Optical Frequency Modulator

Abstract

To provide an optical frequency modulator capable of continuously emitting diffracted light having a desired frequency at a low cost.SOLUTION: An optical frequency modulator comprises: a rotating body 34B which has a rotating axis C and a cylindrical shape extending in a direction parallel to the rotating axis C and rotates at constant speed centering on the rotating axis C; and a plurality of transmission type diffraction gratings 42B formed on the peripheral surface of the rotating body 34B, parallel to the rotating axis C, performing frequency modulation on the incident light (measurement light L1) incident on the peripheral surface of the rotating body 34B during rotation and emitting the frequency-modulated diffracted light (modulated measurement light L1A).SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an optical frequency modulator that performs frequency modulation of light. [Background technology]

[0002] There is known a measurement device that uses optical heterodyne interferometry to detect the distance to a measurement object and the displacement of the measurement object. In optical heterodyne interferometry, one of two types of light with different frequencies is used as a measurement light and the other is used as a reference light, and an interference signal between the measurement light reflected from the measurement object and the reference light reflected from a reference surface is detected, and the distance to the measurement object and the displacement of the measurement object are detected based on this interference signal (see, for example, Patent Documents 1 to 3).

[0003] In optical heterodyne interferometry, known methods for generating measurement light and reference light with different frequencies include using a light source that can emit light of two different frequencies, and splitting the light emitted from the light source into measurement light and reference light, and frequency-modulating one of them using an optical frequency modulator (also called a frequency shifter).In this case, the former method requires the use of an expensive light source, so the latter method is often adopted from the perspective of cost.

[0004] A well-known optical frequency modulator includes an oscillator and a plurality of diffraction gratings formed on the surface of the oscillator (see, for example, Patent Document 4). This optical frequency modulator reflects incident light that is incident on the surface of the oscillator during vibration (reciprocating motion) with the diffraction grating, frequency-modulating (Doppler shifting), and emits the frequency-modulated diffracted light as measurement light or reference light. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-106284 [Patent Document 2] Japanese Patent Application Publication No. 2020-056658 [Patent Document 3] Japanese Patent Application Publication No. 2-160221 [Patent Document 4] JP 2020-165700 A Summary of the Invention [Problem to be solved by the invention]

[0006] When modulating the frequency of light using a diffraction grating, the diffraction grating needs to be moved in the same direction at a predetermined constant speed. In the optical frequency modulator described in Patent Document 4, the diffraction grating is moved by vibrating an oscillator. Therefore, while the oscillator is moving at a constant speed in one direction of oscillation, the diffracted light can be used as measurement light, etc.; however, while the oscillator is moving in the other direction (opposite to the one direction), the frequency of the diffracted light shifts in the opposite direction, making the diffracted light unusable. Furthermore, even when the oscillator's oscillation direction is switched from the other direction to the one direction, the optical frequency modulator described in Patent Document 4 cannot use the diffracted light as measurement light, etc., until the oscillator's moving speed reaches the above-mentioned constant speed. Therefore, the optical frequency modulator described in Patent Document 4 cannot continuously emit diffracted light of a desired frequency.

[0007] Therefore, it is conceivable to use, for example, an acousto-optic element as the optical frequency modulator, but an optical frequency modulator using an acousto-optic element is more expensive than an optical frequency modulator using a diffraction grating, which poses the problem of increased costs.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical frequency modulator that is capable of continuously emitting diffracted light of a desired frequency at low cost. [Means for solving the problem]

[0009] An optical frequency modulator for achieving the object of the present invention comprises a cylindrical rotor having a rotation axis and extending in a direction parallel to the rotation axis, the rotor rotating at a constant speed around the rotation axis, and a plurality of transmission type diffraction gratings formed on the circumferential surface of the rotor and parallel to the rotation axis, the transmission type diffraction gratings frequency-modulating incident light incident on the circumferential surface of the rotor during rotation and emitting frequency-modulated diffracted light.

[0010] According to this optical frequency modulator, each transmission type diffraction grating can be moved (rotated) at a constant speed along a rotational locus centered on the rotation axis, so that each diffraction grating can be maintained in a state where it passes the incident position of the incident light on the rotating body at a constant speed and continuously.

[0011] In an optical frequency modulator according to another aspect of the present invention, a transmission diffraction grating frequency-modulates incident light that enters the interior of the rotor from the outer circumferential surface of the rotor.

