Optical interference measuring device

Abstract

The invention provides a light interference measuring device which provides a guide light irradiation function at low cost without increasing the size of the device. A light interference measurement device is provided with: a first light source that outputs measurement light having a wavelength in the infrared region; a second light source that outputs guided light having a wavelength in the visible region; an optical fiber coupler having at least a first port to which the measurement light is inputted, a second port to which the guide light is inputted, and a third port to which coupled light obtained by coupling the measurement light and the guide light is outputted; a measurement unit which is connected to an optical fiber, irradiates the coupled light to a measurement object, and receives return light reflected by the measurement object; and a processing unit that acquires information relating to the distance, velocity, or vibration of the object to be measured on the basis of an interference signal between the return light and the reference light. The optical fiber coupler is configured from a single-mode fiber having a cutoff wavelength shorter than the wavelength of the measurement light and longer than the wavelength of the guide light, thereby propagating the guide light in a multimode manner.

Description

[0001] This invention patent application is a divisional application of the invention patent application with the invention name “Optical interference measurement device”, the application date of February 8, 2021, and the application number of “202110178051.3”. Technical Field

[0002] The present invention relates to a distance measurement technology utilizing light interference. Background Art

[0003] A technique is known in which coherent measurement light is irradiated onto a measurement object, and distance, speed, vibration, etc. are measured based on an interference signal between reflected light (returned light) of the measurement light and reference light (see Patent Document 1). In such an optical interferometric measurement device, invisible light such as infrared laser is generally used as the measurement light.

[0004] Patent Document 1: International Publication No. 2017 / 187510 Summary of the invention

[0005] Problem that the invention aims to solve

[0006] In sensors used in FA (Factory Automation), there is a strong demand for visually confirming the measurement position, that is, where the measurement light irradiates the measurement object. Therefore, when expanding the optical interferometer measurement device to FA applications, the inventors studied adding a function of irradiating a guide light that visually indicates the measurement position in addition to the measurement light.

[0007] As a method for realizing the guided light irradiation function, a structure in which the guided light irradiation optical system is provided independently from the measurement light irradiation optical system and a structure in which the measurement light and the guided light are combined and irradiated to the measurement object from a common irradiation optical system can be considered. However, the former structure has the problem that it is difficult to align the optical axes of the two irradiation optical systems and leads to the problem of large-scale measurement head. On the other hand, in the case of the latter structure, WDM (Waveling Division Multiplexing) couplers, which are generally used as a means of combining lights of different wavelengths, are difficult to adopt due to their high price. In addition, a method of using a dichroic mirror can also be considered, but there is a problem that the number of components increases and the main body of the device becomes large-scale.

[0008] The present invention has been made in view of the above-mentioned actual situation, and an object of the present invention is to provide a guide light irradiation function of an optical interferometer measurement device at low cost without increasing the size of the device.

[0009] Solutions for solving problems

[0010] The present disclosure includes an optical interference measurement device, characterized in that it comprises: a first light source, which outputs measurement light with a wavelength in the infrared region; a second light source, which outputs guide light with a wavelength in the visible region; an optical fiber coupler, which has at least a first port for inputting the measurement light, a second port for inputting the guide light, and a third port for outputting coupled light obtained by coupling the measurement light and the guide light; a measuring unit, which is connected to the optical fiber, irradiates the coupled light to a measurement object, and receives return light reflected by the measurement object; and a processing unit, which obtains information related to the distance, speed or vibration of the measurement object based on an interference signal between the return light and the reference light, wherein the optical fiber coupler is composed of a single-mode optical fiber having a cutoff wavelength shorter than the wavelength of the measurement light and longer than the wavelength of the guide light, thereby allowing the guide light to propagate in a multi-mode manner.

[0011] According to this structure, since the measuring light and the guide light are irradiated to the same position, the measuring position (the position irradiated by the measuring light) can be visually confirmed by the light spot (spot) that appears on the surface of the measured object. In addition, by using an optical fiber coupler composed of a single-mode optical fiber having a cutoff wavelength shorter than the wavelength of the measuring light and longer than the wavelength of the guide light, a unit for synthesizing the measuring light and the guide light can be realized at a low cost, and the miniaturization of the device body and the measuring unit becomes easy.

