JPH08285875A - Frequency shifter and optical displacement measuring apparatus employing the same - Google Patents

Abstract

PURPOSE: To obtain a stabilized frequency shifter having no temperature dependency, and a highly accurate and reliable optical displacement measuring apparatus, in which a voltage amplitude corresponding to optical phase shift of 2π can be sustained constantly regardless of temperature variation. CONSTITUTION: The frequency shifter comprises an electrooptic element 10 having refractive index variable with the voltage, and a power supply means for applying a sawtooth voltage to the electrooptic element 10 through electrodes 11a, 11b formed thereon. In the frequency shifter 101 where a luminous flux 3 passing through the electrooptic element 10 is frequency modulated by a sawtooth voltage being applied from the power supply means, a predetermined temperature dependency is imparted to the sawtooth voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency shifter and an optical displacement measuring device using the frequency shifter, and in particular, it provides displacement information of a moving object or fluid (hereinafter referred to as "moving object").
It is suitable for non-contact measurement by detecting the frequency shift of scattered light that has undergone Doppler shift according to the moving speed of a moving object.

[0002]

2. Description of the Related Art Conventionally, a laser Doppler velocity meter or a laser encoder (optical displacement measuring device) has been used as a device for non-contact and highly accurately measuring displacement information of a moving object.
Is used. In the laser Doppler velocimeter, a moving object is irradiated with laser light, and the frequency of light scattered by the moving object shifts in proportion to the moving speed (Doppler effect). Measuring speed.

The applicant of the present invention has proposed such a laser Doppler velocimeter in, for example, Japanese Patent Application Laid-Open Nos. 2-262064 and 4-230885. These speedometers do not detect the moving direction of moving objects,
Further, when the speed of the moving object is close to 0, detection tends to be difficult.

In a laser Doppler velocimeter, a frequency shifter using a flat plate of electro-optic crystal (hereinafter referred to as "electro-optic element") is installed in the optical path of two light fluxes, and the frequency shifter causes a predetermined frequency between the two light fluxes. Foord Tatsuo has published a method that can accurately detect even when the moving direction and moving speed of a moving object is close to 0 by making a difference and incident on the moving object (Ap
pl. Phys., Vol.7, 1974, 136-139).

Here, the electro-optic crystal is a crystal in which the refractive index of the medium is changed by an applied electric field, and is, for example, a trigonal system 3 m.
LiNbO3 or LiTaO3, tetragonal 42m (N
H4) H2PO4 (ADP), KH2PO4 (KDP)
Etc.

According to Foord et al., Even when the speed of the moving object is slow, the frequency difference provided between the two light beams is set to an appropriate value by using a frequency shifter so that the speed of the moving object is close to zero. However, the velocity direction can be measured at the same time.

In the electro-optic crystal used for the frequency shifter, if the amount of change ΔE of the voltage applied to the electro-optic crystal per unit time is kept constant, the light after passing through the electro-optic crystal has a phase change amount Δφ per unit time. It will be constant. This allows it to function as a frequency shifter. In reality, since it is difficult to always change the voltage constantly (the voltage becomes infinite), the voltage is driven by the sawtooth wave voltage as shown in FIG.

At this time, if the voltage amplitude of the sawtooth wave falls at a value corresponding to the optical phase shift 2π, the optical phase does not become discontinuous and the voltage is constantly changed. The result equivalent to that is obtained. It should be noted that the voltage amplitude of the sawtooth wave is not only a value at which the optical phase shift becomes 2π, but also 2π.
Although the same effect can be obtained with a value corresponding to an integral multiple of, normally, a voltage having a phase shift of 2π is used because the voltage value becomes large.

A circuit configuration as shown in FIG. 13 is used for driving with a sawtooth wave voltage. FIG. 14 shows the voltage waveform of each part in this case. In FIG. 13, 21 is a constant current circuit, 22 is a switching element such as a transistor or FET, and 2
3 is an oscillation circuit, 24 is a pulse generation circuit, and 25 is an electro-optic crystal. Since the electro-optic crystal 25 can be electrically regarded as a capacitive element (capacitor), a constant current is supplied from the constant-current circuit 21 to the electro-optic crystal 25, and when a charge is charged, the voltage applied to the electro-optic crystal 25 becomes Rises linearly.

On the other hand, the electro-optical crystal 2 is generated by momentarily turning on the switch element 22 in the pulse generating circuit 24.
5 can be discharged, electro-optic crystal 25
The voltage applied to is reduced to approximately zero. By repeating this, the voltage applied to the electro-optic crystal 25 becomes a sawtooth wave. The switching element 2 is synchronized with a clock generated by the oscillator circuit 23 (corresponding to a frequency fr described later).
The drive by the sawtooth wave is repeated by configuring the pulse generation circuit 24 so as to turn on 2 for only a moment.

[0011]

Generally, when an object is irradiated with a light beam having a high coherence such as a laser, the scattered light generated by the fine irregularities on the surface of the object undergoes random phase modulation and is reflected on the observation surface. A speckle pattern, a so-called speckle pattern, is formed. In a laser Doppler velocimeter, when a moving object moves, the change in brightness due to Doppler shift on the detection surface of a photodetector for detecting scattered light is irregular due to the flow of speckle patterns. It is modulated by the change of brightness and the output signal from the photodetector is also modulated by the change of the transmittance (or reflectance) of the object to be measured.

In a laser Doppler velocimeter, generally, the frequency of change in brightness and darkness due to the flow of a speckle pattern and the frequency of change in transmissivity (or reflectivity) of a moving object are compared with the Doppler frequency based on displacement information. Low. Therefore, a method is used in which the output from the photodetector is passed through a high-pass filter to electrically remove low-frequency components, and only the Doppler signal is extracted.

However, the speed of the moving object is slow and Doppler
When the frequency becomes low, the frequency difference between this and the low-frequency fluctuation component becomes small, and there arises a problem that the high-pass filter cannot be used and it is difficult to accurately measure the displacement information of the moving object. In addition, the speed direction cannot be detected in principle.

On the other hand, the above-mentioned method (frequency shifter) announced by Foord et al. Gives a predetermined frequency difference to two light fluxes before irradiating the two light fluxes to a moving object to determine a stationary state and a velocity direction of the moving object. It is possible to measure including this.

There are various configurations of the frequency shifter. For example, when an electro-optic crystal is applied, the ordinary refractive index n _o and the extraordinary refractive index n _{e of} the electro-optical crystal greatly change depending on the temperature. In particular, electro-optic crystals have a very sensitive index of refraction to temperature. Therefore, the frequency shift becomes unstable due to a slight temperature difference or temperature gradient of the electro-optical element. Further, if a temperature gradient is generated in the light beam passage portion, the wavefront of the light beam is distorted, and it becomes difficult to form a strict interference system.

FIG. 6 shows an example in which the temperature characteristic of the voltage amplitude value corresponding to the optical phase shift 2π is experimentally obtained for a certain electro-optic crystal. As shown in FIG. 6, since the voltage corresponding to the optical phase shift 2π has a temperature characteristic, the voltage value corresponding to the optical phase shift 2π becomes equal to the actual voltage amplitude value when the temperature condition changes. As a result, the optical phase becomes discontinuous and accurate velocity information cannot be obtained.

According to the present invention, the temperature characteristic of the electro-optic crystal is canceled by making the amplitude of the sawtooth wave voltage of the driving means of the electro-optic crystal have an appropriate temperature dependence, and the optical phase shift is caused even if the temperature changes. The purpose of the present invention is to provide an optical measuring device capable of constantly maintaining a voltage amplitude value corresponding to the shift 2π, obtaining a stable frequency shifter having no temperature dependence, and using this to detect highly accurate velocity information. To do.

In addition, according to the present invention, the sawtooth wave voltage applied to the electro-optical element forming the frequency shifter for giving a frequency difference to the two light fluxes irradiating the moving object has a temperature dependence, so that the temperature change can be prevented. On the other hand, a frequency shifter with stable accuracy is achieved, and by using this, an appropriate frequency difference is given to the two light fluxes, and displacement information can be detected with high accuracy even when the speed of the moving object is slow. A frequency shifter and an optical displacement measuring device using the same can be achieved.

[0019]

The frequency shifter of the present invention comprises (1) an electro-optical element whose refractive index changes with voltage,
A power supply means for applying a sawtooth wave voltage to the electro-optical element via an electrode formed on the electro-optical element, and a frequency of a light beam passing through the electro-optical element by the sawtooth wave voltage from the power supply means. In the frequency shifter that gives the modulation,
It is characterized in that the sawtooth wave voltage has a predetermined temperature dependency.

In particular, the sawtooth wave voltage is obtained by repeating a predetermined cycle in which the electro-optical element is charged by a constant current circuit to increase the applied voltage and then is instantaneously discharged. The temperature characteristic of the constant current flowing out from the constant current circuit is such that the phase shift of the light flux passing through the electro-optical element is 2πn (n is an integer), and the temperature characteristic of the drive voltage E of the electro-optical element and the temperature characteristic of the electro-optical element. It is characterized in that it is set so as to cancel the temperature characteristic obtained by combining the temperature characteristic of the interelectrode capacitance C.

The optical displacement measuring apparatus according to the present invention (2-1) refracts a light beam from a light source by dividing the light beam into two light beams by a light dividing member and applying a sawtooth wave voltage between the two light beams. A frequency having an electro-optical element whose rate changes, a power supply means for applying a sawtooth wave voltage to the electrooptic element, and a temperature characteristic adding means for making the amplitude of the sawtooth wave voltage from the power supply means temperature dependent. Displacement of the moving object by applying a frequency difference using a shifter, making two light fluxes having the frequency difference incident on a moving object, and detecting scattered light that has undergone Doppler shift by the moving object by a detection means. It is characterized by detecting information.

In particular, the sawtooth wave voltage is obtained by charging the electro-optical element with a constant current circuit to increase the applied voltage and then instantaneously discharging it by repeating a predetermined cycle. The temperature characteristic of the constant current flowing out from the constant current circuit is such that the phase shift of the light flux passing through the electro-optical element is 2πn (n is an integer), and the temperature characteristic of the drive voltage E of the electro-optical element and the temperature characteristic of the electro-optical element. It is characterized in that it is set so as to cancel the temperature characteristic obtained by combining the temperature characteristic of the interelectrode capacitance C.

(2-2) A light beam from a light source is split into two light beams by a light splitting member, and at least one of the two light beams has its refractive index changed by applying a sawtooth wave voltage from a power supply means. When a frequency difference is applied between the two light fluxes via the electro-optical element, the temperature characteristic adding means causes the amplitude of the sawtooth wave voltage to have temperature dependence, and the frequency difference is applied. It is characterized in that the displacement information of the moving object is detected by causing the light beam to enter the moving object and detecting the scattered light that has undergone the Doppler shift at the moving object by the detection means.

(2-3) A light beam from a light source is split into two light beams by a light splitting member, and the two light beams each have an index of refraction which is changed by an applied voltage from a separately provided power supply means. When a frequency difference is imparted between the two light beams via the, a sawtooth wave voltage having an amplitude temperature dependency on the amplitude is applied to at least one electro-optical element by the temperature characteristic adding means. The feature is that the displacement information of the moving object is detected by causing two light beams with a difference to be incident on the moving object and detecting scattered light subjected to Doppler shift by the moving object by the detection means.

In particular, in the configurations (2-2) and (2-3), it is predetermined that the sawtooth voltage is charged instantly after the electro-optical element is charged by the constant current circuit to increase the applied voltage. Of the electro-optical element in which the temperature deviation of the constant current flowing out from the constant current circuit is 2πn (n is an integer) for the phase shift of the light beam transmitted through the electro-optical element. The temperature characteristic of the driving voltage E and the temperature characteristic of the interelectrode capacitance C of the electro-optical element are set so as to be canceled, and the like.

[0026]

FIG. 1 is a perspective view of a frequency shifter according to the present invention and an optical displacement measuring apparatus using the frequency shifter according to a first embodiment of the present invention.

In the figure, 1 is a laser light source, 2 is a collimator, 4 is a beam splitter, 6a to 6d are mirrors, and 7 is a mirror.
Is a moving object that moves at a speed V0 for measuring speed, 8 is a condenser lens, and 9 is a photodetector. 101 is a frequency shifter according to the present invention, which includes two electro-optical elements 10 (10a,
10b) and its drive circuit 102.

In the present embodiment, the temperature characteristic of the electro-optical element 10 is corrected by providing an appropriate temperature characteristic to the amplitude of the sawtooth wave voltage applied to the electro-optical element 10 by a method described later, and there is a temperature change. Also makes it possible to always maintain the voltage amplitude value corresponding to the optical phase shift 2π. As a result, a stable frequency shifter without temperature dependence is obtained.

First, the operation of detecting the velocity information of the moving object 7 in the optical displacement measuring device of FIG. 1 will be described. In FIG. 1, the laser light emitted from the laser 1 becomes a parallel light flux 3 by the collimator lens 2,
The beam splitter 4 splits the light into a light beam 5a and a light beam 5b. The light beam 5a (5b) is reflected by the mirror 6a (6b) and then enters the electro-optical element 10 as a light beam having a polarization direction in the Z axis, and only the light beam 5a is transmitted to the frequency shifter 101.
Undergo a frequency shift at. The light beam 5a (5b) emitted from the frequency shifter 101 is reflected by the mirror 6c (6d) and is incident on the moving object 7 moving in the direction of the arrow at the velocity V0 at the incident angle θ.

The scattered light from the moving object 7 is collected by the condenser lens 8.
Is detected by the photodetector 9 via The frequencies of the scattered light by the two light beams 5a and 5b undergo Doppler shifts of + and -f, respectively, in proportion to the moving speed V0. Here, if the wavelength of the laser light is λ, the frequency f can be expressed by the following equation (1).

F = V0 · sin (θ) / λ (1) The scattered lights that have undergone the Doppler shift of frequencies + f and −f interfere with each other to produce bright and dark light on the light receiving surface of the photodetector 9. The frequency F of the light and darkness that causes the change is the electro-optical element 1
When the frequency difference between the two light fluxes due to 0 is fR, it is given by the following equation (2).

F = 2f = 2V0sin (θ) / λ + fR (2) Then, if the frequency F from the photodetector 9 (hereinafter referred to as Doppler frequency) is measured, The velocity V0 of the moving object 7 is obtained. Then, even if the velocity V0 of the moving object 7 is slow, if the frequency difference fR is set to an appropriate value,
The frequency difference from the low frequency component caused by the change in the speckle pattern flow or the transmittance (or reflectance) of the moving object can be sufficiently taken, and the low frequency component is electrically removed to obtain the Doppler pattern. By extracting only the signal, the speed can be detected even in that case.

Here, for example, assuming that the shape of the electro-optical element 10 is thickness d = 1 mm, length a = 20 mm, and the laser wavelength is λ = 780 nm, the voltage amplitude V = 230 Vol.
When t is set, the phase difference between the two light beams becomes 2π, and when serrodyne driving is performed at the frequency fR, the frequency shifts by fR.

Next, features of the configuration of the frequency shifter 101 of the present invention will be described. In FIG. 1, 10a is a flat plate (electro-optic element) of electro-optic crystal LiNb03. 1
Reference numerals 1a and 11b denote electrodes provided on both surfaces of the electro-optical element 10a, and the electrodes 11 (11a and 11b) are configured to apply an electric field to a transmitting portion of a light beam 5a described later.

FIG. 2 shows an electro-optical element 1 according to this embodiment.
It is an explanatory view of the operation of the frequency shifter using 0. The electro-optic crystal is a crystal whose refractive index changes according to an applied electric field. For example, trigonal 3m LiNb03 or LiT
a0, tetragonal 42m (NH4) H2PO4 (AD
P), KH2PO4 (KDP), etc. Below is LiN
Description will be made taking b03 as an example. The index ellipsoid of LiNb03 (3m) is represented by the following equation.

[0036]

[Equation 1] Therefore, if the change voltage V per unit time is constant, L
The amount of phase change of the light after passing through iNb03 is constant per unit time. That is, it becomes a frequency shifter. In reality, since the voltage becomes infinite when the voltage is constantly changed, the sawtooth wave (serodyne) drive as shown in FIG. 3 is performed.
At that time, one voltage amplitude is driven at a value corresponding to the optical phase 2π so that the optical phase does not become discontinuous at the falling portion.

FIG. 4 shows the electro-optical element 10 in this embodiment.
FIG. 7 is an explanatory diagram of a drive circuit 102 that applies a sawtooth wave voltage to the drive circuit. In the figure, 25 is an electro-optical element (electro-optical crystal).
Is shown.

In this embodiment, the sawtooth wave voltage applied to the electro-optical element 25 is charged by the constant current circuit 21 to increase the applied voltage, and then the instantaneous discharge is repeated by a predetermined cycle. There is.

In the present embodiment, when the constant current value flowing out from the constant current circuit 21 is I and the capacitance of the electro-optic crystal 25 is C, the voltage across the electro-optic crystal 25 rises with a slope of I / C per unit time. . Therefore, the optical phase shift 2π
In order to drop (discharge) the voltage at, the following formula must be established.

E / (I / C) = 1 / f (4) Here, f is the oscillation frequency in the oscillation circuit 23, and E is a voltage corresponding to the optical phase shift 2π of the electro-optic crystal 25. is there. This can be transformed into the following equation.

I = CEf (5) Since the oscillation frequency f is a reference here, it is usually designed so as not to have a temperature characteristic. The capacitance C and the voltage E each have an inherent temperature characteristic depending on the material.

In this embodiment, the temperature characteristic of the constant current value I is set equal to the temperature characteristic of (C × E), so that the equation (5) is established regardless of the temperature change. As a result, the voltage amplitude value corresponding to the optical phase shift 2π can always be maintained, and a frequency shifter having no temperature dependence is realized.

A specific method will be described with reference to FIG. In the figure, the constant current circuit 21 includes a transistor Q1,
It is composed of a constant voltage diode D1, a resistor R1 and a resistor R2, and is supplied with a positive power source Vcc.

Here, the constant current value I flowing out from the collector of the transistor Q1 is approximated by the following equation.

I≈ (Vz−Vbe) / R1 (6) Vz is the Zener voltage of the constant voltage diode D1, and Vbe is the base-emitter voltage of the transistor Q1. Considering the temperature characteristics, the resistance R1 is usually ± several hundred ppm
Since it is as small as / ° C or less, it can be ignored. The temperature characteristic of the base-emitter voltage Vbe is generally about −2 mV / ° C. The zener voltage Vz of the constant voltage diode D1 is shown in FIG.
It has the following temperature characteristics.

Therefore, in this embodiment, the constant current value I is given a desired temperature characteristic by selecting an appropriate constant voltage diode D1.

Considering the electro-optic crystal having the temperature characteristics as shown in FIG. 6, the temperature coefficient of the voltage corresponding to the optical phase shift 2π is about -0.088% / ° C. The temperature coefficient of capacitance of this electro-optic crystal is approximately + 0.064% / ° C, as shown in FIG.

Therefore, in the present embodiment, the temperature coefficient of the constant current value I flowing out from the constant current circuit 21 is the sum of the two temperature coefficients (-
(0.024% / ° C) so that the amplitude of the sawtooth wave has temperature dependence, and the voltage amplitude always maintains the state corresponding to the value corresponding to the optical phase shift 2π. There is.

In this case, the constant voltage diode D1 is actually used.
By using an element with a Zener voltage of about 2.7V for V
z = 2.7, Vbe≈0.6V, temperature coefficient of Vz is approximately −2.5 mV / ° C., temperature coefficient of Vbe is approximately −2 mV /
Since it is ℃, from the formula (6), I≈ (2.7−0.6) /R1=2.1/R1 (7) is obtained. Since the temperature coefficient of (Vz-Vbe) is -2.5-(-2) =-0.5 [mV / ° C] (8), the temperature coefficient of the current I is -0.5 [mV / ° C]. /2.1 [V] × 100 = −0.024 [% / ° C.] (9) That is, the temperature characteristic obtained by combining the temperature coefficient −0.088% / ° C. of the voltage corresponding to the optical phase shift 2π of the electro-optic crystal and the temperature coefficient + 0.064% / ° C. of the capacitance is approximately expressed by the temperature coefficient of the current I. I have canceled. In addition,
Since the temperature characteristics of the Zener voltage are slightly different depending on the current value flowing through the constant voltage diode, it is necessary to design in consideration of the current value.

As described above, in the present embodiment, the sawtooth voltage has an appropriate temperature coefficient so that the voltage amplitude value corresponding to the optical phase shift 2π is always maintained even if the temperature changes. .

In this embodiment, a stable frequency shifter having no temperature dependence can be obtained by this, and a highly accurate speed detecting device is realized.

In the present invention, as the method of giving the temperature characteristic to the voltage amplitude of the sawtooth wave, various methods are applicable without being limited to the above embodiment. Also, it is preferable to change the setting of the temperature characteristics according to the characteristics of the electro-optic crystal used, and in the present invention, the circuit suitable for each is used.

FIGS. 8 to 11 are circuit explanatory diagrams of another embodiment when the sawtooth wave voltage has temperature characteristics in the present invention.

FIG. 8 shows an example in which the temperature characteristics of the constant voltage diode D1, the diode Da and the transistor Q1 are used as in the first embodiment. The temperature characteristic of the diode is about -2 mV /
Since the temperature is ° C, the temperature characteristics are adjusted depending on the number used.

FIG. 9 is a circuit utilizing the temperature characteristics of the constant voltage diode D1 and is mainly designed to prevent the influence of the temperature characteristics of the driving transistor Q1 from appearing. This circuit has the feature that it is easy to apply because it can be designed considering only the temperature characteristics of the constant voltage diode.

FIG. 10 shows an example of a circuit using the thermistor R _th . When it is desired to have a temperature characteristic opposite to that in the figure, it is possible to use a thermistor on the emitter side of the transistor Q1.

FIG. 11 shows a more practical circuit example. In this example, measures are taken to reduce noise, increase the output impedance of the constant current circuit, and remove the influence of the capacitance between the base and collector of the transistor Q1. The capacitor C1 and the cascode-connected transistor Q2 between the base of the transistor Q1 and the power supply Vcc are adopted for the above purpose, but none of them depart from the gist of the present invention.

[0058]

As described above, according to the present invention, the temperature characteristic of the electro-optical crystal is canceled by making the amplitude of the saw-tooth wave voltage of the driving means of the electro-optical crystal have an appropriate temperature dependence. Even if there is a change, the voltage amplitude value corresponding to the optical phase shift 2π can always be maintained, a stable frequency shifter without temperature dependence can be obtained, and the optical frequency detection can be performed with high accuracy by using this. -Type measuring device can be achieved.

Further, according to the present invention, the moving object is irradiated with 2
By using the sawtooth wave voltage applied to the electro-optical element that constitutes the frequency shifter that gives a frequency difference to the light flux with temperature dependence, we achieved a frequency shifter with stable accuracy against temperature changes, and use this A frequency shifter capable of accurately detecting displacement information even when the speed of a moving object is low, and an optical displacement measuring device using the frequency shifter are achieved. be able to.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of the phase shifter of FIG.

FIG. 3 is an explanatory diagram of a sawtooth voltage and a phase shift of an electro-optical element.

FIG. 4 is an explanatory diagram of a drive circuit according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram of temperature characteristics of a constant voltage diode.

FIG. 6 is an explanatory diagram of temperature characteristics of phase shift and applied voltage.

FIG. 7 is an explanatory diagram of temperature characteristics of interelectrode capacitance of the electro-optical element.

FIG. 8 is an explanatory diagram of a constant current circuit used for a frequency shifter.

FIG. 9 is an explanatory diagram of a constant current circuit used for a frequency shifter.

FIG. 10 is an explanatory diagram of a constant current circuit used for a frequency shifter.

FIG. 11 is an explanatory diagram of a constant current circuit used for a frequency shifter.

FIG. 12 is an explanatory diagram of a sawtooth voltage and a phase shift of an electro-optical element.

FIG. 13 is a block diagram when driving with an electro-optical element and a sawtooth wave voltage.

FIG. 14 is an explanatory diagram of voltage waveforms in FIG.

[Explanation of symbols]

 1 Laser Diode 2 Collimator Lens 3, 5a, 5b Laser Beam 4 Beam Splitter 6a, 6b Mirror 7 Object to be Measured 8 Condensing Lens 9 Light-Receiving Element 10a, 10b Electro-Optical Crystal 21 Constant Current Circuit 22 Oscillation Circuit 23 Pulse Generation Circuit 24 Switch element 25 Electro-optic crystal

Claims (10)

[Claims] 1. An electro-optical element whose refractive index changes according to a voltage, and a power supply means for applying a sawtooth wave voltage to the electro-optical element via an electrode formed on the electro-optical element,
In a frequency shifter that frequency-modulates a light beam passing through the electro-optical element by a sawtooth wave voltage from the power supply means, the sawtooth wave voltage has a predetermined temperature dependence. . 2. The sawtooth voltage is obtained by charging an electro-optical element with a constant current circuit to increase an applied voltage and then instantaneously discharging the same at a predetermined cycle. The frequency shifter according to claim 1. 3. The drive voltage E of the electro-optical element, wherein the temperature characteristic of the constant current flowing out from the constant-current circuit is such that the phase shift of the light beam passing through the electro-optical element is 2πn (n is an integer).
3. The frequency shifter according to claim 2, wherein the temperature characteristic obtained by combining the temperature characteristic of 1) and the temperature characteristic of the interelectrode capacitance C of the electro-optical element is set to cancel. 4. An electro-optical element which changes a refractive index by dividing a light beam from a light source into two light beams by a light dividing member and applying a sawtooth wave voltage between the two light beams, and an electro-optical element. A frequency difference is imparted by using a frequency shifter having a power supply means for applying a sawtooth wave voltage and a temperature characteristic adding means for making the amplitude of the sawtooth wave voltage from the power supply means temperature dependent, Optical displacement measurement characterized in that the displacement information of the moving object is detected by making two light beams with a difference incident on the moving object, and detecting scattered light that has undergone Doppler shift by the moving object by a detection means. apparatus. 5. The sawtooth wave voltage is obtained by charging an electro-optical element with a constant current circuit to increase an applied voltage and then instantaneously discharging the same at a predetermined cycle. The optical displacement measuring device according to claim 4. 6. The drive voltage E of the electro-optical element in which the temperature characteristic of the constant current flowing out from the constant current circuit is 2πn (n is an integer) for the phase shift of the light beam passing through the electro-optical element.
6. The optical displacement measuring device according to claim 5, wherein the temperature characteristics obtained by combining the temperature characteristics of 1. and the temperature characteristics of the interelectrode capacitance C of the electro-optical element are set so as to be canceled. 7. An electro-optic device in which a light beam from a light source is split into two light beams by a light splitting member, and at least one of the two light beams changes its refractive index by applying a sawtooth wave voltage from a power supply means. When a frequency difference is applied between the two light beams via an element, the amplitude of the sawtooth wave voltage is made temperature dependent by the temperature characteristic adding means, and the two light beams having the frequency difference are moved. An optical displacement measuring device characterized in that displacement information of the moving object is detected by detecting scattered light which is incident on the object and which has undergone Doppler shift by the moving object, by means of detection means. 8. A light beam from a light source is split into two light beams by a light splitting member, and each of the two light beams is passed through an electro-optical element whose refractive index is changed by an applied voltage from separately provided power source means. When a frequency difference is applied between the two light beams, a sawtooth wave voltage having an amplitude temperature dependency is applied to at least one of the electro-optical elements by a temperature characteristic adding means, and the frequency difference is applied. An optical displacement measuring device characterized in that the displacement information of the moving object is detected by causing the two light fluxes to enter the moving object and detecting the scattered light subjected to the Doppler shift by the moving object by the detecting means. 9. The sawtooth wave voltage is obtained by charging an electro-optical element by a constant current circuit to increase an applied voltage and then instantaneously discharging the same at a predetermined cycle. The optical displacement measuring device according to claim 7 or 8. 10. A temperature characteristic of a drive voltage E of an electro-optical element, wherein a temperature characteristic of a constant current flowing out from the constant current circuit is a phase shift of 2πn (n is an integer) of a light beam passing through the electro-optical element. 10. The optical displacement measuring device according to claim 9, wherein the temperature characteristic obtained by combining the temperature characteristic of the interelectrode capacitance C of the electro-optical element is set to be canceled.