Ranging device

Abstract

A ranging device according to the present invention comprises a light source unit that emits first laser light and reference laser light, a reference interference system that detects first interference light generated by making the first laser light interfere and second interference light generated by making the reference laser light interfere and outputs a first signal, a measurement interference system that receives input of first reflected light generated by reflection of the first laser light at an object and outputs a second signal, and a signal processing system that generates wavelength information about the wavelength of the first laser light on the basis of the first signal and calculates the distance from the ranging device to the object on the basis of the wavelength information and the second signal. A light path for the first laser light and a light path for the reference laser light are provided at the reference interference system such that the first laser light and the reference laser light do not interfere with each other.

Description

distance measuring device

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

[0002] Optical interference using laser light is widely used as a means for acquiring information indicating the distance and / or shape of an object without contact. For example, frequency modulated continuous wave radar (FMCW) LiDAR (Light Detection and Ranging) is known as a three-dimensional measurement device with millimeter accuracy. Optical coherence tomography (OCT) or optical comb optical interference is known as a means for measuring with micrometer accuracy. These are widely used in the medical and / or industrial fields.

[0003] Furthermore, by controlling the optical interference phenomenon with even greater precision, measurements with nanometer accuracy become possible. For example, measurements using a Michelson interferometer with a single wavelength laser are one method for measuring distance differences on the order of nanometers.

[0004] Optical measurements with nanometer accuracy, such as homodyne optical interferometry, are capable of non-contact, highly accurate measurements, but have the drawback of being limited to a measurement range of half the wavelength (submicrometers).This makes it difficult to measure samples that have both nanometer-scale structures and structures on the order of several tens of micrometers.

[0005] Multi-wavelength interference, which is an optical interference technique using two or more single-wavelength laser beams, is expected to solve this problem. Multi-wavelength interference can eliminate the trade-off between measurement range and measurement accuracy, which has been a problem in the past, and can simultaneously achieve a long measurement range and high measurement accuracy.

[0006] For example, Patent Documents 1 and 2 state that by combining the results of optical interference of laser light with different wavelengths, it is possible to eliminate the trade-off between measurement range and measurement accuracy, which has been a conventional problem, and achieve a long measurement range and high measurement accuracy.

[0007] Japanese Patent Application Laid-Open No. 2021-148634 International Publication No. 2008 / 146480 Japanese Utility Model Application Laid-Open No. 5-14867

[0008] In distance measurement methods that use the interference of laser light, the calculated distance information is affected by the temporal fluctuation of the wavelength of the laser light, which results in a decrease in measurement accuracy and a decrease in the stability of measurement results over long periods of time.

[0009] Therefore, the present disclosure provides a distance measuring device that can suppress deterioration in measurement accuracy and long-term stability.

[0010] A distance measuring device according to one aspect of the present disclosure includes: a light source unit that emits a first laser beam and a reference laser beam; a reference interferometer that detects first interference light generated by interfering the first laser beam and second interference light generated by interfering the reference laser beam and outputs a first signal; a measurement interferometer that receives first reflected light generated by reflection of the first laser beam by an object and outputs a second signal; and a signal processing system that generates wavelength information regarding the wavelength of the first laser beam 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. In the reference interferometer, the optical paths of the first laser beam and the reference laser beam are arranged so that the first laser beam and the reference laser beam do not interfere with each other.

[0011] According to the present disclosure, it is possible to suppress a decrease in measurement accuracy and long-term stability.

[0012] FIG. 1 is a block diagram showing the configuration of a distance measuring device according to a first embodiment. FIG. 2 is a block diagram showing the configuration of a light source unit of the distance measuring device according to the first embodiment. FIG. 3 is a diagram showing a specific configuration of a measurement interferometer system of the distance measuring device according to the first embodiment. FIG. 4 is a diagram showing a specific configuration of a reference interferometer system of the distance measuring device according to the first embodiment. FIG. 5 is a diagram for explaining the principle of a first measurement using a single-wavelength laser beam by the distance measuring device according to the first embodiment. FIG. 6 is a diagram for explaining the principle of a second measurement using a plurality of single-wavelength laser beams by the distance measuring device according to the first embodiment. FIG. 7 is a diagram showing the measurement range and measurement accuracy of two measurements by the distance measuring device according to the first embodiment. FIG. 8 is a diagram for explaining the stability of the wavelength and frequency of the single-wavelength laser beam. FIG. 9 is a flowchart showing the operation of the distance measuring device according to the first embodiment. FIG. 10 is a diagram showing the relationship between the frequency of updating wavelength information and the frequency of calculating distance. FIG. 11 is a block diagram showing the configuration of a distance measuring device according to a second embodiment. FIG. 12 is a flowchart showing the operation of the distance measuring device according to the second embodiment. FIG. 13 is a block diagram showing the configuration of a distance measuring device according to a third embodiment. Fig. 14 is a block diagram showing the configuration of a light source unit of a distance measuring device according to a first modified example of the embodiment. Fig. 15 is a block diagram showing the configuration of a distance measuring device according to a second modified example of the embodiment.

[0013] (Summary of the present disclosure) First, definitions of key terms used in this specification are provided below.

[0014] "Measurement accuracy" refers to the degree of accuracy when measuring distance. In other words, measurement accuracy is a measure of how accurately distance information can be obtained. Therefore, the higher the measurement accuracy, the more accurate the measurement.

[0015] The "measurement range" represents the range in the distance direction in which unique distance information can be acquired. In other words, the measurement range represents the range in which distance measurement (ranging) is possible.

[0016] In this specification, both the measurement accuracy and the measurement range are expressed in the same dimension as the distance. Specifically, the units of the measurement accuracy and the measurement range are both expressed in nanometers (nm), micrometers (μm), millimeters (mm), etc. Therefore, "high measurement accuracy" is synonymous with "short measurement accuracy" expressed in the dimension of distance. "low measurement accuracy" is synonymous with "long measurement accuracy" expressed in the dimension of distance. Furthermore, in this specification, measurement accuracy may be simply referred to as "accuracy." Measurement range may be simply referred to as "range."

[0017] Distance measurement within the measurement range is called “absolute distance measurement.” For example, a distance measurement with an accuracy of 10 nm and a measurement range of 1 mm is an absolute distance measurement that can distinguish a difference of 10 nm within a range of 1 mm.

[0018] "Long-term stability" means that there is little temporal fluctuation from the start to the end of the measurement, allowing measurements to be made with consistent accuracy. For example, if the wavelength of the laser light fluctuates over time, long-term stability will decrease. If long-term stability decreases, problems such as limitations on the measurement time may occur.

[0019] Aspects of the distance measuring device according to the present disclosure are as follows.

[0020] A distance measuring device according to a first aspect of the present disclosure includes: a light source unit that emits a first laser beam and a reference laser beam; a reference interferometry system that detects first interference light generated by interfering the first laser beam and second interference light generated by interfering the reference laser beam and outputs a first signal; a measurement interferometry system that receives first reflected light generated by reflection of the first laser beam by an object and outputs a second signal; and a signal processing system that generates wavelength information regarding the wavelength of the first laser beam 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. In the reference interferometry system, the optical paths of the first laser beam and the reference laser beam are arranged so that the first laser beam and the reference laser beam do not interfere with each other.

[0021] This allows the actual wavelength of the laser beam used in the measurement, or a value equivalent thereto, to be obtained from the wavelength information, even if the wavelength of the laser beam fluctuates. The wavelength fluctuation can be fed back to the distance calculation, preventing a decrease in measurement accuracy and long-term stability.

[0022] A distance measuring device according to a second aspect of the present disclosure is the distance measuring device according to the first aspect, and in the distance measuring device according to the second aspect, the light source unit may further emit a second laser light having a wavelength different from that of the first laser light, and the measurement interference system may further receive second reflected light generated by the second laser light being reflected by the object.

[0023] This makes it possible to perform distance measurement using multiwavelength interferometry (MWI) that uses light of multiple wavelengths, thereby achieving high measurement accuracy and a wide measurement range.

[0024] In addition, the reference interference system may detect the interference light generated by interfering with the second laser light and the interference light generated by interfering with the reference laser light, and output a third signal, and the signal processing system may generate second wavelength information regarding the wavelength of the second laser light based on the third signal, and calculate the distance from the distance measuring device to the object based on first wavelength information, which is wavelength information regarding the wavelength of the first laser light, the second wavelength information, and the second signal.

[0025] Note that generating second wavelength information is not essential when using the second laser beam. For example, if the fluctuation in the wavelength of the first laser beam is smaller than the fluctuation in the wavelength of the second laser beam, high measurement accuracy can be ensured based on the interference result of the first laser beam. Therefore, even if second wavelength information regarding the wavelength of the second laser beam is not obtained, high measurement accuracy and a wide measurement range can be achieved.

[0026] A distance measuring device according to a third aspect of the present disclosure is the distance measuring device according to the second aspect, and in the distance measuring device according to the third aspect, the wavelength of the reference laser light may be shorter than the wavelength of the first laser light.

[0027] This makes it possible to measure each wavelength of a plurality of laser beams used in the MWI, thereby improving the measurement accuracy even if the measurement range is expanded.

[0028] A distance measuring device according to a fourth aspect of the present disclosure is the distance measuring device according to the second or third aspect, and in the distance measuring device according to the fourth aspect, the measurement interference system may include a first optical interference system that causes the first laser light and the first reflected light to interfere with each other and emits third interference light generated by the interference between the first laser light and the first reflected light, and causes the second laser light and the second reflected light to interfere with each other and emits fourth interference light generated by the interference between the second laser light and the second reflected light, and a first optical detection system that detects the third interference light and the fourth interference light and outputs the second signal.

[0029] This allows light to be homodyne-interfered for each wavelength, and an interference signal for each wavelength can be obtained as a second signal with high accuracy. By combining the interference signals for each wavelength, the measurement range can be expanded. Details will be described later using FIG. 6.

[0030] In the technology described in Patent Document 1, heterodyne interference is caused between a measurement laser beam and a reference laser beam, a beat signal is detected by a photodetector, and the result of measurement using the measurement laser beam is corrected based on the result. As a condition for heterodyne interference, the wavelength difference between the two laser beams needs to be small, so the reference laser beam limits the wavelength options for the measurement laser beam.

