Optical combiner/decombiner with reduced insertion loss

Abstract

A photonic integrated circuit that includes a plurality of active and passive components on a substrate where one of the components is an optical combiner/decombiner having at least one free space coupler region and a plurality of longitudinal ridge waveguides each extending in the circuit from a first region of the waveguide and coupled at a second region of the waveguide at the free space coupler region. A first dielectric layer formed over the ridge waveguides and the free space coupler region. The first dielectric layer monotonically increases in cross-sectional thickness from the waveguide first region to the second region to reduce signal insertion losses in transitioning from the ridge waveguides to the free space coupler region. The first dielectric layer may be covered with a second passivation layer. The first dielectric layer may be SiO, SiNor SiONand the second passivation layer may be BCB, ZnS or ZnSe.