Precision measuring device and precision measuring method

Abstract

This precision measuring device comprises a first light source, an optical loop optical path upon which measurement light is incident, the measurement light having been emitted from an object to be measured, upon which light-source light from the first light source is incident, a light source multiplexer and an output demultiplexer which are arranged on the optical path of the optical loop optical path, and a light detecting unit that receives output light from the output demultiplexer, wherein the measurement light is incident on the object to be measured once or a plurality of times via the optical loop optical path.

Description

Precision measuring device, precision measuring method

[0001] The present invention relates to a precision measurement device and a precision measurement method that perform precision measurements using an optical frequency comb.This application claims priority to Japanese Patent Application No. 2024-082123, filed on May 20, 2024, the contents of which are incorporated herein by reference.

[0002] Conventionally, in the transport devices of semiconductor manufacturing facilities that manufacture semiconductor circuits with circuit widths on the order of nanometers, and in the stage control of electron microscopes, precise control on the order of nanometers has been made possible by precision measurement technologies such as detecting stage displacement using a diffracted light interference encoder and correcting stage attitude errors using an autocollimator (see, for example, Patent Document 1).

[0003] However, such precision measurements pose problems due to the small intensity changes in the interference light, such as insufficient resolution of the intensity detector and the amount of change being buried in noise. The limitations on measuring minute amounts are often due to insufficient sensitivity and detector resolution, as well as insufficient noise suppression. While there is a desire to improve the precision of such precision measurements to the picometer order, such as interatomic distances, it is extremely difficult to improve the resolution of diffracted light interference encoders by one order of magnitude from their current level.

[0004] One technology that could enable such precise measurements down to the picometer order is a precision measurement device using an optical frequency comb. An optical frequency comb is a laser beam with a frequency spectrum that contains evenly spaced comb-like components. By synchronizing the frequency components of such an optical frequency comb with frequency standards such as atomic clocks or the Global Positioning System (GPS), the laser beam can be used to highly stabilize each frequency. Optical frequency comb devices are also used to determine Japan's national standard for length (meters).

[0005] Japanese Patent Application Laid-Open No. 2000-304507

[0006] However, the specific measurement devices and methods that enable precision measurements using optical frequency combs are still limited to large-scale devices that are used only in a few research laboratories, etc., and there is a demand for practical precision measurement devices and methods that use optical frequency combs and can be used in factories and university laboratories, for example.

[0007] The present invention has been proposed in view of the above-mentioned problems, and has an object to provide a precision measurement device and a precision measurement method that are capable of performing precision measurements using an optical frequency comb.

[0008] In order to solve the above problems, a precision measuring device and a precision measuring method according to one embodiment of the present invention propose the following: (1) A precision measuring device according to aspect 1 of the present invention includes a first light source, an optical loop optical path into which measurement light emitted from an object to be measured upon which light source light from the first light source is incident is incident, a light source multiplexer and an output demultiplexer arranged on the optical path of the optical loop optical path, and a light detection unit that receives output light from the output demultiplexer, and the measurement light is incident on the object to be measured via the optical loop optical path once or multiple times.

[0009] (2) Aspect 2 of the present invention relates to a precision measuring device according to aspect 1, further comprising an optical frequency calculation unit disposed on the optical path of the optical loop optical path, and the optical frequency calculation unit shifts the frequency of light propagating on the optical path of the optical loop optical path by a predetermined frequency.

[0010] (3) Aspect 3 of the present invention is the precision measuring device of aspect 1 or 2, further comprising a coherent optical amplifier section disposed on the optical path of the optical loop optical path for compensating for attenuation of the intensity of light.

[0011] (4) Aspect 4 of the present invention is a precision measuring device according to any one of aspects 1 to 3, further comprising an optical circulator section disposed on the optical path of the optical loop optical path, which separates light directed toward the object to be measured from light emitted from the object to be measured.

[0012] (5) Aspect 5 of the present invention is a precision measuring device according to any one of aspects 1 to 4, further comprising a phase reference light output unit that adjusts the optical path length of a portion of the light emitted from the first light source and separated, and combines the light with the optical path between the output splitter and the optical detection unit.

