Design of polarization-insensitive Bragg gratings in zero-birefringence ridge waveguides

In this paper, we address the problem of designing polarization-insensitive Bragg gratings in zero-birefringence ridge waveguides. It is known that the reflection spectrum of a Bragg grating will be polarization-independent if both the phase-matching condition and the coupling coefficient are polarization-independent. While the use of a zero-birefringence waveguide can guarantee a polarization-independent phase-matching condition, it does not in general lead to a polarization-independent coupling coefficient. Our theoretical analysis indicates, however, that a strictly polarization-independent coupling coefficient is not essential for the achievement of a polarization-insensitive Bragg grating. Our detailed calculations on both corrugation and phase gratings in zero-birefringence ridge waveguides reveal some general design principles. Our results should be useful for the design of a wide range of Bragg-grating-based waveguide devices.