Dynamic response of colliding-pulse mode-locked quantum-well lasers

The colliding-pulse mode-locked scheme, using quantum-well semiconductor lasers, has been reported to be useful for the generation of short optical pulses with a high repetition rate. In this paper, the large signal dynamic process of a monolithic colliding-pulse mode-locked laser diode is simulated using a large signal laser model. The refractive index changes induced by variations of the carrier density and the standing wave effect in the saturable absorber have been taken into account in the simulation     

Tunable monolithic colliding pulse mode-locked quantum-well lasers

The tunabilities of both the wavelength and the pulse-width of monolithic mode-locked semiconductor lasers are demonstrated. Pulses shorter than 1.6 ps, tunable over 8.8 mu m, have been generated by a temperature-tuned monolithic colliding pulse mode-locked (CPM) quantum-well laser. For a fixed wavelength, the pulse-width is independently controlled from 1.2 ps to longer than 3 ps by external bandpass filters. Near transform-limited time-bandwidth products of 0.34 were maintained throughout the tuning processes.<>     

Effect of optical feedback on 60-GHz colliding-pulse semiconductor mode-locked lasers

We have experimentally investigated on the effects of optical feedback on the performance of monolithic colliding-pulse passively mode-locked semiconductor lasers operating at 60 GHz, designed to be efficient sources of millimeter-wave electrical signals. The characteristics of the optical-to-electrical converted signal are investigated for a long and a short external cavity by means of an external photodiode and by using the saturable absorber of the device as an intracavity photodetector. For a power feedback ratio larger than 10/sup -3/, the linewidth of the millimeter-wave signal is severely broadened with respect to the value of 230 kHz measured in unperturbed conditions. We also report that optical feedback causes central frequency shift and instability, and a reduction of the useful colliding-pulse mode-locked operating region in the biasing parameters of the device.     

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.     

Monolithic AlGaAs-GaAs single quantum-well ridge lasers fabricatedwith dry-etched facets and ridges

A process has been developed to allow the fabrication of self-aligned etched-facet ridge lasers. The ridge lasers have both their facets and ridges formed through the use of the chemically assisted ion beam etching technique. The ridge and facet of these lasers are self-aligned so that any misalignment during the photolithography does not affect positioning of the laser ridge with respect to the facet. A cavity with a length as short as 3 μ has been fabricated. The longitudinal mode spacing has been experimentally measured as a function of inverse cavity length for both the n_QW=1 and 2 transitions, and the corresponding dispersion terms have been determined     

A harmonic colliding-pulse mode-locked semiconductor laser forstable subterahertz pulse generation

A 192-GHz, sixth-harmonic colliding-pulse mode-locked InGaAsP-InP strained QW semiconductor laser that has a monolithic periodic saturable-absorber configuration is presented. The generation of nearly transform-limited, 0.75-ps pulses with a side-mode suppression ratio of about 27 dB at the central mode is demonstrated. The temporal repetition rate of the pulses was measured for the first time with the accuracy of the synthesizer by photonic downconversion using optical modulation sidebands. The rate for the pulses under a higher saturable-absorber voltage of -2.33 V had a 10-dB reduction RF-spectrum width of 1.1 MHz with a resolution of 300 kHz. The repetition rate versus reverse voltage was linear in a range from -750 to -900 mV     

Monolithic integration of GaAs-AlGaAs quantum-well lasers with directional couplers using vertical coupling of light

A novel technique for the monolithic integration of a laser and a directional coupler in the GaAs-AlGaAs material system is demonstrated. The combination of single-step molecular beam epitaxy (MBE) on a planar substrate, vertical coupling of light between the active and passive waveguide in a p-n-p-doped structure and the use of a self-aligned fabrication process for the ridge waveguides in the active and passive sections results in a threshold current of 52 mA and an output power of up to 0.6 mW. The directional coupler is completely switched at an applied bias of 4.0 V.     

Improvements in mode-locked semiconductor diode lasers using monolithically integrated passive waveguides made by quantum-well intermixing

By using the technique of quantum-well intermixing (QWI), monolithically integrated passive, and active waveguides can be fabricated. It is shown that mode-locked extended cavity semiconductor lasers with integrated low-loss passive waveguides display superior performance to devices in which the entire waveguide is active: the threshold current is a factor of 3-5 lower, the pulsewidth is reduced from 10.2 ps in the all active laser to 3.5 ps in the extended cavity device and there is a decrease in the free-running jitter level from 15 to 6 ps (10 kHz-10 MHz).     

碰撞锁模染料激光器中激光脉冲的啁啾特性及其色散补偿

从实验上研究了碰撞锁模染料激光器中激光脉冲的啁啾性质.分析了采用两块棱镜组成的棱镜对进行内腔补偿时,棱镜对的色散对输出激光脉冲的宽度、稳定性及光谱特性的影响.     