[0013] (6) A sixth aspect of the present invention is the precision measurement device according to any one of the first to fifth aspects, wherein the optical detection unit includes a second light source that outputs reference comb light to the optical detection unit.

[0014] (7) A seventh aspect of the present invention is the precision measurement device according to any one of the first to sixth aspects, wherein the first light source is a first optical comb device that emits an optical frequency comb.

[0015] (8) Aspect 8 of the present invention is the precision measuring device of aspect 6, wherein the second light source is a second optical comb device that emits an optical frequency comb.

[0016] (9) A precision measurement method of aspect 9 of the present invention is a precision measurement method using a precision measurement device of any one of aspects 1 to 8, and includes at least a step of directing light source light from the first light source toward the object to be measured, and a step of directing measurement light emitted from the object to be measured into the optical loop light path.

[0017] (10) A tenth aspect of the present invention is the precision measurement method of the ninth aspect, further comprising the step of shifting the measurement light incident on the light frequency calculation unit by a predetermined frequency.

[0018] (11) Aspect 11 of the present invention relates to the precision measurement method of aspect 9 or 10, and further includes a step of further including a second light source that outputs a reference comb light to the optical detector, and detecting a beat frequency signal of the output light demultiplexed by the output demultiplexer and the reference comb light by the optical detector.

[0019] According to the present invention, it is possible to provide a precision measurement device capable of performing precision measurement using light, and a precision measurement method using the same.

[0020] FIG. 1 is a schematic diagram showing the configuration of a precision measurement device according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram showing a specific example of an object to be measured according to the first embodiment. FIG. 3 is an explanatory diagram showing an example of a spectrum measurement. FIG. 4 is an explanatory diagram showing a beat frequency signal. FIG. 5 is a schematic diagram showing the configuration of a precision measurement device according to a second embodiment of the present invention. FIG. 6 is a schematic diagram showing the configuration of a precision measurement device according to a first modification of the first embodiment of the present invention. FIG. 7 is a schematic diagram showing the configuration of a precision measurement device according to a first modification of the second embodiment of the present invention. FIG. 8 is a waveform graph obtained as a result of angle measurement in Example 1. FIG. 9(A) is a waveform graph showing an optical frequency comb with zero revolutions, and FIG. 9(B) is a waveform graph showing an optical frequency comb with one revolution. FIG. 10(A) is a graph obtained by performing a fast Fourier transform on the waveform graph of FIG. 9(A), and FIG. 10(B) is a graph obtained by performing a fast Fourier transform on the waveform graph of FIG. 9(B).

[0021] Hereinafter, a precision measuring device and a precision measuring method according to one embodiment of the present invention will be described with reference to the drawings. Note that the embodiment shown below is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0022] 1 is a schematic diagram showing the configuration of a precision measurement device according to a first embodiment of the present invention. A precision measurement device 10 according to this embodiment includes at least an optical comb device (first optical comb device or first light source) 11, an optical comb processor 12, and an optical comb detector (light detector) 13. An object S to be measured by the precision measurement device 10 is disposed on the optical path between the light source-side input terminal In1 and the measurement-side input / output terminal In2 of the optical comb processor 12. It is also preferable that a collimator lens 15 be further disposed on the optical path between the measurement-side input / output terminal In2 of the optical comb processor 12 and the object S to be measured.

[0023] Examples of the object S to be measured by the precision measuring device 10 of this embodiment include a chromatic dispersion autocollimator and a chromatic aberration confocal device, which change the response spectral function of the input optical frequency comb. Also, examples of devices that measure the phase displacement (shift amount) of the input optical frequency comb include a diffracted light interference encoder and a Michelson interferometer.

[0024] The optical comb device (first optical comb device) 11 may be, for example, a device that generates an optical frequency comb spectrum (optical frequency comb) with uniform frequency spacing by controlling the repetition rate and carrier envelope offset frequency of an ultrashort pulse oscillation laser using a ring resonator. Alternatively, for example, an optical frequency comb spectrum (optical frequency comb) with uniform frequency spacing can be generated by using an LN modulator to modulate CW laser light.

[0025] The optical comb processor 12 of this embodiment comprises an optical loop optical path 21 into which measurement light emitted from the object to be measured S to which light source light is incident from the optical comb device 11, and an optical circulator section 22, an optical frequency calculation section 23, a coherent optical amplifier section 24, a light source multiplexer 25, and an output splitter 26 arranged on the optical path of this optical loop optical path 21.

