Optical processor for pulse train identification

• US 5,187,598 A
• Filed: 08/26/1991
• Issued: 02/16/1993
• Est. Priority Date: 08/26/1991
• Status: Expired due to Fees

• Current Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Posluszny, Thomas J., Davis, Dennis W.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): Parsons, David
• Application Number:
  US07/749,752
• Time in Patent Office: 540 Days
• Field of Search: 364/822, 359/29, 359/107, 359/558, 359/559, 359/561, 359/563, 324/77 K
• US Class Current: 359/29
• CPC Class Codes: G01R 23/17 with optical or acoustical auxiliary devices
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G06E 3/005 using electro-optical or opto-electronic means

Abstract

A pulse train in the presence of random noise and other pulse trains is identified by controlling pixels in a raster display in accordance with incoming signals; using the raster display to modulate a laser beam with the pulses; Fourier-transforming the modulated beam, then performing a Cartesian to polar coordinate transformation on the Fourier-transformed beam; inverse Fourier transforming the coordinate-transformed beam, and passing the result through a line spatial filter and focusing the filtered beam on a one-dimensional detector array.

Claims

1. An optical system for identifying a pulse train of signals present input pulse data containing a pulse train and other pulses, comprising:

an optical source means for transmitting an optical beam along an axis in a first direction;

a spatial light modulator means disposed along said axis or receiving said optical beam and for also receiving said input pulse data and for presenting an array of pixels in a raster display representing input pulse data, whereby said optical beam emerges from said spatial light modulator means as a modulated optical beam carrying a data pattern representative of said input pulse data;

a first Fourier transform lens means disposed along said axis for Fourier-transforming said modulated optical beam to an optical beam carrying a Fourier data pattern;

an OASLM means disposed along said axis for receiving said Fourier data pattern on a first side thereof and for storing said Fourier data pattern in a reflectivity pattern on a second side thereof representative of said optical beam carrying a Fourier data pattern;

means for directing a read optical beam along said axis in a second direction opposite said first direction, whereby said read optical beam is reflected from said second side of said OASLM means with a representation of said Fourier data pattern in said first direction as a read modulated beam; and

optical transformation means disposed along said axis in proximity to said second side of said OASLM means for performing a log-polar transformation on said Fourier data pattern, whereby pixels representing said pulse train are represented at an output plane disposed along said axis downstream of said OASLM means as a vertically oriented line of optical radiation displaced from said axis.

2. An optical system according to claim 1, further comprising a filter assembly disposed along said axis downstream of said output plane, said filter assembly comprising second and third Fourier transform lenses bracketing a line spatial filter, all disposed along said axis at positions such that the optical radiation represented at said output plane is filtered by said line spatial filter;

and

a cylindrical lens means disposed along said axis downstream of said filter assembly for focussing the optical radiation emerging from said line spatial filter onto a linear photodetector array oriented along a transverse axis, whereby the optical radiation is collapsed to an energy distribution along said transverse axis that produces a corresponding amplitude distribution in the output of said linear photodetector array.

3. An optical system according to claim 2, in which said optical transformation means comprises:

an amplitude mask disposed along said axis in proximity to said second side of said OASLM means and carrying a predetermined transform amplitude pattern;

a first phase mask disposed along said axis in proximity to said second side of said OASLM means and carrying a predetermined transform phase pattern, said amplitude and first phase masks each having a first side directed toward said OASLM means and an opposite second side;

a second Fourier transform lens means disposed along said axis for Fourier transforming said read modulated beam emerging from said amplitude and first phase mask to a second phase mask disposed along said axis and carrying a predetermined phase modulation pattern; and

a third Fourier transform lens means disposed along said axis for Fourier transforming radiation emerging from said second phase mask to said output plane, said amplitude mask, first phase mask and second phase masks carrying predetermined patterns adapted to perform said log-polar transformation.

4. An optical system according to claim 1, in which said optical transformation means comprises:

an amplitude mask disposed along said axis in proximity to said second side of said OASLM means and carrying a predetermined transform amplitude pattern;

a first phase mask disposed along said axis in proximity to said second side of said OASLM means and carrying a predetermined transform phase pattern, said amplitude and first phase masks each having a first side directed toward said OASLM means and an opposite second side;

a second Fourier transform lens means disposed along said axis for Fourier transforming said read modulated beam emerging from said amplitude and first phase mask to a second phase mask disposed along said axis and carrying a predetermined phase modulation pattern; and

a third Fourier transform lens means disposed along said axis for Fourier transforming radiation emerging from said second phase mask to said output plane, said amplitude mask, first phase mask and second phase masks carrying predetermined patterns adapted to perform said log-polar transformation.

5. An optical system for identifying a pulse train of signals present in input pulse data containing a pulse train and other pulses, comprising:

a laser means for transmitting a laser beam along an axis in a first direction;

a spatial light modulator means disposed along said axis for receiving said laser beam and for also receiving said input pulse data and for presenting an array of pixels in a raster display representing input pulse data, whereby said laser beam emerges from said spatial light modulator means as a modulated laser beam carrying a data pattern representative of said input pulse data;

a Fourier transform lens means disposed along said axis for Fourier-transforming said modulated laser beam to a laser beam carrying a Fourier data pattern;

an OASLM means disposed along said axis for receiving said Fourier data pattern on a first side thereof and for storing said Fourier data pattern in a reflectivity pattern on a second side thereof representative of said laser beam carrying a Fourier data pattern;

an amplitude mask disposed along said axis in proximity to said second side and carrying a predetermined transform amplitude pattern;

a first phase mask disposed along said axis in proximity to said second side and carrying a predetermined transform phase pattern, said amplitude and first phase masks each having a first side directed toward said OASLM means and an opposite second side;

means for directing a read optical beam along said axis in a second direction opposite said first direction toward said second sides of said amplitude and phase masks, whereby said read optical beam traverses said amplitude and first phase masks, is reflected from said second side of said OASLM means with a representation of said Fourier data pattern, and traverses said amplitude and first phase masks in said first direction as a read modulated beam;

a second Fourier transform lens means disposed along said axis for Fourier transforming said read modulated beam to a second phase mask disposed along said axis and carrying a predetermined phase modulation pattern;

a third Fourier transform lens means disposed along said axis for Fourier transforming radiation emerging from said second phase mask to an output plane disposed along said axis downstream of said second phase mask, said amplitude mask, first phase mask and second phase masks carrying predetermined patterns adapted to perform a log-polar transformation on said Fourier data pattern,

whereby pixels representing said pulse train are represented at said output plane as a vertically oriented line displaced from said axis;

a filter assembly comprising fourth and fifth Fourier transform lenses bracketing a line spatial filter, all disposed along said axis downstream of said output plane such that radiation at said output plane is filtered by said line spatial filter; and

a cylindrical lens means disposed along said axis downstream of said filter assembly for focusing radiation emerging from said line spatial filter onto a linear photodetector array oriented along a transverse axis, whereby the radiation distribution present at said output plane is collapsed to an energy distribution along said transverse axis that produces a corresponding amplitude distribution in the output of said linear photodetector array.