JPS6351569B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides time delay, time axis extension, and
The present invention relates to an acousto-optic electrical signal processor that performs compression, inversion, and extraction of specific interval (time) signals.

2. Description of the Related Art Conventionally, there have been acousto-optic signal processing devices that perform real-time processing of electrical signals, such as spatial real-time integration and Fourier transformation, using lens systems, ultrasonic light modulators, and the like. The present invention focuses on the time delay and temporary memory characteristics of the acousto-optic signal processing unit (ultrasonic light modulator, Fourier transform optical system, spatial filter) used in these devices, and uses this to Conventionally, analog signal delay circuits and real-time time axis conversion processing circuits, which required extremely complex circuits and numerous electrical components, were constructed using an acousto-optic system to provide simple time delay and time axis conversion. The purpose is to provide a dexterous signal processor.

For this purpose, the present invention includes a transducer that converts an electrical signal to be processed into an ultrasonic wave, and a transducer for a detection ultrasonic signal that detects the electrical signal converted into an ultrasonic wave while compressing it in time. However, two optical ultrasonic signal processing cells were constructed so that they were arranged spatially with good parallelism, and a liquid substance was used as the ultrasonic propagation medium. Further, lenses 7A and 7B are arranged between these two cells to expand and compress the ultrasonic signal in the cell in the ultrasonic propagation direction, and the specific output diffraction that appears by the above-mentioned detection ultrasonic signal is arranged. An optical spatial filter 8 is provided that allows only light to pass through.

Next, this invention will be specifically explained with reference to the drawings.

FIG. 1 shows an optical ultrasound signal processing cell, which is a component of an acousto-optic electric signal processor of the present invention, and
It is a schematic perspective view of lenses 7A and 7B for ultrasonic expansion and compression. The two cells 3 and 3' shown in the figure have light passage windows 5 and 5' that are large enough for passage of the band-shaped plane wave light (parallel laser light) 9, and a light passage window 5 and 5' that is perpendicular to the traveling direction of the plane wave light 9. Ultrasonic transducers 1, 1' that emit ultrasonic waves, and ultrasonic absorbing members 2, 2' that absorb the ultrasonic waves emitted from the transducers.
It is composed of Further, by using liquid substances 4, 4' as the ultrasonic propagation medium, it is possible to easily set a long ultrasonic propagation distance. Further, the lens system expands or compresses the ultrasonic signal existing in the first cell 3 to the length in the ultrasonic propagation direction, and
to project. Since the ultrasonic waves traveling in the two cells are compression waves of the density of the propagation medium, a phase difference occurs partially in the band-shaped plane wave light 9 that traverses them, and when focused by a lens, a diffraction image appears.

FIG. 2 shows the configuration of an optical processing system that converts electrical signals into diffracted light using the optical ultrasonic signal processing cell and lens system. The laser beam 14 is expanded into band-shaped plane wave light by a magnifying lens system, and the first
The ultrasonic signal passes through the cell 3, and at this time undergoes a phase change due to the ultrasonic signal within the cell. The plane wave light that has undergone this phase change passes through the lens systems 7A and 7B, is expanded or compressed in the direction of ultrasound propagation, and is then
enters cell 3'. The plane wave light that has undergone phase modulation by the ultrasonic wave again in the second cell passes through the lens 7C.
The light is converged at , and an image is formed on an optical spatial filter 8 placed at the focal plane. In such a case, if the ultrasonic signal exists only in the cell 3' and is a sine wave with a frequency f, the diffraction image becomes a bright spot and is generated at a distance d from the optical axis point of the optical spatial filter 8. . The direction of the diffracted light point from the optical axis point is equal to the traveling direction of the ultrasound signal, and the value of d is expressed by the following equation.

d=λFf/v...(1) λ is the wavelength of the light source, F is the focal length of the lens 7C,
v is the speed at which the ultrasonic wave travels through the cell 3'. Also,
It is known that the intensity of the diffracted light is proportional to the square of the signal amplitude when the ultrasound signal amplitude is small.

Next, consider a case where plane wave light crosses two sinusoidal ultrasound waves having different frequencies. If these two ultrasonic waves are both perpendicular to the optical axis and their propagation directions are parallel to each other, the diffracted light will not only indicate the respective ultrasonic frequencies, but also the two frequencies that indicate the sum and difference of each frequency. Appears at the location of the point. Each frequency is f ₁ ,
Assuming f ₂ , the distances d ⁽⁺⁾ and d ^(-) between the optical axis and the diffracted light spot are respectively expressed by the following equations, as in the case of equation (1).

