JPH10300851A - Distance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent axial shift arising between the receiving optical axis of a signal light and the projecting optical axis of a reference light and provide good spatial coherence for a laser beam due to change of the angle of a scanning mirror while the signal light is scanned on an object and returned. SOLUTION: An optical beam LB emitted from a projector 2 is split into a signal light LS and a reference light LR with a first polarizing beam splitter 5. The signal light LS is scanned to an object by a scanning mirror 9. The signal light LS reflecteed from the object and reflected form the scanning mirror 9 again is reflected form a correcting mirror 11 and then injected to the beam splitter 6, where it is combined with the reference light LR. The correcting mirror 11 is angularly controlled with the direction of the signal light LS scanned by the scanning mirror 9 so that the optical axes of the signal light LS and the reference light LR can be almost parallel to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a distance measuring device. In particular, the present invention relates to a distance measuring device that measures a distance to an object by an optical heterodyne method.

[0002]

2. Description of the Related Art In an optical heterodyne type distance measuring apparatus, an axis deviation between a light projecting optical axis where reference light reaches a light receiving section and a light receiving optical axis where signal light reflected by an object reaches a light receiving section. Is present, the spatial coherence of the laser light is reduced due to an axis shift between the two optical axes. When the spatial coherence decreases, the S / N ratio of the distance measuring device deteriorates, and the distance measurement performance decreases. For this reason, it is necessary to precisely adjust the projecting optical axis and the receiving optical axis of the optical heterodyne type distance measuring device, but once the projecting optical axis and the receiving optical axis are fixed, the optical system must be adjusted once. In other words, there is no possibility that an axis deviation will occur during operation other than the aging deviation.

However, in an optical heterodyne type distance measuring device having a mechanism for scanning a laser beam using a scan mirror or the like, when the viewing angle (detection area) is widened and the distance measurement distance is long (for example, about 100 m). However, even if the light projecting optical axis and the light receiving optical axis are precisely adjusted, the axial deviation between the light projecting optical axis and the light receiving optical axis becomes large for the following reasons.

FIG. 10 is a view showing an example of an optical system 51 of a conventional optical heterodyne type distance measuring apparatus in which a laser beam LB is scanned by a scan mirror. In this optical heterodyne type distance measuring device,
LB emitted from the laser beam LB is made incident on the first polarization beam splitter 5, and a part of the laser beam LB is converted into a signal beam LS.
Are transmitted through the first and second polarizing beam splitters 5 and 8, and are further scanned by the scan mirror 9 onto the detection area of the object 10. The signal light LS reflected by the object 10 is
After being reflected by the scan mirror 9, the light is further reflected by the second polarization beam splitter 8, and further reflected by the reflection mirror 52 and the beam splitter 6. On the other hand, part of the laser beam LB that has entered the first polarization beam splitter 5 is reflected by the first polarization beam splitter 5 as reference light LR.

[0005] Thus, the signal light LS reflected back from the object 10 and reflected by the beam splitter 6 and the reference light LR transmitted through the beam splitter 6 interfere with each other to generate a beat signal. The light is received by the element 53, and the distance to the object 10 is measured based on the beat signal.

In such an optical heterodyne type distance measuring apparatus, when the viewing angle is widened and the distance is long, the signal light LS is emitted from the light projecting unit 2 and scanned by the scan mirror 9. It takes time until the light is reflected by the object 10 and returns to the scan mirror 9, and during that time, the scan mirror 9 rotates by a large angle. Therefore, as shown by a broken line or a two-dot chain line in FIG. The deviation of the optical axis becomes large.

More specifically, when the scan mirror 9 is fixed, the signal light LS reflected by the scan mirror 9 at the position indicated by the solid line in FIG. Are reflected by the scan mirror 9 at the same solid line position, and further reflected by the second polarization beam splitter 8, the reflection mirror 52, and the beam splitter 6. At this time, the light receiving optical axis of the signal light LS reflected by the beam splitter 6 matches the light projecting optical axis of the reference light LR transmitted through the beam splitter 6.

However, when the scan mirror 9 is rotating clockwise in FIG. 10, the signal light LS is reflected by the scan mirror 9 at the solid line position in FIG.
Then, the scan mirror 9 is rotated to the position indicated by the broken line. For this reason, the signal light LS is reflected by the second polarization beam splitter 8, the reflection mirror 52, and the beam splitter 6 via a path shown by a broken line, and an axis shift between the reference light LR and the optical axis occurs.

