Abstract: An optical coupler comprises first and second mirrors. The first mirror is positioned with respect to the second mirror so that a resonant cavity is defined between them. A waveguide structure is positioned in the resonant cavity and includes a photonic crystal coupler. A thickness of the resonant cavity is selected so that a phase matching condition is satisfied for resonance in the resonant cavity. At least one of the first and second mirrors may be formed from a structure in an optoelectronic device. Alternatively, at least one of the first and second mirrors is formed from a semiconductor layer. At least one of the first and second mirrors may be formed as a semiconductor distributed bragg reflector, or as a dielectric distributed bragg reflector. At least one of the first and second mirrors may be a mirror in a vertical cavity surface emitting laser (VCSEL) structure.