Wavefront control device and adaptive optics system

Abstract

A wavefront control device to which the present invention is applied is provided with: an optical frequency comb generation unit that emits an optical frequency comb having a plurality of optical pulses disposed in numerical order on a time axis; and a wavefront synthesis unit that distributes the plurality of optical pulses of the optical frequency comb incident from the optical frequency comb generation unit to positions different from each other according to the relative phases thereof with respect to the first optical pulse on a plane crossing the traveling direction of the optical frequency comb, and generates a synthesized wavefront of the optical pulses emitted from the positions different from each other. The optical frequency comb generation unit is provided with a phase control unit that controls the repetition frequency and offset frequency of the optical frequency comb.

Description

[Technical Field]

[0001] The present invention relates to a wavefront control device and an adaptive optics device. This application claims priority based on Japanese Patent Application No. 2021-137394, filed in Japan on August 25, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conventionally, when measuring the shape of an object under measurement, acquiring tomographic images, or performing structural analysis, the captured image is corrected and restored by adaptive optics. Direct images acquired from the object under measurement are distorted due to fluctuations in the environment and space. By correcting this distorted image through wavefront control, a clear image with high contrast is obtained on the imaging surface of a photodetector such as an imaging camera. Measurements using adaptive optics involve wavefront measurement, which measures the shape and state of the acquired wavefront, and wavefront control, which controls the wavefront based on the information about the measured wavefront.

[0003] Known techniques for wavefront measurement include, for example, using a Shack-Hartmann wavefront sensor equipped with a lens array, using a variable mirror whose orientation intersecting surface with respect to the optical axis of the incident light can be adjusted, or directly modulating the phase of the incident wavefront using a spatial light modulator (SLM). Although measurement techniques based on the above methods have been established, the response speed for wavefront measurement is on the order of tens of Hz, and the response speed for wavefront control is on the order of tens of kHz. Therefore, methods for performing wavefront measurement and wavefront control at higher speeds than conventional methods have been investigated.

[0004] Phased arrays are one approach to speed up wavefront measurement and wavefront control. Phased array antennas are realized using multiple antennas arranged in an array and phase-controlled electromagnetic waves, and are used in weather radar and ultrasound diagnostic equipment that use radio waves as electromagnetic waves. By using a phased array antenna, electromagnetic waves with individually controlled phases are emitted from multiple antennas, so wavefront measurement and wavefront control can be performed simultaneously. In recent years, optical phased arrays, which use light as electromagnetic waves, are expected to have applications in LiDAR (light detection and ranging), projectors, and biofluorescence measurement.

[0005] For example, Patent Document 1 and Non-Patent Documents 1 and 2 disclose a waveguide-type optical integrated circuit device as an example of an optical phased array. In these optical integrated circuit devices, a phase adjustment unit is provided in each of the multiple branch waveguides, which are branched from an input waveguide formed in a planar light wave circuit or the like, in the same number as the antennas. The optical waves whose phase is controlled by the phase adjustment unit are emitted from the output end (antenna) of each of the multiple branch waveguides. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2020-112582 [Non-patent literature]

[0007] [Non-Patent Document 1] MCShin, et al., “Chip-scale blue light phased array”, Optics Letters, Vol. 45, No. 7, pp. 1934-1937 (2020). [Non-Patent Document 2] H. Abediasl, et al., “Monolithic optical phased array transceiver in a standard SOI CMOS process”, Optical Express, Vol. 23, No. 5, pp. 6509-6519 (2015). [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Conventional optical phased arrays are composed of waveguide-type optical integrated circuit devices, as exemplified in Patent Document 1 and Non-Patent Documents 1 and 2 mentioned above. However, in waveguide-type optical integrated circuit devices, it is necessary to individually control each of the phase adjustment units, which are equal to the number of branched waveguides, i.e., the same number of phase adjustment units as the number of antennas in the optical phased array. As the number of antennas increases, the space occupied by the multiple phase adjustment units and the phase control devices connected to each of them also increases. It is necessary to independently control and calibrate approximately twice the number of parameters as the number of antennas, and as the number of antennas increases, the control of multiple antennas and the calibration of the parameters of each antenna become complicated. In order to suppress the deterioration of the propagation characteristics of optical waves in the waveguide in waveguide-type optical integrated circuit devices, it is practically necessary to use monochromatic light. As mentioned above, in order to broaden the bandwidth and control the optical waves targeted for wavefront measurement and wavefront control by conventional waveguide-type optical phased arrays at high speed, it is inevitable that the size of the integrated circuit and control device and the number of control parameters will increase. For these reasons, the practicality of conventional waveguide-type optical phased arrays has been low.

