Distance measuring device

Abstract

A distance measuring device includes: a light source unit that emits a first laser beam and a reference laser beam; a reference interference system for detecting first interference light generated by interference of the first laser light and second interference light generated by interference of the reference laser light, and outputting a first signal; a measurement interference system to which first reflected light generated by reflecting the first laser light by the object is input, and which outputs a second signal; and a signal processing system that generates wavelength information relating to the wavelength of the first laser beam on the basis of the first signal, and calculates the distance from the distance measuring device to the object on the basis of the wavelength information and the second signal, and in the reference interference system, the optical path of the first laser beam and the optical path of the reference laser beam are arranged so that the first laser beam and the reference laser beam do not interfere with each other.

Description

Technical Field

[0001] This disclosure relates to a ranging device. Background Technology

[0002] Optical interferometry using lasers is widely used as a means to obtain information representing the distance and / or shape of objects non-contactly. As an example, frequency-modulated continuous wave radar (FMCW) LiDAR (Light Detection and Ranging) is well-known as a three-dimensional measurement device with millimeter-level precision. Furthermore, optical interferometry using optical coherence tomography (OCT) or optical combs is well-known as a means to measure with micrometer-level precision. These are widely used in the medical and / or industrial fields.

[0003] Furthermore, by controlling optical interference phenomena with greater precision, measurements at the nanometer level become possible. For example, measurements using a Michelson interferometer system employing a single-wavelength laser are one method for measuring differences in distances at the nanometer level.

[0004] While nanometer-precision optical measurement, exemplified by homodyne optical interference, enables high-precision, non-contact measurements, it suffers from limitations such as a measurement range being restricted to half the wavelength (submicron units). Therefore, it remains difficult to measure samples with structures exhibiting both nanometer-scale and tens of micrometer-scale features.

[0005] As a solution to this problem, it is hoped that optical interferometry using two or more single-wavelength lasers, i.e., multi-wavelength interferometry, can eliminate the trade-off between the length measurement range and the length measurement accuracy that exists in the current problem, and achieve both a longer length measurement range and higher length measurement accuracy.

[0006] For example, in Patent Documents 1 and 2, by combining the optical interference results of lasers with different wavelengths, it is possible to eliminate the trade-off between the length measurement range and the length measurement accuracy, which are existing problems, and to achieve both a long length measurement range and high length measurement accuracy at the same time.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2021-148634 Patent Document 2: International Publication No. 2008 / 146480 Patent Document 3: Japanese Utility Model Application Publication No. 5-14867 Summary of the Invention

[0008] The problem that the invention aims to solve In distance measurement methods that utilize laser interferometry, the wavelength of the laser fluctuates over time, affecting the calculated distance information. Specifically, this results in reduced measurement accuracy and decreased stability of the measurement results due to long measurement periods.

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

[0010] Methods used to solve problems A ranging device according to the present disclosure comprises: a light source unit that emits a first laser and a reference laser; a reference interferometry system that detects a first interference light generated by interfering with the first laser and a second interference light generated by interfering with the reference laser, and outputs a first signal; a measuring interferometry system that receives a first reflected light generated by the first laser being reflected by an object, and outputs a second signal; and a signal processing system that generates wavelength information related to the wavelength of the first laser based on the first signal, and calculates the distance from the ranging 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 and the reference laser are configured such that the first laser and the reference laser do not interfere with each other.

[0011] Invention Effects According to this disclosure, it is possible to suppress the decline in length measurement accuracy and long-term stability. Attached Figure Description

[0012] Figure 1 This is a block diagram showing the structure of the ranging device according to Embodiment 1.

[0013] Figure 2 This is a block diagram showing the structure of the light source section of the ranging device according to Embodiment 1.

[0014] Figure 3 This is a diagram showing the specific structure of the interferometric system for measuring distances according to Embodiment 1.

[0015] Figure 4 This is a diagram showing the specific structure of the reference interferometric system for the ranging device in Embodiment 1.

[0016] Figure 5 This is a diagram illustrating the principle of a first measurement using a single-wavelength laser, performed by a ranging device according to Embodiment 1.

[0017] Figure 6This is a diagram illustrating the principle of a second measurement using multiple single-wavelength lasers performed by the ranging device of Embodiment 1.

[0018] Figure 7 This is a diagram showing the length measuring range and length measuring accuracy of two measurements performed by the distance measuring device of Embodiment 1.

[0019] Figure 8 It is a graph used to illustrate the stability of the wavelength and frequency of a single-wavelength laser.

[0020] Figure 9 This is a flowchart illustrating the operation of the ranging device according to Embodiment 1.

[0021] Figure 10 This is a graph showing the relationship between the frequency of wavelength information updates and the frequency of distance calculations.

[0022] Figure 11 This is a block diagram showing the structure of the ranging device according to Embodiment 2.

[0023] Figure 12 This is a flowchart illustrating the operation of the ranging device according to Embodiment 2.

[0024] Figure 13 This is a block diagram showing the structure of the ranging device according to Embodiment 3.

[0025] Figure 14 This is a block diagram showing the structure of the light source section of the ranging device in a modified embodiment of the relevant implementation.

[0026] Figure 15 This is a block diagram showing the structure of the ranging device in the second variation of the implementation method. Detailed Implementation

[0027] (Summary of this disclosure) First, the following are the definitions of the main terms used in this specification.

[0028] "Length measurement accuracy" refers to the degree of accuracy in measuring distance. In other words, length measurement accuracy is a measure of how accurately distance information can be obtained. Therefore, the higher the length measurement accuracy, the more accurate the measurement can be.

[0029] "Measuring range" refers to the range of distance directions from which unique distance information can be obtained. In other words, measuring range indicates the range within which distance measurement (distance finding) can be performed.

[0030] In this specification, both measurement accuracy and measurement range are expressed in the same dimension as distance. Specifically, the units for both measurement accuracy and measurement range are expressed in nanometers (nm), micrometers (μm), millimeters (mm), etc. Therefore, "high measurement accuracy" is synonymous with "shorter measurement accuracy" expressed in the dimension of distance. "Low measurement accuracy" is synonymous with "longer measurement accuracy" expressed in the dimension of distance. Furthermore, in this specification, measurement accuracy is sometimes simply referred to as "accuracy," and measurement range is sometimes simply referred to as "range."

[0031] Distance measurement within the measuring range is called "absolute distance measurement". For example, distance measurement with an accuracy of 10 nm and a measuring range of 1 mm is an absolute distance measurement that can distinguish a difference of 10 nm within a 1 mm range.

[0032] "Long-term stability" means that the temporal variation is sufficiently small from the start to the end of the measurement, allowing for consistent length measurement accuracy. For example, if the wavelength of the laser fluctuates over time, long-term stability decreases. Decreased long-term stability can lead to problems such as limitations on the measurement duration.

[0033] Several technical solutions related to the ranging device disclosed herein are described below.

[0034] The ranging device of the first technical solution of this disclosure includes: a light source unit that emits a first laser and a reference laser; a reference interferometry system that detects a first interference light generated by interfering with the first laser and a second interference light generated by interfering with the reference laser, and outputs a first signal; a measuring interferometry system that receives a first reflected light generated by the first laser being reflected by an object, and outputs a second signal; and a signal processing system that generates wavelength information related to the wavelength of the first laser based on the first signal, and calculates the distance from the ranging device to the object based on the wavelength information and the second signal, wherein the optical paths of the first laser and the reference laser in the reference interferometry system are configured such that the first laser and the reference laser do not interfere with each other.

[0035] Therefore, even if the laser wavelength fluctuates, the actual wavelength of the laser used in the measurement can be obtained based on the wavelength information, or an equivalent value. This allows the wavelength fluctuations to be fed back into the distance calculation, suppressing the decline in measurement accuracy and long-term stability.

[0036] Regarding the ranging device of the second technical solution of this disclosure, compared with the ranging device of the first technical solution, in the ranging device of the second technical solution, the light source unit may further emit a second laser with a wavelength different from the first laser, and the measuring interference system may further be input with second reflected light generated by the object reflected by the second laser.

[0037] Therefore, it is possible to perform distance measurement using multi-wavelength interferometry (MWI), which utilizes light of multiple wavelengths. This allows for high measurement accuracy and a large measurement range.

[0038] Alternatively, the reference interferometer system can detect the interference light generated by interfering the second laser and the interference light generated by interfering the reference laser, and output a third signal. The signal processing system generates second wavelength information related to the wavelength of the second laser based on the third signal. Based on the wavelength information related to the wavelength of the first laser, i.e., the first wavelength information, the second wavelength information, and the second signal, the distance from the ranging device to the object can be calculated.

[0039] Furthermore, generating second wavelength information is not always necessary when using a second laser. For example, if the wavelength fluctuation of the first laser is smaller than that of the second laser, high measurement accuracy can be ensured based on the interference results of the first laser. Therefore, even without obtaining second wavelength information related to the wavelength of the second laser, high measurement accuracy and a large measurement range can be achieved.

[0040] Regarding the ranging device of the third technical solution of this disclosure, compared with the ranging device of the second technical solution, in the ranging device of the third technical solution, the wavelength of the reference laser may also be shorter than the wavelength of the first laser.

[0041] Therefore, it is possible to measure the wavelengths of multiple lasers used in MWI, thus improving the measurement accuracy even when the measurement range is expanded.

[0042] Regarding the ranging device of the fourth technical solution of this disclosure, compared with the ranging devices of the second or third technical solutions, the ranging device of the fourth technical solution may also include the measuring interferometric system comprising: a first optical interferometric system that causes the first laser to interfere with the first reflected light and emits a third interference light generated by the interference of the first laser and the first reflected light, and causes the second laser to interfere with the second reflected light and emits a fourth interference light generated by the interference of the second laser 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.

[0043] Therefore, it is possible to achieve zero-difference optical interference for each wavelength, obtaining the interference signal of each wavelength as a second signal with good accuracy. By combining the interference signals of each wavelength, the length measurement range can be increased. For details, please refer to the following: Figure 6 As will be explained later.

[0044] Furthermore, in the technology described in Patent Document 1, a photodetector is used to detect a beat signal by heterodyne interference between the length measuring laser and the reference laser, and the result of length measurement using the length measuring laser is corrected based on the result. Since the wavelength difference between the two lasers needs to be reduced as a condition for heterodyne interference, the selection of the wavelength of the length measuring laser is limited by the reference laser.