[0012] Alternatively, the optical fiber coupler sets a coupling ratio of a path from the first port to the third port in such a manner that a proportion of the measurement light input from the first port that is branched to the third port is high, thereby enhancing the power of the measurement light irradiated to the measurement object. By increasing the proportion of the measurement light guided to the measurement unit, the power of the measurement light projected to the measurement object can be enhanced, and measurement accuracy can be improved.

[0013] The first light source may be a wavelength-sweeping light source that temporally sweeps the wavelength of the coherent measuring light by using a frequency modulated continuous wave (FMCW). Therefore, an interferometer using FMCW can be easily realized.

[0014] Alternatively, the guide light may be red light and propagate in the optical fiber and the optical fiber coupler in a multimode manner. This is because the closer the wavelengths of the measuring light (infrared light) and the guide light are, the smaller the influence of chromatic aberration in the optical system of the measuring unit.

[0015] The measuring unit may include an optical system that corrects chromatic aberration, thereby reducing the deviation of the projection positions of the measuring light and the guide light. Thus, the deviation of the projection positions of the measuring light and the guide light caused by chromatic aberration can be reduced as much as possible.

[0016] Alternatively, the reference light may be light that is reflected by a reference surface portion provided in the optical path between the third port of the optical fiber coupler and the measuring unit, which accounts for less than 10% of the coupled light. In this way, the optical paths of the reference light and the measuring light (return light) can be made the same, thereby improving robustness against temperature changes and vibrations.

[0017] Alternatively, the reference surface may be a surface having a reflectivity of 10% or less by vapor-depositing a partial reflector on the end surface of the optical fiber connected to the measuring unit, or a surface having a reflectivity of 10% or less by utilizing Fresnel reflection, wherein the Fresnel reflection occurs at an interface of refractive indexes at the end surface of the optical fiber connected to the measuring unit. Thus, the structure can be simplified and miniaturized.

[0018] Alternatively, a portion of the measurement light may be branched off by a branching device provided on an optical path between the first light source and the first port of the optical fiber coupler, and used as the reference light, thereby making the optical path of the reference light from the branching device to the processing unit different from the optical path of the guide light. Alternatively, the reference light may be a portion of the coupled light branched off by a branching device provided on an optical path between the third port of the optical fiber coupler and the measuring unit, and an interference signal between the reference light and the light branched off by the return light between the branching device and the measuring unit is input to the processing unit. Alternatively, the optical fiber coupler may further include a fourth port for outputting the coupled light, the reference light may be light output from the fourth port, and an interference signal between the reference light and the light branched off by the return light between the optical fiber coupler and the measuring unit is input to the processing unit, or light reflected by the reference light from a reference surface is input to the fourth port, and the return light is input to the third port, thereby inputting an interference signal between the reference light output from the first port and the return light to the processing unit.

[0019] The present invention can be understood as an optical interferometer measuring device, a distance measuring device, a distance measuring sensor, etc. having at least a part of the above-mentioned structure. In addition, the above-mentioned various units and processes can be combined with each other as much as possible to constitute the present invention.

[0020] Effects of the Invention

[0021] According to the present invention, the guide light irradiation function of the optical interferometer measurement device can be realized at low cost without increasing the size of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a diagram schematically showing the basic structure of an optical interferometer measurement device.

[0023] Figure 2FIG. 1 is a diagram schematically showing the appearance of an optical interferometer measurement device.

[0024] Figure 3 It is a diagram schematically showing the structure of the optical interferometer device according to the first embodiment.

[0025] Figure 4 It is a diagram schematically showing the structure of an optical interferometer device according to the second embodiment.

[0026] Figure 5 It is a diagram schematically showing the structure of an optical interferometer device according to a third embodiment.

[0027] Figure 6 It is a diagram schematically showing a modification of the optical interferometer device according to the third embodiment.

[0028] Figure 7 It is a diagram schematically showing a modification of the optical interferometer device according to the third embodiment.

