Spatial switching using a photoinduced holographic grating

The principles and design of wide-band space-division optical switching devices based on photoinduced holographic-grating matrices are discussed and illustrated. A 488-nm Ar laser is used to inscribe a series of gratings on thick phased arrays of Bi(12)SiO(20) (BSO) electrooptic monocrystals; these gratings are capable of directing collimated 840-nm semiconductor-laser beams from optical fibers to predetermined points on a receptor array. The physics of these phenomena are reviewed; and experimental results are reported on the effects of electrical field and the spatial frequency, the sensitivity of BSO at different wavelengths, the position of the inscribing beam, and the effect of the divergence of the reading beam. A 3-mm-thick crystal of BSO under a 6-kV/cm field inscribed for 20 msec at power density 10 mW/sq cm with a 5-micron-pitch grating can effectively direct 50-microW/sq cm beams for about 2-3 h before erasure. A technique for two-wavelength inscription is also demonstrated.