[0031] A commonly used wavelength-stabilized laser is a HeNe laser. However, in heterodyne interference, the wavelength of the measurement laser light is limited to wavelengths near 633 nm, which is the wavelength of HeNe laser light. Optical elements suitable for wavelengths near 633 nm are expensive, and measurement is difficult when the target is an AR-coated visible lens, for example. Furthermore, because MWI uses lasers with multiple different wavelengths as the measurement laser light, the same number of reference laser light sources must also be prepared. In contrast, the distance measuring device according to this embodiment uses homodyne interference, which allows for a larger absolute difference between the wavelengths of the two laser lights used for measurement than when heterodyne interference is used, thereby improving the wavelength selectivity of the two laser lights. For example, it is possible to select a wavelength suitable for measuring the target, thereby suppressing deterioration in the measurement accuracy and long-term stability of the target. Furthermore, only one reference laser light source is required regardless of the number of wavelengths of the measurement laser light. This allows for a simplified configuration, miniaturization, and cost reduction of the distance measuring device. Furthermore, since a more stable single wavelength laser, such as a HeNe laser, can be used, the accuracy of measuring wavelength is higher than that of other methods, resulting in higher length measurement accuracy and long-term stability than other methods.

[0032] A ranging device according to a fifth aspect of the present disclosure is a ranging device according to the first aspect, wherein in the ranging device according to the fifth aspect, the light source unit may further emit a plurality of second laser lights, the wavelengths of the plurality of second laser lights may be different from each other, and the wavelength of each of the plurality of second laser lights may be different from the wavelength of the first laser light, and the measurement interference system may further receive a plurality of second reflected lights generated by the plurality of second laser lights being reflected by the object.

[0033] This allows laser light of three or more wavelengths to be used for measurement, further expanding the measurement range.

[0034] A distance measuring device according to a sixth aspect of the present disclosure is a distance measuring device according to any one of the first to fifth aspects, and may further include an optical splitter that divides the first laser light emitted from the light source unit into a first part and a second part, and inputs the first part into the reference interference system and the second part into the measurement interference system.

[0035] This makes it possible to input a part of the first laser light used for measurement to the reference interference system with a simple configuration.

[0036] A distance measuring device according to a seventh aspect of the present disclosure is a distance measuring device according to any one of the first to sixth aspects, and in the distance measuring device according to the seventh aspect, the reference interference system may include a second optical 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 optical detection system that detects the first interference light and the second interference light and outputs the first signal.

[0037] This allows homodyne interference of light for each wavelength, thereby accurately obtaining an interference signal of the first laser light and an interference signal of the reference laser light as the first signal. Therefore, the accuracy of wavelength calculation based on the first signal can be improved. Compared to using heterodyne interference, the absolute difference between the wavelengths of the two laser lights used for measurement can be larger, thereby improving the wavelength selectivity of the two laser lights. For example, a wavelength suitable for measuring the object can be selected, thereby suppressing a decrease in the object's measurement accuracy and long-term stability. Furthermore, only one light source of the reference laser light is required regardless of the number of wavelengths of the measurement laser light, thereby simplifying the configuration of the distance measuring device, reducing its size, and reducing its cost. Furthermore, the ability to use a more stable single-wavelength laser, such as a HeNe laser, improves the accuracy of wavelength measurement compared to other methods, resulting in higher measurement accuracy and long-term stability compared to other methods.

[0038] A distance measuring device according to an eighth aspect of the present disclosure is a distance measuring device according to the seventh aspect, wherein the reference interference system may further include an optical path difference changing mechanism that changes the difference between the optical path length of the first laser light passing through the second optical interference system and the optical path length of the reference laser light passing through the second optical interference system.

[0039] This allows the optical path difference to be adjusted to cause a change in the intensity of each of the interference signals of the first laser beam and the reference laser beam.The wavelength of the first laser beam can be calculated with high accuracy based on the change in the intensity of the interference signal. Note that changing the difference in optical path length is not essential.The interference signal of the first laser beam and the interference signal of the reference laser beam may be monitored separately without changing the difference in optical path length.

[0040] The interference signal is used to calculate the spectral information of each of the first laser beam and the reference laser beam. Assuming that the spectral intensities of the first laser beam and the reference laser beam have Gaussian characteristics, the wavelengths required for calculating the length measurement are the peak wavelengths of the respective laser beams.

[0041] Therefore, a ranging device according to a ninth aspect of the present disclosure is a ranging device according to any one of the first to eighth aspects, and in the ranging device according to the ninth aspect, the signal processing system may generate the wavelength information indicating the peak wavelength by calculating the peak wavelength of the first laser light based on the first signal.

[0042] This eliminates the need to obtain the spectrum of laser light, which reduces the complexity of the elements and calculations required for light detection. The simplified element configuration makes it possible to reduce the size and weight of the distance measuring device, and the reduced amount of calculation processing reduces power consumption related to calculations.

[0043] A ranging device according to a tenth aspect of the present disclosure is a ranging device according to any one of the second to fourth aspects, and in the ranging device according to the tenth aspect, the signal processing system may generate 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.

[0044] This allows not only the wavelength of the first laser light but also the wavelength of the second laser light used in the actual measurement or an equivalent value to be used to calculate the distance, thereby improving the measurement accuracy even in the case of MWI.

[0045] A ranging device according to an eleventh aspect of the present disclosure is a ranging device according to any one of the first to tenth aspects, and in the ranging device according to the eleventh aspect, the signal processing system may update the wavelength information when a predetermined condition is satisfied.

[0046] This allows wavelength information to be updated at an appropriate timing. By preventing unnecessary updates of wavelength information, it is possible to reduce the calculation time and / or power consumption required for the calculation, which are the calculation costs required for updating wavelength information.

[0047] A ranging device according to a twelfth aspect of the present disclosure is a ranging device according to any one of the first to eleventh aspects, and in the ranging device according to the twelfth aspect, the signal processing system may include a memory for storing the generated wavelength information, the frequency at which the signal processing system generates the wavelength information may be less than the frequency at which the signal processing system calculates the distance, and the signal processing system may calculate the distance based on the wavelength information stored in the memory and the second signal.

[0048] This allows the frequency of wavelength information generation to be reduced, for example, when drift, which is a long-term fluctuation in wavelength, progresses slowly. Furthermore, the computational cost required to generate wavelength information is generally higher than the computational cost required for length measurement. By reducing the frequency of wavelength information generation, the computational cost can be reduced.

[0049] A ranging device according to a thirteenth aspect of the present disclosure is the ranging device according to the twelfth aspect, and in the ranging device according to the thirteenth aspect, the signal processing system may generate the wavelength information and update the wavelength information stored in the memory when fluctuations in the wavelength of the first laser light exceed a threshold value.

[0050] This reduces the frequency with which wavelength information is generated, thereby reducing the power consumption required to generate wavelength information. For example, wavelength information can be updated when wavelength fluctuations occur to an extent that would affect the distance calculation results. In other words, wavelength information can be updated at an effective and efficient timing.

[0051] A ranging device according to a fourteenth aspect of the present disclosure is a ranging device according to any one of the first to thirteenth aspects, and in the ranging device according to the fourteenth aspect, the light source unit may be provided with an adjustment unit that adjusts the wavelength of the first laser light based on the wavelength information.

[0052] This allows, for example, the fluctuating wavelength to be restored, thereby improving the length measurement accuracy.

[0053] A distance measuring device according to a fifteenth aspect of the present disclosure is a distance measuring device according to any one of the first to fourteenth aspects, and in the distance measuring device according to the fifteenth aspect, the first laser light may be laser light including a plurality of single modes.

[0054] This allows the use of laser light other than single wavelength laser light.

[0055] A distance measuring device according to a sixteenth aspect of the present disclosure is a distance measuring device according to any one of the first to fifteenth aspects, and in the distance measuring device according to the sixteenth aspect, the reference interferometer and the measurement interferometer may share an optical interferometer.

[0056] This allows the distance measuring device to be made smaller and lighter.

[0057] A ranging device according to a seventeenth aspect of the present disclosure is a ranging device according to the first aspect, and in the ranging device according to the seventeenth aspect, a third reflected light generated by the reference laser light being reflected by the object may further be input to the measurement interference system.

[0058] This allows the number of laser light sources to be reduced, thereby realizing a smaller and lighter distance measuring device.

[0059] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0060] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not described in the independent claims are described as optional components.

[0061] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0062] Furthermore, in this specification, terms indicating the relationship between elements, such as parallel or perpendicular, terms indicating the shape of elements, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0063] Furthermore, in this specification, ordinal numbers such as "first" and "second" do not refer to the number or order of components unless otherwise specified, but are used for the purpose of avoiding confusion and distinguishing between components of the same type.

[0064] (First embodiment) [1. Configuration of distance measuring device] First, the configuration of a distance measuring device according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing the configuration of a distance measuring device 1 according to this embodiment.

[0065] 1 is a device that measures the distance to an object 90. For example, the distance measuring device 1 can obtain information indicating the surface shape of the object 90 by measuring the distance to each part of the object 90. Therefore, the distance measuring device 1 can be used, for example, for visual inspection of products and the like.

[0066] 1, the distance measuring device 1 includes a light source unit 10, an optical splitter 20, a reference interferometer system 30, a measurement interferometer system 40, and a signal processing system 50. Although not shown, the distance measuring device 1 may also include a support unit that supports the object 90. The support unit may include a drive unit such as a motor or a piezoelectric element, and may be able to change the attitude and / or position of the object 90.

[0067] 1, the dotted line connecting two blocks constituting the distance measuring device 1 represents the path of light, and the solid arrow connecting two blocks constituting the distance measuring device 1 represents the transmission path and transmission direction of the main signal.

[0068] The light source unit 10 emits a plurality of laser beams. In this embodiment, the plurality of laser beams are single-wavelength laser beams having different peak wavelengths. Specifically, the light source unit 10 emits a first laser beam, a second laser beam, and a reference laser beam. As shown in FIG. 1 , the light source unit 10 includes a measurement light source 11 and a reference light source 12.

