Distance measuring device

Abstract

A distance measuring device is provided with: a light source unit that emits a first laser beam and a reference laser beam; a reference interference system for detecting first interference light generated by interference of the first laser light and second interference light generated by interference of the reference laser light, and outputting a first signal; a measurement interference system to which first reflected light generated by reflecting the first laser light by the object is input, and which outputs a second signal; and a signal processing system that generates wavelength information relating to the wavelength of the first laser beam on the basis of the first signal, and calculates the distance from the distance measuring device to the object on the basis of the wavelength information and the second signal, the reference interference system being a Michelson interferometer.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a distance measuring device. BACKGROUND

[0002] Light interference using a laser is widely used as a means capable of non-contact acquisition of information indicating a distance and / or a shape of an object, and the like. As an example thereof, a LiDAR (Light Detection And Ranging) of a frequency modulated continuous wave (FMCW) system is known as a three-dimensional measuring device of millimeter accuracy. Further, light interference using optical coherence tomography (OCT) or an optical comb is known as a means capable of measurement with micrometer accuracy. They are widely utilized in the medical field and / or the industrial field.

[0003] Further, by controlling a light interference phenomenon with higher accuracy, measurement with nanometer accuracy is enabled. For example, measurement by a Michelson interference system using a single-wavelength laser is one method of measuring a difference in distance in the nanometer unit.

[0004] Nanometer-accuracy optical measurement typified by homodyne optical interference, although enabling non-contact measurement with high accuracy, has a problem that a measurement range is limited to half of a wavelength (submicron unit). Therefore, there is a case where measurement of a sample having a structure in the nanometer unit and a structure in the tens-of-micron unit is difficult.

[0005] As a method of solving the problem, multi-wavelength interference using light interference of two or more single-wavelength lasers is expected. Multi-wavelength interference can eliminate the trade-off between a measurement range and measurement accuracy as a conventional problem, and achieve a longer measurement range and higher measurement accuracy at the same time.

[0006] For example, in Patent Literatures 1 and 2, by combining light interference results of lasers having different wavelengths, the trade-off between a measurement range and measurement accuracy as a conventional problem can be eliminated, and a longer measurement range and higher measurement accuracy can be achieved at the same time.

[0007] Related Art

[0008] Patent Literature

[0009] Patent Literature 1: Japanese Patent Application Publication No. 2021-148634

[0010] Patent Literature 2: International Publication No. 2008 / 146480

[0011] Patent Literature 3: Japanese Realization Publication Hei 5-14867 Utility Model Contents

[0012] Problem to be Solved by the Utility Model

[0013] In a distance measuring method using interference of laser light, the wavelength of the laser light fluctuates (undulates) over time, thereby affecting the distance information calculated. Specifically, the length measurement accuracy decreases, and the stability of the length measurement result decreases due to long-term measurement.

[0014] Therefore, the present disclosure provides a distance measuring device capable of suppressing decrease in length measurement accuracy and long-term stability.

[0015] Means for Solving the Problem

[0016] A distance measuring device according to a technical solution of the present disclosure includes: a light source section that emits first laser light and reference laser light; a reference interference system that detects first interference light generated by interference of the first laser light and second interference light generated by interference of the reference laser light, and outputs a first signal; a measurement interference system that is input with first reflected light generated by reflection of the first laser light by an object, and outputs a second signal; and a signal processing system that generates wavelength information about the wavelength of the first laser light based on the first signal, and calculates a distance from the distance measuring device to the object based on the wavelength information and the second signal. The reference interference system is a Michelson interferometer.

[0017] Effects of the Utility Model

[0018] According to the present disclosure, it is possible to suppress decrease in length measurement accuracy and long-term stability. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a block diagram showing the structure of the distance measuring device according to Embodiment 1.

[0020] Figure 2 is a block diagram showing the structure of the light source section of the distance measuring device according to Embodiment 1.

[0021] Figure 3 is a diagram showing the detailed structure of the measurement interference system of the distance measuring device according to Embodiment 1.

[0022] Figure 4 is a diagram showing the detailed structure of the reference interference system of the distance measuring device according to Embodiment 1.

[0023] Figure 5is a diagram for explaining the principle of the first measurement using a single-wavelength laser performed by the distance measuring apparatus relating to Embodiment 1.

[0024] Figure 6 is a diagram for explaining the principle of the second measurement using a plurality of single-wavelength lasers performed by the distance measuring apparatus relating to Embodiment 1.

[0025] Figure 7 is a diagram showing the measurement range and the measurement accuracy of the two measurements performed by the distance measuring apparatus relating to Embodiment 1.

[0026] Figure 8 is a diagram for explaining the stability of the wavelength and the frequency of the single-wavelength laser.

[0027] Figure 9 is a flowchart showing the operation of the distance measuring apparatus relating to Embodiment 1.

[0028] Figure 10 is a diagram showing the relationship between the update frequency of the wavelength information and the calculation frequency of the distance.

[0029] Figure 11 is a block diagram showing the structure of the distance measuring apparatus relating to Embodiment 2.

[0030] Figure 12 is a flowchart showing the operation of the distance measuring apparatus relating to Embodiment 2.

[0031] Figure 13 is a block diagram showing the structure of the distance measuring apparatus relating to Embodiment 3.

[0032] Figure 14 is a block diagram showing the structure of the light source section of the distance measuring apparatus relating to Modified Example 1 of the Embodiment.

[0033] Figure 15 is a block diagram showing the structure of the distance measuring apparatus relating to Modified Example 2 of the Embodiment.

[0034] BRIEF DESCRIPTION OF DRAWINGS

[0035] 1, 2, 3, 201 distance measuring device; 10, 10A, 110, 210 light source section; 11, 111 measurement light source; 12 reference light source; 13a, 13b, 13c, 13r laser light source; 14 wavelength synthesizing system; 15 adjustment section; 20 optical branching device; 30 reference interference system; 31, 41, 60 optical interference system; 32, 42 optical detection system; 33, 43 beam splitter; 34, 35, 44, 46 mirror; 36 moving mirror; 36a, 36b reflecting surface; 37, 38, 47, 48 photodetector; 40 measurement interference system; 45 dichroic mirror; 50 signal processing system; 51 signal receiving section; 52 memory; 53 processing circuit; 90, 90a, 90b, 90c object DETAILED DESCRIPTION

[0036] (SUMMARY OF THE DISCLOSURE)

[0037] First, the following shows the definition of the main terms used in this specification.

[0038] "Length measurement accuracy" indicates the degree of correctness when measuring a distance. That is, the length measurement accuracy is a scale that judges how correct the distance information is. Therefore, the higher the length measurement accuracy, the more it can be said that the measurement is correct.

[0039] "Length measurement range" indicates the range of the distance direction in which unique distance information can be obtained. That is, the length measurement range indicates the range in which distance measurement (ranging) can be performed.

[0040] In this specification, both the length measurement accuracy and the length measurement range are expressed by the same dimension as the distance. Specifically, both the unit of the length measurement accuracy and the unit of the length measurement range are expressed in nanometers (nm), micrometers (μm), millimeters (mm), or the like. Therefore, "high length measurement accuracy" is synonymous with "short length measurement accuracy" expressed in the dimension of distance. "Low length measurement accuracy" is synonymous with "long length measurement accuracy" expressed in the dimension of distance. Furthermore, in this specification, the length measurement accuracy is sometimes simply referred to as "accuracy". The length measurement range is sometimes simply referred to as "range".

[0041] Distance measurement within the length measurement range is referred to as "absolute distance measurement". For example, distance measurement in the case where the accuracy is 10 nm and the length measurement range is 1 mm is absolute distance measurement in which a difference of 10 nm can be distinguished within a range of 1 mm.

[0042] "Long-term stability" means that the variation over time is sufficiently small during the period from the start to the end of measurement, and that the length measurement can be performed with consistent accuracy. For example, if the wavelength of laser light fluctuates over time, the long-term stability decreases. If the long-term stability decreases, problems such as a limitation on the length measurement time can occur.

[0043] The distance measuring apparatuses according to the present disclosure are described below.

[0044] The distance measuring apparatus according to the first aspect of the present disclosure includes a light source section that emits a first laser light and a reference laser light; a reference interference system that detects first interference light generated by interference of the first laser light and second interference light generated by interference of the reference laser light, and outputs a first signal; a measurement interference system that is input with first reflected light generated by reflection of the first laser light by an object, and outputs a second signal; and a signal processing system that generates wavelength information about the wavelength of the first laser light based on the first signal, and calculates the distance from the distance measuring apparatus to the object based on the wavelength information and the second signal. The reference interference system is a Michelson interferometer.

[0045] Thus, even if the wavelength of the laser light fluctuates, the actual wavelength of the laser light used in the measurement or a value equivalent thereto can be obtained from the wavelength information. The fluctuation of the wavelength can be fed back to the calculation of the distance, and the decrease in the length measurement accuracy and the long-term stability can be suppressed.

[0046] The distance measuring apparatus according to the second aspect of the present disclosure is the distance measuring apparatus according to the first aspect of the present disclosure, in which the signal processing system can generate the wavelength information about the wavelength of the first laser light based on the first signal, and can calculate the distance based on the wavelength information and the second signal.

[0047] The distance measuring apparatus according to the third aspect of the present disclosure is the distance measuring apparatus according to the first aspect of the present disclosure, in which the light source section can also emit second laser light having a wavelength different from that of the first laser light; and the measurement interference system can also be input with second reflected light generated by reflection of the second laser light by the object.

[0048] Thus, distance measurement using multiwavelength interferometry (MWI) using light of multiple wavelengths can be performed. Thus, higher length measurement accuracy and a larger length measurement range can be achieved.

[0049] In addition, the reference interference system can detect interference light generated by interference of the second laser light and interference light generated by interference of the reference laser light, and output a third signal; and the signal processing system can generate second wavelength information about the wavelength of the second laser light based on the third signal, and calculate the distance from the distance measuring apparatus to the object based on first wavelength information about the wavelength of the first laser light, the second wavelength information, and the second signal.

[0050] In addition, it is not necessary to generate the second wavelength information using the second laser. For example, in a case where the fluctuation of the wavelength of the first laser is smaller than the fluctuation of the wavelength of the second laser, the measurement accuracy can be ensured to be higher based on the interference result of the first laser. Therefore, even in a case where the second wavelength information relating to the wavelength of the second laser is not obtained, higher measurement accuracy and a larger measurement range can be achieved.

[0051] The distance measuring device according to the fourth aspect of the present disclosure, for the distance measuring device according to the third aspect, in the distance measuring device according to the fourth aspect, the wavelength of the reference laser can be shorter than the wavelength of the first laser.

[0052] Thus, the wavelengths of the plurality of lasers used by the MWI can be measured, and therefore the measurement accuracy can be improved even if the measurement range is expanded.

[0053] The distance measuring device according to the fifth aspect of the present disclosure, for the distance measuring device according to the third aspect or the fourth aspect, in the distance measuring device according to the fifth aspect, the interference system for measurement can include: a first light interference system that causes the first laser and the first reflected light to interfere with each other, emits third interference light generated by the interference of the first laser and the first reflected light, and causes the second laser and the second reflected light to interfere with each other, and emits fourth interference light generated by the interference of the second laser and the second reflected light; and a first light detection system that detects the third interference light and the fourth interference light, and outputs the second signal.

