JP2023164100A - Angular displacement measurement device and angular displacement measurement method - Google Patents

Abstract

To increase measurement resolution to acquire an angular displacement of an object with high accuracy.SOLUTION: An angular displacement measurement device comprises: an irradiation unit that irradiates light toward an object; a detection unit that detects reflection light that is emitted from the irradiation unit and is reflected from the object, and transmission light that is emitted from the irradiation unit and has transmitted the object; and a processing unit that obtains an angular displacement of the object based on a ratio between the intensity of the detected reflection light and the intensity of the detected transmission light.SELECTED DRAWING: Figure 2

Description

The present invention relates to an angular displacement measuring device and an angular displacement measuring method.

BACKGROUND ART In the production process of precision parts such as semiconductors and high-performance optical parts, the importance of measuring motion errors of machines used for production is increasing. Rotation error is one of the motion errors of linear motion stages of machines used in production. A linear motion stage is usually not attached with a mechanism for measuring rotational motion errors, and non-contact optical angle measurement tends to be selected for measuring rotational errors.

Conventionally, an autocollimation method is a method often used in optical angle measuring devices. However, while the autocollimation method has a high resolution of about 0.05 angular seconds, its measurement range is limited to about 400 angular seconds, and there are limits to the measurement applications to which it can be applied.

On the other hand, as one method for realizing both high resolution and a wide measurement range, there is an angle measurement method using a Fabry-Perot interferometer (for example, Non-Patent Document 1). Among angle measurement methods using a Fabry-Perot interferometer, there is a method using a laser capable of frequency sweeping (for example, Non-Patent Document 2). This method is a measurement method that allows angle information to be obtained continuously over a wide measurement range.

Lin S. T., Yeh S. L., Lin Z. F., Angular probe based on using Fabry-Perot etalon and scanning technique, Optics Express, 18(3), pp. 1794-1800 (2010) Dong J. T., Ji F. Xia H. J., Liu Z. J., Zhang T. D., Yang L., Measurement Science & Technology, 29, 015006(2018)

However, in the angle measurement method described in Non-Patent Document 2, the angular displacement of the object is detected using only transmitted light that has passed through the object. For this reason, there is a problem in that the upper limit of measurement resolution is restricted when processing measurement signals.

One of the objects of the present invention is to provide an angular displacement measuring device and an angular displacement measuring method that increase measurement resolution and acquire the angular displacement of an object with high precision.

In one aspect, the angular displacement measuring device is
an irradiation unit that irradiates light toward a target object;
a detection unit that detects reflected light that is emitted from the irradiation unit and is reflected from the target object, and transmitted light that is irradiated from the irradiation unit and that has passed through the target object;
a processing unit that obtains an angular displacement of the object based on a ratio between the intensity of the detected reflected light and the intensity of the detected transmitted light;
Equipped with

In another aspect, the angular displacement measurement method includes:
Irradiates light towards the target,
Detecting the reflected light that is the irradiated light and is reflected from the target object, and the transmitted light that is the irradiated light that is transmitted through the target object,
An angular displacement of the object is obtained based on a ratio between the intensity of the detected reflected light and the intensity of the detected transmitted light.

According to the present invention, the measurement resolution can be increased and the angular displacement of the target object can be acquired with high accuracy.

FIG. 2 is a schematic diagram showing multiple reflections occurring in a Fabry-Perot interferometer in an optical system according to an embodiment and optical path differences between light components having different numbers of reflections. 1 is a diagram schematically showing an example of a functional configuration of an angular displacement measuring device according to an embodiment. 1 is a diagram schematically showing a hardware configuration example of an angular displacement measuring device according to an embodiment. 1 is a block diagram showing an example of a hardware configuration of a computer according to an embodiment. FIG. 2A and 2B are diagrams for explaining the intensity of an optical frequency comb, in which (a) is a graph showing the intensity in the time domain, and (b) is a graph showing the intensity in the frequency domain. FIG. 3 is a diagram showing simulation results of the dependence of the intensity of light of a certain wavelength on angular displacement. (a) shows the dependence of the intensity of reflected light on angular displacement, (b) shows the dependence of the intensity of transmitted light on angular displacement, and (c) shows the dependence of the intensity of transmitted light on angular displacement. shows the dependence of the ratio of the intensity of transmitted light to the intensity of reflected light, divided by the intensity of , on angular displacement. FIG. 3 is a diagram for explaining the dependence of the light intensity of transmitted light on the angular displacement of light components of two adjacent optical frequency peaks of an optical frequency comb.

[I. One embodiment]
EMBODIMENT OF THE INVENTION Hereinafter, each embodiment regarding the angular displacement measuring device and the angular displacement measuring method of this invention is described with reference to FIG. 1 thru|or FIG.

[1. principle]
First, the angle measurement principle of this embodiment will be explained. FIG. 1 is a diagram schematically showing multiple reflections occurring in a Fabry-Perot interferometer 22 in an optical system according to an embodiment and optical path differences between light components having different numbers of reflections. As shown in FIG. 1, the Fabry-Perot interferometer 22 has an optical device (etalon) composed of two partially reflecting mirrors 22a and 22b arranged in parallel and facing each other. Note that a single undivided optical device may serve as the two partial reflecting mirrors 22a and 22b.

When light enters the Fabry-Perot interferometer 22, the light is repeatedly reflected on the surfaces of the two partially reflecting mirrors 22a and 22b. At this time, interference occurs, and the light intensity of the transmitted light beam LT and the reflected light beam LR depends on the optical path length difference inside the Fabry-Perot interferometer 22. The optical path length difference inside the Fabry-Perot interferometer 22 depends on the angle between the incident light beam L2 and the Fabry-Perot interferometer 22 and on the optical frequency. Therefore, when focusing on a certain optical frequency, the angle can be specified from the strength of the light intensity of the transmitted light and the light intensity of the reflected light from the Fabry-Perot interferometer 22.

