Repetition-frequency multiplication of mode-locked pulses usingfiber dispersion

In this paper, we describe a novel method for generating a highly repetitive optical pulse train using mode-locked pulses and the group-velocity dispersion (GVD) of optical fiber. An optical pulse train at a multiplied repetition frequency oscillation of an initial mode-locked pulse train is obtained by adjusting waveform fiber length in accordance with the mode-locking frequency and the fiber's GVD. A subterahertz optical pulse train (98-196 GHz) was successfully generated with low pulse intensity fluctuation     

Nanometer wavelength conversion of picosecond-optical pulses usingcavity-enhanced highly nondegenerate four-wave mixing in semiconductorlasers

We demonstrate 5.0-nm wavelength conversion of a mode-locked optical pulse train by cavity-enhanced highly nondegenerate four-wave mixing in a 1.53-μm injection-locked bulk InGaAsP V-groove laser. Input pulses having 17 ps duration are broadened to 61 ps due to the filtering imposed by the mixing laser. A simple two-mode rate equation model of an injection-locked semiconductor laser is used to explain the dependence of the output pulse broadening on bias current and injected pump power. The temporal response is improved by decreasing the laser bias current or increasing the injected pump power     

单个微微秒脉冲的研究

由被动锁模钕玻璃激光器产生的锁模脉冲序列中,分别从不同位置选出单脉冲,并研究了它们的时间和光谱特性。实验表明,在时间和光谱分布上满足高斯型的带宽极限脉冲,是呈现在序列的前部。随着序列的延续,光谱宽度显著加宽,并有明显的调制现象。加宽与理论计算符合很好,证明了加宽主要是强光下的自相位调制所引起。最后,对实验中的某些现象进行了讨论。     

Stability of pulse emission and enhancement of intracavity second-harmonic generation in self-mode-locked quantum cascade lasers

We report the observation of stable pulse emission and enhancement of intracavity second-harmonic generation (SHG) in self-mode-locked quantum cascade (QC) lasers. Down-conversion of the detector signal by heterodyning with an RF signal allows the direct observation of the pulsed laser emission in the time domain and reveals a stable train of pulses characteristic of mode-locked lasers. The onset of self-mode locking in QC lasers with built-in optical nonlinearity results in a significant increase of the SHG signal. A pulse duration of /spl sim/12 ps is estimated from the measured increase of the SHG signal in pulsed emission compared to the power expected for the SHG signal in CW emission. This value is in good agreement with the pulse duration deduced from the optical spectral width.     

泵浦抽空状态下的同步泵浦光学参量振荡器

用计算机数字模拟了Nd:YAG锁模激光器倍频光同步泵浦下LiNbO_3光学参量振荡器的脉冲形成过程。泵浦抽空状态下,输出信号脉冲序列中各脉冲的波形与宽度各不相同,起始脉冲窄(～7微微秒),后面脉冲宽(～20微微秒)而且有亚结构。腔长失谐主要降低输出能量,对脉冲加宽作用不大。器件增益对脉冲波形、宽度和腔长失谐量均有影响。     

Noise characterization of a regeneratively mode-locked fiber ringlaser

A regeneratively mode-locked fiber ring laser (RML-FRL) and an active harmonically mode-locked fiber ring laser (ML-FRL) have been characterized for both amplitude and phase noise by investigating the detected RF spectra of the optical pulse trains. Quantification of noise in the optical pulses reveals that the stability of the RML-FRL in terms of noise performance is superior to its ML-FRL counterpart. The optical pulse noise was measured over a frequency band of 100 Hz to 100 kHz and it was found that the pulse amplitude noise reduced from 0.6% in the ML-FRL to 0.3% in the RML-PRL. The total rms noise in the detected optical pulses from the RML-FRL improved by more than 30% compared to that measured for the ML-FRL, with a phase noise improvement of 15 dB at 100 kHz offset frequency from the carrier. An rms timing jitter of 0.38 ps was estimated in the optical pulse train from the ML-FRL, which reduced to 0.26 ps in the RML-FRL. In addition, complete elimination of the relaxation oscillations noise spikes in the detected RF spectrum of the optical pulses from the RML-FRL has been observed     