[0054] Thus, the light heterodyne interference can be performed for each wavelength, and the interference signal of each wavelength can be obtained as the second signal with high accuracy. By combining the interference signals of each wavelength, the measurement range can be increased. For details, as used in the description of the first aspect, the first light interference system and the second light interference system can be used. Figure 6 This will be described later.

[0055] In addition, in the technology described in Patent Literature 1, the measurement laser and the reference laser are heterodyne interfered with each other, a beat signal is detected by a light detector, and the result of the measurement by the measurement laser is corrected based on the result. Since the wavelength difference between the two lasers needs to be reduced as a condition for the heterodyne interference, the selection of the wavelength of the measurement laser is limited by the reference laser.

[0056] As a generally used wavelength-stabilized laser, a HeNe laser can be cited. However, in the case of heterodyne interference, the wavelength of the laser for length measurement is limited to a wavelength in the vicinity of 633 nm, which is the wavelength of a HeNe laser. Optical elements suitable for a wavelength in the vicinity of 633 nm are expensive, and moreover, in the case where the object is a visual-use lens or the like with an AR coating, there is a problem in that it is difficult to measure. Furthermore, since a plurality of lasers of different wavelengths are used as the laser for length measurement in MWI, the same number of light sources for reference lasers also needs to be prepared. In contrast, in the distance measuring apparatus according to the present technical solution, since zero- difference interference is utilized, the absolute value of the difference in the wavelengths of the two lasers used in the measurement can be large compared to the case where heterodyne interference is utilized, and thus the wavelength selectivity of the two lasers can be improved. For example, since a wavelength suitable for the measurement of the object can be selected, the result is that the decrease in the length measurement accuracy and the long-term stability of the object can be suppressed. Furthermore, regardless of the number of wavelengths of the laser for measurement, the light source for the reference laser can be only one. Thus, the distance measuring apparatus can be simplified in structure, downsized, and reduced in cost. Furthermore, since a single-wavelength laser, which is more stable, typified by a HeNe laser, can be used, the accuracy of the measurement of the wavelength is higher than in other ways, and the result is that the length measurement accuracy and the long-term stability are higher than in other ways.

[0057] The distance measuring apparatus according to the sixth technical solution of the present disclosure, for the distance measuring apparatus according to the first technical solution, in the distance measuring apparatus according to the sixth technical solution, the light source unit can also emit a plurality of second lasers; the wavelengths of the plurality of second lasers can be different from each other; the wavelengths of the plurality of second lasers can each be different from the wavelength of the first laser; and the plurality of second reflected lights generated by the reflection of the plurality of second lasers by the object can also be input to the measurement interference system.

[0058] Thus, lasers of three or more wavelengths can be used for measurement. As a result, the length measurement range can be further expanded.

[0059] The distance measuring apparatus according to the seventh technical solution of the present disclosure, for the distance measuring apparatus according to any one of the first technical solution to the sixth technical solution, can also be provided with an optical splitter (optical splitter) that divides the first laser emitted from the light source unit into a first part and a second part, and causes the first part to be input to the reference interference system and the second part to be input to the measurement interference system.

[0060] Thus, a part of the first laser used in the measurement can be input to the reference interference system with a simple structure.

[0061] The distance measuring device according to the eighth aspect of the present disclosure can be the distance measuring device according to any one of the first to seventh aspects, wherein the reference interference system can further include a second light interference system configured to cause the first laser light to interfere to generate the first interference light, and cause the reference laser light to interfere to generate the second interference light, and a second light detection system configured to detect the first interference light and the second interference light, and output the first signal.

[0062] Thus, the light can be homodyned for each wavelength, and the interference signal of the first laser light and the interference signal of the reference laser light can be obtained as the first signal with high accuracy. Thus, the calculation accuracy of the wavelength based on the first signal can be improved. The absolute value of the difference between the wavelengths of the two laser lights used in the measurement can be large, compared with the case of using heterodyne interference, and thus the wavelength selectivity of the two laser lights can be improved. For example, since the wavelength suitable for the measurement of the object can be selected, the result is that the decrease in the length measurement accuracy and the long-term stability of the object can be suppressed. Furthermore, regardless of the number of wavelengths of the laser light used for the measurement, the light source of the reference laser light can be only one. Thus, the distance measuring device can be simplified in structure, downsized, and reduced in cost. Furthermore, since a single-wavelength laser light, which is more stable, typified by a HeNe laser light, can be used, the accuracy of the measurement of the wavelength is higher, compared with other methods, and the result is that the length measurement accuracy and the long-term stability are higher, compared with other methods.

[0063] The distance measuring device according to the ninth aspect of the present disclosure can be the distance measuring device according to the eighth aspect, wherein the reference interference system can further include a light path difference changing mechanism configured to change the difference between the light path length of the first laser light passing through the second light interference system and the light path length of the reference laser light passing through the second light interference system.

[0064] Thus, by adjusting the light path difference, the intensity of the interference signal of each of the first laser light and the reference laser light can be changed. The wavelength of the first laser light can be calculated with high accuracy based on the intensity change of the interference signal. In addition, the change in the difference between the light path lengths is not necessarily required. The interference signal of the first laser light and the interference signal of the reference laser light can be monitored separately without changing the difference between the light path lengths.

[0065] In addition, the spectrum information of each of the first laser light and the reference laser light can be calculated by using the interference signal. If it is assumed that the spectrum intensity of each of the first laser light and the reference laser light has a Gaussian characteristic, the wavelength required for the calculation of the length measurement is the peak wavelength of each laser light.

[0066] Therefore, the distance measuring device according to the 10th aspect of the present disclosure, for any one of the distance measuring device according to the 1st to 9th aspects, in the distance measuring device according to the 10th aspect, the signal processing system can calculate the peak wavelength of the 1st laser based on the 1st signal, thereby generating the wavelength information representing the peak wavelength.

[0067] Therefore, it is not necessary to obtain a spectroscopic spectrum of the laser, and thus it is possible to suppress complication of elements and operation processing required for light detection. It is possible to achieve miniaturization and weight reduction of the distance measuring device due to simplification of the element structure, and reduction of power consumption related to operation due to reduction of processing amount of operation, and the like.

[0068] Therefore, the distance measuring device according to the 11th aspect of the present disclosure, for any one of the distance measuring device according to the 3rd to 5th aspects, in the distance measuring device according to the 11th aspect, the signal processing system can calculate the peak wavelength of the 1st laser and the peak wavelength of the 2nd laser based on the 1st signal, thereby generating the wavelength information representing the peak wavelength of the 1st laser and the peak wavelength of the 2nd laser.

[0069] Therefore, it is not only possible to use the wavelength of the 1st laser, but also possible to use the wavelength of the 2nd laser used in actual measurement or a value equivalent thereto for distance calculation, and thus it is possible to improve the length measurement accuracy even in the case of MWI.

[0070] Therefore, the distance measuring device according to the 12th aspect of the present disclosure, for any one of the distance measuring device according to the 1st to 11th aspects, in the distance measuring device according to the 12th aspect, the signal processing system can update the wavelength information when a predetermined condition is satisfied.

[0071] Therefore, it is possible to update the wavelength information at an appropriate timing. By suppressing unnecessary update of the wavelength information, it is possible to suppress the operation cost required for the update of the wavelength information, such as operation time and / or power consumption required for the operation.

[0072] Therefore, the distance measuring device according to the 13th aspect of the present disclosure, for any one of the distance measuring device according to the 1st to 12th aspects, in the distance measuring device according to the 13th aspect, the signal processing system can include a memory for storing the generated wavelength information; the frequency at which the signal processing system generates the wavelength information can be lower than the frequency at which the signal processing system calculates the distance; and the signal processing system can calculate the distance based on the wavelength information stored in the memory and the 2nd signal.

[0073] Thus, for example, in a case where the drift of the long-term fluctuation of the wavelength progresses gently, the generation frequency of the wavelength information can be reduced. Further, the calculation cost required for the generation of the wavelength information is generally higher than the calculation cost required for the measurement of the length. By reducing the generation frequency of the wavelength information, the calculation cost can be suppressed.

[0074] The distance measuring device according to the 14th aspect of the present disclosure, for the distance measuring device according to any one of the 1st to 13th aspects, in the distance measuring device according to the 14th aspect, the signal processing system can also generate the wavelength information and update the wavelength information stored in the memory in a case where the fluctuation (undulation) of the wavelength of the 1st laser exceeds the threshold value.

[0075] Thus, the generation frequency of the wavelength information can be reduced, so the power consumption required for the generation of the wavelength information can be suppressed. For example, the wavelength information can be updated in a case where the fluctuation of the wavelength occurs to an extent that affects the calculation result of the distance. That is, the wavelength information can be updated at an effective and less wasteful timing.

[0076] The distance measuring device according to the 15th aspect of the present disclosure, for the distance measuring device according to any one of the 1st to 14th aspects, in the distance measuring device according to the 15th aspect, the light source section can also include an adjustment section that adjusts the wavelength of the 1st laser based on the wavelength information.

[0077] Thus, for example, the fluctuated wavelength can be restored, so the length measurement accuracy can be improved.

[0078] The distance measuring device according to the 16th aspect of the present disclosure, for the distance measuring device according to any one of the 1st to 15th aspects, in the distance measuring device according to the 16th aspect, the 1st laser can be a laser including a plurality of single modes.

[0079] Thus, a laser other than a single-wavelength laser can also be used.

[0080] The distance measuring device according to the 17th aspect of the present disclosure, for the distance measuring device according to any one of the 1st to 16th aspects, in the distance measuring device according to the 17th aspect, the reference interference system and the measurement interference system can share an optical interference system.

[0081] Thus, the distance measuring device can be miniaturized and lightened.

[0082] The distance measuring device according to the 18th aspect of the present disclosure, for the distance measuring device according to the 1st aspect, in the distance measuring device according to the 18th aspect, the 3rd reflected light generated by the reflection of the reference laser by the object can also be input to the measurement interference system.​​​​​​​​​

[0083] Thus, the number of laser light sources can be reduced, and thus the distance measuring device can be made smaller and lighter.

[0084] Hereinafter, the embodiments will be described specifically with reference to the drawings.

[0085] In addition, the embodiments described below are indicative of inclusive or specific examples. The numerical values, shapes, materials, arrangement positions and connection modes of the constituent elements, steps, order of steps, and the like indicated in the embodiments below are examples, and the gist thereof is not limited to the disclosure. Furthermore, regarding the constituent elements in the embodiments below, the constituent elements not recited in the independent claims are assumed to be arbitrary constituent elements.

[0086] In addition, each drawing is a schematic view, and is not necessarily strictly illustrated. Thus, for example, the scale and the like are not necessarily consistent in each drawing. Furthermore, in each drawing, the same reference numerals are assigned to substantially the same structures, and repeated description or simplification is omitted.

[0087] Furthermore, in the present specification, the terms indicating the relationship between the elements, the terms indicating the shape of the elements, and the numerical range are not only strictly meant, but also meant to include substantially equivalent ranges, for example, a difference of several percent or the like.

[0088] Furthermore, in the present specification, ordinal terms such as "first", "second", and the like are not meant to refer to the number or order of the constituent elements unless specifically denied, but are used to avoid confusion of the same constituent elements and to distinguish them.

[0089] (Embodiment 1)

[0090] [1. Structure of distance measuring device]

[0091] First, the distance measuring device 1 according to the present embodiment will be described with reference to FIG. 1. Figure 1 The structure of the distance measuring device 1 according to the present embodiment will be described. Figure 1 is a block diagram indicating the structure of the distance measuring device 1 according to the present embodiment.

