 ps     

Pedestal-Free Pulse Source for High Data Rate Optical Time-Division Multiplexing Based on Fiber-Optical Parametric Processes

In this paper, an RF-driven pedestal-free cavity-less 40 GHz pulse source for generation of high-speed optical time-division multiplexing signal is presented. The pulse source is based on pulse compression by means of self-phase modulation in combination with subsequent filtering. Further compression and pedestal removal of the pulse was achieved in one-pump fiber-optic parametric amplifier seeded by a continuous-wave laser source. The obtained idler pulses were characterized by a full-width at half-maximum pulsewidth of 1.2 ps and an SNR of 36 dB. Generation of 320 Gb/s data stream with a Q-factor of 20 dB is successfully demonstrated using the proposed pulse source.     

Timing-jitter-free demultiplexing of an all-optical signal processor based on the intensity-dependent self-wavelength conversion of Raman solitons

An all-optical signal processor based on the self-wavelength conversion of Raman solitons is described. The processor consists of an erbium-doped fiber amplifier (EDFA), a highly nonlinear fiber, and an optical bandpass filter. The timing-jitter-free demultiplexing of the processor was demonstrated by an 80-km transmission experiment. Error-free bit error rate (BER) performance was achieved. Transmitted fourfold optical time-division multiplexing (OTDM) signals with a large timing jitter of about 16 ps for an OTDM signal interval of 25 ps were demultiplexed to 9.95-Gb/s signals without signal degradation.     

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     

Pulse repetition frequency multiplication via intracavity opticalfiltering in AM mode-locked fiber ring lasers

We demonstrate pulse repetition frequency multiplication in AM mode-locked fiber ring lasers using optical filtering realized via an intracavity fiber Fabry-Perot filter (FFP) and show that the generated optical pulses are highly stable in amplitude noise and timing jitter. A 3.477-GHz optical pulse train is generated using a modulation signal of 869.284 MHz, a fourth subharmonic multiple of the 3.48-GHz free spectral range of FFP. The generated optical pulses exhibit a high degree of pulse stability in terms of a large suppression of supermode noise, a low amplitude noise of 0.93 %, and a timing jitter of 1.2 ps     

Synchronization of passively mode-locked erbium-doped fiber lasersand its application to optical communication networks

We synchronized two passively mode-locked erbium-doped fiber lasers using a phase lock loop with a large dynamic range and bandwidth, which is realized by using a novel acoustooptic-modulator-grating scheme. Cross-correlation of the two lasers shows the interlaser jitter is under 2 ps (same as the laser pulse width) for period as long as hours. To prove the quality of phase locking, we apply synchronized lasers in two all-optical network applications, one of which requires the lasers to have the same wavelength and the second requires the lasers to be at different wavelengths. In the single wavelength application, the synchronized lasers drive a cascade of two low-birefringence, polarization maintaining, optical logic gates with switching timing window of 4 and 5 ps, respectively. We obtain nonlinear transmission of ~50% at a switching energy of 8 pJ and contrast ratio of 16 dB, which are comparable performance as that obtained using a single laser. In the different wavelength application, we use 0.8 ps pulses to switch 2 ps pulses in a two-wavelength nonlinear optical loop mirror demultiplexer with timing window of 5.5 ps. Stable switching is reached at a efficiency as high as 90% at switching energy of 0.8 pJ, and a contrast ratio of 20 dB. Excellent agreement is found between the experimental data and the simulated results, which exclude the timing jitter     

Optical time-division multiplexing for very high bit-ratetransmission

Optical time-division multiplexing (OTDM) extends and expands the well-known techniques of electrical time-division multiplexing into the optical domain. In OTDM, optical data streams are constructed by time-multiplexing a number of lower-bit-rate optical streams. Opportunities for very high-speed transmission and switching are created by removing limitations set by the restricted bandwidth of electronics and by capitalizing on the inherent high-speed characteristics of optical devices. An overview of recent work in optical time-division multiplexing and demultiplexing is presented. Design considerations affecting system architecture are described. Emphasis on the factors that limit system performance, such as crosstalk between multiplexed channels. Examples of very high bit-rate optical time-division multiplexed system experiments using short pulses from mode-locked semiconductor lasers and high-speed Ti:LiNbO₃ waveguide switch/modulators are presented     