[0045] HeNe lasers are commonly used lasers with stabilized wavelengths. However, in heterodyne interferometry, the wavelength of the laser used for length measurement is limited to around 633 nm, which is the wavelength of HeNe lasers. Optical components suitable for wavelengths around 633 nm are expensive, and there are difficulties in measuring objects such as viewing lenses with AR coatings. Furthermore, since multiple lasers with different wavelengths are used for length measurement in MWI, the same number of reference laser sources are also required. In contrast, in the distance measuring device of this technical solution, since zero-difference interferometry is used, the absolute value of the difference between the wavelengths of the two lasers used in the measurement can be larger compared to the case of heterodyne interferometry, thus improving the wavelength selectivity of the two lasers. For example, since a wavelength suitable for measuring the object can be selected, the decrease in the length measurement accuracy and long-term stability of the object can be suppressed. In addition, regardless of the number of wavelengths of the measuring laser, only one reference laser source is needed. As a result, the structure of the distance measuring device can be simplified, miniaturized, and the cost reduced. Furthermore, since more stable single-wavelength lasers, such as HeNe lasers, can be used, the accuracy of wavelength measurement is higher compared to other methods. As a result, the length measurement accuracy and long-term stability are higher compared to other methods.

[0046] Regarding the ranging device of the fifth technical solution of this disclosure, compared with the ranging device of the first technical solution, in the ranging device of the fifth technical solution, the light source unit may further emit a plurality of second lasers; the wavelengths of the plurality of second lasers may also be different from each other; the wavelength of each of the plurality of second lasers may also be different from the wavelength of the first laser; the measuring interference system may further be input with a plurality of second reflected light generated by the reflection of the plurality of second lasers by the object.

[0047] Therefore, lasers with wavelengths of three or more can be used for measurement. This allows for a further expansion of the length measurement range.

[0048] Regarding the ranging device of the sixth technical solution of this disclosure, the ranging device of any of the first to fifth technical solutions may further include an optical splitter (beam splitter) that divides the first laser emitted from the light source into a first part and a second part, so that the first part is input to the reference interferometric system and the second part is input to the measuring interferometric system.

[0049] Thus, a portion of the first laser used in the measurement can be input into the reference interferometric system with a simple structure.

[0050] Regarding the ranging device of the seventh technical solution of this disclosure, for the ranging device of any of the first to sixth technical solutions, in the ranging device of the seventh technical solution, the reference interferometric system may also include: a second optical interferometric system that causes the first laser to interfere and emits the first interference light generated by the interference of the first laser, causes the reference laser to interfere and emits the second interference light generated by the interference of the reference laser; and a second optical detection system that detects the first interference light and the second interference light and outputs the first signal.

[0051] Therefore, it is possible to perform zero-difference interference of light at each wavelength, obtaining the interference signal of the first laser and the interference signal of the reference laser as the first signal with good accuracy. This improves the calculation accuracy based on the wavelength of the first signal. Compared to the case using heterodyne interference, the absolute value of the difference between the wavelengths of the two lasers used in the measurement can be larger, thus improving the wavelength selectivity of the two lasers. For example, since a wavelength suitable for the measurement of the object can be selected, the decrease in the measurement accuracy and long-term stability of the object can be suppressed. Furthermore, regardless of the number of wavelengths of the lasers used for measurement, only one reference laser source is needed, thus simplifying, miniaturizing, and reducing the cost of the ranging device. Moreover, since a more stable single-wavelength laser, such as the HeNe laser, can be used, the measurement wavelength accuracy is higher compared to other methods, resulting in higher measurement accuracy and long-term stability compared to other methods.

[0052] Regarding the ranging device of the eighth technical solution of this disclosure, compared with the ranging device of the seventh technical solution, in the ranging device of the eighth technical solution, the reference interferometric system may further include an optical path difference changing mechanism, which changes the difference between the optical path length of the first laser passing through the second optical interferometric system and the optical path length of the reference laser passing through the second optical interferometric system.

[0053] Therefore, by adjusting the optical path difference, it is possible to generate intensity changes in the interference signals of both the first laser and the reference laser. Based on these intensity changes, the wavelength of the first laser can be calculated with high accuracy. Furthermore, changing the optical path length difference is not mandatory. It is also possible to monitor the interference signals of the first laser and the reference laser separately without changing the optical path length difference.

[0054] Furthermore, the spectral information of the first laser and the reference laser is calculated using the interference signal. If it is assumed that the spectral intensity of the first laser and the reference laser has Gaussian characteristics, then the wavelength required for the length measurement calculation is the peak wavelength of each laser.

[0055] Therefore, regarding the ranging device of the ninth technical solution of this disclosure, for the ranging device of any of the first to eighth technical solutions, in the ranging device of the ninth technical solution, the signal processing system can also calculate the peak wavelength of the first laser based on the first signal, thereby generating the wavelength information representing the peak wavelength.

[0056] Therefore, it is not necessary to obtain the laser's spectra, thus reducing the complexity of components and computational processing required for optical detection. This enables the miniaturization and weight reduction of the ranging device due to the simplification of component structure, as well as the reduction of power consumption related to computation due to the reduction of computational processing load.

[0057] Regarding the ranging device of the tenth technical solution of this disclosure, for the ranging device of any of the second to fourth technical solutions, in the ranging device of the tenth technical solution, the signal processing system can also calculate the peak wavelength of the first laser and the peak wavelength of the second laser based on the first signal, thereby generating wavelength information representing the peak wavelength of the first laser and the peak wavelength of the second laser.

[0058] Therefore, not only the wavelength of the first laser, but also the wavelength of the second laser used in the actual measurement, or its equivalent value, can be used for distance calculation, thus improving the length measurement accuracy even in the case of MWI.

[0059] Regarding the ranging device of the eleventh technical solution of this disclosure, for the ranging device of any of the first to tenth technical solutions, in the ranging device of the eleventh technical solution, the signal processing system can also update the wavelength information when the specified conditions are met.

[0060] Therefore, wavelength information can be updated at appropriate times (timed updates). By suppressing updates to unnecessary wavelength information, the computational cost, i.e., computation time and / or power consumption, required for updating wavelength information can be reduced.

[0061] Regarding the ranging device of the twelfth technical solution of this disclosure, for the ranging device of any of the first to eleventh technical solutions, in the ranging device of the twelfth technical solution, the signal processing system may also include a memory for storing the generated wavelength information; the frequency at which the signal processing system generates the wavelength information may also be less than the frequency at which the signal processing system calculates the distance; the signal processing system may also calculate the distance based on the wavelength information stored in the memory and the second signal.

[0062] Therefore, for example, when the long-term fluctuation of wavelength progresses smoothly, the frequency of wavelength information generation can be reduced. Furthermore, the computational cost of generating wavelength information is generally higher than that of length measurement. By reducing the frequency of wavelength information generation, computational costs can be suppressed.

[0063] Regarding the ranging device of the thirteenth technical solution of this disclosure, and the ranging device of the twelfth technical solution, in the ranging device of the thirteenth technical solution, the signal processing system may also generate the wavelength information and update the wavelength information stored in the memory when the fluctuation (undulation) of the wavelength of the first laser exceeds a threshold.

[0064] This reduces the frequency of wavelength information generation, thus suppressing the power consumption required for wavelength information generation. For example, it allows for wavelength information updates even when wavelength fluctuations occur to the extent that they affect distance calculation results. In other words, wavelength information can be updated efficiently with minimal wasted time (timing).

[0065] Regarding the ranging device of the fourteenth technical solution of this disclosure, for the ranging device of any of the first to thirteenth technical solutions, in the ranging device of the fourteenth technical solution, the light source unit may also include an adjustment unit that adjusts the wavelength of the first laser based on the wavelength information.

[0066] Therefore, for example, it is possible to restore the fluctuating wavelength, thus improving the accuracy of length measurement.

[0067] Regarding the ranging device of the fifteenth technical solution of this disclosure, for the ranging device of any of the first to fourteenth technical solutions, in the ranging device of the fifteenth technical solution, the first laser may also be a laser including multiple single modes.

[0068] Therefore, it is also possible to use lasers other than single-wavelength lasers.

[0069] Regarding the ranging device of the sixteenth technical solution of this disclosure, for the ranging device of any of the first to fifteenth technical solutions, in the ranging device of the sixteenth technical solution, the reference interferometric system and the measuring interferometric system may also share an optical interferometric system.

[0070] This enables the miniaturization and weight reduction of ranging devices.

[0071] Regarding the seventeenth technical solution of this disclosure, compared with the distance measuring device of the first technical solution, in the distance measuring device of the seventeenth technical solution, the measuring interferometer system can also be input as a third reflected light generated by the reference laser being reflected by the object.

[0072] This reduces the number of laser light sources, thus enabling the miniaturization and weight reduction of the ranging device.

[0073] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings.

[0074] Furthermore, the embodiments described below are inclusive or specific examples. The numerical values, shapes, materials, constituent elements, arrangement and connection methods of constituent elements, steps, and order of steps shown in the following embodiments are examples and are not intended to limit this disclosure. Moreover, any constituent elements in the following embodiments that are not described in the independent claims are treated as arbitrary constituent elements.

[0075] Furthermore, the figures are schematic diagrams and not necessarily rigorous representations. Therefore, for example, the scales may not be consistent across figures. Additionally, substantially identical structures are assigned the same labels across figures, and repetitive explanations are omitted or simplified.

[0076] 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 merely expressions in a strict sense, but also imply expressions that include substantially equivalent ranges, such as differences of a few percentage points.

[0077] Furthermore, in this specification, ordinal numbers such as "first" and "second" do not refer to the quantity or order of constituent elements unless specifically negated. Rather, they are used to avoid confusion among similar constituent elements and to distinguish them.

[0078] (Implementation Method 1) [1. Structure of the ranging device] First, use Figure 1 The structure of the ranging device according to Embodiment 1 is described. Figure 1 This is a block diagram showing the structure of the ranging device 1 according to this embodiment.

[0079] Figure 1 The distance measuring device 1 shown is a device for measuring the distance to an object 90. For example, by measuring the distance to each part of the object 90, the distance measuring device 1 can obtain information indicating the surface shape of the object 90. Therefore, the distance measuring device 1 can be used, for example, for the appearance inspection of products, etc.

[0080] like Figure 1 As shown, the ranging device 1 includes a light source unit 10, an optical splitter 20, a reference interferometer system 30, a measuring interferometer system 40, and a signal processing system 50. Furthermore, although not shown, the ranging device 1 may also include a support unit for supporting the object 90. The support unit may include, for example, a drive unit such as a motor or piezoelectric element, capable of changing the posture and / or position of the object 90.