[0026] In addition, the optical comb processor 12 has a light source side input terminal In1 that receives the optical frequency comb (light source light) emitted from the optical comb device 11, a measurement side input / output terminal In2 that emits the optical frequency comb to the object to be measured S and receives the optical frequency comb (measurement light) emitted from the object to be measured S, and a detection side output terminal In3 that emits the optical frequency comb (output light) from the output splitter 26 toward the optical comb detection unit 13.

[0027] The optical loop optical path 21 is composed of optical waveguides arranged in a ring shape, and branched optical paths extend from the ring portion between the light source side input terminal In1 and the light source multiplexer 25, between the optical circulator unit 22 and the measurement side input / output terminal In2, and between the output demultiplexer 26 and the detection side output terminal In3. In this embodiment, the optical frequency comb circulates (propagates) through the optical loop optical path 21 in the clockwise direction in FIG.

[0028] The optical circulator unit 22 is composed of a three-port optical circulator that is a non-reciprocal optical system, and transmits the optical frequency comb propagating from the light source multiplexer 25 toward the object under test S via the measurement-side input / output terminal In2, and also reflects the optical frequency comb (measurement light) emitted from the object under test S and propagating via the measurement-side input / output terminal In2 toward the optical frequency calculation unit 23. Such optical circulator unit 22 may be composed of, for example, a Faraday rotator, a half-wave plate, a polarizing beam splitter, a reflecting mirror, a reflecting prism, etc.

[0029] The optical frequency calculation unit 23 is configured, for example, with an acousto-optic element. Such an acousto-optic element adds a predetermined frequency to each frequency component of the optical frequency comb propagating through the optical loop optical path 21 by Doppler shifting due to sound waves of the optical frequency. In other words, it shifts the optical frequency comb by a predetermined frequency. This prevents the first and nth optical calculation information circulating through the optical loop optical path 21 from mixing, and allows optical information from different calculation times to be separated. Note that multiple acousto-optic elements may be provided to create small or large frequency shifts.

[0030] By the optical frequency calculation unit 23, a predetermined frequency is added to the optical frequency comb circulating in the optical loop optical path 21 each time the optical frequency calculation unit 23 is passed, and a frequency-shifted optical frequency comb is generated.

[0031] The coherent optical amplifier 24 is composed of, for example, a rare-earth doped fiber 31, a laser diode 32 that outputs pump light, and a pump light combiner 33. The coherent optical amplifier 24 compensates for the intensity attenuation of the optical frequency comb that has been attenuated by passing through the optical frequency calculator 23, light source combiner 25, output demultiplexer 26, etc., without changing the phase information or spectral information. The coherent optical amplifier 24 can also be composed of a semiconductor optical amplifier (SOA) or the like.

[0032] The light source multiplexer 25 multiplexes the optical frequency comb (light source light) emitted from the optical comb device 11 and the optical frequency comb circulating in the optical loop optical path 21 , and outputs the multiplexed light toward the optical circulator unit 22 .

[0033] Furthermore, the output demultiplexer 26 demultiplexes a portion (output light) of the optical frequency comb circulating in the optical loop optical path 21 toward the optical comb detection unit 13. Most of the optical frequency comb incident on the output demultiplexer 26 is transmitted toward the optical loop optical path 21, and the optical frequency comb (output light) demultiplexed toward the optical comb detection unit 13 is, for example, 10% or less of the incident optical frequency comb.

[0034] The optical frequency comb after frequency shifting in the optical frequency calculation unit 23 is demultiplexed toward the optical comb detection unit 13 in a state where a portion of the optical frequency comb for each circuit of the optical loop optical path 21 overlaps. The optical comb detection unit 13 receives the output light from the output demultiplexer 26. In this embodiment, the optical comb detection unit 13 includes an optical comb device (second optical comb device or second light source) 35 that outputs an optical frequency comb of reference comb light, a photodetector 36, an oscilloscope device 37, a computer 38, and a detector multiplexer 39 to separate the overlapping optical frequency combs. The optical comb detection unit 13 also includes a detector multiplexer 39 that is disposed on the optical path between the optical comb device 35 and the photodetector 36 and multiplexes the optical frequency comb (output light) demultiplexed by the output demultiplexer 26 with the optical frequency comb (reference comb light) output from the optical comb device 35.