Similarly, when the scan mirror 9 is rotating counterclockwise in FIG. 10, the signal light LS is reflected by the scan mirror 9 at the solid line position in FIG.
When the light is reflected and returned at 0, the scan mirror 9 is rotated to the position indicated by the two-dot chain line. Therefore, the signal light LS is 2
The light is reflected by the second polarization beam splitter 8, the reflection mirror 52, and the beam splitter 6 through a path indicated by a chain line, and causes an axis shift between the reference light LR and the optical axis.

As a result, there has been a problem that the coherence of the laser beam LB is reduced, and the distance measuring performance of the optical heterodyne type distance measuring device having a mechanism for scanning the laser beam LB is deteriorated.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and has as its object to reduce the misalignment between the light projecting optical axis and the light receiving optical axis by optical scanning. The object of the present invention is to improve the spatial coherence of the laser beam by preventing the distance, and to improve the distance measuring performance of the distance measuring device.

[0012]

DISCLOSURE OF THE INVENTION In a distance measuring apparatus according to the present invention, a light beam is divided into a signal light and a reference light, and the signal light is scanned on a detection area by an optical scanning means. In the distance measuring device that measures the distance to the object by measuring the phase difference of the reference light, the light reflection direction is variable in the light receiving optical path after the signal light is reflected again by the light scanning unit. It is characterized in that a correction mirror is provided.

[0013] More specifically, the distance measuring device of the present invention comprises a polarization separating means for separating a light beam emitted from a light projecting unit into a signal light and a reference light, and scans the signal light toward a detection area. Optical scanning means for causing the light beam to be reflected by the object, reflected by the light scanning means, and combined with the reference light, and arranged on a light receiving optical path between the light scanning means and the light combining means. And a means for controlling the correction mirror such that the optical axes of the signal light and the reference light having passed through the light combining means substantially coincide with each other.

In the distance measuring device according to the present invention, the signal light is reflected again by the optical scanning means, and then is reflected in the light receiving optical path.
Since the correction mirror in which the light reflection direction is variable is provided, the optical scanning means can be used when the signal light is emitted toward the object and when the signal light is reflected by the object and returns to the optical scanning means. Even if the mirror angle greatly changes, the change in the optical axis of the signal light due to the change in the mirror angle of the optical scanning means can be corrected by the correction mirror.

Therefore, according to the present invention, even if the distance to the object is long, the optical axis of the signal light and the reference light is less likely to be misaligned, and the spatial coherence of the light beam is prevented from lowering. As a result, the S / N ratio of the distance measurement device can be improved, and the distance measurement performance can be improved.

A method of controlling the correction mirror in the distance measuring apparatus in which the signal light is reciprocally scanned by the optical scanning means is as follows: When the signal light is scanned in one direction,
The correction mirror is fixed at the first angle so that the optical axis of the signal light on the light receiving optical path coincides with the optical axis of the reference light, and when the signal light is scanned in the other direction, The correction mirror may be fixed to the second angle so that the optical axis of the signal light and the optical axis of the reference light substantially coincide with each other.

According to this control method, it is only necessary to alternately fix the correction mirror at two angles in accordance with the scanning direction of the signal light, so that the control of the correction mirror is simplified.

Further, a transmittance control means such as PLZT is provided in the light projecting optical path of the signal light, and the signal light is AM-modulated by changing the transmittance of the transmittance control means in a sine wave shape. For example, it is not necessary to obtain an optical beat by causing two light beams having slightly different frequencies to interfere with each other, and the optical beat can be easily generated by the transmittance control means.

Another distance measuring apparatus according to the present invention divides a light beam into signal light and reference light, scans the signal light only in one direction by an optical scanning means, and outputs the signal reflected by an object. In a distance measuring apparatus for measuring a distance to an object by measuring a phase difference between light and a reference light, a correction mirror is provided in a light receiving optical path after signal light is reflected again by the light scanning means, and a light receiving means is provided. It is characterized in that the angle of the correction mirror is fixed such that the optical axis of the signal light on the optical path substantially coincides with the optical axis of the reference light.

