Within the ambitious quest for an electrically pumped version of the optical parametric oscillator (OPO), we demonstrate
the first near-infrared integrated OPO in a direct gap semiconductor. This nonlinear device is based on a selectively
oxidized GaAs/AlAs heterostructure, the same “AlOx” technology that is at the heart of VCSEL fabrication. The
heterostructure and waveguide design allows for type-I form-birefringent phase matching, with a TM00 pump around 1 μm and TE00 signal and idler around 2 μm. Relying on the high non-resonant χ(2) of GaAs, relatively weak guided-wave optical losses, and monolithic SiO2/TiO2 dichroic Bragg mirrors, we observe a threshold of 210 mW at degeneracy in the continuous-wave regime, with a single-pass-pump doubly resonant scheme. Further improvement can be achieved by adopting a double-pump-pass scheme and, in a more fundamental way, by further optimizing the waveguide optical
losses. The latter are induced by a not entirely mastered AlAs oxidation process and are of two distinct types: Rayleighlike
scattering at signal and idler wavelength (α ≤ 1cm-1), due to the interface roughness between GaAs and AlOx layers; and absorption at pump wavelengths (α ≈ 3cm-1), due to volume defects in the GaAs layers adjacent to the aluminum oxide. This result marks a milestone for integrated nonlinear photonics and represents a significant step toward the goal of a broadly tunable coherent light source on chip.