Internal optical loss in semiconductor lasers

Internal optical loss in high-power semiconductor lasers based on quantum-well separate-confinement heterostructures was studied. Calculations show that the major portion of the internal optical loss occurs in the active region and emitters. Making the laser waveguide thicker and the cavity longer reduces the internal optical loss. Two possible approaches to the design of laser heterostructures are considered, and optimal solutions are suggested. The difference in the internal optical loss between lasers on InP and those on GaAs substrates is attributed to the larger cross section of photon absorption by holes in InP. Good agreement between the calculated and experimental values of the internal optical loss in lasers on InP and GaAs substrates is obtained.     

Current-injection efficiency in semiconductor lasers with a waveguide based on quantum wells

A dynamic distributed diffusion-drift model of laser heterostructures, which takes into account carrier capture by quantum wells, is developed. The leakage currents in the lasing mode are calculated for different laser structures without wide-gap emitters: InGaAs/GaAs (lasing wavelength λ = 0.98 μm), InGaAsP/InP (λ = 1.3 μm), and InGaAs/InP (λ = 1.55 μm). It is shown that consideration of the finite carrier-capture time is of major importance for calculating structures with deep quantum wells. The ratio of the leakage currents to the total current in the structures with deep quantum wells (InGaAsP/InP and InGaAs/InP) increases with an increase in the injection current and may reach a few percent when the lasing threshold is multiply exceeded.     

Blue-green ZnSe lasers with a new type of active region

We report the results of an experimental study of molecular-beam epitaxy of ZnSe-based laser heterostructures with a new structure of the active region, which contains a fractional-monolayer CdSe recombination region in an expanded ZnSe quantum well and a waveguide based on a variably-strained, short-period superlattice are reported. Growth of a fractional-monolayer CdSe region with a nominal thickness of 2–3 ML, i.e., less than the critical thickness, on a ZnSe surface (Δa/a∼7%) leads to the formation of self-organized, pseudomorphic, CdSe-enriched islands with lateral dimensions ∼10–30 nm and density ∼2×10¹⁰ cm⁻², which serve as efficient centers of carrier localization, giving rise to effective spatial separation of defective regions and regions of radiative recombination and, as a result, a higher quantum efficiency. Laser structures for optical pumping in the (Zn, Mg) (S, Se) system with a record-low threshold power density (less than 4 kW/cm² at 300 K) and continuous-wave laser diodes in the system (Be, Mg, Zn) Se with a 2.5 to 2.8-ML-thick, fractional-monolayer CdSe active region have been obtained. The laser structures and diodes have an improved degradation resistance. Fiz. Tekh. Poluprovodn. 33, 1115–1119 (September 1999)     

Analysis of radiative efficiency of long wavelength semiconductor lasers

An analysis of the spontaneous emission efficiency of laser diodes which yields C/B/sup 3/2/ where C and B are the Auger and radiative recombination coefficients, respectively, is proposed as a measure of the fundamental band structure and is applied to the temperature and pressure dependence of unstrained 1.5 mu m quantum well lasers.<>     

The performance of double active region InGaAsP lasers

The light-current characteristic and temperature behavior of the double-carrier-confinement (DCC) InGaAsP laser are shown to be largely determined by Auger recombination. The carrier distributions in the two active regions, especially their relative fractions, play a major role in device behavior. A self-consistent, comprehensive numerical laser model is used to analyze a set of devices showing that superlinearity and possibly bistability are due to saturable absorption in the second active region and that a high characteristic temperature is usually tied with a higher threshold current density because of substantial Auger recombination rates in this type of device     

Dynamic single-mode semiconductor lasers with a distributed reflector

Recent progress in the dynamic single-mode (DSM) semiconductor lasers in the wavelength of1.5-1.6mum are reviewed and the basic principle of DSM operation is given. Study of the DSM laser is originated for application to the wide-band optical-fiber communication in the lowest loss wavelength region of 1.5 to 1.65 μm. A DSM laser consists of a mode-selective resonator and a transverse-mode-controlled waveguide, such as the narrow-striped distributed-Bragg-reflector (DBR) laser, so as to maintain a fixed axial mode under the rapid direct modulation. The technology of monolithic integration for optical circuits is applied to realize some of DSM lasers. Structures, static and dynamic characteristics of lasing wavelength, output power, and reliability of the art DSM lasers are reviewed. The dynamic Spectral width of 0.3 nm, the output power of a few milliwatts, and the reliability over a few thousand hours are reported for experimental DSM lasers.     

