The effect of external optical feedback on timing jitter in modulated laser diodes

Laser diodes with optical feedback are numerically modeled using single-mode rate equations. The effects of the optical feedback on the pulse turn-on delay and timing jitter are examined, for gain-switching, periodic and pseudorandom modulation formats. It is shown that there is a change in turn-on delay and a considerable increase in the timing jitter due to the changes in the output power distributions as optical feedback increases. The cause of the increased jitter is found to be the additional intensity noise introduced by the optical feedback.<>     

锁模Cr4+:YAG固体激光器脉冲的时间抖动理论性分析

固体激光器的脉冲稳定性限制了激光器在很多方面的应用.从被动锁模Cr4 :YAG激光器腔内脉冲的传播方程出发,得到了带噪声的非线性Schr(o)dinger方程,进一步分析了脉冲在激光器腔内的时间传播形式,建立了锁模Cr4 :YAG固体激光器振荡脉冲参数的线性扰动方程,推导出了脉冲参数波动的动力学方程以及时间和相位的均方根波动关系式.提出了一个减少锁模Cr4 :YAG固体激光器脉冲时间抖动的实验方案,旨为锁模Cr4 :YAG固体激光器能够用作光纤通信和量子通信中的光源提供理论上的帮助.     

Tunable monolithic mode-locked lasers on InP with low timing jitter

Pulse trains with only 2 ps in width and low root-mean-square timing jitter of 220 fs are demonstrated from fine tunable monolithic 40-GHz laser integrated circuits on GaInAsP-InP. The repetition rate is tunable within 500 MHz by changing only the gain current and the absorber voltage. Simultaneously, the small pulsewidths are kept constant and the timing jitter remains below 300 fs. The determined time-bandwidth products between 0.37 and 0.5 are close to the transform limit and the fiber coupled optical power is /spl ges/1 mW. The fact that pulsewidth and timing jitter remain small over the whole repetition-rate tuning range constitutes an important step toward economic commercial applications, especially if frequency shifts caused by fabrication tolerances have to be compensated.     

单片集成可调谐半导体激光器研究进展

单片集成可调谐半导体激光器的使用为光纤通信系统和智能光网络带来极大的灵活性、可扩展性以及经济性.文章综述了单片集成可调谐半导体激光器的调谐机制、结构特点以及性能比较,概要介绍了最新研究进展情况,分析了相关发展趋势和市场应用前景.     

Q-switched microchip laser with 65 ps timing jitter

Low interpulse timing jitter at a low switching voltage in a Q-switched microchip laser has been reached by using both active and passive modulators     

Reduced timing jitter of two-section 1.55-μm laser diodes undergain-/loss-switching regime at multigigahertz rates

Picosecond pulses at multigigahertz frequencies with low timing-jitter have been generated from two-section 1.55-μm semiconductor lasers. A pulse jitter of ~1 ps was measured at a 5-GHz repetition rate with the laser diodes operated in gain-switching regime. More than 2x lower values were obtained in the loss-switching regime. A timing jitter model has been adapted to treat two-section laser diodes in the two regimes. The superiority of the loss-switching regime is explained by faster laser dynamics around threshold. A good agreement is obtained between calculations and timing jitter measurements     

Locking characteristics of a passively mode-locked monolithic DBR laser stabilized by optical injection

We demonstrate the generation of ultrastable millimeter-wave carriers from a passively mode-locked monolithic InGaAs MQW DBR laser injection locked by a double sideband suppressed carrier modulated optical signal. We investigate the effect of the optical power and the wavelength of the injection signal on the phase noise of the generated millimeter-wave carrier. Once locked, the laser can track the variations in the beat frequency of the injected millimeter-wave signal over an RF frequency range of approximately 172 MHz.     

Harmonically mode-locked glass waveguide laser with 21-fs timing jitter

We report on experimental jitter results of a 10-GHz mode-locked laser. The laser is an actively harmonically mode-locked fiber laser using an erbium-doped glass waveguide as the gain medium. Amplitude noise and corresponding phase noise effects are greatly reduced by the inclusion of an intracavity high-finesse fiber Fabry-Pe/spl acute/rot etalon. Typical results show timing jitter of 21-fs root mean square, integrated from 10 Hz to 100 MHz.     

Actively modelocked dual-wavelength fiber laser with ultra-low inter-pulse-stream timing jitter

We demonstrate a novel dual-wavelength erbium-fiber laser that uses a single nonlinear-optical loop mirror modulator to simultaneously modelock two cavities with chirped fiber Bragg gratings as end mirrors. We show that this configuration produces synchronized soliton pulse trains with an ultra-low RMS inter-pulse-stream timing jitter of 620 fs enabling application to multiwavelength systems at data rates in excess of 130 Gb/s.     

Influence of facet reflections on monolithic widely tunable laser diodes

Monolithic widely tunable laser diodes commonly employ sophisticated grating structures to achieve wide wavelength tuning by exploiting the Vernier effect. The reflection spectra of these gratings are, however, susceptible to any unintended reflections, which cause interference effects and impair the tuning behavior of the laser. The main source of such reflections are the front and rear facet of the device. Their influence on the tuning characteristic is significant and will be discussed in this letter. Furthermore, a statistical yield analysis is presented, which relates device yield to important design parameters.     

Optical DPSK heterodyne detection experiments using DBR laser diodes with external optical feedback

High receiver sensitivity, with 7 dB improvement over a direct detection system, has been achieved in a 400 Mbit/s optical DPSK heterodyne detection experiment using DBR laser diodes with external optical feedback. The influence of the laser output phase noise was evaluated experimentally in good agreement with theory.     