Performance analysis on semiconductor laser amplifier loop mirrors

Operating characteristics of the semiconductor laser amplifier loop mirror (SLALOM) in optical time-division multiplexing (OTDM) applications are investigated in theory. The injection current of the semiconductor laser amplifier (SLA) should be adjusted to realize a flat and high switching window. The channel crosstalk induced by the finite carrier lifetime and the signal timing jitter should be balanced. The optimal switching window width should be slightly wider than half of the OTDM signal bit interval. The control pulse should be narrower than one-third of the OTDM bit interval in order not to deteriorate the bit error rate (BER) performance. Further discussion indicates that the nonlinear gain compression in the SLA becomes a crucial limit for the SLA-based all-optical switches to be used in the terahertz applications     

Effects of crosstalk and timing jitter on all-optical time-divisiondemultiplexing using a nonlinear fiber Sagnac interferometer switch

All-optical time-division demultiplexing using a nonlinear fiber Sagnac interferometer switch (NSIS) is studied with respect to the two main causes that degrade the bit-error-rate (BER) performance: crosstalk and timing jitter. It is shown that unwanted cross-phase-modulation in the reference signal which counter-propagates to the control pulse, as well as the poor extinction of the switch itself, seriously degrades the extinction ratio of the switch, thus increasing the crosstalk from other channels. Numerical calculations clarify the effect of the switching window width, window shape, and the multiplexed channel number on the power penalty in terms of BER performance. Timing jitter between the signal and control pulses is investigated as another degradation factor that causes an error floor in BER performance. It is found that the minimum BER is obtained when the window width is set to the time slot width and the rms value of the jitter must be less than 1/14.1 times the time slot width to ensure that BER<10^-12. To confirm this analysis, precise measurements of BER performance with NSIS-based demultiplexing are performed using amplified gain-switched laser diode pulses, as the relative timing jitter, switching window width, and multiplexed channel number are varied. Good agreement with the analysis is shown. Finally, optimum system design based on a small power penalty and low error floor is described. It is shown that the NSIS has the potential of demultiplexing a 160-Gb/s or 320-Gb/s optical data stream into its 40-Gb/s constituents with only a 4-dB or 7-dB power penalty     

一种新型的全光纤超短光脉冲压缩方案

文章提出了一种基于正常色散递减光纤（ND—DDF）、单模光纤（SMF）和非线性环镜（NOLM）组成的全光纤超短脉冲压缩方案。利用光脉冲在正常色散区的色散递减光纤（ND-DDF）中传输时,在脉冲的中心部分将带上较大线性正啁啾（和普通光纤相比）,当脉冲在SMF中传输时色散致啁啾对其进行补偿从而有一个脉冲压缩的过程,最后利用NOLM对压缩后的脉冲进行进一步的压缩和消基座处理。数值模拟的结果表明：半峰全宽为10ps、能量为74pJ的高斯脉冲经过1km的DDF、79m的SMF和20m的NOLM后,可以获得峰值功率为210W,半峰全宽为120fs且几乎无基座的超短脉冲。     

Signal-to-noise ratio analysis of 100 Gb/s demultiplexing usingnonlinear optical loop mirror

This paper investigates experimentally and theoretically the signal-to-noise ratio (SNR) characteristics of 100 Gb/s all-optical demultiplexing using a nonlinear optical loop mirror (NOLM). The analysis takes into account two effects that degrade the SNR associated with NOLM demultiplexing. First is channel crosstalk originating from the leakage of nontarget channels. Second is the intensity fluctuations of demultiplexed signals caused by the combined effects of timing jitter and a profile of the switching window. Considering these two effects, power penalties associated with NOLM. Demultiplexing are theoretically evaluated using the conventional noise theory of an optical receiver followed by an optical preamplifier. Experimental results of bit error rate measurements for 100 Gb/s demultiplexing using three different NOLMs with different intrinsic crosstalk values, defined by signal transmittance in the absence of control pulses, show that the power penalties are in good agreement with the evaluation based upon our proposed analysis. It can be found from our investigation in demultiplexing from 100 to 10 Gb/s that intrinsic crosstalk of less than -25 dB, corresponding to a coupling ratio, K, of |K-0.5|⩽0.03, is required for the power penalty of less than 1 dB. The root-mean-square (rms) value of the relative timing jitter necessary for obtaining a sufficient timing tolerance width for combining control and signal pulses is determined     

