Intensity noise of mode-locked fiber grating external cavity semiconductor lasers

The noise of hybrid soliton pulse source (HSPS) with linearly chirped Gaussian apodized fiber Bragg grating is analyzed by couple-mode equations including spontaneous emission noise when HSPS is mode-locked. Relative intensity noise (RIN) is calculated using numerical solutions of these equations. It is shown that transform-limited pulses are generated over a wide tuning range around the fundamental mode-locking frequency with low spontaneous noise. However, high noise level affects the operation of device, and therefore transform-limited pulses are not obtainable over a wide tuning range. Linewidth enhancement factor and spontaneous coupling factor are the most effective noise parameters and noise increases with increasing value of these parameters.     

Relative intensity noise of mode-locked fiber grating external cavity semiconductor lasers

The noise of hybrid soliton pulse source (HSPS) with linearly chirped Gaussian apodized fiber Bragg grating is analyzed by couple-mode equations including spontaneous emission noise when the HSPS is mode-locked. Relative intensity noise is calculated using numerical solutions of these equations. It is shown that transform limited pulses are generated over a wide tuning range around the fundamental mode-locking frequency with low spontaneous noise. However, a high noise level affects the operation of device, and therefore transform-limited pulses are not obtainable over a wide tuning range. It is also shown that noise is extremely sensitive to the RF and DC currents, linewidth enhancement factor, gain saturation parameter and spontaneous coupling factor.     

Noise Effects in the Mode-Locked External Cavity Lasers

Effect of high level of spontaneous and carrier noise on mode-locked hybrid soliton pulse source and relative intensity noise is described. Transform limited pulses are not generated over a wide frequency range because of these noises.     

Regenerative mode locking via superposition of higher-order cavity modes in composite cavity fiber lasers

We demonstrate a new method of optical pulse generation in regeneratively mode-locked fiber ring lasers (RML-FRLs). The method is based on generating dominant longitudinal modes in the fiber ring cavity by means of a composite cavity structure and their intermode beating at the photodetector incorporated in the regenerative feedback loop. The beat signal is then used as a modulation signal to generate optical pulses in a regenerative mode-locking scheme, thereby eliminating the requirement for a high-Q rf bandpass filter in a conventional RML-FRL. Optical pulses with a repetition frequency of 3.6 GHz have been generated successfully with a supermode noise suppression of more than 48 dB and a low phase noise of -85 dBc/Hz at 10 kHz offset from the carrier frequency.     

Mode-locked CW dye lasers

Mode-locking of CW dye lasers are described. Three different methods: active mode-locking by acoustic loss modulation, pumping with mode-locked pulses and passive mode-locking by a saturable absorber, all resulted in stable continuous trains of tunable mode-locked pulses of various duration. Best results were obtained using passive mode-locking by a saturable absorber. The pulse lengths for this case were measured by auto-correlation technique to be as short as 1.5 ps. Factors influencing the mode-locking and possible improvements are discussed.     

Timing Jitter in Amplitude Modulated Harmonically Mode-Locked Er-Doped Fiber Ring Lasers

The phase noise and the amplitude noise of optical pulses from the amplitude modulated harmonically mode-locked (AM-HML) Er-doped fiber (EDF) ring laser was investigated by measuring the power spectra of the optical pulses. The root mean square (RMS) timing jitter and the RMS amplitude noise are 1.26 ps and 2.5% (500 Hz-50 kHz), respectively, when the pulse repetition frequency is 1.58 GHz. They are smaller than those in conventional harmonically mode-locked EDF ring lasers.     

8字形腔波长可调谐锁模脉冲光纤激光器

采用非线性光纤环形镜加脉冲锁模技术及可调谐光纤光栅滤波器,对8字形腔被动锁模掺铒光纤激光器进行了波长可调谐输出的实验研究.在EDFA抽运光功率一定的情况下,通过调节偏振控制器和可调谐光纤光栅滤波器,获得了光谱稳定、重复频率1.1 MHz、输出功率起伏小于0.8 dBm、中心波长在1 548~1 570 nm内连续可调的短脉冲输出.该激光器可实现自启动锁模,且长时间稳定工作无需任何调整.     

Simulation of mode-locked surface-emitting lasers through a finite-difference time-domain algorithm

An approach based on the finite-difference time-domain method is developed for simulating the dynamics of passive mode locking in vertical-cavity surface-emitting lasers (VCSELs). The material response is modeled by the effective semiconductor Bloch equations through a resonant polarization term in the Maxwell's equations. Nonlinear gain saturation is incorporated through a gain compression factor in the equation governing the dynamics of the resonant polarization. An extended-cavity VCSEL with a quantum-well saturable absorber is simulated, and stable mode-locking pulses are obtained. Fine features of the spatial profile of the mode-locked pulses are also studied within this approach.     

交叉增益调制型波长转换器噪声特性的研究

对基于半导体光放大器的交叉增益调制型波长转换器相向和同向两种工作方式进行了研究。实验上分别实现了两种工作方式在1550nm波段的波长转换,比较了相同外部条件下两种工作方式的噪声特性,在全面考虑放大自发辐射噪声及其消耗载流子,增益谱的色散性和有源区内部损耗等因素的基础上,运用放大器的分段模型,计算了不同条件下两种方式的输出噪声功率,结果表明：相向型工作方式受放大自发辐射噪声的影响要远大于同向工作方式,输出放大自发辐射噪声功率的大小主要取决于载流子浓度的高低,而载流子空间分布的不均匀程度则决定两种工作方式输出噪声功率的差值大小。     

Synchronous Injection Locking Operation of Monolithic Diode Lasers Mode-Locked Diode Lasers

Synchronized mode-locking of monolithic mode-locked diode lasers has been demonstrated by injecting the light output from a master monolithic mode-locked diode laser. The master diode laser is a 10 GHZ hybridly mode-locked two section InGaASP quantum well laser. The slave lasers are a 10 GHz two section laser which is similar to the master laser, and a 20 GHz three section colliding pulse mode-locking laser. Both the slave lasers were greatly stabilized at 10 GHz frequency by a synchronous mode-locking mechanism under the injection of master laser pulses.     

