Design and numerical analysis of a polarization-insensitive quantum well optoelectronic integrated amplifier-switch

A quantum well optoelectronic integrated amplifier-switch is proposed, in which the device operation mode (amplification or switching) is independent of input light polarization. It is composed of a tensile-strained periodic coupled-double-quantum well heterojunction phototransistor and a compressive strained multi quantum wells laser diode. This structure shows unresolved heavy hole and light hole transitions due to applying tensile strain in absorption region of phototransistor. Hence, the absorption spectra for TE and TM polarizations are almost equal which provide polarization independent operation. A rigorous numerical analysis based on the device rate equations for dynamic response and relative intensity noise is presented, for which we calculate the laser diode gain and phototransistor electroabsorption coefficient. The Hamiltonian of strained quantum well structure is numerically solved by Transfer matrix method taking into accounts the valence band mixing between heavy hole and light hole. In order to calculate the electroabsorption coefficient, the exciton equation is solved numerically in momentum space using Gaussian Quadrature method. Langevin noise in laser part, phototransistor current noise, input power noise and noise due to the internal optical feedback from laser to phototransistor are considered as the device noise sources. It is shown that the higher gain of the phototransistor for TM polarization and lower threshold current of compressive strained laser diode lead to reduction of the RIN in amplification mode.