[0069] The measurement light source 11 emits laser light L1, which is an example of a first laser light. The measurement light source 11 also emits laser light L2, which is an example of a second laser light. The reference light source 12 emits reference laser light Lr. A more specific configuration of the light source unit 10 will be described later with reference to FIG. 2.

[0070] It is generally difficult to maintain a constant wavelength and frequency for laser light, and the wavelength and frequency fluctuate to some extent over time. Wavelength fluctuation is a parameter that indicates the amount of temporal fluctuation in wavelength. Wavelength fluctuation includes not only short-term fluctuation but also long-term drift. Drift means that the average value of short-term fluctuation shifts over time. In this embodiment, the wavelength fluctuation of the reference laser light Lr is smaller than the wavelength fluctuation of the laser lights L1 and L2. Details of wavelength fluctuation will be explained later.

[0071] The optical splitter 20 splits the laser light L1 emitted from the light source unit 10 into light L1r and light L1t and outputs the split light. Light L1r is input to the reference interferometry system 30, and light L1t is input to the measurement interferometry system 40. The optical splitter 20 also outputs the laser light L2 as light L2t without splitting it. Alternatively, the optical splitter 20 may split the laser light L2 into two light beams and output them. One of the two split light beams is input to the reference interferometry system 30, and the other light beam L2t is input to the measurement interferometry system 40.

[0072] The optical splitter 20 splits the intensity of the incident light and outputs the split light in different directions. The optical splitter 20 is, for example, a half mirror, and its intensity split ratio is, for example, but not limited to, 1:1. The intensity of the light L1r may be higher than the intensity of the light L1t, or the intensity of the light L1t may be higher than the intensity of the light L1r. The wavelength of the light does not change when the light is split by the optical splitter 20.

[0073] The reference interference system 30 detects the light obtained by interfering the first laser light and the light obtained by interfering the reference laser light, and outputs a first signal S1 according to the detection result of the interfered light. Specifically, the reference interference system 30 receives the light L1r emitted from the optical branching device 20 and the reference laser light Lr from the reference light source 12. As shown in FIG. 1 , the reference interference system 30 includes an optical interference system 31 and an optical detection system 32.

[0074] The optical interference system 31 is an example of a second optical interference system, and causes the light L1r to interfere and emits interference light L1ri, and causes the reference laser light Lr to interfere and emit interference light Lri. The interference light L1ri is an example of a first interference light, and the interference light Lri is an example of a second interference light. The interference by the optical interference system 31 is homodyne interference.

[0075] The optical detection system 32 is an example of a second optical detection system, and detects the interference light L1ri and Lri and outputs a 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, i.e., the wavelength of the light L1t.

[0076] The specific configurations of the optical interference system 31 and the optical detection system 32 will be described later with reference to FIG.

[0077] The measurement interferometry system 40 receives as input a first reflected light beam generated when the light of the first laser beam irradiated onto the object 90 is reflected by the object 90, and outputs a second signal S2. The measurement interferometry system 40 also receives as input a second reflected light beam generated when the light of the second laser beam irradiated onto the object 90 is reflected by the object 90. Specifically, the measurement interferometry system 40 receives as input a light beam L1t emitted from the optical branching unit 20 and a reflected light beam L1c from the object 90. The measurement interferometry system 40 also receives as input a light beam L2t emitted from the optical branching unit 20 and a reflected light beam L2c from the object 90. As shown in FIG. 1 , the measurement interferometry system 40 includes an optical interferometry system 41 and an optical detection system 42.

[0078] The optical interference system 41 is an example of a first optical interference system, which causes light L1t and reflected light L1c to interfere with each other, thereby emitting a third interference light L1i generated by the interference between light L1t and reflected light L1c, and causes light L2t and reflected light L2c to interfere with each other, thereby emitting a fourth interference light L2i generated by the interference between light L2t and reflected light L2c. The interference caused by the optical interference system 41 is homodyne interference.

[0079] The optical detection system 42 is an example of a first optical detection system, and detects the third interference light L1i and the fourth interference light L2i and outputs a second signal S2 according to the detection results of the third interference light L1i 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.

[0080] The specific configurations of the optical interference system 41 and the optical detection system 42 will be described later with reference to FIG.

[0081] The signal processing system 50 generates wavelength information regarding 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 unit 51, a memory 52, and a processing circuit 53.

[0082] The signal receiving unit 51 acquires the first signal S1 from the reference interferometry system 30 and acquires the second signal S2 from the measurement interferometry system 40. The signal receiving unit 51 stores the acquired first signal S1 and second signal S2 in the memory 52.

[0083] The memory 52 is a storage device such as a non-volatile memory and / or a volatile memory. The memory 52 stores the first signal S1 and the second signal S2. The memory 52 may also store programs and data for operating each component of the distance measuring device 1, as well as wavelength information and distance information obtained by signal processing.

[0084] The processing circuit 53 is a circuit that processes signals output from the reference interferometer 30 and the measurement interferometer 40. Specifically, the processing circuit 53 calculates the peak wavelength of the first laser light based on the first signal S1, and generates wavelength information indicating the calculated peak wavelength. In this embodiment, the processing circuit 53 calculates the peak wavelength λ of the laser light L1 based on the first signal S1. １ and the peak wavelength λ of the laser light L2 ２The 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 processes the second signal S2 output from the measurement interferometer 40 based on a predetermined algorithm to obtain the position of the object 90 as phase information. A typical phase estimation algorithm that can be used is a 4-step phase-shifting algorithm. The processing circuit 53 can calculate the distance from the distance measuring device 1 to the object 90 based on the phase information.

[0085] In this embodiment, the processing circuit 53 calculates the wavelength λ １ The processing circuit 53 calculates a first distance within the first measurement range with a first measurement accuracy based on the interference result corresponding to the wavelength λ １ and wavelength λ ２ The processing circuit 53 calculates a second distance within the second distance measurement range with a second distance measurement accuracy based on the interference results corresponding to the first distance and the second distance. 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.

[0086] Here, the first measurement accuracy is higher than the second measurement accuracy. The second measurement range is longer than the first measurement range. Therefore, in simple terms, the processing circuit 53 calculates the distance within a short measurement range with high measurement accuracy based on the interference results for one wavelength. The processing circuit 53 calculates the distance within a long measurement range with low measurement accuracy based on the interference results for two wavelengths. The specific distance calculation method will be described later.

[0087] The processing circuit 53 is realized by an integrated circuit such as an LSI (Large Scale Integration). For example, the processing circuit 53 may be realized by a dedicated hardware configuration and calculate the distance from the distance measuring device 1 to the object 90. Alternatively, the processing circuit 53 may include a processor and calculate 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 may be a programmable FPGA (Field Programmable Gate Array) or a reconfigurable processor in which the connections and settings of circuit cells in an LSI can be reconfigured.

[0088] [1-1. Light Source Unit] Next, the specific configuration of the light source unit 10 will be described with reference to Fig. 2. Fig. 2 is a block diagram showing the configuration of the light source unit 10 of the distance measuring device 1 according to this embodiment. As shown in Fig. 2, the measurement light source 11 includes laser light sources 13a and 13b and a wavelength combining system 14. The reference light source 12 includes a laser light source 13r.

[0089] The laser light source 13a emits light of wavelength λ １ The laser beam L1 is an example of a first laser beam, and is, for example, a single-wavelength laser beam. １ is the peak wavelength of the laser light L1.

[0090] The laser light source 13b emits light of wavelength λ ２ The laser beam L2 is an example of a second laser beam, and is, for example, a single-wavelength laser beam. ２ is the peak wavelength of the laser light L2, and the wavelength λ １ The wavelength λ is different from １ and wavelength λ ２ The absolute difference between １ -λ ２ The shorter the | is, the longer the measurement range can be.

[0091] The laser light source 13r emits a reference laser beam Lr having a wavelength λr. The reference laser beam Lr is an example of a reference laser beam, and is, for example, a single-wavelength laser beam. The wavelength λr is the peak wavelength of the reference laser beam Lr, and the wavelength λ １ and λ ２ The wavelength λr is different from the wavelength λ １ Shorter.

[0092] The laser light sources 13a and 13b are, for example, semiconductor laser elements. As an example, DFB (Distributed Feedback) laser light sources, which are characterized by high wavelength and frequency stability, can be used for the laser light sources 13a and 13b. 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. A HeNe laser light source is a light source that emits light with less wavelength fluctuation than a semiconductor laser element, i.e., has high wavelength stability over time.

[0093] The wavelength combining system 14 combines the laser beams L1 and L2 emitted from the two laser light sources 13a and 13b, respectively. The wavelength combining system 14 is, for example, a Dense Wavelength Division Multiplexing (DWDM) element or a holographic optical element.

[0094] [1-2. Specific Configuration of Measurement Interferometry System] Next, a specific configuration of the measurement interferometry system 40 will be described. As described above, the measurement interferometry system 40 includes an optical interferometry system 41 and an optical detection system 42. Each component will be described below in order using FIG. 3. FIG. 3 is a diagram showing a specific configuration of the measurement interferometry system 40 of the distance measuring device 1 according to this embodiment.

[0095] In this embodiment, the optical interference system 41 is an optical system that utilizes Michelson interference. As shown in FIG.

[0096] The beam splitter 43 is an optical element that splits the intensity of incident light into multiple beams and emits each of the multiple beams in different directions. The beam splitter 43 is, for example, a half mirror, and splits the incident light into transmitted light and reflected light so that each has the same intensity. Note that the intensity ratio between the transmitted light and the reflected light does not have to be 1:1.

[0097] Specifically, the beam splitter 43 splits the light L1t, which is the laser light L1 from the light source unit 10 and split by the optical splitter 20, into two light beams L1a and L1b. The beam splitter 43 also splits the light L2t, which is the laser light L2 from the light source unit 10, into two light beams L2a and L2b. In the example shown in FIG. 3 , the light beams L1a and L2a are reflected light beams reflected by the beam splitter 43 and are emitted toward the mirror 44. The light beams L1b and L2b are transmitted light beams that have passed through the beam splitter 43 and are emitted toward the object 90.