[0081] In addition, Figure 1In the diagram, the dashed line connecting the two blocks constituting the ranging device 1 represents the path of light. Furthermore, the arrows on the solid lines connecting the two blocks constituting the ranging device 1 represent the main signal transmission path and the direction of signal transmission.

[0082] The light source unit 10 emits multiple laser beams. In this embodiment, the multiple laser beams are single-wavelength lasers with different peak wavelengths. Specifically, the light source unit 10 emits a first laser beam, a second laser beam, and a reference laser beam. Figure 1 As shown, the light source unit 10 includes a measuring light source 11 and a reference light source 12.

[0083] Laser L1, an example of a first laser emitted by light source 11, was measured. Furthermore, laser L2, an example of a second laser emitted by light source 11, was measured. Reference laser Lr was emitted by light source 12. A more detailed structure of the light source unit 10 will be described using... Figure 2 The explanation will follow.

[0084] Furthermore, lasers are typically difficult to maintain at a constant wavelength and frequency; both wavelength and frequency vary to some extent over time. Wavelength fluctuation is a parameter representing the amount of change in wavelength over time. Wavelength fluctuation includes not only short-term variations but also long-term drift. Drift refers to the shift in the average value of short-term variations over time. In this embodiment, the wavelength fluctuation of the reference laser Lr is smaller than that of lasers L1 and L2. Details regarding wavelength fluctuation will be explained later.

[0085] The optical splitter 20 splits the laser L1 emitted from the light source 10 into light L1r and light L1t, and then emits them. Light L1r is input to the reference interferometer 30, and light L1t is input to the measurement interferometer 40. Alternatively, the optical splitter 20 does not split the laser L2 but emits it directly as light L2t. Or, the optical splitter 20 may split the laser L2 into two beams and emit them. One of the two split beams is input to the reference interferometer 30, and the other beam, L2t, is input to the measurement interferometer 40.

[0086] Optical splitter 20 splits the intensity of incident light, causing it to exit in different directions. Optical splitter 20 is, for example, a half-mirror with an intensity splitting ratio of, for example, 1:1, but is not limited to this. Alternatively, the intensity of light L1r can be higher than that of light L1t, or vice versa. During the splitting process by optical splitter 20, the wavelength of the light remains unchanged.

[0087] The reference interferometer system 30 detects the light after interfering the first laser and the light after interfering the reference laser, and outputs a first signal S1 corresponding to the detection result of the interfered light. Specifically, the light L1r emitted from the optical splitter 20 and the reference laser Lr from the reference light source 12 are incident on the reference interferometer system 30. Figure 1 As shown, the reference interference system 30 includes an optical interference system 31 and an optical detection system 32.

[0088] Optical interference system 31 is an example of a second optical interference system, in which light L1r is interfered and emitted as interference light L1ri, and reference laser Lr is interfered and emitted as interference light Lri. Interference light L1ri is an example of a first interference light, and interference light Lri is an example of a second interference light. The interference performed by optical interference system 31 is zero-difference interference.

[0089] The optical detection system 32 is an example of a second optical detection system. It detects the interfering 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 light L1r, that is, the wavelength of light L1t.

[0090] Regarding the specific structures of the optical interferometry system 31 and the optical detection system 32, using Figure 4 This will be explained later.

[0091] The measuring interferometer 40 receives a first reflected light generated by the reflection of light from the first laser beam illuminating the object 90, and outputs a second signal S2. Furthermore, the measuring interferometer 40 also receives a second reflected light generated by the reflection of light from the second laser beam illuminating the object 90. Specifically, the measuring interferometer 40 receives light L1t emitted from the optical splitter 20 and reflected light L1c from the object 90. Furthermore, the measuring interferometer 40 receives light L2t emitted from the optical splitter 20 and reflected light L2c from the object 90. Figure 1 As shown, the measurement interferometric system 40 includes an optical interferometric system 41 and an optical detection system 42.

[0092] Optical interference system 41 is an example of a first optical interference system. It causes light L1t to interfere with reflected light L1c, emitting a third interference beam L1i generated by the interference of light L1t and reflected light L1c. Furthermore, it causes light L2t to interfere with reflected light L2c, emitting a fourth interference beam L2i generated by the interference of light L2t and reflected light L2c. The interference performed by optical interference system 41 is zero-difference interference.

[0093] The optical detection system 42, an example of the first optical detection system, detects the third interference light L1i and the fourth interference light L2i, and outputs a second signal S2 corresponding 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 ranging device 1 to the object 90.

[0094] Regarding the specific structures of the optical interferometry system 41 and the optical detection system 42, using Figure 3 This will be explained later.

[0095] The signal processing system 50 generates wavelength information related to the wavelength of the first laser based on the first signal S1, and calculates the distance from the ranging device 1 to the object 90 based on the wavelength information and the second signal S2. Figure 1 As shown, the signal processing system 50 includes a signal receiving unit 51, a memory 52, and a processing circuit 53.

[0096] The signal receiving unit 51 acquires a first signal S1 from the reference interferometry system 30 and a 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.

[0097] The memory 52 is a storage device such as a non-volatile memory and / or a volatile memory. The first signal S1 and the second signal S2 are stored in the memory 52. ​​Furthermore, the memory 52 may also store programs and data used to operate the various components of the ranging device 1, as well as wavelength information and distance information obtained through signal processing.

[0098] The processing circuit 53 processes the signals output from the reference interferometry system 30 and the measuring interferometry system 40. Specifically, the processing circuit 53 calculates the peak wavelength of the first laser based on the first signal S1, thereby generating wavelength information representing the calculated peak wavelength. In this embodiment, the processing circuit 53 calculates the peak wavelength λ1 of laser L1 and the peak wavelength λ2 of laser L2 based on the first signal S1. The processing circuit 53 calculates the distance from the ranging 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 measuring interferometry system 40 based on a predetermined algorithm to obtain the position of the object 90 as phase information. As a representative phase estimation algorithm, a 4-step phase-shifting algorithm can be used. Based on the phase information, the processing circuit 53 can calculate the distance from the ranging device 1 to the object 90.

[0099] In this embodiment, the processing circuit 53 calculates a first distance within a first measuring range with a first measuring accuracy based on the interference results corresponding to wavelength λ1. Furthermore, the processing circuit 53 calculates a second distance within a second measuring range with a second measuring accuracy based on the interference results corresponding to wavelengths λ1 and λ2. Based on the first and second distances, the processing circuit 53 calculates the distance from the ranging device 1 to the object 90. The processing circuit 53 also calculates the absolute distance from the ranging device 1 to the object 90.

[0100] Here, the first measurement accuracy is higher than the second measurement accuracy. Furthermore, the second measurement range is longer than the first measurement range. Therefore, simply put, processing circuit 53 calculates the distance within a shorter measurement range with higher measurement accuracy based on the interference result of one wavelength. Processing circuit 53 calculates the distance within a longer measurement range with lower measurement accuracy based on the interference result of two wavelengths. The specific distance calculation method will be explained later.

[0101] The processing circuit 53 is implemented using an integrated circuit such as an LSI (Large Scale Integration). For example, the processing circuit 53 may also be implemented using a dedicated hardware structure to calculate the distance from the ranging device 1 to the object 90. Alternatively, the processing circuit 53 may include a processor that executes a program stored in memory 52 to calculate the distance from the ranging device 1 to the object 90. Alternatively, the processing circuit 53 may be a programmable FPGA (Field Programmable Gate Array) or a reconfigurable processor capable of reconfiguring the connections and settings of circuit units within an LSI.

[0102] [1-1. Light Source Section] Next, use Figure 2 The specific structure of the light source unit 10 is explained. Figure 2 This is a block diagram showing the structure of the light source unit 10 of the ranging device 1 according to this embodiment. Figure 2 As shown, the measuring light source 11 includes laser light sources 13a and 13b, and a wavelength synthesis system 14. The reference light source 12 includes a laser light source 13r.

[0103] Laser source 13a emits laser L1 with wavelength λ1. Laser L1 is an example of a first laser, such as a single-wavelength laser. Wavelength λ1 is the peak wavelength of laser L1.

[0104] Laser source 13b emits laser L2 with wavelength λ2. Laser L2 is an example of a second laser, such as a single-wavelength laser. Wavelength λ2 is the peak wavelength of laser L2, which is different from wavelength λ1. The shorter the absolute value of the difference between wavelength λ1 and wavelength λ2 (|λ1-λ2|), the longer the length measurement range can be.

[0105] The laser source 13r emits a reference laser Lr with wavelength λr. The reference laser Lr is an example of a reference laser, such as a single-wavelength laser. Wavelength λr is the peak wavelength of the reference laser Lr; wavelengths λ1 and λ2 are different wavelengths. Wavelength λr is shorter than wavelength λ1.

[0106] Laser sources 13a and 13b are, for example, semiconductor laser elements. As an example, DFB (Distributed Feedback) laser sources, which have high wavelength and frequency stability, can be used in laser sources 13a and 13b. Furthermore, laser source 13r is, for example, a HeNe laser source. The wavelength of the reference laser Lr emitted by laser source 13r is approximately 633 nm. HeNe laser sources have wavelengths with less fluctuation compared to semiconductor laser elements, i.e., they have higher wavelength temporal stability.

[0107] The wavelength combining system 14 combines lasers L1 and L2 emitted from two laser sources 13a and 13b, respectively. The wavelength combining system 14 is, for example, a DWDM (Dense Wavelength Division Multiplexing) element or a holographic optical element.

[0108] [1-2. Specific structure of the interferometric system used for measurement] Next, the specific structure of the measurement interferometry system 40 will be described. As mentioned above, the measurement interferometry system 40 includes an optical interferometry system 41 and an optical detection system 42. Hereinafter, using... Figure 3 Each structure will be explained in turn. Figure 3 This is a diagram showing the specific structure of the measuring interferometric system 40 of the ranging device 1 in this embodiment.

[0109] In this embodiment, the optical interference system 41 is an optical system utilizing Michelson interference. For example... Figure 3 As shown, the optical interference system 41 includes a beam splitter 43 and a reflector 44.

[0110] Beam splitter 43 is an optical element that divides the intensity of incident light into multiple beams, causing each beam to be emitted in a different direction. Beam splitter 43 is, for example, a semi-transparent mirror, which splits the incident light into transmitted light and reflected light, making them of equal intensity. In addition, the intensity ratio of transmitted light to reflected light does not have to be 1:1.

