Optical interferometry device

Abstract

The optical interference distance measuring device (100) includes a first lens (15) that focuses signal light (51A) emitted from an optical transmission component (18) onto an object (19) to be measured, a second lens (16A) for scanning at a first magnification, a third lens (16B) for scanning at a second magnification higher than the first magnification, and a lens switching unit (16) that inserts the second lens (16A) between the first lens (15) and the optical transmission component (18) when scanning at the first magnification, and inserts the third lens (16B) between the first lens (15) and the optical transmission component (18) when scanning at the second magnification, characterized in that the distance between the first lens (15) and the object (19) is maintained in a state in which the signal light (51A) can be focused onto the surface of the object (19).

Description

Technical Field

[0001] The present disclosure relates to an optical interference distance measuring device.

Background Art

[0002] An optical interference distance measuring device using optical coherence tomography (OCT) technology irradiates one of the branched lights in the device onto a measurement target, returns the light generated by reflection from the measurement target into the device, and interferes the light returned into the device with the other branched light to obtain an optical path length and convert it into a distance. Further, Patent Document 1 discloses an optical sensor device in which the wavelength of the light output from the light source is a wavelength sweep type that changes in time series, so that when a large amount of light reflected by the measurement target or scattered outside the measurement target is included, they can be easily separated.

[0003] The optical sensor device described in Patent Document 1 can increase the resolution in the in-plane direction of the measurement surface by increasing the optical magnification of the optical system, but at the same time, there is a problem that the measurement range in the depth direction becomes narrow. As a result, when it is desired to obtain a three-dimensional shape, in addition to scanning in the measurement plane, it is necessary to scan in the depth direction, so the measurement time becomes extremely long.

[0004] Patent Document 2 discloses an invention of an optical coherence tomography device that switches the optical magnification by replacing the objective lens of the optical system. The optical coherence tomography device described in Patent Document 2 can suppress the scanning range in the depth direction to the minimum necessary when performing high-magnification and high-resolution measurement by using the depth information obtained without scanning by low-magnification and low-resolution measurement.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] However, the optical coherence tomography apparatus described in Patent Document 2 had the problem that, when switching optical magnification, it was necessary to change the distance between the object to be measured and the measuring device (working distance) along with changing the objective lens, which prevented rapid measurement.

[0007] The purpose of this disclosure is to provide an optical interference distance measuring device that can switch optical magnification without changing the working distance between the object to be measured and the measuring device. [Means for solving the problem]

[0008] The optical interference distance measuring device disclosed herein comprises a first lens that focuses signal light emitted from a light source onto the object to be measured, and a first magnification Having A second lens and a second magnification higher than the first magnification. Having A third lens and the first magnification measurement In this process, the second lens is inserted between the first lens and the light source, and the second magnification is used. measurement The lens switching unit inserts the third lens between the first lens and the light source to switch between the second lens and the third lens, A signal processing device that generates a command signal to switch to the third lens when acquiring horizontal information on the surface of the object to be measured, generates a command signal to switch to the second lens when acquiring information perpendicular to the surface of the object to be measured, and outputs the command signals to the lens switching unit, The device is characterized in that, even when the second lens and the third lens are switched, the working distance, which is the distance between the first lens and the object to be measured, is maintained in such a state that the signal light can be focused onto the surface of the object to be measured, and the optical path length through the second lens and the first lens at the optical axis center of the second lens is the same as the optical path length through the third lens and the first lens at the optical axis center of the third lens. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide an optical interference distance measuring device that can switch optical magnification without changing the working distance between the object to be measured and the measuring device. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing an example of the configuration of the optical interference distance measuring device according to this embodiment. [Figure 2] This is a block diagram showing an example of the hardware configuration of the signal processing device according to this embodiment. [Figure 3] (A) is a schematic diagram showing the state of the optical sensor head during high-magnification measurement, and (B) is a schematic diagram showing the state of the optical sensor head during low-magnification measurement. [Modes for carrying out the invention]

[0011] The optical interference distance measuring device according to an embodiment will be described below with reference to the drawings. The following embodiment is merely an example, and the embodiments can be combined and modified as appropriate.