[0009] The present invention provides a wavefront control device and an adaptive optics device that can perform high-speed wavefront control with simple control regardless of the number of antennas, and can achieve broadband operation of the optical wave to be controlled. [Means for solving the problem]

[0010] The wavefront control device according to this embodiment includes: an optical frequency comb generation unit that emits an optical frequency comb having a plurality of optical pulses arranged numerically on the time axis; and a wavefront combining unit that distributes each of the plurality of optical pulses of the optical frequency comb incident from the optical frequency comb generation unit to different positions on a plane intersecting the propagation direction of the optical frequency comb according to the relative phase with respect to the first optical pulse, and generates a combined wavefront of the optical pulses emitted from the different positions. The optical frequency comb generation unit includes a phase control unit that controls the repetition frequency and offset frequency of the optical frequency comb.

[0011] In the wavefront control device according to this embodiment, the wavefront combining unit may include a resonator structure having a pair of mirrors arranged opposite each other. The reflective surface of one of the pair of mirrors may reflect a portion of the incident optical frequency comb and transmit at least a portion of the remainder. When considering the combined wavefront of the optical pulses after one round trip of the pair of mirrors, the distance L between the reflective surfaces of the pair of mirrors is expressed by equation (1).

[0012]

number

[0013] In equation (1) above, L rep represents the pulse-to-pulse distance of the optical frequency comb, c represents the speed of light, and f rep This represents the repetition frequency of the optical frequency comb.

[0014] The wavefront control device according to this embodiment may include an adjustment mechanism for adjusting the incident angle of the optical frequency comb incident on at least one of the pair of mirrors. When the pair of mirrors is used, the incident angle on at least one of the mirrors changes, and the composite wavefront may be controlled.

[0015] In the wavefront control device according to this embodiment, the optical frequency comb generation unit may include a wavelength conversion unit that converts the wavelength of the optical frequency comb. The combined wavefront of the optical pulses may be formed not from pulses that have made one round trip, but from interference between pulses that have made any number of round trips.

[0016] The wavefront control device according to this embodiment may include a feedback mechanism that feeds back intensity information of the light wave having the composite wavefront to the phase control unit.

[0017] In the wavefront control device according to this embodiment, the phase control unit may set the ratio of the repetition frequency to the offset frequency to a predetermined value. Furthermore, the wavefront control device according to this embodiment may include an intensity modulator that emits some of the multiple optical pulses emitted from the optical frequency comb generation unit toward the wavefront synthesis unit.

[0018] The adaptive optics apparatus according to this embodiment comprises the wavefront control device and the imaging optical system. The imaging optical system is configured to irradiate an object to be measured with light waves having the combined wavefront emitted from the wavefront combining unit of the wavefront control device, and to receive light waves reflected or transmitted from the object to be measured. [Effects of the Invention]