[0029] Figure 8 It is a diagram schematically showing the structure of an optical interferometer device according to a fourth embodiment.

[0030] Fig. 9 It is a diagram schematically showing a modified example of the optical interferometer measuring device according to the fourth embodiment.

[0031] Fig.10 It is a diagram schematically showing a modified example of the optical interferometer measuring device according to the fourth embodiment.

[0032] Description of symbols

[0033] 1: optical interference measuring device; 10: measuring head; 10a: optical system; 11: measuring light source; 12: guiding light source; 13: optical fiber coupler; 14: circulator; 15: detector; 16: processing unit; 17: AD converter; 20: controller; 31, 32, 40, 41, 51-53, 60-64: optical fiber coupler; 33, 63: differential detector; 34: clock generator; 50: reflector; F1-F10, F40-F45, F60-F63: optical fiber; L1: measuring light; L2: guiding light; L3: coupling light; L4: returning light; L5: reference light; L6: interference signal; MI: main interferometer; SI: sub-interferometer; O: measuring object; Op: light spot; RP: reference surface. DETAILED DESCRIPTION

[0034] <Application Examples>

[0035] Reference Figure 1 , an example of the basic structure and operation of the optical interferometer measurement device to which the present invention is applied is described.

[0036] The optical interferometer measuring device 1 is a device for measuring the distance, speed or vibration of the measuring object O by using optical interference. The optical interferometer measuring device 1 has a measuring head (measuring unit) 10, a measuring light source 11 (first light source) outputting a measuring light L1, a guiding light source 12 (second light source) outputting a guiding light L2, a fiber coupler 13, a circulator 14, a detector 15, a processing unit 16, an AD converter 17, and optical fibers F1 to F5 as main structures. Here, a Fizeau type interferometer is used as an example, but a Mach-Zehnder type, a Michelson type, or other interferometers may also be used. The measuring light L1 uses light having a wavelength in the infrared region, and the guiding light L2 uses light having a wavelength in the visible region.

[0037] When the measuring light L1 is input to the fiber coupler 13 through the optical fiber F1, and the guiding light L2 is input to the fiber coupler 13 through the optical fiber F2, coupled light L3 of the measuring light L1 and the guiding light L2 is output from the fiber coupler 13. The coupled light L3 is guided to the measuring head 10 via the optical fiber F3, the circulator 14, and the optical fiber F4, and is projected from the measuring head 10 to the measuring object O. According to this structure, since the measuring light L1 and the guiding light L2 are irradiated to the same position, the measurement position (the position irradiated by the measuring light L1) can be visually confirmed based on the light spot Op that appears on the surface of the measuring object O.

[0038] The light reflected by the measured object O and received by the measuring head 10 is guided to the optical fiber F4 as the return light L4. On the other hand, a part of the coupled light L3 is reflected at the reference surface RP and guided to the optical fiber F4 as the reference light L5. The interference signal (beat signal) L6 of the return light L4 and the reference light L5 is guided to the detector 15 via the circulator 14, and after being photoelectrically converted, is input to the processing unit 16 via the AD converter 17. The interference signal L6 contains a frequency component corresponding to the optical path difference between the return light L4 and the reference light L5, that is, the distance of the measured object O. Therefore, by performing frequency analysis on the interference signal L6 in the processing unit 16, information such as the distance, speed, and vibration of the measured object O can be obtained.

[0039] Here, as the optical fiber coupler 13, a single-mode optical fiber coupler composed of a single-mode optical fiber having a cutoff wavelength shorter than the wavelength of the measuring light L1 and longer than the wavelength of the guiding light L2 is preferably used. Thus, a synthesis unit for the measuring light L1 and the guiding light L2 can be realized at a low cost. In addition, the guiding light L2 propagates in a multimode, but since it has no effect on the measurement of the distance, etc., it does not become a particular problem.

[0040] The following is a specific configuration example of the optical interferometer measurement device 1. Figure 1 The corresponding parts of the basic structure are marked with the same reference numerals.

