CW operation of semiconductor ring lasers

Semiconductor ring lasers have been fabricated in single quantum well material using electron-beam lithography and SiCl/sub 4/ dry etching. CW operation has been achieved in 84 mu m diameter rings at a threshold current of 24 mA. This low value makes the structure very suitable for monolithic integration in optoelectronic circuits.<>     

CW operation of corner cavity semiconductor lasers

Etched facet semiconductor lasers have been fabricated and tested under CW operating conditions. The lasers consist of stripes formed by proton implantation, a total internal reflection (TIR) corner, and an output coupling facet. Devices with a variety of output coupling geometries were fabricated. Laser threshold currents and spectral characteristics were measured. Threshold current levels of devices with several different aperture sizes are compared to those of structures with standard Fabry-Perot reflectors     

CW room-temperature operation of Y-junction semiconductor ring lasers

CW room-temperature lasing in Y-junction semiconductor ring lasers with radii as small as 50 mu m is reported. The dependence of the threshold current density on device dimensions is examined for radii in the range 50-200 mu m and for waveguide widths of 2-8 mu m. From these quantum-well devices, approximately 1 mW of CW single-frequency Te-polarised lasing output is obtained.<>     

Low-threshold CW operation of square-shaped semiconductor ring lasers (orbiter lasers)

The CW operation of square-shaped semiconductor ring lasers is demonstrated with a threshold current as low as 6 mA. The ring resonator consists of straight waveguides and four total reflection mirrors. The lasers are fabricated using Br/sub 2/ dry etching on an InGaAs/GaAs strained single-quantum-well graded-index separate-confinement heterostructure wafer. The low-threshold CW operation is due to the high differential gain of the wafer and the low-loss total reflection mirror.<>     

Noncatastrophic degradation of GaAs lasers under CW operation

Three types of noncatastrophic degradation have been observed during CW life tests of GaAs injection lasers at 77°K. First, when operated submerged in liquid nitrogen, a comparatively rapid decrease occurs in the power output. This effect appears to be due to the liquid nitrogen environment and is reversible. This phenomenon has not been observed to start until the laser is energized, which suggests that it is due to fine polarizable particles in the liquid nitrogen which are attracted to the junction region. Second, some lasers have been operated on a cold finger in vacuum at current levels less than three or four times threshold for as long as 1000 hours with no significant change in output. The power outputs under such conditions weresimfrac{1}{3}watt. When the current was increased byeond three or four times threshold, however, the light output decreasedsimfrac{1}{2}in several hours, and this degradation was irreversible. Third, a cyclic variation in output occurs when a cold trap is not used; apparently this variation is due to an oil film being slowly deposited on the laser mirrors. This effect is not observed when precautions are taken to prevent the growth of the oil film.     

Power conversion efficiency of semiconductor injection lasers and laser arrays in CW operation

In many applications it is important to optimize the power conversion efficiency of semiconductor lasers and laser arrays. A method for calculating this efficiency which takes into account temperature effects is described, and some calculated results are presented and discussed. It is found that under certain conditions, a small increase in the thermal resistance of the device can result in a large reduction of its efficiency. Temperature effects are important in high-power semiconductor lasers, and in particular in laser arrays, where low thermal resistance heat sinking may be crucial to the device operation.     

CW operation of GaInAsP stripe lasers

A quantitative investigation of the constraints on dc operation of GaInAsP stripe-geometry lasers at room temperature and above has been made. Laser pulse threshold current, its temperature sensitivity, electrical series resistance, and the thermal resistance of the bonded device are critical parameters in this respect. Sets of theoretical curves have been generated that allow expected de thresholds to be determined from the value of the pulsed threshold. Experimental results confirm the accuracy of the expressions. For GaInAsP lasers, the low values of T0reported in the literature (47-80 K) imply that both electrical series resistance and thermal resistance must be minimized in order to obtain stable dc operation over a reasonable temperature range in conventional oxide or proton isolated stripe structures. Both parameters are calculated theoretically for a range of structures. The calculations show that thermal runaway is sensitive to electrical resistance in the range1-10 Omegathis suggests an area where improvements are possible. To this end, the use of tunneling Schottky contacts to a ternary InGaAs p-capping layer has been developed to minimize contact resistance.     

Low-frequency intensity noise in semiconductor lasers

The observed 1/f noise in the light-output power S _p of four different types of heterostructure lasers is explained in terms of spatially uncorrelated gain fluctuations and spontaneous emission fluctuations. Two possible noise sources are suggested: fluctuations in the absorption coefficient and fluctuations in the number of free carriers. Both models are in agreement with the experimental results obtained from index-guided and gain-guided diodes at wavelengths of 1.3 and 0.8 μm. The dependence S_p ∝P^m has been observed with P the average light-output power and m=3/2 under spontaneous emission, a small transition region with m=5/2, m=4 in the superradiation region, and 0⩽m⩽1 in the laser region     

Noise characteristics in repetitively pulsed semiconductor lasers

Timing jitter (phase noise) and power fluctuations (intensity noise) in a semiconductor laser driven with a periodic current waveform, in the large signal regime are investigated theoretically. The temporal behavior of the laser output power is calculated numerically from the modified rate equation with Monte Carlo simulation of the random processes, both free-running and active mode-locked configurations are treated. The temporal width and root-mean-square (rms) timing jitter and energy fluctuation of the pulses are calculated, as are the correlation and spectral properties of the noise     

高温CW半导体激光器的阈值电流

用载流子速率方程分析了高温CW半导体激光器(LD)阈值电流(I_(th))与温度(T)的关系.数值计算结果分别给出了与T有关的腔内损耗、双分子复合和俄歇过程以及载流子泄漏效应对I_(th)的贡献大小.     