The light intensity changes of the transmitted light and reflected light from the Fabry-Perot interferometer 22 are steep, and the conditions under which the light intensity observed at a specific optical frequency peaks are discrete. From this, it becomes possible to specify the angular displacement from the optical frequency at which the optical intensity peaks.

Furthermore, regarding the intensity of the transmitted light and reflected light from the Fabry-Perot interferometer 22, when the intensity of the transmitted light from the Fabry-Perot interferometer 22 is strong, the intensity of the reflected light from the Fabry-Perot interferometer 22 is weak; When the intensity of the transmitted light from the Fabry-Perot interferometer 22 is weak, the intensity of the reflected light from the Fabry-Perot interferometer 22 is strong. Therefore, the intensity ratio between the transmitted light and the reflected light from the Fabry-Perot interferometer 22 is the intensity change of only the reflected light from the Fabry-Perot interferometer 22 or only the transmitted light from the Fabry-Perot interferometer 22. It can be seen that there is a steeper response to angular displacement than when observing .

The angular displacement measuring device and the angular displacement measuring method according to the present embodiment are based on the above-described properties of light interference and the relationship between the intensities of reflected light and transmitted light. Hereinafter, the functional configuration of the angular displacement measuring device will be explained in [2], and the hardware configuration will be explained in [3].

[2. Functional configuration]
FIG. 2 is a diagram schematically showing an example of the functional configuration of the angular displacement measuring device 100 according to the embodiment. The angular displacement measurement device 100 includes a control device 10 and an optical system 20. The control device 10 and the optical system 20 are communicably connected to each other, and the connection method may be either wired or wireless.

[2-1. Optical system]
As shown in FIG. 2, the optical system 20 includes an irradiation section 21, an interference section 22, a propagation section 23, and a detection section 26.

The irradiation unit 21 irradiates light toward the target object. As will be described later, since the interference section 22 is attached (attached) to the object, it can be said that the irradiation section 21 irradiates light toward the interference section. The irradiation unit 21 irradiates light with a single frequency (wavelength) or multiple frequencies (wavelengths). Furthermore, the irradiation unit 21 may stabilize the frequency of the irradiated light and may collimate the diffusion of the irradiated light.

The interference section 22 emits the light emitted from the irradiation section 21 as reflected light and also as transmitted light. In other words, the interference section 22 reflects the incident light and causes it to interfere, thereby emitting light of a specific wavelength as reflected light and transmitted light. A part of the light incident on the interference section 22 is reflected within the interference section 22 and emitted to the outside of the interference section 22 . The number of times the reflected light emitted to the outside of the interference section 22 (hereinafter also simply referred to as reflected light) is reflected within the interference section 22 is from one to a plurality of times. The other part of the light incident on the interference section 22 passes through the interference section 22 and is emitted to the outside of the interference section 22 . The number of times the transmitted light (hereinafter also simply referred to as transmitted light) emitted to the outside of the interference section 22 is reflected within the interference section 22 is from 0 times to a plurality of times. The interference section 22 is detachably attached to the object to be measured.

The propagation section 23 propagates the light emitted from the interference section 22. The propagation section 23 collects and transmits the emitted light. The propagation section 23 includes a first propagation section 24 that propagates the reflected light emitted from the interference section 22 and a second propagation section 25 that propagates the transmitted light emitted from the interference section 22.

The detection unit 26 detects the reflected light reflected from the target object and the transmitted light transmitted through the target object. Since the interference section 22 is attached to the object, it can be said that the detection section 26 detects the reflected light reflected by the interference section 22 and the transmitted light that has passed through the interference section 22. The detection section 26 includes a first detection section 27 that receives the reflected light emitted from the interference section 22 and propagated by the first propagation section 24, and detects the intensity of the light, and a second detection section 27 that receives the reflected light emitted from the interference section 22 and propagated by the first propagation section 24, and detects the intensity of the reflected light. The second detection section 28 receives the transmitted light propagated by the propagation section 25 and detects the intensity of the light. The detection unit 26 transmits the detected intensities of the reflected light and transmitted light to the control device 10.

[2-2. Control device]
As shown in FIG. 2, the control device 10 includes a processing section 11. The processing unit 11 determines the target based on the ratio of the intensity of reflected light detected by the detection unit 26 (first detection unit 27) and the intensity of transmitted light detected by the detection unit 26 (second detection unit 28). Obtain the angular displacement of an object. In other words, the processing unit 11 uses the reflected light detected by the detection unit 26 (first detection unit 27) as a reference for the transmitted light detected by the detection unit 26 (second detection unit 28), and uses it as a reference for the transmitted light detected by the detection unit 26 (second detection unit 28). Get the angular displacement. Further, the processing unit 11 controls the optical system 20, performs various calculations on the data acquired by the optical system 20, and displays the results of the calculations. The ratio is calculated by dividing the intensity of the transmitted light detected by the second detection section 28 by the intensity of the reflected light detected by the first detection section 27, as will be described later. Alternatively, the ratio is calculated by dividing the intensity of reflected light detected by the first detection section 27 by the intensity of transmitted light detected by the second detection section 28, as described later. In other words, the processing unit 11 uses the transmitted light detected by the detection unit 26 (second detection unit 28) as a reference for the reflected light detected by the detection unit 26 (first detection unit 27), and uses it as a reference for the reflected light detected by the detection unit 26 (first detection unit 27). Get the angular displacement.

The processing unit 11 may calculate values necessary for calculating the optical intensity of the optical frequency comb and the above-mentioned ratio, as will be described later.

[3. Hardware configuration]
FIG. 3 is a diagram schematically showing an example of the hardware configuration of the angular displacement measuring device 100 according to the embodiment.