[0012] In another aspect of the present invention, an optical frequency modulator includes a reflector disposed inside a rotor that reflects incident light that has entered the rotor from outside along the rotation axis toward the inner circumferential surface of the rotor, and a transmission diffraction grating that frequency-modulates the incident light that has entered the inner circumferential surface from the reflector and is emitted to the outside of the rotor. This allows for the maximum amount of diffracted light to be obtained without performing difficult optical adjustments.

[0013] An optical frequency modulator according to another aspect of the present invention includes a drive unit that controls the rotation speed and direction of the rotor. [Effects of the Invention]

[0014] The present invention can continuously emit diffracted light of a desired frequency at low cost. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of a measurement device including an optical frequency modulator according to the present invention. [Figure 2] FIG. 1 is a schematic diagram of an optical frequency modulator according to a first embodiment. [Figure 3] FIG. 3 is an enlarged view of the area within the dotted circle A in FIG. 2. [Figure 4] FIG. 4 is an explanatory diagram for explaining a modified example of the diffraction grating of the first embodiment. [Figure 5] FIG. 10 is a schematic diagram of an optical frequency modulator according to a second embodiment. [Figure 6] FIG. 10 is a schematic diagram of an optical frequency modulator according to a third embodiment. [Figure 7] FIG. 7 is an enlarged view of the area within the dotted circle A1 in FIG. 6. [Figure 8] FIG. 10 is a schematic diagram of an optical frequency modulator according to a fourth embodiment. [Figure 9] FIG. 11 is a front view of a rotating body of an optical frequency modulator according to a fifth embodiment, as viewed from the axial side of the rotating shaft. [Figure 10] FIG. 11 is a cross-sectional view of a rotor of an optical frequency modulator according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Measuring equipment] Fig. 1 is a schematic diagram of a measurement device 10 equipped with an optical frequency modulator 16 of the present invention. As shown in Fig. 1, the measurement device 10 measures the distance to a measurement object 9 and the displacement (including minute displacement) of the measurement object 9 using an optical heterodyne interferometry method (optical heterodyne interferometer). Note that the measurement object 9 is provided with a retroreflective member 9a such as a corner cube reflector or a three-sided mirror for measurement by the measurement device 10.

[0017] The measurement device 10 includes a laser light source 12 , a half mirror 14 , an optical frequency modulator 16 , a half mirror 18 , a light receiving unit 20 , and a calculation device 22 .

[0018] The laser light source 12 emits laser light L of a predetermined frequency (wavelength) toward the half mirror 14. The half mirror 14 splits the laser light L incident from the laser light source 12 into measurement light L1 and reference light L2 of the same frequency. The half mirror 14 then emits the measurement light L1 toward the optical frequency modulator 16 and the reference light L2 toward the half mirror 18.

[0019] The optical frequency modulator 16, which will be described in detail later, frequency-modulates (shifts the frequency of) the measurement light L1 incident from the half mirror 14 by Doppler shifting, and emits modulated measurement light L1A having a different frequency from the reference light L2. The amount of frequency shift of the modulated measurement light L1A is not particularly limited and is set to a general value that allows measurement by optical heterodyne interferometry. The modulated measurement light L1A frequency-modulated by the optical frequency modulator 16 is emitted toward the retroreflecting member 9a and is retroreflected by the retroreflecting member 9a to enter the half mirror 18.

[0020] The half mirror 18 outputs to the light receiving unit 20 an interference signal SG (beat signal) between the modulated measurement light L1A incident from the retroreflection member 9a and the reference light L2 incident from the half mirror 14.

[0021] The light receiving unit 20 uses a known photodiode or the like, detects (receives) the interference signal SG incident from the half mirror 14, and outputs a detection signal of the interference signal SG to the calculation device 22.

[0022] The arithmetic device 22 performs predetermined arithmetic processing on the detection signal of the interference signal SG input from the light receiving unit 20, and calculates the distance from the measurement device 10 to the measurement object 9 (retroreflective member 9a). This makes it possible to measure the distance to the measurement object 9 and the displacement of the measurement object 9. Note that the specific calculation method performed by the arithmetic device 22 is a known technique, so a detailed description thereof will be omitted here.

[0023] First to fourth embodiments of the optical frequency modulator 16 will be described below.