[0041] <First Embodiment>

[0042] Reference Figure 2 and Figure 3 , describing the structure of the optical interferometer measuring device according to the first embodiment. Figure 2 is a diagram schematically showing the appearance of an optical interferometer measurement device. Figure 3 FIG. 1 is a diagram schematically showing the hardware configuration of an optical interferometer measurement device.

[0043] The optical interferometer measuring device 1 of the present embodiment is a device that performs distance measurement of a measuring object O by coherent FMCW (Frequency Modulated Continuous Wave). The optical interferometer measuring device 1 generally includes a controller (device body) 20 and a measuring head 10, and irradiation of measuring light and reception of reflected light are performed at the end of the measuring head 10. The controller 20 includes: a measuring light source 11 that outputs measuring light L1, a guide light source 12 that outputs guide light L2, a fiber coupler 13, a circulator 14, a detector 15, an AD converter 17, a processing unit 16, a fiber coupler 31, a fiber coupler 32, a differential detector 33, a clock generator 34, and optical fibers F1 to F10 as main components.

[0044] The circulator 14, the measuring head 10 and the optical fibers F3 to F5 constitute a Fizeau type main interferometer MI, and the optical fiber couplers 31 and 32 and the optical fibers F7 and F8 constitute a sub-interferometer SI. The main interferometer MI is an interferometer for measurement, and the sub-interferometer SI is an interferometer for calibrating the characteristics of the measurement light source 11.

[0045] The measuring light source 11 is a light source capable of outputting coherent measuring light L1. Since it is FMCW, a wavelength scanning light source capable of temporally scanning the wavelength of the measuring light L1 is used. Examples of wavelength scanning light sources include current modulated VCSELs, MEMS driven VCSELs, SSG-DBRs, and the like, and any type of light source can be used. In the present embodiment, a current modulated VCSEL is used due to the advantage of low cost. As the measuring light L1, for example, a near-infrared laser with a wavelength of about 1310nm to 1550nm is used. In addition, in the present embodiment, a wavelength scan is performed based on a triangular wave, but a wavelength scan may also be performed using a sine wave, a sawtooth wave, or other waveforms.

[0046] The guide light source 12 is a light source for outputting the guide light L2. Any wavelength of light can be used as long as it is visible light, and red laser is used in this embodiment. This is because the closer the wavelengths of the measuring light L1 and the guide light L2 are, the smaller the influence of chromatic aberration in the optical system of the measuring head 10. In addition, compared with other colors, the red laser light source has the advantage of low cost.

[0047] The fiber coupler 13 is a 2-input × 2-output fiber coupler. The measurement light L1 is input to the first port of the fiber coupler 13 via the optical fiber F1, and the guide light L2 is input to the second port of the fiber coupler 13 via the optical fiber F2. Then, the coupled light L3 of the measurement light L1 and the guide light L2 is output from the third port and the fourth port. The third port is connected to the optical fiber F3 on the main interferometer MI side, and the fourth port is connected to the optical fiber F6 on the sub-interferometer SI side.

[0048] In this embodiment, a single-mode fiber coupler 13 composed of a single-mode fiber having a cutoff wavelength shorter than the wavelength of the measurement light L1 and longer than the wavelength of the guide light L2 is used. At this time, the coupling ratio (branching ratio) can be set to a coupling ratio of 50% or more for the path from the first port to the third port. This is because by increasing the proportion of the measurement light L1 branched to the main interferometer MI side, the power of the measurement light L1 projected onto the measurement object O can be enhanced, and the measurement accuracy can be improved.

[0049] The circulator 14 is an optical fiber component having the function of outputting light input from the optical fiber F3 to the optical fiber F4 and outputting light input from the optical fiber F4 to the optical fiber F5. An optical fiber coupler may be used instead of the circulator 14.

