Optical waveguide structure including reflective asymmetric cavity

An optical waveguide structure comprising:

• a first layer of relatively low refractive index glass;
• a second layer of relatively high refractive index glass overlying the first layer;
• the second layer being patterned to define optical waveguide portions for propagating light along optical paths;
• a third layer of relatively high refractive index glass overlying the second layer;
• the third layer overlying a first end of a first waveguide portion defined by part of the second layer;
• and an asymmetric cavity extending through the third layer and at least part of the first layer which is adjacent the first end of the first optical waveguide portion and which intersects the optical path defined by the first waveguide portion, said cavity having a steeper slope on a first side thereof which is closest to the waveguide portion than on a second side thereof which is most remote from the waveguide portion;
• the second side of the asymmetrical cavity constituting a mirror surface which is capable of reflecting light to or from said first optical waveguide portion.