[0024] [Optical frequency modulator of the first embodiment] FIG. 2 is a schematic diagram of an optical frequency modulator 16 according to a first embodiment. FIG. 3 is an enlarged view of the area enclosed by the dotted circle A in FIG. 2. As shown in FIGS. 2 and 3, the optical frequency modulator 16 frequency-modulates the measurement light L1 by Doppler shifting and emits modulated measurement light L1A. The optical frequency modulator 16 includes a first mirror 30, a first lens 32, a rotating body 34, a driver 36, a second lens 38, and a second mirror 40. Note that the configuration of the optical frequency modulator 16, other than the rotating body 34 and the driver 36, can be modified as appropriate.

[0025] The first mirror 30 reflects the measurement light L1 incident from the half mirror 14 toward a rotating rotor 34, which will be described later. As a result, the measurement light L1 (corresponding to the incident light of the present invention) is incident at a predetermined angle of incidence on a predetermined position (incident position P) of the rotating rotor 34.

[0026] The first lens 32 is disposed on the optical path of the measurement light L1 between the first mirror 30 and the rotating body 34, and emits the measurement light L1 incident thereon from the half mirror 14 toward the rotating body 34.

[0027] The rotating body 34 is a cylindrical body that has a rotation axis C and extends in a direction parallel to the rotation axis C. The rotating body 34 receives a driving force from a driving unit 36 ​​and rotates about the rotation axis C.

[0028] The driving unit 36 ​​is a known actuator configured, for example, with a motor, gears, etc., and controls the rotation direction and rotation speed of the rotating body 34. The driving unit 36 ​​rotates the rotating body 34 in one direction at a constant speed around the rotation axis C.

[0029] The rotor 34 has an outer peripheral surface 35 (corresponding to the curved surface of the present invention) formed along the circumferential direction of the rotation axis C (hereinafter simply referred to as the circumferential direction). On this outer peripheral surface 35, a plurality of diffraction gratings 42 parallel to the rotation axis C are formed (equally spaced) along the circumferential direction. As a result, while the rotor 34 continues to rotate at a uniform speed, each diffraction grating 42 passes continuously at a uniform speed through an incident position P of the measurement light L1 incident on the rotor 34 at a predetermined incident angle.

[0030] Each diffraction grating 42 is a blazed diffraction grating, a known reflective diffraction grating. When the measurement light L1 is incident on the diffraction grating 42 passing through the incident position P at a constant speed at a predetermined incident angle, the diffraction grating 42 generates specularly reflected reflected light LR and diffracted light (at least first-order diffracted light) that is reflected by the diffraction grating 42 and Doppler-shifted (frequency-modulated). In this embodiment, the first-order diffracted light (or second-order or later diffracted light, not shown) is used as the modulated measurement light L1A. Note that the emission angle of the modulated measurement light L1A, i.e., the amount of frequency shift of the modulated measurement light L1A, is arbitrary. Therefore, the rotation speed of the rotating body 34, the rotation direction of the rotating body 34, the angle of incidence of the measurement light L1, the blazed angle of the diffraction grating 42, and the pitch of the diffraction grating 42 are determined according to the desired amount of frequency shift.

[0031] The second lens 38 is disposed on the optical path of the modulated measurement light L1A emitted from the rotor 34, and emits the modulated measurement light L1A toward the second mirror 40. The second mirror 40 reflects the modulated measurement light L1A incident from the second lens 38 toward the retroreflection member 9a. As a result, the modulated measurement light L1A retroreflected by the retroreflection member 9a enters the half mirror 18, as shown in FIG. 1.

[0032] As described above, in the optical frequency modulator 16 of this embodiment, by forming multiple diffraction gratings 42 around the axis on the outer circumferential surface 35 of the cylindrical rotor 34, each diffraction grating 42 can be moved at a uniform speed (rotated at a uniform speed) along a rotational locus centered on the rotation axis C simply by rotating the rotor 34 at a uniform speed. Therefore, during the uniform rotation except when the rotor 34 starts and stops rotating, each diffraction grating 42 is maintained in a state of continuously passing through the incident position P at a uniform speed. This allows the rotor 34 to continuously emit modulated measurement light L1A of a desired frequency without interruption, without using an expensive acousto-optic element. As a result, modulated measurement light L1A (diffracted light) of a desired frequency can be continuously emitted at low cost.