[0092] Figure 1 The distance measuring device 1 illustrated in FIG. 1 is a device that measures the distance to the object 90. For example, the distance measuring device 1 can obtain information indicating the surface shape of the object 90 by measuring the distance of each portion of the object 90. Thus, for example, the distance measuring device 1 can be used for appearance inspection of products and the like.

[0093] As described above, the distance measuring device 1 according to the present embodiment can be used for various applications. Figure 1As shown, the distance measuring device 1 includes a light source section 10, an optical splitter 20, a reference interference system 30, a measurement interference system 40, and a signal processing system 50. In addition, although not shown, the distance measuring device 1 can include a support section that supports an object 90. The support section can include, for example, a motor, a piezoelectric element, or the like, and can change the posture and / or position of the object 90.

[0094] In addition, in Figure 1 the figure, a broken line connecting the two blocks of the distance measuring device 1 represents the path of light. In addition, an arrow of a solid line connecting the two blocks of the distance measuring device 1 represents the transmission path of a main signal and the transmission direction of the signal.

[0095] The light source section 10 emits a plurality of laser lights. In the present embodiment, the plurality of laser lights are single-wavelength laser lights having mutually different peak wavelengths. Specifically, the light source section 10 emits a first laser light, a second laser light, and a reference laser light. As shown in Figure 1 The light source section 10 includes a measurement light source 11 and a reference light source 12.

[0096] The measurement light source 11 emits a laser light L1 as an example of the first laser light. In addition, the measurement light source 11 emits a laser light L2 as an example of the second laser light. The reference light source 12 emits a reference laser light Lr. A more specific structure of the light source section 10 will be described later. Figure 2 The light source section 10 includes a measurement light source 11 and a reference light source 12.

[0097] In addition, laser light is generally difficult to maintain at a certain wavelength and frequency, and the wavelength and frequency fluctuate to some extent over time. The fluctuation of the wavelength is a parameter that indicates the amount of change in the wavelength over time. In the fluctuation of the wavelength, not only short-term changes but also long-term drifts are included. The drift refers to a shift in the average value of the short-term changes over time. In the present embodiment, the fluctuation of the wavelength of the reference laser light Lr is smaller than the fluctuation of the wavelengths of the laser lights L1 and L2. Details of the fluctuation of the wavelength will be described later.

[0098] The optical splitter 20 divides the laser light L1 emitted from the light source section 10 into a light L1r and a light L1t and emits them. The light L1r is input to the reference interference system 30, and the light L1t is input to the measurement interference system 40. In addition, the optical splitter 20 does not divide the laser light L2 but emits it as it is as a light L2t. Alternatively, the optical splitter 20 can divide the laser light L2 into two lights and emit them. One of the two divided lights is input to the reference interference system 30, and the other light L2t is input to the measurement interference system 40.

[0099] The optical branching unit 20 intensity-divides the incident light and causes it to be emitted in different directions. The optical branching unit 20 is, for example, a half mirror, and the intensity-division ratio is, for example, 1: 1, but is not limited thereto. The intensity of the light L1r can be higher than the intensity of the light L1t, or the intensity of the light L1t can be higher than the intensity of the light L1r. The wavelength of the light does not change at the time of division by the optical branching unit 20.

[0100] The reference-use interference system 30 detects the light after the interference of the first laser and the light after the interference of the reference laser, and outputs a first signal S1 corresponding to the detection result of the light after the interference. Specifically, the light L1r emitted from the optical branching unit 20 and the reference laser Lr from the reference-use light source 12 are incident on the reference-use interference system 30. As shown in FIG. 1, the reference-use interference system 30 includes an optical interference system 31 and an optical detection system 32. Figure 1

[0101] The optical interference system 31 is an example of a second optical interference system, and causes the light L1r to be interfered and emit interference light L1ri, and causes the reference laser Lr to be interfered and emit interference light Lri. The interference light L1ri is an example of first interference light, and the interference light Lri is an example of second interference light. The interference by the optical interference system 31 is homodyne interference.

[0102] The optical detection system 32 is an example of a second optical detection system, and detects the interference light L1ri and Lri, and outputs the first signal S1. The first signal S1 is output to the signal processing system 50. The first signal S1 is used to calculate the wavelength of the light L1r, that is, the wavelength of the light L1t.

[0103] The specific structures of the optical interference system 31 and the optical detection system 32 will be described later. Figure 4

[0104] The measurement-use interference system 40 is input the first reflected light generated by the light irradiated on the object 90 from the first laser being reflected by the object 90, and outputs a second signal S2. In addition, the measurement-use interference system 40 is also input the second reflected light generated by the light irradiated on the object 90 from the second laser being reflected by the object 90. Specifically, the measurement-use interference system 40 is input the light L1t emitted from the optical branching unit 20 and the reflected light L1c from the object 90. Further, the measurement-use interference system 40 is input the light L2t emitted from the optical branching unit 20 and the reflected light L2c from the object 90. As shown in FIG. 1, the measurement-use interference system 40 includes an optical interference system 41 and an optical detection system 42. Figure 1

[0105] ​​​The optical interference system 41 is an example of a first optical interference system that causes the light Llt and the reflected light Llc to interfere with each other, emits third interference light Lli generated by interference between the light Llt and the reflected light Llc, and causes the light L2t and the reflected light L2c to interfere with each other, emits fourth interference light L2i generated by interference between the light L2t and the reflected light L2c. The interference performed by the optical interference system 41 is homodyne interference.

[0106] The optical detection system 42 is an example of a first optical detection system that detects the third interference light Lli and the fourth interference light L2i, and outputs a second signal S2 corresponding to the detection results of the third interference light Lli and the fourth interference light L2i. The second signal S2 is output to the signal processing system 50. The second signal S2 is used to calculate the distance from the distance measuring device 1 to the object 90.

[0107] The specific structures of the optical interference system 41 and the optical detection system 42 will be described later. Figure 3

[0108] The signal processing system 50 generates wavelength information related to the wavelength of the first laser light based on the first signal S1, and calculates the distance from the distance measuring device 1 to the object 90 based on the wavelength information and the second signal S2. As shown in FIG. 1, the signal processing system 50 includes a signal receiving section 51, a memory 52, and a processing circuit 53. Figure 1

[0109] The signal receiving section 51 acquires the first signal S1 from the reference interference system 30 and acquires the second signal S2 from the measurement interference system 40. The signal receiving section 51 stores the acquired first signal S1 and second signal S2 in the memory 52.

[0110] The memory 52 is a storage device such as a non-volatile memory and / or a volatile memory. The first signal S1 and the second signal S2 are stored in the memory 52. In addition, programs and data for causing each constituent element of the distance measuring device 1 to operate, and wavelength information and distance information obtained by signal processing, and the like can also be stored in the memory 52.

[0111] ​​The processing circuit 53 is a circuit that processes signals output from the reference interferometer system 30 and the measurement interferometer system 40. Specifically, the processing circuit 53 generates wavelength information indicating a calculated peak wavelength by calculating the peak wavelength of the first laser based on the first signal S1. In the present embodiment, the processing circuit 53 calculates the peak wavelength λ1 of the laser L1 and the peak wavelength λ2 of the laser L2 based on the first signal S1. The processing circuit 53 calculates the distance from the distance measuring device 1 to the object 90 based on the wavelength information stored in the memory 52 and the second signal S2. For example, the processing circuit 53 acquires the position of the object 90 as phase information by processing the second signal S2 output from the measurement interferometer system 40 based on a prescribed algorithm. As a representative phase estimation algorithm, a 4-step phase-shifting algorithm or the like can be used. The processing circuit 53 can calculate the distance from the distance measuring device 1 to the object 90 based on the phase information.

[0112] In the present embodiment, the processing circuit 53 calculates the first distance within the first length-measurement range with the first length-measurement accuracy based on the interference result corresponding to the wavelength λ1. Further, the processing circuit 53 calculates the second distance within the second length-measurement range with the second length-measurement accuracy based on the interference results corresponding to the wavelengths λ1 and λ2. The processing circuit 53 calculates the distance from the distance measuring device 1 to the object 90 based on the first distance and the second distance. The processing circuit 53 calculates the absolute distance from the distance measuring device 1 to the object 90.

[0113] Here, the first length-measurement accuracy is higher than the second length-measurement accuracy. Further, the second length-measurement range is longer than the first length-measurement range. Thus, simply put, the processing circuit 53 calculates the distance within the shorter length-measurement range with higher length-measurement accuracy based on the interference result of one wavelength amount. The processing circuit 53 calculates the distance within the longer length-measurement range with lower length-measurement accuracy based on the interference result of two wavelength amounts. The specific distance calculation method will be described later.

[0114] The processing circuit 53 is realized by an integrated circuit such as an LSI (Large Scale Integration). For example, the processing circuit 53 can also be realized by a dedicated hardware structure that calculates the distance from the distance measuring device 1 to the object 90. Alternatively, the processing circuit 53 can include a processor that calculates the distance from the distance measuring device 1 to the object 90 by causing the processor to execute a program stored in the memory 52. Alternatively, the processing circuit 53 can be a programmable FPGA (Field Programmable Gate Array) or a reconfigurable processor that can reconfigure the connection and settings of circuit units within an LSI.

[0115] [1-1. Light source section]

[0116] Next, the configuration of the light source section 10 will be described. Figure 2 The configuration of the light source section 10 will be described. Figure 2 is a block diagram showing the configuration of the light source section 10 of the distance measuring device 1 according to the present embodiment. As shown in the figure, the measurement light source 11 is provided with laser light sources 13a and 13b and a wavelength combining system 14. The reference light source 12 is provided with a laser light source 13r. Figure 2

[0117] The laser light source 13a emits laser light L1 of a wavelength λ1. The laser light L1 is an example of first laser light, and is, for example, single-wavelength laser light. The wavelength λ1 is the peak wavelength of the laser light L1.

[0118] The laser light source 13b emits laser light L2 of a wavelength λ2. The laser light L2 is an example of second laser light, and is, for example, single-wavelength laser light. The wavelength λ2 is the peak wavelength of the laser light L2, and is a different wavelength from the wavelength λ1. The shorter the absolute value of the difference between the wavelengths λ1 and λ2 (|λ1-λ2|), the longer the measurement range can be made.

[0119] The laser light source 13r emits reference laser light Lr of a wavelength λr. The reference laser light Lr is an example of reference laser light, and is, for example, single-wavelength laser light. The wavelength λr is the peak wavelength of the reference laser light Lr, and is a different wavelength from the wavelengths λ1 and λ2. The wavelength λr is shorter than the wavelength λ1.

[0120] The laser light sources 13a and 13b are, for example, semiconductor laser elements. As an example, a DFB (Distributed Feedback) laser light source having a higher stability of wavelength and frequency can be used in the laser light sources 13a and 13b. Further, the laser light source 13r is, for example, a HeNe laser light source. The wavelength of the reference laser light Lr emitted by the laser light source 13r is approximately 633 nm. The HeNe laser light source is a light source having a wavelength that has less fluctuation of the emitted light compared to a semiconductor laser element, i.e., a light source having a higher stability of wavelength over time.

[0121] The wavelength combining system 14 combines the laser lights L1 and L2 emitted from the two laser light sources 13a and 13b, respectively. The wavelength combining system 14 is, for example, a DWDM (Dense Wavelength Division Multiplexing) element or a holographic optical element, etc.

