JP4093942B2 - Speedometer, displacement meter, vibrometer and electronic equipment - Google Patents

Description

  The present invention irradiates a moving object to be measured with laser light, detects the frequency shift amount of light according to the moving speed of the object to be measured, and receives the scattered light from the object to detect the speed of the object to be measured. Regarding the total.

  In general, when the light source and the observer are moving relative to each other, the light undergoes a change in frequency due to the Doppler effect. A laser Doppler velocimeter (hereinafter referred to as LDV (Laser Doppler Velocimeter)) uses this effect to irradiate a moving object to be measured with laser light, and to apply a Doppler frequency deviation of scattered light from the object to be measured. The movement is measured and the moving speed of the object to be measured is measured. This LDV was published in 1964 by Yeh and Cummins (Appl. Phys. Lett. 4-10 (1964) 176) and is now widely known and put into practical use.

  FIG. 15 shows an optical system diagram of a conventional typical LDV.

  In FIG. 15, 101 is a laser diode (hereinafter referred to as LD (Laser Diode)) that is a semiconductor laser, 102 is a photodiode (hereinafter referred to as PD (Photo Diode)) that is a light receiving element, and 103 is a diffraction grating. , 104 is a collimator lens (hereinafter referred to as CL), 105 is a mirror, 106 is a condenser lens, 107 is a first light beam of + 1st order diffracted light by the diffraction grating 103, and 108 is -1st order diffracted light by the diffraction grating 103. A second light beam 113 is an object to be measured.

  In the optical system configured as described above, the laser light emitted from the LD 101 is converted into a parallel light beam by the CL 104, and then divided into ± first-order diffracted light at a diffraction angle of θ by the diffraction grating 103 to be first and second light beams 107. , 108. Then, the first and second light beams 107 and 108 are respectively reflected by the mirror 105, and then enter the surface of the object 113 to be measured with an incident angle θ and are superimposed again. The first and second light beams 107 and 108 scattered by the DUT 113 are subjected to Doppler frequency shift and are slightly different from the oscillation frequency of the LD 101. For this reason, the interference waves of the first and second light beams 107 and 108 scattered by the DUT 113 cause a beat. This beat is called a beat signal. The moving speed of the DUT 113 can be obtained by heterodyne detection of the beat frequency of the beat signal by the PD 102. This will be described in detail below.

Now, assuming that the direction in which the DUT 113 moves to the right as shown in FIG. 15 is a positive direction, the first light beam 107 is subjected to a Doppler frequency shift of −f _d and the second light beam 108 is + f _d. The apparent frequency of the first light beam 107 is (f ₀ −f _d ), and the apparent frequency of the second light beam 8 is (f ₀ + f _d ). However, f ₀ is the oscillation frequency of the LD101. At this time, since the electric field of the light emitted from the LD 101 can be expressed as E ₀ · cos (2πf ₀ t), the first light beam 107 is expressed by the following equation 1, and the second light beam 108 is expressed by the following equation 2. It can be expressed as
(Formula 1)
(Formula 2)

However, f ₀ is the frequency of the light emitted from the LD 101, E ₀ is the amplitude of the light emitted from the LD 101, E _A is the amplitude of the first light beam 107, E _B is the amplitude of the second light beam 108, and φ _A is the first The phase of the light beam 107, φ _B is the phase of the second light beam 108.

Since the frequency of light is generally 100 THz (˜10 ¹⁴ Hz), the frequency information of Equation 1 and Equation 2 cannot be directly measured. For this reason, heterodyne detection is generally used as described above, and f ₀ >> f _d holds, so that the interference waves of Equations 1 and 2 are
(Formula 3)
It can be expressed as. However, <> on the left side in Equation 3 represents a time average. Therefore, the frequency of this interference wave can be measured by the PD 102.

  FIG. 16 is a diagram when the measured object 113 moves at the speed V, when two light beams enter the measured object 113 at arbitrary angles α and β, respectively, and receive scattered light at an arbitrary angle γ. .

Strictly speaking, the amount of frequency shift due to the Doppler effect is obtained using the Lorentz transformation based on relativity, but when the moving speed V is sufficiently smaller than the light speed c, it can be obtained approximately as follows. The relative velocities V _A1 and V _B1 of the light from the light sources A and B and the moving object are
(Formula 4)
It can be expressed. The apparent frequencies f _A1 and f _B1 of the light viewed from the DUT 113 are:
(Formula 5)
The respective scattered (reflected) light and the relative velocities V _A2 and V _B2 of the DUT 113 are:
(Formula 6)
It becomes. Therefore, the light frequencies f _A2 and f _B2 viewed from the observation point are
(Formula 7)
It can be expressed as. The difference between the frequency of Expression 7 and the frequency of the incident light is the Doppler frequency shift amount f _d . Now, the beat frequency 2fd of the two light fluxes measured at the observation point is expressed by _c >> V.
(Formula 8)
Thus, it can be seen that it does not depend on the position of the observation point (angle: γ). Since α = β = θ in FIG. 15, in the general LDV optical system of FIG.
(Formula 9)
Is established. Therefore, the moving speed V of the DUT 113 can be obtained by measuring the frequency 2f _d represented by Expression 3 and calculating it using Expression 9.

Equation 9 can also be considered geometrically as follows. FIG. 17 is an enlarged view of a region where the two light beams (first and second light beams 107 and 108) in FIG. 15 overlap again. Two light beams intersect each other at an incident angle θ, and a broken line in the figure indicates a part of an equiwave surface of each light beam. The distance between the broken line and the broken line is the light wavelength λ. Also, the vertical thick line is the bright part of the interference fringes, and when the interval is Δ, this Δ is obtained by the following equation (10).
(Formula 10)

As shown in FIG. 17, when an object (shown by ●) passes perpendicularly to an interference fringe at a speed V, its frequency f is expressed by (Equation 11)
Which is equal to Equation 9.

Further, in the general LDV as described above, the moving speed can be obtained as described above, but the moving direction of the object to be measured cannot be detected. On the other hand, in Japanese Patent Laid-Open No. 3-235060 (Patent Document 1), the moving direction can be detected by rotating the diffraction grating 103 of FIG. 15 at the speed V _g . Thus, when light is reflected by the diffraction grating 103, each light beam undergoes a Doppler frequency shift proportional to V _g , so that the beat frequency 2f _d measured by the PD 102 is
(Formula 12)
It is obtained by. Therefore, since the magnitude relationship of 2f _d is determined by the sign (positive / negative) of the moving speed V with respect to the known speed V _g , the moving direction can be obtained. However, in such an optical system, since the rotation mechanism of the diffraction grating 103 is necessary, the size of the apparatus is increased and the cost is increased. In addition, although it is necessary to keep the rotational speed of the diffraction grating 103 precise, there is a problem that it is difficult to use for precise measurement because errors due to eccentricity, vibration due to rotation, and the like also become problems.

  A speedometer that solves such a problem is disclosed in Japanese Patent Laid-Open No. 4-204104 (Patent Document 2). In Japanese Patent Laid-Open No. 4-204104, a frequency shifter is used, and the moving direction of the object to be measured can be detected by changing the frequency of the incident light beam.

  FIG. 18 shows an optical system diagram of a speedometer disclosed in Japanese Patent Laid-Open No. 4-204104.

According to the speedometer, the light emitted from the laser light source 101 becomes a parallel light beam at the CL 104 and is split into two light beams by a beam splitter (hereinafter referred to as BS) 109. Each light beam is reflected by the mirror 105 and then subjected to a frequency shift of f ₁ and f ₂ by an acoustooptic device (hereinafter referred to as AOM) 110. Then, the light is condensed again on the surface of the measurement object 113 by the diffraction grating 103, and the beat frequency of the scattered light from the measurement object 113 is detected using the PD 102. The frequency 2f _d detected at this time is
(Formula 13)
It becomes. Therefore, since the sign of V changes depending on the moving direction of the device under test 113, the moving direction of the device under test 113 can be detected by the magnitude relationship of 2f _d with respect to the known frequency shift amount | f ₁ −f ₂ |. .

In Japanese Patent Laid-Open No. 8-15435 (Patent Document 3), the frequency is set using an electro-optic element (hereinafter referred to as EOM) 111 shown in FIG. 19 according to the same principle as that of Japanese Patent Laid-Open No. 4-204104. It is changing. More specifically, the light emitted from the LD 101 that is a laser light source is converted into a parallel light beam by the CL 104 and then split into two first and second light beams 107 and 108 by the diffraction grating 103. Both the first and second light beams 107 and 108 enter the EOM 111. At this time, a bias is applied to the second light beam 108 to shift the frequency by f _R. The first and second light beams 107 and 108 are reflected by the mirror 105 and then condensed on the surface of the object 113 to be measured. The beat frequency of scattered light from the surface of the measurement object 113 is detected by the PD 102. The frequency 2f _d detected at this time is
(Formula 14)
It becomes. Therefore, similar to equation 13, the sign of V by the movement direction of the object 113 is changed, it is possible to detect the moving direction by the magnitude relation of 2f _d for known frequency shift amount f _R.

  However, in an optical system that detects the moving direction of the DUT 113 using a frequency shifter such as the AOM 110 and EOM 111, the optical system becomes complicated, and a power source for driving the frequency shifter is required. For example, the voltage required for applying frequency modulation by the AOM 110 is about several tens of volts, and the voltage required for applying frequency modulation by the EOM 111 is about one hundred volts. There is a problem.

In addition, there is a growing demand for downsizing and low power consumption of various sensors including LDV, but the trend is particularly strong in consumer equipment. Since LDV detects scattered light, it varies depending on the object to be measured, but generally the signal light from the object is weak. Although there is a method using a photomultiplier tube which is a photodetector with high photosensitivity, if the photomultiplier tube is used for LDV, the apparatus itself becomes large. That is, it is unsuitable for applying LDV provided with a photomultiplier tube to a small consumer device. For this reason, in order not to hinder downsizing of the apparatus, a photodiode having a low photosensitivity is generally used as the photodetector. Therefore, it is desirable to make as much signal light as possible enter the photodetector. However, due to problems such as the arrangement of optical components, the distance from the light scattering surface of the object to be measured 113 to the condenser lens 106 is often limited, and there is a limit to simply approaching the light receiving system. Increasing the amount of incident light is also conceivable, and a gas laser of He—Ne or Ar ⁺ can be used as a high-power laser light source. From the viewpoint of downsizing the apparatus and reducing power consumption, a semiconductor laser It is desirable to use
JP-A-3-235060 JP-A-4-204104 JP-A-8-15435

  SUMMARY OF THE INVENTION An object of the present invention is to provide a speedometer that can reduce the size and power consumption, and can detect the moving speed of an object to be measured with high accuracy.

In order to solve the above problem, the speedometer of the first invention is:
A semiconductor light emitting element that emits the first light flux from the front end face and emits the second light flux from the rear end face;
An optical branching element that splits the first luminous flux into third, fourth, and fifth luminous fluxes ;
Of the third, fourth, and fifth light beams branched from the first light beam, the third light beam having the same optical axis as the optical axis of the first light beam is changed to the first surface of the object to be measured. A first detection system that irradiates one detection point and irradiates the second detection point on the surface of the object to be measured with the fourth and fifth light beams;
A second detection system for irradiating the first detection point with the second light flux;
A light receiving element that receives scattered light from the first and second detection points;
A signal processing circuit unit for calculating the amount of frequency shift of the scattered light from the output of the light receiving element ,
The direction in which the semiconductor light emitting element emits the first and second light fluxes and the direction in which the light branching element emits the fourth and fifth light fluxes are relative to a plane including the surface of the object to be measured. Almost parallel,
A first plane including the optical axes of the second and third light beams incident on the first detection point is perpendicular to a plane including the surface of the object to be measured ;
The second plane including the optical axes of the fourth and fifth light beams incident on the second detection point is perpendicular to the first plane .

According to the speedometer having the above configuration, the first light flux is emitted from the front end face of the semiconductor light emitting element, while the second light flux is emitted from the rear end face of the semiconductor light emitting element. And the said 1st light beam is branched into the 3rd, 4th, 5th light beam by an optical branching element. Of the third, fourth, and fifth light beams, a third light beam having the same optical axis as that of the first light beam is used as a first detection point on the surface of the object to be measured by the first detection system. While irradiating, the 4th, 5th light beam is irradiated to the 2nd detection point of the surface of a to-be-measured object by a 1st detection system. The first detection point is irradiated with a second light beam by the second detection system. The scattered light from the first and second detection points is received by the light receiving element, and the frequency shift amount of the scattered light is calculated by the signal processing circuit unit from the output of the light receiving element. Since this frequency shift amount is proportional to the moving speed of the object to be measured, the moving speed of the object to be measured can be obtained based on the frequency shift amount.