[0033] (Modification of diffraction grating) Fig. 4 is an explanatory diagram illustrating a modified example of the diffraction grating 42 of the first embodiment. In the above first embodiment, a blazed diffraction grating has been described as an example of the reflective diffraction grating 42, but as shown in Fig. 4, for example, a reflective diffraction grating 42A may be formed by forming the outer peripheral surface 35 of the rotor 34 from glass or the like and forming a plurality of grooves 35a parallel to the rotation axis C in the direction around the axis on this outer peripheral surface 35. In other words, the type of reflective diffraction grating formed on the outer peripheral surface 35 is not particularly limited.

[0034] [Second embodiment] Fig. 5 is a schematic diagram of optical frequency modulator 16 of the second embodiment. As shown in Fig. 5, optical frequency modulator 16 of the second embodiment has basically the same configuration as optical frequency modulator 16 of the first embodiment, except that it includes rotor 34A instead of rotor 34. Therefore, components that are the same in function or configuration as those of the first embodiment are given the same reference numerals and their description will be omitted.

[0035] The rotor 34A of the second embodiment is a cylindrical body extending in a direction parallel to the rotation axis C, and receives a driving force from a drive unit 36 ​​to rotate at a uniform speed about the rotation axis C. This rotor 34A has the same outer circumferential surface 35 and multiple diffraction gratings 42 (or diffraction gratings 42A) as in the first embodiment. Therefore, as in the first embodiment, each diffraction grating 42 can be moved (rotated) at a uniform speed along a rotational locus about the rotation axis C. As a result, the optical frequency modulator 16 of the second embodiment can also achieve the same effects as the first embodiment.

[0036] [Third embodiment] FIG. 6 is a schematic diagram of an optical frequency modulator 16 of a third embodiment. FIG. 7 is an enlarged view of the area within the dotted circle A1 in FIG. 6. In the above-described embodiments, reflective diffraction gratings 42, 42A are formed on the outer peripheral surface 35 of the rotors 34, 34A, but in the third embodiment, as shown in FIGS. 6 and 7, a plurality of transmissive diffraction gratings 42B are formed on the outer peripheral surface 35 or the inner peripheral surface 37 (or both) of the rotor 34B. Note that the optical frequency modulator 16 of the third embodiment has basically the same configuration as the optical frequency modulator 16 of the above-described embodiments, except for the rotor 34B and the diffraction grating 42B. Therefore, components that are identical in function or configuration to those of the above-described embodiments are designated by the same reference numerals, and their description will be omitted.

[0037] Rotating body 34B of the third embodiment is a cylindrical body similar to rotating body 34A of the second embodiment, and receives a driving force from driving unit 36 ​​to rotate at a constant speed about rotation axis C. A plurality of transmission type diffraction gratings 42B are formed on outer peripheral surface 35 of rotating body 34B along the direction around the axis.

[0038] Each diffraction grating 42B is composed of multiple slits 35b (which may be light-transmitting portions such as glass) parallel to the rotation axis C, and multiple slits 35b are formed on the outer peripheral surface 35 (inner peripheral surface 37) at a predetermined pitch along the axial direction. The transmission diffraction grating 42B is not limited to the one shown in FIGS. 6 and 7 ; various known shapes (e.g., transmission blazed diffraction gratings, ruled lines, etc.) may be used instead. As in the above-described embodiments, when measurement light L1 is incident on the diffraction grating 42B passing through the incident position P at a predetermined angle of incidence, modulated measurement light L1A, which is Doppler-shifted diffracted light (at least first-order diffracted light), is transmitted through the diffraction grating 42B and emitted into the interior of the rotor 34B. This modulated measurement light L1A is then guided from the interior of the rotor 34B to the retroreflective member 9a via optical components such as multiple mirrors, prisms, and lenses (not shown).

[0039] In this way, in the third embodiment, the modulated measuring light L1A of a desired frequency can be emitted continuously without interruption from the rotor 34B, and therefore the same effects as in the above embodiments can be obtained.

[0040] [Fourth embodiment] Figure 8 is a schematic diagram of an optical frequency modulator 16 of a fourth embodiment. In the above-described embodiments, the optical frequency modulator 16 includes a cylindrical or columnar rotator 34, 34A, 34B, but as shown in Figure 8, the optical frequency modulator 16 of the fourth embodiment includes a non-cylindrical rotator 34C. Note that the optical frequency modulator 16 of the fourth embodiment has basically the same configuration as the optical frequency modulator 16 of the above-described embodiments except for the inclusion of the rotator 34C, and therefore components that are identical in function or configuration to those of the above-described embodiments are designated by the same reference numerals and their description will be omitted.