[0122] [1-2. Detailed configuration of measurement interference system]

[0123] ​Next, the specific structure of the measurement interferometric system 40 will be described. As described above, the measurement interferometric system 40 includes the optical interferometric system 41 and the light detection system 42. Hereinafter, the measurement interferometric system 40 will be described using the optical interferometric system 41 and the light detection system 42 as an example. Figure 3 Each structure will be described in order. Figure 3 is a view showing the specific structure of the measurement interferometric system 40 of the distance measuring apparatus 1 according to the present embodiment.

[0124] In the present embodiment, the optical interferometric system 41 is an optical system using Michelson interference. As shown in Figure 3 , the optical interferometric system 41 includes a beam splitter 43 and a mirror 44.

[0125] The beam splitter 43 is an optical element that splits the intensity of incident light into a plurality of lights and causes the plurality of lights to be emitted in different directions. The beam splitter 43 is, for example, a half mirror that splits the incident light into transmitted light and reflected light and causes them to have the same intensity. In addition, the intensity ratio of the transmitted light and the reflected light can not be 1:1.

[0126] Specifically, the beam splitter 43 splits the light L1t split by the optical branching device 20 from the laser light L1 from the light source section 10 into two lights L1a and L1b. In addition, the beam splitter 43 splits the light L2t from the laser light L2 from the light source section 10 into two lights L2a and L2b. In the example shown in Figure 3 , the light L1a and the light L2a are reflected light obtained by the beam splitter 43 being reflected and are emitted toward the mirror 44. The light L1b and the light L2b are transmitted light that has transmitted the beam splitter 43 and are emitted toward the object 90.

[0127] The mirror 44 is an example of an optical element that reflects the light L1a and the light L2a from the beam splitter 43 and causes them to be incident on the beam splitter 43. Specifically, the mirror 44 causes the incident light to be specularly reflected. The higher the reflectivity, the less the loss of light, and thus the detection accuracy can be improved. The light L1a and the light L2a incident on the mirror 44 are both reflected by the mirror 44 and re-incident on the beam splitter 43. At least a part of each of the light L1a and the light L2a reflected by the mirror 44 and re-incident on the beam splitter 43 transmits the beam splitter 43.

[0128] The light L1b and the light L2b irradiated to the object 90 are reflected by the object 90 and re-incident on the beam splitter 43 as reflected light L1c and L2c. At least a part of each of the reflected light L1c and the reflected light L2c re-incident on the beam splitter 43 is reflected by the beam splitter 43. In this case, interference occurs between the reflected light L1c and the light L1a and between the reflected light L2c and the light L2a. Figure 3In this diagram, the interference light generated by the zero-difference interference between reflected light L1c and light L1a is denoted as interference light L1i. The interference light generated by the zero-difference interference between reflected light L2c and light L2a is denoted as interference light L2i. Both interference lights L1i and L2i are emitted into the light detection system 42.

[0129] Furthermore, the configuration of the reflector 44 and the object 90 can be interchanged. That is, even when the light from the light source 10 is split into transmitted light and reflected light by the beam splitter 43, the transmitted light can be irradiated by the reflector 44 and the reflected light can be irradiated by the object 90.

[0130] Furthermore, the optical interference system 41 is not limited to an optical system using Michelson interference. The optical interference system 41 can also be an optical system using Fizeau interference or Mach-Zehnder interference, etc.

[0131] like Figure 3 As shown, the light detection system 42 includes a dichroic mirror 45, a mirror 46, and light detectors 47 and 48.

[0132] The dichroic mirror 45 is an example of a wavelength-separating element that separates incident light into light with wavelength λ1 and light with wavelength λ2. Specifically, the dichroic mirror 45 performs wavelength separation on light incident from the beam splitter 43 onto the light detection system 42. In this embodiment, the dichroic mirror 45 directs light with wavelength λ1 toward the photodetector 47 and light with wavelength λ2 toward the photodetector 48. In this embodiment, a mirror 46 is provided for optical path adjustment.

[0133] The reflector 46 causes light of wavelength λ2, separated by the dichroic reflector 45, to be reflected by the mirror and incident on the photodetector 48. Alternatively, the reflector 46 may be omitted, and the photodetector 48 may be positioned at the location of the reflector 46. Alternatively, the reflector 46 may be configured to adjust the optical path of light with wavelength λ1.

[0134] Photodetectors 47 and 48 each include a photoelectric conversion element that generates an electrical signal corresponding to the intensity of the incident light. Photodetector 47 is sensitive to at least wavelength λ1, performs photoelectric conversion on light of wavelength λ1, and outputs an interference signal S21 with a signal level corresponding to its intensity as a second signal S2 to the signal processing system 50. The interference signal S21 is obtained by detecting the interference light L1i of a portion of the laser L1 with the reflected light L1c from the object 90.

[0135] The light detector 48 has sensitivity to at least the wavelength λ2, photoelectrically converts light of the wavelength λ2, and outputs an interference signal S22 having a signal level corresponding to the intensity thereof as the second signal S2 to the signal processing system 50. The interference signal S22 is a signal obtained by detecting interference light L2i of at least a portion of the laser light L2 and the reflected light L2c from the object 90.

[0136] In addition, the configuration of the light detection system 42 is not limited to the above-described example as long as light of each wavelength can be detected. For example, after intensity of light from the beam splitter 43 toward the light detection system 42 is split into two lights, the two split lights can be respectively passed through filters having a transmission band for a specific wavelength component. The filters use, for example, a band-pass filter, but can be a low-pass filter, a high-pass filter, or the like.

[0137] Further, the measurement interference system 40 can not be an optical system using homodyne interference. The measurement interference system 40 can be an optical system using heterodyne interference. In this case, the measurement interference system 40 can not have the dichroic mirror 45 that splits light by wavelength, and the number of light detectors can be one.

[0138] [1-3. Specific configuration of reference interference system]

[0139] Next, the specific configuration of the reference interference system 30 will be described. As described above, the reference interference system 30 includes the light interference system 31 and the light detection system 32. Hereinafter, the reference interference system 30 will be described using the same reference numerals as those of the measurement interference system 40. Figure 4 Each configuration will be described in order. Figure 4 is a view showing the specific configuration of the reference interference system 30 of the distance measuring apparatus 1 according to the present embodiment.

[0140] The light interference system 31 is an optical system using a Sagnac type Michelson interference system. For the light interference system 31, the light L1r that is a portion of the laser light L1 split by the light splitter 20 and the reference laser light Lr are made to be incident at different positions. As shown in Figure 4 The light interference system 31 has a beam splitter 33, mirrors 34 and 35, and a moving mirror 36.

[0141] The beam splitter 33 is an optical element that splits incident light into a plurality of lights by intensity and makes the plurality of lights be emitted in different directions. The beam splitter 33 is, for example, a half mirror that splits incident light into transmitted light and reflected light and makes them have the same intensity. In addition, the intensity ratio of the transmitted light and the reflected light can not be 1:1.

[0142] Specifically, beam splitter 33 splits the light L1r into two beams, L1ra and L1rb. Furthermore, beam splitter 33 splits the reference laser Lr into two beams, Lra and Lrb. Figure 4 In the example shown, light L1ra and light Lra are reflected light reflected by beam splitter 33 and emitted toward mirror 35. Light L1rb and Lrb are transmitted light after passing through beam splitter 33 and emitted toward mirror 34.

[0143] Reflector 34 reflects light L1rb and Lrb toward the movable reflector 36. Reflector 35 reflects light L1ra and Lra toward the movable reflector 36.

[0144] The movable reflector 36 has two reflecting surfaces 36a and 36b. Reflector 36a reflects light beams Lra and L1ra respectively. After being reflected by reflector 36a, Lra and L1ra are reflected by reflector 35 and then incident on beam splitter 33, with at least a portion of them passing through. Reflector 36b reflects light beams Lrb and L1rb respectively. After being reflected by reflector 36b, Lrb and L1rb are reflected by reflector 34 and then incident on beam splitter 33, with at least a portion of them being reflected. Light L1ra, after passing through beam splitter 33, interferes with light L1rb reflected by beam splitter 33 with zero difference, and this interference beam L1ri is incident on photodetector 37. Light Lra, after passing through beam splitter 33, interferes with light Lrb reflected by beam splitter 33 with zero difference, and this interference beam Lri is incident on photodetector 38.

[0145] The movable reflector 36 can change the positions of the reflecting surfaces 36a and 36b. For example, a movable stage is provided to movably support at least one of the reflecting surfaces 36a and 36b. By changing the positions of the reflecting surfaces 36a and 36b, the optical path length of the light traveling within the optical interference system 31 changes. That is, the movable reflector 36 is an example of an optical path difference changing mechanism that changes the difference between the optical path length of the light L1r passing through the optical interference system 31 and the optical path length of the reference laser Lr passing through the optical interference system 31. By adjusting the optical path difference, the interfering lights Lri and L1ri change.

[0146] Furthermore, the optical path difference alteration mechanism of the optical interference system 31 is not limited to the movable reflector 36, as long as it can change the optical path length. For example, the optical interference system 31 may also have an electro-optic modulator (EOM) disposed on the optical path as the optical path difference alteration mechanism.

[0147] like Figure 4 As shown, the light detection system 32 includes photodetectors 37 and 38. Photodetectors 37 and 38 each include a photoelectric conversion element that generates an electrical signal corresponding to the intensity of the incident light.

[0148] The light detector 37 has sensitivity at least to the wavelength λl, photoelectrically converts light of the wavelength λl, and outputs an interference signal Sll having a signal level corresponding to the intensity thereof as the first signal S1 to the signal processing system 50. The interference signal Sll is a signal obtained by detecting interference light Llri generated by homodyne interference of the light Llr that is a part of the laser light Ll.

[0149] The light detector 38 has sensitivity at least to the wavelength λr, photoelectrically converts light of the wavelength λr, and outputs an interference signal S12 having a signal level corresponding to the intensity thereof as the first signal S1 to the signal processing system 50. The interference signal S12 is a signal obtained by detecting interference light Lri generated by homodyne interference of the reference laser light Lr.

[0150] [2. Principle of distance measurement]

[0151] Next, the principle of distance measurement based on the distance measuring device 1 according to the present embodiment will be described.

[0152] For the distance measuring device 1 according to the present embodiment, distance measurement is performed based on multi-wavelength interference (MWI) using a plurality of laser lights. The MWI is capable of eliminating the trade-off between the measurement range and the measurement accuracy by combining the interference results of a plurality of single-wavelength laser lights having mutually different wavelengths, and achieving a longer measurement range and a higher measurement accuracy. Hereinafter, the principle of multi-wavelength interference will be described.

[0153] [2-1. First measurement (using one wavelength)]

[0154] First, the first measurement using one single-wavelength laser light will be described.

[0155] As described using Figure 3 In the homodyne light interference, the single-wavelength laser light is branched by the beam splitter 43, and is irradiated to the mirror 44 that functions as a reference surface and the object 90 that is the object of measurement of distance. The reflected lights from the mirror 44 and the object 90 are caused to interfere by the beam splitter 43. The intensity P of the signal output from the light detector 47 at the time when the light after the interference is detected by the light detector 47 is expressed by the following formula (1). PD The intensity P of the signal output from the light detector 47 at the time when the light after the interference is detected by the light detector 47 is expressed by the following formula (1).