[0050] The measuring head 10 is a unit that projects the coupled light L3 to the measuring object O and receives the light reflected by the measuring object O. The measuring head 10 has a structure in which an optical system 10a is arranged in a cylindrical or square lens barrel with a diameter of about 1.5 cm and a length of about 3 cm. The optical system 10a can be a collimating lens for projecting a parallel light beam, or a focusing lens for converging the light beam to the measuring position on the measuring object O. As the optical system 10a, a lens with corrected chromatic aberration (also called an Achromatic Lens) can be used. Since the wavelengths of the measuring light L1 and the guiding light L2 are different, when a lens with large chromatic aberration is used, the two light rays deviate, and the light spot of the guiding light L2 may not correctly indicate the measuring position. In this regard, by using a lens with corrected chromatic aberration, the deviation of the two light rays can be reduced as much as possible, and the correctness of the projection position of the guiding light L2 can be ensured.

[0051] A reference surface RP is provided on the path between the circulator 14 and the measuring head 10. The reference surface RP is a structure for reflecting a part of the coupled light L3 to form a reference light L5. With such a structure, since the optical paths of the reference light L5 and the measuring light (return light L4) can be formed by the same optical fiber, the influence of temperature changes and vibrations can be offset, and robustness can be improved.

[0052] When the amount of reference light L5 is large, SN deteriorates due to noise such as shot noise that increases with the signal amount. Therefore, the reflectivity of the reference surface RP is preferably less than 50%, and more preferably less than 10%. The method for forming the reference surface RP is not particularly limited. For example, the reference surface RP can also be formed by evaporating a partial reflector on the end face of the optical fiber F4. Alternatively, the end face of the optical fiber F4 can be made a plane perpendicular to the optical axis, and a region filled with an air layer or a refractive index matching material is formed between the optical fiber F4 and the measuring head 10, and the Fresnel reflection occurring at the interface of the refractive index is utilized. Alternatively, the reflection of the lens surface in the optical system 10a of the measuring head 10 can be utilized.

[0053] The return light L4 reflected by the measuring object O and received by the measuring head 10 and the reference light L5 reflected by the reference surface RP have a phase difference corresponding to twice the optical path from the reference surface RP to the measuring object O. Therefore, the return light L4 and the reference light L5 interfere with each other at the reference surface RP, generating an interference signal (beat signal) L6 having a frequency component corresponding to the phase difference. The interference signal L6 is guided to the detector 15 via the circulator 14.

[0054] The detector 15 is a photoelectric conversion element that converts the interference signal L6 input from the optical fiber F5 into an electric signal. The A / D converter 17 converts the electric signal obtained by the detector 15 into a digital signal. The sampling of the AD converter 17 is performed based on the clock signal provided by the clock generator 34.

[0055] The processing unit 16 is a unit that performs frequency analysis on the interference signal after AD conversion and calculates the distance, speed, vibration, etc. of the measurement object O. The processing unit 16 is composed of, for example, a calculation processing device having a processor and a memory. In the processor, a general-purpose processor such as a CPU (central processing unit) and an MPU (micro processing unit) can be used, and a dedicated processor such as an FPGA (field-programmable gate array) and an ASIC (application specific integrated circuit) can also be used. Although not shown in the figure, the information of the distance, speed, vibration, etc. as the calculation result of the processing unit 16 is output to an external device (such as a PLC (programmable logic controller), a robot, an inspection device, a superior computer, etc.) for control of FA equipment, various inspections, etc.

[0056] Both fiber couplers 31 and 32 are single-mode fiber couplers with a coupling ratio of 50%. A sub-interferometer SI is formed by setting a specified optical path difference between optical fiber F7 and optical fiber F8. The coupled light L3 input from optical fiber F6 to the sub-interferometer SI is branched by the fiber coupler 31 and then merged at the fiber coupler 32. At this time, the light passing through the optical fiber F7 and the light passing through the optical fiber F8 interfere with each other in the fiber coupler 32, and a signal in which interference signals with opposite phases are superimposed on the triangular wave is output from the two output ports of the fiber coupler 32. The differential detector 33 (also called a balanced photodetector) converts the signals output from the sub-interferometer SI into electrical signals respectively, and outputs the difference between the two signals. Through this operation, the triangular wave and laser noise between the two signals cancel each other, and the interference signal component is amplified, so that an interference signal with good SN can be obtained. The clock generator 34 is a circuit that generates a clock signal based on the zero-crossing time of the interference signal obtained by the differential detector 33.