[0035] Such an optical comb detection unit 13 detects the optical frequency comb (output light) continuously input from the output splitter 26 and the optical frequency comb (reference comb light) output from the optical comb device 35 using a photodetector element 36, and detects the beats of the optical frequency comb (reference comb light) and the optical frequency comb (output light) in a computer 38 via an oscilloscope device 37.

[0036] The spectrum of the beat of the optical frequency comb (output light) changes, for example, depending on the angular change of the object under test S. The computer 38 converts the beat acquired by the oscilloscope into a spectrum using, for example, a program or software, and calculates and outputs, for example, the amount of angular change of the object under test S.

[0037] In this way, by combining the optical comb processor 12 and the optical comb detector 13, it is possible to read information on the interaction between extremely small displacements of the measurement object and light, which was previously impossible.

[0038] Next, a precision measurement method using the precision measurement device 10 of the first embodiment described above will be described. In the following description, it is assumed that the object S to be measured is a diffraction grating as shown in FIG. 2, and the amount of rotation of the diffraction grating is to be detected.

[0039] First, an optical frequency comb (light source light) is emitted from the optical comb device (first optical comb device) 11 toward the device under test S provided in the optical comb processor 12. The optical frequency comb (light source light) enters the optical comb processor 12 from the light source-side input terminal In1, passes through the optical circulator unit 22 arranged on the optical path of the optical loop optical path 21, is emitted from the measurement-side input / output terminal In2, and is incident on the device under test S. The optical frequency of the optical frequency comb (measurement light) emitted from the diffraction grating, which is the device under test S, changes depending on its rotation angle (rotation position).

[0040] The optical frequency comb (measurement light) emitted from the diffraction grating, which is the object to be measured S, and containing angular information of the diffraction grating, enters the optical comb processor 12 from the measurement side input / output terminal In2, propagates through the optical circulator unit 22 toward the optical frequency calculation unit 23, and travels around (propagates) the optical loop optical path 21 in the clockwise direction in Figure 1.

[0041] When this first round of optical frequency comb (measurement light) circulates around the optical loop optical path 21 of the optical comb processor 12 and is again emitted from the optical circulator section 22 and incident on the diffraction grating, which is the object to be measured S, the optical frequency comb (measurement light) that already has the angle information of the first diffraction grating will receive the optical frequency comb (measurement light) that includes the angle information of the second diffraction grating.

[0042] For example, the spectral function is S １ Then, the response spectrum for the second turn is {S １} ２In this example, an experiment was shown in which a response spectrum was obtained using a diffraction grating. However, for example, when the object to be measured S is a mirror and the amount of movement is to be obtained, if the phase shift of the first optical frequency comb (measurement light) is φ, then the phase shift φ of the second optical frequency comb (measurement light) is added to this, so that the optical frequency comb (measurement light) of the second revolution has a phase shift of 2φ. In this way, by using the present invention, it is possible to perform measurements that utilize the exponentiation of the spectral function or the fact that, when focusing on a specific frequency, the phase shift is multiplied by the number of revolutions.

[0043] In this way, the angular information of the diffraction grating, which is the object to be measured S, is repeatedly calculated each time the optical frequency comb (measurement light) makes multiple circuits on the optical loop optical path 21. By performing such repeated calculations, even a slight change in the angle of the diffraction grating, which is the object to be measured S, can be detected with high accuracy.

[0044] For example, by repeating calculations while the optical frequency comb (measurement light) makes multiple trips around the optical loop optical path 21, the spectral function is exponentiated, making the peaks clearer and facilitating detection, as shown in Fig. 3. (Note that Fig. 3 shows the spectrum separated by frequency shifts for easier understanding.) In principle, there is no limit to the number of trips the optical frequency comb (measurement light) makes around the optical loop optical path 21, i.e., the number of calculations.

[0045] When the optical frequency comb (measurement light) is circulated on the optical loop optical path 21 in this manner, the optical frequency calculation unit 23 separates the optical frequency combs (measurement light) from each other based on the number of times they have circulated. For example, if information from the optical frequency combs (measurement light) from the first circumstance and the nth circumstance is mixed, it becomes difficult to perform separate measurements.

