α-parameter dependence of chirped pulse from injection-moudated semiconductor lasers

It is found from a series of numerical simulations that a simple relation, ΔtΔf_c=0.4α, holds between an amount of down-chirp (Δf_c) and a pulsewidth (Δt) for pulses from an injection-modulated semiconductor laser having a known α-Parametef value. This relation is useful for estimating the amount of chirp existing in pulses. The validity of the relation is examined by a direct observation of chirped pulses using a combination of a streak camera and a spectrometer.     

碰撞锁模环形染料激光器动力学过程的研究

本文在建立碰撞锁模(CPM)激光器数学模型的基础上,对碰撞锁模激光器中激光锁模脉冲形成的动力学过程进行了计算机模拟计算,并对其结果进行了理论分析和讨论,得到了脉冲宽度、脉冲波形及对称性与泵浦速率、腔长、增益介质和可饱和吸收介质在腔内的相对位置等因素间的关系。     

Time-domain master equation for pulse evolution and laser mode-locking

Using the well-known analogy between the space and time domains we derive a temporal master equation (ME) operator which can be applied to any cavity containing dispersive and filtering elements, phase or amplitude modulators, and one nonlinear element. The cavity properties are described in terms of 2 × 2 `KIJL' matrices. We show that this ME correctly reproduces the cavity mode structure in the linear limit. Numerical simulation of an actively mode-locked Fabry–Perot laser with the nonlinear medium at an end mirror gives results in excellent agreement with those found using the more conventional Huygens' integral method. Using a simple perturbation approach based on the nonlinear Schrödinger equation (NLS) we also show that the field in this laser is soliton-like, and give analytic expressions for the soliton parameters.     

半导体激光器脉冲调制理论分析

本文用龙格-库塔法求解高斯脉冲调制下半导体激光器速率方程,对结果进行了分析。推出了较高偏置直流和高斯脉冲调制下计算激光脉冲延迟时间、脉冲宽度和最大调制码率的公式。给出了调制畸变的实验结果。     

Frequency dynamics of semiconductor lasers with atomic absorbers: theory and experiments

In this paper we discuss the spectral behavior of monomode semiconductor laser systems whose output amplitude is constant, but whose frequency may be bistable, multistable, locked or present instabilities. The explored configurations are: (i) a laser diode (Fabry-Pérot) under orthogonal filtered optical feedback; and (ii) an extended-cavity diode laser with an intracavity strongly-saturated resonant vapor. Starting from rate equations for the carrier density and for the radiation field oscillating in the cavity of these systems we describe spectral features which are in very good quantitative agreement with experimental observations.     

Terahertz frequency conversion in bulk and quantum-well semiconductor lasers

Simulation results of frequency conversion up to the terahertz region in semiconductor laser devices, both in bulk and quantum-well structures, are presented with a comparison of traveling wave amplifiers and Fabry—Perot oscillators. In both devices conversion gains greater than 0 dB can be achieved with a proper parameter choice. Interesting features of the conversion gain spectra for the oscillator-converter are pointed out with a discussion of the performances.     

Comparative study of the mode-locking of Nd:GdVO_4 and Nd:YAG lasers with semiconductor saturable absorber mirrors

Stable continuous-wave passive mode-locking of diode-end-pumped Nd:GdVO4 and Nd:YAG lasers with semiconductor saturable absorber mirrors (SESAMs) are reported. The comparative study shows that the Nd:GdVO4 crystal is efficient to decrease the Q-switched mode-locking tendency, and easier to continuous-wave (CW) mode lock than Nd:YAG.     

The frequency noise and spectral linewidth in semiconductor ring lasers

Numerical analyses for power spectral density of frequency noise (FN) and spectral linewidth in monolithic semiconductor ring laser (SRL) operating in the bistable unidirectional regime are performed in this paper. The Langevin noise sources for electric field and carrier density fluctuations are also taken into account in the frequency-domain theoretical model. The influences of several important physical parameters on the FN properties and laser linewidth are clearly demonstrated, including the injection current, linewidth enhancement factor and the particular backscattering coefficient. Due to the particular backscattering in SRLs, the calculated linewidths are relatively higher than that from the conventional Henry formula. The laser linewidth shows an exponential relationship with the backscattering strength.     

Picosecond duration laser pulse generation by simultaneous active-passive mode-locking in Ar+ ion and dye lasers

We use a rate equation model to analyse a technique for the generation of picosecond duration laser pulses in argon pumped dye lasers. The system is based on passive mode-locking of the Ar⁺ laser by saturable absorption of the dye which is inserted in the Ar⁺ laser cavity. Simultaneously, the dye is forced to oscillate in a regime of synchronously pumped mode-locking. The system is relatively simple, does not require the use of an acousto-optical light modulator and can be easily implemented in commercially available lasers. Pulses shorter than 100 ps and having an average power of 20 mW were obtained at a repetition rate of 110 MHz. Good agreement between the model and experimental results was also obtained.     