[0057] When the measuring light source 11 scans the wavelength of the measuring light, it is ideal that the change (slope) of the wavelength over time is linear. This is because, if the wavelength scan is not linear, the beat frequency of the interference signal becomes non-constant, resulting in a decrease in the ranging accuracy. However, in practice, it is difficult to scan the wavelength linearly. In addition, the degree of deviation from linearity depends on the individual characteristics of the measuring light source, so it is difficult to correct in advance.

[0058] Therefore, in this embodiment, in order to correct the nonlinearity of the wavelength scan of the measuring light source 11, as described above, the sampling clock of the AD converter 17 is generated using the sub-interferometer SI. Since the sampling clock is generated based on the measuring light actually output by the measuring light source 11, it becomes a clock signal with unequal intervals corresponding to the slope of the wavelength scan of the measuring light. By using the sampling clock to sample the interference signal of the main interferometer MI at unequal intervals, a result equivalent to sampling at equal intervals can be obtained. As a result, it is possible to achieve an improvement in the reliability of frequency analysis and an improvement in ranging accuracy.

[0059] In addition, other methods may be used to correct the nonlinearity of wavelength scanning. For example, the processing unit 16 may estimate the slope (nonlinearity) of the wavelength scanning based on the interference signal of the secondary interferometer SI, interpolate the interference signal of the main interferometer MI sampled at equal intervals by the AD converter 17, and generate an interference signal with equal interval phases. Alternatively, a reverse deformation may be applied to the control signal for the wavelength scanning of the measuring light source 11 in advance to offset the light source characteristics, thereby ensuring the linearity of the measuring light output from the measuring light source 11.

[0060] According to the above-mentioned structure, the measurement position can be visually confirmed by the guide light projected onto the measurement object, so the convenience and reliability of the device can be improved. In addition, since the measurement light and the guide light are combined by the single-mode fiber coupler 13 and the coupled light is guided to the measurement head 10, it is easy to miniaturize the controller 20 and the measurement head 10. Furthermore, compared with using expensive optical fiber components such as WDM couplers, there is also an advantage that the guide light irradiation function can be realized at a low cost.

[0061] <Second embodiment>

[0062] Figure 4 The optical interferometer measuring device of the second embodiment is shown. The second embodiment is also a configuration example using a Fizeau type interferometer, but the arrangement of the guide light source 12 is different from the first embodiment. The following description will focus on the differences from the first embodiment.

[0063] The measuring light source 11 is connected to the fiber coupler 40. The measuring light L1 is branched by the fiber coupler 40, and is guided to the main interferometer MI via the optical fiber F40, and is guided to the sub-interferometer SI via the optical fiber F45.

[0064] The guide light source 12 is connected to the fiber coupler 41. The guide light L2 is guided to the fiber coupler 13 via the optical fiber F44, the fiber coupler 41, and the optical fiber F42.

[0065] The optical fiber coupler 13 is similar to the first embodiment ( Figure 3 ) is the same as the optical fiber coupler 13 of the measuring head 10. The measuring light L1 is input to the first port of the optical fiber coupler 13 via the optical fiber F40, and the guiding light L2 is input to the second port of the optical fiber coupler 13 via the optical fiber F42. Then, the coupled light L3 of the measuring light L1 and the guiding light L2 is output from the third port of the optical fiber coupler 13. The coupled light L3 is guided to the measuring head 10 via the optical fiber F41.

[0066] An interference signal L6 between the return light L4 and the reference light L5 is guided to the detector 15 via the fiber coupler 13 , the optical fiber F42 , the fiber coupler 41 , and the optical fiber F43 .

[0067] The above-described structure can also produce the same effects as those of the first embodiment.

[0068] <Third Embodiment>

[0069] Figure 5 The main part of the optical interferometer measuring device of the third embodiment is shown. In the third embodiment, the main interferometer MI uses a Michelson interferometer, which is different from the above-mentioned configuration example. Figure 1 to Figure 4In the structural example shown, a reference surface RP is formed on the end face of the optical fiber connected to the measuring head 10. Figure 5 In the structural example of , the reference plane RP is formed by the reflector 50. In the case of this structure, the coupled light L3 branched by the fiber coupler 51 (brancher) provided on the optical path between the fiber coupler 13 and the measuring head 10 and reflected by the reflector 50 is used as the reference light L5. The return light L4 from the measuring head 10 and the reference light L5 from the reflector 50 interfere at the fiber coupler 51, and the interference signal L6 output from the fiber coupler 51 is guided to the detector 15.

