ACHROMATIC WAVE-GUIDE COUPLERS

Achromatic prism/grating and double-grating waveguide input/output couplers are fabricated. The chromatic characteristics of these couplers are measured and are compared with those of conventional prism and grating couplers. The waveguides used consisted of Corning 7059 on a Pyrex substrate, and the prism material was Schott SF1. The experimental results are in excellent agreement with theoretical predictions and demonstrate that as much as several orders of magnitude improvement in the usable wavelength range relative to the uncorrected couplers can be achieved. For the achromatic prism/grating coupler, a usable wavelength range of 33 nm is demonstrated given a tolerance on the coupling angle of +/-0.005-degrees. For the double-grating coupler configuration, the usable range is found to be 12 nm. The corresponding intervals for the uncorrected prism and grating couplers are 6 and 0.08 nm, respectively.