Method and apparatus for improving acousto-electric scanning

• US 3,944,732 A
• Filed: 02/12/1975
• Issued: 03/16/1976
• Est. Priority Date: 02/12/1975
• Status: Expired due to Term

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Inventors: Kino, Gordon S.
• Primary Examiner(s): Libman, George H.
• Assistant Examiner(s): Godfrey, R. John
• Application Number:
  US05/549,380
• Time in Patent Office: 398 Days
• Field of Search: 178/7.6, 178/7.1, 178/DIG. 18, 310/9.8, 310/8.1, 333/30 R, 333/72
• US Class Current: 348/198
• CPC Class Codes: H04N 3/10 by means not exclusively optical-mechanical H04N3/36 takes precedence

Abstract

An acoustically scanned, optical imaging system for converting patterns of light into electrical signals. The system includes a monolithic convolver that scans incident light patterns using two counter propagating acoustic waves. Located in front of the convolver is an opaque grid that places a spatial periodicity into the light patterns. When the frequencies of the two acoustic waves propagating in the convolver are selected so that the difference between them is a function of the spatial periodicity placed in the light patterns, the minimum threshold signal or dark current from the convolver is substantially reduced. The imaging system also includes four alternative signal generating and processing circuits that can provide a one dimensional scan, a fast Fourier transform and a Fresnel transform of the light patterns incident on the convolver. Patterns of colored light also can be convolved into electrical signals by using colored filters as the grid.

Claims

1. Apparatus for detecting the information present in the light from an optical image by acoustically scanning the charge carrier density perturbations in a semiconductor body, comprising:

a. a photosensitive semiconductor body that produces charge carrier density perturbations corresponding to the information in the light that impinges on the semiconductor body, said body having first and second ends;

b. a piezoelectric layer having first and second ends corresponding to the first and second ends of the semiconductor body, said piezoelectric layer propagates acoustic waves between its first and second ends;

c. an intermediate layer of electrically insulated solid material located between the semiconductor body and the piezoelectric layer and in direct physical contact therewith said intermediate layer controlling the number of surface states at the surface of the semiconductor body;

d. a first input electrode on said piezoelectric layer adjacent to the first end of the semiconductor body for generating a first acoustic wave in one direction past the semiconductor body;

e. a second input electrode on said piezoelectric layer adjacent to the second end of the semiconductor body for generating a second acoustic wave in an opposite direction past the semiconductor body, said first and second acoustic waves nonlinearly interact and scan the charge carrier density perturbations in the semiconductor body; and

f. output electrode means on said apparatus for obtaining electrical output signals corresponding to the charge carrier density perturbations in the semiconductor body, whereby the information present in the light is detected.

2. The apparatus of claim 1 wherein said intermediate layer overlies the semiconductor body so that a low density of surface states in the semiconductor body is provided at the innerface therebetween and so that the semiconductor body is protected from contamination during manufacture of the apparatus.

3. The apparatus of claim 1 further including a shielding pad underlying each input electrode and overlying the semiconductor body so that acoustic wave energy loss by interaction with the semiconductor body is reduced.

4. The apparatus of claim 1 wherein the output electrode means includes a first output electrode located on the exposed surface of piezoelectric layer and a second output electrode located on the exposed surface of the semiconductor body.

5. The apparatus of claim 1 wherein said semiconductor body is fabricated from silicon, said piezoelectric layer is fabricated from zinc oxide, and said intermediate layer is fabricated from silicon dioxide.

6. The apparatus of claim 1 wherein said semiconductor body is fabricated from indium antimonide.

7. The apparatus of claim 1 wherein said piezoelectric layer is fabricated from cadmium sulfide.

8. The apparatus of claim 5 wherein the intermediate layer further includes a layer of silicon nitride deposited on the silicon dioxide.

9. The apparatus of claim 5 wherein the intermediate layer further includes a layer of phosphorous glass deposited on the silicon dioxide.