[0098] The mirror 44 is an example of an optical element that reflects the light L1a and L2a from the beam splitter 43 and makes them incident on the beam splitter 43. Specifically, the mirror 44 specularly reflects the incident light. The higher the reflectivity, the less light loss there is, and the higher the detection accuracy can be. Both the light L1a and L2a incident on the mirror 44 are reflected by the mirror 44 and re-enter the beam splitter 43. At least a portion of each of the light L1a and L2a reflected by the mirror 44 and re-entering the beam splitter 43 is transmitted through the beam splitter 43.

[0099] The light beams L1b and L2b irradiated onto the object 90 are reflected by the object 90 and re-enter the beam splitter 43 as reflected light beams L1c and L2c. At least a portion of each of the reflected light beams L1c and L2c re-entering the beam splitter 43 is reflected by the beam splitter 43. In this case, interference occurs between the reflected light beams L1c and L2c and the light beams L1a and L2a. In FIG. 3, the interference light resulting from the homodyne interference between the reflected light beam L1c and the light beam L1a is shown as interference light beam L1i. The interference light resulting from the homodyne interference between the reflected light beam L2c and the light beam L2a is shown as interference light beam L2i. The interference light beams L1i and L2i are output to the optical detection system 42.

[0100] The positions of the mirror 44 and the object 90 can be reversed. That is, when the light from the light source unit 10 is split into transmitted light and reflected light by the beam splitter 43, the transmitted light may be irradiated onto the mirror 44, and the reflected light may be irradiated onto the object 90.

[0101] Furthermore, the optical interference system 41 is not limited to an optical system that uses Michelson interference, but may be an optical system that uses Fizeau interference or Mach-Zehnder interference.

[0102] As shown in FIG. 3, the optical detection system 42 includes a dichroic mirror 45, a mirror 46, and photodetectors 47 and 48.

[0103] The dichroic mirror 45 divides the incident light into a wavelength λ １ of light and wavelength λ ２ Specifically, the dichroic mirror 45 separates the light incident on the photodetection system 42 from the beam splitter 43 into light of wavelength λ and light of wavelength λ. １ The light of wavelength λ is emitted to the photodetector 47. ２ The light is emitted toward the photodetector 48. In this embodiment, a mirror 46 is provided for adjusting the optical path.

[0104] The mirror 46 reflects the wavelength λ ２ The light of wavelength λ is specularly reflected and incident on the photodetector 48. Note that the mirror 46 may not be provided, and the photodetector 48 may be disposed at the position of the mirror 46. Alternatively, the mirror 46 may be configured to reflect the light of wavelength λ １ The light source 12 may be provided for the purpose of adjusting the optical path of the light.

[0105] The photodetectors 47 and 48 each include a photoelectric conversion element that generates an electrical signal corresponding to the intensity of incident light. １ It has sensitivity to wavelength λ １The light L1 is photoelectrically converted into an interference signal S21 having a signal level according to the intensity thereof, and the interference signal S21 is output as a second signal S2 to the signal processing system 50. The interference signal S21 is a signal obtained by detecting interference light L1i between a part of the laser light L1 and reflected light L1c from the object 90.

[0106] The photodetector 48 detects at least the wavelength λ ２ It has sensitivity to wavelength λ ２ The light L2 is photoelectrically converted into an interference signal S22 having a signal level according to the intensity of the light L2, and the interference signal S22 is output as a second signal S2 to the signal processing system 50. The interference signal S22 is a signal obtained by detecting interference light L2i between at least a part of the laser light L2 and reflected light L2c from the object 90.

[0107] Note that the configuration of the optical detection system 42 is not limited to the above example, as long as it is possible to receive light for each wavelength. For example, the light traveling from the beam splitter 43 to the optical detection system 42 may be intensity-split into two beams, and then each of the two beams may be passed through a filter having a transmission band for a specific wavelength component. For example, a band-pass filter is used as the filter, but a low-pass filter, high-pass filter, etc. may also be used.

[0108] Furthermore, the measurement interferometry system 40 does not have to be an optical system that uses homodyne interference. The measurement interferometry system 40 may be an optical system that uses heterodyne interference. In this case, the measurement interferometry system 40 does not need to include a dichroic mirror 45 that splits light into wavelengths, and the number of photodetectors may be one.

[0109] [1-3. Specific Configuration of Reference Interferometry System] Next, a specific configuration of the reference interferometry system 30 will be described. As described above, the reference interferometry system 30 includes an optical interferometry system 31 and an optical detection system 32. Each configuration will be described below in order using FIG. 4. FIG. 4 is a diagram showing a specific configuration of the reference interferometry system 30 of the distance measuring device 1 according to this embodiment.

[0110] The optical interference system 31 is an optical system that uses a Sagnac-type Michelson interferometer. Light L1r, which is a part of the laser light L1 split by the optical splitter 20, and the reference laser light Lr are incident on the optical interference system 31 at different incident positions. As shown in Fig. 4, the optical interference system 31 includes a beam splitter 33, mirrors 34 and 35, and a movable mirror 36.

[0111] The beam splitter 33 is an optical element that splits the intensity of incident light into multiple beams and emits each of the multiple beams in different directions. The beam splitter 33 is, for example, a half mirror, and splits the incident light into transmitted light and reflected light so that each has the same intensity. Note that the intensity ratio between the transmitted light and the reflected light does not have to be 1:1.

[0112] Specifically, the beam splitter 33 splits the light L1r into two lights L1ra and L1rb. The beam splitter 33 also splits the reference laser light Lr into two lights Lra and Lrb. In the example shown in FIG. 4 , the light L1ra and the light Lra are reflected lights reflected by the beam splitter 33 and are emitted toward the mirror 35. The light L1rb and the light Lrb are transmitted lights that have passed through the beam splitter 33 and are emitted toward the mirror 34.

[0113] The mirror 34 reflects the light beams L1rb and Lrb toward the movable mirror 36. The mirror 35 reflects the light beams L1ra and Lra toward the movable mirror 36.

[0114] The movable mirror 36 has two reflecting surfaces 36a and 36b. The reflecting surface 36a reflects the light beams Lra and L1ra, respectively. The light beams Lra and L1ra reflected by the reflecting surface 36a are reflected by the mirror 35 and then incident on the beam splitter 33, where at least a portion of the light beams is transmitted. The reflecting surface 36b reflects the light beams Lrb and L1rb, respectively. The light beams Lrb and L1rb reflected by the reflecting surface 36b are reflected by the mirror 34 and then incident on the beam splitter 33, where at least a portion of the light beams is reflected. The light beams L1ra transmitted through the beam splitter 33 and the light beams L1rb reflected by the beam splitter 33 undergo homodyne interference and are transmitted to the photodetector 37 as interference light beams L1ri. The light Lra transmitted through the beam splitter 33 and the light Lrb reflected by the beam splitter 33 undergo homodyne interference and are incident on the photodetector 38 as interference light Lri.

[0115] The movable mirror 36 can change the positions of the reflecting surfaces 36a and 36b. For example, a movable stage is provided that movably supports 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 through the optical interference system 31 changes. In other words, the movable mirror 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 light Lr passing through the optical interference system 31. By adjusting the optical path difference, the interference light Lri and L1ri change.

[0116] The optical path difference changing mechanism included in the optical interference system 31 may be any mechanism capable of changing the optical path length, and is not limited to the movable mirror 36. For example, the optical interference system 31 may include an electro-optic modulator (EOM) arranged on the optical path as the optical path difference changing mechanism.

[0117] 4, the light detection system 32 includes photodetectors 37 and 38. Each of the photodetectors 37 and 38 includes a photoelectric conversion element that generates an electrical signal according to the intensity of incident light.

[0118] The photodetector 37 detects at least the wavelength λ １ It has sensitivity to wavelength λ １By photoelectrically converting the light L1r, an interference signal S11 having a signal level according to the intensity of the light L1r is output as a first signal S1 to the signal processing system 50. The interference signal S11 is a signal obtained by detecting interference light L1ri generated by homodyne interference of light L1r, which is a part of the laser light L1.

[0119] The photodetector 38 is sensitive to at least the wavelength λr, and performs photoelectric conversion on the light of wavelength λr, thereby outputting an interference signal S12 having a signal level corresponding to the intensity of the light as a 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.

[0120] 2. Principle of Distance Measurement Next, the principle of distance measurement by the distance measuring device 1 according to this embodiment will be described.

[0121] The distance measuring device 1 according to this embodiment performs distance measurement based on multi-wavelength interference (MWI) using multiple laser beams. MWI eliminates the trade-off between measurement range and measurement accuracy by combining the interference results of multiple single-wavelength laser beams with different wavelengths, thereby achieving a long measurement range and high measurement accuracy. The principle of multi-wavelength interference will be explained below.

[0122] [2-1. First Measurement (Using One Wavelength)] First, the first measurement using one single wavelength laser beam will be described.

[0123] As explained with reference to Fig. 3, in homodyne optical interference, a single wavelength laser beam is split by a beam splitter 43 and irradiated onto a mirror 44 that functions as a reference surface and an object 90, the distance of which is to be measured. The reflected light from the mirror 44 and the object 90 is made to interfere with each other by the beam splitter 43. When the interfered light is detected by a photodetector 47, the intensity P of the signal output from the photodetector 47 is ＰＤ is expressed by the following equation (1).

[0124]

[0125] In formula (1), L － =L ｘ -L ｙIt is. ｘ is the distance from the beam splitter 43 to the reflecting surface of the mirror 44. ｙ is the distance from the beam splitter 43 to the object 90. ｋ is the wavelength of the single wavelength laser light. Here, k=1. λ ｋ is calculated based on the first signal S1 output from the reference interference system 30. As a result, L ｘ and λ ｋ are all known values ​​to the processing circuit 53. Therefore, the processing circuit 53 determines the signal strength P ＰＤ Based on this, the distance L from the beam splitter 43 to the object 90 ｙ can be calculated.

[0126] The first measurement has a problem in that the measurement range is relatively short. The relationship between the position of the object 90 and the measurement range will be described below with reference to FIG.

[0127] 5 is a diagram for explaining the first principle of measurement using a single-wavelength laser beam by the distance measuring device 1 according to this embodiment. In FIG. 5, objects 90a, 90b, and 90c respectively represent the object 90 shown in FIGS. 1 and 3, which are located at different positions. When it is not necessary to distinguish between the positions, the description will be made as "object 90."

