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.     

Noise characterization of femtosecond fiber Raman soliton lasers

The broadband amplitude noise and phase noise (timing jitter) measured in femtosecond fiber Raman soliton lasers is discussed. For a single-pass compressor using 300 m of either standard single-mode fiber or polarization preserving fiber, white amplitude noise ⩾50 dB above shot noise at 2 mA photocurrent was measured, for frequencies higher than approximately 100 kHz. This is ≈30 dB larger than the amplitude noise observed from fiber grating pulse compressors. The timing jitter increases with pump power, and at 1.6 W pump power, 5.2 ps r.m.s. timing jitter was measured, given ≈2 ps jitter from the Nd:YAG pump. Longer fibers in the single-pass compressor do not affect the amplitude noise, but increase the timing jitter even further. A synchronously pumped ring cavity reduced the timing jitter substantially, but did not significantly improve the amplitude noise     

All-optical modulation and demultiplexing systems with significanttiming jitter tolerance through incorporation of pulse-shaping fiberBragg gratings

In this letter, we demonstrate the use of a superstructured fiber Bragg grating to preshape optical pulses to obtain optimal operation of nonlinear all-optical switches. Specifically, we demonstrate the conversion of 2.5-ps soliton pulses into 20-ps rectangular pulses at the input to both fiber and semiconductor optical amplifier-based switches, and show that rectangular switching windows can be achieved thereby providing a 5-10-fold reduction in timing jitter sensitivity. Error free penalty free optical time-division-multiplexing switching was readily achieved over a ±7-ps timing mismatch range for the square pulse driven fiber nonlinear optical loop mirror switch versus a ±1-ps range for the switch driven directly with 2.5-ps laser pulses     

10 GHz再生锁模光纤激光器获得光纤超连续谱的研究

报道了利用10GHz再生锁模光纤环形激光器（RML-FRL）获得波长在1528～1563nm连续可调、脉宽为4．6～5．8ps的短脉冲输出作为高稳定的光纤超连续（SC）谱泵浦源。对RML-FRL输出的脉冲直接放大泵浦4．5km色散位移光纤（DSF）,得到20dB带宽46．08nm的SC谱输出,经阵列波导光栅（AWG）谱切片后,得到间隔100GHz、中心波长符合ITUT标准的30信道输出,脉宽在6．5～7．8ps,示波器显示任意信道的抖动均值小于1．4ps。     

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     

Pulse retiming based on XPM using parabolic pulses formed in a fiber Bragg grating

We experimentally demonstrate a novel all-optical all-fiberized pulse retiming scheme incorporating parabolic pulses generated in a linear fashion through pulse shaping in a superstructured fiber Bragg grating. The scheme relies on chirping the signal to be retimed using cross-phase modulation with the broader parabolic clock pulses, and subsequently retiming it through linear propagation in a dispersive medium. We demonstrate the cancellation of up to 4-ps root-mean-square timing jitter for /spl sim/2-ps data.     

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     

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     

基于超连续谱和超结构光纤光栅的波分复用/光码分复用系统

实验验证了基于超连续谱(SC)和超结构光纤光栅(SSFBG)的波分复用/光码分复用(WDM/OCDM)混合系统,超结构光纤光栅实现了对超连续谱光源的双波段同时相位编解码。由于波分复用/光码分复用系统中信道间干涉和噪声的影响,解码输出脉冲的信号波形出现劣化,自相关曲线旁瓣明显增大,自相关峰展宽至8.2 ps。在非线性放大环镜(NALM)的阈值判决作用下,解码输出脉冲的信号波形质量有了明显的改善,自相关峰宽度压缩至4.8 ps,较好地抑制了自相关曲线的旁瓣和噪声。实验中非线性放大环镜的输入信号峰值功率约为8 mW。     

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     

高消光比超短脉冲产生的实验研究

实验研究了一种高消光比短脉冲的产生技术。利用色散补偿光纤线性压缩由增益开关分布反馈激光器出射的光脉冲。而后利用电吸收调制器的非线性吸收特性同步调制光脉冲。利用这种方法在实验上产生了重复频率为10GHz，脉宽为10．4ps，抖动小，高消光比，无基座的短脉冲。此种技术可以应用于40Gbit／s的光时分复用系统中，同时也说明电吸收调制器具有同号脉冲整形功能。     

一种新型的高功率双波长自相似抛物线脉冲激光器

基于正色散单模光纤、掺Yb3+增益光纤和多模光纤光栅,提出了一种可调高功率双波长自相似抛物线脉冲激光器。采用非线性薛定谔方程描述双波长自相似抛物线脉冲的传输和演化过程,并利用分步傅里叶方法进行数值模拟。输入脉冲在正色散单模光纤与掺镱增益光纤中产生自相似抛物线脉冲,多模光纤布拉格光栅对激光器进行双波长选择,通过调节偏振控制器实现双波长稳定运行。数值模拟分析结果表明该激光器的运行是可行且有效的。     