  In addition to the first light flux emitted from the front end face of the semiconductor light emitting element, the second light flux emitted from the rear end face of the semiconductor light emitting element is also used for speed detection, so that the light emitted from the semiconductor light emitting element is efficiently Used for speed detection, the intensity of scattered light from the first and second detection points is increased. As a result, since the S / N (signal / noise) of the signal from the first and second detection points can be increased, there are the following three effects.

  First, there is no need to use a high-sensitivity light receiver, for example, a large light receiver such as a photomultiplier tube, and a light receiver such as a small photodiode can be used as a light-receiving element. The configuration can be reduced in size.

  Second, since the output of the semiconductor light emitting device can be lowered, the power consumption of the speedometer can be reduced.

  Thirdly, since the frequency shift amount of the scattered light from the first and second detection points can be detected with high accuracy, the moving speed can be detected with high accuracy.

  In addition, since the speed in the y-axis direction of the object to be measured can be detected from the first detection point, and the speed in the x-axis direction of the object to be measured can be detected from the second detection point, two-dimensional speed can be detected. it can.

In a speedometer according to an embodiment, the first detection system includes a first optical axis changing unit that changes an optical axis direction of the third, fourth, and fifth light beams emitted from the optical branching element. ,
The second detection system includes a second optical axis changing unit that changes the direction of the optical axis of the second light flux.

  In one embodiment, the optical branching element is a first diffraction grating.

  In one embodiment, the second detection point is formed using ± first-order diffracted light from the first diffraction grating.

  In one embodiment, the two light beams incident on the first detection point are superimposed on the surface of the object to be measured, and the two light beams incident on the second detection point are overlapped on the surface of the object to be measured. Overlay on top.

  In one embodiment, the light intensity of the 0th-order diffracted light by the first diffraction grating and the light intensity of the second light flux are substantially equal.

The speedometer of one embodiment, the top Symbol angle direction is changed by the first optical axis changing portion of the optical axis of the 0-order diffracted light by the first diffraction grating, the direction of the optical axis of the second light flux is above The angle at which the optical axis direction of the + 1st order diffracted light by the first diffraction grating is changed by the first optical axis changing unit is approximately equal to the angle changed by the second optical axis changing unit. The direction of the optical axis of the −1st order diffracted light is substantially equal to the angle changed by the first optical axis changing unit.

The speedometer of one embodiment, the first detection point and said second detection point both you position in the first plane.

  In one embodiment, the optical axis of light incident on the light receiving element from the first detection point is located on a bisector of an angle formed by two light beams incident on the first detection point, and The optical axis of the light incident on the light receiving element from the second detection point is located on the bisector of the angle formed by the two light beams incident on the second detection point.

  A speedometer according to an embodiment is disposed on an optical path of a light beam from the first diffraction grating to the second detection point, and changes a phase of light incident on the second detection point; A second diffraction grating for branching a light beam traveling from the second detection point to the light receiving element, and a first linear polarizer group disposed on an optical path of a plurality of light beams branched by the second diffraction grating, The light receiving elements receive the plurality of light beams that have passed through the first linear polarizer group.

  According to the speedometer of the above embodiment, since the sign of the phase difference of the beat signal from the second detection point is inverted depending on the moving direction of the measured object, the moving direction of the measured object in the x-axis direction is also detected. can do.

  A speedometer according to an embodiment is disposed on an optical path of a light beam from the semiconductor light emitting element to the first detection point, and changes a phase of light incident on the first detection point. A third diffraction grating for branching a light beam from the first detection point toward the light receiving element; and a second linear polarizer group disposed on an optical path of a plurality of light beams branched by the third diffraction grating, The plurality of light beams that have passed through the second linear polarizer group are received by the light receiving element.

  According to the speedometer of the above embodiment, since the sign of the phase difference of the beat signal from the first detection point is inverted depending on the moving direction of the measured object, the moving direction of the measured object in the y-axis direction is also detected. can do.

In the speedometer of one embodiment, when the phase change amount of the light by the phase changing unit is φ ₀ , the φ ₀ satisfies 0 <φ ₀ <λ / 2.

In the speedometer of one embodiment, the φ ₀ is λ / 4.

  In the speedometer of one embodiment, a birefringent material is used as the material of the phase changing unit.

  In one embodiment, the absolute value of the difference between the phase difference of each light beam forming the first detection point and the phase difference of each light beam forming the second detection point is smaller than π / 2.

  In one embodiment, the region where the two light fluxes incident on the first detection point overlap is separated from the region where the two light velocities incident on the second detection point overlap.

  The speedometer according to an embodiment includes a first condenser lens disposed between the first detection point and the light receiving element, and a second collector disposed between the second detection point and the light receiving element. And an optical lens.

  In one embodiment of the speedometer, the first and second condenser lenses are included in a single component including a lens array.

  In one embodiment, when the axis perpendicular to the surface of the object to be measured is the z-axis, the length in the z-axis direction of the region where a plurality of light beams incident on the first detection point overlap is as follows. The length in the z-axis direction of the region where a plurality of light beams incident on the second detection point overlap is longer than the length in the z-axis direction of the region where the surface of the device to be measured is located. Longer than the length in the z-axis direction of the region where the surface of the substrate is located.

In the speedometer of one embodiment, the end surface of the semiconductor light emitting element is processed so that the light amounts of the second, third, fourth, and fifth light beams incident on the first and second detection points are substantially equal. Is given.

  In one embodiment, the light receiving element includes a first light receiving element that receives scattered light from the first detection point, and a second light receiving element that receives scattered light from the second detection point. Each of the first and second light receiving elements is a one-chip element in which two light receiving portions are formed.

  In one embodiment, the first and second light receiving elements are split photodiodes.

  In one embodiment, the light receiving element includes a signal processing circuit.

  In one embodiment, the semiconductor light emitting element is provided between the first optical axis changing unit that changes the direction of the optical axis of the 0th-order diffracted light by the first diffraction grating and the second optical axis changing unit. It is arranged at the approximate midpoint.

  In the speedometer of one embodiment, the semiconductor light emitting element and the light receiving element are integrated by sharing the same substrate.

  In one embodiment, the semiconductor light emitting device is a laser diode.

  In one embodiment, the semiconductor light emitting element has a plurality of light emitting points.

  A speedometer according to an embodiment is disposed between the semiconductor light emitting element and the light branching element, and includes a first diaphragm through which the first light beam passes, the semiconductor light emitting element, and the second optical axis direction changing unit. And a second diaphragm through which the second light flux passes.

  The speedometer according to an embodiment is disposed between the semiconductor light emitting element and the light branching element, and includes a first lens group through which the first light beam passes, the semiconductor light emitting element, and the second optical axis direction. And a second lens group that is arranged between the changer and through which the second light beam passes.

  A displacement meter according to a second invention includes the speedometer according to the first invention, and obtains position information of the object to be measured based on speed information and time information regarding the object to be measured.

  A vibration meter according to a third aspect of the invention includes the speedometer according to the first aspect of the invention, and obtains information related to vibration of the measurement object based on speed information and time information regarding the measurement object.

  According to a fourth aspect of the present invention, there is provided an electronic apparatus including one of the speedometer according to the second aspect and the vibration meter according to the third aspect.

  According to the speedometer of the present invention, the intensity of scattered light from the detection point is increased by efficiently using the light emitted from the semiconductor light emitting element for speed detection. As a result, since the S / N of the signal from the first and second detection points can be increased, there are the following three effects.

  First, there is no need to use a high-sensitivity light receiver, for example, a large light receiver such as a photomultiplier tube, and a light receiver such as a small photodiode can be used as a light-receiving element. The configuration can be reduced in size.

  Second, since the output of the semiconductor light emitting device can be lowered, the power consumption of the speedometer can be reduced.

  Thirdly, since the frequency shift amount of the scattered light from the first and second detection points can be detected with high accuracy, the moving speed can be detected with high accuracy.

  In addition, since the speed in the y-axis direction of the object to be measured can be detected from the first detection point, and the speed in the x-axis direction of the object to be measured can be detected from the second detection point, two-dimensional speed can be detected. it can.

  Before describing the embodiments of the present invention, reference examples will be described in order to make the present invention easier to understand.

Reference example 1

  In FIG. 1, the schematic block diagram of the speedometer of the reference example 1 of this invention is shown. In FIG. 1, only the arrangement of each optical component or the like is shown, and other components or the like that hold each optical component are omitted. Moreover, the broken-line arrow of FIG. 1 shows a coordinate axis.

  The speedometer includes LD1 as an example of a semiconductor light emitting element, PD2 as an example of a light receiving element, CL4a and 4b as an example of first and second lens groups, mirrors 5a and 5b, and an example of a condenser lens. A condenser lens 6, a signal processing circuit unit 10 as an example of a signal processing circuit unit, and stops 12a and 12b as examples of first and second stops are provided.

The LD ₁ is installed at (0, 0, z ₁ ). As an alternative to the LD1, there is an LED (Laser Emitting Diode) or the like, but it is preferable to use an LD rather than an LED. This is because the LD has very good coherence compared to the LED, and the beat due to the interference between the two light beams expressed by the above equation 3 is easily generated. Further, the PD2 is (0,0, z ₂₎ in, CL4a the _{(0, -y 4, z 1} ), CL4b the _{(0, y 4, z 1} ), the mirror 5a is (0, -y ₅ , z ₁ ), the mirror 5 b is set at (0, y ₅ , z ₁ ), the stop 12 a is set at (0, −y ₁₂ , z ₁ ), and the stop 12 b is set at (0, y ₁₂ , z ₁ ). Is done.

  In FIG. 1, reference numeral 7 denotes a first light beam, 8 denotes a second light beam, 14 denotes a detection point (beam overlap region), and 15 denotes a beat signal that travels on the z-axis. The first and second light beams 7 and 8 are emitted from the end face of the LD 1 in parallel with the y-axis. In addition, a plane including the x axis and the y axis, that is, the xy plane substantially coincides with the surface of the DUT 13. Then, (x, y, z) = (0, 0, 0), that is, the detection point 14 is located at the origin.

  In general, the LD 1 is manufactured by subjecting a wafer to a predetermined process and then cleaving the wafer to a certain length and cutting it into chips. Usually, in most electronic devices, laser light emitted from the front end face (front end face) of the LD is used in accordance with various applications, and laser light emitted from the rear end face (rear end face) of the LD is directly applied to the PD. It is receiving light. The output of the PD is fed back to the LD driver to stabilize the light emission intensity of the LD.

  Further, the signal processing circuit unit 10 calculates the frequency shift amount included in the scattered light generated at the detection point 14 from the output S of the PD 2.

  The configuration and function of the optical system shown in FIG. 1 will be described below.

  The first light beam 7 is emitted in parallel with the y axis from the front end surface of the LD 1, and the second light beam 8 is emitted in parallel with the y axis from the rear end surface of the LD 1. The first and second light beams 7 and 8 become ideal parallel light beams via the diaphragm 12 and the CLs 4a and 4b. In general, the intensity distribution of light emitted from the LD 1 has a Gaussian distribution centered on the optical axis, and the way of spreading of the tail of the Gaussian distribution is a far field pattern (FFP) that differs with respect to the polarization direction of the light. For this reason, if the light emitted from the LD 1 is irradiated to the detection point 14 as it is, the light intensity is uneven on the detection point 14 and the intensity of the interference fringes shown in FIG. It becomes difficult to evaluate the accuracy. For this reason, by providing the diaphragms 12a and 12b as shown in FIG. 1, it is possible to cut a portion having a low light intensity outside the light beam emitted from the LD 1 and form a light beam having a uniform light intensity.

  Further, the light emitted from the LD1 travels with a certain angle and spreads. When the measurement object 13 is irradiated with the light as it is, the longer the traveling distance is, the more the wavefront becomes spherical and the plane wave is not generated, so that the interference fringes as shown in FIG. Further, since the light flux of the light spreads, there is a problem that the light intensity is dispersed and the S / N of the signal is deteriorated. For this reason, by providing the CL 4a and 4b at appropriate positions as shown in FIG. 1, the light emitted from the LD 1 can be made into a parallel light flux, so that the wave front of the light becomes a plane wave regardless of the traveling distance.

  The contents described above for each component in FIG. 1 also apply to all the reference examples and examples below, but the description will be given only in this reference example and will be omitted hereinafter.

