Amplitude noise of subharmonically hybrid mode-locked pulsesgenerated from a monolithic semiconductor laser

Broad-band amplitude noise (100 MHz to 20 GHz) of 40 GHz pulses generated by a subharmonically hybrid mode-locked (SHML) monolithic semiconductor laser is investigated. Experiments show that the amplitude noise can only be suppressed at some certain subharmonic numbers, while the phase noise can be suppressed by subharmonic hybrid mode-locking under many subharmonic numbers     

Locking characteristics of a subharmonically hybrid mode-locked multisection semiconductor laser

Locking characteristics of a subharmonically hybrid mode-locked (SH-ML) semiconductor laser are investigated experimentally. The locking bandwidths under the second- and third-order SH-ML operation, as well as under fundamental hybrid mode-locking (FH-ML) condition, are characterized with a variety of microwave power and reverse bias voltage applied to the saturable absorber of the laser. Unique locking characteristics are observed for the third-order SH-ML where the locking bandwidth increases with increasing reverse bias, which is opposite to the FH-ML case. This leads to a locking bandwidth of 56 MHz, 2.3 times broader than that for the FH-ML under the shortest pulse condition.     

Dynamics of monolithic passively mode-locked semiconductor lasers

Monolithic colliding pulse mode-locking (CPM) in semiconductor lasers is compared with self colliding pulse mode-locking (SCPM) through a large signal dynamic computer model which incorporates most of the significant features of semiconductor lasers. These include gain saturation, spontaneous emission, the gain-frequency relation, and the line-width enhancement factor. This new model replicates many of the published experimental results and also gives additional insight into the internal operation of the device. In particular, gain saturation combined with the standing waves created by colliding pulses within the saturable absorber produce a transient gain grating. This is found to have significant effects in locking either the even or the odd modes together in CPM. A performance comparison between CPM and SCPM is completed and some key design parameters of both configurations are explored     

Solid-state repetition-rate tunable semiconductor colliding-pulse mode-locked laser

A monolithic mode-locked semiconductor laser with the capability of tuning its repetition rate while passively mode-locked through solid-state means is reported. Over 200 MHz of tuning is demonstrated with variations in the applied dc bias. Dynamic tuning is demonstrated by applying an ac signal to one section showing a tuning bandwidth over a hundred megahertz. Pulse parameters and timing jitter are also presented for passive and hybrid mode-locking operation.     

Optical pulse shaping by cross-phase modulation in a harmonic mode-locked semiconductor fiber ring laser under large cavity detuning

The authors experimentally investigate the phenomena of the pulse-shape distortion due to the drift of cavity length or modulation frequency in a harmonically mode-locked semiconductor fiber ring laser (SFRL). Also, it is experimentally demonstrated that the optical pulse shaping by cross-phase modulation (XPM) can be applied to enhance the robustness of a harmonic mode-locked semiconductor ring laser to the environmental factors, e.g., the modulation-frequency drift and/or the cavity-length drift. The mechanism of pulse-shape distortion due to the modulation-frequency drift or cavity-length drift is explained and experimentally verified. As the locking condition of the SFRL goes to the rational harmonic mode-locking (RHML) regime, the pulse-shape distortion becomes dominant. To validate the explanation, a simple equation for estimating and comparing the amount of cavity-length detuning in terms of frequency is proposed for comparison, which is called the equivalent frequency detuning (EFD). The distortion mostly appeared in the trailing edge of the pulse. By selectively filtering the XPM-induced red-chirped wavelength components in the rising edge of the pulse, the mode-locked pulse train with large pulse-shape distortion can be reshaped to regenerate a mode-locked pulse train with less pulse-shape distortion than the pulse train without the proposed scheme. This method can be used to reduce the pulse-shape distortion effectively, maintaining the pulse repetition rate under the large modulation-frequency detuning, or equivalently, large cavity-length detuning. The proposed scheme is able to generate the pulse-trains robust to the modulation-frequency drift and/or cavity-length drift of the mode-locked SFRL.     

Characteristics of a high-speed passively mode-locked surface-emitting semiconductor InGaAs laser diode

We have studied the performance of the recently demonstrated high-speed passively mode-locked 980-nm vertical cavity diode lasers (pulsewidth down to /spl tau//sub p//spl sim/15 ps, repetition rate up to 15 GHz) by investigating the dynamics of the saturable p-i-n multiple quantum well InGaAs absorber. The impact of the absorber on the noise characteristics of these new compact short pulse sources is also reported.     

基于饱和吸收镜的被动锁模掺铒光纤激光器

为了研究基于半导体可饱和吸收镜的被动锁模光纤激光器的输出特性,采用1480nm的半导体激光器作为抽运源,利用掺铒光纤作为增益介质,以及光纤环行器、偏振控制器、波分复用器和耦合器等构成了环形腔结构的被动锁模光纤激光器。实验中获得了峰值波长1586nm、光谱宽度4.8nm、重复频率11.2MHz、最大平均输出功率8.4mW的稳定锁模激光脉冲输出。结果表明,调整光纤偏振控制器会使光纤激光器输出脉冲的时域波形略微发生变化,在实际应用中需要注意偏振态变化对锁模光纤激光器输出脉冲时域特性的影响。这一结果对于半导体可饱和吸收镜在被动锁模光纤激光器中的应用及其特性具有一定帮助。     

Actively mode-locked 1.5-μm 10-GHz picosecond fiber laser usinga monolithic semiconductor optical amplifier/electroabsorption modulator

In this letter, we demonstrate a novel 10-GHz actively modelocked polarization-maintaining fiber ring laser that utilizes a single device for gain, loss modulation, optical isolation, and repetition rate adjustment. This monolithic device incorporates a semiconductor optical amplifier with an electroabsorption modulator and provides net gain of 2.1 dB. The repetition rate of the 1.5-μm picosecond pulsetrains can be tuned by 2 ppm through perturbation of the electroabsorption modulator reverse bias     

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.     

