Fractional quasi-phase-matching by Fresnel birefringence

In order to reach the optical parametric oscillation in an isotropic semiconductor, it is of prime importance to enhance the nonlinear conversion efficiency per crystal length unity. In this letter, we describe the concept of fractional quasi-phase-matching which is theoretically shown to provide very high conversion yield, close to those of perfectly phase matched scenarios. The conceptual design in the case of second-harmonic generation is presented, along with predicted performances.