Two-waveguide approach for monolithic active/passive photonic integration on GaAs

Monolithic integration of active and passive photonics is the next step in miniaturisation of semiconductor devices, to streamline their manufacturing and in doing so reduce their cost. However, Si’s inefficiency as a light emitter, and the high absorption from quantum wells or dots in III–V materials, requires that the two materials are heterogeneously integrated. This requires either regrowth or additional packaging steps, which add complication in scaling to mass manufacture, as well as high losses at material interfaces. This work proposes a solution whereby a monolithically grown GaAs/AlGaAs platform with both active and passive devices is achieved by using two vertically stacked waveguides, where only one of them contains quantum dots (QDs). In the gain section, where the InAs QDs emit light centred at 1300 nm, the waveguides are decoupled. By changing the relative environment of the two waveguides, light can be made to evanescently couple into the passive waveguide for low loss passive devices. This change can be brought about either by changing the local etch depth, or by the selective oxidation of Al 0.98 Ga 0.02 As underlayers. For the correct geometry, 94% of optical power can be successfully coupled between the active and passive waveguide. This coupling is simulated on FIMMPROP by Photon Design Ltd.