[0128] 5 shows a graph in which the horizontal axis represents the distance to the object 90 using a predetermined position as a reference point, and the vertical axis represents the distance calculated by the processing circuit 53. As shown in FIG. 5, the processing circuit 53 can calculate the distance from the distance measuring device 1 to the object 90 within a predetermined measurement range. As can be seen from equation (1), the measurement range is calculated by dividing the wavelength of the single-wavelength laser light by λ １ If so, the half wavelength (λ １ / 2).

[0129] In the first measurement, if the measurement range is exceeded, it is not possible to calculate the absolute distance from the distance measuring device 1 to the object 90. For example, in the example shown in Figure 5, the objects 90a, 90b, and 90c are all calculated to be the same distance.

[0130] The wavelength of the single-wavelength laser light is, for example, a wavelength in the near-infrared light band or the visible light band. The near-infrared light band is a wavelength band of approximately 700 nm or more and approximately 2500 nm or less. The visible light band is a wavelength band of approximately 380 nm or more and approximately 780 nm or less. In this case, the measurement range in the first measurement is approximately 190 nm or more and approximately 1250 nm or less. That is, the measurement range in the first measurement is on the order of several hundred nanometers to several micrometers. Thus, the measurement range in the first measurement is relatively narrower than that in the second measurement described below.

[0131] [2-2. Second Measurement (Using Two Wavelengths)] Next, the second measurement, which uses two single-wavelength laser beams having different wavelengths to solve the short measurement range that is an issue with the first measurement, will be described with reference to FIGS. 3 and 6.

[0132] 3, in the distance measuring device 1 according to this embodiment, the light that has interfered in the beam splitter 43 is separated into wavelengths by the dichroic mirror 45 and detected by two photodetectors 47 and 48. As a result, a signal corresponding to the result of the homodyne optical interference for each corresponding wavelength is output from each of the photodetectors 47 and 48. The processing circuit 53 can calculate the distance from the distance measuring device 1 to the object 90 based on the two signals.

[0133] In the second measurement, the two signals are combined to increase the measurement range. The relationship between the position of the object 90 and the measurement range will be described below with reference to FIG.

[0134] 6 is a diagram for explaining the second principle of measurement using two single-wavelength laser beams by the distance measuring device 1 according to this embodiment. In FIG. 6, objects 90a, 90b, and 90c respectively represent the object 90 shown in FIGS. 1 and 3, which are located at different positions. When it is not necessary to distinguish between the positions, the objects will be described as "object 90."

[0135] 6 shows two graphs in which the horizontal axis represents the distance to the object 90 using a predetermined position as a reference point, and the vertical axis represents the distance calculated by the processing circuit 53. Of the two graphs, the upper graph is the same as the graph shown in FIG. 5 and represents the distance calculated based on the signal obtained from one of the two photodetectors 47 and 48. Of the two graphs, the lower graph represents the distance calculated based on the signal obtained from the other of the two photodetectors 47 and 48.

[0136] If you use the two graphs individually, the measurement range will be λ １ / 2 or λ ２ / 2, the order of the measurement range is almost the same as in the first measurement. In the second measurement, the measurement range can be extended by combining the two graphs.

[0137] Specifically, the distances calculated for the objects 90a, 90b, and 90c corresponding to the upper graph are almost the same. However, the distances calculated for the objects 90a, 90b, and 90c corresponding to the lower graph are different. Therefore, by combining the two calculation results, λ １ / 2 and λ ２ / 2. Specifically, the processing circuit 53 calculates the absolute distance from the distance measuring device 1 to the object 90 by combining the first distance obtained by the first measurement and the second distance obtained by the second measurement.

[0138] The measurement range in the second measurement is half the beat wavelength of the two single-wavelength laser beams. For example, if the wavelengths of the two single-wavelength laser beams are λ １ and λ ２ Then, the beat wavelength Λ １２ is expressed by the following equation (2).

[0139]

[0140] This beat wavelength Λ １２ The optical interference due to １２ For example, λ １ and λ２ and are 1550 nm and 1551 nm, respectively, the beat wavelength Λ １２ The distance measurement range in the case of single wavelength interference is about 775 nm, which is on the order of nanometers, whereas the distance measurement range in MWI is expanded to the order of millimeters.

[0141] [2-3. Measurement Accuracy] Next, the measurement accuracy of each of the first measurement and the second measurement will be described.

[0142] The measurement accuracy depends on the wavelength of the single-wavelength laser light used for measurement. Specifically, the shorter the wavelength of the single-wavelength laser light, the higher the measurement accuracy (i.e., the smaller the distance dimension), and the longer the wavelength of the single-wavelength laser light, the lower the measurement accuracy (i.e., the longer the distance dimension).

[0143] When two single-wavelength laser beams are used as in the second measurement, the measurement accuracy depends on the beat wavelength. Specifically, the shorter the beat wavelength, the higher the measurement accuracy (i.e., the smaller the distance dimension), and the longer the beat wavelength, the lower the measurement accuracy (i.e., the longer the distance dimension).

[0144] Since the beat wavelength is longer than the wavelength of the single-wavelength laser light, the second measurement has lower measurement accuracy than the first measurement. １２ Thus, the trade-off between the measurement range and the measurement accuracy is not resolved by simply using the second measurement.

[0145] To resolve this trade-off, MWI achieves both a long measurement range and high measurement accuracy by combining the first measurement and the second measurement. That is, by combining the first measurement, which has a short measurement range but high measurement accuracy, with the second measurement, which has a long measurement range but low measurement accuracy, both a long measurement range and high measurement accuracy are achieved.

[0146] 7 is a diagram showing the measurement range and measurement accuracy of two measurements performed by the distance measuring device 1 according to this embodiment. As shown in FIG. 7, the measurement accuracy in the second measurement (second measurement accuracy) is Am, and the measurement range in the second measurement (second measurement range) is Rm. Furthermore, the measurement accuracy in the first measurement (first measurement accuracy) is As, and the measurement range in the first measurement (first measurement range) is Rs. Both the measurement range and measurement accuracy are expressed in terms of distance, and therefore can be compared.

[0147] As described above and as shown in FIG. 7, Rm > Rs and Am > As hold. Furthermore, in this embodiment, Am ≦ Rs holds. That is, the measurement accuracy Am of the second measurement is equal to or less than the measurement range Rs of the first measurement. This allows a unique combination of the first measurement and the second measurement, making it possible to measure distances with a higher measurement accuracy than the measurement accuracy of the second measurement.

[0148] Here, in order to achieve higher measurement accuracy, it is important to use the accurate value of the wavelength of the laser light L1 used in the first measurement for distance calculation.

[0149] 3. Relationship Between Wavelength and Frequency Stability and Length Measurement Accuracy Next, the relationship between wavelength and frequency stability and length measurement accuracy will be described.

[0150] The wavelength and frequency of the laser light are adjusted by a control unit (not shown) so as to maintain predetermined set values. Specifically, the amount of current supplied to the laser light source and / or the temperature of the laser light source are adjusted to maintain the wavelength constant. In this embodiment, the set wavelength of the light source unit 10 is controlled to be fixed during the measurement period.

[0151] However, due to the characteristics of laser light sources, it is difficult to maintain a completely constant wavelength. As shown in Figure 8, the wavelength of a single-wavelength laser beam changes over time, i.e., fluctuates. Figure 8 is a diagram for explaining the stability of the wavelength of a single-wavelength laser beam. In Figure 8, the horizontal axis represents time, and the vertical axis represents the wavelength or frequency of the single-wavelength laser beam. Figure 8 shows short-term wavelength fluctuations.

[0152] The wavelength fluctuation is represented, for example, by the standard deviation σ shown in Fig. 8. The standard deviation σ can be statistically calculated for the average or median wavelength of the laser light within a finite time period. Note that the wavelength fluctuation may be represented in frequency units instead of wavelength units, or in other units correlated with wavelength.

[0153] As can be seen from the above equation (1), the wavelength λ ｋ When the wavelength fluctuates, a discrepancy occurs between the wavelength of the single-wavelength laser light actually used for measurement and the calculated wavelength. This causes variations in the calculated distance value, which deteriorates the measurement accuracy. Thus, there is a correlation between wavelength fluctuation and measurement accuracy. Specifically, the smaller the fluctuation, the better the measurement accuracy.

[0154] The wavelength stability is expressed as a value that has a negative correlation with the fluctuation of the wavelength of the laser light over time. Specifically, the smaller the fluctuation, the higher the wavelength stability, and the larger the fluctuation, the lower the wavelength stability.

[0155] The laser light source 13a that emits the laser light L1 may be, but is not limited to, a DFB laser light source that has the characteristic of high wavelength (frequency) stability, or a light source device that combines an absorption line of a gas cell and a semiconductor laser as a reference frequency.

[0156] Although DFB lasers have high wavelength stability, if the operating time is long (for example, 30 minutes or more), the wavelength drifts, resulting in poor measurement accuracy. In other words, even if a laser light source with a stable wavelength is used as the light source for emitting the laser light L1, it is not possible to suppress the deterioration of measurement accuracy and long-term stability from a long-term perspective. Note that long-term wavelength fluctuations can be considered as the amount of drift in the peak wavelength.

[0157] In contrast to this, in this embodiment, the processing circuit 53 calculates the wavelength λ based on the first signal S1 output from the reference interference system 30. １Specifically, the processing circuit 53 uses the interference signals S11 and S12 to compare the number of waves in each interference signal, or to perform spectrum comparison by Fourier transform, thereby calculating the wavelength λ １ (See, for example, Patent Document 3.) Then, the processing circuit 53 calculates the calculated wavelength λ １ By using the above, the distance from the distance measuring device 1 to the object 90 is calculated. As a result, even if the wavelength of the laser light L1 fluctuates, the wavelength λ at the time of measurement can be １ Since the distance can be obtained with high accuracy, the measurement accuracy and long-term stability of the distance measuring device 1 can be improved.

[0158] The processing circuit 53 detects the wavelength λ of the laser light L1 used in the first measurement, which requires high accuracy. １ was calculated, but the wavelength λ of the laser light L2 ２ The wavelength λ may be calculated. ２ In order to calculate this, similarly to the laser light L1, the laser light L2 is split into a first light and a second light by the optical splitter 20, the first light is input to the reference interference system 30, and an interference signal is obtained by homodyne interference of the second light.