[3-1. Optical system]
The optical system 20 is composed of a plurality of parts (instruments, devices), and these parts are grouped according to the functions shown in FIG. 2 described above. Therefore, it will be explained below in association with the functional configuration of FIG.

The irradiation unit 21 is a light source 21a. Although it is sufficient in principle for measurement if the light source 21a can emit light of a single wavelength, it is more practical to perform measurement using light of a wide range of wavelengths, so the light source 21a should be a light source that can emit light of a wide range of wavelengths. is desirable. Examples of the light source 21a include a white light source, a swept laser, a femtosecond laser, an optical frequency comb, and the like. Note that the light emitted from the light source 21a does not need to be emitted at regular intervals, and if it is possible to emit light of a plurality of frequencies, the frequency intervals do not need to be constant.

In this example, the light source 21a is an optical frequency comb 21a. Since the optical frequency comb 21a has a discrete frequency spectrum, it is easier to identify the peak wavelength during intensity analysis and the measurement resolution is improved compared to white light having a continuous spectrum. In addition, the laser, which is an optical frequency comb generator built into the optical frequency comb 21a, has a higher intensity than white light, which reduces the influence of noise and allows for highly accurate measurement. Furthermore, since the frequency of the optical frequency comb 21a is controlled with high precision, it is very stable. Therefore, the wavelength of each light beam (collimated light beam LC, reflected light beam LR, and transmitted light beam LT) is also very stable, and the focal length is also stable.

The irradiation unit 21 may include a collimating unit 21b between the light source 21a and a Fabry-Perot interferometer 22, which will be described later. When the light LI emitted from the light source 21a is diffused, the collimator 21b collimates (collimates) the light LI to generate a collimated light beam LC.

The irradiation unit 21 may further include a frequency standard 21c. An example of the frequency standard device 21c is a rubidium oscillator. The frequency standard 21c further stabilizes the frequency of the light source 21a. For example, when using the optical frequency comb 21a, frequency fluctuations may become large due to current noise from the power supply that drives the laser, but by using the frequency standard 21c, the accurate frequency can be determined. By comparing the frequency of the standard device 21c and the optical frequency comb 21a, systematic errors due to light source frequency errors can be reduced. This makes it possible to associate the obtained angular displacement information with accurate frequencies, thereby further improving measurement accuracy.

The interference section 22 is an optical resonator made up of two partial mirrors. An example of an optical resonator is a Fabry-Perot interferometer. As shown in FIG. 1, the Fabry-Perot interferometer 22 has an optical device (etalon) composed of two partially reflecting mirrors 22a and 22b arranged in parallel and facing each other. Light entering the etalon undergoes multiple reflections between two mirrors placed facing each other, causing interference and emitting a specific wavelength. The Fabry-Perot interferometer 22 can be attached to and detached from the object by any method.

The object 30 is an object to be measured. The angular displacement measuring device 100 measures the angular displacement of a moving object (object to be measured) 30. Examples of the object 30 include a semiconductor exposure device and a linear slide of a machine tool.

The light separated by the Fabry-Perot interferometer 22 is detected by the detection unit 26 as reflected light and transmitted light, respectively. The separated light may enter the detection section 26 via the propagation section 23 and be detected, or may directly enter the detection section 26 and be detected. In this embodiment, a configuration including a propagation section 23 will be described as an example. The propagation section 23 is composed of condenser lenses 24a, 25a and optical fibers 24b, 25b.

The first propagation section 24 includes a reflected light beam condensing lens 24a and a reflected light beam optical fiber 24b. The reflected light beam condensing lens 24a and the reflected light beam optical fiber 24b are arranged in the direction in which reflected light emitted from the Fabry-Perot interferometer 22 is reflected. The reflected light beam condensing lens 24a collects the reflected light that is incident on the Fabry-Perot interferometer 22 and is reflected, thereby generating a reflected light beam LR. The reflected light beam optical fiber 24b is arranged at the rear focal plane of the reflected light beam condensing lens 24a, and transmits the reflected light to the first detection section 27.

The second propagation section 25 includes a transmitted light beam condensing lens 25a and a transmitted light beam optical fiber 25b. The transmitted light beam condensing lens 25a and the transmitted light beam optical fiber 25b are arranged in the transmission direction of the transmitted light emitted from the Fabry-Perot interferometer 22. The transmitted light beam condensing lens 25a condenses the transmitted light that has entered and passed through the Fabry-Perot interferometer 22 to generate a transmitted light beam LT. The transmitted light beam optical fiber 25b is arranged at the rear focal plane of the transmitted light beam condensing lens 25a, and transmits the transmitted light to the second detection section 28.

The detection unit 26 is a device having a photodetection function (hereinafter referred to as a photodetection device). Examples of photodetection devices include photodiodes, optical spectrum analyzers that combine spectrometers and photodiodes, and the like. Note that the selection of the photodetection device is determined by the combination with the light source 21a. For example, when a swept laser whose frequency can be sequentially changed is used as the light source 21a, different light intensities can be obtained at different times, so there is no need to select an optical spectrum analyzer for separating the light.

The first detection unit 27 is a first photodetection device 27a. The first light detection device 27a detects the reflected light beam LR transmitted by the reflected light beam optical fiber 24b. The first light detection device 27a transmits the intensity of the detected reflected light flux LR to the control device 10.

In this example, the first light detection device 27a is an optical spectrum analyzer 27a for reflected light flux. The reflected light beam optical spectrum analyzer 27a is a device for spectrally analyzing the reflected light beam LR transmitted by the reflected light beam optical fiber 24b.

The second detection unit 28 is a second photodetection device 28a. The second light detection device 28a detects the transmitted light flux T transmitted by the transmitted light flux optical fiber 25b. The second light detection device 28a transmits the detected intensity of the transmitted light beam LT to the control device 10.

