JPS6227694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention uses ultrasonic propagation in a liquid substance to convert an electrical signal into a signal that changes spatially, that is, in response to position or distance, rather than a temporally changing signal. The present invention relates to an acousto-optic signal processing liquid cell for performing processing.

Traditionally, there have been spatial signal processing devices using optical lens systems and acousto-optic modulators, which are used to compress radar signals, real-time spectrum analyzers, etc.
Widely used. The ultrasonic optical modulator used in the optical modulation part of these devices has a phase modulation effect on the optical wavefront as well as a time delay operation on the electric signal due to ultrasonic propagation, and these two characteristics can be effectively utilized. By combining these, it is possible to easily and quickly realize processes such as integration and analog signal delay, which require extremely complicated device configurations in electrical signal processing. The present invention is an improvement of this ultrasonic optical modulator, in which ultrasonic light propagates in a single direction within the modulator from a vibrator attached to one side of the inner wall of the modulator, which is the basic structure of conventional modulators. The method of emitting sound wave signals has been changed, and the sound waves are transmitted in opposite directions within one modulator.
Moreover, by generating two ultrasonic signals with equal amplitude waveforms, it is possible to perform the operations of two conventional modulators, and to obtain accurate temporal and spatial synchronization of the two ultrasonic signals. Another object of the present invention is to provide a liquid cell for acousto-optic signal processing in which a diffraction bright spot automatically blinks.

For this purpose, in the present invention, a thickness direction oscillator is used as the oscillator that converts an electric signal into an ultrasonic wave and radiates it into the liquid cell, and this oscillator is inserted into the light passing window provided in the liquid cell. The vibrator was placed approximately in the center so that the optical axis of the light passing therethrough was parallel to the vibrator surface. Further, ultrasonic absorbing members were installed on the inner surfaces of both walls of the cell facing the transducer surface, and the cell was filled with a liquid ultrasonic propagation medium.

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

FIG. 1 is a diagram showing the structure of an embodiment of the acousto-optic signal processing liquid cell of the present invention. A pair of light transmitting windows 2a and 2b are provided on a pair of opposing wall surfaces of the rectangular parallelepiped cell 1, and light passes through these windows. Inside the cell 1 is a liquid ultrasonic propagation medium 3.
A thickness-direction transducer 4 that emits ultrasonic waves into this medium straddles the approximately central position of the light transmission window, and the transducer surface is parallel to the traveling direction of the light. It is located in This vibrator is held between a transparent plate placed on the light transmitting window and the inner wall of the cell by a holding material 5 which is elastic and airtight against liquid substances. Ultrasonic absorption members 6a and 6b are attached to a pair of inner walls of the cell facing the vibration surface of the transducer to absorb ultrasonic waves generated from the transducer, thereby preventing unnecessary reflected waves of ultrasonic waves within the cell. are doing. A signal input terminal 7 for applying an electric signal is attached to the vibrator.

FIG. 2 shows the movement of the ultrasonic signals 8a and 8b within the cell and the state of light diffraction due to the ultrasonic waves. Let L be the length of the light transmitting windows 2a and 2b of the cell 1 in the ultrasonic propagation direction. The shape of the ultrasonic wave is a rectangular pulse of 100 sine wave signals to make the propagation state obvious.
% amplitude modulation, the time frequency of the sine wave signal is [Hz], and the period and pulse width of the rectangular pulse are T, W [m]. If the ultrasonic propagation speed in the cell is v [m/s], then the spatial period T _CS of the sine wave signal is T _CS = v/[m] ... (1) Also, the pulse period, pulse The spatial lengths of the widths, T _S and W _S are as follows: T _S =T x v [m] ... (2) W _S = W x v [m] ... (3).

Here, L≫W _S , L≫T _S , T _CS ≪T _S , T _CS
<<Assuming the condition of W _S , if plane wave light is passed through the cell in parallel with the transducer surface from the light transmission window, the plane wave light that has been phase modulated by the ultrasonic signal within the cell will pass through the lens 9. The light is converged by the action of , and a diffraction bright spot is produced on the focal plane 10 of the lens. If the focal length of the lens is F, then from the above assumption, the position of the strongest diffraction bright spot, that is, the first-order diffraction bright spot, is determined by d=λF using the spatial period T _CS of the sine wave signal. /T _CS [m] ...(4) It is given by the formula. d is the distance between the optical axis point and the diffraction bright spot, and λ is the light source wavelength. Therefore, if an optical filter 10 having an aperture on the focal plane given by equation (4) is placed on the front focal plane and the light passing through this filter is detected by the photoelectric converter 11, it can be controlled by an electrical signal. An optical signal is obtained. Note that, as is clear from equation (4), the position of the diffraction bright spot changes depending on the value of T _CS , but remains unchanged with respect to the position and movement of the ultrasound signals 8a and 8b.

