JP2019158488A - Distance measuring device and method - Google Patents

Abstract

To provide a distance measuring device with which it is possible to eliminate the need for a spatial filter and measure an objective distance using a more simplified optical system.SOLUTION: A distance measuring device 10 comprises: an illumination optical system for irradiating a measurement object T with light from a light source 11 by focusing light on it; a diffraction optical element 14 for accepting reflected light from the measurement object T as incident light, and changing the phase of incident light and emitting diffracted light of two preset orders; a light detection element 16 for detecting an interference fringe generated by the diffracted light of two preset orders emitted from the diffraction optical element 14; and a distance calculation unit 17 for calculating an objective distance a from the light detection element 14 to the measurement object T on the basis of the detection result obtained by the light detection element 14.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a distance measuring apparatus and method, and more particularly to an optical distance measuring technique for irradiating and reflecting light on an object and measuring an objective distance to a measurement object based on the reflected light.

  2. Description of the Related Art Conventionally, there has been known an optical measuring device that can measure an objective distance to a measurement object in a non-contact manner using light such as laser light. Such an optical measuring apparatus is applied not only to measuring an objective distance to a measuring object but also to various uses such as measuring a surface shape of the measuring object and measuring a thickness of a thin film.

  For example, Patent Document 1 is arranged on an imaging plane, an amplitude type diffraction grating that diffracts reflected light reflected from a measurement target, a condensing lens that collects diffracted light from the diffraction grating on an imaging plane, and the like. Thus, there is disclosed a distance measuring device having a spatial filter that transmits only two different orders of diffracted light among diffracted lights and blocks other orders of diffracted light.

  The distance measuring device described in Patent Document 1 uses a spatial filter to transmit only two orders of diffracted light set in advance from many orders of diffracted light generated by an amplitude type diffraction grating. Then, the objective distance is measured by causing the two orders of diffracted light to interfere with each other.

  More specifically, in the distance measuring device described in Patent Document 1, an amplitude type diffraction grating having a rectangular wave-shaped transmittance distribution is used. Therefore, in the distance measuring device described in Patent Document 1, not only diffracted light of a specific order desired, for example, ± 1st order diffracted light, but also high order diffracted light or straightly transmitted without being diffracted. Zero-order diffracted light appears.

  Further, in the distance measuring device described in Patent Document 1, in order to cause only two orders of diffracted light to interfere with each other, a Fourier transform is performed using a condensing lens, and a spatial is performed on the Fourier transform plane. The desired two-order diffracted light is filtered and transmitted by the filter.

JP-A-2015-194347 JP 2013-186350 A

  However, in the technique described in Patent Document 1, it is necessary to adjust the positions of the condenser lens and the spatial filter to suitable positions. If this adjustment is not sufficient, the interference fringes are disturbed and distance measurement is performed. It can be difficult. Further, since the spatial filter is required to have high processing accuracy, there is a problem that the configuration of the optical system is complicated.

  The present invention has been made in order to solve the above-described problems, and provides a distance measuring device that does not require a spatial filter and can measure an objective distance using a simplified optical system. With the goal.

  In order to solve the above-described problems, a distance measuring device according to the present invention includes an irradiation optical system that focuses and irradiates light from a light source on a measurement target, and reflected light reflected from the measurement target as incident light. Diffractive optical element that emits two orders of diffracted light set in advance by changing the phase of the incident light, and interference fringes generated by the two orders of diffracted light emitted from the diffractive optical element are detected A light detection element, and a distance calculation unit that calculates an objective distance from the light detection element to the measurement object based on a detection result obtained by the light detection element.

  In the distance measuring apparatus according to the present invention, the diffractive optical element may include a diffraction grating having a concavo-convex structure arranged two-dimensionally and periodically.

  In the distance measuring device according to the present invention, the diffraction grating is a transmission type phase diffraction grating in which the concavo-convex structure has a sinusoidal cross-sectional shape, and a step between a peak and a valley included in the sinusoidal shape. D is D = n (m + 1/2) λ · cos φ, where n is the refractive index of the material of the diffraction grating, m is an integer, m = 0, ± 1,. The wavelength of the emitted light, φ, may satisfy any incident angle of the diffraction grating.

