Abstract: One embodiment provides an apparatus for displaying an image comprising: a first optical substrate comprising at least one waveguide layer configured to propagate light in a first direction, wherein the at least one waveguide layer of the first optical substrate comprises at least one grating lamina configured to extract the light from the first substrate along the first direction; and a second optical substrate comprising at least one waveguide layer configured to propagate the light in a second direction, wherein the at least one waveguide layer of the second optical substrate comprises at least one grating lamina configured to extract light from the second substrate along the second direction; wherein the at least one grating lamina of at least one of the first and second optical substrates comprises an SBG in a passive mode.

Abstract: The invention provides a process for the preparation of ortho- and para-hydroxybenzyl cyanides. The process of the invention comprises the reaction of an aromatic alcohol selected from ortho- and para-hydroxybenzyl alcohols with a cyanide reagent and an ester capable of esterifying the hydroxyl group of the benzyl alcohol.In a preferred form of the process there is employed a route via the reaction of an ortho- or para-hydroxybenzyl formate with a cyanide reagent preferably selected from sodium and potassium cyanides.