An optically programmable mode-locked laser

We demonstrate an optically mode-locked laser that generates a repetitive pattern of ultrashort pulses when driven by a repetitive pattern of optical pulses from an external source. Two modes of operation are described: in one mode of operation the generated pattern is determined directly by the driving pulse train; in the other mode it represents the result of logic operations between elements of the driving pulse train     

The transient evolution of AM mode locking a TEA CO2laser

The evolution of the pulse in an AM mode-locked TEA CO2laser has been investigated. The experiments have been performed by injecting the mode-locked pulses in a high-pressure slave oscillator at various time intervals after the initiation of the mode-lock process. This technique allows the measurements of the pulse widths independent on the pulse energies. A numerical solution of a dynamic model for the mode-locking process accurately predicts the transient evolution. It is shown that the build-up time to reach steady state can be, depending on the modulation depth, considerably larger than the duration of the pulse train.     

Dual Orthogonal Polarization States in an Active Mode-Locked Birefringent Fiber Ring Laser

We report the generation of dual amplitude pulses in an active mode-locked fiber laser within a birefringent cavity. Different to normal mode-locked pulses with identical amplitude and polarization state, and pulses polarized on both x- and y-axes simultaneously exist in the output pulse train. The two orthogonal pulse sequences have different amplitudes and lase at different wavelengths. Dual wavelengths are the result of red shift and blue shift of the x- and y-polarization states of the generated pulses, respectively, due to the detuning phenomena. Locking to individual x- or y-polarized pulse is also obtained by adjusting polarization controllers     

Theory and simulation of the dynamics and stability of actively modelocked lasers

A new model is proposed for the active modulation component of a mode-locked laser cavity. By using Jacobi elliptic functions to capture the periodic forcing to the cavity, we are able to construct exact solutions representing a mode-locked pulse train. Two families of pulse-train solutions are generated: one in which neighboring pulses are in-phase and a second in which neighboring pulses are out-of-phase. We show that only out-of-phase solutions allow for stable mode-locked pulse trains. Further, pulse-to-pulse interactions can generate instabilities that destroy the pulse train altogether or lead to Q-switching.     

FROG measured high-power 185-fs pulses generated by down-chirping of the dispersion-managed breathing-mode semiconductor mode-locked laser

A dispersion-managed breathing-mode mode-locked semiconductor ring laser generates linear down-chirped pulses which are dispersion compensated to duration as short as 185 fs and characterized by second-harmonic generation frequency-resolved optical gating. Down-chirping when compared to up-chirping allows broader mode-locked spectra and shorter pulse generation owing to the temporal and spectral semiconductor gain dynamics. The measured average output power is 14 mW at 323-MHz pulse repetition rate, implying a peak power of /spl sim/230 W, and a focused intensity of /spl sim/4.6 GW/cm/sup 2/. To our knowledge, this is the highest peak power and the shortest pulse generation from an electrically pumped all-semiconductor system, obtained only by linear chirp compensation.     

Experimental study of single picosecond light pulses

Single picosecond light pulses from a mode-locked Nd:glass laser are investigated by several methods. Their temporal structure is studied by two-photon fluorescence. The frequency spectra are measured quantitatively. The energy distribution is simultaneously investigated by three-photon fluorescence, photoelectric measurements, and quantitative studies of the contrast ratio of the two-photon fluorescence. The pulse shape is measured using a method based on the stimulated Raman effect. It is observed that the pulses are weakly asymmetric-the pulse decay is slower (exponential) than the pulse rise (Gaussian). Bandwidth-limited pulses of 4-8 ps are present in the leading part of the pulse train. Substantial frequency broadening develops as the pulse train reaches its maximum and a subpicosecond structure is formed in the trailing part of the pulse train.     

Simulation of mode-locking by nonlinear polarization rotation in a semiconductor optical amplifier

We present a theoretical investigation of a mode locked laser that has a semiconductor optical amplifier (SOA) in its ring cavity. A mode-locked train of narrow pulses is obtained by combining nonlinear polarization rotation in the SOA and a polarization filter whose polarization axis is set such that the tail of optical pulses is removed in each cavity round-trip. The pulse narrowing process is demonstrated numerically and good qualitative agreement with experiments in our previous work is achieved. The pulse performance is largely determined by the ultrafast SOA gain dynamics and the cavity dispersion. Our simulation shows that the laser can produce a pulse train of subpicosecond pulsewidth at a repetition rate of 28 GHz for a moderate SOA current level. We observe that the laser can switch itself on or off depending on the initial pulse.     