[0159] Thus, according to this embodiment, the wavelength λ of the laser light L1 １ Even if the wavelength λ calculated based on the first signal S1 from the reference interference system 30 fluctuates, １ Therefore, the wavelength λ used in the actual measurement １ This can be used to calculate the distance, thereby improving the measurement accuracy and long-term stability of the distance measuring device 1.

[0160] 4. Calculation of Absolute Distance An example of a method for calculating the absolute distance from the distance measuring device 1 to the object 90 using two single-wavelength laser beams with MWI will be described below.

[0161] In the second measurement, the phase of each wavelength is calculated based on the signals from the two photodetectors 47 and 48 shown in FIG. 3, and the difference between the phases is taken as the beat wavelength Λ １２ When the above conditions for MWI are met, the beat wavelength Λ １２The rough distance calculated from the phase of １ From the quotient when dividing by, the wavelength λ of the laser light L1 １ At this time, the wavelength λ of the laser light L1 is determined. １ uses a value calculated based on the first signal S1. Next, in the first measurement, the phase φ of the single wavelength is calculated based on a signal from one of the two photodetectors 47 and 48 shown in FIG. 3 (here, photodetector 47). Based on the above results, the absolute distance x is calculated using the following equation (3).

[0162]

[0163] The main cause of the fluctuation component of the calculated distance x is φ, which is due to fluctuation in the wavelength of the first single-wavelength laser beam. １ By using the value obtained by the calculation as above, the accuracy of calculating the absolute distance can be improved. Furthermore, the optimal wavelength combination is one in which the laser light L1 used in the first measurement has the smallest wavelength fluctuation, i.e., the laser with the highest wavelength stability. Although details will be described later, the method according to the present disclosure can be applied in a similar manner even when the number of wavelengths is three or more.

[0164] 5. Operation (Distance Measuring Method) Next, the operation of the distance measuring device 1 according to this embodiment will be described with reference to Fig. 9. Fig. 9 is a flowchart showing the operation of the distance measuring device 1 according to this embodiment.

[0165] 9 , the distance measuring device 1 first acquires a first signal S1 using the reference interference system 30 (S10). Specifically, the light source unit 10 outputs laser light L1 and / or L2 and reference laser light Lr. Of these, the laser light L1 is split into light L1r and light L1t by the optical splitter 20. The reference interference system 30 causes the light L1r and the reference laser light Lr to interfere with each other using homodyne interference, and detects them, thereby outputting interference signals S11 and S12 to the signal processing system 50 as the first signal S1.

[0166] 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 includes the wavelength λ of the laser light L1. １ The generated wavelength information is stored in the memory 52.

[0167] Next, the distance measuring device 1 acquires a second signal S2 using the measurement interferometry system 40 (S12). Specifically, the measurement interferometry system 40 receives the light L1t and the light L2t (laser light L2), and the reflected light L1c and L2c generated when each of these lights is reflected by the object 90. The measurement interferometry system 40 detects the interference between the light L1t and the reflected light L1c by homodyne interference, and also detects the interference between the light L2t and the reflected light L2c by homodyne interference, thereby outputting interference signals S21 and S22 to the signal processing system 50 as the second signal S2.

[0168] 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). １ By using this, the measurement accuracy can be improved.

[0169] If the ranging process is not to be ended (No in S14), the signal processing system 50 determines whether or not to update the wavelength information (S15). The wavelength information is updated, for example, at a predetermined timing. If the wavelength information is to be updated (Yes in S15), the ranging device 1 acquires the first signal (S10) and updates the wavelength information (S11).

[0170] If the wavelength information is not to be updated (No in S15), the distance measuring device 1 acquires a second signal (S12) and calculates the distance (S13). The wavelength information stored in the memory 52 is used in the distance calculation.

[0171] 10 is a diagram showing the relationship between the frequency of updating wavelength information and the frequency of calculating distances, in which arrows indicate the flow of time and triangles indicate the timing at which the corresponding processing is performed.

[0172] The acquisition of the first signal S1 and the updating of the wavelength information are repeated periodically, for example, at predetermined intervals. The frequency of each of the acquisition of the first signal S1 and the updating of the wavelength information is less 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 updating of the wavelength information, it is possible to reduce the power required for the operation of the reference interferometer system 30 and the signal processing system 50.

[0173] If the wavelength information is not updated, the laser light L1 used to acquire the second signal S2 in step S12 will be light emitted at a timing different from that of the laser light L1 used to generate the wavelength information stored in the memory 52. ​​By using a DFB laser light source or the like with little short-term wavelength fluctuation as the laser light source 13a that emits the laser light L1, it is possible to suppress a decrease in the measurement accuracy. Furthermore, according to this embodiment, by updating the wavelength information stored in the memory 52 at a predetermined timing, the long-term wavelength λ of the laser light L1 can be １ fluctuations, i.e., wavelength λ １ Even if a drift of the distance measuring device 1 occurs, the deterioration of the measurement accuracy can be suppressed. This makes it possible to suppress the deterioration of the measurement accuracy and long-term stability of the distance measuring device 1.

[0174] If the fluctuation of the wavelength information over time is small, the wavelength information stored in the memory 52 may be updated after a wavelength deviation of a certain amount or more occurs from the wavelength at the start of measurement. １ If the fluctuation of the wavelength λ exceeds a threshold, the processing circuit 53 may generate wavelength information and update the wavelength information stored in the memory 52. １ is calculated periodically, and the calculated wavelength λ １ The difference between the value of and the initial value at the start of distance measurement or the wavelength set to the laser light source, i.e., the wavelength λ １ If the fluctuation exceeds a threshold, the wavelength information stored in the memory 52 may be updated. Alternatively, the wavelength information may not be updated, and an error may be output using a display unit and / or a voice output unit to warn the user of a measurement error.

[0175] Alternatively, the wavelength information may be updated at the same frequency as the distance calculation frequency. In this case, a laser light source with large wavelength fluctuations can be used as the laser light source 13a. Since an inexpensive laser light source can be used, the cost of the distance measuring device 1 can be reduced.

[0176] Furthermore, if the measurement is for a short period of time, the wavelength information may be updated only once before the start of the measurement, i.e., the process of step S15 may not be executed.

[0177] Note that the wavelength information is not limited to being updated once before the start of measurement. The wavelength information may be updated when a predetermined condition is met. One of the predetermined conditions is, for example, the passage of a certain period of time. Specifically, the wavelength information may be updated periodically, such as once a day, once a week, or once a month. Periods when no measurement is performed may be treated as if there is no wavelength fluctuation.

[0178] Furthermore, one of the predetermined conditions may be that the wavelength drift is outside a threshold range. Specifically, the wavelength of the laser light may be indirectly measured to confirm that the wavelength drift is within a threshold range (e.g., 1 nm / 8 hours), and the wavelength information may be updated when the wavelength drift falls outside the threshold range. Examples of indirect wavelength monitoring methods include measuring changes in the temperature and / or air pressure around the laser light source, or measuring the temperature of the laser light source itself.

[0179] As described above, the distance measuring device 1 according to this embodiment uses homodyne interference instead of heterodyne interference. While heterodyne interference requires a small wavelength interval between the two light beams, homodyne interference does not have wavelength limitations. Therefore, the distance measuring device 1 has the advantage of high wavelength selectivity for each of the laser beams L1 and L2 used for measurement.

[0180] For example, if the object 90 is a lens with an AR (Anti-Reflection) coating, the laser light irradiated onto the object 90 must be outside the visible light band. In this case, it is desirable to use laser light in the widely used communication wavelength band. According to this embodiment, due to high wavelength selectivity, the wavelength of the measurement laser light can be set to the communication wavelength band, and the reference laser light can be set to a shorter wavelength that improves measurement accuracy. In addition to the advantages of being able to optimize the wavelength of the laser light for the sample and improving measurement accuracy, the use of optical elements that are widely used in optical communications, such as those in the communication wavelength band, also enables cost reduction.

[0181] Furthermore, when heterodyne interference is used, it becomes necessary to use the same number of measurement laser light sources and reference laser light sources, which increases the size and cost of the device. In contrast, the distance measuring device 1 according to this embodiment requires only one laser light source 13r as the reference laser light source, which simplifies the configuration of the distance measuring device, making it more compact and less expensive. Furthermore, since a more stable single-wavelength laser, such as a HeNe laser, can be used, the accuracy of wavelength measurement is higher than with other methods, and as a result, the measurement accuracy and long-term stability are higher than with other methods.

[0182] Second Embodiment Next, a second embodiment will be described.

[0183] The distance measuring device according to the second embodiment differs from the first embodiment mainly in that the light source unit includes an adjustment unit that adjusts the wavelength of the laser light. The following description will focus on the differences from the first embodiment, and the description of the commonalities will be omitted or simplified.

[0184] Fig. 11 is a block diagram showing the configuration of a distance measuring device 2 according to this embodiment. As shown in Fig. 11, the distance measuring device 2 differs from the distance measuring device 1 shown in Fig. 1 in that it includes a light source unit 10A instead of the light source unit 10. The light source unit 10A includes an adjustment unit 15 in addition to the configuration of the light source unit 10.

[0185] The adjusting unit 15 adjusts the wavelength of the first laser light L1 based on the wavelength information. The adjusting unit 15 adjusts the wavelength λ of the first laser light L1 by, for example, controlling the operating temperature and / or the applied current of the laser light source 13a of the measurement light source 11. １ As an example, the adjusting unit 15 adjusts the fluctuating (drifting) wavelength λ １ The value of λ is the initial wavelength at the start of measurement. １ The adjustment unit 15 acquires the wavelength information generated by the processing circuit 53, and adjusts the wavelength λ indicated by the acquired wavelength information. １ exceeds the threshold, the wavelength λ １ Adjust the following.

[0186] FIG. 12 is a flowchart showing the operation of the distance measuring device 2 according to this embodiment.

