Waveguide mirror and method of fabricating a waveguide mirror

A mirror is fabricated by providing a silicon-on-insulator substrate, the substrate comprising: a silicon support layer 103; a buried oxide (BOX) layer 102 on top of the silicon support layer; and a silicon device layer 101 on top of the BOX layer. A via (see figure 4b) which extends to the BOX layer is created in the silicon device layer. A portion of the BOX layer is etched starting at the via and extending laterally away from the via in a first direction to create a channel between the silicon device layer and silicon support layer. An anisotropic etch creates a cavity 105 underneath an overhanging portion of the silicon device layer. The overhanging portion defines a planar underside surface 106 for vertically coupling light into and out of the silicon device layer. A metal coating is applied to the underside surface. Alternatively a mirror may be made by creating a V-groove within the silicon device layer (see figures 6-8). A protective nitride layer (114, figure 4f) is also used to protect the box layer when producing a mirror with only one planar underside (106, figure 4o).