The first and second light beams 7 and 8 emitted from the LD 1 are shaped into parallel light beams by CL4a and 4b, and then reflected by the mirrors 5a and 5b at the reflection angles θ ₁ and θ ₂ , respectively, to be measured. It enters the surface of the object 13 at incident angles θ ₃ and θ ₄ , respectively. Thereby, one detection point 14 is formed on the surface of the DUT 13. And the scattered light which received the frequency shift proportional to the moving speed V of the to-be-measured object 13 is condensed by the condensing lens 6, and received by PD2. The beat frequency 2f _d is detected based on the output S of the PD2. In this case, 2f _d to be detected from the above equation 8,
(Formula 15)
It becomes. In the optical system of this reference example, as shown in FIG. 1, the first and second light beams 7 and 8 emitted from the LD 1 are installed so as to be parallel to the y-axis, and the first light beam 7 in the mirror 5a is While reflecting at the reflection angle θ ₁ , the second light beam 8 is reflected at the reflection angle θ ₂ at the mirror 5b. Since the reflection angle θ ₁ and the reflection angle θ ₂ are equal, the incident angle of the first light beam 7 to the measured object 13 and the incident angle of the second light beam 8 to the measured object 13 are equal. Become. That is, θ ₃ = θ ₄ . Further, as shown in FIG. 2A, the two first and second light beams 7 and 8 after reflection are in the yz plane, and the surface of the DUT 13 is in the xy plane. Therefore, 2f _d detected at this time is obtained from the above equation 15.
(Formula 16)
Thus, the adjustment item of the installation angle of each optical component can be reduced by one.

  Further, as shown in the above equation 3, the beat signal is generated by the interference of two light beams. If the overlapping region of the two light fluxes is shifted as shown in FIG. 2B, the scattered light from the non-overlapping region becomes DC noise and is detected by the PD2, which causes a decrease in S / N. End up. The two light beams emitted from the LD 1 are emitted in parallel to the y-axis and reflected by the mirrors 5 a and 5 b at the same angle and in the same plane, so that both light beams are superposed well on the detection point 14.

  The signal can be obtained not only in the case of overlapping in accordance with this condition but also in the case of overlapping at an arbitrary angle, but the above condition can detect the signal with high accuracy.

  Further, by installing the entire optical system so that the moving direction of the DUT 13 is parallel to the y-axis as shown in FIG. 1, the interference fringe direction (interference fringes are detected as shown in FIG. 17). Since the moving direction of the object 13 to be measured is perpendicular to the extending direction), the moving speed of the object 13 can be detected with high accuracy.

In this reference example, in order for the PD 2 to continuously detect the beat signal 15, an area where two light beams incident on the detection point 14 overlap when the z-axis perpendicular to the surface of the DUT 13 is set. It is necessary to make the length in the z-axis direction longer than the length in the z-axis direction of the region where the surface of the DUT 13 is located. Specifically, as shown in FIG. 3, the unevenness (= h) of the unevenness of the DUT 13 in the z-axis direction is the length of the overlapping region of the first light beam 7 and the second light beam 8 in the z-axis direction. Needs to be smaller than (= d). Here, as shown in FIG. 1, since the angle formed by the two light beams is 2 · θ ₃ , d can be expressed by the following Expression 17.
(Formula 17)

Using the above equation 17, the angle θ ₃ can be set so as to satisfy h <d, and discontinuity of the beat signal can be prevented. This condition is satisfied in all the reference examples and examples hereinafter, and further explanation is omitted.

  Further, the optical axis of the light beam incident on the PD 2 from the detection point 14 substantially coincides with the bisector of the intersection angle of the first and second light beams 7 and 8 incident on the detection point 14. At this time, since the intensity of the scattered light from the first and second light beams 7 and 8 becomes substantially equal, the beat signal 15 becomes clear, so that the moving speed can be detected with high accuracy.

  Further, in FIG. 1, PD2 is in a plane (yz plane) formed by two light beams incident on PD2. That is, PD2 is installed on the z axis. At this time, in addition to the effect of sharpening the beat signal as described above, the signal intensity is also maximized, so that the S / N can be improved.

  Furthermore, in FIG. 1, LD1 is installed so that it may be located in the middle point between mirror 5a, 5b. At this time, since LD1 and PD2 are arranged on the same z-axis, they can be incorporated on the front and back sides of the same substrate. That is, LD1 and PD2 can be integrated on the same substrate. Thereby, the whole apparatus structure can be reduced in size.

  In this reference example, the case where the light emitted from the LD 1 is converted into a parallel light beam by the CL 4a and 4b has been described as an example. However, when the beat signal intensity is weak, for example, the distance between the CL 4a and 4b and the LD 1 The CLs 4a and 4b may be arranged so that the light beam is gradually converged by shifting from the focal length of the light source, and the light beam is sufficiently focused at the detection point 14. Further, a lens may be arranged so as to pass through two light beams incident on the detection point 14. That is, a lens may be arranged on the optical path between the mirrors 5a and 5b and the detection point 14. In this way, since the light beam is sufficiently narrowed when entering the detection point 14, the amount of light per unit area at the detection point 14 increases, and the signal intensity obtained by the PD 2 increases. Therefore, a beat signal with improved S / N can be detected, and the moving speed of the DUT 13 can be detected with high accuracy. In the following reference examples and examples, the CL is arranged so that the light beam incident on the detection point becomes a parallel light beam, and the lens for condensing the light beam incident on the detection point is omitted. Similarly, it is not limited to the parallel light flux.

  Further, in FIG. 1, the condenser lens 6 is installed between the PD 2 and the detection point 14. The condensing lens 6 condenses the beat signal scattered from the detection point 14 onto the PD2, so that the signal intensity obtained by the PD2 increases. Such a condensing lens is also commonly installed in the following reference examples and examples, but description of the condensing lens is omitted.

Further, the beat signal 15 becomes clearer as the two light beams incident on the detection point 14 become equal, and the movement speed can be detected with high accuracy by the PD 2. In Equation 3, the value of E _A + E _B is a constant value because it is the amount of light emitted from the LD 1. For this reason, when E _A = E _B , the beat intensity (Peak to Peak) of the beat signal 15 is maximized. On the other hand, as the balance is lost, that is, as the deviation between E _A and E _B increases, the beat strength decreases. In the present reference example, by appropriately processing both end faces of the LD 1, the light amounts of the first light beam 7 and the second light beam 8 incident on the detection point 14 can be made equal, and the beat signal 15 is clearly displayed. Since it can be detected, the moving speed can be detected with high accuracy. In all the following reference examples and examples, the processing is performed on both end faces of the LD so that the light intensities of the two light beams incident on the respective detection points are equal to each other.

Reference example 2

  In FIG. 4, the schematic block diagram of the speedometer of the reference example 2 of this invention is shown. In FIG. 4, only the arrangement of each optical component or the like is shown, and the illustration of components or the like that hold other optical components is omitted. Also, the broken-line arrows in FIG. 4 indicate coordinate axes. 4, the same reference numerals as those in FIG. 1 are assigned to the same components as those shown in FIG.

  The speedometer includes an LD 1, PDs 2 a and 2 b as examples of light receiving elements, CL 4 a and 4 b, diffraction gratings 3 a and 3 b, condenser lenses 6 a and 6 b as examples of condenser lenses, a signal processing circuit unit 10, and a diaphragm 12 a, 12b.

The LD1 is (0,0, z ₁₎ to, PD2a, 2b the _{(± x 2, 0, z} 2), the diffraction grating 3a, 3b in the _{(0, ± y 3, z} 1), CL4a, 4b Is set to (0, ± y ₄ , z ₁ ), the condenser lenses 6a and 6b are set to (0, ± y ₆ , z ₆ ), and the stops 12a and 12b are set to (0, ± y ₁₂ , z ₁ ). The

In FIG. 4, 7 is a first light beam, 7a and 7b are ± 1st order diffracted lights of the diffraction grating 3a, 8 is a second light beam, 8a and 8b are ± 1st order diffracted lights of the diffraction grating 3b, and 13 is a measured object. 14a and 14b are detection points (beam overlapping regions), and 15a and 15b are beat signals. The detection points 14a and 14b are formed at (0, ± y ₁₄ , 0). The surface of the DUT 13 substantially coincides with the xy plane.

The signal processing circuit unit 10 calculates the frequency shift amount included in the scattered light generated at the detection point 14a from the output Sa of the PD 2a, and calculates the frequency shift amount included in the scattered light generated at the detection point 14b as the output S _b of the PD 2b. Calculate from

  Hereinafter, the configuration and function of the optical system in FIG. 4 will be described.

  The first light beam 7 is emitted from the front end surface of the LD 1 and the second light beam 8 is emitted from the rear end surface of the LD 1. The first and second light beams 7 and 8 become parallel light beams through the CLs 4a and 4b after passing through the apertures 12a and 12b. Thereafter, the first and second light beams 7 and 8 are divided into a plurality of light beams by the diffraction gratings 3a and 3b, respectively. Here, since the diffraction gratings 3a and 3b divide the incident light beam into equal angles, and the division angle depends on the wavelength of the incident light beam, the two light beams can be easily overlapped at the detection points 14a and 14b. Therefore, the diffraction gratings 3a and 3b are suitable as an optical branching element in this reference example.

  FIG. 4 shows only ± 1st order diffracted light 7a, 7b, 8a, 8b among ± nth order diffracted light (n is a natural number including zero). Detection points 14a and 14b are formed by the ± first-order diffracted lights 7a, 7b, 8a and 8b. The beat signal 15a scattered from the detection point 14a is detected by the PD 2a via the condenser lens 6a, while the beat signal 15b scattered from the detection point 14b is detected by the PD 2b via the condenser lens 15b. Using the detected beat signals 15a and 15b, the moving speed of the DUT 13 is detected in the same manner as in the first reference example.

  In general, when coherent light is incident on an optically rough surface, scattered light from the surface is reflected in various directions, and thus a light and dark pattern called a speckle pattern appears due to interference of the scattered light. While the bright part is incident on the PDs 2a and 2b, the PDs 2a and 2b can detect the beat signal and detect the moving speed of the object 13 to be measured. However, when the dark part is incident on the PDs 2a and 2b continuously, so-called dropout occurs. It becomes a signal insensitive state called. In this reference example, since two detection points 14a and 14b are formed and signals are detected by two light receiving systems, even if one output cannot be detected due to dropout, the other output is detected. Thus, a signal insensitive state can be prevented.

  In the optical system of this reference example, the diffraction gratings 3a and 3b are used for splitting the light beam. However, in order to increase the beat signal intensity, it is necessary to increase the amount of light incident on the detection points 14a and 14b. . In general, the light beam is divided into zero-order diffracted light, ± first-order diffracted light,... ± n-order diffracted light by the diffraction grating into each order equiangle, but the optical distance difference depending on the groove depth of the diffraction grating is 1 When / 4, the optical path length difference due to reflection becomes ½ of the wavelength, and the phase of the light is shifted by π, so that the 0th-order diffracted light is hardly emitted. When such conditions are applied to the diffraction gratings 3a and 3b, the intensity of the ± first-order diffracted lights 7a, 7b, 8a, and 8b is about 40.5% on one side with respect to the amount of incident light, and becomes the maximum. Since the amount of incident light is maximized, the beat signals 15a and 15b can be detected with high sensitivity. The above is the case where light enters the diffraction gratings 3a, 3b perpendicularly, that is, the diffraction gratings 3a, 3b are arranged perpendicular to the optical axis of the incident light. In the example, the diffraction gratings 3a and 3b are tilted in the −z direction so that the first and second light beams 7 and 8 that are incident light beams are incident on the object to be measured 13. It is necessary to adjust the groove depth of the diffraction gratings 3a and 3b in accordance with the inclination angles of 3a and 3b.

  Further, in the optical system of this reference example, as shown in FIG. 4, the LD 1 is installed so that the two light beams emitted from the LD 1 are parallel to the y axis, and the grooves of the diffraction gratings 3a and 3b extend. Is parallel to the yz plane. Therefore, the first, second, and third planes form isosceles triangular prisms (broken lines at the left and right ends (± y direction) in the figure, and the isosceles triangles that form the top and bottom surfaces of the isosceles triangular prism are shown) . Here, the first plane is a plane including the + 1st order diffracted light beam 7a by the diffraction grating 3a and the + 1st order diffracted light beam 8a by the diffraction grating 3b. The second plane is a plane including a −1st order diffracted light beam 7b by the diffraction grating 3a and a −1st order diffracted light beam 8b by the diffraction grating 3b. The third plane is a plane including the surface of the DUT 13.

  When the first, second, and third planes form an isosceles triangular prism, the distance and direction of the interference fringes shown in FIG. 17 are equal at the detection point 14a and the detection point 14b. Even if the signal from one of the detection points 14b becomes insensitive due to dropout, the speed error detected from both detection points 14a and 14b can be minimized.

  Further, the interference fringes extend as shown in FIG. 17 by installing the entire optical system so that the line connecting the detection points 14a and 14b is the x axis and the moving direction of the DUT 13 is the y axis direction. Since the direction and the moving direction of the DUT 13 are perpendicular, the moving speed of the DUT 13 can be measured with high accuracy.