[0019] According to the wavefront control device and adaptive optics device of the present invention, wavefront control can be performed at high speed with simple control regardless of the number of antennas, and the bandwidth of the controlled optical wave can be broadened. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic diagram of a wavefront control device according to a first embodiment of the present invention. [Figure 2] This is a schematic diagram of the electric field distribution on the time axis (upper panel) and the intensity distribution on the frequency axis (lower panel) of an optical frequency comb. [Figure 3]Figure 1 is a schematic diagram illustrating the principle of the wavefront synthesis section of the wavefront control device shown. [Figure 4] Figure 1 is a schematic diagram illustrating the wavefront synthesis process in the wavefront synthesis section of the wavefront control device shown. [Figure 5] This is a schematic diagram of a wavefront measurement system according to a second embodiment of the present invention. [Figure 6] Figure 5 is a schematic diagram showing an example of a two-dimensional wavefront distribution in a wavefront measurement system. [Figure 7] This is a schematic diagram of a wavefront control device according to a second embodiment of the present invention. [Figure 8] Figure 7 is a schematic diagram showing an example of the phase distribution of multiple optical pulses distributed across a predetermined plane of the wavefront control device shown. [Figure 9] This is a schematic diagram of a first modified example of the wavefront control device according to the present invention. [Figure 10] This is a schematic diagram of a second modified example of the wavefront control device according to the present invention. [Figure 11] This is a schematic diagram of a third modified example of the wavefront control device according to the present invention. [Figure 12] This is a schematic diagram illustrating the wavefront synthesis process in the wavefront synthesis section of a third modified example of the wavefront control device according to the present invention. [Modes for carrying out the invention]

[0021] Hereinafter, embodiments of the wavefront control device and adaptive optics apparatus according to the present invention will be described with reference to the drawings.

[0022] [First Embodiment] As shown in Figure 1, the wavefront control device 11 of the first embodiment according to the present invention comprises an optical frequency comb generation unit 21 and a wavefront combining unit 22. The optical frequency comb generation unit 21 generates an optical frequency comb (hereinafter sometimes referred to as an optical comb) LC1 and emits the generated optical frequency comb LC1 toward the wavefront combining unit 22. The optical frequency comb generation unit 21 comprises at least an optical frequency comb generator 30 and a phase control unit 50, and further comprises an optical fiber 42, a fiber collimator 44, and a plane mirror 46.

[0023] The optical frequency comb generator 30 generates one optical frequency comb LC1 and emits it from the emission end. As shown in FIG. 2, the optical frequency comb LC1 is a series of optical pulses LP1, LP2, ···, LP n , LP n+1 , ··· arranged at intervals of each other. n is an arbitrary natural number and represents the number on the time axis of the optical pulse. Hereinafter, a plurality of optical pulses LP1, LP2, ···, LP n , LP n+1 , ··· may be collectively referred to as a plurality of optical pulses LPn. The optical frequency comb LC1 has a plurality of optical pulses LPn arranged in order of number on the time axis. The plurality of optical pulses LPn have information on the longitudinal mode on the frequency axis. Each of the optical pulses LPn has a predetermined frequency distribution. The frequency of each of the optical pulses LPn changes continuously on the time axis.

[0024] The plurality of optical pulses LPn oscillate at a constant repetition time T rep . When the optical frequency comb LC1 on the time axis shown in the upper part of FIG. 2 is Fourier-transformed and observed on the frequency axis, as shown in the lower part of FIG. 2, a large number of frequency modes arranged at intervals of each other are observed. That is, the optical frequency comb LC1 has a plurality of frequency modes FM1, FM2, ···, FM m , FM m+1 , ··· arranged at intervals of each other on the frequency axis, that is, the horizontal axis in the lower part of FIG. 2. m is an arbitrary natural number and represents the number on the frequency axis of the spectrum. Hereinafter, a plurality of frequency modes FM1, FM2, ···, FM m , FM m+1 , ··· may be collectively referred to as a plurality of frequency modes FMm. The interval between the centers of adjacent frequency modes FM m , FM m+1 on the frequency axis is the repetition frequency f rep . The repetition time T rep is expressed by equation (2).

[0025]

Equation

[0026] Each of the multiple optical pulses LPn is composed of a superposition of many longitudinal modes propagating within the resonator of the light source. The optical frequency comb LC1, which is an optical pulse train, is composed of a carrier wave (also called a carrier), which is a wave of the superposition of longitudinal modes, and a wave packet that constitutes its envelope (also called an envelope). Since the velocities of the carrier wave and the wave packet are different, a phase difference arises over time. A predetermined repetition time T is reached on the time axis. rep In the light pulse train that is repeatedly emitted each time, the light pulses LP are adjacent to each other on the time axis. n LP n+1 During this time, the phase difference Δφ is expressed by equation (3). n+1 This occurs.