[0111] Specifically, beam splitter 43 splits the light L1t from laser L1, which has been split by optical splitter 20, into two beams, L1a and L1b. Furthermore, beam splitter 43 splits the light L2t from laser L2, which has been split by optical splitter 20, into two beams, L2a and L2b. Figure 3 In the example shown, light L1a and light L2a are reflected light obtained by beam splitter 43 and are emitted toward mirror 44. Light L1b and L2b are transmitted light that have passed through beam splitter 43 and are emitted toward object 90.

[0112] The reflector 44 is an example of an optical element that reflects light L1a and L2a from the beam splitter 43, causing it to re-enter the beam splitter 43. Specifically, the reflector 44 causes the incident light to be reflected by a mirror surface. The higher the reflectivity, the less light is lost, thus improving detection accuracy. Light L1a and L2a incident on the reflector 44 are reflected by the reflector 44 and re-enter the beam splitter 43. At least a portion of each of the light L1a and L2a reflected by the reflector 44 and re-entering the beam splitter 43 passes through the beam splitter 43.

[0113] Lights L1b and L2b, irradiated onto object 90, are reflected by object 90 and, as reflected light L1c and L2c, are again incident on beam splitter 43. At least a portion of each of the reflected light L1c and L2c, re-incident on beam splitter 43, is reflected by beam splitter 43. In this case, interference occurs between the reflected light L1c and L2c and light L1a and L2a. Figure 3 In this diagram, the interference light generated by the zero-difference interference between reflected light L1c and light L1a is denoted as interference light L1i. The interference light generated by the zero-difference interference between reflected light L2c and light L2a is denoted as interference light L2i. Both interference lights L1i and L2i are emitted into the light detection system 42.

[0114] Furthermore, the configuration of the reflector 44 and the object 90 can be interchanged. That is, even when the light from the light source 10 is split into transmitted light and reflected light by the beam splitter 43, the transmitted light can be irradiated by the reflector 44 and the reflected light can be irradiated by the object 90.

[0115] Furthermore, the optical interferometer system 41 is not limited to an optical system using Michelson interferometry. The optical interferometer system 41 can also be an optical system using Fizeau interferometry or Mach-Zehnder interferometry, etc.

[0116] like Figure 3 As shown, the light detection system 42 includes a dichroic mirror 45, a mirror 46, and light detectors 47 and 48.

[0117] The dichroic mirror 45 is an example of a wavelength-separating element that separates incident light into light with wavelength λ1 and light with wavelength λ2. Specifically, the dichroic mirror 45 performs wavelength separation on light incident from the beam splitter 43 onto the light detection system 42. In this embodiment, the dichroic mirror 45 directs light with wavelength λ1 toward the photodetector 47 and light with wavelength λ2 toward the photodetector 48. In this embodiment, a mirror 46 is provided for optical path adjustment.

[0118] The reflector 46 causes light of wavelength λ2, separated by the dichroic reflector 45, to be reflected by the mirror and incident on the photodetector 48. Alternatively, the reflector 46 may be omitted, and the photodetector 48 may be positioned at the location of the reflector 46. Alternatively, the reflector 46 may be configured to adjust the optical path of light with wavelength λ1.

[0119] Photodetectors 47 and 48 each include a photoelectric conversion element that generates an electrical signal corresponding to the intensity of the incident light. Photodetector 47 is sensitive to at least wavelength λ1, performs photoelectric conversion on light of wavelength λ1, and outputs an interference signal S21 with a signal level corresponding to its intensity as a second signal S2 to the signal processing system 50. The interference signal S21 is obtained by detecting the interference light L1i of a portion of the laser L1 with the reflected light L1c from the object 90.

[0120] The photodetector 48 is sensitive to at least wavelength λ2, performs photoelectric conversion on the light of wavelength λ2, and outputs an interference signal S22 with a signal level corresponding to its intensity as a second signal S2 to the signal processing system 50. The interference signal S22 is obtained by detecting the interference light L2i of at least a portion of the laser L2 with the reflected light L2c from the object 90.

[0121] Furthermore, the structure of the optical detection system 42 is not limited to the example described above, as long as it can receive light at each wavelength. For example, after the light from the beam splitter 43 toward the optical detection system 42 is split into two beams by intensity, the two split beams can be passed separately through filters that have a transmission band for specific wavelength components. The filters can be, for example, bandpass filters, but can also be low-pass filters, high-pass filters, etc.

[0122] Furthermore, the measuring interferometer system 40 may not be an optical system utilizing zero-difference interferometry. The measuring interferometer system 40 may also be an optical system utilizing heterodyne interferometry. In this case, the measuring interferometer system 40 may not have a dichroic reflector 45 for wavelength division of light, and the number of photodetectors may be only one.

[0123] [1-3. Specific structure of the reference interferometric system] Next, the specific structure of the reference interferometry system 30 will be described. As mentioned above, the reference interferometry system 30 includes an optical interferometry system 31 and an optical detection system 32. Hereinafter, the following will be used... Figure 4 Each structure will be explained in turn. Figure 4 This is a diagram showing the specific structure of the reference interferometric system 30 of the ranging device 1 in this embodiment.

[0124] The optical interferometer system 31 is an optical system using a Sagnac-type Michelson interferometer system. Light L1r, which is part of the laser L1 split by the optical splitter 20, and the reference laser Lr are incident on the optical interferometer system 31 at different incident positions. For example... Figure 4 As shown, the optical interference system 31 includes a beam splitter 33, mirrors 34 and 35, and a movable mirror 36.

[0125] Beam splitter 33 is an optical element that splits incident light into multiple beams based on intensity, causing each beam to be emitted in a different direction. Beam splitter 33 can be, for example, a semi-transparent mirror, which splits the incident light into transmitted and reflected light, ensuring they have the same intensity. Furthermore, the intensity ratio of transmitted to reflected light does not necessarily have to be 1:1.

[0126] Specifically, beam splitter 33 splits the light L1r into two beams, L1ra and L1rb. Furthermore, beam splitter 33 splits the reference laser Lr into two beams, Lra and Lrb. Figure 4 In the example shown, light L1ra and light Lra are reflected light reflected by beam splitter 33 and emitted toward mirror 35. Light L1rb and Lrb are transmitted light after passing through beam splitter 33 and emitted toward mirror 34.

[0127] Reflector 34 reflects light L1rb and Lrb toward the movable reflector 36. Reflector 35 reflects light L1ra and Lra toward the movable reflector 36.

[0128] The movable reflector 36 has two reflecting surfaces 36a and 36b. Reflector 36a reflects light beams Lra and L1ra respectively. After being reflected by reflector 36a, Lra and L1ra are reflected by reflector 35 and then incident on beam splitter 33, with at least a portion of them passing through. Reflector 36b reflects light beams Lrb and L1rb respectively. After being reflected by reflector 36b, Lrb and L1rb are reflected by reflector 34 and then incident on beam splitter 33, with at least a portion of them being reflected. Light L1ra, after passing through beam splitter 33, interferes with light L1rb reflected by beam splitter 33 with zero difference, and this interference beam L1ri is incident on photodetector 37. Light Lra, after passing through beam splitter 33, interferes with light Lrb reflected by beam splitter 33 with zero difference, and this interference beam Lri is incident on photodetector 38.

[0129] The movable reflector 36 can change the positions of the reflecting surfaces 36a and 36b. For example, a movable stage is provided to movably support at least one of the reflecting surfaces 36a and 36b. By changing the positions of the reflecting surfaces 36a and 36b, the optical path length of the light traveling within the optical interference system 31 changes. That is, the movable reflector 36 is an example of an optical path difference changing mechanism that changes the difference between the optical path length of the light L1r passing through the optical interference system 31 and the optical path length of the reference laser Lr passing through the optical interference system 31. By adjusting the optical path difference, the interfering lights Lri and L1ri change.

[0130] Furthermore, the optical path difference alteration mechanism of the optical interference system 31 is not limited to the movable reflector 36, as long as it can change the optical path length. For example, the optical interference system 31 may also have an electro-optic modulator (EOM) disposed on the optical path as the optical path difference alteration mechanism.

[0131] like Figure 4 As shown, the light detection system 32 includes photodetectors 37 and 38. Photodetectors 37 and 38 each include a photoelectric conversion element that generates an electrical signal corresponding to the intensity of the incident light.

[0132] The photodetector 37 is sensitive to at least wavelength λ1, performs photoelectric conversion on light of wavelength λ1, and outputs an interference signal S11 with a signal level corresponding to its intensity as the first signal S1 to the signal processing system 50. The interference signal S11 is obtained by detecting the interference light L1ri generated by the zero-difference interference of light L1r, which is part of the laser L1.

[0133] The photodetector 38 is sensitive to at least wavelength λr, performs photoelectric conversion on light of wavelength λr, and outputs an interference signal S12 with a signal level corresponding to its intensity as the first signal S1 to the signal processing system 50. The interference signal S12 is obtained by detecting the interference light Lri generated by the zero-difference interference of the reference laser Lr.

[0134] [2. The principle of distance measurement] Next, the principle of distance measurement based on the distance measuring device 1 of this embodiment will be explained.

[0135] For the ranging device 1 of this embodiment, ranging is based on multi-wavelength interferometry (MWI) using multiple lasers. By combining the interference results of multiple single-wavelength lasers with different wavelengths, MWI can eliminate the trade-off between the measuring range and the measuring accuracy, achieving a longer measuring range and higher measuring accuracy. The principle of multi-wavelength interferometry will be explained below.

[0136] [2-1. First determination (using one wavelength)] First, let's explain the first measurement that used a single-wavelength laser.

[0137] If used Figure 3 As explained, for zero-difference optical interferometry, a single-wavelength laser is split by beam splitter 43 and irradiated onto a mirror 44, which functions as a reference surface, and an object 90, which is the object of distance measurement. The beam splitter 43 causes interference between the reflected light from the mirror 44 and the object 90. When the light after interference is detected by the photodetector 47, the intensity P of the signal output from the photodetector 47 is... PD It is represented by the following formula (1).

[0138] [Formula 1] In equation (1), L is － =L x -L y L x L is the distance from beam splitter 43 to the reflecting surface of mirror 44. y It is the distance from beam splitter 43 to object 90. λ k This refers to the wavelength of a single-wavelength laser. Here, k=1. λ k The calculation is based on the first signal S1 output from the reference interferometric system 30. The result is L. x and λ k All of these values ​​are known to the processing circuit 53. Therefore, the processing circuit 53 can process the signal strength P. PD To calculate the distance L from beam splitter 43 to object 90. y .

[0139] In the first measurement, there was a problem with the relatively short measurement range. The following will use... Figure 5 Explain the relationship between the position of the object at 90° and the length measurement range.

