Influence of Facet Coating on the Dual Wavelength Operation of Asymmetric Ingaas–Gaas Quantum-Well Lasers

A low-reflectivity SiNyOz film was deposited on one facet of asymmetric In xGa1 - xAs–GaAs quantum-well (QW) laser diodes containing three different QW compositions with the indium fractions ${x}=0.25, 0.21$, and 0.15, located, respectively, from the n-doped to p-doped sides of the device. Lasing is only observed on the two higher In-content QWs. The reduction of the reflectivity of one facet, with the other as-cleaved, leads to an increase in the transition cavity length, below which the diode initially lases on the shorter wavelength QW $({x} = 0.21)$ at threshold and above which the diode lases on the longer wavelength QW $({x} = 0.25)$. No lasing occurs on the shortest wavelength QW $({x} = 0.15)$. With sufficient current injection simultaneous lasing on the two QWs is observed. When dual-wavelength emission occurs the facet reflectivity determines whether the short or long wavelength emitting QW lases first as the pump current is increased. A separation of up to 31 nm between the two wavelengths is observed under the dual wavelength emission conditions.