[0027]

number

[0028] In the spectral distribution of the optical frequency comb LC1, the frequency mode FM m Repeat frequency f rep The remaining frequency when the frequency is virtually extended to 0 (zero) at intervals of f is the offset frequency f ceo This is also called the carrier envelope offset (CEO). The offset time T of the optical frequency comb LC1. ceo This is expressed by equation (4).

[0029]

number

[0030] A predetermined repetition time T on the time axis. rep In a light pulse train in which light pulses are repeatedly emitted, there is a phase difference, i.e., a phase difference Δφ. n+1 The period is the offset time T ceoThis completes one cycle. The center frequency f of the nth frequency mode of the optical frequency comb LC1. n The repetition frequency is f rep and offset frequency f ceo It can be expressed as in equation (5) using and .

[0031]

number

[0032] Repetition frequency f in the optical frequency comb LC1 is on the order of MHz to GHz. rep and offset frequency f ceo By controlling this, the phase relationship of multiple optical pulses LPn can be freely set and controlled. Repetition frequency f rep and offset frequency f ceo It stabilizes with the precision of an atomic clock and locks precisely to each predetermined value with high accuracy.

[0033] The optical frequency comb generator 30 is capable of emitting an optical comb, and the repetition frequency f of the emitted optical comb rep and offset frequency f ceo Each of these is configured to be independently controllable as described later. The configuration of the optical frequency comb generator 30 may be changed as appropriate, as long as the optical comb can be emitted and controlled as described above. Although not shown, the optical frequency comb generator 30 is composed of a resonator of a mode-locked laser diode (MLLD) equipped with an erbium (Er) doped fiber, a polarization controller and a delay controller. The optical frequency comb generator 30 may be composed of, for example, a linear waveguide for add / drop made of quartz on a glass substrate and a ring waveguide connected between the linear waveguides. The optical frequency comb generator 30 may be composed of a ring-type resonator made of silicon nitride on a silicon (Si) substrate. The optical frequency comb generator 30 may be composed of a toroidal micro-resonator with a flange portion provided at the tip of a protrusion on a Si substrate. The optical frequency comb generator 30 may be composed of a resonator made of crystal.

[0034] As shown in Figure 1, the phase control unit 50 is connected to the optical frequency comb generator 30, and the repetition frequency f of the optical frequency comb LC1 emitted from the optical frequency comb generator 30 rep and offset frequency f ceo The phase control unit 50 is connected to, for example, a function generator (not shown) provided in the optical frequency comb generator 30. The function generator supplies a high-frequency signal to the resonator that generates the optical frequency comb LC1 in the optical frequency comb generator 30, and controls the repetition frequency f of the optical frequency comb LC1. rep and offset frequency f ceo It directly affects the function. The phase control unit 50 is provided to manipulate the output of the high-frequency signal of the function generator and is, for example, a computer connected to the function generator. The repetition frequency f by the phase control unit 50 rep and offset frequency f ceo Details of the control will be described later.

[0035] As shown in Figure 1, the incident end of the optical fiber 42 is connected to the optical frequency comb generator 30. A fiber collimator 44 is connected to the outgoing end of the optical fiber 42. The fiber collimator 44 collimates the optical frequency comb LC1 propagating through the optical fiber 42 and directs it toward the reflective surface 46a of the plane mirror 46. The plane mirror 46 reflects the optical frequency comb LC1 incident on the reflective surface 46a toward the wavefront combining unit 22. The plane mirror 46 is provided with an adjustment mechanism 146 that allows the reflective surface 46a to be rotated. The adjustment mechanism 146 is, for example, a rotating stage having a rotation axis that extends vertically through the center of the reflective surface 46a in a plan view and a motor that rotates the rotation axis. When the reflective surface 46a is rotated in the direction of the arrow by the adjustment mechanism 146, the angle of the optical frequency comb LC1 emitted from the reflective surface 46a toward the wavefront combining unit 22 changes.

