Planar waveguide structure with tightly curved waveguides

A waveguide structure comprising:

• a substrate;
• an integrated waveguide, defined by a core surrounded by cladding supported by the substrate, comprising:
• a first straight waveguide for receiving an optical signal for propagation in a direction of propagation;
• a curved waveguide having a local radius of curvature, an input optically coupled to the straight waveguide, and an output;
• and
• a second straight waveguide optically coupled to the output of the curved waveguide and for the optical signal propagated through the first straight waveguide and curved waveguide;
• and,
• a plurality of first trenches spaced apart in the direction of propagation disposed in the cladding along a first side of at least the curved waveguide, the first trenches disposed substantially the same distance from the curved waveguide, the plurality of spaced apart first trenches defining trenched and untrenched sections of the cladding, whereby light in the curved waveguide propagates alternately past trenched and untrenched sections, the trenched sections having a material within where the material has a lower index of refraction than at least one of a waveguide core of the curved waveguide and a waveguide cladding of the curved waveguide, at least some of the plurality of first trenches disposed to provide enhanced confinement of the optical signal in a region proximate the curved waveguide, said enhanced confinement being higher than a confinement of the curved waveguide absent said trenches.