Temperature rise at mirror facet of CW semiconductor lasers

A relationship is derived for the temperature rise at the mirror facet of semiconductor lasers. The analytical result is based on the model of C.H. Henry et al. (1979) as applied to CW lasers and a thermal model. The effects of active layer length and its thickness, surface recombination velocity, output intensity, and an effective thermal length are delineated for the temperature rise. A comparison with experimental results reported in the literature shows good agreement for the facet temperature rise. A by-product is an approximate relationship for the temperature distribution along the lasing direction     

Millimetre-wave signal generation using pulsed semiconductor lasers

A novel technique for millimetre-wave signal generation using a pulsed semiconductor laser is proposed and demonstrated. Optical filtering is used to select only two modes and suppress all other modes in the optical spectrum of the laser. The two selected modes beat together in a photodiode to generate a millimetre-wave signal with 100% modulation depth     

Rotational nonequilibrium and line-selected operation in CW DF chemical lasers

A numerical analysis of rotational nonequilibrium effects in CW DF chemical lasers is presented. The rotational master equations incorporate the effects of simultaneous mixing, chemical pumping, rotational cross relaxation, and radiative emission. Rotational cross relaxation is described by "exponential gap" models in which ΔJ is unrestricted. Results of this analysis indicate that rotational equilibrium can be a poor assumption for high J levels even under small-signal conditions. The model predictions are in good qualitative agreement with observed multiline resonator spectra. Performance loss due to rotational nonequilibrium is predicted to be modest (∼15 percent) for multiline operation, with larger losses predicted for line-selected modes. Criteria for efficient line-selected operation are presented.     

Stable single-longitudinal-mode operation under high-speed direct modulation in cleaved-coupled-cavity GaInAsP semiconductor lasers

We describe a new self-aligned coupled-cavity laser formed by a simple variation of the usual cleaving procedures. Such cleaved-coupled-cavity (CCC or C3) lasers were highly single-longitudinal-moded with spectral and stability as good as those obtained from frequency-selective feedback lasers such as distributed feedback and distributed Bragg reflector lasers under high-speed direct modulation.     

Phase noise and spectral line shape in semiconductor lasers

Experimental results concerning the study of phase noise in single-mode semiconductor lasers are reported, which show a strict connection between phase and intensity noise. In particular, phase-noise spectrum is found to present a sharp peak at the same peak frequency of intensity-noise spectrum, a fact which is proven to be responsible for the appearance of satellite peaks in the emission line shape. Direct measurements of the line shape, performed by means of a Fabry-Perot interferometer, are in agreement with the line shape evaluated by using phase-noise spectrum measurements.     

Reduction of optical phase noise in semiconductor lasers

There are several applications of highly coherent semiconductor lasers, especially in coherent optical-fibre communications systems and optical-fibre sensors. Optical phase noise is extremely important in these applications. Here we report preliminary results from a simple technique whereby phase noise in semiconductor lasers may be reduced. Initial results demonstrate a phase-noise reduction of typically 20 dB. Developments of the technique should permit reduction towards the shot noise limit.     

Semiclassical theory of noise in multielement semiconductor lasers

We present a derivation of the noise spectra of multielement semiconductor lasers. We model the noise by a set of Langevin sources which drive a system of small-signal field equations. The Langevin sources are normalized to transition rates within the laser and general formulas for relative intensity, frequency fluctuation, and field spectra are produced. We evaluate the formulas for several specific cases of interest, including those of a passive-active resonator and active-active coupled cavity resonator. In each case, the linewidth is governed by effective α-parameter(s) which generally differ from the material parameter. In the active-active cavity, the linewidth consists of two parts, one which is similar to the Schawlow-Townes linewidth, and a second which is proportional to the FM modulation index.     

单模半导体激光器的相位噪声

一、前言 对半导体激光器的内在噪音如散粒噪音、模式噪音等已经作过很多研究。近年来随着采用大接收灵敏度检测器、使用光放大器和具有紧凑空间通道的多路复用技术以及自差、外差式光纤通讯系统等的进展,光纤通讯系统中使用的半导体激光器的内在相位噪音已成为上述技术的基本限制,因而对单模半导体激光器的相位噪音和光谱线型的理论研究和实验观测已为众争学者注目。 通常的激光理论并没有正确地讨论在室温下工作的单模半导体激光器的特性,首先对注入式半导体激光器线宽与光功率关系进行仔细测量后,发现在300K时,带宽⊿f比用通常激光理论计算的半导体激光器的带宽大50倍,但他们没有解释这种异常增宽的原因。     

负频反馈半导体激光器的量子噪声

相干光通信系统和相干光学测量对LD的噪声特性要求十分严格,因此LD的噪声及其抑制一直是近年来人们十分关注的问题.为了抑制LD的量子噪声,已采用了几种方法,但这又带来了机械稳定性的问题.最近报道了用NFFB抑制LD的线宽和FM噪声,对此也已有了理论解释但是在的分析中未引入反馈项,相当于开环的情况;的分析中则将反馈项引到了相位方程中,这是不符合客观情况的.本文给出的模型不仅解释了FM噪声的抑制,而且也解释了AM噪声的增大.得到的线宽与实验