Even in this distance measuring apparatus, since the deviation of the optical axis between the signal light and the reference light can be suppressed, the spatial coherence of the light beam can be reduced even if the distance of the object to be detected becomes long. It is possible to prevent the decrease, improve the S / N ratio of the distance measuring device, and improve the distance measuring performance. Moreover, in this case, since the correction mirror may be fixed at a fixed position, the control position accuracy of the correction mirror does not require high accuracy, and the configuration can be simplified.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

(Configuration of Optical System) FIG. 1 is a diagram showing an optical system 1 of a distance measuring device according to an embodiment of the present invention. First, the optical system 1 will be described. The light projecting unit 2 includes a laser diode 3 for generating a laser beam LB, and a collimating lens 4 for collimating the laser beam LB emitted from the laser diode 3. The laser diode 3 emits a continuous wave (Continuous Wave), and the light projecting unit 2 emits a collimated laser beam LB. A first polarizing beam splitter 5 is disposed in front of the light projecting unit 2, and the laser beam LB emitted from the light projecting unit 2 is converted by the first polarizing beam splitter 5 into a signal light LS and a reference light LR.
Is separated into The first polarization beam splitter 5 is an S-polarized component (hereinafter, the direction of the S-polarized light is determined based on the polarization direction of the light component transmitted through the first polarization beam splitter 5).
And the P-polarized component (hereinafter referred to as P based on the polarization direction of the light component reflected by the first polarization beam splitter 5).
(Determining the direction of polarization), the signal light LS passes through the first polarization beam splitter 5 and becomes S-polarized light, and the reference light LR is reflected by the first polarization beam splitter 5 and becomes P-polarized light. It becomes light.

A beam splitter 6 is disposed on the reflection side of the first polarization beam splitter 5, and the reference light LR of the P-polarized light component reflected by the first polarization beam splitter 5 is incident on the beam splitter 6.

On the transmission side of the first polarization beam splitter 5, a PLZT 7, a second polarization beam splitter 8, and a scan mirror 9 are arranged, and a signal of an S-polarized component transmitted through the first polarization beam splitter 5 is provided. Optical LS is PL
Pass through ZT7. PLZT7 has a 500 kHz sin
The transmittance is controlled by a wave, and the signal light LS passing through the PLZT 7 is converted into 500 kHz AM modulated light by the PLZT 7. Here, the signal light LS modulated by the PLZT 7
Is the maximum light intensity of P ₀ , and the laser beam LB by PLZT7
Let ν be the modulation frequency and t be the time, and the signal light LS is represented by √ (2P ₀ ) sin (2πνt).

Since the polarization direction of the second polarization beam splitter 8 matches the polarization direction of the first polarization beam splitter 5, the signal light LS modulated by the PLZT 7 is transmitted through the second polarization beam splitter 8 and scanned. The light is reflected by the mirror 9 and scanned by the scan mirror 9 toward the detection area of the object 10. When the object 10 is a reflector (a collection of a large number of optical corner cubes), the signal light LS rotates by 90 degrees when reflected by the object 10, so that the signal light LS is P Reflected as polarized light. The signal light LS reflected by the object 10 returns to the scan mirror 9 again, and is reflected by the scan mirror 9.
Since this signal light LS is light of the P polarization component, it is reflected by the second polarization beam splitter 8. On the reflection side of the second polarization beam splitter 8, a correction mirror 11 is arranged. The rotation angle of the correction mirror 11 can be precisely controlled by a control motor such as a pulse step motor.

When the object 10 does not rotate the direction of polarization of the laser beam LB when reflecting the laser beam LB, such as a cat's eye (reflection mark), the second polarization beam splitter 8 By inserting a quarter-wave plate (not shown) between the scan mirror 9 and the scan mirror 9, the laser beam LB reflected by the object 10 can be reflected by the second polarization beam splitter 8.

A beam splitter 6 such as a half mirror is disposed on the reflection side of the correction mirror 11, and the reference light LR of the P-polarized component reflected by the first polarization beam splitter 5 and the reflection by the correction mirror 11. The signal light LS of the P-polarized component is partially reflected by the beam splitter 6 and partially transmitted. The signal light LS partially reflected by the beam splitter 6 and the reference light LR partially transmitted by the beam splitter 6 are mixed and received by the light receiving element 12. The signal light LS partially transmitted by the beam splitter 6 and the reference light LR partially reflected by the beam splitter 6 are mixed and received by the light receiving element 13.

Since the signal light LS and the reference light LR that have entered the light receiving elements 12 and 13 have the same polarization directions, an optical beat is generated, and a beat signal is generated between the two light receiving elements 12 and 13. Further, the photocurrent (beat signal) output from the light receiving element 12 and the photocurrent (beat signal) output from the light receiving element 13 are input to the differential amplifier 14 and converted into an electric signal by the differential amplifier 14. .