[0041] Rotating body 34C is a semi-cylindrical body (or a semi-cylinder) extending in a direction parallel to rotation axis C, and has a curved surface 50 (outer peripheral surface) that forms part of a circumference centered on rotation axis C when viewed from the axial direction of rotation axis C (the side perpendicular to the plane of paper in FIG. 8). Rotating body 34C receives a driving force from driving unit 36 ​​and rotates at a constant speed about rotation axis C.

[0042] A plurality of diffraction gratings 42 (or diffraction gratings 42A) are formed on the curved surface 50 along the axial direction. When the rotor 34C is formed in a semi-cylindrical shape, a transmission-type diffraction grating 42B similar to that in the third embodiment may be formed instead of the reflection-type diffraction gratings 42, 42A. This allows the rotor 34C to continuously emit the modulated measurement light L1A of the desired frequency while the diffraction grating 42 passes the incident position P at a constant speed in accordance with the rotation of the rotor 34C. As a result, in the fourth embodiment, the modulated measurement light L1A (pulsed light) of the desired frequency can be emitted from the optical frequency modulator 16.

[0043] In the above fourth embodiment, the rotating body 34C is formed as a semi-cylinder (semi-cylinder), but there is no particular limitation to this as long as it has a shape having a curved surface (outer surface) that forms part of a circumference centered on the rotation axis C, such as a quarter-cylinder (quarter-cylinder).

[0044] [Fifth embodiment] Fig. 9 is a front view (top view, side view) of a rotor 34B of an optical frequency modulator 16 according to the fifth embodiment, viewed from the axial direction of a rotation axis C. Fig. 10 is a cross-sectional view of the rotor 34B of the optical frequency modulator 16 according to the fifth embodiment.

[0045] In the third embodiment, a plurality of transmission type diffraction gratings 42B are formed on the rotor 34B, and the measurement light L1 incident from the outer peripheral surface 35 side of the rotor 34B into the rotor 34 is frequency-modulated by each diffraction grating 42B. In contrast, in the fifth embodiment, the measurement light L1 emitted from the inner peripheral surface 37 side of the rotor 34B to the outside of the rotor 34 is frequency-modulated by each diffraction grating 42B.

[0046] 9 and 10, the optical frequency modulator 16 of the fifth embodiment has basically the same configuration as the optical frequency modulator 16 of the third embodiment, except that the measurement light L1 enters the interior of the rotor 34B from the outside of the rotor 34B along the rotation axis C, and a reflector 54 is fixedly disposed inside the rotor 34B. Therefore, components that are the same in function or configuration as those of the third embodiment are given the same reference numerals, and descriptions thereof will be omitted.

[0047] The reflector 54 is, for example, a mirror (reflecting mirror) or a pentaprism, and is arranged (fixed) on the rotation axis C inside the rotating body 34B so as not to be rotatable around the axis. The reflector 54 reflects the measurement light L1, which has entered the rotating body 34B from the outside along the rotation axis C, at a right angle, and causes this measurement light L1 to be incident on the inner circumferential surface 37 of the rotating body 34B. The reflection direction of the measurement light L1 by the reflector 54 may be changed as appropriate as long as the measurement light L1 can be incident on the inner circumferential surface 37.

[0048] Like the diffraction gratings 42B of the third embodiment, each diffraction grating 42B of the fifth embodiment is a transmission grating formed on the outer peripheral surface 35 or the inner peripheral surface 37 (or both) of the rotor 34B, and uses slits 35b (see FIG. 7), a transmission blazed diffraction grating, rulings, etc. Each diffraction grating 42B frequency-modulates the measurement light L1 incident on the inner peripheral surface 37 from the reflector 54 while the rotor 34B is rotating. As a result, the frequency-modulated modulated measurement light L1A is emitted to the outside of the rotor 34B.

[0049] In this way, in the optical frequency modulator 16 of the fifth embodiment, a reflector 54 is placed inside the rotating body 34B, and the measuring light L1 is transmitted from the inside to the outside of the rotating body 34B. This measuring light L1 is frequency-modulated by each diffraction grating 42B, thereby obtaining the maximum light intensity of modulated measuring light L1A without performing optically difficult adjustments.

