Fabrication of optical logic device using GaAs/AlGaAs double heterostructure lasers

Abstract

Optical logic device using cross coupling of two semiconductor lasers with GaAs/AlGaAs double heterostructures is proposed. In the proposed device, the two laser cavities are placed crossed at right angles and the carrier density profile in the crossed area is shared. The internal photon density of one laser cavity interacts with that of the other through the shared carrier density profile. The interaction mechanism is optical quenching. Nonlinear quenching characteristics are introduced by separation of the electrode of the control laser. As laser mirrors, rooftop reflectors are employed which makes possible integration of laser diodes, overcoming the limit of the cleaved mirror of crystal facet for discrete devices. By employing the rooftop reflectors, input light and output light can be separated and give complimentary outputs. Rooftop reflectors have characteristics of total internal reflection and improves the energy efficiency of the laser via minimization of mirror loss. Semiclassical approach is used to model the proposed optical logic device. Operation characteristics are calculated from the Maxwell-Bloch equations at the control laser. It is found that the interaction factor decreases where the shared carrier density is exhausted by the large photon density of the control laser and that there is hardly any more interaction for large photon density of the control laser. The initial interaction factor is determined by the width of the intersection region. Bistable characteristics are obtained for large values of the initial interaction factor. The proposed optical logic circuit is fabricated. Fabrication process of the rooftop reflector is improved through simultaneous etching of the window of contact stripe and the window of rooftop reflector etching, which leads to lowering of threshold current density. The fabricated device performs nonlinear quenching operation as well as linear quenching operation and the efficiency of logic operation through n...