10. A monolithic convolver for converting incident light images into corresponding electrical signals by acoustic scanning, comprising:

a. a photosensitive semiconductor substrate wherein the incident light generates corresponding perturbations in the charge carrier density of the substrate;

b. a transparent piezoelectric layer through which the incident light is transmitted;

c. means for generating counterpropagating acoustic surface waves that travel through the piezoelectric layer and nonlinearly interact, said waves acoustically scan the perturbations in charge carrier density of the substrate;

d. an intermediate layer of electrically insulated solid material sandwiched between the piezoelectric layer and the semiconductor substrate, said piezoelectric layer being located sufficiently close to the substrate that the acoustic surface waves interact with the perturbations in the charge carrier density; and

said intermediate layer controlling the number of surface states at the surface of the semiconductor body;

e. means for obtaining electrical output signals from said counterpropagating acoustic surface waves in the piezoelectric layer, whereby the incident light images are converted into corresponding electrical signals.

11. The monolithic convolver of claim 10 further including:

a. an optical grid of uniformly spaced apart opaque elements that place a spatial periodicity l into the light before said light reaches the semiconductor substrate; and

b. means for predetermining the frequencies of said counterpropagating waves such that the difference between said frequencies substantially equals an integral multiple of the periodicity introduced into the incident light.

12. An improved acousto-electric convolver for converting incident light images into corresponding electrical signals by acoustic scanning of the type having a photosensitive semiconductor body that produces conductivity perturbations therein corresponding to the incident light images, a piezoelectric layer for counterpropagating acoustic waves past the semiconductor body, means for generating said acoustic waves in the piezoelectric layer, and output means on said piezoelectric layer for converting the acoustic waves into electrical output signals, the improvement comprising:

a. means located in front of the semiconductor body for introducing a spatial periodicity into the incident light before said light reaches the semiconductor body; and

b. means for generating said acoustic waves with predetermined frequencies such that the difference between said frequencies substantially equals an integral multiple of the periodicity introduced into the incident light.

13. The apparatus of claim 12 wherein said spatial periodicity introducing means includes an optical grid of uniformly spaced apart opaque elements that block the incident light before it reaches the semiconductor body.

14. The apparatus of claim 12 wherein the spatial periodicity introducing means places a period l into the incident light and the acoustic wave generating means predetermines the waves such that (ω

₁ - ω

₂) l/V = 2Nπ

where N is any integer, V is the acoustic velocity of the waves in the piezoelectric layer, and ω

₁, ω

₂ are the respective frequencies of the acoustic waves.

15. An improved acousto-electric convolver for converting incident light images into corresponding electrical signals by acoustic scanning of the type having a photosensitive semiconductor body that produces conductivity perturbations in the charge carrier density corresponding to the light images, a piezoelectric layer, the semiconductor body, means for generating said acoustic waves in the piezoelectric layer, and output means on said piezoelectric layer for converting the acoustic waves into electrical output signals, the improvement comprising:

a. means located in front of the semiconductor body for introducing a Fourier component with an effective wave number K into the charge carrier density of the semiconductor body; and

b. means for generating in the piezoelectric layer said acoustic waves with propagation constants K, and K₂ predetermined such that

space="preserve" listing-type="equation">K.sub.1 - K.sub.2 ±

K = 0

where K is said effective wave number of the Fourier component.

16. The improved convolver of claim 15 wherein said Fourier component introducing means includes an optical grid of uniformly spaced apart opaque elements, said elements having a spacing of distance l and wherein said propagation constants K₁, and K₂ are predetermined such that ##EQU16##

17. The improved convolver of claim 15 further including means for spacing said Fourier component introducing means from the piezoelectric layer such that said introducing means does not electrically interact with said acoustic waves.

18. A method for converting incident light images into corresponding electrical signals by acoustic scanning, comprising the steps of:

a. impinging the incident light onto a photosensitive semiconductor body wherein conductivity perturbations are produced corresponding to the image;

b. introducing a spatial periodicity of period l into the incident light before said light impinges on the semiconductor body;

c. scanning the semiconductor body with nonlinearly interacting counterpropagating acoustic waves having predetermined frequencies, said waves correspondingly interact in accordance with the charge carrier density perturbations in the semiconductor body and thereby produce electrical output signals corresponding to the incident light images; and

d. predetermining the frequencies of the acoustic waves so that the difference between said frequencies substantially equals an integral multiple of the periodicity l introduced into the incident light.