[0050] For example, in the optical frequency modulator 16 of the first and second embodiments described above, in which a reflective diffraction grating 42 is formed on the outer peripheral surface 35 of a cylindrical or cylindrical rotor 34, to output the maximum light intensity of modulated measurement light L1A, two types of angle adjustment are required: adjustment of the angle of incidence of the measurement light L1 incident on the diffraction grating 42 and adjustment of the blazed angle of the diffraction grating 42. Furthermore, if the diffraction grating 42 is a blazed diffraction grating, the measurement light L1 is incident obliquely on the diffraction grating 42, which tends to diffuse the modulated measurement light L1A (diffracted light). Therefore, as shown in FIG. 1, it is necessary to place the first lens 32 on the optical path of the measurement light L1 and the second lens 38 on the optical path of the modulated measurement light L1A. In this case, it is also necessary to adjust the optical axis of the first lens 32 to be parallel to the optical path of the measurement light L1 and the optical axis of the second lens 38 to be parallel to the optical path of the modulated measurement light L1A.

[0051] For example, in a simple transmission-type optical frequency modulator (see FIG. 2 in JP 2004-287029 A) having a disk and multiple transmission-type diffraction gratings formed along the same circumference centered on the central axis of the disk, when the measurement light L1 is incident perpendicularly to the disk (transmission-type diffraction grating), modulated measurement light L1A (zeroth-order diffracted light) with the maximum light intensity is obtained in the same direction. However, even in this case, two types of angle adjustment are required: adjustment of the incident angle of the measurement light L1 with respect to the disk and adjustment of the angle of the disk.

[0052] In contrast, in the optical frequency modulator 16 of the fifth embodiment, the measurement light L1 can be made perpendicular to the inner circumferential surface 37 (diffraction grating 42B) simply by adjusting the angle of the reflector 54, thereby outputting the maximum intensity of modulated measurement light L1A. Furthermore, when the measurement light L1 accurately enters the interior of the rotor 34B along the rotation axis C, the angle of the reflecting surface of the reflector 54 is also set to 45 degrees with respect to the rotation axis C. As a result, the maximum intensity of modulated measurement light L1A can be obtained without performing optically difficult adjustments. Furthermore, when an optical element capable of refracting light by 90 degrees, such as a pentaprism, is used as the reflector 54, the angle of the reflector 54 is easier to adjust. Furthermore, the arrangement (position) of the first lens 32 and the second lens 38 is also easier to calculate the emission direction of the modulated measurement light L1A (diffracted light) than when a blazed diffraction grating is used, which facilitates adjustment of their arrangement (position).

[0053] [others] In each of the above embodiments, the measurement light L1 is frequency-modulated by the optical frequency modulator 16, but the reference light L2 may also be frequency-modulated.

[0054] In each of the above embodiments, the optical frequency modulator 16 used in the measurement device 10 that measures the distance to the measurement object 9 and the displacement of the measurement object 9 using optical heterodyne interferometry has been used as an example, but the present invention can be applied to optical frequency modulators used for various purposes. [Explanation of symbols]

[0055] 9 Measurement object 9a Retroreflective member 10. Measuring equipment 12 Laser light source 14 Half Mirror 16 Optical Frequency Modulator 18 Half Mirror 20 Light receiving part 22 Arithmetic unit 30 1st Mirror 32 First lens 34, 34A~34C Rotating body 35 Outer surface 35a groove 35b slit 36 Drive unit 37 Inner surface 38 Second lens 40 Second Mirror 42, 42A, 42B Diffraction grating 50 curved surface 54 Reflector C rotation axis L laser light L1 measurement light L1A modulated measurement light L2 reference beam LR reflected light P incident position SG Interference signal

Claims

1. a cylindrical rotor having a rotation axis and extending in a direction parallel to the rotation axis, the rotor rotating at a constant speed around the rotation axis; a plurality of transmission type diffraction gratings formed on the circumferential surface of the rotating body and parallel to the rotation axis, the transmission type diffraction gratings frequency-modulating incident light that is incident on the circumferential surface of the rotating body during rotation and emitting frequency-modulated diffracted light; Equipped with The optical frequency modulator includes a transmission type diffraction grating that modulates the frequency of the incident light that enters the interior of the rotating body from the outer peripheral surface of the rotating body.

2. 2. The optical frequency modulator according to claim 1, further comprising a drive unit for controlling the rotation speed and direction of the rotor.

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