Here, k is the enlargement/reduction ratio of the lens system, and the signal of frequency f ₁ is input to the first cell 3, and the signal of frequency f ₂ is input to the second cell 3'. The intensity of the diffracted light is 2
When two ultrasonic signal amplitudes are small, both the sum and difference frequencies are proportional to the square of the product of the two ultrasonic amplitudes.

From the above, one of the two sinusoidal ultrasonic waves is amplitude-modulated with the electrical signal to be processed, and the other is modulated with a constant amplitude rectangular pulse having a width less than a fraction of the minimum period of the electrical signal. If amplitude modulated, (2)
By detecting the sum/difference frequency diffracted light shown by the equation with the optical spatial filter 8 and photoelectrically converting it, it is possible to obtain a signal in which the time axis of the electrical signal is expanded, compressed, or reversed. This situation will be explained with reference to an embodiment of the present invention shown in FIG. In this embodiment, cells 3, 3', lenses 7A, 7B, 7C, and optical spatial filter 8 are integrated in consideration of operational accuracy and simplicity. Band-shaped plane wave light 9 enters into the cell through a light passing window 5 provided in the cell 3. At this time, if no ultrasonic signal exists in the cell 3, the plane wave light 9 passes through the cell 3 as it is, and the length in the ultrasonic traveling direction is expanded or reduced by the lens systems 7A and 7B, and the plane wave light 9 passes through the cell 3 as it is. 3'. In cell 3', a sinusoidal signal of frequency f ₂ amplitude-modulated by the electrical signal to be processed is
The signal is applied to the electrical signal input terminal 6', is converted into an ultrasonic signal 11 by the ultrasonic transducer 1', and travels within the cell in the direction of the arrow. The band-shaped plane wave light 9 which has undergone a phase change by crossing this ultrasonic signal 11 is converged by the lens 7C to generate _f2 frequency diffracted light, but this diffracted light is blocked by the optical spatial filter 8. and does not appear outside the signal processor. Here, if the above-mentioned sine wave signal of frequency f ₁ is pulse amplitude modulated and applied from the first electrical signal input terminal 6 provided in the cell 3, a pulsed ultrasonic signal is emitted into the cell. , (kf ₁ ±f ₂ ) frequency diffraction of the light intensity proportional to the squared amplitude of the ultrasonic signal in a portion spatially overlapping with this pulsed ultrasonic signal 12 in the optical axis direction in the second cell 3'. Light appears. This diffracted light is filtered through an optical spatial filter 8.
The signal passes through an aperture prepared in advance and is emitted to the outside of the signal processor.

