激光二极管阵列的窄线宽、可调谐输出

外腔反馈的激光二极管阵列(LDA)可获得窄线宽、可调谐的光谱输出。外腔由快轴准直镜、准直光学系统和闪耀光栅组成。由于阵列中各发光单元的排列弯曲导致不同波长的光原路返回,引起谱线展宽,在输出光路中加入光谱滤波器,使激光二极管阵列的线宽进一步窄化。这样,激光二极管阵列的输出光谱由自由运转时的2 nm压缩到0.12 nm,在恒定温度23 ℃时,实现了激光在806～818 nm的调谐,调谐范围达12 nm。

Narrow-Linewidth Microwave Generation Using a Self-Injected DBR Laser Diode

A novel technique for generating narrow-linewidth microwave or millimeter-wave signals is proposed. In this scheme, a delayed self-injected distributed Bragg reflector laser diode, which is tuned by a low-frequency square-wave voltage, is used to generate two correlated lightwaves simultaneously. Experiments show that the 10-dB linewidth of generated microwave signals is reduced from 147 MHz to 68 kHz utilizing the proposed self-injection technique.

Comparative study on the broadening of exciton luminescence linewidth due to phonon in zinc-blende and wurtzite GaN epilayers

Linewidth broadening of exciton luminescence in wurtzite and zinc-blende GaN epilayers was investigated as a function of temperature with photoluminescence. A widely accepted theoretical model was used to fit the experimental data, so that the coupling parameters between exciton and acoustic and longitudinal optical phonons were obtained for both structures. It was found that the coupling constants of both exciton-acoustic optical phonon coupling and exciton-longitudinal optical phonon coupling for zinc-blende GaN are almost twice as much as the corresponding values of wurtzite GaN. These results show that the relatively strong exciton-phonon scattering seems to be characteristic to zinc-blende GaN film. (C) 2002 American Institute of Physics.

A narrow photoluminescence linewidth of 19.2 meV at 1.35 mu m from In0.5Ga0.5As/GaAs quantum island structure grown by molecular beam epitaxy

A self-organized In0.5Ga0.5As/GaAs quantum island structure emitting at 1.35 mum at room temperature has been successfully fabricated by molecular beam epitaxy via cycled (InAs)(1)/GaAs)(1)monolayer deposition method. The photoluminescence measurement shows that a very narrow linewidth of 19.2 meV at 300 K has been reached for the first time, indicating effective suppression of inhomogeneous broadening of optical emission from the In0.5Ga0.5As island structure due to indium segregation reduction by introducing an AlAs layer and the strain reduction by inserting an In0.2Ga0.8As layer overgrown on the top of islands. The mound-like morphology of the islands elongated along the [1 (1) over bar0] azimuth are observed by the atomic force microscopy measurement, which reveals the fact that strain in the islands is partially relaxed along the [1 (1) over bar0] direction. Our results present important information for the fabrication of 1.3 mum wavelength quantum dot devices.

Linewidth of the infrared absorption spectra due to bound-to-continuum transition in GaAs/AlxGa1-xAs multiple quantum well structures

We have observed an extremely narrow absorption spectrum due to bound-to-continuum transition in GaAs/AlxGa1-xAs multiple quantum wells (MQWs). Its linewidth is only about one tenth of the values reported previously. Our calculation indicates that the broadening of the excited state in the continuum has little contribution to the absorption linewidth. We have grown a sample whose MQW region contains two kinds of wells with a minor thickness inhomogeneity. Its resultant absorption linewidth is six times as large as that of homogeneous well sample, which is in good agreement with our theoretical analysis. Thus we can suggest that the wider absorption spectra reported by many authors may be due to the well width inhomogeneity. (C) 1998 American Institute of Physics. [S0003-6951(98)03430-5]

ELECTRIC-FIELD-INDUCED EXCITON-LINEWIDTH BROADENING IN SHORT-PERIOD GAAS/GAXAL1-XAS SUPERLATTICES

We have investigated the Wannier-Stark effect in GaAs/GaAl1-xAs superlattices under electric fields by photocurrent spectroscopy measurements in the range of temperatures 10-300 K. The linewidth of the Oh Stark-ladder exciton was found to increase significantly along with an increase in peak intensity when the electric field increases. We present a mechanism based on an enhanced interface roughness scattering of electronic states due to Wannier-Stark localization in order to explain this increased broadening with electric field. This electric-field-related scattering mechanism will weaken the negative differential conductance effects in superlattices predicted by Esaki and Tsu.

BROADENING OF THE EXCITONIC LINEWIDTH DUE TO SCATTERING OF 2-DIMENSIONAL FREE-CARRIERS

By photoluminescence measurements we find that at low temperature the linewidth of the excitonic luminescence broadens with increasing electron density in the wider well from a photoexcited type-I-type-II mixed GaAs/AlAs asymmetric double quantum well structure, which even makes the excitonic linewidth at 77 K larger than at 300 K above a certain excitation intensity. We verify that the broadening is due to the scattering of two-dimensional carriers to excitonic states. Based on the theory of the scattering of carriers to excitonic states, we calculate the broadening of the excitonic linewidth. Our experimental results are convincing for verifying the theoretical prediction. (C) 1995 American Institute of Physics.

Photoluminescent properties of organic film in flat optical microcavity

The microcavity is sandwiched between a quarterwavelength distributed Bragg reflector(DBR) and a metal Ag reflective mirror. A single layer of a Tris(8-quinolinolato)aluminum (Alq) film was used as the light-emitting layer. The photoluminescent properties of the optical microcavity and that of the Alq film were studied at the same excitation condition. Compared with the Alq film,the significantly narrowed spectral emission linewidth from 90 nm to 10 nm was observed, the PL emission intensity of the microcavity at the resonant mode is enhanced by the order of 1. The spectral narrowing and intensity enhancement of the microcavity is attributed to the microcavity effect.

Effects of spontaneously induced coherence on absorption of a ladder-type atom

This paper investigates the effects of spontaneously induced coherence on absorption properties in a nearly equispaced three-level ladder-type system driven by two coherent fields. It find that the absorption properties of this system with the probe field applied on the lower transition can be significantly modified if this coherence is optimized. In the case of small spontaneous decay rate in the upper excited state, it finds that such coherence does not destroy the electromagnetically induced transparency (EIT). Nevertheless, the absorption peak on both sides of zero detuning and the linewidth of absorption line become larger and narrower than those in the case corresponding to the effects of spontaneously induced coherence; while in the case of large decay rate, it finds that, instead of EIT with low resonant absorption, a sharp absorption peak at resonance appears. That is, electromagnetically induced absorption in the nearly equispaced ladder-type system can occur due to such coherent effects.

Lasing without or with inversion in an open four-level system with a phase-fluctuation driving field

The effect of exit rate and the ratio of atomic injection rate on gain behaviour has been investigated, and the effects of phase fluctuation on absorption, dispersion and population difference in an open four-level system have been analysed by using numerical simulation from the steady linear, analytical solution. The variation of the linewidth, Rabi frequency of the driving field, the exit rate or the ratio of atomic injection rate can change the lasing properties in the open system. The presence of finite linewidth due to driving-field phase fluctuation prevents the open four-level atomic system from obtaining a high refractive index along with zero absorption.