Optical correlator using light phase modulation and two reflective spatial light modulators

• US 5,523,881 A
• Filed: 06/07/1995
• Issued: 06/04/1996
• Est. Priority Date: 04/03/1992
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Boysel, R. Mark, Florence, James M.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Parker, Kenneth
• Application Number:
  US08/486,126
• Time in Patent Office: 363 Days
• Field of Search: 359/306, 359/243, 359/560, 359/561, 359/290, 359/291, 359/292, 359/847, 359/849, 359/1, 359/29, 359/107, 359/108, 364/210, 364/211, 364/278, 364/279, 364/280, 364/822, 364/826, 364/827, 364/819, 364/713, 382/211, 382/212, 382/209, 382/276, 382/278, 382/280
• US Class Current: 359/561
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G03H 1/08 Synthesising holograms, i.e. holograms synthesized from objects or objects from hologramsusing electric digital computers G06F; G06T
• CPC Class Codes: G03H 1/0841 Encoding method mapping the synthesized field into a restricted set of values representative of the modulator parameters, e.g. detour phase coding
• CPC Class Codes: G03H 1/2294 Addressing the hologram to an active spatial light modulator
• CPC Class Codes: G03H 2001/0066 for wavefront matching wherein the hologram is arranged to convert a predetermined wavefront into a comprehensive wave, e.g. associative memory recognition using holographic masks G06V10/88
• CPC Class Codes: G03H 2001/085 Kinoform, i.e. phase only encoding wherein the computed field is processed into a distribution of phase differences
• CPC Class Codes: G03H 2001/0858 Cell encoding wherein each computed values is represented by at least two pixels of the modulator, e.g. detour phase coding
• CPC Class Codes: G03H 2223/13 Phase mask
• CPC Class Codes: G03H 2225/24 Having movable pixels, e.g. microelectromechanical systems [MEMS]
• CPC Class Codes: G03H 2225/31 Amplitude only
• CPC Class Codes: G03H 2225/32 Phase only
• CPC Class Codes: G03H 2225/55 Having optical element registered to each pixel
• CPC Class Codes: G03H 2240/41 Binary
• CPC Class Codes: G03H 2240/42 Discrete level
• CPC Class Codes: G09F 9/372 the positions of the elements being controlled by the application of an electric field

Abstract

An optical signal processor which employs a coherent light source, two spatial light modulators and a beam splitter. Light is from the source is reflected from the beam splitter and sent to a first spatial light modulator, then sent through the beam splitter, a Fourier transform is performed and the transformed light is then reflected from the second spacial light modulator. The light form the second spacial light modulator is then inverse transformed and returned to the beam splitter where it is reflected to a readout detector. The signal read out is the correlation map between an input image from the first modulator and a filter image of the second modulator.

Claims

1. An optical signal processor operable to receive coherent light from a coherent light source, said optical signal processor comprising:

a. an optical transmissive/reflective element that is operable to receive said coherent light from said coherent light source and to substantially reflect said coherent light;

b. a first spatial light modulator operable to receive said coherent light from said transmissive/reflective element and to modulate an input image onto said coherent light to form a modulated light signal comprising said input image modulated upon said coherent light, said first spatial light modulator further operable to direct said light signal toward said transmissive reflective element, which allows a substantial amount of said modulated light signal to pass through it;

c. a first transformer operable to receive said modulated light signal and to perform a first domain transformation thereupon;

d. a second spatial light modulator operable to receive said transformed, modulated light signal and to modulate a filter image thereupon to form a filtered/transformed signal, said second spatial light modulator comprising

i. a first modulating element switchable between at least two discrete, addressable states;

ii. a second modulating element, switchable between at least two discrete, addressable states, said second modulating element being adjacent to said first modulating element and formed such that said second modulating element will effect a phase difference between light incident thereon and light incident on and acted upon by said first modulating element, the responses from said first and second modulating elements being combinable into a single response having a phase state that is one of a plurality of discrete phase states that are dependent upon the addressed states of said first and second modulating elements; and

e. a second transformer operable to receive said filtered/transformed signal and to perform a second domain transformation thereupon, said second domain transformation being the inverse of said first domain transformation, resulting in an output correlation signal.

2. The optical signal processor of claim 1 and further comprising an optical detector that is operable to receive said output correlation signal and provide an optical correlation map that shows the degree of correlation between the input image and the filter image.

3. The optical signal processor of claim 1 wherein said coherent light source is a laser diode.

4. The optical signal processor of claim 1 wherein said optical transmissive/reflective element operates to reflect light of one polarization, and transmit light of another polarization.

5. The optical signal processor of claim 4 and further comprising a polarizer interposed between the coherent light source and the optical transmissive/reflective element whereby the coherent light passing therethrough is imparted with the needed polarization to be reflected toward said first spatial light modulator by the transmissive/reflective element.

6. The optical signal processor of claim 1 wherein said optical transmissive/reflective element is comprised of a plurality of discrete reflective elements operable to direct light from said coherent light source to said first spatial light modulator to said first transformer and from said second spatial light modulator to said second transformer.

7. The optical signal processor of claim 1 wherein said spatial light modulators are deformable mirror devices.

8. An optical signal processor operable to receive coherent light from a coherent light source, said optical signal processor comprising:

a. an optical transmissive/reflective element that is operable to receive said coherent light from said coherent light source and to substantially reflect said coherent light;

b. a first deformable mirror device operable to receive said coherent light from said transmissive/reflective element and to modulate an input image onto said coherent light to form a modulated light signal comprising said input image modulated upon said coherent light, said first spatial light modulator further operable to direct said light signal toward said transmissive reflective element, which allows a substantial amount of said modulated light signal to pass through it;

c. a first lens operable to receive said modulated light signal and to perform a first domain transformation thereupon;

d. a second deformable mirror device operable to receive said transformed, modulated light signal and to modulate a filter image thereupon to form a filtered/transformed signal, said second deformable mirror device comprising

i. a first deformable mirror switchable between at least two discrete, addressable states;

ii. a second deformable mirror switchable between at least two discrete, addressable states, said second deformable mirror being adjacent to said first deformable mirror and formed such that said second deformable mirror will effect a phase difference between light incident thereon and light incident on and acted upon by said first deformable mirror, the responses from said first and second deformable mirrors being combinable into a single response having a phase state that is one of a plurality of discrete phase states that are dependent upon the addressed states of said first and second deformable mirrors; and

e. a second lens operable to receive said filtered/transformed signal and to perform a second domain transformation thereupon, said second domain transformation being the inverse of said first domain transformation, resulting in an output correlation signal.

9. The optical signal processor of claim 8 and further comprising an optical detector that is operable to receive said output correlation signal and provide an optical correlation map that shows the degree of correlation between the input image and the filter image.

10. The optical signal processor of claim 8 wherein said optical transmissive/reflective element operates to reflect light of one polarization, and transmit light of another polarization.

11. The optical signal processor of claim 8 and further comprising a polarizer interposed between the coherent light source and the optical transmissive/reflective element whereby the coherent light passing therethrough is imparted with the needed polarization to be reflected toward said first deformable mirror device by the transmissive/reflective element.

12. The optical signal processor of claim 8 wherein said optical transmissive/reflective element is comprised of a plurality of discrete reflective elements operable to direct light from said coherent light source to said first spatial light modulator to said first transformer and from said second spatial light modulator to said second transformer.