Abstract
Waveguide coupling gratings are bound to be widely used in future integrated-optic devices and microsystems. However, the problem of grating coupling efficiency has not received a convincing and practicable solution so far. The main reason is that light radiation into a medium with lower refractive index nc (air, for instance) is always accompanied by light radiation into the medium with larger refractive index ns (substrate). The relative intensity of the radiation into the substrate is ns/nc or more. It is known that only coupling at an angle larger than critica1 provides high excitation efficiency; but this solution is difficult to implement in practice. Therefore the problem of unidirectional coupling, which has been constantly addressed during the last 20 years, remains very actual. Recently, a new and promising solution to this problem was proposed by M. Matsumoto [1] and by M. Li and S.Y. Sheard [2]. They consider light propagation in a waveguide having a grating with a parallelogram groove shape and obtain a definite "blazing effect", i.e. unidirectional light outcoupling from a waveguide.
© 1996 Optical Society of America
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