19. The method of claim 18 wherein the step of scanning the semiconductor body, includes:

a. propagating a first acoustic wave of frequency ω

, proximate to the semiconductor body in a plane parallel therewith and from one end thereof; and

b. counterpropagating a second acoustic wave of frequency ω

₂ proximate to the semiconductor body in a plane parallel to the body and from an end thereof opposite to said first acoustic wave.

20. The method of claim 19 wherein the step of predetermining the frequencies of the acoustic waves includes predetermining said frequencies ω

₁, ω

₂ such that ##EQU17## where V is the acoustic velocity of the waves;

l is the periodicity, and N is any integer.

21. The method of claim 18 wherein the step of introducing a spatial periodicity into the incident light includes interrupting a portion the light with an opaque grating means before said light impinges on the semiconductor body.

22. An improved acousto-electric convolver for converting incident light images into corresponding electrical signals by acoustic scanning of the type having a photosensitive semiconductor body that produces charge carrier perturbations therein corresponding to the incident light images, a piezoelectric layer for counterpropagating acoustic waves past the semiconductor body, means for generating said acoustic waves in the piezoelectric layer, and output means on said piezoelectric layer for converting the acoustic waves into electrical output signals, the improvement comprising:

a. means located in front of the semiconductor body for introducing at least two spatial periodicities into the incident light before said light reaches the semiconductor body; and

b. means for generating said acoustic waves with predetermined frequencies such that the differences between said frequencies substantially equal integral multiples of the periodicities introduced into the incident light.

23. The convolver of claim 22 wherein said periodicity introducing means includes at least two filter grids each having a plurality of uniformly spaced apart filter strips thereon that block a predetermined portion of the spectrum of incident light before said light reaches the semiconductor body.

24. The convolver of claim 22 wherein said acoustic wave generating means, includes:

a. at least two signal generators that propagate in the same direction waves having propagation constants K₁ and K₂ ; and

b. at least one signal generator that propagates in an opposite direction a wave having a propagation constant K₃, the frequencies of the aforesaid waves are predetermined such that;

space="preserve" listing-type="equation">|K.sub.1 - K.sub.3 |>

0

space="preserve" listing-type="equation">|k.sub.2 - k.sub.3 |>

0

25. an improved apparatus for detecting the information present in the light from an optical image of the type having a photosensitive semiconductor body that produces charge carrier density perturbations corresponding to the information in the light that impinges on the body, a piezoelectric layer having first and second ends for counterpropagating interacting acoustic waves past the semiconductor body, a first input electrode on said piezoelectric layer adjacent to said first end for generating a first acoustic wave in one direction past the semiconductor body, a second input electrode on said piezoelectric layer adjacent to said second end for generating a second acoustic wave in an opposite direction past the semiconductor body, and output electrode means on said apparatus for converting the interacting acoustic waves into electrical output signals corresponding to the charge carrier density perturbations in the semiconductor body, the improvement comprising:

a. means located in front of the semiconductor body for introducing a spatial periodicity into the incident light before said light reaches the semiconductor body;

b. a first signal generator for generating a relatively short scanning pulse;

c. a second signal generator for generating a signal of frequency ω

₁ ;

d. first mixer means connected to the first and second signal generators for combining the relatively short scanning pulse from the first signal generator with the signal of frequency ω

₁ from the second signal generator, the output of said first mixer means being connected to said first input electrode;

e. a third signal generator for generating a relatively long reading pulse;

f. a fourth signal generator for generating a signal of frequency ω

₂ ;

g. second mixer means connected to the third and fourth signal generator for combining the relatively long reading pulse from the third signal generator with the signal of frequency ω

₂ from the fourth signal generator, the output of said second mixer means being connected to said second input electrode, said frequencies ω

₁, ω

₂ are predetermined such that the difference between the frequencies substantially equals an integral multiple of the periodicity introduced into the light by the periodicity introducing means.

26. The apparatus of claim 25 further including:

a. means connected to the output electrode means for intensity modulating the scan of an oscilloscope; and

b. means connected to the oscilloscope for driving the scan of said oscilloscope in correspondence with the motion of the optical image, whereby the visual output of the oscilloscope is a one dimensional scan of the optical image.

