JPS6351568B2 - - Google Patents

Description

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

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 base compression circuits, which required extremely complex circuits and numerous electrical components, were constructed using an acousto-optical method, and are now available for simple time delays and time base compressors. The purpose is to provide a 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. are arranged opposite to each other with good parallelism to constitute an optical ultrasound signal processing cell using a liquid substance as an ultrasound propagation medium, and only a specific output diffracted light appearing by the detection ultrasound signal passes through. An optical spatial filter was provided.

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

FIG. 1 is a schematic perspective view of an optical ultrasound signal processing cell that is a component of the acousto-optic electrical signal processor of the present invention. This cell includes light transmission windows 5, 5' having a size sufficient for passage of band-shaped plane wave light 9, ultrasonic transducers 1, 1' that emit ultrasonic waves perpendicular to the traveling direction of the plane wave light 9, and , an ultrasonic absorbing member 2 that absorbs ultrasonic waves emitted from this vibrator,
2'. Furthermore, by using the liquid substance 4 as the ultrasonic propagation medium, it is possible to easily set a long ultrasonic propagation distance. Since the ultrasonic wave traveling in this cell is a compressional wave of the density of the propagation medium, a phase difference occurs partially in the band-shaped plane wave light 9 that traverses the ultrasonic wave, and a diffraction image appears when focused by a lens.

FIG. 2 shows the configuration of an optical processing system that converts electrical signals into diffracted light by the optical ultrasonic signal processing cell. The laser beam 14 is expanded into band-shaped plane wave light by a lens system, passes through the cell 3, and at this time undergoes a phase change by the ultrasonic signal within the cell.
The light is converged by the lens 7 and formed into an image on the surface of the optical spatial filter 8 disposed at the focal plane. At this time, if the ultrasonic signal is a sine wave with a frequency f, the diffraction image becomes a bright spot at a distance d from the optical axis point of the optical spatial filter 8.
occurs in a remote location. 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 7, v
is the speed at which the ultrasound waves travel through the cell. Furthermore, 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 two sinusoidal ultrasound waves having different frequencies exist in the cell 3. 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
Assuming f ₁ and 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).

In addition, the intensity of the diffracted light is as follows for both the sum and difference frequencies:
It is proportional to the square of the product of two ultrasound amplitudes.

From the above, if one of the two sinusoidal ultrasonic waves is amplitude-modulated with the electrical signal to be processed, and the other is amplitude-modulated with a rectangular pulse having a width less than a fraction of the minimum period of the electrical signal, , shown in equation (2),
By detecting the sum/difference frequency diffracted light with an optical spatial filter 8 and photoelectrically converting it, a signal can be obtained in which the time axis of the electrical signal is compressed to 1/2.
This situation will be explained with reference to an embodiment of the present invention shown in FIG. In this embodiment, the cell 3, lens 7, optical spatial filter 8
It has an integrated structure. Band-shaped plane wave light 9 enters the cell through a light transmission window 5 provided in the cell 3. A sine wave signal of frequency f ₁ that has been amplitude-modulated by the electrical signal to be processed is applied to the electrical signal input terminal 6, converted to an ultrasound signal 11 by the ultrasound transducer 1, and transmitted inside the cell. Proceed in the direction of the arrow. The band-shaped plane wave light 9 which has undergone a phase change by crossing the ultrasonic signal 11 is converged by the lens 7 to generate f ₁ frequency diffracted light, but this diffracted light is blocked by the optical spatial filter 8. and does not appear outside the signal processor. Here, from the second electric signal input terminal 6' provided in the cell 3,
When the above-mentioned sine wave signal of frequency f ₂ is modulated in pulse amplitude and applied and a pulsed ultrasonic signal is emitted into the cell, the part that spatially overlaps with this pulsed ultrasonic signal 12 in the optical axis direction is (f ₁ ±f ₂ ) frequency diffracted light with a light intensity proportional to the squared amplitude of the ultrasonic signal appears. This diffracted light passes through an aperture prepared in advance in the optical spatial filter 8 and is emitted to the outside of the signal processor. Since the ultrasonic signal 11 and the pulsed ultrasonic signal 12 are traveling in opposite directions through the cell at the same speed, the spatial width of the pulsed ultrasonic signal 12 within the cell is equal to the width of the light passing window 5 in the ultrasonic propagation direction. If it is sufficiently smaller than the minimum spatial period of the electrical signal to be processed, it will be as if the ultrasonic signal 11 were scanned by the pulsed ultrasonic signal 12. The relative velocity of these two ultrasound signals is twice the ultrasound velocity, and the amplitude of the ultrasound pulse is constant, so the signal obtained by the scanning is 1/2 the electrical signal to be processed in time. It is compressed into . Furthermore, between the front surface of the light passing window 5 and the lens 7,
If an optical fixed pattern filter having an aperture approximately equal to the spatial width of the pulsed ultrasound is installed, it becomes a time delay device with a gate function. 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 ultrasonic waves are arbitrary, and the delay time of the electrical signal to be processed is the value obtained by dividing the distance from the ultrasonic transducer 1 to the opening of the fixed pattern by the ultrasonic velocity within the cell. becomes. Furthermore, in order to simultaneously perform time delay and time axis compression, a method of widening the aperture width of the fixed pattern and narrowing the pulsed ultrasonic wave for scanning may be considered. in this case,
Time axis compression and time delay are performed in the same manner as in the previous example, and the gate function is eliminated. In order to correct output errors due to ultrasonic attenuation within the cell, more accurate signal processing can be expected if the light intensity distribution of the light beam incident on the cell is changed using an optical filter. An area type optical filter may be used for the optical filter provided in this window portion. In this case, a light beam whose cross section is rectangular is used due to the combination of cylindrical lenses, and as a result, the effective usage rate of the light beam is increased.

The present invention has the above-described configuration, and by using the simple acousto-optic electrical signal processor of the present invention, it is possible to compress the time axis of electrical signals, time delay having a gate function, and further achieve these two types. This has the effect of allowing combinational signal processing to be performed in analog fashion in real time.

[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 is a cell, 4 is a liquid substance, 5 is a light transmission window, 6 and 6' are electrical signal input terminals, and 7 is a lens,
8 is an optical spatial filter, 9 is a band plane wave light, A
indicates the (f ₁ + f ₂ ) frequency diffraction bright spot, B indicates (f ₁
−f ₂ ) indicates a frequency diffraction bright spot.

Claims (1)

[Claims] 1. A plurality of ultrasonic transducers 1 and 1' provided on the inner surface of a cell that keeps a liquid substance in a cubic shape and vibrating upon receiving an external electric signal; an ultrasonic absorbing member 2, 2' provided on the opposite side of the cell for absorbing ultrasonic waves propagating in the liquid substance; an ultrasonic signal processing cell having a light transmission window 5 opened in the longitudinal direction of the ultrasonic propagation path; a lens 7 for receiving the output light of the ultrasonic signal processing cell; and a lens 7 provided at the focal point of the lens. an acousto-optic electrical signal processor comprising: an acousto-optic electrical signal processor comprising: an acousto-optic electrical signal processor, wherein the laser light enters the plurality of ultrasonic propagation paths after entering through a light transmission window provided in the ultrasonic signal processing cell; An acousto-optic electrical signal processor, characterized in that the ultrasonic transducers in the cell are arranged so as to pass at right angles to the ultrasonic transducer.