In this example, the second light detection device 28a is an optical spectrum analyzer 28a for transmitted light flux. The transmitted light beam optical spectrum analyzer 28a is a device for spectrally analyzing the transmitted light beam LT transmitted by the transmitted light beam optical fiber 25b.

[3-2. Control device]

In this example, the control device 10 is realized by a general-purpose information processing device (computer). FIG. 4 is a block diagram schematically showing a hardware (HW) configuration example of the control device (computer) 10 according to the embodiment. The computer 10 may include, for example, a processor 10a, a memory 10b, a storage section 10c, an IF (Interface) section 10d, an IO (Input/Output) section 10e, and a reading section 10f as a HW configuration.

The processor 10a is an example of an arithmetic processing device that performs various controls and calculations. The processor 10a may be communicably connected to each block within the computer 10 via a bus 10i. Examples of the processor 10a include integrated circuits (ICs) such as a central processing unit (CPU) and a graphics processing unit (GPU). In this example, the processing unit 11 is the processor 10a. The processor 10a calculates the values necessary for measuring angular displacement in this embodiment.

The memory 10b is an example of HW that stores information such as various data and programs. Examples of the memory 10b include one or both of a volatile memory such as a DRAM (Dynamic Random Access Memory), and a non-volatile memory such as a PM (Persistent Memory).

The storage unit 10c is an example of HW that stores information such as various data and programs. Examples of the storage unit 10c include various storage devices such as magnetic disk devices such as HDDs (Hard Disk Drives), semiconductor drive devices such as SSDs (Solid State Drives), and nonvolatile memories. Examples of nonvolatile memory include flash memory, SCM (Storage Class Memory), and ROM (Read Only Memory).

Furthermore, the storage unit 10c may store a program 10g (angular displacement measurement program) that implements all or part of various functions of the computer 10.

For example, the processor 10a of the control device 10 expands the program 10g stored in the storage unit 10c into the memory 10b and executes it, thereby operating the angular displacement measuring device 100 (processing unit 11) shown in FIG. function can be realized. Further, the first detection unit 27 and the second detection unit 28 illustrated in FIG. good.

The IF unit 10d is an example of a communication IF that performs connection with a network, control of communication, and the like. For example, the IF section 1d may include an adapter compliant with LAN (Local Area Network) such as Ethernet (registered trademark), optical communication such as FC (Fibre Channel), or the like. For example, the control device 10 may be communicably connected to the optical system 20 via the IF section 10d. Further, for example, the program 10g may be downloaded from the network to the computer 10 via the communication IF and stored in the storage unit 10c.

The IO unit 10e may include one or both of an input device and an output device. Examples of the input device include a keyboard, mouse, touch panel, and the like. Examples of the output device include a monitor, a projector, and a printer. For example, information and instructions may be input from the input device of the IO section 10e to the irradiation section 21, interference section 22, first detection section 27, and second detection section 28 shown in FIG. 2 described above. Further, for example, the information detected (obtained) by the first detection section 27 and the second detection section 28 shown in FIG. 2 described above may be output to an output device and displayed.

The reading unit 10f is an example of a reader that reads information (data) and program information recorded on the recording medium 10h. The reading unit 10f may include a connection terminal or device to which the recording medium 10h can be connected or inserted. Examples of the reading unit 10f include a USB (Universal Serial Bus) compliant adapter, a drive device that accesses a recording disk, a card reader that accesses a flash memory such as an SD card, and the like. Note that the program 1g may be stored in the recording medium 10h, or the reading unit 10f may read the program 10g from the recording medium 10h and store it in the storage unit 10c.

Examples of the recording medium 10h include non-transitory computer-readable recording media such as magnetic/optical disks and flash memories. Examples of magnetic/optical discs include flexible discs, CDs (Compact Discs), DVDs (Digital Versatile Discs), Blu-ray discs, and HVDs (Holographic Versatile Discs). Examples of flash memory include semiconductor memories such as USB memory and SD cards.

The HW configuration of the control device 10 described above is an example. Therefore, the number of HWs within the control device 10 may be increased or decreased (eg, adding or deleting arbitrary blocks), dividing, integrating in any combination, adding or deleting buses, etc., as appropriate. For example, in the control device 10, at least one of the IO section 10e and the reading section 10f may be omitted.

[4. Angular displacement measurement method]
Although the measurement principle of this embodiment was briefly explained in [1], the angular displacement measuring method of this embodiment will be explained in detail below. First, the properties of the optical frequency comb 21a will be explained in [4-1], and then the optical path difference generated in the Fabry-Perot interferometer 22 will be explained in [4-2]. Finally, the simulation results are explained in [4-3].

[4-1. Properties of optical frequency comb]
The properties of the optical frequency comb 21a used in the optical system according to the embodiment will be explained with reference to FIG. FIG. 5 is a diagram for explaining the intensity of the optical frequency comb 21a. FIG. 5(a) is a graph showing the light intensity of the optical frequency comb 21a in the time domain, and FIG. 5(b) is a graph showing the light intensity in the frequency domain. As shown in FIG. 5A, in the time domain, the pulse trains are arranged at intervals of the reciprocal of the frequency interval ν _rep between output peaks, that is, 1/ν _rep . As shown in FIG. 5(b), in the frequency domain, the peak intensity groups are arranged at intervals of ν _rep . In the frequency domain, the frequency ν _i of each output peak is expressed by the following formula.

Here, ν _rep : frequency interval between output peaks, ν _ceo : carrier envelope offset frequency, i: integer.

The wavelength of light in vacuum having a frequency ν _i is expressed by the following formula.

In this embodiment, an angular displacement measuring device is generated using the properties of equations (1) and (2). Note that the calculations based on equations (1) and (2) may be performed in the processing unit 11 of the control device 10.