27. An improved apparatus for detecting the information present in the light from an optical image of the type having a photosensitive semiconductor body that produces charge carrier density perturbations corresponding to the information in the light that impinges on the body, a piezoelectric layer having first and second ends for counterpropagating interacting acoustic waves past the semiconductor body, a first input electrode on said piezoelectric layer adjacent to said first end for generating a first acoustic wave in one direction past the semiconductor body, a second input electrode on said piezoelectric layer adjacent to said second end for generating a second acoustic wave in an opposite direction past the semiconductor body, and output electrode means on said apparatus for converting the interacting acoustic waves into electrical output signals corresponding to the charge carrier density perturbations in the semiconductor body, the improvement comprising:

a. means located in front of the semiconductor body for introducing a spatial periodicity into the incident light before said light reaches the semiconductor body;

b. first means connected to the first input electrode for generating thereat a signal of frequency ω

₁ + μ

t where ω

₁ is the continuous frequency component of the signal and μ

t is a chirp signal having a chirp rate μ

over time t;

c. second means connected to the second input electrode for generating thereat a signal of frequency ω

₂ - μ

t where ω

₂ is the continuous frequency component of the signal and μ

t is a chirp signal having a chirp rate μ

over time t, said signal frequencies ω

₁, ω

₂ are predetermined such that the difference between the frequencies substantially equals an integral multiple of the periodicity introduced into the light by the periodicity introducing means; and

d. output electrode means connected to said apparatus having an output signal of frequency ω

₁ + ω

₂ modulated by the Fourier transform of the image.

28. The apparatus of claim 27 further including:

a. spectrum analyzer means connected to the output electrode means for intensity modulating the scan of an oscilloscope; and

b. means connected to the oscilloscope for driving the scan of said oscilloscope in correspondence with the motion of the optical image, whereby the visual output of the oscilloscope is a Fourier transform of the image.

29. An improved apparatus for detecting the information present in the light from an optical image of the type having a photosensitive semiconductor body that produces conductivity perturbations corresponding to the information in the light that impinges on the body, a piezoelectric layer having first and second ends for propagating interacting acoustic waves past the semiconductor body, a first input electrode on said piezoelectric layer adjacent to said first end for generating a first acoustic wave in one direction past the semiconductor body, a second input electrode on said piezoelectric layer adjacent to said second end for generating a second acoustic wave in an opposite direction past the semiconductor body, and output electrode means on said apparatus for converting the interacting acoustic waves into electrical output singals corresponding to the conductivity perturbations in the semiconductor body, the improvement comprising:

a. means located in front of the semiconductor body for introducing a spatial periodicity into the incident light before said light reaches the semiconductor body;

b. first means connected to said first input electrode for generating thereat a signal of frequency ω

₁ + μ

₁ t where ω

₁ is a signal of constant frequency and μ

₁ t is a chirp signal having a chirp rate of μ

₁ over time t;

c. second means connected to said second input electrode for generating thereat a signal of frequency ω

₂, said signal frequencies ω

₁, ω

₂ are predetermined such that the difference between the frequencies substantially equals an integral multiple of the periodicity introduced into the light by the periodicity introducing means;

d. third means for generating a signal of frequency ω

₃ + μ

₂ t, where ω

₃ is a signal of constant frequency and μ

₂ t is a chirp signal having a chirp rate of μ

₂ over time t; and

e. mixing means connected to both said output electrode means and said third signal generator means for subtracting the output signal obtained from the third signal generator means from the output signal obtained from the output electrode means, whereby said mixing means has an output signal that is modulated by the Fresnel transform of the optical image.

30. The apparatus of claim 29 further including:

a. dispersive filter means connected to the output of said mixer means for intensity modulating the scan of an oscilloscope; and

b. means connected to the oscilloscope for driving the scan said oscilloscope in correspondence with the motion of the optical image, whereby the visual output of the oscilloscope is the optical image itself.