[0012] Figure 1 is a schematic diagram showing an example configuration of an optical interference distance measuring device 100 according to this embodiment. The optical interference distance measuring device 100 comprises a wavelength-swept light source 1, an optical splitter 2, an optical circulator 3, a reference reflection point 4, an optical sensor head 5, an optical heterodyne receiver 6, an analog-to-digital converter (ADC) 7, a digital-to-analog converter (DAC) 8, a signal processing device 9, a reference clock 10, a splitter 11, a phase-locked loop (PLL) 12, and a switch 13. Each of the wavelength-swept light source 1, optical splitter 2, optical circulator 3, reference reflection point 4, optical sensor head 5, and optical heterodyne receiver 6 is connected by an optical transmission path such as an optical fiber.

[0013] The wavelength-swept light source 1 outputs light (wavelength-swept light) whose frequency changes over time to the optical splitter 2. The wavelength-swept light source 1 performs frequency sweeping (wavelength sweeping). Therefore, the wavelength-swept light source 1 outputs light whose frequency changes over time to the optical splitter 2. For example, as the wavelength-swept light source 1, a laser light source whose wavelength can be controlled by controlling the resonator length, or a laser light source whose wavelength changes depending on the amount of injected current can be used. The wavelength-swept light source 1 may output light that alternately repeats continuous triangular wave-like up-chirps and down-chirps by performing frequency sweeping, or it may output light that repeats sawtooth wave-like up-chirps, or it may output light that repeats sawtooth wave-like down-chirps, or it may output a pulsed up-chirp or down-chirp chirp pulse signal.

[0014] The optical splitter 2 splits the light output by the wavelength-swept light source into signal light 21 and reference light 22. The optical splitter 2 outputs the split signal light 21 to the optical circulator 3 and the split reference light 22 to the optical heterodyne receiver 6.

[0015] The optical circulator 3 outputs the signal light 21 branched by the optical splitter 2 to the reference reflection point 4, and outputs the reflected light 51B from the object 19 input from the reference reflection point 4 side, or the internally reflected light from the reference reflection point 4, as reflected light 31 to the optical heterodyne receiver 6.

[0016] The reference reflection point 4 receives the signal light 21 branched by the optical splitter 2 via the optical circulator 3. The reference reflection point 4 performs internal reflection, partially reflecting the input signal light 21 within itself. The internally reflected light from the reference reflection point 4 is output to the optical heterodyne receiver 6 via the optical circulator 3. The signal light 21 that passes through the reference reflection point 4 without internal reflection is output to the optical sensor head 5. Examples of the reference reflection point 4 include a partial reflection mirror or a connector end face.

[0017] The optical sensor head 5 branches off from the optical splitter 2, emits the signal light 51A that has passed through the reference reflection point 4 toward the object 19 to be measured, and receives the reflected light 51B generated by reflection from the object 19. The optical sensor head 5 outputs the received reflected light 51B as reflected light 31 to the optical heterodyne receiver 6 via the reference reflection point 4 and the optical circulator 3. A first lens 15, which is an objective lens, is provided at the end of the optical sensor head 5 on the side of the object 19. Behind the first lens 15 on the side of the reference reflection point 4, there are provided a second lens for scanning at a first magnification (hereinafter referred to as "low magnification") and a third lens for scanning at a second magnification higher than the first magnification (hereinafter referred to as "high magnification"), and a lens switching unit 16 for switching between the second lens and the third lens according to the required magnification is provided. In the present embodiment, the first lens 15 is held together with the housing 17 of the optical interference distance measuring device 100 while maintaining a constant distance from the object 19. The lens switching unit 16 switches between the second lens and the third lens based on the command signal 123 output from the signal processing device 9. For example, when the command signal 123 instructs scanning at low magnification, the lens switching unit 16 inserts the second lens between the first lens 15 and the light source (optical transmission component 18 described later), and when the command signal 123 instructs scanning at high magnification, the lens switching unit 16 inserts the third lens between the first lens 15 and the light source (optical transmission component 18 described later). Also, the distance between the first lens 15 and the object 19 is defined, for example, as the distance from the flange position attached to the first lens 15 to the surface of the object 19 facing the optical interference distance measuring device 100. And the distance between the first lens 15 and the object 19 is maintained in a state where the signal light 51A can be focused on the surface of the object 19 during scanning. That is, the distance between the first lens 15 and the object 19 is such that the first lens 15 focuses the signal light 51A on the surface of the object 19 during scanning. As a result, the distance between the first lens 15 and the object 19 is within the measurement range of the optical interference distance measuring device 100 during scanning.

