Method and apparatus for improving acousto-electric scanning

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.

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 K.sub.2 predetermined such that
• K.sub.1 - K.sub.2 .+-. K = 0
• where K is said effective wave number of the Fourier component.

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.

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 .omega..sub.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 .omega..sub.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 .omega..sub.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 .omega..sub.2 from the fourth signal generator, the output of said second mixer means being connected to said second input electrode, said frequencies .omega..sub.1, .omega..sub.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.

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 .omega..sub.1 + .mu.t where .omega..sub.1 is the continuous frequency component of the signal and .mu.t is a chirp signal having a chirp rate .mu. over time t;
• c. second means connected to the second input electrode for generating thereat a signal of frequency .omega..sub.2 - .mu.t where .omega..sub.2 is the continuous frequency component of the signal and .mu.t is a chirp signal having a chirp rate .mu. over time t, said signal frequencies .omega..sub.1, .omega..sub.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 .omega..sub.1 + .omega..sub.2 modulated by the Fourier transform of the image.

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 .omega..sub.1 + .mu..sub.1 t where .omega..sub.1 is a signal of constant frequency and .mu..sub.1 t is a chirp signal having a chirp rate of .mu..sub.1 over time t;
• c. second means connected to said second input electrode for generating thereat a signal of frequency .omega..sub.2, said signal frequencies .omega..sub.1, .omega..sub.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 .omega..sub.3 + .mu..sub.2 t, where .omega..sub.3 is a signal of constant frequency and .mu..sub.2 t is a chirp signal having a chirp rate of .mu..sub.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.

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 K.sub.2 in said piezoelectric layer, said propagation constants K, and K.sub.2 being predetermined so that
• K.sub.1 - K.sub.2 .+-. K = 0
• where K is said effective wave number of the Fourier component.

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.

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.