Terahertz frequency conversion in bulk and quantum-well semiconductor lasers

Simulation results of frequency conversion up to the terahertz region in semiconductor laser devices, both in bulk and quantum-well structures, are presented with a comparison of traveling wave amplifiers and Fabry—Perot oscillators. In both devices conversion gains greater than 0 dB can be achieved with a proper parameter choice. Interesting features of the conversion gain spectra for the oscillator-converter are pointed out with a discussion of the performances.     

Thermal modeling of GaAs-based semiconductor disk lasers

Thermal characteristics including the temperature, the heat flux, and the temperature gradient of GaAs-based semiconductor disk lasers (SDLs) under various conditions are modeled using the finite element method. The effects of the substrate thickness, the pump spot radius, the heatspreader, and the pump power on the thermal properties of laser are simulated, and the maximum temperature rise in active region is highlighted. Numerical analysis predicts that SiC is an ideal substitute for diamond as a heatspreader. Instead of the sophisticated completely-etched substrate, the use of a high-thermal-conductivity heatspreader along with partly-etched substrate can provide sufficient thermal management to the laser.     

Degradation of high-power semiconductor quantum-well lasers

A mechanism of degradation of semiconductor quantum-well lasers with a stripe contact more than 50 µm wide is proposed. This mechanism implies formation of several lasing channels at a carrier ambipolar diffusion length smaller than the contact width. The carrier diffusion length decreases with time due to the increase in the number of defects; as a result, the number of lasing channels increases and lasing spectrum is filled. The shape of the lasing spectrum can be used to predict the laser service life.     

Microscopic simulation of semiconductor lasers at telecommunication wavelengths

We consider two GaAs-based laser materials emitting at telecommunication wavelengths, namely the dilute nitride (GaIn)(NAs) as well as Ga(AsSb), and model their optical properties by including scattering and dephasing on a microscopic basis. The theory shows an excellent agreement with experiment without the inclusion of fit parameters such as phenomenological scattering times. By careful comparison of measurements and computations, one can extract controversial bandstructure parameters such as the band offset.     

Experimental analysis of mode-hopping in bulk semiconductor lasers

In this work we experimentally study mode-hopping in bulk semiconductor lasers. This stochastic process is ruled by Kramers statistics with a decay rate depending on the laser parameters of the temperature of the substrate and the pumping current. For a general combination of these parameters the average residence times in the two active modes are not equal, resulting in an asymmetric probability distribution for the modal intensities. We show that, by choosing an appropriate path in the parameter space, we can vary the residence times of the two modes while holding their ratio constant. Along this path, the shape of modal intensities distributions are constant up to a scaling factor which is a function of the laser parameters. Then, the system can be described by a single Langevin equation. The effect of adding noise to the pumping current is also investigated. PACS 42.65.Sf; 42.55.Sa; 42.50.-p     

Second-harmonic generation in GaAs-based quantum-cascade lasers

We report second-harmonic (SH) and sum-frequency generation in GaAs-based quantum-cascade lasers. A doping dependence study of the second-order susceptibility in one of the investigated structure is shown. We also demonstrate that grating-coupled surface emission is a highly efficient way to couple out the SH radiation.     

Second-harmonic generation in GaAs-based quantum-cascade lasers

We report second-harmonic (SH) and sum-frequency generation in GaAs-based quantum-cascade lasers. A doping dependence study of the second-order susceptibility in one of the investigated structure is shown. We also demonstrate that grating-coupled surface emission is a highly efficient way to couple out the SH radiation.     