Next, the ultrasonic signal 11 and the pulsed ultrasonic signal 1 are enlarged or reduced and projected into the second cell 3'.
Consider the relative motion of the two. First, if the movements of the two ultrasound signals are in the same direction within the second cell 3' and the magnification/reduction ratio of the lens system is 1, then the two ultrasound signals are equivalent to the second The robots travel in the same direction at the same speed inside the cell 3'. At this time, the pulsed ultrasound signal 12 travels through the cell 3' while keeping a state overlapping with a specific portion of the ultrasound signal 11, so the optical spatial filter 8
The sum/difference frequency diffracted light obtained by passing through the ultrasonic signal 11 indicates the value of a specific portion of the ultrasound signal 11. Further, this value is held and output while the pulsed ultrasonic signal 12 is present in the first cell 3. Therefore, it is possible to sample and hold the electrical signal applied to the cell 3'. In order to improve sampling accuracy, it is necessary to use a thin pulsed ultrasonic signal that is less than a fraction of the minimum period of the electrical signal. Next, consider the case where two ultrasonic signals travel in opposite directions at equivalent speeds within the second cell 3' depending on the orientation of the cells 3, 3' or the lens system. In this case, if the spatial width of the pulsed ultrasonic signal 12 in the second cell 3' is sufficiently small compared to the width of the light passing window 5 in the ultrasonic propagation direction and the minimum spatial period of the electrical signal to be processed, it will appear as if the ultrasonic wave The signal 11 is scanned by the pulsed ultrasonic signal 12. The relative speed of these two ultrasound signals is twice the speed of each ultrasound, and since the amplitude of the ultrasound pulse is constant, the signal obtained by the scanning is equal to the electrical signal to be processed in time. It is compressed to /2. Further, if an optical fixed pattern filter having an aperture as large as the spatial width of the pulsed ultrasound is installed between the front surface of the light passing window 5 and the lens 7C, a time delay device having a gate function can be obtained. That is, the pulsed ultrasound for scanning, which was used for time axis compression in the previous example, is used for gate control, and only when the pulsed ultrasound exists overlapping the opening of the optical fixed pattern filter, the diffracted light is The configuration provides the following. In this case, the width and period of the pulsed ultrasound are arbitrary, and the delay time of the electrical signal to be processed is determined by the distance from the ultrasound transducer 1 to the aperture of the fixed pattern (the distance from the fixed pattern projected onto the light passing window 5). It is the value obtained by dividing the distance in the cell 3 by the ultrasonic velocity within the cell 3. Further, in order to perform time delay and time axis compression at the same time, it is possible to widen the aperture width of the fixed pattern and narrow the pulsed ultrasonic wave for scanning. In this case, time base compression and time delay are performed in the same manner as in the previous example, and the gate function is eliminated. Next, consider the case where the magnification and reduction ratios of the lens system are set to values other than 1. When the pulsed ultrasound signal in the first cell 3 is magnified by k times by the lens system and projected onto the second cell 3', the speed of the pulsed ultrasound signal in the same cell also becomes k times. For,
When k is 1 or more, if the two ultrasonic signals travel in the same direction, the pulsed ultrasonic signal 12 will equivalently pass and scan the ultrasonic signal 11 within the cell 3'. In this case, the temporal change in the amount of light obtained by passing through the optical spatial filter 8 is based on a time axis of a part of the electrical signal applied to the cell 3', that is, the overlapping part of the two ultrasonic signals 11 and 12. The waveform is reversed and expanded or compressed. When k=2, the time axis is reversed and no expansion or compression is performed. Also, the two ultrasonic signals are
If the electrical signals travel equivalently in opposite directions within the cell 3', the time axis of the electrical signal is compressed. Furthermore, if k is 1 or less and the two ultrasonic signals are configured to travel in the same direction, the time axis of the electrical signal will be expanded. These processes of time axis expansion, compression, and reversal can be performed arbitrarily depending on the expansion and reduction ratios of the lens system and the arrangement of the two cells. In addition, in order to correct the output error due to ultrasonic attenuation inside the cell,
If the light intensity distribution of the light beam incident on the cell is changed using an optical filter, more accurate signal processing can be expected. An area type optical filter may be used for the optical filter provided in this window portion. In this case,
The combination of cylindrical lenses allows the use of a light beam with a rectangular cross section, thereby increasing the effective utilization rate of the light beam.

The present invention has the above-described configuration, and by using the simple acousto-optic electric signal processor of the present invention, it is possible to extend the time axis of an electric signal, compress it, reverse it, and time delay having gate functions. It has the effect that signal processing using a combination of these several types can be executed in real time in an analog manner.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an optical ultrasound signal processing cell used in the present invention, FIG. 2 is a diagram showing an optical processing system of the present invention, and FIG. 3 is a diagram showing one embodiment of the present invention. In the figure, 1 and 1' are ultrasonic transducers, 2 and 2' are ultrasonic absorption members, 3 and 3' are cells, 4 and 4' are liquid substances, 5 and 5' are light transmission windows, and 6 and 6 ' is an electric signal input terminal, 7A, 7B, 7C, and 7D are lenses, 8 is an optical spatial filter, 9 is a band plane wave light, 15 is an optical filter, and A is a (f ₁ - f ₂ ) frequency diffraction bright spot. , B indicates a (f ₁ +f ₂ ) frequency diffraction bright spot.

Claims (1)

[Scope of Claims] 1. One or more ultrasonic transducers 1, 1' that are provided on the inner surface of a cell that holds a liquid substance and that vibrate upon receiving an external electrical signal; one or more ultrasonic absorbing members 2, 2' provided on opposite sides of the cell for absorbing ultrasonic waves propagating in the liquid substance; first and second ultrasonic signal processing cells provided in the cells and having light transmission windows 5, 5' opened in the propagation path direction of the ultrasonic waves; the first and second ultrasonic waves; a first and a third receiving the light transmitted through the signal processing cell;
lenses 7A, 7C; an optical spatial filter 8 provided at the focal position of the third lens 7C; and an optical spatial filter 8 provided on the light receiving window side of the second ultrasonic signal processing cell; an acousto-optic electrical signal processor, comprising: a second lens 7B that receives the output light of the laser beam and converts it into a parallel laser beam;
The ultrasonic transducers are respectively arranged so as to pass perpendicularly to the ultrasonic propagation path in the ultrasonic signal processing cell, and after the parallel laser beam passes through the first cell, An acousto-optic electrical signal processor characterized in that the first and second lenses 7A and 7B are arranged so that the light flux is expanded or contracted while being re-injected into the cell as a parallel light beam.