Polarization Independent Coupling In Prism- And Grating-Loaded Optical Waveguides

Abstract

Computer simulations indicate that polarization independent coupling can be achieved in both prism-and grating-loaded optical waveguide consisting of dielectric multilayers supported by a metal plate. It is shown that a double-layer dielectric structure supported by a metal plate can be designed to achieve the phase matching between TE and TM guided waves. At optical frequencies, a metal, such as silver, behaves like a plasma medium with a negative dielectric constant, and a simple metal-dielectric interface can support a surface plasmon mode. The mutual effects of the guided modes and the plasmon mode are examined in detail. Furthermore, both prism and grating are considered for use in conjunction with the waveguide structure to provide the coupling mechanism, which is explained on the basis of leaky-wave phenomenon. The composite waveguide structure, including either a prism or a grating, is analyzed as a rigorous boundary-value problem. The propagation constant, including both phase and attenuation constants, is obtained as the real and imaginary parts of a complex eigenvalue of the waveguide. It is shown that the phase and attenuation constants of TE and TM modes can both be matched. Thus, high-efficiency polarization-independent couplers can indeed be designed.