(Processing Circuit) FIG. 2 is a block diagram showing a signal processing circuit 21 in the optical heterodyne type distance measuring apparatus. The signal processing circuit 21 includes the light receiving element 12,
The signal processing unit 13 has a function of processing a signal from the control unit 13 to calculate a distance to the target object 10 and driving and controlling the light projecting unit 2, the PLZT 7, the scan mirror 9, and the correction mirror 11.

The laser diode drive circuit 22 drives the laser diode 3 continuously (CW) in response to a drive signal from a control unit (microcomputer) 26 to make the laser diode 3 emit light continuously.

The PLZT drive circuit 23 controls the transmittance of the PLZT 7 with a 500 kHz sine wave according to a control signal from the control unit 26.

The optical scanner drive circuit 24 rotates the scan mirror 9 at a predetermined angular speed in a predetermined angle range according to a control signal from the control unit 26.

The correction mirror control circuit 25 includes a control unit 26
, The rotation angle of the correction mirror 11 is controlled in synchronization with the rotation angle of the scan mirror 9 as described later.

The reception signal processing portion of the signal processing circuit 21
AM demodulation circuit 27, DC cut filter 28, phase shifter 2
9, first and second mixing circuits 30 and 31, low-pass filters (LPFs) 32 and 33, and a distance calculator 34. Thus, the signal output from the differential amplifier 14 enters the AM demodulation circuit 27 and is demodulated into a signal of 500 kHz. After the signal demodulated by the AM demodulation circuit 27 passes through the DC cut filter 28, the signal is mixed by the first mixing circuit 30 with the same 500 kHz sine wave as that modulated by the PLZT 7, and
In the mixing circuit 31, a signal (cos wave) obtained by shifting the sine wave of 500 kHz by 90.degree.
And mixed. The signals output from the first mixing circuit 30 and the second mixing circuit 31 pass through low-pass filters 32 and 33, respectively, to remove high-frequency components. The DC signals I and Q that have passed through the low-pass filters 32 and 33 are sent to a distance calculator 34,
Then, a distance R to the object 10 is calculated based on the signals I and Q, and the obtained distance R is output as distance measurement data.

According to the signal processing circuit 21 having such a configuration, the distance R to the object 10 can be obtained based on the following principle. Now, it is assumed that the modulation frequency by PLZT7 is ν (= 500 kHz), the time is t, and the modulation signal by PLZT7 is represented by sinωt. Further, the phase difference between the reference light LR and reciprocating the signal light LS between the object 10 and phi, when the intensity of the signal output from the differential amplifier 14 and A ^2/2, the differential amplifier 14 Is represented by Asin (ωt + φ)... The first mixing circuit 30 adds this signal to
When mixing with the same sine wave as PLZT7, that is, sinωt, the following mixing signal is obtained. Asin (ωt + φ) · sinωt = (A / 2) [cosφ−cos
(2ωt + φ)] When this mixing signal passes through the low-pass filter 32, only the DC component passes, and I = (A / 2) cosφ... Is obtained.

The same sine wave as that of the PLZT 7 is applied to the phase shifter 2.
9, a 90 ° phase shift results in a cos wave, ie, cosω.
Since t is mixed with the equation signal in the second mixing circuit 31, the next mixing signal is obtained. Asin (ωt + φ) · cosωt = (A / 2) [sinφ + sin
(2ωt + φ)] When this mixing signal passes through the low-pass filter 33, only the DC component passes, and Q = (A / 2) sinφ... Is obtained.

In the distance calculating section 34, the phase shift φ from the signals I and Q from the low-pass filters 32 and 33 is obtained.
Can be obtained by the following equation. φ = arctan (Q / I) ...

The phase shift φ generated while the laser beam LB travels the reciprocating distance 2R between the target 10 and the laser beam LB can be expressed as φ = 2πν (2R / c), where c is the speed of light. From the equation and the equation, R = (cφ) / (4πν) = [c / (4πν)] · arctan (Q / I) is obtained. That is, the distance calculation unit 34 can calculate the distance R to the object 10 from the outputs I and Q of the low-pass filters 32 and 33 based on the equation.