半导体激光器的调频特性

本文讨论了半导体激光器(LD)的直接调频(FM)特性,指出随着偏置电流的增大,FM响应降低,伪强度调制(IM)响应增大,并给出了一种新的描述FM能力的方法.     

Four-wave mixing and optical modulation in a semiconductor laser

There is a direct connection between nearly degenerate four-wave mixing in a semiconductor laser and optical modulation in the laser field. It can be understood using a model of an unlocked, optically injected laser, which emphasizes the effect of the laser resonator on the optical interactions. This model correctly describes the observed spectral characteristics and their dependence on the intrinsic parameters of the semiconductor laser. This is used to develop a simple and accurate technique using a single experimental setup for the parasitic-free characterization of the intrinsic laser parameters, including the relaxation resonance frequency, the total relaxation rate, the nonlinear relaxation rate, and the linewidth enhancement factor. Other parameters, such as the spontaneous carrier lifetime, the photon lifetime, the differential and nonlinear gain parameters, and the K factor, are determined from the power dependencies of these parameters. This technique requires only two CW lasers closely matched in wavelength and is applicable to semiconductor lasers of any wavelength and any dynamic bandwidth     

Multicolor single-wavelength sources generated by a monolithic colliding pulse mode-locked quantum well laser

The authors report on the separation of single longitudinal modes from the mode-locked program spectrum of a 300-GHz monolithic colliding pulse mode-locked (CPM) semiconductor quantum-well laser. Experimentally, the selected longitudinal mode shows a 10-dB reduction of low-frequency relative intensity noise compared to that of the selected mode from the same laser in continuous-wave (CW) lasing conditions. The strong phase coherence among the passively mode-locked longitudinal modes reduces the partition noise of the unlocked CW laser.<>     

用半导体吸收体实现陶瓷激光器被动锁模研究进展

新型陶瓷材料近年来开始作为激光增益材料,具有低成本、大尺寸、制备时间短、热导率高等优点。大功率飞秒激光器是近年来超短脉冲激光制备的一大热点。本文探讨了使用半导体可饱和吸收镜实现被动锁模大功率陶瓷飞秒激光器的可行性,研究现状以及未来趋势。     

Stabilisation of mode-locked pulses using travelling-wave semiconductor laser amplifier

Numerical and experimental results show, for the first time, that a saturated travelling-wave laser amplifier (TWLA) can be used to amplify and limit the amplitudes of pulses from an actively mode-locked semiconductor laser while removing unwanted secondary pulses.<>     

Pulse-amplitude equalization in a rational harmonic mode-locked fiber laser using nonlinear modulation

In this letter, a simple technique for the pulse-amplitude equalization of high repetition rate pulses generated from a rational harmonic mode-locked fiber ring laser was demonstrated. The principle is based on nonlinear modulation of the modulator and a theoretical explanation based on time-domain analysis was given. Amplitude equalized short pulses up to the seventh rational harmonic mode-locking were obtained with an optimum bias level and modulation depth of the modulator, which agrees well with the simulation result and demonstrates the efficiency of this method.     

Amplification of mode-locked semiconductor diode laser pulses in erbium-doped fibre amplifier

Amplification of picosecond pulses from an actively mode-locked semiconductor diode laser in an erbium-doped fibre amplifier pumped at 532 nm is demonstrated. Peak emission was centred on 1.536 mu m and a saturated amplifier gain of 13 dB yielded less than 10 ps pulses with a peak power of 0.58 W at 600 MHz. Optimisation of the mode-locked oscillator allowed amplified peak pulse powers greater than 3 W to be generated.<>     

Cross-phase modulation in a semiconductor laser amplifierdetermined by a dispersive technique

Cross-phase modulation in a semiconductor laser diode amplifier is reported. A simple expression for the chirp imparted on a weak signal pulse by the action of a strong pump pulse is derived. A novel dispersive technique for characterizing the resulting nonlinear chirp is introduced and used in the present experiment. A maximum frequency excursion of 16 GHz, due to the cross-phase modulation, was measured. A value of 6 was found for α_xpm, which is a factor for characterizing the cross-phase modulation in a similar manner to the conventional linewidth enhancement factor α     

Tunable dual-wavelength actively mode-locked fiber laser with anF-P semiconductor modulator

A novel actively mode-locked fiber laser for generating dual-wavelength picosecond pulses is proposed by using a Fabry-Perot laser diode as the modulator in the ring cavity. A linear chirped fiber grating was used as a wavelength selector and produces temporal-spectral multiplexing of the pulses in the gain medium to reduce gain cross-saturation effects. About 2-GHz stable dual-wavelength pulses with a wavelength spacing of 0.92 nm at room temperature were experimentally demonstrated and the wavelengths could be tuned in a range of about 3 nm     

半导体激光器强度调制特性的谐波分析

本文研究了已调半导体激光器(LD)的谐波产生的原因,以及抑制谐波的方法.     

Supermode selection of a subterahertz-harmonic colliding-pulse mode-locked semiconductor laser using continuous-wave light injection

The supermode of a 192-GHz sixth-harmonic colliding-pulse mode-locked semiconductor laser can be selected by continuous-wave (CW) light injection adjusted to the unlocked fundamental cavity modes. This selection scheme offers a technique for wide-range simultaneous multiwavelength allocation at each fundamental mode spacing and will be useful for providing standard light sources for wavelength-division multiplexed (WDM) systems.