  The optical axis of the light beam incident on the PD 2a from the detection point 14a substantially coincides with the bisector of the intersection angle of the two light beams (+ 1st order diffracted beams 7a and 8a) incident on the detection point 14a, and the detection point 14b. The optical axis of the light beam incident on the PD 2b from the light beam approximately coincides with the bisector of the intersection angle of the two light beams (-1st order diffracted light 7b, 8b) incident on the detection point 14b. In such a case, since the intensity of the scattered light from the two light beams becomes substantially equal at each of the detection points 14a and 14b, the beat signals 15a and 15b are sharpened. Can be detected.

  In the optical system of this reference example, as shown in FIG. 4, the PDs 2a and 2b are installed in the regular reflection direction (incident angle = reflection angle) with respect to the xy plane in the first plane and the second plane, respectively. Generally, when light traveling straight is reflected, the intensity is reflected most strongly in the regular reflection direction. Therefore, it is possible to detect the beat signal with the highest sensitivity by installing the light receiving system as described above.

  In FIG. 5, the schematic block diagram of the modification of the speedometer of this reference example is shown. In FIG. 5, only the arrangement of each optical component and the like is shown, and other components and the like for holding each optical component are omitted. In addition, broken line arrows in FIG. 5 indicate coordinate axes. In FIG. 5, the same components as those shown in FIG. 4 are denoted by the same reference numerals as those of the components in FIG.

The speedometer of FIG. 5 is different from the speedometer of FIG. 4 in that a quarter-wave plate 16 through which the first-order diffracted light 8b by the diffraction grating 3b passes is provided at (−x ₁₆ , y ₁₆ , z ₁₆ ). . The quarter wave plate 16 is an example of a phase changing unit.

  In general, by setting the optical axis of the quarter-wave plate 16 to be inclined by 45 ° with respect to the polarization direction of incident light, the phase of the light of the slow axis component is delayed by π / 2 compared to the fast axis component. Therefore, linearly polarized light is converted into circularly polarized light. In FIG. 5, the −1st order diffracted light 8 b between the ¼ wavelength plate 16 and the DUT 13 is circularly polarized by the ¼ wavelength plate 16. The beat signals detected by the PDs 2a and 2b when the four light beams (± first-order diffracted lights 7a, 7b, 8a, and 8b) enter the device under test 13 as shown in FIG. 5 will be described.

Each light beam (± first-order diffracted light 7a, 7b, 8a, 8b) divided by the diffraction gratings 3a, 3b is expressed as follows assuming that the distances from the diffraction gratings 3a, 3b to the detection points 14a, 14b are equal. be able to. However, only the slow axis component after passing through the quarter-wave plate 16 is shown for the light beam passing through the quarter-wave plate 16 (-1st order diffracted light 8b).
(Formula 18)
(Formula 19)
(Formula 20)
(Formula 21)

Here, E _1a , E _1b , E _2a , and E _2b are light amplitudes, f ₀ is the light frequency, and t is time.

Next, assuming that the movement direction of the object to be measured 13 is positive in the + y-axis direction, the components of each light beam scattered by the object to be measured 13 are Doppler frequency shift components caused by the moving speed V of the object to be measured 13. Assuming f _d , the above equations 18 to 21 are
(Formula 22)
(Formula 23)
(Formula 24)
(Formula 25)
It becomes. Therefore, the beat signals 15a and 15b detected by the PDs 2a and 2b are
(Formula 26)
(Formula 27)
It becomes. In the above equation 27, the sign of the phase component in the cosine of the second term differs depending on the moving direction of the device 13 to be measured: + π / 2 when moving in the + y direction, and −π / 2 when moving in the −y direction. Become.

  6A to 6C show beat signals 15a and 15b. More specifically, FIG. 6A shows the beat signal 15a expressed by the above equation 26. This beat signal 15 a does not depend on the moving direction of the DUT 13. FIG. 6B shows the beat signal 15b when the DUT 13 moves in the left direction (−y direction), and FIG. 6C shows the DUT 13 moving in the right direction (+ y direction). A beat signal 15b is shown.

6A to 6C, it can be seen that the phase of the beat signal 15 b is shifted by π / 2 depending on the moving direction of the DUT 13. Therefore, by installing a linear polarizer (not shown) between the PD 2b and the detection point 14b in the direction in which the slow axis component passes and detecting the beat signals 15a and 15b , The moving direction can be detected. Thus, by providing the quarter wavelength plate 16 through which the −1st order diffracted light 8b passes, the speed and moving direction of the DUT 13 can be detected.

However, in order to detect the moving direction of the DUT 13, it is only necessary to determine whether the phase of the beat signal 15b is advanced or delayed with respect to the phase of the beat signal 15a. If the phase difference from 15b is ξ,
(Formula 28)
If it is in the range. At this time, the phase change amount by the phase change means: φ is
(Formula 29)
It is necessary to be. As a material for the member that gives such a light phase difference, a birefringent material having a refractive index different from that of the light incident direction is generally used. This birefringent material is suitable as a material for the phase changing means.

However, in an actual optical system, the distances to the detection points 14a and 14b of the respective light fluxes differ due to deviations caused by the installation of the respective optical components. At this time, the scattered light from each detection point 14a, 14b is
(Formula 30)
(Formula 31)
(Formula 32)
(Formula 33)
It becomes. However, for the −1st order diffracted light 8b, only the slow axis components after passing through the quarter-wave plate 16 are shown, and φ _1a , φ _1b , φ _2a , and φ _2b represent the light beams (± first order diffracted light 7a, 7b, 8a, 8b), and φ ₀ is the phase change amount by the phase change means. Therefore, the beat signals 15a and 15b detected by the PDs 2a and 2b are
(Formula 34)
(Formula 35)
It becomes. From the above Equation 28, Equation 34, and Equation 35, the phase condition required for movement direction detection is
(Formula 36)
It becomes. By installing each optical component so as to satisfy the above expression 36, it is possible to detect the moving direction of the DUT 13. When the quarter wave plate 16 is used as an example of the phase changing means, the above equation 36 is
(Formula 37)
Thus, it is possible to take a margin in the arrangement of each optical component with respect to the phase component variation of each light beam (± first-order diffracted light 7a, 7b, 8a, 8b).

  Further, the quarter wavelength plate 16 is provided in three light beams other than the −1st order diffracted light 8b (± 1st order diffracted lights 7a, 7b and 8a), and is not provided only in the −1st order diffracted light 8b. The moving direction of the DUT 13 can be detected by the same phase difference logic as described above. That is, if each of the ± first-order diffracted lights 7a, 7b, and 8a passes through the quarter-wave plate, the minus-first-order diffracted light 8b does not pass through the quarter-wave plate and the measured object 13 moves. The direction can be detected.

  The discussion regarding the detection of the moving direction of the object to be measured 13 and the phase difference in the modified example of the speedometer of the present reference example is the same in the following reference examples and reference examples. In the subsequent reference examples and examples, Omitted.

  In FIG. 7, the schematic block diagram of the other modification of the speedometer of this reference example is shown. In FIG. 7, only the arrangement of each optical component is shown, and other components that hold each optical component, signal processing circuits for detected signals, and the like are omitted. A broken arrow indicates a coordinate axis. In FIG. 7, the same components as those shown in FIG. 5 are denoted by the same reference numerals as those of the components in FIG.

  The speedometer of FIG. 7 detects a point using a single-part condenser lens array 17 instead of the condenser lenses 6a and 6b for detecting the two beat signals 15a and 15b, and the beat signals 15a and 15b. 5 is different from the speedometer of FIG. 5 in that PD2 to be formed is formed in the same chip as LD1. The condensing lens array 17 is an example of a lens array.

  With the above configuration, the optical system shown in FIG. 7 can reduce the number of parts as compared with the optical systems shown in FIGS. 5 and 6, and the PD 2 is integrated with the LD 1 in one chip, so that the apparatus can be downsized. Furthermore, since the area of the light receiving element can be further reduced by using a split-type PD instead of a plurality of PDs integrated into one chip, the manufacturing cost of the PD can be reduced, and further downsizing of the apparatus can be achieved. The apparatus configuration for reducing the number of parts in FIG. 7 is the same in the following reference examples and examples, and description thereof will be omitted in the following reference examples and examples.

  FIG. 8 shows a schematic diagram (viewed from + z-axis direction) of the speedometer of FIG. 7 viewed from above. 8 shows an enlarged view of a small circle drawn by a dotted line in the upper part of FIG. That is, the lower part of FIG. 8 is an enlarged view near the detection points 14a and 14b.

The larger the distance between the detection point 14a and the detection point 14b, the larger the apparatus, and the smaller the amount of light that can be received by the condenser lens array 17. In addition, even at the phase difference point of each light beam (± first-order diffracted light 7a, 7b, 8a, 8b), if the detection points are separated from each other, the phase difference increases, and it becomes difficult to detect the moving direction of the DUT 13. . The distance between the detection point 14a and the detection point 14b is determined by the diffraction angle α by the diffraction gratings 3a and 3b. If the detection point 14a and the detection point 14b overlap with each other, the beat signal from each of the detection points 14a and 14b becomes noise and is detected by the PD 2. Therefore, from FIG.
(Formula 38)
It is necessary to set the pitch of the diffraction gratings 3a and 3b, the diameter W of the diaphragms 12a and 12b, the distance L between the components, and the like so as to satisfy the above. The same applies to the distance between the detection points in the following reference examples and examples, and the description thereof will be omitted in the following reference examples and examples.

Reference example 3

  In FIG. 9, the schematic block diagram of the speedometer of the reference example 3 of this invention is shown. In FIG. 9, only the arrangement of each optical component or the like is displayed, and other components or the like that hold each optical component are omitted. In addition, broken line arrows in FIG. 9 indicate coordinate axes. In FIG. 9, the same components as those shown in FIG. 7 are denoted by the same reference numerals as those shown in FIG.

  The speedometer of FIG. 9 includes LD1, PD2, diffraction gratings 3a, 3b, CL4a, 4b, BS9a, 9b, 9c, 9d, signal processing circuit unit 10, diaphragms 12a, 12b, quarter wavelength plate 16, and lens array. As an example, a condensing lens array 27 is provided.

The LD1 in the (0,0, z _1), PD2 is (0,0, z _2), the diffraction grating 3a, 3b in the _{(0, ± y 3, z} 1), CL4a, 4b is (0, ± y ₄ , z ₁ ), BS 9a, 9b, 9c, 9d at (± x ₉ , ± y ₉ , z ₉ ), stop 12 at (0, ± y ₁₂ , z1), 1/4 wavelength plate 16 is installed at (−x ₁₆ , y ₁₆ , z ₁₆ ), and the condenser lens array 17 is installed at (0, 0, z ₁₇ ).

In FIG. 9, 7 is a first light beam, 7a and 7b are ± first-order diffracted light by the diffraction grating 3a, 7c and 7d are light beams obtained by dividing the + 1st-order diffracted light 7a by BS 9a, and 7e and 7f are −1 next time. A light beam obtained by dividing the folded light 7b at the BS 9b, 8 is a second light beam, 8a and 8b are ± first-order diffracted light by the diffraction grating 3b, 8c and 8d are light beams obtained by dividing the + first-order diffracted light 8a at the BS 9c, 8e, 8f is a light beam obtained by dividing the −1st-order diffracted light 8b by BS 9d, 13 is an object to be measured, 14a, 14b, 14c, and 14d are detection points (beam overlapping regions), and 15a, 15b, 15c, and 15d are beat signals. ing. The detection points 14a and 14b are formed at (± x ₁₄ , 0, 0), and the detection points 14c and 14d are formed at (0, ± y ₁₄ , 0). And the surface of the DUT 13 that irradiates the light beams 7c, ..., 7f and the light beams 8c, ..., 8f substantially coincides with the xy plane.

  The signal processing circuit unit 10 calculates the frequency shift amount included in the scattered light generated at each detection point 14a, 14b, 14c, 14d from the output S of the PD.

  The configuration and function of the optical system in FIG. 9 will be described below.

  The first light beam 7 is emitted from the front end surface of the LD 1 and the second light beam 8 is emitted from the rear end surface of the LD 1. The first and second light beams 7 and 8 become parallel light beams by passing through the apertures 12a and 12b and then passing through the CLs 4a and 4b. Thereafter, the first and second light beams 7 and 8 are divided into a plurality of light beams by the diffraction gratings 3a and 3b, respectively.