[0018] The optical heterodyne receiver 6 performs heterodyne processing to combine the reference light 22 supplied from the wavelength sweeping light source 1 and the reflected light 31 received by the optical sensor head 5, which are split by the optical splitter 2. Then, the light combined by the heterodyne processing is photoelectrically converted by, for example, a photodiode (PD) to obtain a received signal (beat signal) as an electrical signal.

[0019] On the other hand, the optical heterodyne receiver 6 combines the reference light 22 split by the optical splitter 2 and the reflected light 31, which is the internally reflected light generated by the internal reflection of the signal light 21 split by the optical splitter 2 at the reference reflection point 4, and further obtains an internal received signal as an electrical signal by photoelectrically converting the combined light. The optical heterodyne receiver 6 outputs the signal 61, which is the obtained received signal and internal received signal, to the ADC 7.

[0020] The reference clock 10 generates a reference clock signal. The reference clock 10 outputs the generated reference clock signal to the splitter 11. The splitter 11 splits the reference clock signal generated by the reference clock 10 to the signal processing device 9 and the PLL 12.

[0021] The PLL 12 generates the second clock signals 121 and 122 in synchronization with the reference clock signal split by the splitter 11. The PLL 12 outputs the generated second clock signal 121 to the DAC 8, and also outputs the generated second clock signal 122 to the switch 13.

[0022] The DAC 8 generates the first clock signal 81 used by the ADC 7 in synchronization with the second clock signal 121 generated by the PLL 12. The DAC 8 outputs the generated first clock signal 81 to the switch 13. Details of the first clock signal will be described later.

[0023] In this embodiment, the DAC8 generates the first clock signal 81 of the ADC7 in synchronization with the second clock signal 121 generated by the PLL12. However, the optical interference distance measuring device 100 may also include a separate circuit for generating a clock, and the DAC8 may generate the first clock signal 81 of the ADC7 in synchronization with the clock generated by that circuit. Furthermore, the frequency of the first clock signal 81 does not need to be synchronized with the frequency of the second clock signal 121.

[0024] Switch 13 switches the clock signal of ADC7 to either the first clock signal 81 generated by DAC8 or the second clock signal 122 generated by PLL12. For example, when the optical interference distance measuring device 100 acquires the first frequency fluctuation reference signal data described later, switch 13 switches the clock signal of ADC7 to the second clock signal 122 generated by PLL12. For example, when the optical interference distance measuring device 100 acquires measurement data related to the object 19 described later, switch 13 switches the clock signal of ADC7 to the first clock signal 81 generated by DAC8.

[0025] The ADC7 samples the internally received signal acquired by the optical heterodyne receiver 6 in synchronization with the second clock signal 121 generated by the PLL 12 and acquired via the switch 13. The ADC7 outputs the received signal 71, which is the internally received signal converted into a digital signal, to the signal processing device 9.