[0140] Figure 5 This diagram illustrates the principle of a first measurement using a single-wavelength laser based on the ranging device 1 of this embodiment. Figure 5 In the diagram, objects 90a, 90b, and 90c respectively represent... Figure 1 and Figure 3 The object 90 shown is located in different positions. Where there is no need to distinguish the positions, it will be referred to as "object 90" for explanation.

[0141] exist Figure 5 The graph shows the horizontal axis representing the distance from the object 90 to the specified position as a reference point, and the vertical axis representing the distance calculated by the processing circuit 53. (See figure below.) Figure 5 As shown, the processing circuit 53 can calculate the distance from the ranging device 1 to the object 90 within the specified length measuring range. According to equation (1), when the wavelength of the single-wavelength laser is λ1, the length measuring range is half of its wavelength (λ1 / 2).

[0142] In the first measurement, when the measuring range was exceeded, the absolute distance from the ranging device 1 to the object 90 could not be calculated. For example, in Figure 5 In the example shown, objects 90a, 90b, and 90c are all calculated to have the same distance.

[0143] The wavelength of a single-wavelength laser is, for example, in the near-infrared or visible light band. The near-infrared band is approximately 700 nm to approximately 2500 nm. The visible light band is approximately 380 nm to approximately 780 nm. In this case, the length measurement range of the first measurement is approximately 190 nm to approximately 1250 nm. That is, the length measurement range of the first measurement is from several hundred nanometers to several micrometers. Thus, the length measurement range of the first measurement is relatively narrower compared to the second measurement described later.

[0144] [2-2. Second determination (using two wavelengths)] Next, use Figure 3 and Figure 6 This will be explained by a second measurement using two single-wavelength lasers with mutually different wavelengths, which addresses the problem of the first measurement, namely, a short length measurement range.

[0145] like Figure 3 As shown, in the ranging device 1 of this embodiment, the light interfered by the beam splitter 43 is split into wavelengths by a dichroic mirror 45 and detected by two photodetectors 47 and 48. The result is that the photodetectors 47 and 48 output signals corresponding to the results of the homodyne interference at each corresponding wavelength. The processing circuit 53 is able to calculate the distance from the ranging device 1 to the object 90 based on the two signals.

[0146] In the second measurement, the length measurement range is extended by combining the two signals. The following uses... Figure 6 Explain the relationship between the position of the object at 90° and the length measurement range.

[0147] Figure 6 This diagram illustrates the principle of a second measurement using two single-wavelength lasers based on the ranging device 1 of this embodiment. Figure 6 In the diagram, objects 90a, 90b, and 90c respectively represent... Figure 1 and Figure 3The objects 90 shown are located in different positions. Where it is not necessary to distinguish their positions, they will be referred to as "object 90" for explanation.

[0148] exist Figure 6 The graph shows the horizontal axis representing the distance from the object 90 to a specified position as a reference point, and the vertical axis representing the distance calculated by the processing circuit 53. In the two graphs, the upper graph is... Figure 5 The figures shown are identical, representing distances calculated based on signals obtained from one of the two photodetectors 47 and 48. The lower figure in both figures represents distances calculated based on signals obtained from the other of the two photodetectors 47 and 48.

[0149] If the two graphs are used separately, the length measurement ranges are λ1 / 2 or λ2 / 2 respectively, so the order of magnitude of the length measurement range is almost unchanged compared to the first measurement. In the second measurement, by combining the two graphs, the length measurement range can be lengthened.

[0150] Specifically, the distances calculated for objects 90a, 90b, and 90c corresponding to the upper diagram are approximately the same. However, the distances calculated corresponding to the lower diagram are different. Therefore, by combining the two calculation results, the distance can be calculated using a measuring range longer than either λ1 / 2 or λ2 / 2. Specifically, the processing circuit 53 combines the first distance obtained through the first measurement with the second distance obtained through the second measurement to calculate the absolute distance from the ranging device 1 to the object 90.

[0151] The second measurement range is half the beat frequency wavelength of the two single-wavelength lasers. For example, when the wavelengths of the two single-wavelength lasers are λ1 and λ2, the beat frequency wavelength Λ 12 It is represented by the following formula (2).

[0152] [Formula 2] Based on the beat frequency wavelength Λ 12 Optical interference, capable of producing a frequency equivalent to the beat frequency wavelength Λ 12 Distance measurement at half the length measurement range. For example, when λ1 and λ2 are 1550 nm and 1551 nm respectively, the beat frequency wavelength Λ 12 The length measurement range becomes 1.2 mm, while the length measurement range under single-wavelength interference is approximately 775 nm, which is on the nanometer scale. In contrast, the length measurement range of MWI is expanded to the millimeter scale.

[0153] [2-3. Length Measurement Accuracy] Next, the measurement accuracy of the first and second measurements will be explained.

[0154] The accuracy of length measurement depends on the wavelength of the single-wavelength laser used in the measurement. Specifically, the shorter the wavelength of the single-wavelength laser, the higher the accuracy of length measurement (i.e., the smaller the value in the distance dimension), and the longer the wavelength of the single-wavelength laser, the lower the accuracy of length measurement (i.e., the longer the value in the distance dimension).

[0155] When using two single-wavelength lasers as in the second measurement, the length measurement accuracy depends on the beat frequency wavelength. Specifically, the shorter the beat frequency wavelength, the higher the length measurement accuracy (i.e., the smaller the accuracy in the distance dimension), and the longer the beat frequency wavelength, the lower the length measurement accuracy (i.e., the longer the accuracy in the distance dimension).

[0156] Because the beat frequency wavelength is longer than the wavelength of a single-wavelength laser, the length measurement accuracy is lower in the second measurement compared to the first measurement. That is, the length measurement accuracy of the second measurement is lower due to the longer beat frequency wavelength Λ. 12 And the measurement deteriorates. Thus, if only the second measurement is used, the trade-off between the length measurement range and the length measurement accuracy has not been eliminated.

[0157] To eliminate the trade-off between the two, the MWI combines the first and second measurements, thereby achieving both a longer measurement range and higher measurement accuracy. Specifically, by combining the first measurement, which has a shorter measurement range but higher accuracy, with the second measurement, which has lower accuracy but a longer measurement range, both a longer measurement range and higher measurement accuracy are achieved.

[0158] Figure 7 This is a diagram showing the length measuring range and length measuring accuracy based on two measurements of the distance measuring device 1 according to this embodiment. (See diagram for example.) Figure 7 As shown, let the second measurement accuracy (second measurement precision) be Am, and the second measurement range (second measurement range) be Rm. Furthermore, let the first measurement accuracy (first measurement precision) be As, and the first measurement range (first measurement range) be Rs. Since both the measurement range and measurement precision are expressed in terms of distance, they can be compared.

[0159] As mentioned above, in addition to Figure 7 As shown, Rm > Rs, and Am > As holds true. Furthermore, in this embodiment, Am ≤ Rs holds true. That is, the measurement accuracy Am of the second measurement is less than or equal to the measurement range Rs of the first measurement. Therefore, a unique combination of the first and second measurements can be performed, enabling distance measurement with a higher measurement accuracy than that of the second measurement.

[0160] Here, in order to achieve higher length measurement accuracy, it is important to use the accurate value of the wavelength of the laser L1 used for the first measurement in the distance calculation.

[0161] [3. The relationship between wavelength and frequency stability and length measurement accuracy] Next, the relationship between the stability of wavelength and frequency and the accuracy of length measurement will be explained.

[0162] The wavelength and frequency of the laser are adjusted by a control unit (not shown) to maintain a preset value. Specifically, the wavelength is kept constant by adjusting the current supplied to the laser source and / or the temperature of the laser source. In this embodiment, the set wavelength of the light source 10 is controlled and fixed during the measurement period.

[0163] However, due to the characteristics of laser light sources, it is difficult to maintain a completely constant wavelength. For example... Figure 8 As shown, the wavelength of a single-wavelength laser varies over time, i.e., it fluctuates. Furthermore, Figure 8 This is a graph used to illustrate the wavelength stability of a single-wavelength laser. In Figure 8 In the diagram, the horizontal axis represents time, and the vertical axis represents the wavelength or frequency of a single wavelength laser. Figure 8 This indicates short-term wavelength fluctuations.

[0164] Wavelength fluctuations, for example, are caused by Figure 8 The standard deviation σ is shown. The standard deviation σ can be statistically calculated relative to the average or median wavelength of the laser over a finite time period. Alternatively, wavelength fluctuations can be expressed in frequency units rather than wavelength units, or in other wavelength-related units.

[0165] According to equation (1) above, if the wavelength λ k Wavelength fluctuations occur when there is a deviation between the wavelength of the single-wavelength laser actually used for measurement and the calculated wavelength. Therefore, the measurement accuracy deteriorates due to this discrepancy in the calculated distance value. Thus, there is a correlation between wavelength fluctuations and measurement accuracy. Specifically, the smaller the fluctuation, the better the measurement accuracy.

[0166] Furthermore, wavelength stability is represented by a value that has a negative correlation with the fluctuation of the laser wavelength corresponding to time variations. Specifically, the smaller the fluctuation, the higher the wavelength stability; the larger the fluctuation, the lower the wavelength stability.

[0167] In addition, the laser source 13a that emits laser L1 can be a DFB laser source with high wavelength (frequency) stability, or a light source device that combines the absorption line of the gas cavity and the semiconductor laser as a reference frequency, but is not limited to these.

[0168] Furthermore, while DFB lasers exhibit high wavelength stability, wavelength drift occurs over longer operating times (e.g., exceeding 30 minutes), leading to decreased length measurement accuracy. In other words, even using a wavelength-stable laser source as the emission source for laser L1 cannot completely suppress the decline in length measurement accuracy and long-term stability from a long-term perspective. Additionally, long-term wavelength fluctuations can be viewed as a shift in the peak wavelength.

[0169] In contrast, in this embodiment, the processing circuit 53 calculates the wavelength λ1 based on the first signal S1 output from the reference interferometer system 30. Specifically, the processing circuit 53 uses the interferometer signals S11 and S12 to compare the number of waves in each interferometer signal, or to perform a spectral comparison based on Fourier transform, thereby calculating the wavelength λ1 (for example, see Patent Document 3). Furthermore, the processing circuit 53 uses the calculated wavelength λ1 to calculate the distance from the ranging device 1 to the object 90. Thus, even if the wavelength of the laser L1 fluctuates, the wavelength λ1 at the measurement point can be obtained with good accuracy, thereby improving the length measurement accuracy and long-term stability of the ranging device 1.

