Improved operation characteristics of long-wavelength lasers using strained MQW active layers

Long-wavelength semiconductor lasers and amplifiers with strained MQW structures as active layer materials in the region of 1.48-1.55 μm are reported. Various improvements in device performance by employing the strained MQW structures were experimentally demonstrated in high-power operation at 1.48 μm, high-speed operation with narrow linewidth at 1.55 μm, and polarization-insensitive optical amplification in the 1.5 μm band. A compressively strained InGaAsP/InGaAsP MQW structure was used for high-power operation. The maximum power could be increased by introducing a compressive strain into the well layers, as theoretically predicted. This increase can be attributed to the suppression of Auger nonradiative recombination and intravalence band absorption. High-speed characteristics were tested on two different active layer materials. The compressively strained InGaAsP/InGaAsP MQW structure proved to be better than the strained InGaAs/InGaAsP MQW structure as an active layer material because of its high differential gain at low threshold current due to a smaller valence band density of states and small carrier life time. Compressively strained InGaAs/AlGaInAs MQW structure, having larger quantum confinements due to larger band offsets than the InGaAsP-based structures, were employed for the high-speed laser. The relaxation frequency was estimated to be 26 GHz, and a small linewidth enhancement factor of 1.5 was obtained. Polarization insensitive optical amplification in the semiconductor laser amplifiers (SLAs) was demonstrated by using the tensile strained MQW structure. The device length and strain were optimized for polarization insensitive amplification