Noise of mode-locked lasers

A theory of noise in mode-locked lasers is developed that applies to additive pulse mode-locked and Kerr lens mode-locked systems. Equations of motion are derived for pulse energy, carrier linewidth, frequency pulling, and timing jitter. The effect of gain fluctuations, mirror vibrations, and index fluctuations are determined. Measurements that can determine all four fluctuation spectra are described. Experimental data in the literature are compared with theory     

Tm-doped mode-locked fiber lasers

Ultrashort pulse fiber lasers are increasingly used in various areas for scientific as well as industrial purposes. In contrast to ultrashort pulse lasers based on ytterbium- and erbium-doped fibers, the dispersion of silica fibers in the amplification band of thulium-doped fibers around 2 μm is typically anomalous, which has fundamental impact on the pulse propagation. In this paper, mode-locked thulium-doped fiber lasers operating in different pulse propagation schemes are presented. The transfer of various concepts into the 2 μm wavelength range, which have been successfully applied for pulse parameter scaling in the 1 and 1.5 μm spectral region, are discussed on the basis of experimental and numerical results.     

完全锁模半导体激光器

本文对含F-P标准具的外腔半导体激光器进行了主动锁模研究。适当选择F-P标准具参数可形成单一的纵模群振荡,并可因此得到完全锁模光脉冲。实验中得到了脉宽为13.5ps、重复频率为925MHz的光脉冲输出。     

Resonant tunneling injection quantum-well lasers

We report, for the first time, the observation of resonant tunneling induced negative differential characteristics in the light-current (L-I) and light-voltage (L-V) curves of a single-quantum-well semiconductor laser. Broad-stripe lasers have exhibited CW threshold current density of 50 A/cm² at 77 K, with a sharp decrease in output light power at 68 A/cm², which corresponds to a resonant point in the current-voltage (I-V) characteristics of the device. Peak to valley ratios of more than 1.5:1 were observed in the L-I and L-V curves     

Linewidth enhancement in quantum-well lasers

We have developed explicit approximations for the Hnewidth enhancement factor in quantum-well lasers. These simple expressions represent a quick and easy means of calculating the linewidth enhancement factor under a variety of operating conditions, and help us to understand the physics influencing this important parameter.     

Gain spectra of quantum-well lasers

The gain spectrum and its sensitivity to carrier density is calculated for a model quantum-well heterostructure semiconductor laser for a range of quantum-well widths. The gain spectra, especially for narrow wells, show better mode-to-mode gain discrimination than for the equivalent bulk laser. Good carrier confinement helps obtain this desirable feature.     

Impedance characteristics of quantum-well lasers

We derive theoretical expressions for the impedance of quantum-well lasers below and above threshold based on a simple rate equation model. These electrical laser characteristics are shown to be dominated by purely electrical parameters related to carrier capture/transport and carrier re-emission. The results of on-wafer measurements of the impedance of high-speed In_0.35Ga_0.65 As/GaAs multiple-quantum-well lasers are shown to be in good agreement with this simple model, allowing us to extract the effective carrier escape time and the effective carrier lifetime, and to estimate the effective carrier capture/transport time     

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.     

Theory of mode-locked semiconductor lasers

We present a theoretical study of semiconductor mode-locked lasers at a phenomenological level. We use the slow absorber model of New and Haus, but extend the analysis by taking into account the shift in the gain maximum due to the changing number of carriers. In our analysis of the resulting equation, we show that due to stability requirements the shortest attainable pulse duration is limited. The use of self-phase modulation due to a slow medium can at most lead to a shortening of the pulse by a factor of 2. We show that the shifting of the gain maximum due to the changing number of carriers in the laser is a crucial aspect in the operation of mode-locked semiconductor lasers. We further find that the end mirrors must be reflecting more than about half of the light intensity to prevent a self-pulsation type instability similar to the relaxation oscillation     

波长可调谐被动锁模光纤激光器

为在光纤激光器中获得特定中心波长的锁模激光,进行了采用非线性光纤环形镜锁模的掺Yb3+光纤激光器的波长可调谐实验研究。获得了自启动锁模、中心波长在1030nm~1081nm范围内连续调谐的锁模脉冲输出;在中心波长1053nm时,测得光谱带宽6nm、脉冲宽度234.375ps、输出功率2.05mW、重复频率3.842MHz。这种被动锁模光纤激光器的锁模过程可以完全自启动,几乎不受外界环境变化的影响,可以长时间稳定工作,不仅可以提供特定中心波长的锁模激光,而且有望成为其它科学研究工作的中心波长可调谐的宽带锁模光纤激光种子源。     

High-power passively mode-locked semiconductor lasers

We have developed optically pumped passively mode-locked vertical-external-cavity surface-emitting lasers. We achieved as much as 950 mW of mode-locked average power in chirped 15-ps pulses, or 530 mW in 3.9-ps pulses with moderate chirp. Both lasers operate at a repetition rate of 6 GHz and have a diffraction-limited output beam near 950 nm. In continuous-wave operation, we demonstrate an average output power as high as 2.2 W. Device designs with a low thermal impedance and a smooth gain spectrum are the key to such performance. We discuss design and fabrication of the gain structures and, particularly, their thermal properties