We demonstrate spatial filtering by using the azo-chromophore-based nonlinear optical effect of self-beam polarization modulation and optical threshold processing. The real-time image-processing scheme is described by use of an optical configuration composed of an action-beam probe-beam system, Fourier-transform operation, and an azo-chromophore-doped film as a spatial filter. As Disperse Red 1 dye (DR1) doped in an N -poly(vinylcarbazole) (PVK) film with N -ethylcarbazole (ECZ) of low glass-transition temperature exhibits self-polarization rotation after thin-film transmission, a linearly polarized probe beam in the film is observed, even through a crossed analyzer. In addition, this film permits optical threshold processing by introducing an action beam with different intensity and wavelength from those of the probe beam with object information. Changing the action-beam intensity results in a decrease or an increase in the transmitted probe-beam power through the analyzer. When a DR1 PVK ECZ film is placed at the Fourier plane on the probe-beam path, the filter functions can be modulated in real time by manipulation of the intensity ratio between the action beam and the spatial-frequency components at the film plane. The spatial frequencies of an original input image can be manipulated as they pass through the film. These effects are responsible for the photoisomerization of DR1 molecules in the low-glass-transition-temperature polymer matrix. 1998 Optical Society of America S0740-3224(98)02007-4

[Optical Society of America ]

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