31. An improved apparatus for detecting the information present in the light from an optical image of the type having a photosensitive semiconductor body that produces charge carrier density perturbations corresponding to the information in the light that impinges on the body, a piezoelectric layer having first and second ends for counterpropagating interacting acoustic waves past the semiconductor body, a first input electrode on said piezoelectric layer adjacent to said first end for generating a first acoustic wave in one direction past the semiconductor body, a second input electrode on said piezoelectric layer adjacent to said second end for generating a second acoustic wave in an opposite direction past the semiconductor body, and output electrode means on said apparatus for converting the interacting acoustic waves into electrical output signals corresponding to the charge carrier density perturbations in the semiconductor body, the improvement comprising:

a. means located in front of the semiconductor body for introducing a Fourier component with an effective wave number K into the charge carrier density of the semiconductor body;

b. first means connected to the first input electrode for generating thereat a first digitally coded signal, said first digital signal having a propagation constant K, in said piezoelectric layer; and

c. second means connected to the second input electrode for generating thereat a second digitally coded signal, said second digital signal having a propagation constant K₂ in said piezoelectric layer, said propagation constants K, and K₂ being predetermined so that

space="preserve" listing-type="equation">K.sub.1 - K.sub.2 ±

K = 0

where K is said effective wave number of the Fourier component.

32. The apparatus of claim 31 further including:

a. matched filter means connected to the output electrode means and digitally coded to correspond to the output therefrom such that the output from said matched filter means is a signal pulse corresponding to a spot on the image.

33. Apparatus for detecting the information present in the light from an optical image by acoustically scanning the charge carrier density perturbations in a semiconductor body, comprising:

a. a photosensitive semiconductor body that produces charge carrier density perturbations corresponding to the information in the light that impinges on the semiconductor body, said body having first and second ends;

b. a piezoelectric layer having first and second ends corresponding to the first and second ends of the semiconductor body, said piezoelectric layer propagates acoustic waves between its first and second ends;

c. an intermediate layer located between the semiconductor body and the piezoelectric layer and in direct physical contact therewith;

d. a first input electrode on said piezoelectric layer adjacent to the first end of the semiconductor body for generating a first acoustic wave in one direction past the semiconductor body;

e. a second input electrode on said piezoelectric layer adjacent to the second end of the semiconductor body for generating a second acoustic wave in an opposite direction past the semiconductor body, said first and second acoustic waves nonlinearly interact and scan the charge carrier perturbations in the semiconductor body;

f. output electrode means on said apparatus for obtaining electrical output signals corresponding to the conductivity perturbations in the semiconductor body, whereby the information present in the light is detected; and

g. means located proximate to the input electrodes for concentrating the first and second acoustic waves propagating in the piezoelectric layer.

34. The apparatus of claim 33 wherein the means for concentrating the propagating acoustic waves is a constriction fabricated in the piezoelectric layer of the apparatus.

35. The apparatus of claim 33 wherein the piezoelectric layer includes:

a. first and second electrode sections for mounting said first and second input electrodes;

b. a wave guide portion centrally located between said first and second electrode sections wherein the first and second concentrated acoustic waves nonlinearly interact; and

c. first and second wave constriction sections located between the first and second electrode sections and the wave guide portion wherein said first and second acoustic waves generated by the input electrodes are concentrated for propagation in the wave guide portion.

36. An improved acousto-electric convolver for converting incident light images into corresponding electrical signals by acoustic scanning of the type having a photosensitive semiconductor body that produces conductivity perturbations therein corresponding to the incident light images, a piezoelectric layer for counter-propagating acoustic waves past the semiconductor body, means for generating said acoustic waves in the piezoelectric layer, and output means on said piezoelectric layer for converting the acoustic waves into electrical output signals, the improvement comprising:

a. means located in front of the semiconductor body for introducing a spatial periodicity into the incident light before said light reaches the semiconductor body;

b. means for generating said acoustic waves with predetermined frequencies such that the difference between said frequencies substantially equals an integral multiple of the periodicity introduced into the incident light; and

c. means located proximate to the acoustic wave generating means for concentrating the acoustic waves propagating in the piezoelectric layer.

37. The apparatus of claim 36 wherein the means for concentrating the acoustic waves is a constriction fabricated in the piezoelectric layer of the apparatus.