[0170] In addition, the processing circuit 53 calculates the wavelength λ1 of the laser L1 used in the first measurement, which requires high precision, but it can also calculate the wavelength λ2 of the laser L2. To calculate the wavelength λ2, similar to the laser L1, the laser L2 is split into a first beam and a second beam by the optical splitter 20, and the first beam is input into the reference interference system 30 to obtain an interference signal based on the zero-difference interference of the second beam.

[0171] Thus, according to this embodiment, even if the wavelength λ1 of the laser L1 fluctuates, since the wavelength λ1 calculated based on the first signal S1 from the reference interferometer system 30 is used, the wavelength λ1 used in the actual measurement can still be used for distance calculation. Therefore, the length measurement accuracy and long-term stability of the ranging device 1 can be improved.

[0172] [4. Calculation of absolute distance] The following is an example of a method for calculating the absolute distance from the ranging device 1 to the object 90 using two single-wavelength lasers via MWI.

[0173] In the second determination, based on from Figure 3 The signals from the two photodetectors 47 and 48 shown are used to calculate the phase of each wavelength, and the difference between them is taken as the beat frequency wavelength Λ. 12 The phase. Under the condition that the above-mentioned MWI is satisfied, based on the beat frequency wavelength Λ 12The wavenumber N of laser L1 is determined by dividing the approximate distance calculated from the phase by the quotient calculated from the wavelength λ1 of laser L1, which has less frequency fluctuation. At this time, the wavelength λ1 of laser L1 uses the value calculated based on the first signal S1. Next, in the first measurement, based on the signal from... Figure 3 Calculate the phase of a single wavelength from the signal of one of the two photodetectors 47 and 48 shown (here, photodetector 47). Based on the above results, the absolute distance x is calculated using the following equation (3).

[0174] [Formula 3] The main reason for the fluctuation component of the calculated distance x is This is due to the wavelength fluctuation of the first single-wavelength laser. Therefore, by using the value calculated using the wavelength λ1 of the laser L1 used in the first measurement, the accuracy of the absolute distance calculation can be improved. Furthermore, the laser L1 used in the first measurement is the laser with the smallest wavelength fluctuation, that is, the laser with the highest wavelength stability, which is the optimal combination of wavelengths. Details will be explained later, but even if there are three or more wavelengths, the method of this disclosure can be applied in the same manner.

[0175] [5. Action (Distance Measurement Method)] Next, use Figure 9 The operation of the ranging device 1 in this embodiment will be explained. Figure 9 This is a flowchart illustrating the operation of the ranging device 1 according to this embodiment.

[0176] like Figure 9 As shown, firstly, the ranging device 1 uses the reference interferometry system 30 to obtain the first signal S1 (S10). Specifically, the light source unit 10 outputs laser L1 and / or L2, and a reference laser Lr. Laser L1 is split into light L1r and light L1t by the optical splitter 20. The reference interferometry system 30 detects the interference of light L1r and the reference laser Lr by zero-difference interference, thereby outputting the interference signals S11 and S12 as the first signal S1 to the signal processing system 50.

[0177] 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 represents the wavelength λ1 of the laser L1. The generated wavelength information is stored in the memory 52.

[0178] Next, the ranging device 1 uses the measuring interferometer system 40 to acquire the second signal S2 (S12). Specifically, for the measuring interferometer system 40, the input light L1t and light L2t (laser L2), and the reflected light L1c and L2c generated by the reflection of these lights by the object 90, respectively. The measuring interferometer system 40 detects the interference of light L1t with the reflected light L1c by zero-difference interference, and detects the interference of light L2t with the reflected light L2c by zero-difference interference, and outputs the interference signals S21 and S22 as the second signal S2 to the signal processing system 50.

[0179] Next, the signal processing system 50 calculates the distance (S13) based on the wavelength information stored in the memory 52 and the second signal S2. By using the wavelength λ1 represented by the wavelength information, the length measurement accuracy can be improved.

[0180] If the ranging process has not ended ("No" in S14), the signal processing system 50 determines whether to update the wavelength information (S15). The wavelength information is updated, for example, at a preset time point (timing). If the wavelength information is updated ("Yes" in S15), the ranging device 1 acquires the first signal (S10) and updates the wavelength information (S11).

[0181] Without updating the wavelength information ("No" in S15), the ranging device 1 acquires the second signal (S12) and calculates the distance (S13). In the distance calculation, the wavelength information stored in the memory 52 is used.

[0182] Figure 10 This is a graph showing the relationship between the frequency of wavelength information updates and the frequency of distance calculations. In Figure 10 In the diagram, arrows represent the flow of time, and triangles indicate the points in time when corresponding processing is performed (timing).

[0183] The acquisition of the first signal S1 and the updating of the wavelength information are performed periodically, for example, at predetermined intervals. The frequency of acquiring the first signal S1 and updating the wavelength information is lower than the frequency of acquiring the second signal S2 and calculating the distance. By reducing the frequency of acquiring the first signal S1 and updating the wavelength information, the power required for the operation of the reference interferometer system 30 and the signal processing system 50 can be suppressed.

[0184] If the wavelength information is not updated, the laser L1 used when obtaining the second signal S2 in step S12 becomes light emitted at a different time point (timing) than the laser L1 used when generating the wavelength information stored in memory 52. ​​By using a DFB laser source or the like, which has less short-term wavelength fluctuation, as the laser source 13a for emitting laser L1, the decrease in length measurement accuracy can be suppressed. Furthermore, according to this embodiment, by updating the wavelength information stored in memory 52 at a predetermined time point (timing), the decrease in length measurement accuracy can be suppressed even if long-term wavelength λ1 fluctuations of laser L1 occur, i.e., wavelength λ1 drift occurs. As a result, the decrease in length measurement accuracy and long-term stability of the ranging device 1 can be suppressed.

[0185] When the wavelength information fluctuates little with respect to time, the wavelength information stored in memory 52 can be updated after a certain wavelength deviation occurs from the wavelength at the start of the measurement. Specifically, the signal processing system 50 can also generate wavelength information and update the wavelength information stored in memory 52 when the wavelength λ1 of the first laser L1 fluctuates beyond a threshold. That is, the processing circuit 53 can also periodically calculate the wavelength λ1, and update the wavelength information stored in memory 52 when the difference between the calculated wavelength λ1 value and the initial value at the start of the ranging or the set wavelength for the laser source, i.e., when the wavelength λ1 fluctuates beyond a threshold. Alternatively, the wavelength information can be updated, and an error message can be output using a display unit and / or an audio output unit to warn the user of a measurement error.

[0186] Alternatively, the frequency of wavelength information updates and the frequency of distance calculations can be the same. In this case, a laser source with a large wavelength fluctuation can be used as the laser source 13a. Since an inexpensive laser source can be used, the cost of the ranging device 1 can be reduced.

[0187] Furthermore, for short-term measurements, the wavelength information can be updated only once before the measurement begins. That is, step S15 can be omitted.

[0188] Furthermore, wavelength information updates are not limited to a single update before the measurement begins. Updates can also be performed under specified conditions, such as the passage of a certain period. Specifically, wavelength information updates can be performed periodically, such as once a day, once a week, or once a month. Periods without measurements can also be treated as periods without wavelength fluctuations.

[0189] Furthermore, one of the specified conditions can also be that the wavelength drift is outside the threshold range. Specifically, it can also be confirmed whether the wavelength drift is within the threshold range (e.g., 1 nm / 8 hours) by indirectly measuring the wavelength of the laser, and the wavelength information can be updated even when the wavelength drift is outside the threshold range. As indirect methods of wavelength monitoring, there are methods such as measuring changes in the temperature and / or air pressure around the laser source, or measuring the temperature of the laser source itself.

[0190] As described above, the ranging device 1 according to this embodiment does not use heterodyne interferometry, but rather null-difference interferometry. Unlike heterodyne interferometry, which requires reducing the wavelength interval between the two light beams, null-difference interferometry does not have wavelength limitations. Therefore, the ranging device 1 has the advantage of higher wavelength selectivity for both the lasers L1 and L2 used for measurement.

[0191] For example, if the object 90 is a lens with an AR (Anti-Reflection) coating, the laser irradiating the object 90 needs to be a laser outside the visible light band. In this case, it is desirable to use a laser in a widely available communication wavelength band. According to this embodiment, since the wavelength selectivity is high, the wavelength of the laser used for measurement can be set to the communication wavelength band, and the reference laser can be set to a shorter wavelength with higher length measurement accuracy. This not only has the advantages of being able to optimize the laser wavelength for the sample and improve length measurement accuracy, but also enables the use of optical components widely available in optical communication, such as those in the communication wavelength band, thereby achieving cost reduction.

[0192] Furthermore, when using heterodyne interferometry, the same number of measuring laser sources and reference laser sources are required, leading to increased device size and cost. In contrast, in the ranging device 1 of this embodiment, only one laser source 13r is needed as the reference laser source, thus simplifying, miniaturizing, and reducing the cost of the ranging device structure. Moreover, a more stable single-wavelength laser, such as a HeNe laser, can be used, resulting in higher accuracy in wavelength measurement compared to other methods, leading to higher length measurement accuracy and long-term stability.

[0193] (Implementation Method 2) Next, the second implementation method will be described.

[0194] In the ranging device of Embodiment 2, the main difference from Embodiment 1 is that the light source unit includes an adjustment unit for adjusting the wavelength of the laser. Hereinafter, the description will focus on the differences from Embodiment 1, omitting or simplifying the description of the commonalities.

[0195] Figure 11This is a block diagram illustrating the structure of the ranging device 2 according to this embodiment. (For example...) Figure 11 As shown, the ranging device 2 and Figure 1 Compared to the ranging device 1 shown, the difference is that a light source unit 10A replaces the light source unit 10. In addition to the structure of the light source unit 10, the light source unit 10A also has an adjustment unit 15.

[0196] The adjustment unit 15 adjusts the wavelength of the first laser based on wavelength information. For example, the adjustment unit 15 adjusts the wavelength λ1 of the laser L1 by controlling the operating temperature and / or applied current of the laser source 13a of the measurement light source 11. As an example, the adjustment unit 15 adjusts the value of the fluctuating (drifted) wavelength λ1 to return it to the wavelength λ1 at the start of the measurement, which is the initial state. The adjustment unit 15 acquires the wavelength information generated by the processing circuit 53 and adjusts the wavelength λ1 if the wavelength λ1 indicated by the acquired wavelength information exceeds a threshold.

[0197] Figure 12 This is a flowchart illustrating the operation of the ranging device 2 in this embodiment.