Enhancement of the Performance of a Reflective SOA-Based Hybrid WDM/TDM PON System With a Remotely Pumped Erbium-Doped Fiber Amplifier

A passive optical network (PON) architecture based on a hybrid wavelength-division multiplexing (WDM) and time-division multiplexing (TDM) PON system with a remotely pumped erbium-doped fiber amplifier (EDFA) is presented as an excellent candidate for use in a next-generation optical access network. The remotely pumped EDFA operates as a bidirectional amplifier and provides a 15-dB gain to both upstream signals and seed light sources, so the sensitivity of upstream transmission is greatly improved. An upstream transmission of 1.25 Gb/s with a low seed channel power of -14 dBm is made feasible over a total reach of 25 km for 32-WDM channels and 16-TDM splits by the use of the remotely pumped EDFA. This scheme has advantages that it uses a single transmission fiber for both down-and up-stream signals and that it reduces the Rayleigh scattering contribution.     

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     

10 GHz超低抖动光短脉冲源

报道了一种新型的重复频率为10 GHz,脉宽为5.3 ps,抖动为184 fs的高稳定光短脉冲源.将大信号调制半导体激光器产生的10 GHz光脉冲,先送入LiNbO3电光相位调制器增强负啁啾,并使光谱进一步展宽,再通过色散补偿光纤(DCF)压缩脉冲啁啾,可得到光短脉冲.由于大信号调制激光器输出的光脉冲本身具有负啁啾,而通过相位调制器的光脉冲在不同的时间间隔内既有正啁啾也有负啁啾,通过适当调整进入相位调制器的光脉冲时延,使其通过相位调制器后累加产生更大的负啁啾,再利用正色散光纤压缩啁啾,从而得到低抖动且无基座的光短脉冲.     

色散补偿法获得5GHz,6.8ps超短光脉冲

利用色散位移光纤压缩从１．５５μｍ增益调制ＤＦＢ激光器中出射的红移啁啾光脉冲。在最优光纤压缩长度下，光脉冲宽度由４２．６ｐｓ压缩至６．８ｐｓ，压缩比为６．３     

All-optical address extraction for optical routing

This paper describes the optical circuit that enables to extract address from a transmitted cell in an all-optical manner. Nonlinear optical loop mirrors (NOLM's) are used as all-optical switches in order to confirm the operation of the proposed circuit. The control pulses synchronized with address bits are generated from the transmitted cell. The address bits are successfully extracted without any electronic control circuit. The factors that limit an attainable bit rate are discussed. If we use NOLM composed of a 2-km-long fiber, 110 Gb/s is attainable for the 4 ps FWHM input pulse with RZ format     

Real-time Fourier transformations performed simultaneously overmultiwavelength signals

The real-time Fourier transformation (RTFT) has been previously proposed and demonstrated for a multitude of applications in the areas of optical communications, temporal signal processing, switching, filtering, time-division multiplexing, etc. Here, we present a technique for performing the RTFT simultaneously over all the channels of a multiwavelength (wavelength-division multiplexing) signal traveling in a single optical fiber. The technique only requires the reflection of the original signal in an appropriately designed structure of superimposed chirped fiber gratings. To demonstrate our proposal, we design a real-time optical spectrum analyzer operating on three different wavelength channels. The design is proved to function correctly by means of numerical simulations     

Beat-detect OTDM demultiplexer

We propose a novel ultrafast (instantaneous response), low-power, and simple demultiplexer for optical time-division multiplexed signals. It requires no ultrafast optical devices such as all-optical gates or electroabsorption modulators. Only a power combiner and a dispersive medium are required as optical components, thus making the system very simple. Furthermore, the separation of control pulses is not required, which also helps to simplify the system. A design optimization in terms of the signal-to-noise ratio was performed, and equations that provide design parameters were derived. The effect of the wavelength fluctuation and the timing jitter of signal pulses were evaluated based on a numerical analysis, which indicated that this demultiplexer shows a small bit error rate (<10^-10), even under a large wavelength fluctuation (~7.2 nm, 43% of the pulse spectral width) or a large timing jitter (~0.45 ps, 18% of the signal period) in the case of demultiplexing from 400 to 6.67 GHz. Demultiplexing of pulse trains with 2.5-ps separation (corresponding to 400-GHz repetition) was experimentally demonstrated