[0046] Therefore, the optical frequency calculation unit 23 generates an optical frequency comb that has been frequency-shifted by adding a predetermined frequency each time the optical frequency comb circulating through the optical loop optical path 21 passes through. As a result, for example, the spectral function of the first circumstance and the spectral function of the second circumstance are separated by the difference in frequency and do not mix with each other (see FIG. 3).

[0047] To achieve this frequency shift, the acousto-optic element that constitutes the optical frequency calculation unit 23 realizes the frequency shift of the optical frequency comb by utilizing the principle that when an optical frequency comb of a predetermined frequency is diffracted, it undergoes a Doppler shift corresponding to the velocity component of the sound wave.

[0048] Next, the optical frequency comb (output light) that has been branched off from the output splitter 26 arranged on the optical path of the optical loop optical path 21 and has circulated on the optical loop optical path 21 an arbitrary number of times is incident on the optical comb detection unit 13, where it is combined with the optical frequency comb (reference comb light) emitted from the optical comb device (second optical comb device) 35, and then received by the photodetector element 36.

[0049] Then, the optical frequency comb (output light) is compared with the optical frequency comb (reference comb light) by a computer 38 via an oscilloscope device 37, and the angular change (displacement) of the diffraction grating, which is the object to be measured S, is calculated and output from the difference in frequency components.

[0050] Generally, when detecting and analyzing an optical frequency comb with a repetition rate of, for example, 100 MHz or less, it is difficult to separate and observe each of the comb teeth (each mode is called a longitudinal mode), which are the frequency components that make up the spectrum of the optical frequency comb (the spacing between longitudinal modes is 1 pm or less), because this is below the diffraction limit with a typical spectrometer.

[0051] For this reason, the optical comb detector 13 of this embodiment uses a method known as dual comb spectroscopy, as shown in FIG. 4, to generate beat frequency signals from two optical frequency combs, i.e., an optical frequency comb serving as measurement light and an optical frequency comb serving as reference comb light, and performs detection.

[0052] As described above, according to the precision measurement device 10 and precision measurement method of this embodiment, the optical frequency comb obtained from the object to be measured is circulated through the optical loop optical path 21, and a frequency shift is performed for each circumnavigation to separate optical frequency combs with different circumnavigation numbers, thereby raising the spectral information of the object to be measured contained in the optical frequency comb to a power and multiplying the phase information by the number of circumnavigations.

[0053] 5 is a schematic diagram showing the configuration of a precision measurement device according to a second embodiment of the present invention. Components similar to those in the first embodiment are given the same reference numerals, and redundant explanations will be omitted. A precision measurement device 40 according to this embodiment includes an optical comb device (first optical comb device) 11, an optical comb processor 42, an optical comb detector 43, and a phase reference light generator (phase reference light output unit) 44.

[0054] The optical comb processor 42 of this embodiment includes an optical loop optical path 21 formed on the optical path between the optical comb device 11 and the object to be measured S, an optical circulator section 22 arranged on the optical path of this optical loop optical path 21, an optical path length compensation section 57, an optical frequency calculation section 23, a coherent optical amplifier section 24, a light source multiplexer 25, an output splitter 26, and a light source light splitter 51 for phase reference light.

[0055] The optical path length compensator 57 is composed of a photodetector element, an electro-optic modulator (EOM), and the like. The EOM is an element that electrically controls the intensity (amplitude) modulation, phase modulation, and polarization state of the optical frequency comb using, for example, the electro-optic effect of lithium niobate. The optical path length compensator 57 detects fluctuations in the optical path length within the optical comb processor 42, such as fluctuations in the optical path length due to temperature changes, and controls the optical path length so that it does not change.