Second-harmonic generation in three-well and bound-to-continuum GaAs-based quantum-cascade lasers

We present efficient second-harmonic generation in state of the art GaAs-based quantum-cascade lasers with nonlinear output powers up to 100 μW. The nonlinear output was significantly improved by applying an AlGaAs waveguide structure, which guides both, the fundamental and nonlinear light. We further show the influence of the doping in the active region on the nonlinear light generation by comparing two similar structures with different doping levels. PACS 42.55.Px; 42.65.Ky; 81.05.Ea     

Generalised multiple-lateral-mode rate equation modelling of lasers with selective quantum-well intermixing for improved beam quality

A numerical model in terms of rate equations for lateral mode amplitudes for analysing static and dynamic properties of moderately broad stripe (tens of microns) laser diodes is proposed and used for modeling lasers with longitudinally or laterally intermixed passive areas. Introduction of passive diffractive regions is shown to offer some improvement of the laser beam, and the potential of further improvement of the beam by Intermixing lateral fringes along the stripe is discussed.     

Dynamic modelling of electrooptically modulated vertical compound cavity surface emitting semiconductor lasers

A generalized rate equation model is used to simulate the interrelated amplitude and frequency modulation properties of Electrooptically Modulated Vertical Compound Cavity Surface Emitting Semiconductor Lasers in both large and small signal modulation regimes. It is shown that the photon lifetime in the modulator subcavity provides the ultimate limit for the 3 dB modulation cutoff frequency. It is shown that there is an optimum design (number of periods) of both the intermediate and top multistack reflectors to maximise the large-signal modulation quality.     

Frequency-tunable semiconductor lasers

Recent advances in frequency-tunable semiconductor lasers are reviewed. They are classified into hybrid and monolithic tunable lasers. Monolithic tunable lasers based on distributed Bragg reflector or distributed feedback laser structures are most attractive for practical applications. The device structures and the tuning characteristics are described, with emphasis on the tuning range, spectral linewidth and frequency-switching time. Recent system experiments using monolithic tunable lasers in an optical communication area are also described.An Invited Paper     

可调谐半导体激光器研究及进展

可调谐半导体激光器是新一代密集波分复用系统以及全光网络中光子交换的关键光电子器件 ,它的运用使得光纤传输系统容量大大增加 ,灵活性和可扩展性大大增强 ,目前已经实现了宽波长范围的连续或准连续调谐 ,并有相应的产品投放市场 .文章介绍了各种基于不同谐振腔结构的可调谐激光器以及各自的调谐机理 ,对不同类型器件在制作以及实际应用中的优缺点进行了比较 .同时总结了国外可调谐半导体激光器的最新进展 ,并对我国可调谐半导体激光器的研制提出了相应的要求     

Carrier dynamics and gain saturation in quantum-well lasers

A Monte Carlo technique has been developed to investigate the carrier dynamics and static gain saturation in graded-index separate confinement heterostructure quantumwell laser structures. The calculated electron relaxation times and gain compression coefficient show good agreement with published experiments.     

Electron-phonon scattering in asymmetric semiconductor quantum-well structures

We calculate scattering rates of intrasubband and intersubband electronic transitions in asymmetric single quantum wells (QW's) and step QW's due to interface phonons, confined bulk-like LO phonons, and half-space LO phonons. The relative importance of the different phonon modes is analyzed. The results show that the electron-phonon scattering rates have intimate relation to the QW parameters.     

Gigahertz modulation of GaAs-based bipolar cascade vertical cavity surface-emitting lasers

The high-frequency modulation characteristics of GaAs-based bipolar cascade vertical cavity surface-emitting lasers operating at 980 nm with GaAs tunnel junctions and p-doped Al0.98Ga0.02As oxide apertures have been measured. We achieve -3 dB laser output modulations of 6.5 GHz for two-stage and 9.4 GHz for three-stage devices in response to small-signal current injection at an operating temperature of -50 degrees C.     

Diode-pumped bulk erbium-ytterbium lasers

A comprehensive review of the work done by our group, during the last few years, on diode-pumped cw operating bulk Er : Yb phosphate glass is presented. The high performance of this laser in terms of output power, laser slope efficiency, single longitudinal and transverse mode operation, laser tunability and frequency stability, amplitude noise, and active mode-locking operation, are considered. The combination of this high performance and potential low cost makes these laser devices attractive for a variety of applications including spectroscopy, metrology, optical radars, optical communications, and all optical switching.Prof. F. P. Schäfer on the occasion of his 65th birthday