[0156] [Formula 1]

[0157] (I)

[0158] In formula (1), L － = L x − L y . L xis the distance from the beam splitter 43 to the reflecting surface of the mirror 44. L y is the distance from the beam splitter 43 to the object 90. λ k is the wavelength of the single-wavelength laser. Here, k = 1. λ k is calculated on the basis of the first signal S1 output from the reference interferometer system 30. As a result, L x and λ k are values known to the processing circuit 53. Therefore, the processing circuit 53 can calculate the distance L PD from the beam splitter 43 to the object 90 on the basis of the signal intensity P y .

[0159] In the first measurement, there is a problem that the measurement range is relatively short. Hereinafter, the relationship between the position of the object 90 and the measurement range will be described using Figure 5 .

[0160] Figure 5 is a view for explaining the principle of the first measurement based on the distance measuring device 1 of the present embodiment using a single-wavelength laser. In Figure 5 , the objects 90a, 90b, and 90c respectively indicate Figure 1 and Figure 3 the object 90 shown in FIG. 1 is located at different positions. In a case where it is not necessary to distinguish the positions, it is described as "the object 90".

[0161] In Figure 5 , a view in which the distance to the object 90 from a prescribed position is indicated on the horizontal axis and the distance calculated by the processing circuit 53 is indicated on the vertical axis is shown. As Figure 5 indicated, the processing circuit 53 can calculate the distance from the distance measuring device 1 to the object 90 within a prescribed measurement range. According to equation (1), in a case where the wavelength of the single-wavelength laser is λ1, the measurement range is half the wavelength (λ1 / 2).

[0162] In the first measurement, in a case where the measurement range is exceeded, the absolute distance from the distance measuring device 1 to the object 90 cannot be calculated. For example, in the example shown in Figure 5 , the objects 90a, 90b, and 90c are all calculated as the same distance.

[0163] The wavelength of a single-wavelength laser is, for example, in the near-infrared or visible light band. The near-infrared band is approximately 700 nm to approximately 2500 nm. The visible light band is approximately 380 nm to approximately 780 nm. In this case, the length measurement range of the first measurement is approximately 190 nm to approximately 1250 nm. That is, the length measurement range of the first measurement is from several hundred nanometers to several micrometers. Thus, the length measurement range of the first measurement is relatively narrower compared to the second measurement described later.

[0164] [2-2. Second measurement (using two wavelengths)]

[0165] Next, use Figure 3 and Figure 6 To illustrate, a second measurement is performed using two single-wavelength lasers with mutually different wavelengths, which addresses the problem of the first measurement, namely, the short length measurement range.

[0166] like Figure 3 As shown, in the ranging device 1 of this embodiment, the light interfered by the beam splitter 43 is split into wavelengths by a dichroic mirror 45 and detected by two photodetectors 47 and 48. The result is that the photodetectors 47 and 48 output signals corresponding to the results of the homodyne interference at each corresponding wavelength. The processing circuit 53 is able to calculate the distance from the ranging device 1 to the object 90 based on the two signals.

[0167] In the second measurement, the length measurement range is extended by combining the two signals. The following uses... Figure 6 Explain the relationship between the position of the object at 90° and the length measurement range.

[0168] Figure 6 This diagram illustrates the principle of the second measurement using two single-wavelength lasers based on the ranging device 1 of this embodiment. Figure 6 In the diagram, objects 90a, 90b, and 90c respectively represent... Figure 1 and Figure 3 The objects 90 shown are located in different positions. Where it is not necessary to distinguish their positions, they will be referred to as "object 90" for explanation.

[0169] exist Figure 6 The diagram shows two figures as described below: the horizontal axis represents the distance from the specified position to the object 90, and the vertical axis represents the distance calculated by the processing circuit 53. In the two figures, the upper figure is similar to... Figure 5 The diagrams shown are identical, representing distances calculated based on signals received from one of the two photodetectors 47 and 48. The lower section of both diagrams represents distances calculated based on signals received from the other of the two photodetectors 47 and 48.

[0170] If only two graphs are used individually, the measurement range is λ1 / 2 or λ2 / 2, respectively, so the order of magnitude of the measurement range hardly changes compared with the first measurement. In the second measurement, by combining the two graphs, it is possible to make the measurement range longer.

[0171] Specifically, the distances calculated by the subject 90a, 90b, 90c corresponding to the graphs of the upper section are approximately the same as each other. However, the distances calculated by the subject 90a, 90b, 90c corresponding to the graphs of the lower section are different from each other. Therefore, by combining the two calculation results, it is possible to calculate the distance with a measurement range longer than either of λ1 / 2 and λ2 / 2. Specifically, the processing circuit 53 combines the first distance obtained by the first measurement and the second distance obtained by the second measurement, thereby calculating the absolute distance from the distance measuring device 1 to the subject 90.

[0172] The measurement range of the second measurement is half of the beat wavelength of the two single-wavelength lasers. For example, when the wavelengths of the two single-wavelength lasers are λ1 and λ2, the beat wavelength Λ 12 is expressed by the following equation (2).

[0173] [Equation 2]

[0174] (2)

[0175] By light interference based on this beat wavelength Λ 12 , distance measurement can be performed at a measurement range of half of the beat wavelength Λ 12 . For example, in the case where λ1 and λ2 are 1550 nm and 1551 nm, respectively, the beat wavelength Λ 12 becomes 2.4 mm, and the measurement range becomes 1.2 mm. The measurement range of the MWI is expanded to the order of millimeters, compared with the measurement range of the order of 775 nm, which is the case of single-wavelength interference, and the order of nanometers.

[0176] [2-3. Measurement accuracy]

[0177] Next, the measurement accuracy of each of the first measurement and the second measurement will be described.

[0178] The measurement accuracy depends on the wavelength of the single-wavelength laser used in the measurement. Specifically, the shorter the wavelength of the single-wavelength laser, the higher the measurement accuracy (i.e., the smaller in the dimension of distance), and the longer the wavelength of the single-wavelength laser, the lower the measurement accuracy (i.e., the larger in the dimension of distance).

[0179] In the case of using two single-wavelength lasers as in the 2nd measurement, the length measurement accuracy depends on the beat wavelength. Specifically, the shorter the beat wavelength, the higher the length measurement accuracy (i.e., the smaller in the dimension of distance), and the longer the beat wavelength, the lower the length measurement accuracy (i.e., the larger in the dimension of distance).

[0180] Since the beat wavelength is longer than the wavelength of the single-wavelength laser, the length measurement accuracy becomes lower in the 2nd measurement than in the 1st measurement. That is, the length measurement accuracy of the 2nd measurement becomes worse due to the beat wavelength Λ 12 Thus, if only the 2nd measurement is used, the trade-off between the length measurement range and the length measurement accuracy is not eliminated.

[0181] In order to eliminate the trade-off, in the MWI, both the longer length measurement range and the higher length measurement accuracy are achieved by combining the 1st measurement and the 2nd measurement. That is, by combining the 1st measurement which has a shorter length measurement range but a higher length measurement accuracy with the 2nd measurement which has a lower length measurement accuracy but a longer length measurement range, both the longer length measurement range and the higher length measurement accuracy are achieved.

[0182] Figure 7 is a graph showing the length measurement range and the length measurement accuracy based on the two measurements of the distance measuring device 1 of the present embodiment. As shown in Figure 7 , let the length measurement accuracy of the 2nd measurement (2nd length measurement accuracy) be Am, and let the length measurement range of the 2nd measurement (2nd length measurement range) be Rm. Further, let the length measurement accuracy of the 1st measurement (1st length measurement accuracy) be As, and let the length measurement range of the 1st measurement (1st length measurement range) be Rs. Since the length measurement range and the length measurement accuracy are expressed in the dimension of distance, comparison can be made.

[0183] As described above, and as shown in Figure 7 , Rm > Rs, and Am > As hold. Further, in the present embodiment, Am ≤ Rs holds. That is, the length measurement accuracy Am of the 2nd measurement is equal to or lower than the length measurement range Rs of the 1st measurement. Thereby, the combination of the 1st measurement and the 2nd measurement can be uniquely made, so distance measurement can be made with a higher length measurement accuracy than the length measurement accuracy of the 2nd measurement.

[0184] Here, in order to achieve a higher length measurement accuracy, it is important to use the correct value of the wavelength of the laser L1 to be used in the 1st measurement in distance calculation.

[0185] [3. Relationship between stability of wavelength and frequency and length measurement accuracy]

[0186] Next, the relationship between the stability of wavelength and frequency and the length measurement accuracy is described.

[0187] The wavelength and frequency of the laser are adjusted by a control unit (not shown) to maintain a preset value. Specifically, the wavelength is kept constant by adjusting the current supplied to the laser source and / or the temperature of the laser source. In this embodiment, the set wavelength of the light source 10 is controlled and fixed during the measurement period.

[0188] However, due to the characteristics of laser light sources, it is difficult to maintain a completely constant wavelength. For example... Figure 8 As shown, the wavelength of a single-wavelength laser varies over time, i.e., it fluctuates. Furthermore, Figure 8 This is a graph used to illustrate the wavelength stability of a single-wavelength laser. In Figure 8 In the diagram, the horizontal axis represents time, and the vertical axis represents the wavelength or frequency of a single wavelength laser. Figure 8 This indicates short-term wavelength fluctuations.

[0189] Wavelength fluctuations, for example, are caused by Figure 8 The standard deviation σ is used to represent this. The standard deviation σ can be statistically calculated for the average or median wavelength of the laser over a finite time period. Alternatively, wavelength fluctuations can be expressed in frequency units rather than wavelength units, or in other wavelength-related units.

[0190] According to equation (1) above, if the wavelength λ k Wavelength fluctuations occur when there is a deviation between the wavelength of the single-wavelength laser actually used for measurement and the calculated wavelength. Therefore, the measurement accuracy deteriorates due to this discrepancy in the calculated distance value. Thus, there is a correlation between wavelength fluctuations and measurement accuracy. Specifically, the smaller the fluctuation, the better the measurement accuracy.

[0191] Furthermore, wavelength stability is represented by a value that has a negative correlation with the fluctuation of the laser wavelength corresponding to time variations. Specifically, the smaller the fluctuation, the higher the wavelength stability; the larger the fluctuation, the lower the wavelength stability.

[0192] In addition, the laser source 13a that emits laser L1 can be a DFB laser source with high wavelength (frequency) stability, or a light source device that combines the absorption line of the gas cavity and the semiconductor laser as a reference frequency, but is not limited to these.

[0193] Furthermore, while DFB lasers exhibit high wavelength stability, wavelength drift occurs with longer operating times (e.g., exceeding 30 minutes), leading to decreased length measurement accuracy. In other words, even using a wavelength-stable laser source as the emission laser L1 cannot completely suppress the decline in length measurement accuracy and long-term stability from a long-term perspective. Moreover, long-term wavelength fluctuations can be viewed as a shift in peak wavelength.

[0194] In contrast, in this embodiment, the processing circuit 53 calculates the wavelength λ1 based on the first signal S1 output from the reference interferometer system 30. Specifically, the processing circuit 53 uses the interferometer signals S11 and S12 to compare the number of waves in their respective interferometer signals, or to perform a spectral comparison based on Fourier transform, thereby calculating the wavelength λ1 (for example, see Patent Document 3). Furthermore, the processing circuit 53 uses the calculated wavelength λ1 to calculate the distance from the ranging device 1 to the object 90. Thus, even if the wavelength of the laser L1 fluctuates, the wavelength λ1 at the point of measurement can be obtained with good accuracy, thereby improving the length measurement accuracy and long-term stability of the ranging device 1.