(Control of Mirror for Correction) In such an optical heterodyne type distance measuring apparatus, the laser beam LB
When light is reflected by the scan mirror 9 and irradiates the object 10 and reflected by the object 10 and returns, it is assumed that the correction mirror 11 is fixed because the scan mirror 9 is rotating. As described in the example, an axis shift occurs between the projection optical axis of the reference light LR and the light reception optical axis of the signal light LS.

The correction mirror 11 is controlled so as to correct this axis deviation. That is, as shown in FIG. 3, when the scan mirror 9 scans the signal light LS while rotating clockwise (scanning rightward), the correction mirror 1
1 rotates counterclockwise, stops at the PA position, and
The light projecting optical axis of S is corrected, and the light projecting optical axis of the signal light LS incident on the beam splitter 6 and the light receiving light axis of the reference light LR are substantially matched.

Conversely, when the scan mirror 9 is scanning the signal light LS while rotating counterclockwise (scanning leftward), the correction mirror 11 rotates clockwise as shown in FIG. Then, it stops at the PB position and corrects the light projection optical axis of the signal light LS, so that the light projection light axis of the signal light LS incident on the beam splitter 6 and the light receiving light axis of the reference light LR substantially coincide.

FIGS. 5A, 5B and 5C are diagrams specifically showing control timings of the scan mirror 9 and the correction mirror 11. FIG. FIGS. 5A and 5B show a horizontal synchronization signal and a vertical drive signal of the optical scanner drive circuit 24 for driving the scan mirror 9, and the signal light LS is transmitted by the scan mirror 9 as shown in FIG. 200 horizontally
Two-dimensional scanning (raster scanning) is performed at an angle of 50 mrad in the vertical direction with mrad. On the other hand, the correction mirror 11
Repeats a counterclockwise PA position as shown in FIG. 3 and a clockwise PB position as shown in FIG. 4 alternately in synchronization with the falling edge of the vertical synchronization signal of the scan mirror 9. As a result, the axis deviation between the light receiving optical axis of the signal light LS reflected by the beam splitter 6 and the light projecting optical axis of the reference light LR passing through the beam splitter 6 is corrected.

Here, the PA position in the counterclockwise direction and the PB position in the clockwise direction of the correcting mirror 11 are, for example, assuming the detection distance of the object 10 (for example, 80 m).
You just have to decide. Alternatively, it may be determined experimentally.

Therefore, even if the object 10 which is long distance away is measured, the axis deviation between the signal light LS and the reference light LR reflected by the object 10 is corrected by the correction mirror 11, so that
Spatial coherence is improved, the S / N ratio of the signal is improved, and the distance measurement performance is improved.

FIG. 7 shows the signal processing circuit 21 when the correction mirror 11 is fixed at the center position.
FIG. 9 is a diagram showing a result obtained by simulating an S / N ratio of the target, where the horizontal axis represents the distance of the object 10 and the vertical axis represents the S / N ratio.
Ratio. Table 1 shows a part of the simulation results.

[0045]

[Table 1]

As can be seen from FIG. 7, the correction mirror 11
Is fixed, the S / N ratio rapidly deteriorates as the distance from the object 10 increases.

FIG. 8 is a diagram showing a result obtained by simulation of the S / N ratio of the signal processing circuit 21 when the correction mirror 11 is controlled on the assumption that the object 10 is at a distance of 80 m. The horizontal axis is the distance of the object 10,
The vertical axis is the S / N ratio. Table 2 shows part of the simulation results.

[0048]

[Table 2]

As can be seen from FIG. 8, the correction mirror 11
Is controlled, the distance to the object 10 is approximately 40 m
As described above, the S / N ratio is improved as compared with the case where the correction mirror 11 is fixed. For example, the S / N ratio of the optical heterodyne type distance measuring device is from 17 dB to 26 dB when the distance of the object 10 is 80 m, and from 11 dB to 23 dB when the distance of the object 10 is 100 m, as compared with the case where the correction mirror 11 is fixed. Has been improved. On the other hand, the S / N ratio at a short distance is reduced, but since the short distance originally has a sufficient margin, distance measurement is possible even if the S / N ratio is reduced to some extent.

(Second Embodiment) The control angle of the correction mirror 11 may be changed continuously in synchronization with the rotation angle of the scan mirror 9. That is, FIG.
(A) As shown in (b) and (c), when the scan mirror 9 rotates clockwise, the correction mirror 1
1 is rotated counterclockwise, and when the scan mirror 9 is rotated counterclockwise, the correction mirror 1 is rotated.
Rotate 1 clockwise. However, since strict precision is required for the control angle of the correction mirror 11, it is practical to fix the correction mirror 11 alternately at two positions according to the rotation direction of the scan mirror 9 as described above. It is.