[0070] Figure 6 and Figure 7 This is a modified example of the third embodiment. Figure 6 In the structure of Michelson type main interferometer MI, a part of the measuring light L1 is branched out by the optical fiber coupler 52 (brancher) arranged on the optical path between the measuring light source 11 and the optical fiber coupler 13, and used as the reference light L5. Figure 7 In the structure, the coupled light L3 coupled by the optical fiber coupler 13 is output from the third port and the fourth port, the coupled light L3 on the third port side is used for measurement, and the coupled light on the fourth port side is used as reference light L5.

[0071] Such a structure can also produce the same effects as those of the above-mentioned embodiment.

[0072] <Fourth Implementation Method>

[0073] Figure 8 The main part of the optical interferometer measuring device according to the fourth embodiment is shown. The fourth embodiment is different from the above-mentioned configuration example in that a Mach-Zehnder interferometer is used as the main interferometer MI.

[0074] The main interferometer MI includes fiber couplers 60, 61, and 62 and optical fibers F60 to F63. In addition, a differential detector 63 is provided instead of the detector 15 in the above-mentioned configuration example.

[0075] The coupled light L3 input via the optical fiber F3 is branched by the optical fiber coupler 60 (brancher) and guided to the optical fibers F60 and F63, respectively. The coupled light L3 branched to the optical fiber F60 side is guided to the measuring head 10 via the optical fiber coupler 62 and the optical fiber F61, and projected onto the measuring object O. The return light L4 reflected by the measuring object O is input to the optical fiber coupler 61 from the measuring head 10 via the optical fiber F61, the optical fiber coupler 62 and the optical fiber F62. On the other hand, the coupled light branched to the optical fiber F63 side is input to the optical fiber coupler 61 as the reference light L5. Moreover, the return light L4 and the reference light L5 interfere in the optical fiber coupler 61, and a signal in which interference signals with opposite phases are superimposed on a triangular wave is output from the two output ports of the optical fiber coupler 61. The differential detector 63 converts the signals output from the main interferometer MI into electrical signals, respectively, and outputs the difference between the two signals. Through this operation, an interference signal with good SN can be obtained.

[0076] Fig. 9 This is a modified example of the fourth embodiment. Fig. 9 In the structure of the present invention, in the main interferometer MI of the Mach-Zehnder type, a part of the measuring light L1 is branched out by the optical fiber coupler 63 (brancher) provided on the optical path between the measuring light source 11 and the optical fiber coupler 13, and used as the reference light L5. The guide light source 12 is connected to the optical fiber coupler 64, and the guide light L2 is input to the optical fiber coupler 13 via the optical fiber coupler 64 and the optical fiber F62, and is coupled with the measuring light L1.

[0077] in addition, Fig.10 This is also a variation of the fourth embodiment. Fig.10 In the structure, the coupled light L3 coupled by the optical fiber coupler 13 is output from the 3rd port and the 4th port, the coupled light L3 on the 3rd port side is used for measurement, and the coupled light on the 4th port side is used as reference light L5.

[0078] The above-described structure can also produce the same effects as those of the above-described embodiment.

[0079] <Others>

[0080] The above-mentioned embodiments are merely illustrative examples of the structure of the present invention. The present invention is not limited to the above-mentioned specific embodiments, and various modifications can be made within the scope of its technical concept. For example, Figure 3 and Figure 4 The structure of the sub-interferometer SI shown is similar to Figures 5 to 10 The main interferometer MI is appropriately combined.