[0195] In addition, the processing circuit 53 calculates the wavelength λ1 of the laser L1 used in the first measurement, which requires high precision, but it can also calculate the wavelength λ2 of the laser L2. To calculate the wavelength λ2, similarly to the laser L1, the laser L2 is split into a first beam and a second beam by the optical splitter 20, and the first beam is input into the reference interferometer system 30 to obtain an interference signal based on the zero-difference interference of the second beam.

[0196] Thus, according to this embodiment, even if the wavelength λ1 of the laser L1 fluctuates, since the wavelength λ1 calculated based on the first signal S1 from the reference interferometer system 30 is used, the wavelength λ1 used in the actual measurement can still be used for distance calculation. Therefore, the length measurement accuracy and long-term stability of the ranging device 1 can be improved.

[0197] [4. Calculation of absolute distance]

[0198] The following is an example of a method for calculating the absolute distance from the ranging device 1 to the object 90 using two single-wavelength lasers via MWI.

[0199] In the second determination, based on from Figure 3 The signals from the two photodetectors 47 and 48 shown are used to calculate the phase of each wavelength, and the difference between them is taken as the beat frequency wavelength Λ. 12 The phase. Under the condition that the above-mentioned MWI is satisfied, based on the beat frequency wavelength Λ 12 The wavenumber N of laser L1 is determined by dividing the approximate distance calculated from the phase by the quotient calculated from the wavelength λ1 of laser L1, which has less frequency fluctuation. At this time, the wavelength λ1 of laser L1 uses the value calculated based on the first signal S1. Next, in the first measurement, based on the signal from... Figure 3 The phase φ of a single wavelength is calculated from the signal of one of the two photodetectors 47 and 48 shown (here, photodetector 47). Based on the above results, the absolute distance x is calculated using the following equation (3).

[0200] [Formula 3]

[0201] (3)

[0202] The main cause of fluctuation in the calculated distance x is φ, which is due to fluctuation in the wavelength of the first single-wavelength laser. Therefore, by using the value calculated using the wavelength λ1 of the laser L1 used in the first measurement, it is possible to improve the calculation accuracy of the absolute distance. Furthermore, the laser L1 used in the first measurement is a laser with the smallest fluctuation in wavelength, i.e., the highest stability in wavelength, and is the optimal combination of wavelengths. Details will be described later, but even if the number of wavelengths is three or more, the method relating to the present disclosure can be applied in the same order.

[0203] [5. Action (distance measurement method)]

[0204] Next, the distance measuring device 1 uses the first signal S1 (S10). Specifically, the light source section 10 outputs the laser L1 and / or L2 and the reference laser Lr. Among these, the laser L1 is split into the light L1r and the light L1t by the optical splitter 20. The reference interference system 30 detects the light L1r and the reference laser Lr by heterodyne interference, and thereby outputs the interference signals S11 and S12 as the first signal S1 to the signal processing system 50. Figure 9 The operation of the distance measuring device 1 relating to the present embodiment will be described. Figure 9 is a flowchart showing the operation of the distance measuring device 1 relating to the present embodiment.

[0205] As shown in Figure 9 , first, the distance measuring device 1 acquires the first signal S1 using the reference interference system 30 (S10). Specifically, the light source section 10 outputs the laser L1 and / or L2 and the reference laser Lr. Among these, the laser L1 is split into the light L1r and the light L1t by the optical splitter 20. The reference interference system 30 detects the light L1r and the reference laser Lr by heterodyne interference, and thereby outputs the interference signals S11 and S12 as the first signal S1 to the signal processing system 50.

[0206] Next, the signal processing system 50 generates wavelength information based on the first signal S1, and updates the wavelength information stored in the memory 52 (S11). The wavelength information is information indicating the wavelength λ1 of the laser L1. The generated wavelength information is stored in the memory 52.

[0207] Next, the distance measuring device 1 acquires the second signal S2 using the measurement interference system 40 (S12). Specifically, for the measurement interference system 40, the light L1t and the light L2t (laser L2) and the reflected lights L1c and L2c generated by reflection of these lights by the object 90 are input. The measurement interference system 40 detects the light L1t and the reflected light L1c by heterodyne interference, and detects the light L2t and the reflected light L2c by heterodyne interference, and outputs the interference signals S21 and S22 as the second signal S2 to the signal processing system 50.

[0208] Next, the signal processing system 50 calculates the distance based on the wavelength information stored in the memory 52 and the second signal S2 (S13). By using the wavelength λ1 represented by the wavelength information, the length measurement accuracy can be improved.

[0209] In the case where the distance measurement processing is not ended (NO in S14), the signal processing system 50 determines whether or not the update of the wavelength information is performed (S15). The update of the wavelength information is performed, for example, at a predetermined time point (timing). In the case where the update of the wavelength information is performed (YES in S15), in the distance measurement device 1, the acquisition of the first signal (S10) and the update of the wavelength information (S11) are performed.

[0210] In the case where the update of the wavelength information is not performed (NO in S15), in the distance measurement device 1, the acquisition of the second signal (S12) and the calculation of the distance (S13) are performed. In the calculation of the distance, the wavelength information stored in the memory 52 is used.

[0211] Figure 10 is a graph showing the relationship between the update frequency of the wavelength information and the calculation frequency of the distance. In Figure 10 , the arrow indicates the flow of time, and the triangular mark indicates the time point at which the corresponding processing is performed.

[0212] The acquisition of the first signal S1 and the update of the wavelength information are repeatedly performed, for example, periodically at every predetermined period. The frequency of each of the acquisition of the first signal S1 and the update of the wavelength information is lower than the frequency of each of the acquisition of the second signal S2 and the calculation of the distance. By reducing the frequency of the acquisition of the first signal S1 and the update of the wavelength information, the power required for the operation of the reference interferometer system 30 and the signal processing system 50 can be suppressed.

[0213] In the case where the wavelength information is not updated, the laser light L1 used when the second signal S2 is acquired in step S12 becomes light emitted at a time point different from the time point at which the laser light L1 used when the wavelength information stored in the memory 52 is generated. By using a DFB laser light source or the like, which has less fluctuation in wavelength in the short term, as the laser light source 13a that emits the laser light L1, the decrease in the length measurement accuracy can be suppressed. Furthermore, according to the present embodiment, by updating the wavelength information stored in the memory 52 at a predetermined time point, even in the case where the fluctuation in the wavelength λ1 of the laser light L1 in the long term, that is, the drift in the wavelength λ1 occurs, the decrease in the length measurement accuracy can be suppressed. Thus, the decrease in the length measurement accuracy and the long-term stability of the distance measurement device 1 can be suppressed.

[0214] In a case where the fluctuation of the wavelength information with respect to time is small, the update of the wavelength information stored in the memory 52 can also be performed after a deviation of the wavelength of a certain amount or more from the wavelength at the start of the measurement. Specifically, the signal processing system 50 can also generate the wavelength information and update the wavelength information stored in the memory 52 in a case where the fluctuation of the wavelength λl of the first laser light Ll exceeds a threshold value. That is, the processing circuit 53 can also periodically perform the calculation of the wavelength λl and update the wavelength information stored in the memory 52 in a case where the value of the calculated wavelength λl and the initial value at the start of the measurement or the difference from the set wavelength of the laser light source, that is, the fluctuation of the wavelength λl exceeds a threshold value. Further, instead of the update of the wavelength information, an error output can be performed by using a display portion and / or a sound output portion or the like, thereby warning the user of a measurement error.

[0215] Alternatively, the update frequency of the wavelength information and the calculation frequency of the distance can also be the same. In this case, as the laser light source 13a, a laser light source having a large fluctuation of the wavelength can be used. Since an inexpensive laser light source can be used, the cost reduction of the distance measuring device 1 can be achieved.

[0216] Further, in a case of a short period of measurement, the update of the wavelength information can also be only once before the start of the measurement. That is, the processing of step S15 can also not be performed.

[0217] In addition, the update of the wavelength information is not limited to once before the start of the measurement. The update of the wavelength information can also be performed in a case where a prescribed condition is satisfied. One of the prescribed conditions is, for example, the elapse of a certain period. Specifically, the update of the wavelength information can also be performed periodically, such as once a day, once a week, or once a month. The period in which the measurement is not performed can be treated as if there is no fluctuation of the wavelength.

[0218] Further, one of the prescribed conditions can also be that the fluctuation of the wavelength is outside the range of a threshold value. Specifically, the update of the wavelength information can also be performed in a case where the fluctuation of the wavelength is outside the range of a threshold value by indirectly measuring the wavelength of the laser light to confirm whether the fluctuation of the wavelength is within the range of the threshold value (for example, 1 nm / 8 hours). As the indirect method of monitoring the wavelength, there are a method of measuring the change in the temperature and / or the air pressure of the surroundings of the laser light source or a method of measuring the temperature of the laser light source itself or the like.

[0219] As described above, according to the distance measuring device 1 of the present embodiment, instead of using heterodyne interference, homodyne interference is used. In the homodyne interference, there is no restriction on the wavelength, unlike the heterodyne interference in which the interval of the wavelengths of the two lights needs to be reduced. Therefore, in the distance measuring device 1, there is an advantage that the selectivity of the wavelength of each of the laser lights Ll and L2 used for the measurement is high.

[0220] For example, in the case where the object 90 is a lens with an AR (Anti Reflection) coating, the laser light to be irradiated to the object 90 needs to be laser light other than the visible light band. In this case, it is desirable to use laser light of a communication wavelength band that is widely spread. According to the present embodiment, since the wavelength selectivity is high, it is possible to set the wavelength of the measurement laser light to the communication wavelength band, and set the reference laser light to short wavelength with higher length measurement accuracy. Not only does this have the advantage of being able to optimize the wavelength of the laser light for the sample, and being able to improve the length measurement accuracy, but it is also possible to use optical elements that are widely spread in optical communication in the communication wavelength band and the like, and thus low cost can be achieved.

[0221] Furthermore, in the case of using heterodyne interference, since the same number of measurement laser light sources and reference laser light sources need to be used, the device becomes large and the cost increases. In contrast, in the distance measuring device 1 according to the present embodiment, only one laser light source 13r is used as the reference laser light source, so it is possible to achieve simplification, miniaturization, and low cost of the structure of the distance measuring device. Furthermore, it is possible to use a single wavelength laser light, which is more stable, typified by HeNe laser light, so the accuracy of the measurement of the wavelength is higher than other methods, and as a result, the length measurement accuracy and the long-term stability are higher than other methods.

[0222] (Embodiment 2)

[0223] Next, the embodiment 2 will be described.

[0224] In the distance measuring device according to the embodiment 2, the main difference from the embodiment 1 is that the light source unit is provided with an adjustment unit that adjusts the wavelength of the laser light. Hereinafter, the differences from the embodiment 1 will be described, and the commonalities will be omitted or simplified.

[0225] Figure 11 is a block diagram showing the structure of the distance measuring device 2 according to the present embodiment. As shown in Figure 11 , the distance measuring device 2 differs from the distance measuring device 1 shown in Figure 1 in that the light source unit 10A is provided instead of the light source unit 10. The light source unit 10A is provided with the adjustment unit 15 in addition to the structure of the light source unit 10.