ここで、λ：入射光の真空中の波長、ｎ：第一部分反射鏡２２ａと第二部分反射鏡２２ｂの間の屈折率、ｌ：第一部分反射鏡２２ａと第二部分反射鏡２２ｂとの間の距離、θ：第一部分反射鏡２２ａの法線とファブリー・ペロ干渉計２２内の光軸の成す角度、または、第二部分反射鏡２２ｂの法線とファブリー・ペロ干渉計２２内の光軸の成す角度である。 [4-2. Optical path difference caused by Fabry-Perot interferometer]
Returning to FIG. 1, the optical path difference caused by multiple reflections occurring in the Fabry-Perot interferometer 22 will be explained. FIG. 1 is a schematic diagram showing multiple reflections occurring in the Fabry-Perot interferometer 22 and optical path differences between light components having different numbers of reflections. A collimated light beam LC emitted from the light source 21a and collimated by the collimator 21b enters the Fabry-Perot interferometer 22, and is multiple-reflected by the first partial reflection mirror 22a and the second partial reflection mirror 22b. The phase difference δ between two components having an optical path difference of one round trip among the multiple reflection components is expressed as follows.

Here, λ: wavelength of incident light in vacuum, n: refractive index between the first partial reflection mirror 22a and the second partial reflection mirror 22b, l: between the first partial reflection mirror 22a and the second partial reflection mirror 22b. distance, θ: the angle between the normal to the first partial reflecting mirror 22a and the optical axis in the Fabry-Perot interferometer 22, or the normal to the second partial reflecting mirror 22b and the optical axis in the Fabry-Perot interferometer 22 It is the angle formed by

Generally, the former and latter angles of θ are different, but the refractive index of the space on the incident side of the first partial reflecting mirror 22a and the refractive index of the space between the first partial reflecting mirror 22a and the second partial reflecting mirror 22b If they are the same, they are the same angle. In this embodiment, since the refractive index of the space on the incident side of the first partial reflecting mirror 22a and the refractive index of the space between the first partial reflecting mirror 22a and the second partial reflecting mirror 22b are different, in the operation example described later. The angle θ represents the angle between the normal line of the second partial reflecting mirror 22b and the optical axis within the Fabry-Perot interferometer 22.

The reflected light reflected from the Fabry-Perot interferometer 22 includes a light component that is incident on the first partial reflection mirror 22a and reflected by the first partial reflection mirror 22a, and a light component that is reflected by the first partial reflection mirror 22a and the second partial reflection mirror 22b. It includes a light component that is incident, reflected between the first partial reflection mirror 22a and the second partial reflection mirror 22b, and then exits from the first partial reflection mirror 22a. The light component transmitted to the first partial reflecting mirror 22a side is condensed by the reflected light beam condensing lens 24a, and becomes a reflected light beam LR.

The transmitted light that passes through the Fabry-Perot interferometer 22 includes a light component that enters the first partial reflection mirror 22a and the second partial reflection mirror 22b and is transmitted without being reflected by the second partial reflection mirror 22b, and a first partial reflection component. It includes a light component that enters the mirror 22a and the second partial reflection mirror 22b, is reflected between the first partial reflection mirror 22a and the second partial reflection mirror 22b, and then passes through the second partial reflection mirror 22b. The light component transmitted to the second partial reflecting mirror 22b side is condensed by the transmitted light beam condensing lens 25a, and becomes a transmitted light beam LT.

The intensity of the reflected light beam LR detected by the optical spectrum analyzer 27a for reflected light beam and the intensity of the transmitted light beam LT detected by the optical spectrum analyzer 28a for transmitted light beam are each transmitted to the control device 10.

The processing unit 11 of the control device 10 divides the intensity of the transmitted light (transmitted light flux intensity ⁾ |A _t | ² by the intensity of the reflected light (reflected light flux intensity) |A _r | The ratio of the intensity of transmitted light (transmitted luminous flux intensity) |A _t | ² to (luminous flux intensity) |A _r | ² is calculated. The processing unit 11 of the control device 10 may calculate a value necessary to calculate the ratio.

ここでＲ_１：第一部分反射鏡２２ａの反射率、Ｒ_２：第二部分反射鏡２２ｂの反射率である。また、δ：多重反射成分のうち１往復だけ光路差のある二つの成分の位相差である（式３）。 The reflectance R _FP of the Fabry-Perot interferometer 22 is expressed as the ratio of the reflected luminous flux intensity |A _r | ² to the incident luminous flux intensity |A _i | ² as follows. Note that the complex amplitude A _r of the reflected light beam LR is calculated by a general formula using the complex amplitude A _i of the collimated light beam LC.

Here, R ₁ is the reflectance of the first partial reflecting mirror 22a, and R ₂ is the reflectance of the second partially reflecting mirror 22b. Further, δ is the phase difference between two components having an optical path difference of one round trip among the multiple reflection components (Formula 3).

The transmittance T _FP of the Fabry-Perot interferometer 22 is expressed as the ratio of the transmitted luminous flux intensity |A _t | ² to the incident luminous flux intensity |A _i | ² as follows. Note that the complex amplitude A _t of the transmitted light beam LT is calculated by a general formula using the complex amplitude A _i of the collimated light beam LC.

From equations (4) and (5), the ratio of transmitted light flux intensity |A _t | ² to reflected light flux intensity |A _r | ² can be calculated using the following equation.

From equation (3) and equation (6), the following equation is obtained.