[0198] like Figure 12 As shown, firstly, in the ranging device 2, the adjustment unit 15 sets the wavelength of the laser used for measurement (S20). Specifically, the adjustment unit 15 sets the wavelength λ1 of laser L1 and the wavelength λ2 of laser L2 to predetermined values ​​as initial values. The initial values ​​of wavelengths λ1 and λ2 are set, for example, based on the measurement accuracy required for measuring the distance to the object 90 (e.g., checking the surface shape).

[0199] Next, in the ranging device 2, a first signal S1 is acquired using the reference interferometry system 30 (S21). The signal processing system 50 generates wavelength information (S22) based on the first signal S1. The wavelength information represents the wavelength λ1 of the laser L1. The generated wavelength information is stored in the memory 52. ​​Furthermore, steps S21 and S22 are related to... Figure 9 The steps S10 and S11 shown are the same.

[0200] Next, the adjustment unit 15 adjusts the wavelength λ1 of the laser L1 (S23). Specifically, the adjustment unit 15 adjusts the temperature of the laser source 13a and / or the applied current, etc., based on the wavelength λ1 represented by the wavelength information stored in the memory 52, so that the value of the wavelength λ1 becomes the initial value of the wavelength λ1 of the laser L1. In addition, if the difference between the wavelength λ1 represented by the wavelength information stored in the memory 52 and the initial value of the wavelength λ1 of the laser L1 is less than a threshold, the adjustment process (S23) can be omitted.

[0201] Next, the ranging device 2 uses the measuring interferometer system 40 to acquire the second signal S2 (S24). Then, the signal processing system 50 calculates the distance based on the wavelength information stored in the memory 52 and the second signal S2 (S25). By using the wavelength λ1 represented by the wavelength information, the measurement accuracy can be improved. Furthermore, steps S24 and S25 are related to... Figure 9 The steps S12 and S13 shown are the same.

[0202] If the ranging process has not ended ("No" in S26), the signal processing system 50 determines whether to adjust the wavelength λ1 (S27). The wavelength λ1 adjustment is performed, for example, at a preset time point (timing). If the wavelength λ1 adjustment is performed ("Yes" in S27), the ranging device 2 performs the acquisition of the first signal (S21), the generation of wavelength information (S22), and the adjustment of wavelength λ1 (S23).

[0203] Without adjusting the wavelength λ1 ("No" in S27), the ranging device 2 acquires the second signal (S24) and calculates the distance (S25). In the distance calculation, the wavelength information stored in the memory 52 is used.

[0204] Thus, according to the ranging device 2 of this embodiment, since fluctuations in the wavelength λ1 of the laser L1 used in ranging can be suppressed, the length measurement accuracy can be improved. Furthermore, the adjustment unit 15 can also adjust the wavelength λ2 of the laser L2, further improving the length measurement accuracy.

[0205] Furthermore, whether to adjust the wavelength λ1, similar to whether to update the wavelength information in Embodiment 1, can also be determined based on the fluctuation, i.e., the amount of drift, of the wavelength λ1. Moreover, if it is a short-term measurement, the adjustment of the wavelength λ1 can be performed only once before the measurement begins. That is, the processing in step S27 can be omitted.

[0206] (Implementation Method 3) Next, the third implementation method will be described.

[0207] In the ranging device of Embodiment 3, the main difference from Embodiment 1 lies in the fact that the reference interferometer system and the measuring interferometer system share the same optical interferometer system. Hereinafter, the description will focus on the differences from Embodiment 1, omitting or simplifying the description of the commonalities.

[0208] Figure 13 This is a block diagram illustrating the structure of the ranging device 3 according to this embodiment. (For example...) Figure 13 As shown, the ranging device 3 and Figure 1Compared to the ranging device 1 shown, the reference interferometer system 30 and the measuring interferometer system 40 share a single optical interferometer system 60. In this case, it is not necessary to branch the laser L1 emitted from the measuring light source 11. Therefore, the ranging device 3 may also be without an optical splitter 20.

[0209] Thus, according to this embodiment, since the constituent elements of the ranging device 3 can be reduced, the ranging device 3 can be miniaturized and lightweight. Furthermore, the operation of the ranging device 3 is the same as that of the ranging device 1. In addition, like the ranging device 2 of the second embodiment, the ranging device 3 may also have an adjustment unit 15 included in the light source unit 10.

[0210] (Variation example) Next, variations of the embodiments will be described. The main difference between Variation 1 and Variation 2 shown below and the embodiments lies in the structure of the light source section. Since the structure other than the light source section is the same as in the embodiments, descriptions will be omitted or simplified.

[0211] [Variation Example 1] In Variation Example 1, the main difference from the other embodiments lies in the fact that the number of wavelengths of the single-wavelength laser used for ranging is three. The following description focuses on the differences from the other embodiments, omitting or simplifying the descriptions of commonalities.

[0212] Figure 14 This is a block diagram showing the structure of the light source section 110 of the rangefinding device in the modified example. (See diagram for example.) Figure 14 As shown, 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 synthesis system 14. Since the laser light sources 13a and 13b are the same as in the embodiment, their description is omitted.

[0213] Laser source 13c is, for example, a semiconductor laser element that emits a laser of a predetermined single wavelength when supplied with current. Laser source 13c is an example of a third laser source, emitting a laser L3 with a wavelength λ3. Wavelength λ3 is an example of a third wavelength, and laser L3 is an example of one of a plurality of second lasers. Wavelength λ3 is a wavelength different from both wavelengths λ1 and λ2. In this embodiment, wavelength λ3 is longer than either wavelength λ1 or wavelength λ2. For example, the difference between wavelength λ3 and wavelength λ1 can be made more than 10 times the difference between wavelength λ2 and wavelength λ1. By setting a large difference between the two wavelengths, the difference in beat frequency wavelengths can be increased. As a result, the length measurement range and accuracy can be set in stages, thus enabling accurate measurement of absolute distance.

[0214] The wavelength combining system 14 combines the lasers L1, L2, and L3 emitted from three laser sources 13a, 13b, and 13c. The wavelength combining system 14 is, for example, a DWDM element or a holographic optical element.

[0215] Regarding the structure of the ranging device in this modified example other than the light source unit 110 and... Figure 1 The distance measuring device 1 shown Figure 11 The distance measuring device 2 shown or Figure 13 The structure of the ranging device 3 shown is the same. In this case, the optical detection system 42 of the measuring interferometry system 40 is equipped with a photodetector for detecting light of wavelength λ3. Alternatively, the optical detection system 42 can also detect beat frequency light via heterodyne interference.

[0216] In the case where three single-wavelength lasers with mutually different wavelengths can be used, as in this modified example, there are three combinations of two single-wavelength lasers. Therefore, a second measurement can be performed based on at least one of the three combinations. Specifically, it is possible to perform a measurement based on the beat frequency wavelength Λ. 12 Beat frequency wavelength Λ 13 and beat frequency wavelength Λ 23 At least one corresponding length measurement accuracy and a second measurement under the length measurement range, wherein the beat frequency wavelength Λ 12 It is obtained based on the interference of laser L1 with wavelength λ1 and laser L2 with wavelength λ2; beat frequency wavelength Λ 13 It is obtained based on the interference of laser L1 with wavelength λ1 and laser L3 with wavelength λ3; the beat frequency wavelength Λ 23 It is obtained based on the interference of laser L3 with wavelength λ3 and laser L2 with wavelength λ2.

[0217] In addition, the beat frequency wavelength Λ 12 It is expressed by equation (2). Furthermore, the beat frequency wavelength Λ 13 and Λ 23 It is represented by the following equations (4) and (5) respectively.

[0218] [Formula 4] In this variation, λ1 < λ2 < λ3 is satisfied. Furthermore, |λ1 - λ3| is set to be sufficiently large compared to |λ1 - λ2|. Simply put, it is set to λ1 ≈ λ2. This results in a beat frequency wavelength Λ 12 and beat frequency wavelength Λ 13 The difference is significant. For example, let λ1, λ2, and λ3 be set to 1550nm, 1551nm, and 1600nm, respectively. In this case, according to equations (2) and (4), the beat frequency wavelength Λ 12 Approximately 2.4 mm, beat frequency wavelength Λ 13It is approximately 50 μm. Furthermore, since λ1≈λ2, the beat frequency wavelength Λ 13 Roughly equal to the beat frequency wavelength Λ 23 .

[0219] The processing circuit 53 of this variant utilizes the beat frequency wavelength Λ 12 Λ 13 and Λ 23 The two distances from the first measurement are combined with the results of the first measurement to calculate the distance from the ranging device to the object 90. Specifically, the processing circuit 53 calculates the absolute distance from the ranging device to the object 90 by combining the first distance obtained from the first measurement with two second distances obtained from the second measurement.

[0220] Processing circuit 53 utilizes the beat frequency wavelength obtained from the laser with the smallest wavelength and frequency fluctuations among all single-wavelength lasers emitted from light source unit 110. Here, since the wavelength fluctuation of laser L1 is the smallest, the beat frequency wavelength Λ is used. 13 and beat frequency wavelength Λ 12 Furthermore, in the first measurement, the processing circuit 53 also utilizes the interference results of the laser with the smallest wavelength fluctuation among all the single-wavelength lasers emitted by the light source 110.

[0221] Here, if we set the absolute distance from the probe to the object being measured as x, then the absolute distance x is represented by the following equation (6).

[0222] A and B are the absolute distances x at the first point from the probe to the object at a distance of 90 degrees. i The included beat frequency wavelength Λ 12 And the wavenumber of wavelength λ1. Furthermore, θ i Corresponding to the positions of the first, second, and third parts of the object 90, the phase represents the interference result based on the wavelength λ1 obtained from the first measurement. In addition, equation (6) is equivalent to extending equation (3) to three wavelengths. Furthermore, the first, second, and third parts are different parts of the surface of the object 90.

[0223] The second measurement is performed using the combination of longest beat frequency wavelengths. The distance calculated in this second measurement is an example of a third distance calculated with third measurement accuracy within the third measurement range. Furthermore, the third measurement accuracy is lower than both the second and first measurement accuracy. The third measurement range is longer than both the second and first measurement ranges. Simply put, the second measurement is performed using the combination with the longest measurement range.

[0224] Here, the processing circuit 53 determines the beat frequency wavelength Λ based on the combination of wavelength λ1 and wavelength λ2.12 The phase. Processing circuit 53 is based on the determined beat frequency wavelength Λ 12 The phase of the second measured beat frequency wavelength Λ 13 The wavenumber A is used for counting. Specifically, the wavenumber Λ is based on the beat frequency wavelength. 12 The calculated distance divided by the beat frequency wavelength Λ 13 Calculate the beat frequency wavelength Λ from the components of the obtained quotient. 13 The wave number A.