Complete characterization of ultrashort pulse sources at 1550 nm

This paper reviews the use of frequency-resolved optical gating (FROG) to characterize mode-locked lasers producing ultrashort pulses suitable for high-capacity optical communications systems at wavelengths around 1550 nm, Second harmonic generation (SHG) FROG is used to characterize pulses from a passively mode-locked erbium-doped fiber laser, and both single-mode and dual-mode gain-switched semiconductor lasers. The compression of gain-switched pulses in dispersion compensating fiber is also studied using SHG-FROG, allowing optimal compression conditions to be determined without a priori assumptions about pulse characteristics. We also describe a fiber-based FROG geometry exploiting cross-phase modulation and show that it is ideally suited to pulse characterization at optical communications wavelengths. This technique has been used to characterize picosecond pulses with energy as low as 24 pJ, giving results in excellent agreement with SHG-FROG characterization, and without any temporal ambiguity in the retrieved pulse     

调Q及连续掺Yb光纤激光器中的自锁模研究

在用半导体激光器抽运的单包层掺Yb调Q光纤激光器中观察到了清晰稳定的自锁模脉冲序列。脉冲包络形状为调Q脉冲。每个锁模脉冲的幅值由其在调Q脉冲中的相应位置决定。经过分析，认为自相位调制是调Q光纤激光器中产生锁模的主要原因。自相位调制的存在使得光脉冲的频谱被展宽，当这种展宽和腔的模式间隔相差不多时，腔内的模式便能相互作用，直到它们之间产生一个固定的相位关系。也即形成锁模。在此基础上。去掉声光晶体，并用两个光栅作为腔镜，实现了全光纤法布里-珀罗(F-P)腔锁模光纤激光器。改变腔结构，分别采用光栅和光纤反射圈作为前后腔镜，同样观察到了锁模脉冲。经过观察发现，锁模脉冲的产生和掺Yb光纤的浓度、长度、抽运功率的大小有着密切的关系。这为锁模脉冲的产生提供了一种新的方法。     

Spectral measurement of the noise in continuous-wave mode-lockedlaser pulses

A theoretical analysis of the noise of a periodic optical pulse train is presented. It is shown that the amplitude fluctuation, the pulsewidth fluctuation, the pulse timing jitter, and the cross correlations between any two of these three noise parameters can be separately quantified by comparing the noise power spectra of the fundamental pulses and those of the second-harmonic pulses. The noise characteristics of an actively mode-locked Nd:YLF laser are presented to demonstrate this technique     

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     

The Study on the Variation of the Cavity Length''''s Influence on the Output Pulse Train of the Actively Mode-Locked Fiber Laser

1 Introduction The actively mode-locked fiber laser is a very poten-tially valuable light source applied to ultrafast OpticalTi me Division Multiplexed ( OTDM) communicationsystems,optoelectronic sampling systems ,etc .,for itcan generate very short (the duration of the pulseisjustseveral ps or evenless) ,highrepetition-rate (the repeti-tion-rate can be 40 GHz or more) optical pulse train.However ,fiber ringlasers are very sensitive to environ-mental perturbations such as temperature fluct…     

Extreme chirped pulse oscillator (XCPO) using a theta cavity design

We demonstrate an extreme chirped pulse mode-locked laser, simultaneously generating near-transform-limited 3.9-ps optical pulses and /spl sim/510-ps linearly chirped output from the oscillator. The design overcomes fundamental limitations of energy extraction and nonlinearities induced by gain dynamics so that we can increase the dc current of the semiconductor optical amplifier up to 600 mA without distortion of the pulse characteristics. The maximum average power of the stretched pulses from the 1.95-GHz harmonically mode-locked semiconductor laser is measured to be 13.4 mW at 600 mA.     

主动锁模和调Q Nd:YAG激光倍频同步泵浦染料激光器特性研究

本文介绍一种主动锁模和调Q Nd:YAG激光倍频同步泵浦可调谐染料激光器。由此激光器已获得脉冲宽度为70ps,脉冲能量为0.1μJ,调Q重复率达7kHz,调谐范围为580～610nm的微微秒脉冲,本文还研究了这一激光器的时间和频谱特性,分析了腔长失配对脉宽和中心波长的影响。