  In the distance measuring device according to the present invention, the diffraction grating is a reflection type phase diffraction grating in which the concavo-convex structure has a sinusoidal cross-sectional shape, and a step between a peak and a valley included in the sinusoidal shape. D is D = (m + 1/2) λ · cos φ / 2, where m is an integer, m = 0, ± 1,..., Λ is the wavelength of the light emitted from the light source, and φ is the above-mentioned Any incident angle of the diffraction grating) may be satisfied.

  In the distance measuring device according to the present invention, the diffractive optical element includes a liquid crystal layer and a plurality of electrodes arranged along a surface of the liquid crystal layer, and the liquid crystal layer is formed from each of the plurality of electrodes. A spatial light modulator may be provided that individually applies a voltage and performs phase modulation on the incident light incident on the liquid crystal layer.

  The distance measuring device according to the present invention further includes a condensing lens that condenses the two orders of diffracted light emitted from the diffractive optical element, and the light detecting element condenses light by the condensing lens. The interference fringes generated by the two orders of diffracted light may be detected, and the distance calculation unit may calculate an objective distance from the condenser lens to the measurement target.

  Further, in the distance measuring device according to the present invention, the diffractive optical element may further include a function of condensing the two-order diffracted light emitted in a direction perpendicular to the diffraction direction and the optical axis. .

  In the distance measuring device according to the present invention, the irradiation optical system includes a light source lens that collects light from the light source, and a beam splitter that directs light emitted from the light source lens toward the measurement target. Also good.

  The distance measuring method according to the present invention includes an irradiation step of condensing and irradiating light from a light source on a measurement target, and changing the phase of the incident light using reflected light reflected from the measurement target as incident light. A diffraction step for emitting two orders of diffracted light set in advance, a light detection step for detecting interference fringes generated by the two orders of diffracted light emitted by the diffraction step with a light detection element, and A distance calculation step of calculating an objective distance from the light detection element to the measurement object based on the detection result obtained in the light detection step.

  According to the present invention, the diffractive optical element that changes the phase of the incident light reflected from the measurement object and emits two preset orders of diffracted light is provided, so that a spatial filter is not required and simplification is achieved. The objective distance can be measured using the optical system.

FIG. 1 is a schematic diagram showing a configuration of a distance measuring apparatus according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the principle of distance measurement according to the embodiment of the present invention. FIG. 3 is a diagram for explaining diffraction by the diffractive optical element according to the embodiment of the present invention. FIG. 4 is a diagram for explaining the relationship between diffracted light of different orders and the light spot interval according to the embodiment of the present invention. FIG. 5 is a diagram for explaining the relationship between the light spot interval and the optical path difference according to the embodiment of the present invention. FIG. 6 is an image example showing interference fringes generated on the detection surface according to the embodiment of the present invention. FIG. 7 is a block diagram illustrating a configuration example of a computer that realizes the distance calculation unit according to the embodiment of the present invention. FIG. 8 is a flowchart for explaining the operation of the distance measuring apparatus according to the embodiment of the present invention. FIG. 9 is a diagram showing a modification of the distance measuring device according to the embodiment of the present invention.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. 1 to 9.
[Embodiment]
FIG. 1 is a schematic diagram showing a configuration of a distance measuring apparatus 10 according to an embodiment of the present invention.
The distance measuring device 10 irradiates and reflects light on the measurement target T, and measures the objective distance to the measurement target T based on the reflected light.

  The distance measuring device 10 includes a light source 11, a light source lens 12, a beam splitter 13, a diffractive optical element 14, a condensing lens 15, a light detection element 16, and a distance calculation unit 17. For example, the distance measuring device 10 may be housed in a casing (not shown) with the above-described configuration.