Density-matrix theory of semiconductor lasers with relaxation broadening model-gain and gain-suppression in semiconductor lasers

The density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments. The dipole moment is given theoretically by thek . pmethod and is calculated for various semiconductor materials. As a result, gain and gain-suppression for a variety of crystals covering wide wavelength region are calculated. It is found that the linear gain is larger for longer wavelength lasers and that the gain-suppression is much larger for longer wavelength lasers, which results in that single-mode operation is more stable in long-wavelength lasers than in shorter-wavelength lasers, in good agreement with the experiments.     

905nm隧道带间级联非耦合双有源区半导体激光器

通过对有源区、波导层、限制层和隧道结的分析 ,设计了激射波长为905nm的隧道带间级联非耦合双有源区半导体激 光器。采用金属有机物化学汽相淀积(MOCVD)系统外延法生长了器件,并经过光刻、 腐蚀、解理和焊装等工艺,制备了激射波长为905nm的隧道带间级联 非耦合双有源区半导体激光器。腔面 未镀膜时,在1.2A的脉冲注入电流下,器件的峰值波长为904.4nm,垂直远场为单峰,发 散角为25.8°,表明两个有源区的光场未发生耦合,斜率效率为1.12W/A,为相同结构单有源区器件的1.9倍。     

Tunable semiconductor lasers: a tutorial

Tunable semiconductor lasers have been listed in numerous critical technology lists for future optical communication and sensing systems. This paper summarizes a tutorial that was given at OFC '03. It includes some discussion of why tunable lasers might be beneficial, an outline of basic tuning mechanisms, some examples of tunable lasers that have been commercialized, and a discussion of control techniques. More extensive data is given for the widely-tunable sampled-grating distributed-Bragg-reflector (SGDBR) type of laser, including data for such lasers integrated monolithically with modulators to form complete transmitter front ends. A summary of reliability data for the SGDBR laser is also given. It is concluded that tunable lasers can reduce operational costs, that full-band tunability is desirable for many applications, that monolithic integration offers the most potential for reducing size, weight, power and cost, and that sufficient reliability for system insertion has been demonstrated.     

Injection-locked semiconductor lasers with delayed optoelectronicfeedback

Optical injection and optoelectronic feedback are efficient techniques to externally control the spectral characteristics of a semiconductor laser. This paper presents theoretical and experimental results about the effects of a delayed optoelectronic feedback loop on the stability of an optically injected diode laser. In particular, negative feedback configurations (out-of-phase carrier reinjection) are shown to widen the injection-locking domain of the laser and reduce its unstable region. On the contrary, in positive feedback configurations (in-phase carrier reinjection), the laser diode generates a modulation with tunable multigigahertz frequency     

小发散角高功率半导体激光器研究

在量子阱半导体激光器中,量子尺寸引起的衍射效应使半导体激光器的光束质量很差。分别限制结构的垂直结平面发散角在40°左右,使得光束整形系统比较复杂,限制了半导体激光器的直接应用。为解决这一问题,提出了降低垂直结平面发散角的要求。回顾了小发散角半导体激光器的技术发展及应用,对具有小发散角的模式扩展波导结构进行了理论模拟和实验验证,获得了优化的结构。采用MOCVD外延技术生长了外延片,制作了高峰值功率脉冲激光器,获得了快轴发散角小于25,°峰值功率大于80W的半导体激光器,在激光引信应用中获得良好效果。     