[4-3. simulation result]
FIG. 6 shows data as a result of simulating the dependence of the light intensity ratio on the angular displacement of the optical spectrum for one frequency among the plurality of frequencies shown in FIG. 5(b). FIG. 6(a) shows the dependence of the ratio of the intensity of reflected light to the intensity of incident light on the angular displacement of the optical spectrum, and FIG. 6(b) shows the dependence of the ratio of the intensity of transmitted light to the intensity of incident light. , which shows the dependence of the optical spectrum on the angular displacement, and Figure 6(c) shows the dependence of the intensity of the transmitted light on the angular displacement of the optical spectrum on the ratio of the intensity of the transmitted light to the intensity of the reflected light, which is the intensity of the transmitted light divided by the intensity of the reflected light. indicates a dependence on

The horizontal axes in FIGS. 6(a) to 6(c) represent the angle of light incident on the Fabry-Perot interferometer 22 attached to the object, specifically, the normal line of the second partial reflection mirror 22b and the Fabry-Perot interferometer 22. 3 shows changes in the angle θ formed by the optical axis within the Perot interferometer 22. The vertical axis in FIG. 6(a) shows the reflected light flux intensity ratio _RFP , the vertical axis in FIG. 6(b) shows the transmitted light flux intensity ratio _TFP , and the vertical axis in FIG. 6(c) shows the reflected light flux It represents the ratio of the transmitted luminous flux intensity |A _t | ² to the intensity |A _r | ² , and is calculated using equation (6). Here, R ₁ =0.9, R ₂ =0.9, n=1, λ=1550 nm, and l=50 mm.

The positions (angles) at which the respective peaks in FIGS. 6(a) to 6(c) exist coincide with each other based on the law of conservation of energy in physics. Note that the position (angle) where each peak exists differs depending on the frequency. The graph in FIG. 6(c) shows the displacement for a steeper angle than the graphs in FIGS. 4(a) and 4(b). Angular displacement can be detected from the angle that takes the local minimum value in Figure 6(a) and the angle that takes the local maximum value in Figure 6(b), but the angular displacement can be detected from the angle that takes the local maximum value in Figure 6(c). It is thought that the accuracy of angle measurement will be higher if this is done.

How to view FIGS. 6(a) to 6(c) will be briefly explained. For example, when light is incident at an angle of approximately 0.1, the reflected luminous flux intensity ratio R _FP near the angle 0.1 in FIG. 6(a) is 0.0, and the angle 0.1 in FIG. 6(b) is The transmitted light flux intensity ratio T _FP in the vicinity is 1.0. Given a slight angular displacement from the angle of about 0.1 where R _FP is 0.0 and T _FP is 1.0, R _FP will increase from 0.0 while T _FP will decrease from 1.0. It can be seen from FIG. 6 that the sum of R _FP and T _FP is always 1, and for example, at an angle where R _FP is 0.8, T _FP is 0.2.

Although the relationship between the change in angle and the change in light intensity can be seen from each of FIGS. 6(a) and (b), this relationship can be seen more clearly in FIG. 6(c). In Figures 6(b) and 6(c), peaks exist at the same angle, but compared to the slope of the peaks present in Figure 6(b) with respect to angular displacement, the peaks present in Figure 6(c) It is clear that the slope with respect to the angular displacement is large. In this way, by dividing the transmitted light flux intensity ratio T _FP by the reflected light flux intensity ratio R _FP , the peak becomes more prominent and the change in light intensity with respect to the change in angle becomes larger. As a result, angular displacement can be detected in detail, making it possible to provide a highly sensitive and high-resolution angular displacement measuring device and method. The same argument can be made by taking the ratio of the transmitted light flux intensity |A _t | ² and the reflected light flux intensity |A _r | ² instead of the ratio of R _FP and T _FP described above.

FIG. 7 shows the ratio of the optical spectrum of two adjacent optical frequency peaks of the optical frequency comb 21a observed by the reflected light beam optical spectrum analyzer 27a to the optical spectrum observed by the transmitted light beam optical spectrum analyzer 28a. This is the result of calculating the dependence of on angular displacement. Here, R ₁ =0.9, R ₂ =0.9, n=1, λ=1550 nm, l=50 mm, and ν _rep =100 MHz. In FIG. 7, it can be seen that the optical components of two adjacent optical frequency peaks of the optical frequency comb 21a have peaks at different angular displacements. Therefore, it is considered that the angle can be determined more accurately by dividing the spectrum with each optical spectrum analyzer 27a, 28a.

[4-4. Operation example]
The operation of the angular displacement measuring device 100 will be described with reference to FIGS. 2 and 3. The irradiation unit 21 (optical frequency comb 21a) of the optical system 20 irradiates the object 30 with light. The frequency of the irradiated light may be stabilized by the frequency standard device 21c. The irradiation light LI emitted from the light source 21a is collimated by the collimating section 21b, and a collimated light beam LC is generated.

When the values in the optical frequency comb 21a, for example, ν _rep : frequency interval between output peaks and ν _ceo : carrier envelope offset frequency, are set in advance, the irradiation unit 21 transmits these values to the control device 10. It's okay.

The collimated light beam LC enters the interference unit 22 (Fabry-Perot interferometer 22) mounted on the object 30, is multiple reflected by the first partial reflection mirror 22a and the second partial reflection mirror 22b, and interferes with each other.

The interference unit 22 has a value in the Fabry-Perot interferometer 22, for example, λ: the wavelength of the incident light in vacuum, n: the refractive index between the first partial reflection mirror 22a and the second partial reflection mirror 22b, and l: the first portion. Distance between the reflecting mirror 22a and the second partial reflecting mirror 22b, θ: Angle formed by the normal line of the second partially reflecting mirror 22b and the optical axis in the Fabry-Perot interferometer 22, R1: Angle of the first partially reflecting mirror 22a If the reflectance, R2: the reflectance of the second partial reflection mirror 22b, and δ: the phase difference between two components with an optical path difference of one round trip among the multiple reflection components, are set in advance, these values are controlled. It may also be transmitted to the device 10.