[0026] The signal processing device 9 calculates a first frequency variation reference signal data, which serves as a reference for the frequency variation of the light output by the wavelength-swept light source 1, based on the internally received signal converted into a digital signal by the ADC 7. The signal processing device 9 stores the calculated first frequency variation reference signal data in the storage unit 44, which will be described later, and also outputs the calculated first frequency variation reference signal data 91 to the DAC 8.

[0027] The calculation of the first frequency fluctuation reference signal data in the signal processing device 9 is as follows: The signal processing device 9 performs a Hilbert transform on the internally received signal converted into a digital signal by the ADC7, thereby determining the instantaneous frequency f of the internally received signal. ref (t) is calculated, and the instantaneous frequency f is calculated. ref By multiplying (t) by K (where K is a positive integer), the frequency component Kf ref Calculate the first frequency variation reference signal data for (t).

[0028] In this embodiment, the DAC8 generates a first frequency fluctuation reference signal, which is the first clock signal 81, by converting the first frequency fluctuation reference signal data calculated by the signal processing device 9 into an analog signal, in synchronization with the second clock signal 121 generated by the PLL 12. The DAC8 outputs the generated first frequency fluctuation reference signal to the switch 13.

[0029] The ADC7 samples the received signal acquired by the optical heterodyne receiver 6 in synchronization with the first frequency-varying reference signal generated by the DAC8 and acquired via the switch 13. The ADC7 outputs the received signal 71, which has been converted into a digital signal, to the signal processing device 9. By sampling the received signal in synchronization with the first frequency-varying reference signal, the nonlinearity of the wavelength-swept light is compensated for.

[0030] The signal processing device 9 generates and outputs a command signal 123 to switch between the second lens and the third lens in order to obtain a received signal 71 sufficient to calculate measurement data for the object 19. The signal processing device 9 calculates measurement data for the object 19 based on the received signal 71 converted into a digital signal by the ADC 7. When calculating measurement data for the object 19, the signal processing device 9 determines whether the received signal 71 contains sufficient information for calculating measurement data for the object 19, and if the information relating to the horizontal direction (i.e., parallel direction) of the surface of the object 19 is insufficient, it generates a command signal 123 to switch to the third lens and outputs it to the lens switching unit 16. Furthermore, when calculating measurement data for the object 19, the signal processing device 9 determines whether the received signal 71 contains sufficient information for calculating measurement data for the object 19, and if the information relating to the perpendicular direction (orthogonal direction) to the surface of the object 19 is insufficient, it generates a command signal 123 to switch to the second lens and outputs it to the lens switching unit 16.

[0031] If the frequency of the wavelength-swept light output by the wavelength-swept light source 1 is linear, the time delay between the reference light 22 and the reflected light 31 produced by reflection from the object 19 will be constant, and the frequency of the beat signal obtained by combining the reference light 22 and the reflected light 31 will also be constant. Therefore, the frequency spectrum based on this beat signal will show a sharp peak at a specific frequency. The signal processing device 9 can calculate the position information of the object 19 being measured based on the result of a Fast Fourier Transform (FFT) that includes this specific frequency.

[0032] The signal processing device 9 outputs the calculated measurement data 92 to an output unit 14 located outside the optical interference distance measuring device 100. Examples of measurement data calculated by the signal processing device 9 include information indicating the distance from the optical interference distance measuring device 100 to the object 19, or information indicating the position of the object 19. The output unit 14 is a display device such as an LCD (liquid crystal display), or an output device such as a printer or plotter.

[0033] Figure 2 is a block diagram showing an example of the hardware configuration of the signal processing device 9 according to this embodiment. As shown in Figure 2, the signal processing device 9 is composed of a computer in which each of the following components—a CPU (Central Processing Unit) 41 (processor), main memory 42, input / output interface (I / O interface) 43, and storage unit 44—are connected to a system bus 45. The signal processing device 9 may be composed of multiple computers connected by a network, or it may be composed of processing circuits.

