JPS6136978Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for polarizing a light beam, and more particularly to an ultrasonic light deflection device that utilizes the interaction between sound waves and light.

Information processing devices using light beams have many features such as high speed, high density, and the ability to perform parallel processing, and various systems have been devised so far. Among these devices, devices that have a mechanism for accessing a light beam often require an optical deflector that can deflect the light beam at high speed and randomly. Such optical deflectors include those that utilize the electro-optic effect and those that utilize the acousto-optic effect, but acousto-optic devices have the advantage of being compact and easy to optically adjust. Ultrasonic optical deflectors that utilize this effect are widely used.

It is well known that high-frequency acoustic vibrations excited in a solid or liquid act as a phase grating for light waves, diffracting a portion of the incident light beam.
An ultrasonic optical deflector is one of the light control elements based on the above principle, which changes the wavelength of the excited sound wave,
It has the function of changing the emission angle of the diffracted light beam. The normally used sound waves are volume waves without velocity dispersion. Therefore, changing the wavelength of sound waves is generally achieved by changing the frequency of the driving electrical signal of a piezoelectric or magnetostrictive transducer that excites the sound waves. As is well known, in this type of optical deflector, the intensity of the diffracted light beam relative to the driving frequency decreases with a deviation from the Bragg angle as the frequency changes, since the angle of incidence of the incident light beam on the deflector is fixed. In addition, because the electroacoustic conversion efficiency of the transducer that drives the sound wave has a band characteristic around the center frequency, it has a band characteristic as a whole.

The number of deflection points of the ultrasonic optical deflector is proportional to the bandwidth if the diameter of the optical beam is constant. Therefore, in order to increase the number of deflection points, it is necessary to widen the bandwidth. As described above, since the polarized light intensity has band characteristics, the wider the used bandwidth, the larger the change in the polarized light intensity within the band. Usually, the bandwidth of an optical deflector is defined as a frequency width that can obtain a deflected light intensity within 3 dB of the maximum deflected light intensity.

In a configuration in which the above ultrasonic optical deflector is used to read out an optical memory forming a dot array or a hologram array, since the intensity of the deflected light varies, the signal light that is transmitted or reproduced by the dots or holograms to be read out may vary. level fluctuates greatly. For this reason, signals are often detected incorrectly. In addition, since there are noise components emitted by other components, such as noise light generated by the hologram itself, in order to ensure a certain level of signal-to-noise ratio,
The fluctuation in the intensity of the deflected light of the optical deflector is large even at 3 dB, and it is necessary to further reduce this fluctuation.

Conventional methods for compensating the intensity of polarized light include separating a part of the main polarized light that is deflected by an ultrasonic optical deflector, or using undiffracted light that is not used as polarized light, -1st-order diffracted light, etc. There is a method of constructing a control feedback system that detects the intensity, compares it with a certain standard, detects the difference, and controls the level of the high-frequency signal supplied to the ultrasonic optical deflector. In order to obtain a large number of deflection points with a limited bandwidth, the diameter of the light beam is usually large, 5 mm to 8 mm, and the incident position of the light beam must be adjusted to prevent thermal disturbances generated in the deflection medium. It is necessary to keep it a certain distance away from the electroacoustic transducer that generates the sound waves. The speed of sound waves in the medium is slow, 3000 to 4000 m/s. Therefore, it takes 2 to 5 μs for the level-controlled sound wave flux to act on the light beam and change the intensity of the polarized light.
Therefore, the feedback system configured as described above for compensating for the intensity fluctuation of the deflected light becomes slow, and cannot achieve a high-speed optical deflection function.

An object of the present invention is to provide an ultrasonic optical deflector that can compensate for fluctuations in the intensity of deflected light of an ultrasonic optical deflector and has the function of deflecting a light beam at high speed.