[0187] 12, first, in the distance measuring device 2, the adjustment unit 15 sets the wavelength of the laser light for measurement (S20). Specifically, the adjustment unit 15 sets the wavelength λ of the laser light L1. １ and the wavelength λ of the laser light L2 ２ is set to a predetermined value as an initial value. １ and λ ２ The initial value of is determined based on, for example, the measurement accuracy required for measuring the distance to the object 90 (for example, inspecting the surface shape).

[0188] Next, the distance measuring device 2 acquires a first signal S1 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 the wavelength λ of the laser light L1. １ The generated wavelength information is stored in the memory 52. ​​Note that steps S21 and S22 are the same processes as steps S10 and S11 shown in FIG.

[0189] Next, the adjusting unit 15 adjusts the wavelength λ of the laser light L1. １ Specifically, the adjusting unit 15 adjusts the wavelength λ indicated by the wavelength information stored in the memory 52 (S23). １ Based on this, the wavelength λ １ The value of is the wavelength λ of the laser light L1 １The temperature and / or applied current of the laser light source 13a is adjusted so that the wavelength λ indicated by the wavelength information stored in the memory 52 becomes the initial value. １ and the wavelength λ of the laser light L1 １ If the difference between the initial value and the calculated value is less than the threshold, the adjustment process (S23) may be omitted.

[0190] Next, the distance measuring device 2 acquires the second signal S2 using the measurement interferometer 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). The wavelength λ indicated by the wavelength information is used to calculate the distance. １ By using the above, it is possible to improve the measurement accuracy. Steps S24 and S25 are the same processes as steps S12 and S13 shown in FIG.

[0191] If the distance measurement process is not to be ended (No in S26), the signal processing system 50 １ It is determined whether or not the wavelength λ is to be adjusted (S27). １ The wavelength λ is adjusted, for example, at a predetermined timing. １ When the adjustment of wavelength λ is performed (Yes in S27), the distance measuring device 2 acquires the first signal (S21), generates wavelength information (S22), and adjusts the wavelength λ １ The adjustment (S23) is performed.

[0192] wavelength λ １ If the adjustment is not performed (No in S27), the distance measuring device 2 acquires the second signal (S24) and calculates the distance (S25). The wavelength information stored in the memory 52 is used in the distance calculation.

[0193] In this way, according to the distance measuring device 2 of this embodiment, the wavelength λ of the laser light L1 used for distance measurement １ The adjustment unit 15 further adjusts the wavelength λ of the laser light L2. ２ may be adjusted to further improve the measurement accuracy.

[0194] In addition, the wavelength λ １ Whether or not to adjust the wavelength λ is determined in the same manner as whether or not to update the wavelength information in the first embodiment.１ Alternatively, the wavelength λ may be determined based on the drift amount, which is the fluctuation of the wavelength λ. １ If the measurement is for a short period of time, the adjustment may be performed only once before the start of the measurement, i.e., the process of step S27 may not be executed.

[0195] Third Embodiment Next, a third embodiment will be described.

[0196] The distance measuring device according to embodiment 3 differs from embodiment 1 mainly in that the reference interferometer and the measurement interferometer share an optical interferometer system. The following description will focus on the differences from embodiment 1, and the description of the commonalities will be omitted or simplified.

[0197] Fig. 13 is a block diagram showing the configuration of a distance measuring device 3 according to this embodiment. As shown in Fig. 13, in the distance measuring device 3, the reference interferometer 30 and the measurement interferometer 40 share a single optical interferometer 60, unlike the distance measuring device 1 shown in Fig. 1. In this case, there is no need to split the laser light L1 emitted from the measurement light source 11. Therefore, the distance measuring device 3 does not need to include an optical splitter 20.

[0198] As described above, according to the present embodiment, the number of components included in the distance measuring device 3 can be reduced, thereby realizing a smaller and lighter distance measuring device 3. The operation of the distance measuring device 3 is the same as that of the distance measuring device 1. Furthermore, the light source unit 10 of the distance measuring device 3 may include an adjustment unit 15, similar to the distance measuring device 2 according to the second embodiment.

[0199] (Modifications) Next, modifications of the embodiments will be described. Modifications 1 and 2 described below differ from the respective embodiments mainly in the configuration of the light source unit. Since the configuration other than the light source unit is the same as the respective embodiments, the description will be omitted or simplified.

[0200] [Variation 1] Variation 1 differs from each of the embodiments mainly in that the number of wavelengths of the single-wavelength laser light used for distance measurement is three. The following description will focus on the differences from each of the embodiments, and description of the commonalities will be omitted or simplified.

[0201] Fig. 14 is a block diagram showing the configuration of a light source unit 110 of a distance measuring device according to Modification 1. As shown in Fig. 14, the light source unit 110 includes a measurement light source 111 and a reference light source 12. The measurement light source 111 includes 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 in the embodiment, and therefore a description thereof will be omitted.

[0202] The laser light source 13c is, for example, a semiconductor laser element, and emits laser light of a predetermined single wavelength when a current is supplied. The laser light source 13c is an example of a third laser light source, and emits laser light of a wavelength λ ３ The laser beam L3 has a wavelength λ ３ is an example of a third wavelength, and the laser light L3 is an example of one of the plurality of second laser lights. ３ is the wavelength λ １ and wavelength λ ２ In this embodiment, the wavelength λ ３ is the wavelength λ １ and wavelength λ ２ In this case, for example, the wavelength λ ３ and wavelength λ １ The difference between this and wavelength λ ２ and wavelength λ １ The difference between the two wavelengths may be set to 10 times or more. By providing a large difference between the two wavelengths, the difference in beat wavelength can be increased. As a result, the measurement range and measurement accuracy can be set in stages, allowing the absolute distance to be measured with high accuracy.

[0203] The wavelength combining system 14 combines the laser beams L1, L2, and L3 emitted from the three laser light sources 13a, 13b, and 13c, respectively. The wavelength combining system 14 is, for example, a DWDM element or a holographic optical element.

[0204] The configuration of the distance measuring device according to this modification, other than the light source unit 110, is the same as that of the distance measuring device 1 shown in Fig. 1, the distance measuring device 2 shown in Fig. 11, or the distance measuring device 3 shown in Fig. 13. At this time, the optical detection system 42 of the measurement interference system 40 detects a wavelength λ ３Alternatively, the optical detection system 42 may detect the beat light by heterodyne interference.

[0205] When three single-wavelength laser beams having different wavelengths can be used as in this modification, there are three combinations of two single-wavelength laser beams. Therefore, the second measurement can be performed based on at least one of the three combinations. Specifically, １ Laser light L1 and wavelength λ ２ The beat wavelength Λ due to interference with the laser light L2 １２ , wavelength λ １ Laser light L1 and wavelength λ ３ The beat wavelength Λ due to interference with the laser light L3 １３ , and wavelength λ ３ Laser light L3 and wavelength λ ２ The beat wavelength Λ due to interference with the laser light L2 ２３ The second measurement can be performed with a length measurement accuracy and a length measurement range that correspond to at least one of the above.

[0206] The beat wavelength Λ １２ is expressed by equation (2). In addition, the beat wavelength Λ １３ and Λ ２３ are respectively expressed by the following equations (4) and (5).

[0207]

[0208] In this modification, λ １ <λ ２ <λ ３ Also, |λ １ -λ ３ | is | λ １ -λ ２ Simply put, λ １ ≒λ ２ As a result, the beat wavelength Λ １２ and beat wavelength Λ １３ For example, λ １ , λ ２ , λ ３are set to 1550 nm, 1551 nm, and 1600 nm, respectively. In this case, from equations (2) and (4), the beat wavelength Λ １２ is the beat wavelength Λ, which is about 2.4 mm. １３ is about 50 μm. １ ≒λ ２ Therefore, the beat wavelength Λ １３ is the beat wavelength Λ ２３ is approximately equal to

[0209] The processing circuit 53 according to this modification uses the beat wavelength Λ １２ ,Λ １３ and Λ ２３ The processing circuit 53 performs a second measurement using two of the first and second distances, and combines the result of the first measurement with the result of the first measurement to calculate the distance from the distance measuring device to the object 90. Specifically, the processing circuit 53 calculates the absolute distance from the distance measuring device to the object 90 by combining the first distance obtained by the first measurement and the two second distances obtained by the second measurement.

[0210] The processing circuit 53 uses a beat wavelength based on the laser light having the smallest fluctuation in wavelength and frequency among all the single-wavelength laser lights emitted by the light source unit 110. In this example, since the wavelength fluctuation of the laser light L1 is smallest, the beat wavelength Λ １３ and beat wavelength Λ １２ In the first measurement, the processing circuitry 53 also uses the interference result of the laser light with the smallest wavelength fluctuation among all the single-wavelength laser lights emitted by the light source unit 110.

[0211] Here, if the absolute distance from the probe to the measurement object is denoted by x, the absolute distance x is expressed by the following equation (6).

[0212] (6) x = (A × Λ １３ +B×λ １ +θ ｉ ×λ １ ) / 2

[0213] A and B are the absolute distance x from the probe to the first location of the object 90, respectively. ｉ Beat wavelength Λ contained within １２ and wavelength λ １ Also, θｉ corresponds to the positions of the first portion, the second portion, and the third portion of the object 90, and the wavelength λ obtained in the first measurement １ represents the phase of the interference result based on the above equation (6). Note that equation (6) corresponds to equation (3) expanded to three wavelengths. Note that the first portion, the second portion, and the third portion are different portions on the surface of the object 90.

[0214] The second measurement is performed with a combination that results in the longest beat wavelength. The distance calculated in this second measurement is an example of a third distance calculated with a third measurement accuracy within a third measurement range. Note that the third measurement accuracy is lower than the second measurement accuracy and the first measurement accuracy. The third measurement range is longer than the second measurement range and the first measurement range. Simply put, the second measurement is performed with a combination that results in the longest measurement range.

[0215] Here, the processing circuit 53 detects the wavelength λ １ and wavelength λ ２ Based on the combination of １２ The processing circuit 53 determines the phase of the determined beat wavelength Λ. １２ Based on the phase of １３ Specifically, the wave number A of the beat wavelength Λ is counted. １２ The distance calculated based on the beat wavelength Λ １３ The beat wavelength Λ is calculated using the components of the quotient obtained by dividing by １３ The wave number A is calculated.

