Design to minimize aberrations of focusing grating coupler under wavelength shift

An optical disk write/read head using integrated optics has been demonstrated by S. Ura et al.1 Figure 1 is a schematic drawing of a typical device.2 The light is emitted from a laser diode at one end of the slab (Point R1). The light is trapped in an optical film on the slab and travels in the form of a guided wave in one dimension. The light is diffracted by a grating which consists of modulation in the depth of the film or variation in the index. One order of the diffracted light comes to a focus at Point R2.