[0034] The CPU 41 is an integrated circuit (IC) that performs arithmetic processing. In addition to the CPU 41, other arithmetic elements such as a digital signal processor (DSP), graphics processing unit (GPU), network processor, or field programmable gate array (FPGA) may also be used. The CPU 41, upon execution of the optical interference distance measurement program according to this embodiment, calculates a first frequency fluctuation reference signal data from the internally received signal converted into a digital signal by the ADC 7, and also functions as a calculation function that calculates information indicating the distance from the optical interference distance measurement device 100 to the object 19, or information indicating the position of the object 19, and as a lens switching control function that generates and outputs a command signal 123 for switching the second lens and the third lens in order to obtain a received signal 71 sufficient to calculate the information indicating the distance from the optical interference distance measurement device 100 to the object 19, or information indicating the position of the object 19. As a result, the CPU 41 functions as a calculation unit and a lens switching control unit upon execution of the optical interference distance measurement program. The optical interference distance measurement program is provided, for example, on a recording medium on which these are recorded.

[0035] The main memory 42 is composed of a volatile storage device such as RAM (Random Access Memory) or a non-volatile storage device such as ROM (Read Only Memory). The storage unit 44 is composed of a non-volatile storage device such as an HDD (Hard Disk Drive) or flash memory.

[0036] The I / O interface 43 is a port to which the ADC7, DAC8, splitter 11, output unit 14, lens switching unit 16, etc., are connected.

[0037] Figure 3(A) is a schematic diagram showing the state of the optical sensor head 5 during high-magnification measurement suitable for horizontal scanning of the surface of object 19. During high-magnification measurement, signal light 21 transmitted via the reference reflection point 4 is emitted from an optical transmission component 18 provided at the end of an optical fiber connected to the reference reflection point 4, and is focused by the third lens 16B and the first lens 15 to illuminate object 19. The first lens 15 has its focal point on the surface of object 19 and focuses the signal light 51A emitted from the optical transmission component 18 onto object 19. The third lens 16B emits the signal light 51A emitted from the optical transmission component 18 toward the first lens 15, contributing to the focusing of the signal light 51A onto object 19 by the first lens. The third lens 16B is a planar optical element composed of optical glass or resin with a predetermined refractive index, or an air gap. Furthermore, the first lens 15 is an optical element formed from optical glass or resin having a predetermined refractive index, and shaped to have a spherical or aspherical surface. The third lens 16B may also be an optical element formed from optical glass or resin having a predetermined refractive index, and shaped to have a spherical or aspherical surface.

[0038] Figure 3(B) is a schematic diagram showing the state of the optical sensor head 5 during low-magnification measurement, which is suitable for scanning perpendicular to the surface of object 19. During low-magnification measurement, signal light 21 is emitted from an optical transmission component 18 located at the end of an optical fiber connected to the reference reflection point 4, and is focused by the second lens 16A and the first lens 15 to illuminate object 19. The first lens 15 has its focal point on the surface of object 19 and focuses the signal light 51A emitted from the optical transmission component 18 onto object 19. The second lens 16A emits the signal light 51A emitted from the optical transmission component 18 toward the first lens 15, contributing to the focusing of the signal light 51A onto object 19 by the first lens. The second lens 16A is a flat plate optical element composed of optical glass or resin with a predetermined refractive index, or an air gap. The second lens 16A may be an optical element formed from optical glass or resin having a predetermined refractive index, with a spherical or aspherical shape. By making at least one of the second lens 16A and the third lens 16B a flat optical element, the cost of the optical interference distance measuring device 100 can be reduced, and the error in the observed distance measurement value can be reduced between high-magnification mode and low-magnification mode.