极低时间抖动的飞秒激光技术（特邀）

飞秒激光器的时间抖动（或定时抖动）是指其输出脉冲的时域位置相对于理想周期信号的短期随机偏差。在毫秒量级的时间尺度上,飞秒激光器的脉冲序列具有严格的一致性,其定时抖动甚至低至阿秒量级。飞秒激光器的这种独特性质及其支持的前沿应用构成了“阿秒时间精度的超快光子学”这一全新的超快研究分支。文中回顾了近年来飞秒激光器定时抖动研究进展、高时间分辨率的定时抖动测量技术、以及不同类型的飞秒激光源能够达到的最低抖动水平。最后介绍了低抖动飞秒激光器在大科学装置同步、高速模数转换、绝对测距、相干脉冲合成等领域的应用。     

Subharmonic synchronous and hybrid mode-locking of a monolithic DBR laser operating at millimeter-wave frequencies

A detailed comparison of subharmonic synchronous and subharmonic hybrid mode-locking of a monolithic distributed Bragg reflector (DBR) laser operating at 33 GHz is presented. Optical injection at the 20th subharmonic frequency (1.65 GHz) has produced a locking range of 10 MHz with negligible amplitude modulation. In comparison, electrical injection at the 4th subharmonic frequency (5.83 GHz) has shown higher levels of amplitude modulation and a narrower locking range (4 MHz). While subharmonic hybrid mode-locking remains a simple and cost effective solution for the generation of low timing jitter high-repetition rate optical pulse trains, subharmonic synchronous mode-locking shows superior performance with regard to reduced amplitude modulation and larger locking range.     

An analysis of the effect of chip timing jitter in MC-CDMA systems

We investigate the effect of chip synchronization error (or chip timing jitter) in a multicarrier-code division multiple access (MC-CDMA) scheme. The chip timing jitter is modeled by a stationary random process with a known statistic, and the error produced by the jitter is reduced to an additive source of noise. This decomposition is useful because it allows for the use of analytical methods for the computation of the error probability. First, the analysis has been applied to the simple Gaussian channel; afterwards, it has been extended to a multipath fading channel typical of large indoor areas. Use of a semi-analytical approach has been the key factor in obtaining reliable results at moderate computational complexity     

Strongly sub-Poissonian electrical noise in 1.55-/spl mu/m DBR tunable laser diodes

We report terminal electrical noise measurements on 1.55-/spl mu/m DBR tunable laser diodes in the 1 Hz-1 MHz frequency range, performed using an electrical correlation method. These measurements are compared with a comprehensive electrical model based on rate equation formalism. Taking into account diffusion phenomenon and structural parameters, we obtain a complete agreement between the model and the measurements above threshold and a quite similar tendency below threshold. The influence of Bragg section bias is also discussed.     

Gordon-Haus timing jitter reduction in dispersion-managed solitoncommunications

An analytic theory is presented which demonstrates that the noise induced Gordon-Haus timing jitter in arbitrary dispersion-managed transmission systems is reduced by the power-enhancement factor required to support a dispersion-managed solitons provided the path-average soliton period is much greater than the dispersion-map period. The analysis further predicts the behaviour of the amplitude, width, and quadratic chirp fluctuations due to the amplified spontaneous emission (ASE) noise     

Quantum-limited timing jitter in actively modelocked lasers

Expressions for the quantum-limited timing jitter in an actively modelocked fiber laser are derived. We identify a set of characteristic constants that govern the timing jitter for the cases using amplitude modulation (AM) and phase modulation (PM) as the active modelocking elements. We find that when using AM, the Gordon-Haus jitter is proportional to the square of the group-velocity dispersion and reaches a minimum value for the case of low dispersion. Using PM, the Gordon-Haus jitter increases only linearly proportional to group-velocity dispersion, and there exists an optimum group-velocity dispersion that minimizes the jitter. We compare the theory to recent experiments of the timing jitter for an active harmonically modelocked fiber laser.     

Theory of timing jitter in actively mode-locked lasers

An analysis of the pulse-to-pulse timing jitter in an actively mode-locked laser is presented. The model includes spontaneous emission noise, mode-locker driver phase noise, and cavity length detuning. Analytical expressions for the laser pulse train phase noise spectrum, the intensity power spectrum, and the RMS timing jitter are given. The timing fluctuations are characterized by a time constant proportional to the cavity round-trip time times the number of locked modes squared divided by the modulation depth. The contribution from the mode-locker driver phase noise will dominate unless high-stability RF sources are used. The residual timing jitter due to spontaneous emission noise is very sensitive to cavity detuning     

Minimisation of timing jitter in CDMA code tracking

A method for chip waveform design that minimises the tracking jitter in code division multiple access (CDMA) synchronisation is presented. The method is based on the use of prolate spheroidal wave functions. Examples of optimised waveforms are given and their performance compared to other conventional pulse shapes in terms of timing error variance and bandwidth occupancy.     

The effect of timing jitter on MC-DS-CDMA

In this paper, we consider the effect of timing jitter on the performance of a multicarrier direct-sequence code-division multiple-access system for both uplink and downlink transmission, assuming orthogonal spreading sequences. Theoretical expressions are derived for the performance degradation caused by the timing jitter, in the presence of a multipath channel. Assuming an additive white Gaussian noise channel, perfect power control, and full load, it is shown that the performance degradation for the downlink transmission is independent of the number of subcarriers, of the spreading factor, and of the spectral contents of the jitter at the receiving mobile station, but only depends on the jitter variance. Under the same assumptions, we point out that, if the jitter spectra of all transmitting mobile stations are the same, the degradation on the uplink is the same as the degradation on the downlink.