Mode-locking of cw dye laser using externally modulated pumping laser

A new mode-locking method of tunable dye laser is described. This simple and practical method requires only an external intensity modulator to the pumping source. After the simple analytical considerations, the experimental work was done using an Ar laser pumped Rhodamin 6G dye laser and an acousto-optic modulator. As results, stable continuous trains of mode-locked pulses were obtained throughout in the ordinary lasing range 570–630 nm. The pulse width, estimated to be 30–50 ps by SHG autocorrelation measurements, is limited by the bandwidth of Lyot filter used. It is also shown experimentally that this method can be applicable for the suppression of the growth of double pulses in passive mode-locking with saturable absorber (DODCI).     

490 fs pulse generation from a passive C-band AlGaInAs/InP quantum well mode-locked laser

We report femtosecond pulses from a passive C-band two-section AlGaInAs/InP mode-locked laser with a monolithically integrated passive waveguide made by quantum well intermixing. Without any external pulse compression, Lorentzian pulses are generated at a repetition frequency of ~38 GHz with 490 fs pulse duration, which is, to the best of our knowledge, the shortest pulse from any directly electrically pumped quantum well semiconductor mode-locked laser. The mode-locking range is relatively large and the ultranarrow pulse width is very stable over a broad range of driving conditions.     

Wavelength-tunable, passively mode-locked fiber laser based on graphene and chirped fiber Bragg grating

We demonstrate a wavelength-tunable, passively mode-locked erbium-doped fiber laser based on graphene and chirped fiber Bragg grating. The saturable absorber used to enable passive mode-locking in the fiber laser is a section of microfiber covered by graphene film, which allows light-graphene interaction via the evanescent field of the microfiber. The wavelength of the laser can be continuously tuned by adjusting the chirped fiber Bragg grating, while maintaining mode-locking stability. Such a system has high potential in tuning the mode-locked laser pulses across a wide wavelength range.     

C. 超短激光光源

本文对超短激光脉冲的产生、压缩技术的最新发展做了详细评述。     

氧化石墨烯被动锁模掺镱光纤激光器多脉冲现象的实验研究

利用氧化石墨烯作为可饱和吸收体,在被动锁模全正常色散掺镱光纤激光器中研究了多脉冲的现象,在同一抽运功率不同偏振态下,实验获得了矩形脉冲谐波锁模、耗散孤子谐波锁模、准谐波锁模,脉冲峰值周期性调制,脉冲簇、脉冲束、混沌多重脉冲的多脉冲现象,插入激光腔内的2nm窄带滤波器具有限制增益带宽、对脉冲塑形、诱导多脉冲产生的作用,调节偏振控制器相当于改变腔内增益,是实现不同类型多脉冲现象的主要原因,本实验研究有利于加深对多脉冲动力学行为在正常色散区域氧化石墨烯锁模掺镱光纤激光器中的理解。     

Passive mode locking of lasers by crossed-polarization gain modulation

We report on a novel approach for inducing passive mode locking of lasers without using any saturable absorber but exploiting the polarization degree of freedom of light. In our scheme, passive mode locking is achieved by crossed-polarization gain modulation caused by the reinjection of a polarization-rotated replica of the laser output after a time delay. The reinjection time delay defines resonance tongues that correspond to mode-locking operation. Numerical continuation reveals that the cw solution is destabilized through a Hopf bifurcation that defines the onset of multimode operation which evolves sharply into a mode-locked solution. Our approach can be applied to a large variety of laser systems. For vertical-cavity surface-emitting lasers, we demonstrate stable mode-locked pulses at repetition rates in the GHz range and pulse widths of few tens of picoseconds.     

自启动被动锁模掺铒光纤激光器的研究

在非线性光纤环形镜非线性开关效应和块状半导体波导饱和吸收效应的共同作用下，实现了掺铒光纤激光器的自启动被动锁模，获得了十分稳定的锁模脉冲序列，观察到高次谐频锁模脉冲输出。分析了非线性光纤环形镜的非线性开关反射特性。     

Diode-end-pumped passively mode-locked Nd:GGG laser with a semiconductor saturable mirror

We report on the passive mode-locking of a diode-end-pumped neodymium-doped gadolinium gallium garnet (Nd:GGG) crystal with a semiconductor saturable absorber mirror (SESAM). Continuous wave (CW) mode-locking was obtained. The mode-locked pulse duration was estimated to be ∼17.5 ps with a maximum average output power of 0.4 W. The mode-locked pulses have a repetition rate of 121.5 MHz. To our knowledge, this is the first demonstration of passive mode-locking of the diode pumped Nd:GGG lasers.     

Application of the coherent photon seeding technique to synchronously pumped and hybridly mode-locked dye lasers

The mode-locking performances of synchronously pumped and hybridly mode-locked dye lasers self-stabilized by coherent photon seeding (CPS) are investigated experimentally. The variation of the optimum values of the feedback parameters and the pulse quality of the stabilized laser with the cavity detuning is studied over a wide range of this parameter. The results presented for the case of pure synchronous pumping complement those previously reported for the generation of transform-limited pulses of variable length. The first experiment on the application of CPS to a conventional dual-jet hybridly mode-locked laser confirms the predictions of the numerical modelling.