Optical image processing and optical implementation of binary logic operations are very interesting area in optics. In recent decades, various mathod of optical image processing and optical logic gate are represented. Photoinduced anisotropy(PIA) is one of the attractive candidates for optical image processing. In this theses, the characteristics of PIA in amorphous $As_2S_3$ thin film and their applications in optical image processing are investigated. Coherent method using polarization hologram and incoherent method using PIA induced by incoherent beam are studied in details.
In the coherent method, the polarization hologram which is constructed by interference of orthogonal polarizations is recorded on amorphous $As_2S_3$ thin film and their diffraction characteristics are investigated. Ar ion laser beam(λ =514.5nm) and He-Ne laser beam(λ=632. 8nm) are used to record and read the polarization hologram, respectively. When two recording beams have orthogonal linear polarization, the diffraction efficiency is not depended on polarization angle of linar polarized reading beam but the polarization of diffracted beam are strongly depended on the polarization of reading beam. On the contrary, only diffraction efficiencies are given by a function of reading beam polarization, when two recording beam have orthogonal circular polarization. From these result, two inputs, A and B, are recorded at a point on the amorphous $As_2S_3$ thin film by using orthogonal circular polarization, and image A and B are selectively reconstructed at the proper polarization state of the reading beam. By using polarization behavior of polarization hologram which is constructed by orthogonal linear polarization, logic gates such as XOR, AND etc are suggested and experimented.
From the diffraction efficiencies of polarization hologram, photoinduced birefringence, Δn=nx-ny, of amorphous $As_2S_3$ thin film are determined. When anisotropy is induced by 200mW/$cm^2$ Ar ion laser beam(λ =514. 5nm), the saturation value of the birefrengence is found to be $2.8\pm 0.3 \times 10^{-3}$ at He-Ne laser wavelength( λ =632.8nm).
In the incoherent methods, spatial light modulator(SLM) using PIA is fabricated and applied to addition and subtraction of two images. In this method, two images are recorded by incoherent Ar ion laser beams which are linearly polarized and have different polarization angle. They are reconstructed by using a linearly polarized reading beam passing through $As_2s_3$ thin film and analyzer. In this SLM, the transmission axis of the polarizer is perpendicular to the polarization of the reading beam.
Boolean logic operations are optically implemented by using photoinduced anisotropy in amorphous $As_2S_3$ thin film. The logic gate consists of a pair of π/2 crossed polarizers and two binary inputs which are encoded by photoinduced anisotropy. The encoding is made by using Ar ion laser beam and the logic operation is read by He-Ne laser beam. The analytic expressions of the output intensities of the reading beam are derived in terms of the third-order nonlinear susceptibilities of the thin film and the polarization angle of the reading beam. The experiment is carried out for two binary inputs placed between a polarizer and an analyzer. All sixteen Boolean logic operations are realized upon thresholding the reading beam intensity at the output plane.