[0039] Reflected light 51B, generated when signal light 51A is reflected by object 19, is incident on the optical transmission component 18. The reflected light 51B incident on the optical transmission component 18 is input to the optical heterodyne receiver 6 via the reference reflection point 4 and the optical circulator 3. In this embodiment, in order to align the positions of the interference spectra of the signal light and the reference light in high-magnification mode and low-magnification mode, the optical path length through the second lens 16A and the first lens 15 at the optical axis center of the second lens 16A is configured to be the same as the optical path length through the third lens 16B and the first lens 15 at the optical axis center of the third lens 16B. This configuration suppresses errors in the observed distance measurement value between high-magnification mode and low-magnification mode.

[0040] The lens switching unit 16 switches between the second lens 16A and the third lens 16B based on the command signal 123 output from the signal processing unit 9. The signal processing unit 9 also outputs the reflected light from the surface of the second lens 16A or the third lens 16B as reflected light 31 to the optical heterodyne receiver 6, and determines the completion of the switching of the lens switching unit 16 based on the interference signal between the reflected light 31 from the surface of the second lens 16A or the third lens 16B and the reference light 22. Specifically, the signal processing unit 9 detects the phase difference of the interference signal obtained by heterodyne processing of the reflected light 31 with the reference light 22 using FFT processing and makes a determination. This determination allows for instantaneous determination of the lens switching.

[0041] This embodiment is characterized in that the distance between the first lens 15 and the object 19 is maintained at a predetermined constant value, and the optical path length through the second lens 16A and the first lens 15 at the optical axis center of the second lens 16A is the same as the optical path length through the third lens 16B and the first lens 15 at the optical axis center of the third lens 16B.

[0042] In this embodiment, assuming the above-mentioned distance and optical path length conditions, the second lens 16A and the third lens 16B, each provided on the light source side (i.e., the optical transmission component 18 side) of the first lens 15, are moved and switched in a direction perpendicular to the optical axis of the signal light 51A. By switching the second lens 16A and the third lens 16B, a beam expander-like effect is achieved that changes the spot diameter of the signal light 51A irradiating the object 19, making it possible to switch between a high-magnification state suitable for horizontal scanning of the surface of the object 19 and a low-magnification state suitable for vertical (depth) scanning of the surface of the object 19.

[0043] The respective distances, refractive indices of the first lens 15, second lens 16A, and third lens 16B, the curvature of the surfaces of the first lens 15 and second lens 16A, and the thicknesses of the first lens 15, second lens 16A, and third lens 16B are pre-optimized so that the spot diameter of the signal light 51A illuminating the object 19 is suitable for scanning at a desired magnification. As a result, the scanning magnification can be changed by switching between the second lens 16A and the third lens 16B by moving them perpendicular to the optical axis of the signal light 51A. Furthermore, by configuring the second lens 16A and the third lens 16B to be made of the same material with the same refractive index, and so that the optical axis center thickness of the second lens 16A and the optical axis center thickness of the third lens 16B are the same, the error in the observed distance measurement value can be reduced between high-magnification mode and low-magnification mode.

[0044] In this embodiment, the second lens 16A and the third lens 16B are moved perpendicular to the optical axis of the signal light 51A. However, the focus of the signal light 51A on the object 19 may be adjusted by moving either the second lens 16A or the third lens 16B parallel to the optical axis of the signal light 51A. Furthermore, when moving the second lens 16A and the third lens 16B perpendicular to the optical axis of the signal light 51A, the lens switching unit 16 may be moved not only vertically but also rotationally to move the second lens 16A and the third lens 16B perpendicular to the optical axis of the signal light 51A.

[0045] As described above, according to this embodiment, a lens switching unit 16 is provided to switch between the second lens 16A and the third lens 16B in order to switch between high magnification mode and low magnification mode. Furthermore, by keeping the distance between the first lens 15 and the object 19 to be measured constant, high-speed measurement becomes possible without moving the object to be measured or the optical interference distance measuring device 100 (without changing the working distance). In addition, even when the object to be measured is large, there is no risk of the optical interference distance measuring device 100 interfering with the object to be measured.