Ultrashort pulse formation and evolution in mode-locked fiber lasers

Passive mode-locking in fiber lasers is investigated by numerical and experimental means. A non-distributed scalar model solving the nonlinear Schr?dinger equation is implemented to study the starting behavior and intra-cavity dynamics numerically. Several operation regimes at positive net-cavity dispersion are experimentally accessed and studied in different environmentally stable, linear laser configurations. In particular, pulse formation and evolution in the chirped-pulse regime at highly positive cavity dispersion is discussed. Based on the experimental results a route to highly energetic pulse solutions is shown in numerical simulations.     

Passive Q-switch and mode-locking modulators for Nd:hosted lasers

Four kinds of currently available Nd:hosted laser passive Q-switch and mode-locking modulators: plastic dye sheet, LiF:F₂⁻ color center crystal, Cr⁺⁴ :YAG crystal and RG1000 colored glass filter were investigated in detail and summarized for comparison for the first time. The LiF:F₂⁻ crystal with outstanding annealability, long lifetime, low cost and operability at high repetition rates is highly recommended.     

Triple mode-locking of Ar+ and dye lasers

We report a new technique of generating highly synchronous simultaneous pulse trains at three wavelengths, two of which are continuously tunable over a moderate range. A series of oscillographs shows the time-resolved Ar⁺ pulses and the effects of varying the two cavity lengths with respect to each other. Preliminary correlation measurements indicate low jitter.     

脉冲半导体激光器时基脉冲的实验对比测量

以脉冲半导体激光器为例，对3种测量激光脉冲时基抖动技术进行了对比实验。这3种测量技术分别是：基于宽带取样示波器的时基抖动测量技术;基于相位比较检相器的相位噪声测量技术和基于频谱仪的谐波频谱分析技术。对比研究发现：基于宽带取样示波器的时基抖动测量技术适用于脉冲宽带及脉冲抖动较大的光脉冲；基于频谱仪的谐波频谱分析技术适用于低重复频率光脉冲的抖动测量；基于相位比较检相器的相位噪声技术测量精度高、动态范围大、结果可靠，对于高重复频率的超短光脉冲，建议选用相位噪声测量技术测量激光脉冲的时基抖动。     

Gbit/s rate bipolar pulse modulation of semiconductor injection lasers

Using a bipolar drive current pulse shape and very low threshold (9 mA) lasers, zero-background pseudorandom optical pulses were generated and detected at a rate of up to 4 Gbit/s without a pattern effect. The drive current pulse consists of a forward pulse followed by a reverse pulse, each of 70 ps duration and about 400 mA amplitude. No DC bias was applied, which is a necessary condition for pattern-effect-free modulation.     

Comparative studies of semiconductor saturable absorber mirror mode-locking dynamics in pulsed diode-end-pumped picosecond Nd:GdVO4 and Nd:YAG lasers

Ultrashort pulses were generated in passively mode-locked Nd:YAG and Nd:GdVO4 lasers pumped by a pulsed laser diode with 10-Hz repetition rate. Stable mode-locked pulse trains were produced with the pulse width of 10 ps. The evolution of the mode-locked pulse was observed in the experiment and was discussed in detail. Comparing the pulse evolutions of Nd:YAG and Nd:GdVO4 lasers, we found that the buildup time of the steady-state mode-locking with semiconductor saturable absorber mirrors (SESAMs) was relevant to the upper-state lifetime and the emission cross-section of the gain medium.     

Optically pumped terahertz lasers with high pulse repetition frequency: theory and design

Optically pumped terahertz （THz） lasers with high pulse repetition frequency are designed. Such a laser includes two parts： the optically pumping laser and the THz laser. The structures of the laser are described and analyzed. The rate equations for the pulsed THz laser are given. The kinetic process and laser pulse waveform for this kind of laser are numerically calculated based on the theory of rate equations. The theoretical results give a helpful guide to the research of such lasers.     

Theoretical analysis of optical pulse position modulation communication systems using semiconductor lasers

In this paper the performance of a pulse position modulation (PPM) optical system is analysed both for direct and coherent detection schemes taking into account time jitter of the semiconductor laser. This phenomenon can introduce a large sensitivity penalty if the system parameters are not accurately selected. In particular, the optimum value of the PPM order is strongly influenced by the laser time jitter, and the modulation index cannot be chosen below a threshold value that, with the assumed laser parameters, is about 0.7.     

Stable Q-switch mode-locking of Nd:YVO<Subscript>4</Subscript> lasers with a semiconductor saturable absorber

This paper reports on a passively mode-locked and Q-switched Nd:YVO₄ laser generating picosecond pulses with an average output power exceeding 7 W. In a first step Q-switch mode-locking was obtained by self Q-switching of a mode-locked oscillator with appropriate cavity design, pump power and output coupling. In a second system the Q-switching was actively controlled and stabilized by modulating the resonator internal losses with an acousto-optic modulator. In the Q-switch mode-locking operation the laser provided 12.8 ps long mode-locked pulses with a repetition rate of 80 MHz. The repetition rate of the Q-switch envelope was 185 kHz. The maximum pulse energy of a single ps pulse was 0.55 μJ which is 5.5 times the pulse energy measured for cw mode locking. The total energy of the pulses within the Q-switch envelope was 42 μJ. PACS  42.55.Xi; 42.60.Fc; 42.60.Gd