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     

Nonlinearly strain-chirped fiber Bragg grating with an adjustabledispersion slope

In this letter, we demonstrate an adjustable dispersion slope compensator for waveform distortion compensation based on a nonlinearly strain-chirped fiber Bragg grating. The dispersion slope of the device can be tuned up to -18.9 ps/nm² with a bandwidth >2.4 nm. After transmission through a 120-km-long dispersion-shifted fiber, the resulting waveform distortion for a 2.65-ps pulse is successfully compensated by using this device     

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     

Numerical Analysis on Transmission Characteristics of a Bragg Grating Assisted Mismatched Fiber Coupler

Based on mode-coupled theory, a Bragg grating assisted mismatched fiber coupler is analyzed theoretically. At the same time, a detailed numerical analysis on transmission characteristics of the coupler is carried out when it considers the arcs of two fibers in the coupling region of the coupler or not, and the optimized design on the Bragg grating assisted mismatched fiber coupler for wavelength-division multiplexing/ demultiplexing is proposed.     

主动锁模光纤环形激光器的悬臂梁调谐法

利用悬臂梁来对光纤光栅的Bragg波长进行调谐,并将可调谐光纤光栅用于主动锁模光纤环形激光器中,获得了5.24nm的波长调谐范围。同时,在1547.883nm处,获得了脉宽为55ps,谱宽为0.017nm锁模脉冲输出。     

Simultaneous interrogation of fiber Bragg grating sensors using anacoustooptic tunable filter

We describe a novel technique to provide demultiplexing of fiber Bragg grating sensors, interrogated using interferometric wavelength shift detection. Amplitude modulation of multiple radio frequency driving signals allows an acoustooptic tunable filter to provide wavelength demultiplexing. We demonstrated a noise limited strain resolution of 150 nanostrain/√(Hz) and a crosstalk better than -50 dB     

Electron–Hole Plasma-Induced Spectral Blueshift of Optical-Data Injection Mode-Locked Semiconductor Optical Amplifier Fiber Laser

Under an optical nonreturn-to-zero (NRZ) data injection at 10 Gbit/s, the 10-GHz mode-locking and pulsed return-to-zero (RZ) clock extraction from a semiconductor optical amplifier (SOA) based fiber ring is investigated in this paper. The diagnoses on gain and intracavity-power-controlled anomalous blueshifted spectrum and subpicosecond timing jitter are demonstrated. By increasing the injecting power of the optical NRZ data from ${-}3$ to 8 dBm into the SOA bias at different currents, the mode locking is completed with a dc level greatly decreasing from 480 to 50 $mu$ W (only 1.5% of the mode-locked pulse power at 3 mW), corresponding to a pulse/dc amplitude contrast ratio up to 18 dB. Increasing the SOA bias current up to 350 mA significantly suppresses the timing jitter from 1.8 ps to 345 fs, and the extracted RZ clock pulse is shortened from 55 to 27 ps. The pulsewidth of the amplified SOAFL is compressed from 11 ps to 836 fs after dispersion compensation. At constant data injection level, the increasing SOA bias or gain oppositely redshifts the mode-locked SOA fiber ring laser (SOAFL) spectrum by 5 nm. The amplifier spontaneous emission of SOA at short wavelength region (${sim} {hbox {1520}}$ nm) is eliminated with increasing NRZ data power, whereas the mode-locking gain peak arises and blueshifts from 1558 to 1552 nm due to the band-filling effect. Such a blueshift in mode-locking spectrum becomes more significant in SOA at lower bias (or gain) condition. A theoretical model interprets the correlation between the nonlinear gain suppression-induced variation of electron–hole plasma in SOA and the blueshifted mode-locking SOAFL spectrum, which is occurred when the gain saturation condition for the SOA becomes more pronounced.      

Dual Semiconductor Laser System With Rapid Time-Delay for Ultrafast Measurements

We present a dual semiconductor laser system at 1.55 mum with femtosecond pulse widths and very low timing jitter for rapid pump-probe measurements. Synchronizing the two lasers to the same low-noise radio frequency-oscillator allows the use of an electrical phase shifter for the relative time delay between the lasers. This leads to a large scanning window that nearly matches the pulse period of 2.5 ns, as well as achieving a discrete time step of below 100 fs. The timing jitter of the complete dual laser system including all electronics is only 540 fs across the whole time delay. The nonlinear pulse compression using especially designed comb-like dispersion profiled fiber leads to autocorrelation widths of 310 fs. The system performance, i.e., the high time resolution is demonstrated by optical cross correlation of the pump and probe pulse, showing a very low full-width at half maximum of 1.3 ps