  FIG. 9 shows only ± 1st order diffracted light 7a, 7b, 8a, 8b among ± nth order diffracted light (n is a natural number including zero). In general, the light beam is divided into zero-order diffracted light, ± first-order diffracted light,..., ± n-order diffracted light, and equilateral angles by the diffraction grating. If it is 4, the optical path length difference due to reflection becomes 1/2 of the wavelength, and the phase of the light is shifted by π, so that the 0th-order diffracted light is hardly emitted. That is, the light reflected by the grooves of the diffraction grating and the light reflected by portions other than the grooves of the diffraction grating are shifted in phase by π when the optical path length difference is ½ of the wavelength of the incident light. Folding light hardly occurs. When such conditions are applied to the diffraction gratings 3a and 3b, the intensity of the ± first-order diffracted lights 7a, 7b, 8a, and 8b of the diffraction gratings 3a and 3b is one side with respect to the amount of incident light (+ n-order diffracted light or -n-order diffracted light). The maximum is about 40.5%. As a result, the amount of light incident on the detection points 14a, 14b, 14c, and 14d is maximized, so that the beat signals 15a, 15b, 15c, and 15d can be detected with high sensitivity. The above is the case where light enters the diffraction gratings 3a and 3b perpendicularly and the diffraction gratings 3a and 3b are arranged perpendicular to the optical axis of the light. In this reference example shown in FIG. Strictly speaking, since the diffraction gratings 3a and 3b are tilted in the −z direction in order to cause the incident light beams (first and second light beams 7 and 8) to enter the object to be measured 13, the groove depths of the diffraction gratings 3a and 3b are strictly speaking. Adjustment to match this angle is required.

  The first light beam 7 is divided into two light beams (± first-order diffracted lights 7a and 7b) by the diffraction grating 3a, and the second light beam 8 is divided into two light beams (± first-order diffracted lights 8a and 8b) by the diffraction grating 3b. Is done. Further, these four light beams (± first-order diffracted lights 7a, 7b, 8a, 8b) are divided into eight light beams 7c, 7d, 7e, 7f, 8c, 8d, 8e, 8f by BSs 9a, 9b, 9c, 9d. The Further, one of the two light beams (± first-order diffracted light 7a, 7b) is divided into four light beams 7c, 7d, 7e, 7f by BS 9a, 9b, and the other two light beams (± first-order diffracted light 8a, 8b). ) Is divided into four light beams 8c, 8d, 8e, and 8f by BSs 9c and 9d. More specifically, the + 1st order diffracted light 7a is divided into light beams 7c and 7d by the BS 9a, and the −1st order diffracted light 7b is divided into light beams 7e and 7f by the BS 9b. Similarly, the + 1st order diffracted light 8a is divided into light beams 8c and 8d by BS9c, and the −1st order diffracted light 8b is divided into light beams 8e and 8f by BS9d. In this case, the BSs 9a, 9b, 9c, and 9d function as an optical branching element and divide incident light into two light beams having a light intensity of 1: 1. Further, since the BS 9a, 9b, 9c, and 9d can reduce the loss of the light amount due to the division, the light amount applied to the detection points 14a, 14b, 14c, and 14d increases, and the beat signals 15a, 15b, 15c, and 15d. The signal strength can be prevented from decreasing.

In the optical system of this reference example, since the light beams incident on the detection points 14a and 14b are incident from ± y directions, bright and dark interference fringes are formed in the x-axis direction as shown in FIG. Speed is detected. For this reason, the y-axis component with respect to the movement of the DUT 13 can be detected based on the beat signals 15a and 15b detected from the detection points 14a and 14b. That is, the moving speed V _y of the DUT 13 in the y-axis direction can be detected.

In the present optical system, the light beams 7c, 7e, 8c, 8e divided by the BSs 9a, 9b, 9c, 9d form detection points 14c, 14d. Since all the light beams 7c, 7e, 8c, and 8e incident on the detection points 14c and 14d are incident from the ± x directions, the light and darkness of the interference fringes is formed in the y-axis direction. For this reason, the x-axis component of the moving speed of the DUT 13 can be detected based on the beat signals 15c and 15d detected from the detection points 14c and 14d. That is, the moving speed V _x of the DUT 13 in the x-axis direction can be detected.

  As described above, in the optical system of this reference example, the two-dimensional moving speed can be measured, and the moving direction of the object to be measured and the optical axis of the light incident on the detection point are adjusted in order to obtain the moving speed. There is no need.

  Further, as described in Reference Example 1 above, if the overlapping region of the two light beams incident on each of the detection points 14a, 14b, 14c, and 14d is shifted, a shifted region (as shown in FIG. 2B) ( Scattered light from the area where the two light beams do not overlap is detected as DC noise, which lowers the S / N. As shown in FIG. 9, in the optical system of this reference example, the two light beams emitted from the LD 1 are installed so as to be parallel to the y-axis, and the groove directions of the diffraction gratings 3a and 3b (the direction in which the grooves extend) Since it is parallel to the yz plane, the first plane, the second plane, and the third plane form an isosceles triangular prism as in Reference Example 2. Here, the first plane is a plane including the + 1st order diffracted light beam 7a by the diffraction grating 3a and the + 1st order diffracted light beam 8a by the diffraction grating 3b. That is, the first plane includes the optical axes of the two light beams 7d and 8d incident on the detection point 14a. The second plane is a plane including a −1st order diffracted light beam 7b by the diffraction grating 3a and a −1st order diffracted light beam 8b by the diffraction grating 3b. That is, the second plane includes two light beams 7f and 8f incident on the detection point 14b. The third plane is a plane including the xy plane. When the first plane, the second plane, and the third plane form an isosceles triangular prism, the interval and direction of the interference fringes shown in FIG. 17 are equal at the detection point 14a and the detection point 14b. Even if the signal from one of the detection points 14a and 14b becomes insensitive due to dropout, the speed error detected from both detection points 14a and 14b can be minimized.

The angle formed by the plane including the two light beams incident on the detection point 14c with respect to the xy plane is equal to the angle formed by the plane including the two light beams incident on the detection point 14d with respect to the xy plane, and BSs 9a, 9b, 9c and 9d are installed so that the incident angles of all the light beams incident on the detection points 14c and 14d are equal. As a result, the signal from one of the detection points 14c and 14d becomes insensitive due to the dropout, as in the case of detecting the velocity V _y in the y-axis direction of the DUT 13 using the detection points 14a and 14b. In addition, it is possible to minimize an error in speed detected from both detection points 14c and 14d.

  Further, the optical axis of the light beam incident on the PD 2 from the detection point 14a substantially coincides with the bisector of the intersection angle of the two light beams 7d and 8d incident on the detection point 14a. Further, the optical axis of the light incident on the PD 2 from the detection point 14b substantially coincides with the bisector of the intersection angle of the two light beams 7f and 8f incident on the detection point 14b. The optical axis of the light incident on the PD 2 from the detection point 14c substantially coincides with the bisector of the intersection angle of the two light beams 7c and 7e incident on the detection point 14c. The optical axis of the light incident on the PD 2 from the detection point 14d substantially coincides with the bisector of the intersection angle of the two light beams 8c and 8e incident on the detection point 14d. In such a case, since the intensities of scattered light from the two light beams incident on the detection points 14a, 14b, 14c, and 14d are substantially equal, the beat signals 15a, 15b, 15c, and 15d are sharpened. The moving speed of the object 13 can be detected with high accuracy.

  The -1st order diffracted light 8b by the diffraction grating 3b is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 16 before being divided by the BS 9d. Therefore, the light beams 8e and 8f from the BS 9d are incident on the object to be measured 13 as circularly polarized light. The light beams 7c, 7d, 7e, 7f, 8c, 8d, 8e, and 8f from the BSs 9a, 9b, 9c, and 9d form detection points 14a, 14b, 14c, and 14d. Specifically, the light beam 7d and the light beam 8d form a detection point 14a, the light beam 7f and the light beam 8f form a detection point 14b, the light beam 7c and the light beam 7e form a detection point 14c, and the light beam 8c and The light beam 8e forms a detection point 14d. Beat signals 15a, 15b, 15c, and 15d scattered from the detection points 14a, 14b, 14c, and 14d are detected by the PD 2 via the condenser lens array 27. The principle of detecting the moving speed of the DUT 13 based on the output S of the PD 2 is the same as in the first and second reference examples.

  In the optical system of the present reference example, the beat signal 15a and the beat signal 15b have different signal intensities, but the beat signal 15a, beat signal 15a, By 15b, the moving speed Vy of the DUT 13 and the y-axis component of the moving direction of the DUT 13 can be detected. Further, the moving speed Vx of the DUT 13 can be detected by the beat signals 15c and 15d detected from the detection points 14c and 14d. Since the phase of the light beam 8e incident on the detection point 14d passes through the quarter wavelength plate 16 and becomes circularly polarized light, the same principle as the detection of the moving direction of the object to be measured 13 in Reference Example 2 is used. The x-axis component in the moving direction can be detected. In short, the beat signals 15a, 15b, 15c, and 15d can detect the moving speeds Vx and Vy of the object 13 in the x and y axis directions, and can detect the moving direction of the object 13 in the x and y axis directions. .

  As described above, in the optical system according to the present reference example, it is not necessary to adjust and arrange the moving direction of the DUT 13 and the axis of the optical system, and it is possible to detect the speed information and the moving direction regarding an arbitrary xy plane motion. it can. The conditions for handling the phase relating to the detection of the moving direction for both the x component and the y component are the same as those in the reference example 2.

  Further, as shown in FIG. 9, detection points 14 a and 14 b for detecting the y-direction component of the moving speed of the measured object 13 are formed on the x-axis, and the x-direction component of the moving speed of the measured object 13 is set. By forming the detection points 14c and 14d for detection on the y-axis, it is possible to detect velocity components in two directions orthogonal to each other in the DUT 13. As a result, the moving speed of the DUT 13 can be detected with high accuracy.

  In FIG. 10, the schematic block diagram of the modification of the speedometer of this reference example is shown. In FIG. 10, only the arrangement of each optical component or the like is shown, and other components or the like that hold each optical component are omitted. In addition, broken line arrows in FIG. 10 indicate coordinate axes. In FIG. 10, the same components as those shown in FIG. 9 are denoted by the same reference numerals as the components shown in FIG.

  The speedometer shown in FIG. 10 includes LD1, PD2, diffraction gratings 3a and 3b, CL4a and 4b, a signal processing circuit unit 10, apertures 12a and 12b, and a first substrate 19. The first substrate 19 is provided with a quarter-wave plate 16, diffraction gratings 18a, 18b, 18c, and 18d, and a condensing lens array 37 as an example of a lens array. A quarter-wave plate 16 is disposed on the diffraction grating 18d.

The LD1 is (0,0, z _1), the PD2 is (0,0, z _2), the diffraction grating 3a, 3b is _{(0, ± y 3, z} 1) , the CL4a, at 4b (0, the ± y _4, z _1), the diaphragm 12a, 12b is (0, the _{± y 12, z 1),} 1/4 -wavelength plate 16 is installed in the _{(-x 16, y 3, z} 16). The condenser lens array 37 is located at (0, 0, z ₁₆ ).

In FIG. 10, 7 is a first light beam, 7a and 7b are ± first-order diffracted light by the diffraction grating 3a, 7c and 7d are light beams obtained by dividing the + 1st-order diffracted light 7a by the diffraction grating 18a, and 7e and 7f are A light beam obtained by dividing the −1st order diffracted light 7b by the diffraction grating 18b, 8 is a second light beam, 8a and 8b are ± 1st order diffracted light by the diffraction grating 3b, 8c and 8d are + 1st order diffracted light 8a by the diffraction grating 18c. The luminous flux obtained by the division, 8e and 8f are the luminous flux obtained by dividing the −1st-order diffracted light 8b by the diffraction grating 18d, 13 is an object to be measured, 14a, 14b, 14c and 14d are detection points (beam overlapping regions), Reference numerals 15a, 15b, 15c and 15d denote beat signals. The detection points 14a and 14b are formed at (± x ₁₄ , 0, 0), and the detection points 14c and 14d are formed at (0, ± y ₁₄ , 0). And the surface of the DUT 13 that irradiates the light beams 7c, ..., 7f and the light beams 8c, ..., 8f substantially coincides with the xy plane.

  The signal processing circuit unit 10 calculates the frequency shift amount included in the scattered light generated at each detection point 14a, 14b, 14c, 14d from the output S of the PD2.

  Hereinafter, the configuration and function of the optical system of FIG. 10 will be described.

  The first light beam 7 is emitted from the front end surface of the LD 1 and the second light beam 8 is emitted from the rear end surface of the LD 1. The first and second light beams 7 and 8 become parallel light beams by passing through the apertures 12a and 12b and then passing through the CLs 4a and 4b. Thereafter, the first and second light beams 7 and 8 are divided into a plurality of light beams by the diffraction gratings 3a and 3b, respectively. FIG. 9 shows only ± 1st order diffracted light 7a, 7b, 8a, 8b among ± nth order diffracted light (n is a natural number including zero).

  The first light beam 7 is divided into two light beams (± first-order diffracted lights 7a and 7b) by the diffraction grating 3a, and the second light beam 8 is divided into two light beams (± first-order diffracted lights 8a and 8b) by the diffraction grating 3b. Is done. The two light beams (± first-order diffracted lights 7a and 7b) from the diffraction grating 3a are divided into four light beams 7c, 7d, 7e and 7f by the diffraction gratings 18a and 18b, and the + 1st-order diffracted light 7a of the diffraction grating 3a is diffracted. While being divided into two light beams 7c and 7d by the grating 18a, the −1st order diffracted light 7b of the diffraction grating 3a is divided into two light beams 7e and 7f by the diffraction grating 18b. Further, the + 1st order diffracted light 8a of the diffraction grating 3b is divided into two light beams 8c and 8d by the diffraction grating 18c, and the −1st order diffracted light 8b of the diffraction grating 3b is divided into two light beams 8e and 8f by the diffraction grating 18d. The Here, like the diffraction gratings 3a and 3b, the diffraction gratings 18a, 18b, 18c, and 18d hardly emit 0th-order diffracted light because the depth of the groove is 1/4 of the wavelength of the incident light. The intensity of ± first-order diffracted light is maximum. As a result, the amount of light incident on each detection point 14a, 14b, 14c, 14d is maximized, and the beat signal intensity can be maximized.

  Further, the −1st order diffracted light 8b of the diffraction grating 3b is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 16 before being divided by the diffraction grating 18d. Therefore, the light beams 8e and 8f are incident on the surface of the object to be measured 13 as circularly polarized light. The diffraction gratings 18a, 18b, 18c, and 18d are inclined at arbitrary angles with respect to the x-axis and y-axis directions in the first substrate 19, respectively. The light beams 7c, 7d, 7e, 7f, 8c, 8d, 8e, and 8f emitted from the diffraction gratings 18a, 18b, 18c, and 18d form detection points 14a, 14b, 14c, and 14d. More specifically, the light beam 7d and the light beam 8d form a detection point 14a, the light beam 7f and the light beam 8f form a detection point 14b, the light beam 7c and the light beam 7e form a detection point 14c, and the light beam 8c and the light beam. 8e forms a detection point 14d. The angle at which the diffraction gratings 18a, 18b, 18c, and 18d are tilted in the first substrate 19 and the distance from the first substrate 19 to the object to be measured 13 form the detection points 14a, 14b, 14c, and 14d as described above. Is set to That is, on the surface of the object 13 to be measured, the light beam 7d and the light beam 8d overlap each other, the light beam 7f and the light beam 8f overlap each other, the light beam 7c and the light beam 7e overlap each other, and the light beam 8c and the light beam 8e overlap each other. The angle and the above distance are set.

  In the speedometer of FIG. 10, since the diffraction gratings 18a, 18b, 18c, and 18d are formed on the same substrate, it is possible to prevent positional deviation due to the installation of the diffraction gratings 18a, 18b, 18c, and 18d. Therefore, the speedometer shown in FIG. 10 can reduce the light flux overlap problem at the detection points 14a, 14b, 14c, and 14d as compared with the speedometer shown in FIG.

  In the speedometer of FIG. 10, beat signals 15a, 15b, 15c, and 15d scattered from the detection points 14a, 14b, 14c, and 14d are detected by the PD 2 via the condenser lens array 37. The detection principle of the moving speed of the DUT 13 based on the output of the PD 2 is the same as that in the first reference example.

  10 has four detection points 14a, 14b, 14c, and 14d formed on the surface of the object 13 as in the case of the speedometer of FIG. 9, and thus the two-dimensional movement of the object 13 is measured. Detection of speed and direction of movement is possible.

  In the speedometer of FIG. 10, the diffraction gratings 18a, 18b, 18c, 18d, the quarter-wave plate 16 and the condenser lens array 37 are incorporated into the first substrate 19 and become a single component. The number of parts can be reduced as compared with the 9 speedometer. Therefore, the number of steps for assembling the speedometer of FIG. 10 can be reduced, and the manufacturing cost can be reduced.

  In the velocimeter of FIG. 10, the diffraction gratings 18a, 18b, 18c, 18d, the quarter-wave plate 16 and the condenser lens array 37 are a single component, and therefore the diffraction gratings 18a, 18b, 18c, 18d. The accuracy of installing the quarter-wave plate 16 and the condenser lens array 37 in the optical system is higher than that of the speedometer of FIG. 9, and the condition given by the above equation 35 in detecting the moving direction of the object 13 to be measured The design margin that satisfies the equation increases.

  In this reference example, the number of detection points is increased in order to detect the velocity in the x direction as compared to the reference example 2. In the reference example 2, the condition that the detection points for detecting the velocity in the y direction are separated from each other is specified by the above expression 36. In this reference example, the two detection points for detecting the moving speed in the x direction of the object to be measured are similarly required to be separated from each other. The conditional expression is different from the above expression 36, and the installation angle of the diffraction gratings 18a, 18b, 18c, 18d, the distance between the DUT 13 and the LD1, the distance between the LD1 and the diffraction grating 3, and the installation of the diffraction gratings 3a, 3b. Due to the angle. The derivation is omitted. In addition, this condition is similarly required for the subsequent reference examples and examples, but the description of the conditions is omitted in the subsequent reference examples and examples.

  In the reference example 1 and this modification, the −1st order diffracted light 8b of the diffraction grating 3b passes through the quarter-wave plate 16, but the + 1st order diffracted light 7a of the diffraction grating 3a and −1 of the diffraction grating 3a. Only the first-order diffracted light 7b and the + 1st-order diffracted light 8a of the diffraction grating 3b may pass through the quarter-wave plate. That is, the + 1st order diffracted light 7a of the diffraction grating 3a is disposed so as to pass through, the first phase changing unit that changes the phase of the + 1st order diffracted light 7a, and the −1st order diffracted light 7b of the diffraction grating 3a is disposed to pass therethrough. , A second phase changing unit that changes the phase of the −1st order diffracted light 7b, and a third phase changing unit that is arranged so that the + 1st order diffracted light 8a of the diffraction grating 3b passes and changes the phase of the + 1st order diffracted light 8a. It may be provided.

  In the reference example 1 and the modification, the angle formed by the fourth plane including the optical axes of the two light beams 7c and 7e incident on the detection point 14c with respect to the xy plane and the two incident on the detection point 14d. The fifth plane including the optical axes of the light beams 8c and 8e is substantially equal to the angle formed with respect to the xy plane, and the incident angles of the light beams 7c and 7e with respect to the sixth plane are approximately the same; The incident angles of the light beams 8c and 8e with respect to the sixth plane may be substantially the same. In this case, even if the signal from one of the detection points 14c and 14d becomes insensitive due to dropout, the speed error detected from both the detection points 14c and 14d can be minimized. Such a setting may also be used in the following reference examples and examples.

Reference example 4

  In FIG. 11, the schematic block diagram of the speedometer of the reference example 4 of this invention is shown. In FIG. 11, only the arrangement of each optical component is shown, and other components for holding each optical component are omitted. In addition, broken arrows in FIG. 11 indicate coordinate axes. In FIG. 11, the same reference numerals as those in FIGS. 1 and 10 are assigned to the same components as those shown in FIGS. 1 and 10.

  The speedometer of FIG. 11 includes LD1, PD2, CL4a, 4b, mirrors 5a, 5b, a signal processing circuit unit 10, apertures 12a, 12b, a first substrate 19 and a second substrate 20.

  The first substrate 19 is provided with a quarter-wave plate 16, diffraction gratings 18a, 18b, 18c, and 18d, and a condensing lens array 37 as an example of a condensing lens. A quarter wavelength plate 16 is disposed on the diffraction grating 18d. The second substrate 20 is provided with diffraction gratings 23a and 23b and a condensing lens array 47 as an example of a lens array.

The LD1 in the (0,0, z _1), PD2 is (0,0, z _2), the CL4a, 4b is _{(0, ± y 4, z} 1) , the mirror 5a, 5b are (0, ± y ₅ , z ₁ ), apertures 12a and 12b are (0, ± y ₁₂ , z ₁ ), and quarter-wave plate 16 is (−x ₁₆ , y ₁₆ , z ₁₆ ) and diffraction gratings 18a and 18b. , 18c, 18 d in the _{(± x 18, ± y 18} , z 16), the first substrate 19 in the (0,0, z _16), the second substrate 20 to (0,0, z _3), the diffraction The gratings 23a and 23b are located at (0, ± y ₃ , z ₃ ), the condenser lens array 37 is located at (0, 0, z ₁₆ ), and the condenser lens array 47 is located at (0, 0, z ₃ ). ing.

  In FIG. 11, 7 is a first light beam, 7a and 7b are ± first-order diffracted lights by the diffraction grating 3a, 7c and 7d are light beams obtained by dividing the + 1st-order diffracted light 7a by the diffraction grating 18a, and 7e and 7f are A light beam obtained by dividing the −1st order diffracted light 7b by the diffraction grating 18b, 8 is a second light beam, 8a and 8b are ± 1st order diffracted light by the diffraction grating 3b, 8c and 8d are + 1st order diffracted light 8a by the diffraction grating 18c. The luminous flux obtained by the division, 8e and 8f are the luminous flux obtained by dividing the −1st-order diffracted light 8b by the diffraction grating 18d, 13 is an object to be measured, 14a, 14b, 14c and 14d are detection points (beam overlapping regions), Reference numerals 15a, 15b, 15c and 15d denote beat signals. The surface of the measurement object 13 irradiated with the light beams 7c, ..., 7f and the light beams 8c, ..., 8f substantially coincides with the xy plane.

  The signal processing circuit unit 10 calculates the frequency shift amount included in the scattered light generated at each of the detection points 14a, 14b, 14d, and 14d from the output S of the PD2.

  In the speedometer of the present reference example shown in FIG. 11, the first and second light beams 7 and 8 emitted from both end faces of the LD 1 are used without using the diffraction gratings 3a and 3b, as compared with the speedometer shown in FIG. Mirrors 5a and 5b and a second substrate 20 are added. Further, the diffraction gratings 23a and 23b are integrally formed on the second substrate 20 of the same substrate. That is, the diffraction gratings 23 a and 23 b are incorporated in the second substrate 20. The second substrate is installed in parallel to the first substrate 19.

  In such a speedometer of this reference example, the principle relating to detection of the moving speed and direction of movement of the object 13 to be measured is the same as that of the speedometers of the reference examples 1 and 2. In the speedometer of this reference example, since all the elements for splitting the light beam are arranged in a plate shape, it is possible to prevent positional deviation and angular deviation due to the installation of the diffraction gratings 23a and 23b. Furthermore, when the first substrate 19 and the second substrate 20 are made of, for example, a glass plate, an installation error or the like when an element for splitting the light beam is incorporated into the housing can be greatly reduced. As described above, the speedometer of this reference example can greatly reduce the light beam overlapping failure at the detection points 14a, 14b, 14c, and 14d due to the installation error with respect to the installation of each optical component, thereby greatly increasing the yield in the device assembly process. Can be improved.

  In FIG. 12, the schematic block diagram of the modification of the speedometer of this reference example is shown. In FIG. 12, only the arrangement of each optical component is shown, and other components for holding each optical component are omitted. Moreover, the broken-line arrows in FIG. 12 indicate coordinate axes. In FIG. 12, the same components as those shown in FIG. 11 are denoted by the same reference numerals as the components shown in FIG.

  The speedometer shown in FIG. 12 includes an integrated first board 19 and second board 20 of the speedometer shown in FIG. That is, the speedometer of FIG. 12 includes an optical block 21 instead of the first substrate 19 and the second substrate 20. This optical block 21 divides each light beam. Diffraction gratings 33 a and 33 b are formed on the upper surface of the optical block 21, and diffraction gratings 28 a, 28 b, 28 c and 28 d are formed on the lower surface of the optical block 21. Further, a condensing lens array 57 that guides beat signals 15a, 15b, 15c, and 15d to the PD 2 is formed near the center of the optical block 21 from the upper surface to the lower surface. The condensing lens array 57 is an example of a lens array. A quarter wavelength plate 16 is provided on a part of the lower surface of the optical block 21 so as to cover the diffraction grating 28d. The thickness of the optical block 21 can be set arbitrarily. With these configurations, the moving speed and moving direction of the DUT 13 can be detected. The principle of detecting the moving speed and moving direction of the DUT 13 is the same as that of the reference example 3 and its modification.

  In the speedometer of FIG. 12, since the first substrate 19 and the second substrate 20 are integrated as compared with the speedometer of FIG. 11, an assembly process that causes an installation error of optical components can be further reduced, and the apparatus The yield of the assembly process can be improved.

  In the reference example 4 and this modification, the −1st order diffracted light 8b of the diffraction gratings 23b and 33b has passed through the quarter-wave plate 16, but the + 1st order diffracted light 7a of the diffraction gratings 23a and 33a, the diffraction grating Only the −1st order diffracted light 7b of 23a and 33a and the + 1st order diffracted light 8a of the diffraction gratings 23b and 33b may pass through the quarter-wave plate. That is, the first-order diffracted light 7a of the diffraction gratings 23a and 33a is arranged so that the + 1st-order diffracted light 7a passes therethrough, and the first-phase diffracted light 7b of the diffraction gratings 23a and 33a passes through the first phase changing unit that changes the phase of the + 1st-order diffracted light 7a. The second phase changing unit for changing the phase of the −1st order diffracted light 7b and the second phase changing unit for changing the phase of the + 1st order diffracted light 8a are arranged so that the + 1st order diffracted light 8a of the diffraction gratings 23b and 33b passes through. A three-phase changing unit may be provided.

  In FIG. 13, the schematic block diagram of the speedometer of the Example of this invention is shown. In FIG. 13, only the arrangement of each optical component is shown, and other components for holding each optical component are omitted. Further, the broken-line arrows in FIG. 13 indicate coordinate axes. In FIG. 13, the same components as those shown in FIGS. 5 and 12 are designated by the same reference numerals as those of the components shown in FIGS.

  In the speedometer of FIG. 13, LD1, PDs 32a and 32b as examples of the first and second light receiving elements, diffraction gratings 3, CL4a and 4b as examples of the first diffraction grating, and examples of the first optical axis changing unit. Mirrors 5a, 5c, 5d, a mirror 5b as an example of a second optical axis changing unit, a signal processing circuit unit 10, apertures 12a and 12b, a quarter wave plate 16a as an example of first and second phase changing units, 16b and a condensing lens array 17 as an example of a lens array. Between the condensing lens array 17 and the PD 32a, a diffraction grating 22a as an example of a third diffraction grating and a linear polarizer group 43a as an example of a second linear polarizer group are arranged. A diffraction grating 22b as an example of a second diffraction grating and a linear polarizer group 43b as an example of a first linear polarizer are arranged between the condenser lens array 17 and the PD 32b.

The LD1 in the (0,0, z _1), PD32a is (0,0, z ₂₎ in, PD32b the _{(0, -y 2, z 2} ), the diffraction grating 3 is (0, y _3, z to _1), CL4a, 4b is (0, the ± y _4, z _1), the mirror 5a, 5b are (0, ± y _5, the z _1), the diaphragm 12a, 12b is (0, ± y _12, z ₁ ), the quarter-wave plate 16a is (0, y _16a , z _16a ), the quarter-wave plate 16b is (-x ₁₆ , -y _16b , z _16b ), and the condenser lens array 17 is ( 0, −y ₁₇ , z ₁₇ ), the diffraction grating 22a is (0, 0, z ₂₂ ), the diffraction grating 22b is (0, −y ₂₂ , z ₂₂ ), and the linear polarizer group 43a is (0, 0). , Z ₂₃ ), the linear polarizer group 43 b is installed at (0, −y ₂₃ , z ₂₃ ).

In FIG. 13, 7 is the first light beam, 7g is the 0th-order diffracted light of the diffraction grating 3, 7h is the 1st-order diffracted light of the diffraction grating 3, 7i is the -1st-order diffracted light of the diffraction grating 3, and 8 is the second light beam. , 13 are objects to be measured, 14a and 14b are detection points (beam overlap regions), and 15a and 15b are beat signals. Incidentally, the detection point 14a whereas formed at the origin (0,0,0), the detection point 14b is formed on the (0, -y _14, 0). The surface of the DUT 13 substantially coincides with the xy plane. The detection point 14a is an example of a first detection point, and the detection point 14b is an example of a second detection point.

The signal processing circuit unit 10 calculates the frequency shift amount included in the scattered light generated at the detection point 14a from the output Sa of the PD 32a, and calculates the frequency shift amount included in the scattered light generated at the detection point 14b as the output S _b of the PD 32b. Calculate from

  Hereinafter, the configuration and function of the optical system of FIG. 13 will be described.

  The first light beam 7 is emitted from the front end surface of the LD 1 and the second light beam 8 is emitted from the rear end surface of the LD 1. The first and second light beams 7 and 8 become parallel light beams by passing through the stops 12a and 12b and the CLs 4a and 4b. Thereafter, the second light beam 8 is reflected by the mirror 5b, converted into circularly polarized light via the quarter-wave plate 16b, and enters the detection point 14a. On the other hand, after passing through CL4a, the first light beam 7 is divided into a plurality of ± nth order diffracted lights (n is a natural number including 0) by the diffraction grating 3 (in FIG. Only the first-order diffracted beams 7h and 7i are shown.) Since the diffraction grating 3 is installed perpendicular to the optical axis of the first light beam 7, the 0th-order diffracted light 7g is emitted from the diffraction grating 3 coaxially with the optical axis of the first light beam 7 emitted from the LD1. Then, the 0th-order diffracted light 7g is reflected by the mirror 5a and enters the detection point 14a. The zero-order diffracted light 7g and the second light beam 8 are superimposed on the detection point 14a. That is, the detection point 14 a is formed by the 0th-order diffracted light 7 g and the second light beam 8.

  Further, since the grooves of the diffraction grating 3 are installed so as to be parallel to the z-axis, the ± first-order diffracted lights 7h and 7i are emitted from the diffraction grating 3 at the same emission angle in a plane parallel to the xy plane. That is, the plane including the ± first-order diffracted lights 7h and 7i is parallel to the xy plane. After the ± first-order diffracted light 7h and 7i are reflected at equal angles by the mirrors 5c and 5d, the + 1st-order diffracted light 7i enters the detection point 14b, and the −1st-order diffracted light 7d is circularly polarized through the quarter-wave plate 16a. And is incident on the detection point 14b. On the detection point 14b, the + 1st order diffracted light 7h and the −1st order diffracted light 7i are superimposed. That is, the detection point 14b is formed by the + 1st order diffracted light 7h and the −1st order diffracted light 7i.

  As described above, by using the transmissive diffraction grating 3 as a means for splitting the light beam, the target second detection point 14b can be formed. In addition, since the conditions regarding the installation of each optical component relating to the two light beams incident on the detection point 14a are the same as those in the reference example 1, description thereof is omitted.

  Further, the plane including the ± first-order diffracted lights 7h and 7i diffracted by the diffraction grating 3 is parallel to the xy plane as described above, is reflected by the mirrors 5c and 5d, and enters the detection point 14b at the same incident angle. At this time, the plane including the two light beams incident on the detection point 14a is perpendicular to the plane including the two light beams incident on the detection point 14b. At this time, these two planes are both perpendicular to the plane including the surface of the DUT 13 (the surface on which the detection points 14a and 14b are formed). The detection points 14b formed by the ± first-order diffracted beams 7h and 7i exist on the y axis, and the interference fringes formed at the detection points 14b are perpendicular to the x axis. As a result, the moving speed of the DUT 13 in the x-axis direction can be detected with high accuracy.

  FIG. 14 shows an enlarged view near the detection point 14a and the light receiving system in FIG. However, in FIG. 14, the diffracted light by the diffraction grating 22a is only shown as ± first-order diffracted light, and other diffracted light by the diffraction grating 22a is not shown. Further, illustration of the condensing lens array 17 is also omitted. Although only the detection point 14a is shown in FIG. 14, the beat signal 15a and the beat signal 15b can be treated as having the same other conditions except that the incident angle with respect to the condenser lens array 17 is different. Therefore, hereinafter, only the beat signal 15a from the detection point 14a will be described, and description of the beat signal 15b from the detection point 14b will be omitted.

  One of the two light beams incident on the detection point 14a passes through the quarter-wave plate 16b and is thus converted into circularly polarized light. The two light fluxes are scattered on the surface of the object to be measured 13 and enter the diffraction grating 22a as a beat signal 15a. The diffraction grating 22a is desirably such that the light amount of the 0th-order diffracted light and the light amount of the ± mth-order diffracted light (m> 1) are sufficiently smaller than the light amount of the ± 1st-order diffracted light with respect to the wavelength of the incident light. . The grooves of the diffraction grating 22a are preferably formed so as to extend in parallel to the x axis.

The beat signal 15a diffracted by the diffraction grating 22a passes only a component in a specific direction by the linear polarizer group 43a. Linear polarizer group 43a includes a linear polarizer 43a ₁ through the + 1st-order diffracted light diffracted by the diffraction grating 22a, consisting of the linear polarizer 43a ₂ Metropolitan passing -1st-order diffracted light diffracted by the diffraction grating 22a. The optical axes of these linear polarizers are installed in directions orthogonal to each other. Although not shown, the linear polarizer group 43b also includes a linear polarizer that passes + 1st order diffracted light diffracted by the diffraction grating 22b and a linear polarizer that passes -1st order diffracted light diffracted by the diffraction grating 22b.

Here, an example of setting the optical axis in the present embodiment will be described. The light emitted from the LD 1 is linearly polarized light that vibrates parallel to the x axis. At this time, the optical axis of the quarter wavelength plate 16b is set to form 45 ° with respect to the x and y planes. For example, the quarter-wave plate 16b is installed so that the fast axis is on the straight line y = x and the slow axis is on the straight line y = −x. At this time, the optical axes of the linear polarizers 43a ₁ and 43a ₂ are set in either the y = x or y = −x direction, respectively. In FIG. 14, the direction of the optical axis of the linear polarizer 43a ₁ is set in the y = x axis direction, and the direction of the optical axis of the linear polarizer 43a ₂ is set in the y = −x direction.

Since the optical axis is set as described above, the components passing through the linear polarizer 43a ₁ are the linearly polarized light of the 0th-order diffracted light 7g and the fast axis component of circularly polarized light. The components passing through the linear polarizer 43a ₂ are the linearly polarized light of the 0th-order diffracted light 7g and the slow axis component of circularly polarized light. The first signal 15a ₁ included in the beat signal 15a is detected by the first light receiving unit 32a ₁ , and the second signal 15a ₂ included in the beat signal 15a is detected by the second light receiving unit 32a ₂ . Since these signals include phase information, the movement direction in the y direction of the DUT 13 can be detected according to the principle described in Reference Example 2 above. As described above, the description of the detection of the moving speed and moving direction of the DUT 13 using the detection point 14b is omitted, but the beat signal 15b from the detection point 14b is received by the PD 32b, so that the x-axis direction is detected. It is possible to detect the moving speed and moving direction of the object 13 to be measured. Although not shown, the PD 32b includes a first light receiving unit for detecting the first signal included in the beat signal 15b and a second light receiving unit for detecting the second signal included in the beat signal 15b. Yes.

  In addition, when both the first and second phase changing means (1/4 wavelength plates 16a and 16b) are installed, the two-dimensional moving speed and moving direction can be detected. Only one of the second phase changing means may be installed.

  In the present embodiment, it is desirable to make the light amount of the 0th-order diffracted light from the diffraction grating 3 equal to the light amount of the second light beam 8 in order to accurately detect the beat signal at the detection point 14a. For this reason, in this embodiment, since it is necessary to provide a difference in the amount of light between the first light beam 7 and the second light beam 8 emitted from the LD 1, processing is performed on both end faces of the LD 1 so as to cause this difference. Yes.

Furthermore, in the optical system of the present embodiment, the beat signal is divided by the diffraction grating from one detection point to detect the moving direction. Therefore, in the above equation 36,
(Formula 39)
φ _1a = φ _1b , φ _2a = φ _2b
It becomes. Therefore, the phase difference of each light beam is always (Equation 40).
Beat signal phase difference = φ ₀ (= π / 2)
Thus, the accuracy with respect to the installation of each optical component can be significantly reduced with respect to the optical systems of Reference Examples 2 to 4.

  Further, since the scattered light from the detection points 14a and 14b is condensed by the condenser lens array 17, the number of parts is reduced, and the optical system can be simplified. Therefore, the yield in the speedometer assembly process can be further improved.

  In the above embodiments and Reference Examples 1 to 4, the LD 1 may be a light source that emits a plurality of light emitting points from the same chip, for example, a monolithic light source that emits a plurality of light beams from one side. However, in the present invention, the first light beam 7 emitted from the front end surface of the LD 1 and the second light beam 8 emitted from the rear end surface of the LD 1 are used for speed sensing. The amount of light for stabilizing the light intensity of the LD 1 is monitored by, for example, a light receiving element (not shown) installed so as to monitor the amount of light cut by the diaphragms 12a and 12b. With such a configuration, the energy of the light emitted from the LD 1 can be used most efficiently for speed sensing, and a sufficient output of the beat signal 15 can be obtained without increasing the output of the LD 1.

  Further, the PDs 2, 2a, 2b, 32a, and 32b in the above embodiments and Reference Examples 1 to 4 may be light receiving elements with built-in circuits. That is, the PDs 2, 2a, 2b, 32a, 32b may incorporate signal processing circuits. Then, the output from PD2, 2a, 2b, 32a, 32b is amplified in the same chip, and signal processing such as waveform shaping, frequency counting, etc. is performed, so that the number of parts is smaller than when these ICs are configured separately. Since the device is reduced, not only the apparatus is downsized, but also the electromagnetic noise from the wires connecting the components can be reduced, so that the speed of the object to be measured 13 can be detected with high accuracy.

  In addition, the Doppler velocimeters in the above-described embodiments and Reference Examples 1 to 4 are for detecting the moving speed of the object 13 to be measured, but can be easily obtained from the speed information by capturing the time information in the subsequent signal processing. Can be converted into a displacement amount. For example, in a widely used electronic device, it can be applied to a displacement meter that detects a paper feed amount of a printer or a copier. In particular, since the LDV interference fringe interval is generally a few μm level, the resolution as a displacement meter can be raised to the μm level, and the resolution can be further increased to the submicron level by electric signal processing. Furthermore, since LDV can detect the speed by reflected light from a moving object, it does not require any special processing on the measurement target, and is particularly suitable for application as a high resolution encoder. In addition, currently widely used optical mice recognize movement information of speckle patterns on the detection surface as an image by a CCD (charge coupled device) or the like, and detect the movement amount. It can also be applied to an optical mouse. As described above, the speedometers of all of these Examples and Reference Examples 1 to 4 can be applied to a displacement meter and a vibration meter that detect displacement. That is, the position information of the object to be measured may be obtained based on the speed information and the time information regarding the object to be measured by the displacement meter including the speedometer. Moreover, you may obtain the information regarding the vibration of a to-be-measured object with the vibrometer provided with the said speedometer based on the speed information and time information regarding to-be-measured object. Here, “information related to vibration” means vibration amplitude, frequency, phase, and the like.

  Further, one of the speedometer, the displacement meter, and the vibration meter may be provided in the electronic device.

  Further, the speedometer of the present invention can be used in a displacement information detection device that calculates displacement information based on speed information and time information of an object to be measured.

FIG. 1 is a schematic configuration diagram of a speedometer according to Reference Example 1 of the present invention. FIG. 2A is a schematic diagram in the vicinity of the detection point showing ideal conditions in the reference example 1, and FIG. 2B is a schematic diagram of the detection point in the reference example 1. FIG. 3 is a diagram for explaining the unevenness of the object to be measured and conditions in the vicinity of the detection point. FIG. 4 is a schematic configuration diagram of a speedometer according to Reference Example 2 of the present invention. FIG. 5 is a schematic configuration diagram of a modified example of the speedometer of Reference Example 2 described above. 6A to 6C are diagrams for explaining detection of the moving direction of the object to be measured based on the phase information of the beat signal. FIG. 7 is a schematic configuration diagram of another modification of the speedometer of the reference example 2 described above. FIG. 8 is a schematic diagram for explaining conditions required for detection points. FIG. 9 is a schematic configuration diagram of a speedometer according to Reference Example 3 of the present invention. FIG. 10 is a schematic configuration diagram of a modified example of the speedometer of Reference Example 3 described above. FIG. 11 is a schematic configuration diagram of a speedometer according to Reference Example 4 of the present invention. FIG. 12 is a schematic configuration diagram of a modified example of the speedometer of the reference example 4. FIG. 13 is a schematic configuration diagram of a speedometer according to an embodiment of the present invention. FIG. 14 is an enlarged view of the detection point and the vicinity of the light receiving system in FIG. FIG. 15 is a schematic configuration diagram of a main part of a conventional LDV. FIG. 16 is a diagram for explaining an expression that links the moving speed of the DUT and the Doppler shift frequency . FIG. 17 is an enlarged view showing the overlap of light beams in the vicinity of the detection point of the conventional LDV . FIG. 18 is a schematic configuration diagram of a main part of another conventional LDV. FIG. 19 is a schematic configuration diagram of a main part of still another conventional LDV.

Explanation of symbols

1 LD
3 Diffraction gratings 4a, 4b CL
5a, 5b, 5c, 5d Mirror 7 First light beam 7g Zero-order diffracted light 7h of diffraction grating 3 First-order diffracted light 7i of diffraction grating 3 -1st-order diffracted light 8 of diffraction grating 3 Second light beam 10 Signal processing circuit section 12a, 12b Aperture 13 DUTs 14a, 14b Detection points 15a, 15b Beat signal 17 Condensing lens arrays 16a, 16b 1/4 wavelength plates 22a, 22b Diffraction gratings 43a, 43b Linear polarizer groups 32a, 32b PD
43a ₁ , 43a ₂ linear polarizer

Claims (32)

A semiconductor light emitting element that emits the first light flux from the front end face and emits the second light flux from the rear end face;
An optical branching element that splits the first luminous flux into third, fourth, and fifth luminous fluxes ;
Of the third, fourth, and fifth light beams branched from the first light beam, the third light beam having the same optical axis as the optical axis of the first light beam is changed to the first surface of the object to be measured. A first detection system that irradiates one detection point and irradiates the second detection point on the surface of the object to be measured with the fourth and fifth light beams;
A second detection system for irradiating the first detection point with the second light flux;
A light receiving element that receives scattered light from the first and second detection points;
A signal processing circuit unit for calculating the amount of frequency shift of the scattered light from the output of the light receiving element ,
The direction in which the semiconductor light emitting element emits the first and second light fluxes and the direction in which the light branching element emits the fourth and fifth light fluxes are relative to a plane including the surface of the object to be measured. Almost parallel,
A first plane including the optical axes of the second and third light beams incident on the first detection point is perpendicular to a plane including the surface of the object to be measured;
A speedometer characterized in that a second plane including the optical axes of the fourth and fifth light beams incident on the second detection point is perpendicular to the first plane . The speedometer according to claim 1,
The first detection system includes a first optical axis changing unit that changes the direction of the optical axis of the third, fourth, and fifth light beams emitted from the optical branching element,
The speed sensor according to claim 2, wherein the second detection system includes a second optical axis changing unit that changes an optical axis direction of the second light flux. The speedometer according to claim 1,
A speedometer, wherein the optical branching element is a first diffraction grating. The speedometer according to claim 3,
A velocimeter characterized in that the second detection point is formed using ± first-order diffracted light from the first diffraction grating. The speedometer according to claim 1,
The two light beams incident on the first detection point are superimposed on the surface of the object to be measured, and the two light beams incident on the second detection point are superimposed on the surface of the object to be measured. Speedometer to do. The speedometer according to claim 3,
A speedometer characterized in that the light intensity of the zero-order diffracted light by the first diffraction grating and the light intensity of the second light beam are substantially equal. The speedometer according to claim 3,
Angle direction of the optical axis of the 0-order diffracted light by the upper Symbol first diffraction grating is changed by the first optical axis changing unit changes the direction of the optical axis of the second light flux by the second optical axis changing unit Approximately equal to the angle
The angle at which the direction of the optical axis of the + 1st order diffracted light by the first diffraction grating is changed by the first optical axis changing unit is such that the direction of the optical axis of the −1st order diffracted light by the first diffraction grating is the first optical axis. A speedometer characterized by being substantially equal to an angle changed by a changing unit. The speedometer according to claim 1 ,
Speedometer, characterized in position to Rukoto to the first detection point and said second detection point both the first plane. The speedometer according to claim 1,
An optical axis of light incident on the light receiving element from the first detection point is located on a bisector of an angle formed by two light beams incident on the first detection point,
A speedometer, wherein an optical axis of light incident on the light receiving element from the second detection point is positioned on a bisector of an angle formed by two light beams incident on the second detection point. The speedometer according to claim 3,
A first phase changing unit arranged on an optical path of a light beam extending from the first diffraction grating to the second detection point, and changing a phase of light incident on the second detection point;
A second diffraction grating for branching a light beam from the second detection point toward the light receiving element;
A first linear polarizer group disposed on an optical path of a plurality of light beams branched by the second diffraction grating,
A speedometer, wherein the light receiving element receives the plurality of light beams that have passed through the first linear polarizer group. The speedometer according to claim 1,
A second phase changing unit arranged on an optical path of a light beam from the semiconductor light emitting element to the first detection point, and changing a phase of light incident on the first detection point;
A third diffraction grating for branching a light beam directed from the first detection point to the light receiving element;
A second linear polarizer group disposed on an optical path of a plurality of light beams branched by the third diffraction grating,
A speedometer, wherein the light receiving element receives the plurality of light beams that have passed through the second linear polarizer group. In velocimeter according to claim 1 0 or 1 1,
When the phase change amount of light by the phase changer and phi _0, speedometer, characterized in that the phi ₀ satisfies _{0 <φ 0 <λ / 2} . In velocimeter according to claim 1 2,
The speedometer is characterized in that the φ ₀ is λ / 4. In velocimeter according to claim 1 0 or 1 1,
A speedometer, wherein a birefringent material is used as a material of the phase changing portion. In velocimeter according to claim 1 3 or 1 4,
A speedometer, wherein an absolute value of a difference between a phase difference of each light beam forming the first detection point and a phase difference of each light beam forming the second detection point is smaller than π / 2. The speedometer according to claim 5,
A speedometer characterized in that an area where two light beams incident on the first detection point overlap is separated from an area where two light velocities incident on the second detection point overlap. The speedometer according to claim 1,
A first condenser lens disposed between the first detection point and the light receiving element;
A speedometer, comprising: a second condenser lens disposed between the second detection point and the light receiving element. The speedometer according to claim 17 ,
The speedometer according to claim 1, wherein the first and second condenser lenses are included in a single component comprising a lens array. The speedometer according to claim 1,
When the axis perpendicular to the surface of the object to be measured is the z axis,
The length in the z-axis direction of the region where the plurality of light beams incident on the first detection point overlap is longer than the length in the z-axis direction of the region where the surface of the object to be measured is located,
The speed in the z-axis direction of the region where the plurality of light beams incident on the second detection point overlap is longer than the length in the z-axis direction of the region where the surface of the object to be measured is located. Total. The speedometer according to claim 1,
The end surface of the semiconductor light emitting element is processed so that the light amounts of the second, third, fourth, and fifth light beams incident on the first and second detection points are substantially equal. Speedometer. The speedometer according to claim 1,
The light receiving element includes a first light receiving element that receives scattered light from the first detection point, and a second light receiving element that receives scattered light from the second detection point,
The speedometer according to claim 1, wherein each of the first and second light receiving elements is a one-chip element in which two light receiving portions are formed. In velocimeter according to claim 2 1,
The speedometer according to claim 1, wherein the first and second light receiving elements are split photodiodes. The speedometer according to claim 1,
A speedometer, wherein the light receiving element includes a signal processing circuit. The speedometer according to claim 3,
The semiconductor light emitting device is
It is arranged at a substantially midpoint between the first optical axis changing unit that changes the direction of the optical axis of the 0th-order diffracted light by the first diffraction grating and the second optical axis changing unit. Speedometer. The speedometer according to claim 1,
The semiconductor light emitting element and the light receiving element share the same substrate and are integrated. The speedometer according to claim 1,
A speedometer, wherein the semiconductor light emitting element is a laser diode. The speedometer according to claim 1,
A speedometer, wherein the semiconductor light emitting element has a plurality of light emitting points. The speedometer according to claim 1,
A first diaphragm disposed between the semiconductor light emitting element and the light branching element and through which the first light flux passes;
A speedometer, comprising: a second diaphragm disposed between the semiconductor light emitting element and the second optical axis direction changing unit, through which the second light flux passes. The speedometer according to claim 1,
A first lens group disposed between the semiconductor light emitting element and the light branching element and through which the first light flux passes;
A speedometer comprising: a second lens group disposed between the semiconductor light emitting element and the second optical axis direction changing unit, and through which the second light flux passes.   A displacement meter comprising the speedometer according to claim 1, wherein position information of the device under test is obtained based on speed information and time information regarding the device under test.   A vibrometer comprising the speedometer according to claim 1, wherein information relating to vibration of the object to be measured is obtained based on speed information and time information regarding the object to be measured. Velocimeter according to claim 1, an electronic device, characterized in that it comprises one of vibrometer according to displacement meter and claim 3 1 of claim 3 0.