The reflected light reflected from the interference section 22 is transmitted to the first detection section 27 by the first propagation section 24 . The reflected light emitted from the Fabry-Perot interferometer 22 is condensed by the reflected light beam condensing lens 24a to generate a reflected light beam LR, which is transmitted to the reflected light beam optical spectrum analyzer 27a through the reflected light beam optical fiber 24b. The reflected light beam optical spectrum analyzer 27 a receives the reflected light beam LR and transmits the detected intensity to the control device 10 .

The transmitted light that has passed through the interference section 22 is transmitted to the second detection section 28 by the second propagation section 25 . The transmitted light emitted from the Fabry-Perot interferometer 22 is condensed by a transmitted light beam condenser lens 25a to generate a transmitted light beam LT, which is transmitted to an optical spectrum analyzer 28a for transmitted light beams through an optical fiber 25b for transmitted light beams. The transmitted light beam optical spectrum analyzer 28 a receives the transmitted light beam LT and transmits the detected intensity to the control device 10 .

The processing unit 11 of the control device 10 calculates necessary values based on the values received from the irradiation unit 21, the interference unit 22, and the detection unit 26. The processing unit 11 calculates the intensity ratio of the transmitted light flux intensity |A _t | ² to the reflected light flux intensity |A _r | ² based on equation (8). The processing unit 11 outputs the received values and the results calculated based on the received values in various formats.

Note that the processing unit 11 may correct the value detected by the detection unit 26. For example, the simulation results in FIG. 6 are results based on the assumption that the light is not attenuated in the interference section 22, but the intensity of each of the reflected light and transmitted light is multiplied by a predetermined parameter (attenuation coefficient) according to the degree of attenuation. It may be corrected by Thereby, it is possible to perform simulations also for attenuated reflected light and transmitted light.

[4-5. Modified example]
In the above, the ^processing unit 11 calculates the intensity ratio by dividing the transmitted light flux intensity _| A _t | ² by the reflected light flux intensity |A _r | ² ; The intensity ratio can also be calculated by dividing by |A _t | ² .

In this case, from equations (4) and (5), the ratio of reflected light flux intensity |A _r | ² to transmitted light flux intensity |A _t | ² can be calculated using equation (6) in the same manner as described above. In this case as well, the peak becomes more prominent and the change in light intensity with respect to the change in angle becomes larger, as in FIG. 6(c). As a result, angular displacement can be detected in detail, making it possible to provide a highly sensitive and high-resolution angular displacement measuring device and method.

Also, from equations (3) and (6), the angle θ between the normal to the first partial reflecting mirror 22a and the optical axis within the Fabry-Perot interferometer 22, or the angle θ between the normal to the second partial reflecting mirror 22b and the Fabry - The angle θ formed by the optical axis within the Perot interferometer 22 can be calculated using equation (7) in the same manner as described above.

[5. effect]
(1) The angular displacement measurement device 100 includes an irradiation unit 21 that irradiates light toward the target object 30, a reflected light that is irradiated from the irradiation unit 21 and reflected from the target object 30, and a light emitted from the irradiation unit 21. A detection unit 26 (27, 28) that detects the transmitted light that is irradiated from the target object 30 and that is transmitted through the object 30, and the intensity of the detected reflected light and the detected transmitted light It includes a processing unit 11 that obtains the angular displacement of the target object 30 based on the ratio. By taking the ratio of reflected light and transmitted light, changes in light intensity with respect to angular displacement are emphasized, so resolution when measuring angular displacement can be improved.

(2) The angular displacement measuring device 100 further includes an interference section 22, which emits the light emitted from the irradiation section 21 by the Fabry-Perot interferometer 22 as reflected light and as transmitted light. Emits light. The light emitted from the irradiation unit 21 is multiple reflected by the Fabry-Perot interferometer 22 and interferes with each other, so that the Fabry-Perot interferometer 22 can extract reflected light and transmitted light of a specific wavelength.

(3) The ratio is calculated by dividing the intensity of the detected transmitted light by the intensity of the detected reflected light, or dividing the intensity of the detected reflected light by the intensity of the detected transmitted light. Calculated by dividing. By taking advantage of the property of light interference that the peaks of light intensity with respect to the angle of transmitted light and reflected light correspond to each other, it is possible to emphasize changes in light (intensity) with respect to angular displacement without performing complex calculations. I can do it.

(4) The interference unit 22 is attached to the object 30, the light irradiated from the irradiation unit 21 enters the interference unit 22, and the detection unit 26 (27, 28) detects the reflected light reflected by the interference unit 22, The transmitted light transmitted through the interference section 22 is detected. By attaching the Fabry-Perot interferometer 22 to the object 30, reflected light and transmitted light necessary for measuring the angular displacement of the object can be extracted.

(5) The irradiation unit 21 irradiates light from a light source capable of emitting a plurality of frequencies. Although it is sufficient for the light source 21a to emit light of a single frequency (wavelength) for the measurement principle according to this embodiment, more practical measurements can be performed if the light source 21a can emit light of multiple frequencies (wavelengths). I can do it.