[0036] The wavefront combining unit 22 combines the multiple optical pulses LPn contained in the incident optical frequency comb LC1 into each optical pulse LP at position P1 in the direction of propagation of the optical frequency comb LC1 (i.e., a position on the optical path of the optical frequency comb LC1, and the position of the output surface 46b of the plane mirror 46). n Phase φ n They are distributed to different locations according to the order. n Distributed optical pulse LP n Phase φ n The interference of these elements creates a predetermined wavefront. (Photon pulse LP) n Phase φ n The repetition frequency f of the optical frequency comb is rep and offset frequency f ceo It is controlled by the ratio of this. This means that the wavefront, which is the transverse mode, can be manipulated using the frequency, which is the longitudinal mode. Phase φ of multiple optical pulses LPn on the time axis n This relationship is converted into a relationship between the positions at which each of the multiple optical pulses LPn is irradiated at position P1. Multiple optical pulses LPn distributed to different positions at a predetermined position P1 are wavefront-combined on the exit side of position P1 to form a composite wavefront WP.

[0037] The wavefront combining unit 22 is composed of, for example, an MPC optical system 60 that constitutes a multipass cavity (MPC). The MPC optical system 60 includes a concave mirror 62 and a plane mirror 64. The concave mirror 62 is positioned so that the optical frequency comb LC1 reflected by the plane mirror 46 of the optical frequency comb generation unit 21 can be directly incident on it. The concave mirror 62 is positioned ahead of the reflective surface 46a of the plane mirror 46 in the direction of propagation of the optical frequency comb LC1. The plane mirror 64 is positioned ahead of the concave mirror 62 in the direction of propagation of the optical frequency comb LC1 that is incident on the wavefront combining unit 22 and passes through the concave mirror 62. The plano-convex lens 66 is positioned ahead of the plane mirror 64 in the direction of propagation of the optical frequency comb LC1 that is incident on the wavefront combining unit 22 and passes through the concave mirror 62.

[0038] The concave mirror 62 has a reflective surface 62a that specularly reflects almost the entire incident optical frequency comb LC1. The plane mirror 64 has a reflective surface 64a that specularly reflects a portion of the incident optical frequency comb LC1 and transmits at least a portion of the remainder. The reflective surface 64a faces the reflective surface 62a in the direction of propagation of the optical frequency comb LC1 (i.e., on the optical axis). In the MPC optical system 60, the concave mirror 62 and the plane mirror 64 constitute a resonator. Each of the concave mirror 62, the plane mirror 64, and the plano-convex lens 66 is made of a material that can transmit the optical frequency comb LC1, for example, quartz or optical glass. Each of the reflective surfaces 62a and 64a is made of a dielectric multilayer film or a metal vapor-deposited film, etc., taking into consideration the wavelength of the optical frequency comb LC1, in order to exhibit the above-described transmission characteristics.

[0039] The distance L between the reflective surfaces L of the concave mirror 62a and the reflective surface 64a of the plane mirror 64 is expressed as shown in equations (6) and (7).

[0040]

number

[0041] In equation (7), c represents the speed of light, L rep represents the pulse-to-pulse distance of the optical frequency comb LC1. As shown in Figure 3, the optical frequency comb LC1 incident on the MPC optical system 60 first passes through the concave mirror 62 and propagates in the forward direction D1 toward the reflective surface 64a of the plane mirror 64. In the optical frequency comb LC1, the optical pulses LP are transmitted over time. n Repeated time T afterwards rep Open the light pulse LP n+1 This continues. Therefore, the reflective surface 64a is first subjected to the optical pulse LP. n It is incident, and the repetition time T rep After the elapsed time, light pulse LP n+1 The optical frequency comb LC11 incident on the reflective surface 64a is specularly reflected and propagates in the return direction D2, which has a component opposite to the forward direction D1. At least a portion of the remaining optical frequency comb LC12 incident on the reflective surface 64a passes through the plane mirror 64.