[0225] Furthermore, as a subsequent second measurement, the processing circuit 53 determines the beat frequency wavelength Λ based on the combination of wavelengths λ1 and λ3. 13 The phase. Processing circuit 53 is based on the determined beat frequency wavelength Λ 13 The phase of the wavenumber B of the first measured wavelength λ1 is counted. Specifically, this is done by counting the wavenumber B based on the beat frequency wavelength Λ. 13 The calculated distance is divided by the wavelength λ1, and the wave number B of wavelength λ1 is calculated from this distance.

[0226] Finally, as the first determination, the processing circuit 53 determines the phase θ1 of the wavelength λ1. The processing circuit 53 is able to calculate the absolute distance x based on wavenumbers A and B and the phase θ1 of the wavelength λ1 using the above equation (6). i .

[0227] As described above, by using multiple beat frequency wavelengths to perform multiple second measurements, the length measurement range can be further expanded.

[0228] Alternatively, absolute distance can be calculated using methods other than those described above. For example, the Excessfraction method can be used: the absolute distance is calculated by using the consistent phase combination of all wavelengths of the laser.

[0229] [Variation Example 2] In Variation Example 2, the main difference from the other embodiments lies in the use of the reference laser emitted by the reference light source 12 for distance measurement. The following description focuses on the differences from the other embodiments, omitting or simplifying the explanation of commonalities.

[0230] Figure 15 This is a block diagram showing the structure of the ranging device 201 in the modified example 2. For example... Figure 15 As shown, the ranging device 201 and Figure 1 Compared to the ranging device 1 shown, the light source unit 210 replaces the light source unit 10. The light source unit 210 includes a laser light source 13a and a laser light source 13r. In addition, the light source unit 210 may also include a wavelength synthesis system 14.

[0231] like Figure 2As shown, laser source 13r is the source from which the reference laser Lr is emitted. In this modified example, the reference laser Lr is input not only to the reference interferometry system 30 but also to the measurement interferometry system 40. That is, the reference laser Lr is also used as a second laser for measurement. Specifically, the reference laser Lr is split into light L2r (Lr) input to the reference interferometry system 30 and light L2t input to the measurement interferometry system 40 by the optical splitter 20. Therefore, the measurement interferometry system 40 receives the reflected light L2c from the object 90 input to the reference laser Lr.

[0232] Therefore, the number of light sources in the light source unit 210 can be reduced, thus enabling miniaturization and weight reduction of the ranging device 201. Furthermore, the operation of the ranging device 201 is the same as that of the ranging device 1. In addition, like the ranging device 2 in Embodiment 2, the light source unit 210 of the ranging device 201 may also include an adjustment unit 15.

[0233] (Other implementation methods) The ranging device for one or more technical solutions has been described above based on the embodiments, but this disclosure is not limited to these embodiments. Various modifications conceived by those skilled in the art to these embodiments, as well as forms constructed by combining the constituent elements of different embodiments, are also included within the scope of this disclosure, provided they do not depart from its spirit.

[0234] For example, in the above embodiments and variations, the processing circuit 53 calculates the absolute distance from the ranging device to the object 90, but it is not limited to this. The processing circuit 53 may also output the first and second distances to other devices after calculation. For example, the processing circuit 53 may send the first and second distances to another computer, which will then calculate the absolute distance. Alternatively, the processing circuit 53 may send the first and second distances to a display and display them, or it may output them to a printer and print them onto paper or other media. Thus, the first and second distances can be displayed to the user, allowing the user to calculate the absolute distance manually. In this way, the processing circuit 53 may also choose not to perform the absolute distance calculation.

[0235] Furthermore, the wavelength of at least one of the two single-wavelength lasers can be changed. For example, the wavelength of the laser with greater wavelength fluctuation can be swept. Thus, the combination of the two wavelengths can be changed, thereby achieving a length measurement range and accuracy suitable for the object 90. In addition, the device can be miniaturized compared to having three or more laser sources.

[0236] Alternatively, two single-wavelength lasers can be used: one consisting of a laser branched from a single wavelength laser and the other consisting of a laser whose frequency has been shifted. For example, an acousto-optic modulator (AOM) can be used to shift the frequency.

[0237] Furthermore, the first laser emitted by the measuring light source 11 can also be a laser containing multiple single modes. For example, the first laser can also be an optical frequency comb laser. Since the spectrum of an optical frequency comb laser is discrete, it is a laser composed of frequency lines arranged at equal intervals.

[0238] Furthermore, wavelength fluctuations do not necessarily have to be the standard deviation σ. For example, wavelength fluctuations can be 3σ. Alternatively, wavelength fluctuations can be the variance σ of the laser frequency over a finite time period. 2 Furthermore, wavelength fluctuations can also be the difference between the maximum and minimum wavelengths of a laser beam over a finite time period.

[0239] Furthermore, when the light source unit has three or more laser light sources, two of them may emit single-wavelength lasers of the same wavelength. Moreover, the frequency fluctuations of these two single-wavelength lasers of the same wavelength may also be identical. Alternatively, one of the two single-wavelength lasers of the same wavelength may be used in the first measurement, and the other in the second measurement. In other words, the first single-wavelength lasers used in both the first and second measurements may be lasers emitted from different laser light sources.

[0240] Furthermore, the measurement accuracy Am of the second measurement can also be larger 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, and Am>Rs, distance measurement can be performed with substantially the same level of accuracy as in the case where Am≤Rs.

[0241] In addition, wavelength information may not be the peak wavelength of the laser, but rather information representing the spectroscopic spectrum of the laser.

[0242] Furthermore, the general or specific technical solutions of this disclosure can also be implemented by a system, apparatus, method, integrated circuit, or computer program. Alternatively, they can be implemented by a computer-readable non-transitory recording medium such as an optical disc, HDD, or semiconductor memory storing the computer program. Furthermore, they can be implemented by any combination of system, apparatus, method, integrated circuit, computer program, and recording medium.

[0243] Furthermore, the above-described embodiments may be modified, replaced, added, or omitted in various ways within the scope of the claims or their equivalents.

[0244] Industrial applicability This disclosure can be used in ranging devices that can suppress the decline in length measurement accuracy and long-term stability, such as devices for inspecting surface shapes.

[0245] Explanation of icon numbers 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 synthesis system; 15 Adjustment unit; 20 Optical splitter; 30 Reference interference system; 31, 41, 60 Optical interference system; 32, 42 Optical detection system; 33, 43 Beam splitter; 34, 35, 44, 46 Reflector; 36 Moving reflector; 36a, 36b Reflecting surface; 37, 38, 47, 48 Photodetector; 40 Measurement interference system; 45 Dichroic reflector; 50 Signal processing system; 51 Signal receiving unit; 52 Memory; 53 Processing circuit; 90, 90a, 90b, 90c Object.

Claims

1. A ranging device, have: The light source emits a first laser and a reference laser. Using an interferometric system, a first interference light generated by interfering the first laser and a second interference light generated by interfering the reference laser are detected, and a first signal is output. The measuring interferometer system receives a first reflected light generated by the reflection of the first laser by the object and outputs a second signal. as well as The signal processing system generates wavelength information related to the wavelength of the first laser based on the first signal, and calculates the distance from the ranging device to the object based on the wavelength information and the second signal. In the reference interference system, the optical paths of the first laser and the reference laser are configured in such a way that the first laser and the reference laser do not interfere with each other.

2. The ranging device as described in claim 1, The light source also emits a second laser with a different wavelength than the first laser. The measuring interferometer is also input to a second reflected light generated by the second laser being reflected by the object.

3. The ranging device as described in claim 2, The wavelength of the reference laser is shorter than the wavelength of the first laser.

4. The ranging device as described in claim 2, The measurement interferometric system includes: A first optical interference system, comprising: interfering the first laser with the first reflected light to emit a third interference light generated by the interference of the first laser with the first reflected light; and interfering the second laser with the second reflected light to emit a fourth interference light generated by the interference of the second laser with the second reflected light; and The first optical detection system detects the third interference light and the fourth interference light, and outputs the second signal.

5. The ranging device as described in claim 1, The light source also emits multiple second lasers. The wavelengths of the multiple second lasers are different from each other. The wavelengths of the plurality of second lasers are different from the wavelengths of the first laser. The measuring interferometer is also input to a plurality of second reflected lights generated by the reflection of the plurality of second lasers by the object.

6. The ranging device as described in claim 1, It also includes an optical splitter that divides the first laser emitted from the light source into a first part and a second part, so that the first part is input to the reference interferometric system and the second part is input to the measurement interferometric system.

7. The ranging device as described in claim 1, The reference interferometric system includes: A second optical interference system interferes with the first laser, emitting the first interference light generated by the interference of the first laser; interferes with the reference laser, emitting the second interference light generated by the interference of the reference laser; and The second optical detection system detects the first interference light and the second interference light, and outputs the first signal.

8. The ranging device as described in claim 7, The reference interferometer system further includes an optical path difference alteration mechanism, which alters the difference between the optical path length of the first laser passing through the second optical interferometer system and the optical path length of the reference laser passing through the second optical interferometer system.

9. The ranging device as described in any one of claims 1 to 8, The signal processing system calculates the peak wavelength of the first laser based on the first signal, thereby generating wavelength information representing the peak wavelength.

10. The ranging device as described in any one of claims 2 to 4, The signal processing system calculates the peak wavelength of the first laser and the peak wavelength of the second laser based on the first signal, thereby generating wavelength information representing the peak wavelength of the first laser and the peak wavelength of the second laser.

11. The ranging device as described in any one of claims 1 to 8, The signal processing system updates the wavelength information when the specified conditions are met.

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

13. The ranging device as described in claim 12, When the wavelength fluctuation of the first laser exceeds a threshold, the signal processing system generates the wavelength information and updates the wavelength information stored in the memory.

14. The ranging device as described in any one of claims 1 to 8, The light source unit includes an adjustment unit that adjusts the wavelength of the first laser based on the wavelength information.

15. The ranging device as described in any one of claims 1 to 8, The first laser is a laser comprising multiple single modes.

16. The ranging device as described in any one of claims 1 to 8, The reference interferometer system and the measurement interferometer system share the same optical interferometer system.

17. The ranging device as claimed in claim 1, The measuring interferometer is also input with a third reflected light generated by the reference laser being reflected by the object.

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