Rand C. Sherman

Hybrid incoherent optical pattern recognition system

A pattern recognition system that uses incoherent spatial filtering to recognize images directly from a narrowband phosphor television monitor is described. Images of real objects are captured with a television camera. These images are then edge-enhanced electronically and displayed on the TV monitor. The monitor output is used directly as the input to a holographic correlator. An optical multichannel analyzer at the correlation plane is used to analyze the shape of the correlation function and to determine the position of its peak. Experimental results agree well with theory. Concepts for handling rotation, aspect angle, and scale variations of the input are discussed.

Optical erasure of one- and two-photon holograms in fe-doped linbo3

Abstract The dynamics of erasure of holographic gratings formed by one-photon and two-photon photorefractive processes in iron-doped (150 ppm) LiNbO3 have been studied as a function of wavelength of the erasing light. For a given wavelength and intensity of this light, the time constant for erasure of holograms recorded at 0.61 μm by a two-photon process is similar to that for erasure of one-photon holograms of the same grating spacing recorded at 0.488 μm. Thus the same ultimate traps appear to be involved in both recording processes. The minimum photon energy required to empty these traps is not greater than 1.9 eV. Rapid erasure occurs when the photon energy is above 2.35 eV.

Infrared holographic gratings in lithium niobate optical waveguides by a two-step process

Abstract Holographic gratings with diffraction efficiencies ranging up to 25% can be formed by intersecting cw infrared beams of 1·06 μm wavelength light in single-mode titanium-indiffused LiNbO3 optical waveguides, provided that the guide has been sensitized by passing a broad beam of relatively high intensity red light through it prior to introducing the infrared beams. Such gratings are stable in the dark for at least 24 hours, but can be erased by exposure to a guided beam of visible light. Holograms of diffraction efficiencies of up to 25% can also be formed without the visible-light sensitization step if high-intensity pulses of 1·06 μm light are used. The sensitivity of these holographic recording phenomena appears to vary from wave-guide and from point to point within a given waveguide.

Optical erasure of one- and two-photon holograms in lithium niobate

Abstract The dynamics of optical erasure of holographic gratings formed by one-photon and two-photon photorefractive processes in iron-doped (150 ppm) LiNbO3 have been studied as a function of wavelength of the erasing light. At a given erasing wavelength and intensity, the time constant for erasure of holograms recorded at 0.61 μm by a two-photon process is similar to that for erasure of one-photon holograms of the same grating spacing recorded at 0.488 μm; thus the same ultimate traps appear to be involved in both recording processes. The minimum photon energy required to empty these traps is not greater than 1.9 eV. Rapid erasure occurs when the photon energy is above 2.35 eV. These results will be compared with erasure dynamics in nominally undoped LiNbO3, and with the recording dynamics in the doped and undoped materials; and the implications for photorefractive recording mechanisms will be discussed.