[0056] The phase reference light generating device 44 includes an optical loop light path 52 for generating the phase reference light and an optical frequency calculation unit 53 for generating the phase reference light, which is arranged in the optical loop light path 52. The optical frequency calculation unit 53 adds the same predetermined frequency as the optical frequency calculation unit 23 to perform a frequency shift. The phase reference light generating device 44 adjusts the optical path length of a portion of the optical frequency comb (light source light) output from the optical comb device (first optical comb device) 11 and demultiplexed, and multiplexes the portion into the optical path between the output demultiplexer 26 and the optical comb detection unit 43. Specifically, in the phase reference light generating device 44, a portion of the optical frequency comb (light source light) output from the optical comb device 11 is demultiplexed by the phase reference light source light demultiplexer 51 and input to the optical frequency comb. The generated optical frequency comb (phase reference light) is then multiplexed with the optical frequency comb (output light) demultiplexed by the output demultiplexer 26 of the optical comb processor 42, and input to the optical comb detection unit 43.

[0057] According to the precision measuring device 40 of this embodiment having such a configuration, by incorporating the optical path length compensation unit 57, which is a Michelson interference optical system, into the optical comb processor 42 and also using a phase reference light whose frequency is shifted, it becomes possible to measure the object S to be measured, whose phase is displaced, with high measurement accuracy.

[0058] (Variation 1 of the First Embodiment) In the first and second embodiments, the object to be measured S is shown as the most preferable example when performing precise phase or spectrum measurements. However, this requires expensive optical measurement equipment. In practice, there are many measurements that do not require such precision. Below, a precision measurement device that simplifies the present invention for phase or spectrum measurements will be described.

[0059] 6 is a schematic diagram showing a first modification of the precision measuring device of the first embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, and redundant explanations will be omitted. The precision measuring device 60 of this embodiment is the same as the first embodiment of FIG. 1, except that it does not include the optical frequency calculation unit 23 and the coherent optical amplifier 24.

[0060] In this variant example 1, when the first round of optical frequency comb (measurement light) circulates around the optical loop optical path 21 of the optical comb processor 62 and is again emitted from the optical circulator section 22 and incident on the diffraction grating, which is the object to be measured S, the first round of optical frequency comb (measurement light) that already has information about the object to be measured S will receive the second round of optical frequency comb (measurement light) that includes angle information of the diffraction grating.

[0061] Next, the optical frequency comb (output light) that has been branched off from the output splitter 26 arranged on the optical path of the optical loop optical path 21 and has circulated on the optical loop optical path 21 an arbitrary number of times is incident on the optical comb detection unit 63, where it is combined with the optical frequency comb (reference comb light) emitted from the optical comb device (second optical comb device) 35, and then received by the photodetector element 36.

[0062] Then, via an oscilloscope device 37, a computer 38 separates the optical frequency combs (measurement light) with different numbers of revolutions on the time axis. This separates, for example, the spectral function of the first revolution and the spectral function of the second revolution based on the time difference, preventing them from mixing with each other. The spectral function thus obtained is converted into a waveform based on frequency by analysis such as a Fourier transform. Furthermore, the computer 38 compares the optical frequency comb (output light) with the optical frequency comb (reference comb light) and calculates and outputs the amount of displacement from the object under test S based on the difference in frequency components.

[0063] Generally, when detecting and analyzing an optical frequency comb with a repetition rate of, for example, 100 MHz or less, it is difficult to separate and observe each of the comb teeth (each mode is called a longitudinal mode), which are the frequency components that make up the spectrum of the optical frequency comb (the spacing between longitudinal modes is 1 pm or less), because this is below the diffraction limit with a typical spectrometer.

[0064] For this reason, the optical comb detector 63 of this embodiment uses a method known as dual comb spectroscopy, as shown in FIG. 4, to generate beat frequency signals from two optical frequency combs, i.e., an optical frequency comb serving as measurement light and an optical frequency comb serving as reference comb light, and performs detection.

[0065] As described above, according to the precision measurement device 60 and precision measurement method of this embodiment, the optical frequency comb obtained from the device under test is circulated through the optical loop optical path 21, and optical frequency combs with different circulating times on the time axis are separated from each other, thereby exponentiating the spectral information of the device under test contained in the optical frequency comb and multiplying the phase information by the circulating times. Furthermore, it is possible to prevent the spectra of optical frequency combs with different circulating times from being mixed together.

[0066] (Second Modification of the First Embodiment) In FIG. 1, the optical comb device 11 is used as the light source, but if simple measurements are acceptable, the optical comb device 11 does not need to be used.