Effect of the active region thickness on characteristics of semiconductor lasers based on asymmetric AlGaAs/GaAs/InGaAs heterostructures with broadened waveguide

The effect of the active region thickness on the basic characteristics of high-power semiconductor lasers based on AlGaAs/GaAs/InGaAs asymmetric separate-confinement heterostructures grown by MOCVD epitaxy has been studied. It is shown that the threshold current, temperature sensitivity of the threshold current density, internal quantum efficiency of stimulated emission, and differential quantum efficiency are improved as the active region thickness increases. It is demonstrated that the maximum attainable optical emission power of a semiconductor laser and the internal quantum efficiency of photoluminescence are the most sensitive to defect formation in the heterostructure and become lower as the critical thickness of the strained In_xGa_1–x As layer in the active region is exceeded.     

Study of the emission extraction efficiency of mesa-LEDs with a narrow-gap InAsSb active region

A series of light-emitting diodes (LEDs) (emission peak wavelength λ_max = 3.6 μm) with cone-shaped mesas, which have concave lateral surfaces and heights between 10 to 130 μm, has been developed. The dependence of the emission efficiency for these LEDs on mesa height has been studied at different injection currents at the temperatures 77 and 298 K. The form of the dependence observed is in agreement with the results of theoretical calculations. It is shown that the effective absorption coefficient, caused by emission extraction from the crystal, may be as large as 3 cm⁻¹ for LEDs with the highest mesa (130 μm) among the diodes in this series. The emission extraction coefficient is close to 30% at the temperature 298 K and 94% at 77 K.     

Q-switching of semiconductor lasers

A scheme forQ-switching semiconductor lasers is proposed and analyzed. The method is based upon electrooptic switching of the Bragg reflectivity of the grating reflectors forming the cavity of the semiconductor laser. The basic configuration, the operating principles, and the dynamic behavior of these lasers are described. Although the maximum initial inversion in this laser system is limited to a rather low value, the peak output power is found to be higher than the value usually obtained in a CW GaAs double-heterostructure (DH) laser by two orders of magnitude. A pulsewidth shorter than 100 ps is shown to be obtainable.     

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.     

Theoretical investigation on semiconductor lasers with passivewaveguides

Semiconductor lasers with vertically integrated passive waveguides are theoretically studied using the coupled mode theory and exact calculation. Formulas for the threshold current density and the far-field patterns are derived. The physical concepts of the modulation of the beam divergence by passive waveguides are given. The exact calculated results show that the beam divergence can be greatly improved by paying a price of only a slight increase of the threshold current density. The operation mode selection is discussed. Attention is also paid to the appearance of side lobes for very narrow far-field patterns. Discussions are given for device design     

长腔半导体激光器中的纵模行为

实验发现并从理论上证明腔长很长的质子轰击条形GaAs-GaAlAs激光器,能在阈值以上某较宽电流范围内实现稳定单纵模工作.     

Spectral characteristics of semiconductor lasers with optical feedback

Optical feedback-induced changes in the output spectra of several GaAlAs lasers operating at 0.83 μm are described. The feedback radiation obtained from a mirror 60 cm away from the laser is controlled in intensity and phase. Spectral line narrowing or broadening is observed in each laser depending on the feedback conditions. Minimum linewidths observed with feedback are less than 100 kHz. Improved wavelength stability is also obtained with optical feedback resulting in 15 dB less phase noise. An analytical model for the three-mirror cavity is developed to explain these observations.     

Analysis of the emission efficiency of powerful semiconductor lasers under closed-mode threshold lasing conditions

A new model describing the decrease in the emission efficiency and optical output power of a semiconductor laser above the lasing threshold of the Fabry-Perot mode is suggested. The mechanism of deterioration of the output-power characteristics is described in the suggested model in terms of the achievement of closed-mode threshold conditions. Rate equations are used to analyze how the closed-mode threshold conditions are satisfied in semiconductor lasers.