(Third Embodiment) Although not shown,
The scanning direction by the scan mirror 9 may be scanned in one direction, and the correction mirror 11 may be fixed at a position corresponding to the scanning direction. For example, the signal light LS is scanned only rightward by the scan mirror 9, and the correction mirror 11 is fixed at the PA position in FIG. Alternatively, the signal light LS is scanned only by the scan mirror 9 in the leftward direction, and the correction mirror 11 is fixed at the PB position in FIG.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical system of a distance measuring device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a signal processing circuit of the distance measuring device.

FIG. 3 is a diagram showing a state of correction of an axis shift by a correction mirror.

FIG. 4 is a diagram illustrating a state of correction of axis deviation by a correction mirror.

5A and 5B are diagrams illustrating a horizontal synchronization signal and a vertical synchronization signal of a scan mirror driving circuit, and FIG. 5C is a diagram illustrating a control signal of a correction mirror;

FIG. 6 is a diagram illustrating a state in which signal light is two-dimensionally scanned.

FIG. 7 shows a case where a correction mirror is fixed.
FIG. 4 is a diagram illustrating a relationship between an object distance and an S / N ratio.

FIG. 8 is a diagram illustrating a relationship between a distance of an object and an S / N ratio when a correction mirror is controlled.

FIG. 9 is a diagram illustrating another embodiment of the present invention,
(A) and (b) are diagrams showing a horizontal synchronization signal and a vertical synchronization signal of a scan mirror driving circuit, and (c) is a diagram showing a control signal of a correction mirror.

FIG. 10 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 2 Projection unit 5 First polarization beam splitter 6 Beam splitter 7 PLZT 9 Scan mirror 11 Correction mirror 12, 13 Light receiving element LB Laser light LS Signal light LR Reference light

 ──────────────────────────────────────────────────続 き Continuation of front page (71) Applicant 597066429 1000 William Pitt Way Pittsburgh, PA 15238, U.S.A. S. A. (72) Inventor Yoshihiko Tamura William Pittway 1000, Pittsburgh, Pennsylvania, USA, within Optmation Inc.

Claims (5)

[Claims] An optical beam is divided into a signal beam and a reference beam, the signal beam is scanned on a detection area by an optical scanning unit, and a phase difference between the signal beam and the reference beam reflected by the object is measured. In a distance measuring device for measuring a distance to an object, a correction mirror having a variable light reflection direction is provided in a light receiving optical path after signal light is reflected again by the optical scanning means. Distance measuring device. A polarization beam splitter for splitting the light beam emitted from the light projecting unit into a signal light and a reference light; an optical scanning means for scanning the signal light toward a detection area; and a light reflected by an object. Signal light reflected again by the scanning unit, a light combining unit that combines the reference light, and a correction mirror that is disposed on a light receiving optical path between the light scanning unit and the light combining unit and that can adjust the angle, 2. The distance measuring device according to claim 1, further comprising: a unit that controls the correction mirror such that the optical axes of the signal light and the reference light that have passed through the light combining unit substantially coincide with each other. 3. 3. The optical scanning means reciprocally scans the signal light, and when the signal light is scanned in one direction, the optical axis of the signal light on the light receiving optical path coincides with the optical axis of the reference light. As described above, the correction mirror is fixed at the first angle, and when the signal light is scanned in the other direction, the optical axis of the signal light on the light receiving optical path is substantially coincident with the optical axis of the reference light. The distance measuring device according to claim 1, wherein the correction mirror is fixed at a second angle. 4. A signal control apparatus, wherein a transmittance control means such as PLZT is provided in a light projecting optical path of a signal light, and the signal light is AM-modulated by changing the transmittance of the transmittance control means into a sine wave shape. The distance measuring device according to claim 1, wherein 5. A light beam is divided into a signal light and a reference light, and the signal light is scanned only in one direction by an optical scanning means, and a phase difference between the signal light reflected by the object and the reference light is measured. In the distance measuring device for measuring the distance to the object, a correction mirror is provided in the light receiving optical path after the signal light is reflected again by the optical scanning means, and the optical axis of the signal light on the light receiving optical path is referred to. A distance measuring device, wherein an angle of a correction mirror is fixed so that an optical axis of light substantially coincides with the optical axis.