GB1485068A - Optical couplers - Google Patents

Abstract

1485068 Waveguide coupling; diffraction gratings INSTRUMENTS SA 20 Nov 1975 [20 Nov 1974] 47861/75 Heading G2J Coupling into thin waveguide layer 9 is performed by a reflection diffraction grating 8 disposed between the layer 9 and the substrate 5. In Fig. 2, grating 8 is formed in a layer 6, e.g. 100 microns thick, by copying in a resin from an original. A metal coating 7, e.g. 600 Š thick, is applied to layer 6. The original grating may be obtained by holograph printing of a photo-sensitive surface, or by engraving in a metal. An original grating may be used instead of a copy. Substrate 5 may be of "Pyrex" (Registered Trade Mark) and waveguide layer 9 may be a dielectric resin layer of a few microns thickness. Layer 9 is obtained by evaporation or "turntable" deposition' or by copying in situ in a polymerizable resin by a process similar to that used for mirror copies ( a drop of resin is squeezed by a flat mirror). Conditions for good coupling are given in terms of the grating pitch, the angle of incidence, the refractive index of layer 9, the refractive index of the substrate 5 and the wavelength of the light.