[0067] 1, the light source (first light source) 11 may be a light source other than an optical frequency comb device, including, but not limited to, a semiconductor laser device, an LED, a halogen lamp, etc. When precise and accurate measurements are required, a coherent light source is preferred, and an optical frequency comb device is more preferred, but when such is not the case, the above can be used as the light source, and in some cases, non-coherent light may also be used.

[0068] According to the precision measuring device of the second modification of this embodiment with such a configuration, any light source can be used for the light source 11, which makes it easier to manufacture the device and reduces costs. Similarly, in the first modification of the precision measuring device of the first embodiment shown in FIG. 6, if a simple measurement is required, the light source of the second modification can be used without using the optical comb device 11.

[0069] (Variation 1 of Second Embodiment) FIG. 7 is a schematic diagram showing the configuration of a precision measurement device according to Variation 1 of the second embodiment of the present invention. Note that the same components as those in the second embodiment are denoted by the same reference numerals, and redundant explanations will be omitted. The precision measurement device 70 according to Variation 1 of the second embodiment includes an optical comb device (first optical comb device) 11, an optical comb processor 72, and an optical comb detector 73. This is the same as the second embodiment except that it does not include the optical comb device 35 that generates the reference comb light, the detector multiplexer 39, the phase reference light generator 44, or the optical path length compensator 57. Note that the light source (first light source) 11 may be the same as that in Variation 2 of the first embodiment.

[0070] Without the reference comb light or phase reference light, it is not possible to guarantee the correct accuracy, but the measurement results will not pose any practical problems. According to the precision measurement device 70 of the first modification of the second embodiment of the present invention having such a configuration, the device configuration is simplified, and it is possible to reduce the cost and the size of the precision measurement device 70 as a whole.

[0071] 7, the precision measuring device 70 of the first modification of the second embodiment uses the coherent light amplifier 24, but it may not have the coherent light amplifier 24. This simplifies the device configuration, thereby achieving further cost reduction and further miniaturization of the entire precision measuring device.

[0072] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims.

[0073] For example, it is possible to detect and measure not only phase shifts and spectral changes due to the optical response of the object S to be measured, but also minute changes due to the optical response of the object S to be measured, such as changes in polarization and light intensity.

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0075] Example 1 A precision measurement device based on Modification 1 of the first embodiment shown in FIG. 6 was fabricated. An optical loop optical path was formed between a first optical comb device and a device under test, and two polarization-maintaining couplers were arranged on the optical path of the optical loop optical path as a light source multiplexer and an output demultiplexer. The polarization-maintaining coupler was arranged so that a portion of the optical frequency comb separated from the output demultiplexer was combined with the optical frequency comb output from the second optical comb device. A photodiode, an oscilloscope, and a computer were also arranged. A collimator lens was installed on the path of the optical frequency comb output from the device under test. The polarization-maintaining coupler as the output demultiplexer output 60% of the incident optical frequency comb toward the optical loop optical path and 40% toward the oscilloscope. The polarization-maintaining coupler to which the optical frequency comb from the second optical comb device is input combines a portion of the optical frequency comb separated by the polarization-maintaining coupler as an output demultiplexer with the optical frequency comb output from the second optical comb device, and outputs 50% of the combined signal toward the oscilloscope. The first and second optical comb devices each include a laser light source, a quarter-wave plate, a half-wave plate, and a polarizing plate, arranged in the direction of the output of the optical frequency comb (center wavelength: 1.5 μm, repetition frequency: 92 MHz, output method: fiber output).

[0076] FIG. 8 shows a waveform graph obtained as a result of angle measurement. In FIG. 8, the vertical axis represents light intensity and the horizontal axis represents time. In the waveform graph in FIG. 8, the waveform with high light intensity is the waveform of the optical frequency comb with zero revolutions, and the waveform with low light intensity is the waveform of the optical frequency comb with one revolution. FIG. 9(A) shows the waveform of the optical frequency comb with zero revolutions enlarged on the time axis, and FIG. 9(B) shows the waveform of the optical frequency comb with one revolution. FIG. 10(A) shows a graph obtained by fast Fourier transforming the waveform in FIG. 9(A), and FIG. 10(B) shows a graph obtained by fast Fourier transforming the waveform in FIG. 9(B). In FIGS. 10(A) and 10(B), the vertical axis represents amplitude and the horizontal axis represents frequency.

