Abstract

Waveguide input-output couplers are key components in many integrated optical devices. Prism and grating couplers are two of the most commonly used types of waveguide couplers, but the characteristics of these components are highly wavelength-dependent. Both the coupling angle of an out-coupled beam and the coupling efficiency of an incoupled beam are strong functions of wavelength. For many applications these chromatic characteristics place tight constraints on the stability and bandwidth of the laser source that is used. In this paper a method to achromatize waveguide input-output couplers is described. The basic approach involves the use of an external diffraction grating to correct for the angular dispersion of the conventional coupler types. Two specific configurations are considered: a hybrid prism/grating coupler and a double-grating coupler. Expressions are derived for values of the grating parameters that produce achromatic coupling. It is shown that, for typical waveguide materials and performance specifications, double-grating couplers can be used to obtain an achromatic wavelength range of approximately 10 nm, and hybrid prism/grating couplers can potentially yield an achromatic range of the order of 200 nm.

© 1990 Optical Society of America