  The light source 11, the light source lens 12, and the beam splitter 13 constitute an irradiation optical system that collects and emits light emitted from the light source 11 onto the measurement target T.

  The light source 11 is a device that emits light of a single wavelength (monochromatic light) used for distance measurement. As the light source 11, a semiconductor laser device, a monochromatic light such as a sodium lamp, or a device that emits light having a single wavelength by a white light source and a narrow band-pass filter can be used.

  The light source lens 12 condenses the light emitted from the light source 11 and emits it to the beam splitter 13.

  The beam splitter 13 is disposed on the optical path O of the light collecting system, reflects the light from the light source 11 collected by the light source lens 12, and irradiates the light spot A of the measurement target T along the optical path O. . The beam splitter 13 causes the reflected light reflected in the direction of the optical path O among the reflected light diffusely reflected by the light spot A to enter the diffractive optical element 14.

  The diffractive optical element 14 is disposed on the optical path O, and the reflected light from the measurement target T that has passed through the beam splitter 13 is incident thereon. The diffractive optical element 14 controls incident light according to preset diffraction characteristics, and changes only the phase of the incident light and emits only two orders of preset diffraction light based on the diffraction characteristics.

  More specifically, the diffractive optical element 14 is configured by a diffraction grating in which a concavo-convex structure is two-dimensionally and periodically arranged. In the present embodiment, a case where a transmissive phase diffraction grating is used as the diffractive optical element 14 will be described. However, a reflective phase diffraction grating may be used.

  The diffractive optical element 14 is an element in which a fine concavo-convex structure is formed on the surface of an optical substrate such as quartz or ZnSe, and the intensity distribution of incident light can be shaped into a desired distribution by utilizing the light diffraction phenomenon by the concavo-convex structure. It is. More specifically, the diffractive optical element 14 can output only the required order of diffracted light, for example, ± 1st order diffracted light, and can not emit other unnecessary orders of diffracted light.

  In the diffractive optical element 14, the concavo-convex structure may have, for example, a sinusoidal cross-sectional shape. By having a sinusoidal cross-sectional shape, the diffractive optical element 14 can emit only ± first-order diffracted light and remove higher-order diffracted light.

In addition, since the diffractive optical element 14 according to the present embodiment is a transmissive phase diffraction grating, the step D between the peak and the valley of the sine wave shape is the optical path length in order to remove the 0th-order diffracted light. Thus, a configuration satisfying the following expression (1) can be obtained.
D = n (m + 1/2) λ · cos φ (1)
In the above formula (1), n is the refractive index of the material of the diffractive optical element 14, m is an integer (m = 0, ± 1,...), Λ is the wavelength of light emitted from the light source 11, and φ is An arbitrary incident angle in the diffractive optical element 14 is shown.

On the other hand, when a reflective phase diffraction grating is used as the diffractive optical element 14, the step D between the peaks and valleys of the sine wave shape can be configured to satisfy the following expression (2) in terms of the optical path length.
D = (m + 1/2) λ · cos φ / 2 (2)
In the above equation (2), m is an integer (m = 0, ± 1,...), Λ is the wavelength of light emitted from the light source 11, and φ is an arbitrary incident angle in the diffractive optical element 14.

  In the above formulas (1) and (2), the step D may be designed to be π in the phase. That is, the phases of the diffracted light emitted from the diffractive optical element 14 cancel each other, and the zeroth-order diffracted light is removed.

  Further, the grating period d of the phase type grating which is the diffractive optical element 14 is sufficiently larger than the wavelength λ of the light from the light source 11, for example, d> 10λ. Thereby, it can be set as the structure sufficient for practical use as a phase type | mold grating.

  Under the above conditions, for example, in order to obtain ± 1st order diffracted light, the grating shape of the diffractive optical element 14 is changed based on the spatial optical path distribution obtained by inverse Fourier transform of the distribution of the emitted light of the desired order. It is sufficient to design (see Patent Document 2).