[0226] The adjustment section 15 adjusts the wavelength of the first laser based on the wavelength information. The adjustment section 15 adjusts the wavelength λ1 of the laser L1, for example, by controlling the operation temperature and / or the applied current of the laser light source 13a of the measurement light source 11. As an example, the adjustment section 15 adjusts the value of the wavelength λ1 that has fluctuated (drifted) so as to return to the wavelength λ1 at the start of the measurement that is the initial state. The adjustment section 15 acquires the wavelength information generated by the processing circuit 53, and performs adjustment of the wavelength λ1 in a case where the wavelength λ1 indicated by the acquired wavelength information exceeds a threshold value.

[0227] Figure 12 is a flowchart showing the operation of the distance measuring device 2 according to the present embodiment.

[0228] As shown in Figure 12 , first, in the distance measuring device 2, the adjustment section 15 sets the wavelength of the laser for measurement (S20). Specifically, the adjustment section 15 sets the wavelength λ1 of the laser L1 and the wavelength λ2 of the laser L2 as initial values to predetermined values. The initial values of the wavelengths λ1 and λ2 are set based on the required measurement accuracy and the like for the distance measurement (for example, the inspection of the surface shape) of the object 90, for example.

[0229] Next, in the distance measuring device 2, the first signal S1 is acquired using the reference interference system 30 (S21). The signal processing system 50 generates wavelength information based on the first signal S1 (S22). The wavelength information is information indicating the wavelength λ1 of the laser L1. The generated wavelength information is stored in the memory 52. In addition, the steps S21 and S22 are the same processing as the steps S10 and S11 shown in Figure 9 .

[0230] Next, the adjustment section 15 adjusts the wavelength λ1 of the laser L1 (S23). Specifically, the adjustment section 15 adjusts the temperature and / or the applied current of the laser light source 13a based on the wavelength λ1 indicated by the wavelength information stored in the memory 52 so that the value of the wavelength λ1 becomes the initial value of the wavelength λ1 of the laser L1. In addition, in a case where the difference between the wavelength λ1 indicated by the wavelength information stored in the memory 52 and the initial value of the wavelength λ1 of the laser L1 is less than a threshold value, the adjustment processing (S23) can be omitted.

[0231] Next, the distance measuring device 2 acquires the second signal S2 using the measurement interference system 40 (S24). Next, the signal processing system 50 calculates the distance based on the wavelength information stored in the memory 52 and the second signal S2 (S25). By using the wavelength λ1 indicated by the wavelength information, it is possible to improve the measurement accuracy. In addition, the steps S24 and S25 are the same processing as the steps S12 and S13 shown in Figure 9 .

[0232] In the case where the distance measurement processing is not ended (NO in S26), the signal processing system 50 determines whether or not the adjustment of the wavelength λl is performed (S27). The adjustment of the wavelength λl is performed, for example, at a predetermined timing. In the case where the adjustment of the wavelength λl is performed (YES in S27), in the distance measurement device 2, the acquisition of the first signal (S21), the generation of the wavelength information (S22), and the adjustment of the wavelength λl (S23) are performed.

[0233] In the case where the adjustment of the wavelength λl is not performed (NO in S27), in the distance measurement device 2, the acquisition of the second signal (S24) and the calculation of the distance (S25) are performed. In the calculation of the distance, the wavelength information stored in the memory 52 is used.

[0234] Thus, according to the distance measurement device 2 relating to the present embodiment, since the fluctuation of the wavelength λl of the laser light Ll used in the distance measurement can be suppressed, the measurement accuracy can be improved. In addition, the adjustment section 15 can also adjust the wavelength λ2 of the laser light L2, and the measurement accuracy can be further improved.

[0235] In addition, whether or not the adjustment of the wavelength λl is performed can also be determined based on the fluctuation, i.e., the drift amount, of the wavelength λl, as in the case of whether or not the update of the wavelength information is performed in Embodiment 1. Further, in the case of measurement for a short period, the adjustment of the wavelength λl can also be performed only once before the start of the measurement. That is, the processing of step S27 can also not be performed.

[0236] (Embodiment 3)

[0237] Next, Embodiment 3 will be described.

[0238] In the distance measurement device relating to Embodiment 3, compared with Embodiment 1, the main difference is that the reference interference system and the measurement interference system share the optical interference system. Hereinafter, the description will be focused on the difference from Embodiment 1, and the common description will be omitted or simplified.

[0239] Figure 13 is a block diagram showing the configuration of the distance measurement device 3 relating to the present embodiment. As shown in Figure 13 , compared with the distance measurement device 1 shown in Figure 1 , the distance measurement device 3 shares one optical interference system 60 between the reference interference system 30 and the measurement interference system 40. In this case, the laser light Ll emitted from the measurement light source 11 does not need to be branched. Therefore, the distance measurement device 3 can not have the optical splitter 20.

[0240] Thus, according to the present embodiment, since the components that the distance measuring device 3 has can be reduced, the distance measuring device 3 can be made small and light. In addition, the operation of the distance measuring device 3 is the same as that of the distance measuring device 1. Further, the distance measuring device 3 can also have the adjustment section 15 in the light source section 10, like the distance measuring device 2 of the second embodiment.

[0241] (Modified Examples)

[0242] Next, modified examples of the embodiments will be described. The modified example 1 and the modified example 2 shown below are mainly different from the embodiments in the structure of the light source section. The structure other than the light source section is the same as that of the embodiments, and thus the description thereof will be omitted or simplified.

[0243] [Modified Example 1]

[0244] In the modified example 1, the number of wavelengths of the single-wavelength laser used in the distance measurement is three, which is different from the embodiments. Hereinafter, the description will be focused on the difference from the embodiments, and the description of the common points will be omitted or simplified.

[0245] Figure 14 is a block diagram showing the structure of the light source section 110 of the distance measuring device relating to the modified example 1. As shown in Figure 14 , the light source section 110 has the measurement light source 111 and the reference light source 12. The measurement light source 111 has three laser light sources 13a, 13b, and 13c and a wavelength combining system 14. The laser light sources 13a and 13b are the same as those of the embodiments, and thus the description thereof will be omitted.

[0246] The laser light source 13c is, for example, a semiconductor laser element, and emits a laser light of a predetermined single wavelength when supplied with a current. The laser light source 13c is an example of the third laser light source, and emits a laser light L3 having a wavelength λ3. The wavelength λ3 is an example of the third wavelength, and the laser light L3 is an example of one of the plurality of second laser lights. The wavelength λ3 is a wavelength different from the wavelength λ1 and the wavelength λ2. In the present embodiment, the wavelength λ3 is longer than either of the wavelength λ1 and the wavelength λ2. At this time, for example, the difference between the wavelength λ3 and the wavelength λ1 can be made 10 times or more the difference between the wavelength λ2 and the wavelength λ1. By making the difference between the two wavelengths large, the difference in the beat wavelength can be made large. As a result, the length measurement range and the length measurement accuracy can be set in stages, and thus the absolute distance can be measured with high accuracy.

[0247] The wavelength combining system 14 combines the laser lights L1, L2, and L3 emitted from the respective three laser light sources 13a, 13b, and 13c. The wavelength combining system 14 is, for example, a DWDM element or a holographic optical element.

[0248] The structure of the distance measuring device relating to the present modified example other than the light source section 110 is the same as that of theFigure 1 The structure of the distance measuring device 1, Figure 11 The distance measuring device 2 or Figure 13 The distance measuring device 3 is the same. At this time, the light detection system 42 of the measurement interference system 40 has a light detector for detecting light of the wavelength λ3. Alternatively, the light detection system 42 can detect beat light by heterodyne interference.

[0249] In the case where three single-wavelength lasers having mutually different wavelengths can be used as in this modification, the combinations of two single-wavelength lasers are three. Therefore, the second measurement can be performed based on at least one of the three combinations. Specifically, the second measurement can be performed in the length measurement accuracy and the length measurement range corresponding to at least one of the beat wavelengths Λ 12 , the beat wavelength Λ 13 , and the beat wavelength Λ 23 corresponding to at least one of the beat wavelengths Λ 12 obtained based on the interference of the laser L1 of the wavelength λ1 and the laser L2 of the wavelength λ2; the beat wavelength Λ 13 obtained based on the interference of the laser L1 of the wavelength λ1 and the laser L3 of the wavelength λ3; and the beat wavelength Λ 23 obtained based on the interference of the laser L3 of the wavelength λ3 and the laser L2 of the wavelength λ2.

[0250] In addition, the beat wavelength Λ 12 is represented by Expression (2). Furthermore, the beat wavelengths Λ 13 and Λ 23 are represented by Expressions (4) and (5), respectively.

[0251] [Expression 4]

[0252] (4)

[0253] (5)

[0254] In this modification, λ1< λ2< λ3 is satisfied. Furthermore, |λ1- λ3| is set to be sufficiently larger than |λ1- λ2|. In other words, λ1≈ λ2 is set. As a result, the beat wavelengths Λ 12 and Λ 13 are made to be significantly different. For example, λ1, λ2, and λ3 are set to 1550 nm, 1551 nm, and 1600 nm, respectively. At this time, according to Expressions (2) and (4), the beat wavelength Λ 12 is approximately 2.4 mm, and the beat wavelength Λ 13 is approximately 50 μm. In addition, since λ1≈ λ2, the beat wavelength Λ 13 is approximately equal to the beat wavelength Λ 23 .

[0255] The processing circuit 53 relating to this modification example uses two of the beat wavelengths Λ 12 , Λ 13 , and Λ 23 to perform the 2nd measurement, and combines the results of the 1st measurement, thereby calculating the distance from the distance measuring device to the object 90. Specifically, the processing circuit 53 combines the 1st distance obtained by the 1st measurement with the two 2nd distances obtained by the 2nd measurement, thereby calculating the absolute distance from the distance measuring device to the object 90.

[0256] The processing circuit 53 uses the beat wavelength obtained based on the laser light of which the fluctuation (undulation) of the wavelength and the frequency is the smallest among all the single-wavelength laser light emitted by the light source section 110. Here, since the fluctuation of the wavelength of the laser light L1 is the smallest, the beat wavelengths Λ 13 and Λ 12 are used. Further, in the 1st measurement, the processing circuit 53 also uses the interference result of the laser light of which the fluctuation of the wavelength is the smallest among all the single-wavelength laser light emitted by the light source section 110.

[0257] Here, if the absolute distance from the probe to the measurement object is assumed to be x, the absolute distance x is represented by the following equation (6).

[0258] (6) x = (A x A 13 + B x λ1 + θ i x λ1) / 2

[0259] A and B are the wave numbers of the beat wavelength Λ i and the wavelength λ1, respectively, included in the absolute distance x 12 from the probe to the 1st portion of the object 90. Further, θi corresponds to the position of each of the 1st portion, the 2nd portion, and the 3rd portion of the object 90, and represents the phase of the interference result based on the wavelength λ1 obtained by the 1st measurement. In addition, equation (6) corresponds to extending equation (3) to three wavelengths. Further, the 1st portion, the 2nd portion, and the 3rd portion are mutually different portions of the surface of the object 90.

[0260] The 2nd measurement is performed by the combination of the longest beat wavelength. The distance calculated in this 2nd measurement is an example of the 3rd distance calculated with the 3rd measurement accuracy in the 3rd measurement range. In addition, the 3rd measurement accuracy is lower than the 2nd measurement accuracy and the 1st measurement accuracy. The 3rd measurement range is longer than the 2nd measurement range and the 1st measurement range. In other words, the 2nd measurement is performed by the combination of the longest measurement range.

