An investigation into methods for achromatizing the coupling angle characteristics of waveguide input/output couplers is described. The basic approach involves correcting the inherent angular dispersion of conventional waveguide couplers with a diffraction grating. Two configurations are analyzed in detail: a hybrid prism/grating coupler and a double grating coupler. Expressions are derived for values of the grating parameters that produce achromatic coupling. A method is also presented to predict the achromatic wavelength range and maximize it with the available degrees of freedom. For a coupling angle tolerance of 0.005°, it is found that with double grating couplers achromatic wavelength ranges of the order of 10 nm can be obtained, and that with prism/grating couplers this range can be as large as 200 nm.
© 1991 Optical Society of America
Original Manuscript: January 23, 1990
Published: March 20, 1991
Kevin E. Spaulding and G. Michael Morris, "Achromatic waveguide input/output coupler design," Appl. Opt. 30, 1096-1112 (1991)