[0077] As shown in Figures 8, 9A, and 9B, it was found that optical frequency combs with different numbers of turns could be separated. Furthermore, as shown in Figures 10A and 10B, the full width at half maximum of the graph in Figure 10A was 14.1000 MHz, while the full width at half maximum of the graph in Figure 10B was 12.9615 MHz. Therefore, it was found that looping the optical frequency comb using an optical loop light path sharpened the intensity curve, enabling precise measurements.

[0078] The present invention contributes to a paradigm shift that transcends the limitations of mobile (wireless) communication electronics, and to wireless communication technology that can support, for example, sixth-generation mobile communication systems (6G) by seamlessly connecting optical communication and mobile communication. For example, it can realize a precision measurement device and a precision measurement method that dramatically improves the length measurement accuracy, which was previously generally on the order of nanometers, to, for example, the order of 100 picometers or 10 picometers. Therefore, it has industrial applicability.

[0079] 10...Precision measurement device 11...Optical comb device (first optical comb device) 12...Optical comb processor 13...Optical comb detection unit 15...Collimator lens 21...Optical loop optical path 22...Optical circulator unit 23...Optical frequency calculation unit 24...Coherent optical amplifier unit 25...Light source multiplexer 26...Output demultiplexer 31...Rare earth doped fiber 32...Laser diode 33...Pump light multiplexer 35...Optical comb device (second optical comb device) 35A...Light source (second light source) 36...Photodetector element 37...Oscilloscope device 38...Computer 39...Detection unit multiplexer 40...Precision measurement device 42...Optical comb processor 43...Optical comb detection unit 44...Phase reference light forming device (phase reference light output unit) 51...Light source light demultiplexer for phase reference light 52...Optical loop optical path 53...Optical frequency calculation unit 57: Optical path length compensation unit 60: Precision measurement device 62: Optical comb processor 63: Optical comb detection unit 70: Precision measurement device 72: Optical comb processor 73: Optical comb detection unit S: Object to be measured

Claims

1. A precision measuring device comprising: a first light source; an optical loop optical path into which measurement light emitted from an object to be measured upon which light source light from the first light source is incident; a light source multiplexer and output demultiplexer arranged on the optical path of the optical loop optical path; and a light detection unit that receives output light from the output demultiplexer, wherein the measurement light is incident on the object to be measured via the optical loop optical path once or multiple times.

2. The precision measuring device according to claim 1, further comprising an optical frequency calculation unit disposed on the optical path of said optical loop optical path, said optical frequency calculation unit shifting the frequency of light propagating on the optical path of said optical loop optical path by a predetermined frequency.

3. A precision measuring device according to claim 1 or 2, further comprising a coherent optical amplifier arranged on the optical path of said optical loop optical path to compensate for attenuation of the optical intensity.

4. A precision measuring device as described in claim 1 or 2, further comprising an optical circulator section disposed on the optical path of the optical loop optical path, which separates the light directed toward the object to be measured from the light emitted from the object to be measured.

5. A precision measuring device as described in claim 1 or 2, further comprising a phase reference light output section that adjusts the optical path length of a portion of the light emitted from the first light source and separated, and combines it with the optical path between the output splitter and the optical detection section.

6. The precision measuring device according to claim 1 or 2, wherein the optical detection unit includes a second light source that outputs reference comb light to the optical detection unit.

7. The precision measuring device according to claim 1 or 2, wherein the first light source is a first optical comb device that emits an optical frequency comb.

8. The precision measurement device according to claim 6, wherein the second light source is a second optical comb device that emits an optical frequency comb.

9. A precision measurement method using the precision measurement device according to claim 1 or 2, comprising at least the steps of: irradiating light source light from the first light source toward the object to be measured; and irradiating measurement light emitted from the object to be measured into the optical loop light path.

10. A precision measurement method according to claim 9, further comprising a step of shifting the measurement light incident on said optical frequency calculation unit by a predetermined frequency.

11. The precision measurement method according to claim 9, further comprising a step of: providing a second light source that outputs a reference comb light to the optical detection unit; and detecting, by the optical detection unit, a beat frequency signal between the output light split by the output splitter and the reference comb light.

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