[0081] <Additional Note 1>

[0082] An optical interference measurement device (1), characterized in that it comprises: a first light source (11) which outputs a measurement light (L1) having a wavelength in the infrared region; a second light source (12) which outputs a guide light (L2) having a wavelength in the visible region; an optical fiber coupler (13) which has at least a first port for inputting the measurement light (L1), a second port for inputting the guide light (L2), and a third port for outputting a coupled light (L3) obtained by coupling the measurement light (L1) and the guide light (L3); A measuring unit (10) irradiates the coupled light (L3) to a measuring object (O) and receives a return light (L4) reflected by the measuring object (O); and a processing unit (16) obtains information related to the distance, speed or vibration of the measuring object (O) based on an interference signal (L6) between the return light (L4) and the reference light (L5), wherein the optical fiber coupler (13) is composed of a single-mode optical fiber having a cutoff wavelength shorter than the wavelength of the measuring light (L1) and longer than the wavelength of the guide light (L2).

Claims

1. An optical interferometry device, characterized in that: have: a first light source that outputs measurement light having a wavelength in the infrared region; a second light source that outputs guided light having a wavelength in the visible region; An optical fiber coupler having at least a first port for inputting the measuring light, a second port for inputting the guiding light, and a third port for outputting coupled light obtained by coupling the measuring light and the guiding light; a measuring unit connected to the optical fiber, irradiating the coupled light to the measured object, and receiving the return light reflected by the measured object; as well as a processing unit that obtains information related to the distance, speed or vibration of the measurement object based on the interference signal between the return light and the reference light, The fiber coupler is composed of a single-mode optical fiber having a cutoff wavelength shorter than the wavelength of the measuring light and longer than the wavelength of the guiding light, thereby causing the guiding light to propagate in a multi-mode manner.

2. The optical interferometry device according to claim 1, characterized in that: The optical fiber coupler sets a coupling ratio of a path from the first port to the third port so that a proportion of the measurement light input from the first port that is branched to the third port is high, thereby increasing the power of the measurement light irradiated to the measurement object.

3. The optical interferometry device according to claim 1 or 2, characterized in that: The first light source is a wavelength-sweeping light source that temporally sweeps the wavelength of coherent measuring light by using a frequency modulated continuous wave (FMCW).

4. The optical interferometry device according to any one of claims 1 to 3, characterized in that: The guided light is red light, and propagates in the optical fiber and the optical fiber coupler in a multi-mode manner.

5. The optical interferometry device according to any one of claims 1 to 4, characterized in that: The measuring unit includes an optical system in which chromatic aberration is corrected, thereby reducing a deviation in projection positions of the measuring light and the guide light.

6. The optical interferometry device according to any one of claims 1 to 5, characterized in that: The reference light is light in which 10% or less of the coupled light is partially reflected by a reference surface provided on an optical path between the third port of the optical fiber coupler and the measuring unit.

7. The optical interferometry measuring device according to claim 6, characterized in that: The reference surface is a surface having a reflectivity of less than 10% by vapor-depositing a partial reflector on the end face of the optical fiber connected to the measuring unit, or a surface having a reflectivity of less than 10% by utilizing Fresnel reflection, wherein the Fresnel reflection occurs at the interface of the refractive index at the end face of the optical fiber connected to the measuring unit.

8. The optical interferometry device according to any one of claims 1 to 5, characterized in that: A part of the measurement light is branched off as the reference light using a branching device provided on the optical path between the first light source and the first port of the optical fiber coupler, thereby making the optical path of the reference light from the branching device to the processing unit different from the optical path of the guide light.

9. The optical interferometry device according to any one of claims 1 to 5, characterized in that: The reference light is light obtained by branching a part of the coupled light by a branching device provided on an optical path between the third port of the optical fiber coupler and the measuring unit, and An interference signal between the reference light and the light obtained by branching the return light between the brancher and the measuring unit is input to the processing unit.

10. The optical interferometry device according to any one of claims 1 to 5, characterized in that: The optical fiber coupler also has a fourth port for outputting the coupled light. The reference light is light output from the fourth port, and An interference signal between the reference light and the light branched from the return light between the fiber coupler and the measuring unit is input to the processing unit, or The reference light reflected by the reference surface is input to the fourth port, and the return light is input to the third port, whereby an interference signal between the reference light output from the first port and the return light is input to the processing unit.

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