[0046] Furthermore, in this embodiment, by configuring the optical path length through the second lens 16A and the first lens 15 at the optical axis center of the second lens 16A and the optical path length through the third lens 16B and the first lens 15 at the optical axis center of the third lens 16B, the error in the observed distance measurement value can be reduced between high magnification mode and low magnification mode.

[0047] By configuring either the second lens 16A or the third lens 16B to be a planar optical element, the cost of the optical interference distance measuring device 100 can be reduced, and the error in the observed distance measurement value can be further reduced between high-magnification mode and low-magnification mode.

[0048] By configuring the second lens 16A and the third lens 16B to be made of the same material with the same refractive index, and so that the optical axis center thickness of the second lens 16A and the optical axis center thickness of the third lens 16B are the same, the error in the observed distance measurement value can be further reduced between high-magnification mode and low-magnification mode.

[0049] By determining whether to switch between the second lens 16A and the third lens 16B by the lens switching unit 16 based on the interference signal between the reflected light from either the surface of the second lens 16A or the surface of the third lens 16B and the reference light 22, the lens switching can be determined more quickly, and even objects that are large in the depth direction can be measured at high speed. [Explanation of Symbols]

[0050] 1 Wavelength sweep light source, 2 Optical splitter, 3 Optical circulator, 4 Reference reflection point, 5 Optical sensor head, 6 Optical heterodyne receiver, 7 ADC, 8 DAC, 9 Signal processing unit, 10 Reference clock, 11 Splitter, 12 PLL, 13 Switch, 14 Output unit, 15 First lens, 16 Lens switching unit, 16A Second lens, 16B Third lens, 17 Housing, 18 Optical transmission components, 19 Object, 41 CPU, 42 Main memory, 43 I / O interface, 44 Memory unit, 51A Signal light, 51B Reflected light, 100 Optical interference distance measuring device.

Claims

1. A first lens that focuses the signal light emitted from the light source onto the object to be measured, A second lens having a first magnification, A third lens having a second magnification higher than the first magnification, A lens switching unit that inserts the second lens between the first lens and the light source when measuring at the first magnification, and inserts the third lens between the first lens and the light source when measuring at the second magnification, to switch between the second lens and the third lens, A signal processing device that generates a command signal to switch to the third lens when acquiring horizontal information on the surface of the object to be measured, generates a command signal to switch to the second lens when acquiring information perpendicular to the surface of the object to be measured, and outputs the command signals to the lens switching unit, It has, Even when switching between the second lens and the third lens, The working distance, which is the distance between the first lens and the object to be measured, is maintained in such a state that the signal light can be focused onto the surface of the object to be measured. The optical path length through the second lens and the first lens at the optical axis center of the second lens is the same as the optical path length through the third lens and the first lens at the optical axis center of the third lens. An optical interference distance measuring device characterized by the following.

2. The second lens and the third lens are both planar optical elements. The optical interference distance measuring device according to claim 1, characterized by the following:

3. The second lens and the third lens are each made of the same material, and the optical axis center thickness of the second lens and the optical axis center thickness of the third lens are the same. An optical interference distance measuring device according to claim 1 or claim 2, characterized by the above.

4. The lens switching unit determines the switching between the second lens and the third lens based on the interference signal between the reflected light from either the surface of the second lens or the surface of the third lens and the reference light branched from the signal light. An optical interference distance measuring device according to claim 1 or claim 2, characterized by the above.

5. The optical heterodyne receiver further comprises an optical heterodyne receiver that converts light obtained by combining the reference light from the light source and the reflected light from the object to be measured into a received signal, converts light obtained by combining the internally reflected light generated by the reflection of the signal light inside the optical interference distance measuring device with the reference light into an internal received signal, and outputs a signal consisting of the received signal and the internal received signal, The signal processing device calculates the measurement data of the object to be measured based on the signal output from the optical heterodyne receiver. An optical interference distance measuring device according to claim 1 or claim 2, characterized by the above.