Asymmetric multiple-quantum-well heterostructure laser systems: conception, performance, and characteristics

A new type of laser diodes and amplifiers based on asymmetric quantum-well heterostructures having active layers of different thickness and/or compositions has been considered. Bistable switching and regimes of regular radiation pulsation at two or three remote wavelengths in the range of 790 to 850 nm in the GaAs-AlGaAs bi- and triple-quantum-well heterostructures are described. Influence of non-linear processes including gain suppression due to carrier heating on lasing regimes has been examined. Transformation of gain bands for TE and TM modes in dependence on the pump current has been studied for asymmetric four-quantum-well structures. The interval of tuning amplification wavelengths in the system reaches up to 70 nm. Keywords: quantum-well laser diodes, non-linear effects, bistability, regular pulsation, gain spectra

HgCdTe-based quantum cascade lasers operating in the GaAs phonon Reststrahlen band predicted by the balance equations method

HgCdTe-based quantum cascade lasers operating in the GaAs phonon Reststrahlen band with a target wavelength of 36 mkm are theoretically investigated using the balance equations method. The optimized active region designs, which are based on three and two quantum wells, exhibit a peak gain exceeding 100 cm(-1) at 150 K. We analyze the temperature dependences of the peak gain and predict the maximum operation temperatures of 170 K and 225 K for three- and two-well designs, respectively. At high temperatures (T > 120 K), the better temperature performance of the two-well design is associated with a larger spatial overlap of the weakly localized lasing wavefunctions as well as a higher population inversion

Эффекты насыщения усиления в квантово-каскадных лазерах ТГц-диапазона

The effect of gain saturation in quantum-cascade structures with 2–4 quantum wells per period is herein analyzed on the basis of a system of balance equations. It is shown that the nonlinearity parameter decreases with an increase in the relaxation rate of laser levels, but the total current through the structure also increases. The use of the proposed multiphoton designs leads to a decrease in the non-linearity parameter without increasing the operating current. For example, in a two-photon scheme of laser transitions with the same transition probabilities and differential gains, two times slower saturation of the gain with an increase in the photon density is achieved, which leads to a high generation efficiency than in single-photon schemes.На основе системы балансных уравнений проведен анализ эффекта насыщения усиления в квантово-каскадных структурах с 2–4 квантовыми ямами в периоде. Показано, что параметр нелинейности уменьшается при увеличении скорости релаксации лазерных уровней, но при этом растет полный ток через структуру. Использование предложенных многофотонных дизайнов приводит к уменьшению параметра нелинейности без увеличения рабочего тока. Например, в двухфотонной схеме лазерных переходов при одинаковых вероятностях переходов и коэффициентах дифференциального усиления достигается в 2 раза более медленное насыщение коэффициента усиления с ростом плотности фотонов, что обусловливает более высокую эффективность генерации, чем в однофотонных схемах

Spectral line broadening in quantum wells due to Coulomb interaction of current carriers

A theoretical analysis of emission line broadening due to Coulomb interaction of carriers is performed. An analytical approximation for the spectral line shape function with exponential decays is derived by using the perturbation theory for many-body electron–hole systems for both non-degenerate and degenerate conditions. An explanation of the experimentally observed spectral line asymmetry and the linewidth change as a function of the temperature and the excitation level is given