According to the present invention, an ultrasonic optical deflector, a high frequency oscillator that emits a high frequency signal according to an access signal that accesses the optical deflector, and a high frequency oscillator that detects the code of the access signal and emits the access signal according to the code. a sign inversion circuit that transmits or inverts the sign; a D/A converter that generates an analog level according to the signal sent from the sign inversion circuit; It consists of a current-controlled attenuator that controls the level of a high-frequency signal that oscillates a high-frequency oscillator, and a high-frequency amplifier that amplifies the high-frequency signal that passes through the attenuator and supplies it to the ultrasonic optical deflector. It is possible to obtain an optical deflection device in which the band characteristic of the intensity of the deflected light deflected by the acoustic wave optical deflector is flat and which is capable of high-speed deflection.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a principle configuration diagram showing a basic circuit system for driving a conventionally well-known ultrasonic optical deflection element, in which 1 is an ultrasonic optical deflection element, and 2 is an access code 4 represented by 6 bits. A high frequency oscillator 3 that oscillates a high frequency signal corresponding to the high frequency oscillator 2 is a high frequency broadband amplifier that amplifies the output signal of the high frequency oscillator 2 and supplies it to the ultrasonic optical deflection element 1.

FIG. 2 is a diagram showing typical operating characteristics of the system shown in FIG. 1, and shows the relationship between the oscillation frequency of the high-frequency oscillator 2 and the intensity of the deflected light. Although the oscillation level of the high-frequency oscillator 2 is almost constant regardless of the oscillation frequency, it exhibits a band characteristic as shown in the figure due to the characteristics of the ultrasonic optical deflection element 1 described above. The correspondence between the access code 4 input to the high frequency oscillator 2 and the frequency of the oscillation signal output is as shown in FIG. FIG. 3 is a principle configuration diagram showing the first embodiment of the present invention, in which 1 is an ultrasonic optical deflection element, 2 is a high-frequency oscillator that oscillates a high-frequency sine wave signal according to an access code 4, and 6 is a 6 This is a sign inverting circuit that detects the sign of access code 4 expressed in bits and inverts the sign of all bits of branched access code 9 or passes it through without inverting.For example, if the MSB is 0, At certain times, the sign of all bits is inverted, and when the MSB is 1, all bits are passed through as is. 7 is an access signal 1 whose sign is determined by the sign inversion circuit 6;
A D/A converter 8 outputs an analog current corresponding to 0 to the high-frequency oscillator 2 according to the analog current 11 output from the D/A converter 7 and amplified to a desired level by the operational amplifier 5. Oscillation signal 12
The current-controlled attenuator 3 is a high-frequency broadband amplifier that amplifies the output signal of the high-frequency oscillator controlled as described above and supplies it to the ultrasonic light deflection element 1.

Next, the operation of this embodiment will be explained.