(6) The angular displacement measurement device 100 includes:
An optical frequency comb 21a,
a collimating section 21b that collimates the femtosecond laser beam LI emitted from the optical frequency comb 21a to generate a collimated light beam LC;
a Fabry-Perot interferometer 22 attached to the object 30;
a reflected light beam condensing lens 24a that condenses a reflected light beam LR when the collimated light beam LC is incident on the Fabry-Perot interferometer 22;
an optical fiber 24b for reflected light flux disposed at the rear focal plane of the reflected light flux condensing lens 24a;
a reflected light beam optical spectrum analyzer 27a that spectrally analyzes the light transmitted by the reflected light beam optical fiber 24b;
a transmitted light beam condensing lens 25a that condenses a transmitted light beam LT when the collimated light beam LC is incident on the Fabry-Perot interferometer 22;
an optical fiber 25b for transmitted light flux disposed at the rear focal plane of the transmitted light flux condensing lens 25a;
an optical spectrum analyzer 28a for transmitted light flux that spectrally analyzes the light transmitted by optical fiber 25b for transmitted light flux;
a frequency standard 21c for stabilizing the laser oscillation frequency of the optical frequency comb 21a;
has
The light acquired by the reflected light beam optical spectrum analyzer 27a is used as a reference for the light acquired by the transmitted light beam optical spectrum analyzer 28a.
With the above configuration, the stable spectrum of the optical frequency comb 21a can be utilized and the frequency standard 21c can further stabilize the spectrum. Furthermore, the Fabry-Perot interferometer 22 can extract reflected light and transmitted light of a specific frequency. Further, the reflected light spectrum analyzer 27a can spectrally analyze the reflected light to obtain its intensity, and the transmitted light spectrum analyzer 28a can spectrally analyze the transmitted light to obtain its intensity. By using the light acquired by the reflected light beam optical spectrum analyzer 27a as a reference for the light acquired by the transmitted light beam optical spectrum analyzer 28a, changes in the intensity of light with respect to angular displacement are emphasized. The resolution during measurement can be improved.

The irradiation unit 21 may include an optical frequency comb 21a. Since the optical frequency comb 21a has the above-mentioned advantages, the peak wavelength can be easily identified during intensity analysis, measurement resolution is improved, and highly accurate measurement can be expected. Furthermore, the wavelengths of the respective light beams (collimated light beam LC, reflected light beam LR, and transmitted light beam LT) are also very stable, and the focal length is also stable.

The irradiation unit 21 may further include a frequency standard 21c. The frequency standard device can further stabilize the frequency of the light from the light source 21a.
[II. others]

Note that the present invention is not limited to the embodiments described above. For example, various changes that can be understood by those skilled in the art may be made to the embodiments described above without departing from the spirit of the present invention. For example, any combination of the embodiments and modifications described above may be adopted as other modifications of the embodiments described above without departing from the spirit of the present invention.

In the embodiment described above, an example has been described in which the optical system includes condenser lenses 24a and 25a and optical fibers 24b and 25b. Alternatively, the configuration may be such that the light separated from the Fabry-Perot interferometer 22 is directly detected by the light detection devices 27a and 28a without the condensing lenses 24a and 25a and the optical fibers 24b and 25b.

100 Angular displacement measuring device 10 Information processing device (computer)
11 Processing section 20 Optical system 21 Irradiation section 21a Optical frequency comb 21b Collimating section 21c Frequency standard 22 Interference section (Fabry-Perot interferometer)
22a First partial reflecting mirror 22b Second partial reflecting mirror 23 Propagation section 24 First propagation section 24a Reflected beam condensing lens 24b Reflected beam optical fiber 25 Second propagation section 25a Transmitted beam condensing lens 25b Transmitted beam optical fiber 26 Detection section 27 First detection part (detection part)
27a First photodetection device (optical spectrum analyzer for reflected light flux)
28 Second detection section (detection section)
28a Second photodetection device (optical spectrum analyzer for transmitted light flux)
30 Target LI Irradiation light (femtosecond laser light)
LC Collimated luminous flux LR Reflected luminous flux LT Transmitted luminous flux

Claims (7)

an irradiation unit that irradiates light toward a target object;
a detection unit that detects reflected light that is emitted from the irradiation unit and is reflected from the target object, and transmitted light that is irradiated from the irradiation unit and that has passed through the target object;
a processing unit that obtains an angular displacement of the object based on a ratio between the intensity of the detected reflected light and the intensity of the detected transmitted light;
An angular displacement measuring device comprising: The angular displacement according to claim 1, further comprising an interference section that emits the light irradiated from the irradiation section by the Fabry-Perot interferometer as the reflected light and as the transmitted light. measuring device. The ratio is calculated by dividing the intensity of the detected transmitted light by the intensity of the detected reflected light, or by dividing the intensity of the detected reflected light by the intensity of the detected transmitted light. The angular displacement measuring device according to claim 1 or 2, characterized in that: The interference section is attached to the object,
The light emitted from the irradiation section enters the interference section,
The angular displacement measuring device according to claim 2, wherein the detection section detects reflected light reflected by the interference section and transmitted light transmitted through the interference section. The angular displacement measuring device according to claim 1 or 2, wherein the irradiation unit irradiates light from a light source capable of emitting a plurality of frequencies. optical frequency comb,
a collimating unit that collimates the femtosecond laser beam irradiated from the optical frequency comb to generate a collimated beam;
A Fabry-Perot interferometer attached to the object to be measured,
a reflected light beam condensing lens that collects a reflected light beam when the collimated light beam is incident on the Fabry-Perot interferometer;
an optical fiber for reflected light flux disposed on the rear focal plane of the reflected light flux condensing lens;
an optical spectrum analyzer for reflected light flux that spectrally analyzes the light transmitted by the optical fiber for reflected light flux;
a transmitted light beam condensing lens that condenses a transmitted light beam when the collimated light beam is incident on the Fabry-Perot interferometer;
an optical fiber for transmitted light flux disposed on the rear focal plane of the transmitted light flux condensing lens;
an optical spectrum analyzer for transmitted light flux that spectrally analyzes the light transmitted by the optical fiber for transmitted light flux;
a frequency standard for stabilizing the laser oscillation frequency of the optical frequency comb;
has
An angular displacement measuring device characterized in that the light acquired by the optical spectrum analyzer for the reflected beam is used as a reference for the light acquired by the optical spectrum analyzer for the transmitted beam. Irradiates light towards the target,
detecting the reflected light that is the irradiated light and is reflected from the object, and the transmitted light that is the irradiated light that is transmitted through the object;
An angular displacement measuring method, characterized in that an angular displacement of the object is obtained based on a ratio between the intensity of the detected reflected light and the intensity of the detected transmitted light.

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