[0042] The optical frequency comb LC11 has a concave mirror 62 with a reflective surface 6 2 The light is specularly reflected by a and travels again in the forward direction D1 as optical frequency comb LC2, and is incident on the reflective surface 64a of the plane mirror 64. A portion of optical frequency comb LC21 of optical frequency comb LC2 that is incident on the reflective surface 64a is specularly reflected and travels again in the return direction D2. At least a portion of the remaining optical frequency comb LC22 of optical frequency comb LC2 that is incident on the reflective surface 64a is transmitted through the plane mirror 64. Optical frequency comb LC21 is specularly reflected by the reflective surface 62a of the concave mirror 62 and travels again in the forward direction D1 as optical frequency comb LC3 (not shown), and is incident on the reflective surface 64a of the plane mirror 64. Optical frequency comb LCk, like optical frequency combs LC1 and LC2, is split into optical frequency comb LCk1 and optical frequency comb LCk2 at the reflective surface 64a of the plane mirror 64. k represents a natural number greater than or equal to 3. As k increases, the amount of light from optical frequency comb LCk decreases. In the MPC optical system 60, the branching from optical frequency comb LCk to optical frequency combs LCk1 and LCk2 is repeated as described above until the amount of light in optical frequency comb LCk is almost gone.

[0043] As shown in Figure 4, the exit surface 64b of the plane mirror 64, opposite to the reflective surface 64a, is a surface that intersects the direction of propagation (optical axis) of the optical frequency comb LC1 and the central axis AX of the resonator, and is positioned at a predetermined position P1 in the direction of propagation of the optical frequency comb LC1. The central axis AX passes through the centers of the concave mirror 62 and the plane mirror 64, respectively. Multiple optical frequency combs LCp2 are incident at different positions on the exit surface 64b, pass through the exit surface 64b, and are incident on the plano-convex lens 66, which is omitted in Figure 4. p represents a natural number. Each of the multiple optical frequency combs LCp2 has a phase φ along the circumferential direction centered on the central axis AX on the exit surface 64b. n They correspond to each other and are emitted from different positions.

[0044] As shown in Figure 3, for example, at a certain time, at position P2, which is ahead of position P1 in the direction of propagation of the optical frequency comb LC1, at least the optical pulse LP of the optical frequency comb LC12 is present. n+1 and optical pulse LP of optical frequency comb L22 nAt position P2, multiple optical pulses LPn arrive at their respective phases φ. n They are distributed to different positions accordingly. As shown in Figure 4, at the emission surface 64b of the plane mirror 64, multiple light pulses LPn are distributed along the circumferential direction with respect to the central axis AX in phase φ. n Corresponding to and at different positions PO n The light is distributed as follows: Due to the focusing function of the reflective surface 62a of the concave mirror 62, the radius of the annular distribution centered on the central axis AX when multiple light pulses LPn are distributed is shortest at the emission surface 64b of the plane mirror 64.

[0045] Since the MPC optical system 60 is composed of passive optical systems, no mechanical drive time is incurred. In the MPC optical system 60, multiple optical pulses LPn are generated at different positions PO on the output surface 64b of the plane mirror 64 solely by the phenomenon at the speed of light in which the optical frequency comb LC1 reciprocates between the concave mirror 62 and the plane mirror 64 and is branched at the reflective surface 64a of the plane mirror 64. n They are distributed almost simultaneously. More specifically, by the phenomenon at the speed of light described above, at different positions PO on the exit surface 64b of the plane mirror 64, n Each of them is a light pulse LP n The timing at which the optical frequency comb LC1 reaches the emission surface 64b is shifted so that the signal can pass through.

[0046] As shown in Figure 4, the phases from the emission surface 64b of the plane mirror 64 are φ1, φ2, ..., φ n ,φ n+1 Multiple light waves LW1, LW2, ..., LW n LW n+1 ,... are emitted simultaneously. Below, we refer to the light waves LW1, LW2,..., LW n Sometimes, the terms ,··· are collectively referred to as the light wave LWn. Positions PO1, PO2,···, PO n These are sometimes collectively referred to as optical wave POn. Multiple optical waves LWn interfere with each other and emit an optical wave LL with a combined wavefront WP, as shown in Figure 1.