  The condensing lens 15 condenses the two orders of diffracted light by the diffractive optical element 14. In the present embodiment, the condensing lens 15 is composed of, for example, a convex lens, is disposed on the optical path O, and condenses the two orders of diffracted light emitted from the diffractive optical element 14 onto the imaging plane Q.

  The light detection element 16 detects interference fringes generated by two orders of diffracted light emitted from the diffractive optical element 14 and outputs a detection result. More specifically, the light detection element 16 has a detection surface I and detects interference fringes on the detection surface I. As the light detection element 16, for example, a light receiving element arranged in one dimension such as a CCD (Charged Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor) linear image sensor, or a photodiode array can be used.

  The distance calculation unit 17 performs an arithmetic process from the detection result obtained by the light detection element 16, extracts the period length of the interference fringes, and the objective from the condenser lens 15 to the measurement target T based on the obtained period length. Calculate the distance. Details of the configuration of the distance calculation unit 17 will be described later.

[Principle of distance measurement]
Next, the principle of distance measurement in the distance measuring apparatus 10 according to the present invention will be described with reference to FIGS.

  In FIG. 2, only the light collecting system of the distance measuring device 10 is shown as the main part, and the projection optical system is omitted. 2 to 5, in the diffractive optical element 14 composed of a phase diffraction grating, one longitudinal direction (perpendicular to the plane of the paper) of the grating is defined as the X direction, and the other longitudinal direction (vertical direction in the plane of the paper) of the grating is defined as Y. The direction perpendicular to the lattice plane (the horizontal direction on the paper surface) is the Z direction.

  In addition, the lens originally has two principal points depending on the incident direction of light, and the positions thereof are different, but in the following, in order to avoid complication of the mathematical expression, the condenser lens 15 is composed of a thin single lens, Assuming that there is only one principal point at the lens center, each equation was derived.

As shown in FIG. 2, the objective distance from the measurement target T to the principal point M, that is, the position of the condenser lens 15 is a, the distance from the principal point to the imaging plane Q is b, and the focal length of the condenser lens 15 is set. Where f is represented by the following formula (3) by the imaging formula (lens formula).

As can be seen from the above equation (3), the position of the imaging plane Q also changes in accordance with the change in the objective distance a from the condenser lens 15 to the measurement target T.
Further, as shown in FIG. 3, the interval between the concavo-convex structures formed on the diffractive optical element 14, that is, the grating period is d, the diffraction order is k (k = 0, ± 1, ± 2,...), The wavelength of the light source 11 is λ, and the diffraction angle θk of each diffracted light. In this case, the optical path difference ΔL between adjacent diffracted lights is expressed by the following formula (4).

  Furthermore, as shown in FIG. 4, the diffracted light emitted from the diffractive optical element 14 forms a plurality of light spots in the Y direction on the imaging plane Q by the condenser lens 15. Here, the diffraction angles of diffracted lights of two different orders k and k ′ are θk and θk ′, the light spots by these diffracted lights are Ak and Ak ′, and the light spot from the point A0 where the optical axis and the imaging plane intersect. When the distances along the Y direction to Ak and Ak ′ are W1 and W2, the deviation width W in the Y direction of these light spots Ak and Ak ′ is expressed by the following equation (5).

Here, in the above equation (5), the grating period d of the concavo-convex structure in the actual diffractive optical element 14 is sufficiently larger than kλ and k′λ, and kλ / d and k′λ / d are sufficiently small values. Therefore, equation (5) is approximated as the following equation (6).

  On the other hand, as shown in FIG. 5, the interval between the light spots Ak and Ak ′ on the imaging surface Q is W, and the diffracted light from the light spots Ak and Ak ′ reaches the detection surface I of the light detection element 16. Let V be the reached point. A point where a line extending in the Z direction from the intermediate point between the light spots Ak and Ak ′ and the detection surface I of the light detection element 16 intersect is defined as V0, and V0 to V along the Y direction on the detection surface I is defined as V0. Let P be the distance. When the distance from the imaging plane Q to the detection plane I is c, the optical path length Lk of the diffracted light from the light spot Ak to the arrival point V can be obtained by the three-square theorem. However, since the light spot interval W and the distance P are sufficiently small compared to the distance c, it can be approximated as the following equation (7).