[0216] Furthermore, the processing circuitry 53 measures the wavelength λ as the second measurement. １ and wavelength λ ３ Based on the combination of １３ The processing circuit 53 determines the phase of the determined beat wavelength Λ. １３ Based on the phase of １ Specifically, the wave number B of the beat wavelength Λ is counted. １３ The distance calculated based on the wavelength λ １ By dividing by the wavelength λ １ The wave number B is calculated.

[0217] Finally, the processing circuitry 53 calculates the wavelength λ as the first measurement. １ Phase θ １ The processing circuit 53 determines the wave numbers A and B and the wavelength λ １ Phase θ １ Based on this, the absolute distance x is calculated by the above equation (6). ｉ can be calculated.

[0218] As described above, by performing a plurality of second measurements using a plurality of beat wavelengths, the measurement range can be further expanded.

[0219] Note that the absolute distance may be calculated by a method other than the above. For example, the excess fraction method may be used, which calculates the absolute distance by matching the phase combination of all wavelengths of the laser used.

[0220] [Modification 2] Modification 2 differs from each of the embodiments mainly in that the reference laser light emitted by the reference light source 12 is used for distance measurement. The following description will focus on the differences from each of the embodiments, and the description of the commonalities will be omitted or simplified.

[0221] Fig. 15 is a block diagram showing the configuration of a distance measuring device 201 according to Modification 2. As shown in Fig. 15, the distance measuring device 201 is different from the distance measuring device 1 shown in Fig. 1 in that it includes a light source unit 210 instead of the light source unit 10. The light source unit 210 includes a laser light source 13a and a laser light source 13r. The light source unit 210 may also include a wavelength combining system 14.

[0222] As shown in FIG. 2 , the laser light source 13r is a light source that emits a reference laser light Lr. In this modification, the reference laser light Lr is input not only to the reference interferometry system 30 but also to the measurement interferometry system 40. That is, the reference laser light Lr is also used as a 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 interferometry system 30 and light L2t that is input to the measurement interferometry system 40. Therefore, the reflected light L2c of the reference laser light Lr that is reflected by the object 90 is input to the measurement interferometry system 40.

[0223] This allows the number of light sources included in the light source unit 210 to be reduced, thereby achieving a smaller and lighter range finding device 201. The operation of the range finding device 201 is the same as that of the range finding device 1. In addition, the range finding device 201 may have the light source unit 210 including the adjustment unit 15, similar to the range finding device 2 according to the second embodiment.

[0224] While the distance measuring device according to one or more aspects has been described above based on the embodiments, the present disclosure is not limited to these embodiments. As long as they do not deviate from the gist of the present disclosure, various modifications conceivable by a person skilled in the art to the present embodiments and embodiments constructed by combining components of different embodiments are also included within the scope of the present disclosure.

[0225] For example, in the above-described embodiment and modified example, the processing circuitry 53 calculates the absolute distance from the distance measuring device to the object 90. However, this is not limiting. After calculating the first distance and the second distance, the processing circuitry 53 may output the calculated first distance and the second distance to another device. For example, the processing circuitry 53 may transmit the first distance and the second distance to another computer, causing the other computer to calculate the absolute distance. Alternatively, the processing circuitry 53 may transmit the first distance and the second distance to a display and display them on the display, or may output them to a printer and print them on a medium such as paper. This allows the first distance and the second distance to be presented to a user, allowing the user to manually calculate the absolute distance. In this way, the processing circuitry 53 does not need to calculate the absolute distance.

[0226] Furthermore, the wavelength of at least one of the two single-wavelength laser beams may be changeable. For example, the wavelength of the laser beam with the larger wavelength fluctuation may be swept. This allows the combination of the two wavelengths to be changed, thereby achieving a measurement range and measurement accuracy suitable for the target object 90. Furthermore, the device can be made more compact than when three or more laser light sources are provided.

[0227] Alternatively, one laser beam split from a single wavelength laser beam into two and the other laser beam with a shifted frequency may be used as the two single wavelength laser beams. As a means for shifting the frequency, for example, an acousto-optic modulator (AOM) can be used.

[0228] The first laser beam emitted by the measurement light source 11 may be a laser beam containing multiple single modes. For example, the first laser beam may be an optical frequency comb laser beam. An optical frequency comb laser beam has a spectrum consisting of discrete, evenly spaced frequency lines.

[0229] Furthermore, the wavelength fluctuation does not have to be the standard deviation σ. For example, the wavelength fluctuation may be 3σ. Alternatively, the wavelength fluctuation may be the dispersion σ of the frequency of the laser light within a finite time. ２ Alternatively, the wavelength fluctuation may be the difference between the maximum and minimum wavelength values ​​of the laser light within a finite period of time.

[0230] Furthermore, when the light source unit includes three or more laser light sources, two of the laser light sources may emit single-wavelength laser light of the same wavelength. Furthermore, the frequency fluctuations of the two single-wavelength laser light of the same wavelength may be the same. The first measurement may use one of the two single-wavelength laser light of the same wavelength, and the second measurement may use the other of the two single-wavelength laser light of the same wavelength. In other words, the first single-wavelength laser light used in each of the first and second measurements may be laser light emitted from different laser light sources.

[0231] Furthermore, the measurement accuracy Am of the second measurement may be greater than the measurement range Rs of the first measurement. When the difference between the measurement accuracy Am of the second measurement and the measurement range Rs of the first measurement is small, i.e., Am > Rs, it is possible to measure the distance with an accuracy substantially equivalent to that when Am ≦ Rs.

[0232] Furthermore, for example, the wavelength information may be information indicating the spectrum of the laser light, rather than the peak wavelength of the laser light.

[0233] Furthermore, the general or specific aspects of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, or a computer program. Alternatively, the general or specific aspects may be realized as a computer-readable non-transitory recording medium such as an optical disk, a HDD, or a semiconductor memory on which the computer program is stored. Alternatively, the general or specific aspects of the present disclosure may be realized as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium.

[0234] Furthermore, various modifications, substitutions, additions, omissions, etc. can be made to the above-described embodiments within the scope of the claims or their equivalents.

[0235] The present disclosure can be used as a distance measuring device that can suppress deterioration in measurement accuracy and long-term stability, and can be used, for example, in a surface shape inspection device.

[0236] 1, 2, 3, 201 Distance measuring device 10, 10A, 110, 210 Light source unit 11, 111 Measurement light source 12 Reference light source 13a, 13b, 13c, 13r Laser light source 14 Wavelength combining system 15 Adjustment unit 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 Movable mirror 36a, 36b Reflecting surface 37, 38, 47, 48 Photodetector 40 Measurement interference system 45 Dichroic mirror 50 Signal processing system 51 Signal receiving unit 52 Memory 53 Processing circuit 90, 90a, 90b, 90c Object

Claims

1. A distance measuring device comprising: a light source unit that emits a first laser light and a reference laser light; a reference interference system that detects a first interference light generated by interfering with the first laser light and a second interference light generated by interfering with the reference laser light and outputs a first signal; a measurement interference system that receives a 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 regarding 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; wherein in the reference interference system, the optical path of the first laser light and the optical path of the reference laser light are arranged so that the first laser light and the reference laser light do not interfere with each other.

2. The distance measuring device of claim 1, wherein the light source unit further emits a second laser light having a wavelength different from that of the first laser light, and the measurement interference system further receives second reflected light generated when the second laser light is reflected by the object.

3. A distance measuring device as described in claim 2, wherein the wavelength of the reference laser light is shorter than the wavelength of the first laser light.

4. The distance measuring device of claim 2, wherein the measurement interference system includes: a first optical interference system that causes the first laser light and the first reflected light to interfere with each other, and that causes the second laser light and the second reflected light to interfere with each other, and that emits a third interference light generated by the interference between the first laser light and the first reflected light, and that causes the second laser light and the second reflected light to interfere with each other, and a first optical detection system that detects the third interference light and the fourth interference light and outputs the second signal.

5. The distance measuring device of claim 1, wherein the light source unit further emits a plurality of second laser beams, the wavelengths of the plurality of second laser beams being different from one another, and the wavelength of each of the plurality of second laser beams being different from the wavelength of the first laser beam, and the measurement interference system further receives a plurality of second reflected beams generated by the plurality of second laser beams being reflected by the object.

6. A distance measuring device as described in claim 1, further comprising an optical splitter that splits the first laser light emitted from the light source unit into a first part and a second part, inputs the first part to the reference interference system, and inputs the second part to the measurement interference system.

7. The distance measuring device of claim 1, wherein the reference interference system includes: a second optical 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 emit the second interference light generated by the interference of the reference laser light; and a second optical detection system that detects the first interference light and the second interference light and outputs the first signal.

8. A distance measuring device as described in claim 7, wherein the reference interference system further includes an optical path difference changing mechanism that changes the difference between the optical path length of the first laser light passing through the second optical interference system and the optical path length of the reference laser light passing through the second optical interference system.

9. A distance measuring device as described in any one of claims 1 to 8, wherein the signal processing system generates the wavelength information indicating the peak wavelength by calculating the peak wavelength of the first laser light based on the first signal.

10. A distance measuring device as described in any one of claims 2 to 4, 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.

11. The distance measuring device according to any one of claims 1 to 8, wherein the signal processing system updates the wavelength information when a predetermined condition is satisfied.

12. A distance measuring device as described in any one of claims 1 to 8, wherein the signal processing system includes a memory for storing the generated wavelength information, the frequency with which the signal processing system generates the wavelength information is less than the frequency with which the signal processing system calculates the distance, and the signal processing system calculates the distance based on the wavelength information stored in the memory and the second signal.

13. The distance measuring device according to claim 12, wherein the signal processing system generates the wavelength information and updates the wavelength information stored in the memory when fluctuations in the wavelength of the first laser light exceed a threshold value.

14. A distance measuring device according to any one of claims 1 to 8, wherein the light source unit includes an adjustment unit that adjusts the wavelength of the first laser light based on the wavelength information.

15. A distance measuring device according to any one of claims 1 to 8, wherein the first laser light is a laser light including a plurality of single modes.

16. A distance measuring device according to any one of claims 1 to 8, wherein the reference interferometer and the measurement interferometer share an optical interferometer.

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