[0261] Here, the processing circuit 53 determines the phase of the beat wavelength Λ 12 based on the combination of the wavelength λ1 and the wavelength λ2. The processing circuit 53 determines the beat wavelength Λ 12the phase of the beat wavelength Λ 13 the wave number A of the beat wavelength Λ 12 the distance calculated based on the beat wavelength Λ 13 the wave number A of the beat wavelength Λ 13

[0262] Further, as the next 2nd measurement, the processing circuit 53 determines the phase of the beat wavelength Λ 13 based on the combination of the wavelength λ1 and the wavelength λ3. The processing circuit 53 counts the wave number B of the wavelength λ1 based on the phase of the beat wavelength Λ 13 determined. Specifically, the wave number B of the wavelength λ1 is calculated by dividing the distance calculated based on the beat wavelength Λ 13 by the wavelength λ1.

[0263] Finally, as the 1st measurement, the processing circuit 53 determines the phase θ1 of the wavelength λ1. The processing circuit 53 can calculate the absolute distance x i based on the wave numbers A and B, and the phase θ1 of the wavelength λ1, by the above-described equation (6).

[0264] As described above, by performing the 2nd measurement multiple times using multiple beat wavelengths, it is possible to further expand the range of the distance measurement.

[0265] In addition, the calculation of the absolute distance can be performed in a manner other than the above-described manner. For example, the Excess fraction method can be employed, in which the calculation of the absolute distance is performed by using the combination of the phases of all the wavelengths of the laser light.

[0266] [Modified Example 2]

[0267] In Modified Example 2, the main difference from each of the embodiments is that the reference laser light emitted from the reference light source 12 is used for distance measurement. Hereinafter, the description will be made focusing on the difference from each of the embodiments, and the description of the common points will be omitted or simplified.

[0268] Figure 15 is a block diagram showing the structure of the distance measuring device 201 relating to Modified Example 2. As shown in Figure 15 , the distance measuring device 201 has a light source section 210 instead of the light source section 10 compared to the distance measuring device 1 shown in Figure 1 . The light source section 210 has the laser light source 13a and the laser light source 13r. In addition, the light source section 210 can have the wavelength synthesizing system 14.

[0269] As shown in Figure 2 ​As shown, the laser light source 13r is a light source that emits the reference laser light Lr. In the present modification, the reference laser light Lr is input not only to the reference interferometer system 30 but also to the measurement interferometer system 40. That is, the reference laser light Lr is also used as the second laser light for measurement. Specifically, the reference laser light Lr is split by the optical splitter 20 into light L2r (Lr) that is input to the reference interferometer system 30 and light L2t that is input to the measurement interferometer system 40. Thus, for the measurement interferometer system 40, the reflected light L2c after reflection by the object 90 is input from among the reference laser light Lr.

[0270] Thus, the number of light sources provided in the light source section 210 can be reduced, so that the distance measuring device 201 can be made smaller and lighter. In addition, the distance measuring device 201 operates in the same manner as the distance measuring device 1. Furthermore, the distance measuring device 201 can also be provided with the adjustment section 15, like the distance measuring device 2 of Embodiment 2.

[0271] (Other Embodiments)

[0272] The distance measuring device relating to one or more technical solutions has been described based on the embodiments, but the present disclosure is not limited to these embodiments. As long as the gist of the present disclosure is not deviated from, the configurations obtained by applying various modifications that can be thought of by those skilled in the art to the present embodiments and the configurations obtained by combining the constituent elements of different embodiments are also included in the scope of the present disclosure.

[0273] For example, in the above-described embodiments and modifications, an example in which the processing circuit 53 calculates the absolute distance from the distance measuring device to the object 90 is shown, but it is not limited thereto. The processing circuit 53 can also output the first distance and the second distance to other devices after calculating them. For example, the processing circuit 53 can also transmit the first distance and the second distance to another computer, and the absolute distance can be calculated by the other computer. Alternatively, the processing circuit 53 can also transmit the first distance and the second distance to a display and cause the display to display, or can output to a printer and cause it to print on a medium such as paper. Thus, the user or the like can be prompted with the first distance and the second distance, so that the user can calculate the absolute distance by manual calculation. In this way, the processing circuit 53 can also not perform the calculation of the absolute distance.

[0274] Furthermore, it is also possible to change the wavelength of at least one of the two single-wavelength lasers. For example, it is also possible to sweep the wavelength of the laser light for which the wavelength fluctuation is larger. Thus, it is possible to change the combination of the two wavelengths, so that a distance measuring range and a distance measuring accuracy that are suitable for the object 90 can be achieved. Furthermore, compared to the case where three or more laser light sources are provided, the device can be made smaller.

[0275] Moreover, as the two single-wavelength lasers, a laser in which one single-wavelength laser is branched into two, and a laser in which the other laser is frequency-shifted can be used. As a means of frequency-shifting, for example, an acousto-optic modulator (AOM) can be used.

[0276] Moreover, the first laser emitted by the light source 11 for measurement can also be a laser including a plurality of single modes. For example, the first laser can also be an optical frequency comb laser. An optical frequency comb laser is a laser composed of frequency lines arranged at equal intervals because the spectrum is discrete.

[0277] Moreover, the fluctuation in wavelength can not be the standard deviation σ. For example, the fluctuation in wavelength can be 3σ. Alternatively, the fluctuation in wavelength can be the variance σ of the frequency of the laser in a limited time 2 Moreover, the fluctuation in wavelength can be the difference between the maximum and minimum values of the wavelength of the laser in a limited time.

[0278] Moreover, in a case where the light source unit includes three or more laser light sources, two of the laser light sources can emit single-wavelength lasers of the same wavelength. Moreover, the fluctuations in the frequencies of the two single-wavelength lasers of the same wavelength can be the same. It is also possible to use one of the two single-wavelength lasers of the same wavelength in the first measurement, and to use the other of the two single-wavelength lasers of the same wavelength in the second measurement. In other words, the first single-wavelength laser used in each of the first measurement and the second measurement can be a laser emitted from a different laser light source.

[0279] Moreover, the measurement length accuracy Am of the second measurement can be greater than the measurement length range Rs of the first measurement. In a case where the difference between the measurement length accuracy Am of the second measurement and the measurement length range Rs of the first measurement is small, and Am > Rs, the distance can be measured with substantially the same degree of accuracy as in a case where Am ≤ Rs.

[0280] Moreover, for example, the wavelength information can not be the peak wavelength of the laser, but information indicating the spectral distribution of the laser.

[0281] Moreover, the global or specific technical solutions of the present disclosure can be realized by a system, an apparatus, a method, an integrated circuit, or a computer program. Alternatively, the present disclosure can also be realized by a computer-readable non-transitory recording medium, such as an optical disc, an HDD, or a semiconductor memory, which stores the computer program. Moreover, the present disclosure can also be realized by any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium.

[0282] Moreover, each of the above-described embodiments can be variously changed, replaced, added, omitted, or the like within the scope of the claims or equivalents thereof.

[0283] Industrial applicability

[0284] The present disclosure can be used for a distance measuring device capable of suppressing a decrease in length measuring accuracy and long-term stability, for example, in a surface shape inspection device or the like.

Claims

1. A distance measuring device characterized by comprising: a light source section that emits a first laser light and a reference laser light; a reference interference system that detects a first interference light generated by causing the first laser light to interfere and a second interference light generated by causing the reference laser light to interfere, and outputs a first signal; a measurement interference system that is inputted with a first reflected light generated by the first laser light being reflected by an object, and outputs a second signal; and a signal processing system that generates wavelength information about a wavelength of the first laser light based on the first signal, and calculates a distance from the distance measuring device to the object based on the wavelength information and the second signal, the reference interference system is a Michelson interferometer.

2. The distance measuring device according to claim 1, characterized in that the signal processing system generates the wavelength information about the wavelength of the first laser light based on the first signal, and calculates the distance based on the wavelength information and the second signal.

3. The distance measuring device according to claim 1, characterized in that the light source section further emits a second laser light having a wavelength different from that of the first laser light, the measurement interference system is further inputted with a second reflected light generated by the second laser light being reflected by the object.

4. The distance measuring device according to claim 3, characterized in that the wavelength of the reference laser light is shorter than the wavelength of the first laser light.

5. The distance measuring device according to claim 3, characterized in that the measurement interference system includes: a first light interference system that causes the first laser light and the first reflected light to interfere, emits a third interference light generated by the interference of the first laser light and the first reflected light, and causes the second laser light and the second reflected light to interfere, and emits a fourth interference light generated by the interference of the second laser light and the second reflected light; and a first light detection system that detects the third interference light and the fourth interference light, and outputs the second signal.

6. The distance measuring device according to claim 1, characterized in that the light source section further emits a plurality of second laser lights, the plurality of second laser lights have wavelengths different from each other, the plurality of second laser lights each have a wavelength different from that of the first laser light, the measurement interference system is further inputted with a plurality of second reflected lights generated by the plurality of second laser lights being reflected by the object.

7. The distance measuring device according to claim 1, characterized by further comprising an optical splitter that divides the first laser light emitted from the light source section into a first portion and a second portion, and causes the first portion to be inputted to the reference interference system and the second portion to be inputted to the measurement interference system.

8. The distance measuring device according to claim 1, characterized in that the reference interference system includes: a second light interference system that causes the first laser light to interfere, and emits the first interference light generated by the interference of the first laser light, and causes the reference laser light to interfere, and emits the second interference light generated by the interference of the reference laser light; and a second light detection system that detects the first interference light and the second interference light, and outputs the first signal. ​ ​ 9. The distance measuring device according to claim 8, wherein The reference interference system further includes a path difference changing mechanism that changes the difference between the optical path length of the first laser light that passes through the second optical interference system and the optical path length of the reference laser light that passes through the second optical interference system.

10. The distance measuring device according to any one of claims 1 to 9, wherein The signal processing system generates the wavelength information indicating the peak wavelength of the first laser light by calculating the peak wavelength of the first laser light based on the first signal.

11. The distance measuring device according to any one of claims 3 to 5, wherein The signal processing system generates the wavelength information indicating the peak wavelength of the first laser light and the peak wavelength of the second laser light by calculating the peak wavelength of the first laser light and the peak wavelength of the second laser light based on the first signal.

12. The distance measuring device according to any one of claims 1 to 9, wherein The signal processing system updates the wavelength information when a prescribed condition is satisfied.

13. The distance measuring device according to any one of claims 1 to 9, wherein The signal processing system includes a memory that stores the generated wavelength information, The signal processing system generates the wavelength information less frequently than the signal processing system calculates the distance, The signal processing system calculates the distance based on the wavelength information stored in the memory and the second signal.

14. The distance measuring device according to claim 13, wherein The signal processing system generates the wavelength information and updates the wavelength information stored in the memory when the fluctuation of the wavelength of the first laser light exceeds a threshold value.

15. The distance measuring device according to any one of claims 1 to 9, wherein The light source section includes an adjustment section that adjusts the wavelength of the first laser light based on the wavelength information.

16. The distance measuring device according to any one of claims 1 to 9, wherein The first laser light is a laser light that includes a plurality of single modes.

17. The distance measuring device according to any one of claims 1 to 9, wherein The reference interference system and the measurement interference system share an optical interference system.

18. The distance measuring device according to claim 1, wherein The measurement interference system is further inputted with a third reflected light that is generated when the reference laser light is reflected by the object.

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