Next, consider the brightness of the bright spot. In conventional ultrasonic optical modulators, the propagation direction of the ultrasonic waves is unidirectional, so it can be regarded as a one-dimensional moving grating, and if the spatial period of the ultrasonic waves is sufficiently small compared to the aperture length of the light transmission window,
The brightness of the bright spot is proportional to the square of the ultrasound signal amplitude value,
It is known that when the ultrasonic intensity is constant, the brightness of the bright spot is also constant. In the present invention, since two ultrasonic waves having the same amplitude and frequency exist in the same liquid cell and are moving in opposite directions,
When the plane light that has passed through these two ultrasound waves converges on one point, the phase change of the plane wave light that has passed through each ultrasound wave is different in time, and the diffraction bright spot blinks. FIG. 3 is a diagram showing blinking of bright spots. Figure a shows a case where two ultrasonic waves emitted from the transducer 4 form one continuous sine waveform. At this moment, the entire cell can be regarded as a one-dimensional grating, so the diffraction bright spot reaches its maximum brightness. show. Figure b shows a case where time has elapsed since the time in figure a, and the two ultrasonic waves have each moved 1/4 spatial period in opposite directions.
At this time, the phases of the two ultrasound waves are [n
+1/2] spatial period (n; integer), and the phase shift of the plane wave light that has passed through each ultrasound also causes a shift of [n + 1/2] period at the bright spot position on the focal plane, Theoretically, the luminance of the bright spot becomes zero. Therefore, the diffraction bright spot obtained by the liquid cell according to the present invention blinks automatically due to ultrasonic propagation, and the blinking period T _f is given by T _f =T _CS /(4v) [S] ...(5) It will be done.

The present invention has the above configuration, and two ultrasonic signals emitted from one transducer 4 into the liquid ultrasonic propagation medium 3 in the cell 1 are transmitted in opposite directions with the same spatial frequency and amplitude. It has the characteristic of propagation. Therefore, if the phase-modulated plane wave light that passes through these two ultrasonic waves is converged by the lens 9,
Due to the periodic phase shift of the plane wave light that has passed through each ultrasonic wave, the diffracted light bright spot automatically blinks, and this period has a property determined by the ultrasonic velocity v in the cell 1 and the ultrasonic frequency. have Therefore, if an acousto-optic signal processing device is configured using the liquid cell according to the present invention, it is possible to easily separate the blinking frequency signal of the output light using an electric filter, and to prevent external optical noise to the device. Low frequency noise in the optical system caused by mechanical vibration etc. can be easily eliminated, and furthermore, the output signal after photoelectric conversion can be handled as an alternating current signal. Furthermore, the characteristic that two ultrasonic waves move in opposite directions at the same speed can be applied to a conventional acousto-optic correlator and used for detecting pattern symmetry, determining the center position, etc.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the movement of ultrasonic waves in a liquid cell and the position of a diffraction bright spot, and FIG. 3 is a diagram showing blinking of a diffraction bright spot. 1 is a cell, 2a and 2b are light transmission windows, 3 is a liquid ultrasonic propagation medium, 4 is a thickness direction vibrator, 5 is a holding material, 6a and 6b are ultrasonic absorbing members, and 7 is a signal input terminal.

Claims (1)

[Claims] 1 contains a liquid ultrasonic propagation medium therein,
A liquid cell for acousto-optic signal processing that inputs an ultrasonic traveling wave and a plane wave light into the medium and modulates the phase of the plane wave light with the ultrasonic traveling wave, the liquid cell being provided on both opposing walls of the cell. light transmission windows 2a, 2b for passing the plane wave light flux into the cell;
a thickness direction oscillator 4 disposed straddling substantially the center of the light transmission window and having a vibrating surface parallel to the traveling direction of the plane wave light beam; a holding member 5 for dividing the ultrasonic propagation medium into two; and a holding member 5 provided on the inner wall of each of the cells facing the pair of thickness vibration surfaces of the vibrator to prevent the ultrasonic wave generated from the vibrator surface. Ultrasonic absorbing members 6a and 6b for absorbing and extinguishing a pair of ultrasonic waves propagating in a sound wave propagation medium; and a signal input terminal 7 for supplying a drive electric signal to the thickness direction vibrator. A liquid cell for acousto-optic signal processing characterized by: