JP2001330669A - Laser diode-type distance and displacement meter with double external resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser diode-type distance and displacement meter in which a measurement error is corrected by a double external resonator. SOLUTION: One laser diode 3 is used to cast its radiation light an object 7. A semitransparent mirror (a reference reflector) 6 is placed in the halfway of its optical path to obtain reflected light. Returned light is made incident in an on-line manner on a photodiode 2 which is built in the laser diode 3. The position of the object and the position of the mirror are specified by an FFT method. Thereby, a submicron-order error which exists in a measuring system can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance / displacement meter using return light of a laser diode. More specifically, the present invention relates to a laser diode type distance / displacement meter in which a measurement error is corrected by a double external resonator.

[0002]

2. Description of the Related Art Since the practical use of lasers, laser interferometers have been used for measuring distance and displacement, and have been widely used for position measurement and alignment. This type of micro position sensor has been widely used for robot sensing, machine control, measurement / monitoring of dimensional expansion / contraction, and surface shape measurement.

Recently, various techniques belonging to a frequency modulation type laser diode interferometer for measuring a displacement of submicron (1 μm or less) have been proposed. For example, G. Beheim and K. Fritzsi
(K. Fritsch) Remote Distance Measurement Using Laser Diodes
ters), vol. 21, (1985), pp. 93-94. T. Kubota, Nara (M. Nara) and T. Yoshino (T. Yoshino) have developed an interferometer for measuring displacement and distance in the field of Optics Letter, 1
2 (1987), pp. 310-312, by Kato, Kikuchi, Yamaguchi and Ozono (J. Kato, N. Kikuc)
hi, I. Yamaguchi and S. Ozono) on the measurement of the optical feedback displacement sensor using a laser diode and its performance improvement.
easurement Science & Technology), 6 volumes (199
5) pages 45-52. More recently, T. Uchiyama and G. Lai
A method for measuring the displacement of optically captured particles using a laser diode phase sensor has been proposed, and the IEEE Application Society (IEEE Ind.
ustryApplication Society) at the 1998 Annual Meeting (1998).
It is described on page 9.

In general, an interferometer using a laser diode as a light source has a very simple structure and can be reduced in size and weight. In these interferometer methods, the optical power is also modulated by the injection current of the laser diode. Furthermore, the measurement accuracy of these interferometer methods is also affected by the fluctuation of the emission frequency of the laser diode. If the temperature fluctuation of the laser diode is not kept at 1/500 ° K (= 2 × 10 ⁻³ ° K), the measurement accuracy will be 1 even if the external resonator length is assumed to be about 10 cm due to the frequency fluctuation. It has been estimated that it is practically extremely difficult to keep the wavelength at the / 20 wavelength.

On the other hand, there has been proposed a laser diode interferometer of a frequency modulation type which measures the distance by a method of counting the number of resonance peak values or a method of finding the resonance frequency of an interference signal. There are two examples of the former method. One is Shinohara, Yoshida,
S. Shinohara, H. Yoshida, H. I
keda, K. Nishide, and M. Sumi). This method has a wide dynamic range in the measurement distance, and has relatively high accuracy with a simple structure, and is based on IEEE Transaction on Instrumentation and Measurement.
surement), 41 (1992), pp. 40-44. The other one is Kikuta, Iwata, Nagata
(H. Kikuta, K. Iwata, and R. Nagata). This measures the distance using the wavelength shift of the output light of a laser diode. Applied Optics, 25 (1986), 29
Pages 76-2980.

On the other hand, an example of the latter method is given. This was proposed by T. Kobayashi and was published in the Japanese Journal of Optics, vol.
988), pages 279-284.

A method for measuring the absolute value of the distance is described in Applied Optics, 25, by K. Kikuta, K. Iwata, and Nagata.
Volume (1986), pp. 2976-2980. That is, in this method, two interferometers are combined, one interferometer for reference, and the other for measuring a target distance. By combining the distance measurement method by this method with FFT (Fast Fourier Transform, fast Fourier transform), the method can be applied to a target object that performs multiple reflections, and the measurement accuracy of the resonance frequency can be improved. This combination method is based on M. Suematsu and Takeda
(M.Takeda), AppliedOptic
tics), Vol. 30, (1991), 4046-4055
Listed on the page and published.

As described above, if the reference interferometer is used,
There is an advantage that uncertainty in the relationship between laser current and laser frequency modulation can be avoided. However, the sensor system has a disadvantage that the configuration is complicated.

On the other hand, Japanese Patent Laid-Open No.
No. 9-257415 discloses that a moving or vibrating DUT is irradiated with a laser light beam frequency-modulated in a triangular wave shape and a laser light beam delayed in phase by the laser light, and the beat light is emitted. Methods have been proposed to detect and measure position and displacement. Japanese Patent Application Laid-Open No. 09-072711 (March 18, 1997) by Kaneko, Umemura and Koshimoto discloses that a laser diode and a photodiode are integrated and mounted on a piezo element. A device has been proposed in which an element is oscillated around a minimum value of a photodiode output, and the center of oscillation is controlled to the minimum value by an integrated value of the photodiode output to detect displacement.

Further, Japanese Patent Application Laid-Open No. 09-033 by Watanabe
No. 214 proposes a method in which a modulated laser diode output light is reflected by a target mirror to form an external resonator, and measurement is performed using an interference signal obtained by the external resonator. . Japanese Patent Application Laid-Open No. 06-129812 (published May 13, 1994) by Nishikawa and Ohno discloses a length measuring device in which a heterodyne interferometer is used to correct errors due to fluctuations in the oscillation wavelength and beat frequency of a laser diode. Has been proposed. Since the above-mentioned patent publication employs an interferometer technique, accuracy can be obtained for a target object, but the configuration is complicated.

[0011]

According to the distance and displacement measurement methods known from the above-mentioned literature and patent publication, the phase difference between a pair of laser light beams is determined from an object by an interferometer method. The distance and displacement corresponding to the phase difference were detected. However, the configuration of the interferometer becomes large and complicated, the workability is inferior, and adjustment and maintenance are troublesome. Further, the above methods have the following disadvantages. In the modulation used to determine the phase difference by the interferometer method, the modulation frequency is significantly lower than the corresponding frequency of the optical wavelength, so that the parameter may change during the measurement, and this change is on the order of submicron. Causes an error in the measurement of the distance. Since two laser beams are used in the interferometer, a measurement error occurs due to a change in a parameter of hardware constituting an optical path. Particularly, a phase difference occurs due to an environmental change such as a temperature change or a path change of a minute portion during measurement, and a distance error occurs.

Since the paths of the two laser beams are different, even if the output light of one laser diode is apparently divided into two, two waves having different phases by several hundred to several thousand cycles interfere. Therefore, a wavelength change caused by a state change in the laser diode enters the measurement system as an error. A basic object of the present invention is to provide a distance / displacement meter capable of eliminating the general disadvantages based on the above-mentioned interferometer method and the specific disadvantages when performing submicron precision measurement. is there. A more detailed object of the present invention utilizes a single laser diode,
At the same time that the emitted light hits the target object, a reflected light is obtained by placing a translucent mirror in the middle of the optical path. The above-mentioned specific defect can be removed by removing sub-micron-order errors existing in the measurement system by removing the target defect and specifying the target object position and the mirror position by the FFT method. An object of the present invention is to provide a laser diode type distance / displacement meter with a heavy external resonator.

[0013]

In order to achieve the above object, a laser diode type distance / displacement meter with a double external resonator according to the present invention is basically provided with a laser diode having a monitoring photodiode inside. A lens arranged to face a light emitting surface of the laser diode, for aligning a light beam output from the laser diode to obtain parallel light, and a parallel light obtained from the laser diode via the lens. Input a return light to the photodiode attached to the laser diode by reflecting a part of the laser diode,
A reference reflector for forming a phase reference required for measuring the distance and displacement of the target object, a laser diode driving device for applying a direct current and a modulation current to the laser diode to obtain light emission, and the photodiode A phase calculation device for analyzing the distance / displacement information and the phase reference information included in the return light input to the photodiode and calculating the distance / displacement of the target object; It is configured.

In the laser diode distance / displacement meter with a double external resonator, the double external resonator is formed by a first light transmission space between the reference reflector and the laser diode. A first external resonator, and a second external resonator formed by a second light transmission space between the target object and the laser diode;
In addition, the first external resonator and the second external resonator are partially formed on the same optical path with a common space, and can compensate for an error caused by a change in environmental conditions. It can be configured as follows.

In the laser diode type distance / displacement meter with a double external resonator, the reference reflector is provided along an optical axis connecting the laser diode and the object to be irradiated with a laser beam of the laser diode. The laser diode may be arranged between the laser diode and the target object, and the transmittance may be set at the wavelength so that the target object is irradiated with a sufficient laser light beam.

In the laser diode type distance / displacement meter with a double external resonator, the laser diode driving device applies a sawtooth waveform current to the laser diode to give information necessary for phase analysis in the signal arithmetic device. Sawtooth waveform generator, a DC source for supplying a DC current to the laser diode, and a laser current stabilizing means for keeping DC light input from the laser diode to the photodiode constant. be able to.

In the laser diode type distance / displacement meter with a double external resonator, resonance signals from the reference reflector and the target object are detected by the same photodiode, and the initial phase of each signal is determined by a common trigger timing. It can be configured to be obtained.

In the laser diode type distance / displacement meter with a double external resonator, the resonance signal from the reference reflector and the target object is separated by an electronic circuit, the respective phases are detected, arithmetic processing is performed, and It is possible to use a lock-in phase detection method and a pulse counting method for obtaining a phase from a signal time delay and a signal period for phase detection.

In the laser diode type distance / displacement meter with a double external resonator, the laser diode driving device supplies an arbitrary modulation current to the laser diode to transmit information necessary for phase analysis in the signal operation device. And a DC current source for supplying a DC current to the laser diode, and a laser current stabilizing means for keeping DC light input from the laser diode to the photodiode constant. be able to.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of a laser diode type distance / displacement meter with a double external resonator according to the present invention. The photodiode 2 is built in the laser diode 3 and monitors the output light power of the laser diode 3 to perform feedback control. An aspherical lens is used as the optical system 5 disposed on the projection path of the laser diode 3, and has a function of collimating the laser light output from the laser diode 3 into a parallel light beam. The purpose is to adjust the rate at which the return light from the target object 7 is collimated and fed back to the laser diode 3. The signal operation device 1 analyzes the resonance signal due to the return light by the output of the photodiode 2,
It comprises an electronic circuit for calculating the position of the target object 7 and its displacement or a computer device including a specific algorithm.

The laser diode driving device 4 supplies an injection current to the laser diode 3, and is configured to supply a direct current and a modulation signal current to the laser diode 3. The target object 7 is a reference reflector 6
And is adjusted so that a part of the reflected light can be returned to the laser diode 3. The return light from the reference reflector 6 also enters the laser diode 3. When the reflected light from the reference reflector 6 and the reflected light from the target object 7 are incident on the laser diode 3, a double external resonator is formed, thereby causing oscillation. These optical signals are simultaneously detected by the photodiode 2 integrated with the laser diode 3 and integrated, and the oscillation information is detected at the same time, and is input to the signal operation device 1 constituted by a personal computer through the A / D converter. . The laser resonator signal contains displacement and distance information.

The device having the above-mentioned configuration has a double external resonator. The light output power of the laser diode 3 is monitored by the photodiode 2 mounted in the laser diode 3. This optical output power is determined by a composite resonator consisting of four reflectors. The internal cavity of the laser diode 3 is formed between two side walls in the laser diode, and the spacing between the mode frequencies is determined by the effective length of the laser diode and the effective refractive index of the semiconductor material forming the laser. One of the external resonators is formed between the reference reflector 6 outside the laser and the side wall of the laser diode 3. Still another is formed between the target object 7 and the side wall. The mode frequency interval corresponding to each external resonator is determined by the effective length of the resonator. This effective length is usually much larger than the effective length of the resonator region formed inside the laser diode.

Under the condition that the mode number of the mode frequency determined by the external resonator is an integral multiple of that of the internal resonator, the phase of the return light beam from the external resonator or the object is determined by the internal resonator. Since the phase of the light beam coincides with the external structure, laser resonance is obtained with the external structure. If the amount of feedback from both the reflector and the object is small, the interferences are considered to be independent of each other. When the injection current of the laser diode is modulated by an external input wave, the optical frequency of the laser diode is also modulated in the same manner as the external input wave. By using the part where the current-frequency modulation is linear,
Positive feedback and negative feedback by the external resonator occur periodically with respect to the current modulation.

The laser oscillation frequency is determined by the speed and the distance from the laser diode to the reflector and the object, and changes periodically with time. FIG. 2 shows a state in which a resonance signal from an external resonator is processed by an analog circuit together with waveforms. Reference reflector 6
Since the distance between the target object 7 and the laser diode 3 is different, the resonator formed by the reference reflector 6 and the resonator formed by the target object 7 have different resonance frequencies.

The injection current (signal A) shown in FIG. 2 not only changes the optical frequency, but also changes the total output light power of the laser diode. The resonance signal from the external resonator is
The signal is superimposed on the light intensity modulation and becomes a signal (C), and this current limits the range in which the signal can be amplified. Therefore, in order to remove this light intensity modulation before amplification, subtraction by a modulation signal is performed by a difference circuit (signal D). By this processing, the signal can be further digitized and processed. The pulse signal (B) synchronized with the rise of the signal (A) is used as a trigger for taking timing.

The resonance frequency is proportional to the length of the external resonator. The distance L _{2 of the} target object is given as a function of the distance L ₁ of the reference reflector: L ₂ = L ₁ (f ₂ / f ₁ ) (1) The resonance frequency is used to determine the distance L ₂ to the target object. Here, f ₁ and f ₂ are the reference reflectors 6 respectively.
And the resonance frequency of the resonator including the target object 7, and is detected by the power spectrum of the signal. In the above (1), the only parameter for determining the distance L ₂ of the target object, the reference reflector distance L ₁
In it, it is possible to calibrate the distance L ₁ in advance. Therefore, the modulation ratio of the optical frequency versus the injection current and its drift (fluctuation) is not important in such a system. Phase information is also included in the resonance signal. If the distance between the reference reflector and the object does not change, these resonances occur exactly in accordance with the timing of the modulation signal current (signal B in FIG. 2). The resonance peak represents the phase component of the signal, and moves with the position of the target object. The resonance period of the signal corresponds to the optical path length of one wavelength. If the signal phase corresponding to the resonance frequency of the target object is lock-in detected,
From the phase of the resonance signal, the distance to the target object can be detected with a sensitivity much shorter than the wavelength of light.

However, due to changes in the operating temperature of the laser diode and changes in the injection current, noise and drift exist in the optical frequency. With the introduction of a reference reflector, these errors in the phase measurement can be reduced. Furthermore, since the resonance signal from the reference reflector and the resonance signal from the target object use the same trigger, errors due to the trigger can be reduced. Since the same light source is used for the resonator of the reference reflector and the resonator of the target object, the floating of the optical frequency is considered to be the same. The longer the resonator, the greater the phase error. If the reference reflector is firmly fixed, the phase variation is purely due to the frequency variation of the laser diode, and to compensate for the phase of the target object, this frequency is equal to the ratio of the target object distance to the reference reflector. Fluctuations are returned. That is, φ ₂ ′ = φ ₂ −φ ₁ f ₂ / f ₁ (2) is obtained. Here, φ ₂ and φ ₂ ′ are the phases of the resonance signal before and after compensation, respectively, and φ ₁ is the phase of the resonance signal of the reference reflector.

FIG. 2 is an explanatory diagram showing signals of respective parts of the apparatus shown in FIG. The resonance signal of the double external resonator is pre-processed by an analog processing circuit as shown in FIG. That is, the output of the laser diode driving device 4 is a sawtooth waveform modulation signal (A) that changes periodically with the DC bias current.
Is applied to the laser diode 3. The light intensity signal detected by the photodiode 2 is a double resonance signal (C) superimposed on the sawtooth light intensity signal, which is converted from the optical signal to a current signal. The signal current is converted into a voltage signal before removing the sawtooth change in light intensity with reference to the current modulation wave.

FIG. 3 shows the resulting voltage signal as a function of time. Since the obtained signal contains resonance information, this signal is digitized by the A / D converter using a trigger pulse synchronized with the rise of the sawtooth waveform as a start synchronization signal. Since the peak position of the trigger pulse serves as a reference for calculating the phase of the interference signal, the timing of the trigger pulse is important for calculating the phase in displacement / distance measurement. The measured data is analyzed using a Fourier transform technique to determine the resonance frequency and the initial phase. The resonance frequency can be easily extracted from the power spectrum.
If a pair of resonance frequencies corresponding to the reference reflector 6 and the target object 7 are read, the distance between the target object 7 can be calculated by the above-mentioned equation (1).

FIG. 4 shows a power spectrum obtained by Fourier-transforming the frequency (D) shown in FIG. Since the injection current of the semiconductor laser can be modulated at high speed, the sampling frequency here is determined by the sampling frequency of the A / D converter used. For the phase measurement, a Fourier transform component at a pair of resonance frequencies is used, and this principle is the same as the lock-in phase detection method. That is, a coefficient in a pair of resonance frequency Fourier transforms is calculated, and the phase of the signal is calculated from the real part and the imaginary part.

FIG. 5 shows removal of the error phase signal obtained by the phase calculation method using the Fourier transform and the error phase signal by the reference reflector. FIG. 5A shows an error phase signal when the phase is obtained from the Fourier coefficient of the resonance only in the reference reflector 6, and FIG. 5B shows the phase from the Fourier coefficient of the resonance only in the target object 7. Is a phase error signal obtained when is obtained.

FIG. 6 shows the phase error of the target object 7 obtained by referring to the phase error of the reference reflector 6.
Shows the value after performing the processing in FIG. FIG.
In FIG. 5, it can be seen that the phase error is smaller than that of any of the portions shown in FIGS. 5 (a) and 5 (b). Since the phase measurement is performed as a function of time, a pair of phase values corresponding to a pair of resonance frequencies is obtained by one signal acquisition and one Fourier analysis. Therefore, the relative displacement between the reference reflector 6 and the target object 7 is given by the phase change between both resonators. Assuming that the distance to the reference reflector 6 does not change, the laser diode 3
The measurement error due to the optical frequency fluctuation is reduced according to the above-mentioned equation (2).

FIG. 7 is a block diagram showing a first embodiment of the present invention, which further embodies the basic configuration shown in FIG. In this embodiment, a mirror fixed to PZT is used as the target object 7, and the characteristics of PZT are evaluated. The part corresponding to the above-described signal operation device 1 includes a computer 11, an A / D converter 12, and a differential amplifier 13 forming a subtraction circuit. The laser diode driving device 4 includes a driver and a saw-tooth waveform generator 14. By using a cable, the laser diode 3 and the signal operation device 1 can be installed separately. The laser diode 3, the photodiode 2, and the reference reflector 6 form a sensor unit, and the sensor unit is an integrated unit of these component parts. Such a sensor system is assembled in consideration of compactness, and can be assembled small and lightweight. Therefore, there is a feature that the measurement object can be compactly configured by integrating the target object 7 and the sensor unit.

FIG. 8 is a graph showing a measurement example of the operation of the mirror of the apparatus shown in FIG. In this example, the piezo oscillator P
When the ZT is driven by a triangular wave drive voltage having a frequency of 0.2 Hz, the obtained displacement (vibration) of the mirror is shown. This was obtained by measurement using the laser diode type distance / displacement meter with a double external resonator shown in FIG.

Next, in order to examine the operation of the signal operation device 1 in the present measuring instrument, the measured phase floating is shown in FIG.
9A shows an initial phase determined by reflected return light from the reference reflector 6, FIG. 9B shows an initial phase determined by reflected return light from the target object 7, and FIG. These are data respectively representing the results obtained by subtracting the phase shift of the return light from the reference reflector 6 from the phase shift of the return light from the. From these data, it can be seen that the stability of the measurement system is improved by the presence of the reference reflector 6. When the PZT is displaced minutely by nanometers, the hysteresis characteristic of the movement can be ignored. However, when displaced over a large range, the hysteresis characteristic becomes remarkable. FIG. 10 shows the expansion and contraction of the piezoelectric element with respect to the applied voltage measured by the system shown in FIG. 7, and the hysteresis characteristics are measured.

FIG. 11 shows a second embodiment of the present invention which embodies the basic configuration shown in FIG. FIG.
In FIG. 7, the same elements as those shown in FIG. 7 are denoted by the same reference numerals. The difference from FIG. 7 is that the aspheric lens 5 and the reference reflector 6 are connected not by a space but by an optical fiber 20. When the space between the lens 5 and the reference reflector 6 is supplied in a space, it is necessary to arrange the space so that the optical axis of the lens 5 and the optical axis of the reference reflector 6 coincide with each other. Has been fixed. However, when the two are connected by the optical fiber 20, the position can be moved flexibly because the flexibility of the optical fiber 20 is used. The reference reflector can use a fiber end face or a lens end face.

FIG. 12 shows partly a third embodiment of the device according to the invention. 12, the same elements as those shown in FIG. 7 are denoted by the same reference numerals. The difference from FIG. 7 is that the objective lens 21 is
And the target object 7 which is a measured surface, and the measured surface has a structure for mechanically scanning in the X-axis direction and the Y-axis direction perpendicular to the optical axis. Scanning in both the X and Y directions is performed by a stepping motor or a stage equipped with a piezoelectric element under computer control.
In the present embodiment, insertion of the objective lens 21 and X and Y
By continuing the observation while specifying the position of the target object by scanning the axis, the three-dimensional shape of the target object 7 can be favorably observed.

FIG. 13 partially shows a fourth embodiment according to the present invention. 13, the same elements as those shown in FIG. 7 are denoted by the same reference numerals. The amplitude of the modulation signal (sawtooth waveform) provided in the laser diode driving device 4 changes according to the length of the optical fiber 20-i. Further, 22 is an optical switch, 20-1 to 20-n are n
A reference reflector mounted on one end of each of the optical fibers 20-1 to 20-n according to the contact position of the optical switch, and a distance for causing the light beam to enter the target object 7 in parallel. By changing the distance, a different reference distance can be set, so that the measurable distance can be changed.

Various modifications can be made to the embodiment described in detail above within the scope of the present invention.

[0040]

According to the laser diode type distance / displacement meter with a double external resonator according to the present invention, a reference reflector is added to a measuring system to form a reference resonator, thereby reducing the optical frequency drift of the laser diode. Since the resulting measurement error can be corrected, it is possible to stably measure the absolute distance and the displacement of several nanometers, which were not possible with the conventional method. In addition, since the measurement system includes a laser resonator, it is possible to stably measure a distance of several meters with an accuracy of 1 mm or less. The phase error can be reduced by using a reference resonator constituted by a reference reflector. This makes it possible to apply this laser diode type distance / displacement meter to various applications, such as robot sensors, machining control, monitoring of expansion and contraction,
And it can be used for surface roughness measurement.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic embodiment of a laser diode type distance / displacement meter with a dual external resonator according to the present invention.

FIG. 2 is a main circuit section and a waveform diagram for explaining a schematic operation of the embodiment of FIG. 1;

FIG. 3 is a graph showing the output voltage signal of the subtraction circuit as a function of time.

FIG. 4 shows a power spectrum obtained by Fourier-transforming the frequency (D) shown in FIG.

FIG. 5 shows removal of an error phase signal obtained by a phase calculation method using a Fourier transform, and removal of the error phase signal by a reference reflector. FIG. The error phase signal obtained when the phase is obtained, and the part shown in FIG. 3B is a phase error signal obtained when the phase is obtained from the Fourier coefficient of resonance only in the target object.

FIG. 6 is a graph showing a phase error of a target object obtained by referring to a phase error of a reference reflector.

FIG. 7 is a block diagram showing a first embodiment of the present invention in which the basic configuration shown in FIG. 1 is further embodied.

FIG. 8 is a graph of a measured output of displacement when the mirror is displaced by PZT in the embodiment of FIG. 7;

9A and 9B are diagrams showing the floating of the phase measured to check the operation of the signal operation device in the measuring instrument, wherein FIG. 9A shows the initial phase determined by the reflected return light from the reference reflector 6; , (B) is the initial phase determined by the reflected return light from the target object, and (c) is the subtraction of the floating light phase from the reference reflector 6 from the floating light phase from the target object 7. It is a graph each showing the result obtained by doing.

10 shows expansion and contraction of a piezoelectric element with respect to an applied voltage measured by the system shown in FIG. 7, and a hysteresis characteristic is measured.

11 is a block diagram showing a second embodiment of the present invention in which the basic configuration shown in FIG. 1 is further embodied.

FIG. 12 is a block diagram showing a third embodiment of the present invention in which the basic configuration shown in FIG. 1 is further embodied.

FIG. 13 is a block diagram showing a fourth embodiment of the present invention in which the basic configuration shown in FIG. 1 is further embodied.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 signal operation device 2 photodiode 3 laser diode 4 laser diode driving device 5 lens (aspherical lens) 6 reference reflector 7 target object 11 computer (PC) 12 A / D converter 13 differential amplifier 14 sawtooth waveform generator 20 light Fiber 21 Objective lens 22 Optical switch

Continuing from the front page (72) Inventor Seki Akira 1-22-6 Hirosawa, Hamamatsu-shi, Shizuoka Prefecture 5-23 Hirosawa House (72) Inventor Shigenobu Shinohara 2-2 Anmacho, Hamamatsu-shi, Shizuoka Prefecture Anmacho Park Homes 404 (72 ) Inventor Wang Ning 3-22-1, Hamamatsu International Exchange Hall, Hamamatsu City, Shizuoka Prefecture (72) Inventor Takahiko Sato 2099-6 Neken, Hamakita City, Shizuoka Prefecture F-term (reference) 2F065 AA06 AA09 EE00 FF13 FF51 FF61 GG06 HH03 JJ01 JJ18 LL00 LL02 LL04 LL10 MM03 NN02 NN08 NN17 PP12 PP22 QQ01 QQ03 QQ16 QQ25 QQ26 5F073 AB21 AB27 AB28 AB29 BA09 FA02 GA12 GA24 5J084 AA05 BA04 BA36 BA51 BB02 BB31 CA08 CA31 CA49 EA04

Claims (7)

[Claims] 1. A laser diode having a monitoring photodiode therein, and a lens arranged to face a light emitting surface of the laser diode and aligning a light beam output from the laser diode to obtain parallel light. Reflecting a part of the parallel light obtained from the laser diode through the lens and returning the light to the photodiode attached to the laser diode,
A reference reflector for forming a phase reference necessary for measuring displacement, a laser diode driving device for supplying a direct current and a modulation current to the laser diode to obtain light emission, and the photodiode connected to the photodiode, A phase calculation device for analyzing the distance / displacement information and the phase reference information included in the return light input to obtain the distance / displacement of the target object,
Laser diode type distance / displacement meter with dual external resonator. 2. The laser diode distance / displacement meter with a double external resonator according to claim 1, wherein the double external resonator transmits first light between the reference reflector and the laser diode. A first external resonator formed by a space, and a second external resonator formed by a second light transmission space between the target object and the laser diode; The external resonator and the second external resonator are partially formed on the same optical path with a common space, and are configured to be able to compensate for errors caused by changes in environmental conditions. Laser diode type distance / displacement meter with dual external resonator. 3. The laser diode distance / displacement meter with a dual external resonator according to claim 1, wherein the reference reflector connects the laser diode and the target object to be irradiated with a laser beam of the laser diode. Along the optical axis, disposed between the laser diode and the target object, and the transmittance is set at the wavelength so that the target object is irradiated with a sufficient laser light beam. A laser diode distance / displacement meter with a dual external resonator. 4. A laser diode type distance / displacement meter with a dual external resonator according to claim 1, wherein the laser diode driving device applies a sawtooth waveform current to the laser diode and performs a phase analysis in the signal operation device. A sawtooth waveform generator for giving necessary information to the laser diode, a DC source for supplying a DC current to the laser diode, and a laser current stabilization for keeping DC light input from the laser diode to the photodiode constant. And a laser diode type distance / displacement meter with a dual external resonator. 5. The laser diode type distance / displacement meter with a dual external resonator according to claim 1, wherein resonance signals from the reference reflector and the target object are detected by the same photodiode, and each of the signals is detected by a common trigger timing. A laser diode type distance / displacement meter with a dual external resonator, wherein an initial phase of the signal is obtained. 6. The laser diode type distance / displacement meter with a double external resonator according to claim 1, wherein a resonance signal from the reference reflector and the target object are separated by an electronic circuit, and respective phases are detected. A laser diode type distance / displacement with a double external resonator, wherein a lock-in phase detection method is used for phase detection and a pulse counting method for obtaining a phase from a signal time delay and a signal period is used for phase detection. Total. 7. The laser diode type distance / displacement meter with a dual external resonator according to claim 1, wherein the laser diode driving device applies an arbitrary modulation current to the laser diode and outputs a phase in the signal operation device. A modulation waveform generator for providing information necessary for analysis, a DC source for supplying a DC current to the laser diode, and a laser current stabilization for maintaining a constant DC light input from the laser diode to the photodiode. Laser diode type distance / displacement meter with dual external resonators.