[0047] The position POn from which multiple optical pulses LPn are emitted is determined by the phase difference Δφ between the optical frequency combs LCp2. n+1 The incident position of the optical frequency comb LCp2 at the exit surface 64b changes depending on the angle that the direction of propagation of the optical frequency comb LCp, which undergoes multiple reflections between the concave mirror 62 and the plane mirror 64, makes with respect to the central axis AX, as described above. The curvature of the reflective surface 62a of the concave mirror 62 is designed taking into account the incident position of the optical frequency comb LCp2 at the exit surface 64b. The incident position of the optical frequency comb LCp2 at the exit surface 64b is determined by the phase φ of the optical pulse LPn of the optical frequency comb LC1, as will be described later. n It is set and controlled by the relationship between these two factors.

[0048] Here, the phase difference between pulses is Δφ. n+1 This can be expressed as shown in equation (3).

[0049]

number

[0050] Pulse-to-pulse phase difference Δφ n+1 The repetition frequency is f rep and offset frequency f ceo If we can completely control it, it will be constant for all n, resulting in a constant phase difference Δφ.

[0051] The wavefront control device 11 described above uses multiple optical wave LW n LW n+1 Phase φ n ,φ n+1 Equation (9) holds true for this.

[0052]

number

[0053] As can be seen from equation (9), the optical wave LW n LW n+1 Phase difference Δφ n+1 The repetition frequency f of the optical frequency comb LC1 is rep and offset frequency fceo is determined only by two parameters, the phase difference Δφ n+1 is (φ n+1 - φ n ). The repetition frequency f rep and the offset frequency f ceo are completely controlled, the phase difference Δφ n+1 is constant regardless of n. Based on equations (5) and (9), by controlling the repetition frequency f rep and the offset frequency f ceo to their respective predetermined values, the phase difference Δφ between adjacent optical pulses LP n , LP n+1 on the time axis of the optical frequency comb LC1 can be controlled. From the emission surface 64b of the plane mirror 64 disposed at the position P1, an optical wave LL having a composite wavefront WP that depends on the phase difference Δφ controlled by the phase control unit 50 for the repetition frequency f rep and the offset frequency f ceo is emitted. At that time, the composite wavefront WP depends on the phase difference Δφ controlled by the phase control unit 50 for the repetition frequency f rep and the offset frequency f ceo . From the emission surface 64b of the plane mirror 64 of the MPC optical system 60, optical waves LW n , φ n+1 , ··· having a plurality of phases φ n , LW n+1 , ··· are emitted. From this, each emission point of the optical wave LWn acts as an emission point of an optical antenna or of a plurality of individually phase-modulated optical waves in an optical phased array.

[0054] Multiple optical frequency combs LCp2 pass through a plane mirror 64 and are incident on a plano-convex lens 66 positioned ahead of the plane mirror 64 in the direction of propagation of the multiple optical frequency combs LCp2. The plano-convex lens 66 has a convex surface 66a and a flat surface 66b. The plano-convex lens 66 is positioned auxiliaryly to adjust the optical axis of each of the multiple optical frequency combs LCp2 emitted from the plane mirror 64, adjust the beam divergence direction, and cause the multiple optical frequency combs LCp2 to interfere with each other. If the multiple optical frequency combs LCp2 interfere with each other, a composite lens such as a camera lens may be positioned auxiliaryly instead of the plano-convex lens 66. The plano-convex lens 66 may be omitted when it is not necessary to adjust the optical axis or beam divergence direction to cause the multiple optical frequency combs LCp2 to interfere with each other.

[0055] As described above, the wavefront control device 11 of the first embodiment comprises an optical frequency comb generation unit 21 and a wavefront combining unit 22. The optical frequency comb generation unit 21 emits an optical frequency comb LC1 having a plurality of optical pulses LPn arranged in numerical order on the time axis. The optical frequency comb generation unit 21 sets the repetition frequency f of the optical frequency comb LC1. rep and offset frequency f ceo The wavefront combining unit 22 controls the relative phase φ of each of the multiple optical pulses LPn of the optical frequency comb LC1 incident from the optical frequency comb generation unit 21 with respect to the first optical pulse LP1 (omitted in Figure 2) on the plane 66b of the plano-convex lens 66 (a plane intersecting the direction of propagation of the optical frequency comb). n Depending on the position PO n The wavefront combining unit 22 distributes the light pulses LP emitted from different positions. n A composite wavefront WP is generated.