The correspondence between the access code 9 input to the D/A converter 7 and the analog level 11 outputted from it is the fourth one.
As shown in the figure, it is assumed here that it has bipolar output characteristics. That is, when the input access codes 9 are all 0, that is (0, 0, ..., 0), the negative maximum level is all 1, that is (1, 1, ...,
1), the maximum positive level is transmitted. Now the third
In the figure, input access code 4 is (0, 0,...,
0). This access code 4 is input to a high frequency oscillator 2, and the high frequency oscillator 2 has a frequency of 1. Oscillates a sine wave signal. At the same time, since the MSB of access code 4 is 0, sign inverting circuit 6 inverts all bits of access code 9 that is branched and inputted, and sends it to D/A converter 7 as (1, 1, ..., 1). . Since the D/A converter 7 has the correspondence relationship between the input code and the output analog level as shown in FIG. 4, it outputs the maximum positive level. On the other hand, if the access code 4 is (1, 1, . . . , 1), the high frequency oscillator 2 oscillates a sine wave signal with a frequency of 2. In this case, since MBS is 1, the sign inversion circuit 6 inputs the input access code 9
pass through as is. At this time, the D/A converter 7
The output analog level of outputs the maximum positive level. Therefore, the correspondence relationship between the access code 9 input to the sign inversion circuit 6 and the analog level output from the D/A converter 7 is as shown in FIG.
An analog output 11 output from the D/A converter 7 and amplified by the operational amplifier 5 is supplied as a control current to a current-controlled attenuator 8 that controls the level of the oscillation signal 12 of the high-frequency oscillator 2. The principle of this current control type attenuator 8 is to change the resistance value by controlling the bias current of the diode.
A typical example of the characteristic representing the relationship between Ic and the transmittance Trf of a high frequency signal has a nonlinear characteristic as shown in FIG. For example, by adjusting the offset voltage of the operational amplifier 5 and superimposing the analog output of the D/A converter 7 on a bias current having a current value indicated by I _B in FIG.
2 level to the analog output 11 of the D/A converter 7.
It can be changed according to. Therefore, the correspondence relationship between the access code 4 and the high frequency signal level 14 after passing through the current controlled attenuator 8 is as follows.
As shown in the figure, a valley-like characteristic is shown in which the high-frequency signal level becomes low when the access code (1, 0, . . . , 0) corresponds to the center. The output level of the high-frequency oscillator 2 controlled as described above is input to the broadband high-frequency amplifier 3 that linearly amplifies it, and after amplification is supplied to the ultrasonic optical deflection element 1. On the other hand, as shown in FIG. 2, when the drive level is flat with respect to frequency, the band characteristic of the light intensity deflected by the ultrasonic light deflection element 1 forms a peak with the center frequency being the maximum. Therefore, by adopting the configuration of the present invention, if the gain of the operational amplifier 5 is set correctly, the band characteristics of the polarized light intensity will be flat as shown in FIG. 8, with the above two characteristics canceling each other out. Become.

The sign inversion circuit 6, which is one of the constituent elements of the above two embodiments, can be constructed easily and inexpensively using several commercially available integrated circuits.

In this invention, the intensity of the deflected light is made constant using only an electronic circuit, and unlike the method described previously in which the propagation of sound waves is interposed in the feedback control system, the deflection speed of the ultrasonic light deflection element is reduced. As explained above, according to the present invention, it is possible to obtain an ultrasonic light deflection device that has a small number of components, has little variation in the intensity of deflected light, and has high speed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of a conventional ultrasonic light deflection device, and FIG. 2 is a diagram showing the correspondence between access codes and deflection light intensity in the configuration of FIG. 1. FIG. 3 is a diagram showing an embodiment of the present invention, and FIG. 4 is a diagram showing the correspondence between input codes and output levels of a D/A converter. FIG. 5 is a diagram showing the correspondence between the input sign of the sign inversion circuit and the output level of the D/A converter. Figure 6 shows the characteristic curve of the current-controlled attenuator, Figure 7 shows the level of the high-frequency signal output from the current-controlled attenuator, and Figure 8 shows when the configuration of the embodiment shown in Figure 3 is used. represents the band characteristics of the polarized light intensity. In the figure, 1... Ultrasonic optical deflection element, 2... High frequency oscillator, 3... High frequency broadband amplifier, 4... Access code, 5... Operational amplifier, 6... Sign inversion circuit, 7...
D/A converter, 8...Current control type attenuator.

Claims (1)

[Scope of utility model registration request] an ultrasonic light deflection element; a high frequency oscillator that generates a high frequency sine signal having a frequency corresponding to a parallel input digital code indicating a light deflection position of the ultrasonic light deflection element; and the high frequency signal input to the ultrasonic light deflection element. The ultrasonic light deflection element comprises a current-controlled attenuator that controls the amplitude of the sine signal, and means for applying a control current to the current-controlled attenuator, and is configured such that the diffraction efficiency of the ultrasonic light deflection element is constant regardless of the frequency. Further, the means for applying the control current includes a sign inverting circuit for inverting all bits of a code greater or less than a parallel input digital code corresponding to the maximum deflection efficiency of the ultrasonic optical deflection element; 1. An ultrasonic light deflection device comprising a circuit for D/A converting output.