また、光スポットＡｋから到達点Ｖへの回折光の光路長Ｌｋ’も、光路長Ｌｋと同様にして、次の式（８）のように近似できる。

Further, the optical path length Lk ′ of the diffracted light from the light spot Ak to the arrival point V can be approximated as in the following equation (8), similarly to the optical path length Lk.

  Therefore, the optical path difference ΔL between these optical path lengths Lk and Lk ′ is obtained by the following equation (9). On the detection surface I, interference fringes are generated by this optical path difference ΔL. More specifically, when the optical path difference ΔL is an integer j (j is an integer equal to or greater than 0) times the wavelength λ of light, a bright line is generated on the detection surface I.

Here, among the bright lines generated on the detection surface I, the interval between adjacent bright lines is the interference fringe pitch p, which corresponds to the case of j = 1 in Expression (9). Therefore, the interference fringe pitch p of the interference fringes generated on the detection surface I of the light detection element 16 is obtained by the following equation (10) by modifying the equation (9).

At this time, since the light spot interval W is obtained by Expression (6), if this is substituted into Expression (10), Expression (11) is obtained.

Further, the order difference between the diffraction orders k and k ′ is Δk, and the distance b from the principal point of the condenser lens 15 to the imaging plane Q and the distance c from the imaging plane Q to the detection plane I are expressed as a condenser lens. The distance L from the 15 principal points to the detection surface I is replaced. In this case, equation (11) becomes the following equation (12).

Therefore, it can be seen that the interference fringe pitch p is obtained by a function depending on the distance L from the principal point of the condenser lens 15 to the detection surface I.
At this time, the distance b from the principal point of the condenser lens 15 to the imaging plane Q is the objective from the measurement target T to the principal point M, that is, the position of the condenser lens 15, as shown in the above-described equation (3). It is represented by the distance a and the focal length f of the condenser lens 15. Thus, equation (12) can be transformed into equation (13).

Here, the focal length f of the condenser lens 15, the distance L from the principal point of the condenser lens 15 to the detection surface I, and the order difference Δk of the diffraction orders k and k ′ are known values. As a result, it can be seen that the interference fringe pitch p is a function of the objective distance a from the measurement target T to the principal point M, that is, the position of the condenser lens 15. Therefore, by measuring the interference fringe pitch p detected on the detection surface I of the light detection element 16, the objective distance a to the measurement target T can be obtained by the following equation (14).

  FIG. 6 is an analysis example of the detection result obtained by the light detection element 16. Here, the horizontal axis indicates the pixel position [pic] of the image along the Y direction perpendicular to the interference fringes, and the vertical axis indicates the light intensity (no unit) at each pixel position. The obtained detection result has a substantially sine wave shape, and its peak position corresponds to a bright line. Therefore, the actual distance indicating the interference fringe pitch p can be calculated from the number of pixels existing between the peak positions.

FIG. 7 is a block diagram showing a configuration of the distance calculation unit 17 that performs the arithmetic processing related to the calculation of the objective distance a described above.
The distance calculation unit 17 includes a computing device 102 having a CPU 103 and a main storage device 104 connected via a bus 101, a communication control device 105, an I / F 106, an external storage device 107, a display device 108, and the like, It can be realized by a program for controlling these hardware resources.

As shown in FIG. 7, the light detection element 16 is connected to the distance calculation unit 17 via the I / F 106, and outputs the obtained detection result to the distance calculation unit 17 via the I / F 106.
The display device 108 is composed of a liquid crystal display or the like, and displays the calculation result of the objective distance a by the arithmetic device 102.

  The communication control device 105 is a control device for connecting various external electronic devices via a communication network. The communication control device 105 may send the calculation result of the objective distance a to the outside via a communication network.

[Operation of distance measuring device]
The operation of the distance measuring apparatus 10 having the above-described configuration will be described with reference to the flowchart of FIG.

  First, the measurement target T is arranged on the distance measuring device 10. Also, initial adjustments such as the light amount of the light source 11 and the exposure time are performed.

  Thereafter, the light emitted from the light source 11 is collected by the light source lens 12 and irradiated toward the measurement target T by the beam splitter 13 (step S1). Next, the light reflected from the measurement target T passes through the beam splitter 13 and enters the diffractive optical element 14. The diffractive optical element 14 controls incident light according to preset diffraction characteristics, changes the phase of the incident light, and emits only two orders of preset diffraction light based on the diffraction characteristics (step S2). .

  Next, the two orders of diffracted light emitted from the diffractive optical element 14 are collected by the condenser lens 15. The interference fringes generated by the two orders of diffracted light are detected by the light detection element 16 (step S3).

  Thereafter, the light detection element 16 inputs the detected interference fringe information to the distance calculation unit 17. And the distance calculation part 17 calculates based on the principle of the distance measurement mentioned above, and calculates the objective distance a of the measuring object T (step S5).

  As described above, according to the present embodiment, the distance measurement apparatus 10 uses the reflected light reflected from the measurement target T as incident light, and changes the phase of the incident light to set two orders of diffraction in advance. Since the diffractive optical element 14 that emits only light is included, a spatial filter is not necessary, and the objective distance a can be measured using a more simplified optical system.

  Further, since the diffractive optical element 14 emits only two orders of diffracted light set in advance, a lens for performing Fourier transform, which is necessary in the technology using the conventional amplitude type diffraction grating, is unnecessary. It becomes. Therefore, the distance measuring apparatus 10 can measure the objective distance a without performing precise position adjustment in the optical system such as installing a spatial filter at the position of the Fourier transform plane.

  Further, the distance measuring device 10 according to the present embodiment emits diffracted light without blocking part of incident light in the diffractive optical element 14. Therefore, compared with the case where an amplitude type diffraction grating is used, the distance measuring apparatus 10 according to the present embodiment can obtain higher diffraction efficiency with respect to diffracted light of a desired order. As a result, distance measurement can be performed using light with stronger signal intensity.

  In the embodiment described above, the distance measuring apparatus 10 includes the condenser lens 15 and configures the convergent light. However, since the distance measuring device 10 does not need to form a Fourier transform surface on the image plane Q, instead of the condenser lens 15, as shown in FIG. It may be configured.

  Alternatively, a configuration may be employed in which interference fringes generated by two orders of diffracted light emitted from the diffractive optical element 14 are directly detected by the light detecting element 16 without using the condenser lens 15. . In this case, the distance measuring device 10 measures the distance from the detection surface I of the light detection element 16 to the measurement target T as the objective distance a.

  Further, in the distance measuring apparatus 10 according to the embodiment described above, two in the direction orthogonal to the diffraction direction of the diffractive optical element 14 and the optical axis are provided on the optical path O between the diffractive optical element 14 and the light detection element 16. Means for collecting the diffracted light of the order may be provided. Examples of the condensing means include a cylindrical lens using light refraction and a reflecting mirror. Further, the diffractive optical element 14 itself may be provided with a lens function to constitute a light collecting means. By further providing such a light condensing means, the distance measuring device 10 can further increase the signal intensity of the diffracted light.

  Moreover, the distance measuring device 10 according to the described embodiment has been described with respect to the case where the diffractive optical element 14 configured by a phase diffraction grating is provided. However, the diffractive optical element 14 is not limited to a phase diffraction grating, and for example, a spatial light modulator can be used.

  The spatial light modulator has, for example, a liquid crystal layer and a plurality of electrodes arranged along the surface of the liquid crystal layer, and a voltage is individually applied to the liquid crystal layer from each of the plurality of electrodes. Phase modulation is performed on incident incident light, and only two orders of diffracted light set in advance are emitted. By using the spatial light modulator, the orders of the two diffracted lights to be emitted can be made variable according to the application.

  Although the embodiments of the distance measuring device and the distance measuring method of the present invention have been described above, the present invention is not limited to the described embodiments, and those skilled in the art within the scope of the invention described in the claims. Various modifications that can be envisaged are possible.

  DESCRIPTION OF SYMBOLS 10 ... Distance measuring device, 11 ... Light source, 12 ... Light source lens, 13 ... Beam splitter, 14 ... Diffractive optical element, 15 ... Condensing lens, 16 ... Photodetection element, 17 ... Distance calculation part, T ... Measurement object, Q DESCRIPTION OF SYMBOLS ... Imaging surface, I ... Detection surface, a ... Objective distance, p ... Interference fringe pitch, 101 ... Bus, 102 ... Arithmetic unit, 103 ... CPU, 104 ... Main memory, 105 ... Communication control device, 106 ... I / F, 107 ... external storage device, 108 ... display device.

Claims (9)

An irradiation optical system for condensing and irradiating light from a light source on a measurement target;
A diffractive optical element that emits two orders of diffracted light set in advance by changing the phase of the incident light as reflected light reflected from the measurement object;
A light detecting element for detecting interference fringes generated by the two orders of diffracted light emitted from the diffractive optical element;
A distance calculation device comprising: a distance calculation unit that calculates an objective distance from the light detection element to the measurement object based on a detection result obtained by the light detection element. The distance measuring device according to claim 1,
The diffractive optical element includes a diffraction grating having a concavo-convex structure arranged two-dimensionally and periodically. The distance measuring device according to claim 2,
The diffraction grating is a transmissive phase diffraction grating in which the concavo-convex structure has a sinusoidal cross-sectional shape, and a step D between a peak and a valley included in the sinusoidal shape is D = n (m + 1 / 2) λ · cos φ (where n is the refractive index of the material of the diffraction grating, m is an integer, m = 0, ± 1,..., Λ is the wavelength of light emitted from the light source, φ is An arbitrary incident angle of the diffraction grating) is satisfied. The distance measuring device according to claim 2,
The diffraction grating is a reflection type phase diffraction grating in which the concavo-convex structure has a sinusoidal cross-sectional shape, and a step D between a peak and a valley included in the sinusoidal shape is D = (m + 1/2) λ.・ Cosφ / 2 (where m is an integer, m = 0, ± 1,..., Λ is the wavelength of light emitted from the light source, φ is an arbitrary incident angle of the diffraction grating) A distance measuring device characterized by. The distance measuring device according to claim 1,
The diffractive optical element has a liquid crystal layer and a plurality of electrodes arranged along the surface of the liquid crystal layer, and individually applies a voltage to the liquid crystal layer from each of the plurality of electrodes, and the liquid crystal A distance measuring device comprising: a spatial light modulator that performs phase modulation on the incident light that enters the layer. In the distance measuring device according to any one of claims 1 to 5,
A condenser lens that condenses the two-order diffracted light emitted from the diffractive optical element;
The light detection element detects interference fringes generated by the two orders of diffracted light collected by the condenser lens;
The distance calculation unit calculates an objective distance from the condenser lens to the measurement target. In the distance measuring device according to any one of claims 1 to 6,
The diffractive optical element further includes a function of condensing the emitted two-order diffracted light in a direction perpendicular to the diffraction direction and the optical axis. In the distance measuring device according to any one of claims 1 to 7,
The irradiation optical system is
A light source lens for condensing light from the light source;
A distance measuring device comprising: a beam splitter that directs light emitted from the light source lens toward the measurement target. An irradiation step of condensing and irradiating light from a light source on a measurement target;
Diffraction step of emitting two orders of diffracted light set in advance by changing the phase of the incident light with the reflected light reflected from the measurement object as incident light,
A light detection step of detecting interference fringes generated by the two orders of diffracted light emitted in the diffraction step with a light detection element;
A distance calculation method comprising: a distance calculation step of calculating an objective distance from the light detection element to the measurement object based on a detection result obtained in the light detection step.

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