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Real Time Incoherent to Coherent Image Conversion

IP.com Disclosure Number: IPCOM000090272D
Original Publication Date: 1969-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Myers, RA: AUTHOR [+3]

Abstract

For many applications of optical information processing, a coherent optical image input is required. This is especially true if the Fourier transform of the object is to be passed through a matched spatial filter. Normally, such a coherent image is obtained from an opaque object at the expense of the time required to expose and develop a duplicate transparency of the object, since an opaque object usually destroys the coherence of an incident beam of light. In this method, the coherent image is obtained in real time and without the need for an intermediate hard copy.

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Real Time Incoherent to Coherent Image Conversion

For many applications of optical information processing, a coherent optical image input is required. This is especially true if the Fourier transform of the object is to be passed through a matched spatial filter. Normally, such a coherent image is obtained from an opaque object at the expense of the time required to expose and develop a duplicate transparency of the object, since an opaque object usually destroys the coherence of an incident beam of light. In this method, the coherent image is obtained in real time and without the need for an intermediate hard copy.

There are several possible methods which can be used for this conversion. All of them involve a key basic principle. The light from the incoherently illuminated object must be made to modulate the output of the coherent beam such that there is a one-to-one correspondence between the intensity of illumination and the depth of modulation. Drawing A shows an arrangement of such a device in which the incoherent image modulates the local reflectivity of an electro-optic mirror 10 on which a coherent beam is incident. Mirror 10 consists of a sandwich of photoconductor 12, dielectric reflecting mirror 14, electro-optic crystal 16, and ground plane 18. Free charges are deposited on the surface of photoconductor 12 and the bulk of the resultant electric field appears across crystal 16. For proper orientation of the crystal and sufficient deposited charge, the voltage induces one-quarter wave of phase retardation between the perpendicularly polarized components of an oncoming coherent light beam and thus causes the polarization of the beam to be rotated by 90 degrees after a double pass of the crystal. Hence, a coherent beam passing through polarizer 20 located in front of mirror 10 is extinguished on reflection from mirror 14 of sandwich mirror 10 and after a second pass through polarizer 20. The coherent beam can be a laser beam.

If light from an external, incoherently illuminated object is now allowed to impinge at a point on photoconductor 12, it increases the local conductivity of such photoconductor and allows the deposited charge to leak off through photoconductor 12, mirror 14, and crystal 16 to ground plane 18. Where charge leaks off, the voltag...