[0056] In the wavefront control device 11 of the first embodiment, the phase control unit 50 controls two parameters of the optical frequency comb LC1 in the optical frequency comb generation unit 21; the repetition frequency f rep and offset frequency f ceoBy controlling each of these to a predetermined value, multiple optical pulses LPn that were arranged in numerical order on the time axis before being incident on the wavefront combining unit 22 can be distributed at the speed of light to the plane 66b of the plano-convex lens 66, i.e., to the transverse mode. In the wavefront control device 11 of the first embodiment, when multiple optical pulses LPn have been distributed, regardless of the number of distributions, each optical pulse LP n The repetition frequency f rep and offset frequency f ceo Phase φ controlled solely by n It is possible to have a state in which the information is obtained. In the wavefront control device 11 of the first embodiment, each is the phase φ from the plane 66b of the plano-convex lens 66. n Optical pulse LP having n A composite wavefront WP formed by the interference of these waves can be emitted. Conventional wavefront control methods, such as waveguide-type optical phased arrays and conventional radio wave phased arrays, branch the optical waves or radio waves to more than the number of phases to be controlled (i.e., the number of distributions), or prepare multiple wave sources and control the phase of each of the multiple optical waves and radio waves. The wavefront control device 11 of the first embodiment is completely different from waveguide-type optical phased arrays and conventional radio wave phased arrays, and uses two control parameters of one optical frequency comb LC1; repetition frequency f rep and offset frequency f ceo By controlling only this, the optical pulse LP is distributed onto the plane 66b of the plano-convex lens 66. n Phase φ n This controls the optical pulse LP. n The location PO to which it is distributed n Each of these can be operated as an optical antenna to control the combined wavefront WP. In the wavefront control device 11 of the first embodiment, unlike conventional wavefront control methods, it is not necessary to perform individual phase control on the multiple optical signals after distribution (i.e., optical pulses LPn), and there is no need to arrange a phase control unit for performing phase control on each of the multiple optical signals. In the wavefront control device 11 of the first embodiment, there is no need to perform calibration between the multiple phase control units. For these reasons, according to the wavefront control device 11 of the first embodiment, the repetition frequency f can be controlled regardless of the increase in the number of antennas. rep and offset frequency f ceoWavefront control can be performed at high speed with a simple control operation that involves controlling the antennas. According to the wavefront control device 11 of the first embodiment, miniaturization can be achieved without increasing the number of antennas.

[0057] In the wavefront control device 11 of the first embodiment, one optical frequency comb LC1 is used as the optical signal of the optical antenna. The optical frequency comb LC1 has a broadband spectral distribution, as illustrated in the lower part of Figure 2. In the wavefront control device 11 of the first embodiment, multiple frequency mode FMs constitute the spectral distribution of the optical frequency comb LC1. m Each frequency f m That is, the repetition frequency f rep and offset frequency f ceo This allows for high-precision control of the phase φ of multiple optical pulses LPn that form a composite wavefront WP. According to the wavefront control device 11 of the first embodiment, the phase φ n (i.e., the phase φ of each optical antenna) n Before distributing at position P1, the optical frequency comb generation unit 21 generates the repeating frequency f rep and offset frequency f ceo This can be controlled with high precision at the level of an atomic clock. According to the wavefront control device 11 of the first embodiment, the optical frequency comb LC1 has multiple frequency modes FM m Because it has a broad spectral distribution, it is easy to broaden the bandwidth of the light wave being controlled.

[0058] In the wavefront control device 11 of the first embodiment, the optical frequency comb LC1 emitted from the optical frequency comb generator 30 is wavelength-converted in the optical frequency comb generation unit 21, thereby easily achieving further broadbanding of the optical wave to be controlled. For example, as shown in Figure 1, a wavelength conversion unit 70 may be placed in the middle of the optical fiber 42 of the optical frequency comb generation unit 21. The wavelength conversion unit 70 may be incorporated into the optical frequency comb generator 30, or it may be provided in the region through which the optical frequency comb LC1 passes between the fiber collimator 44 and the plane mirror 46. The wavelength conversion unit 70 includes a material or crystal capable of converting the spectral distribution of the optical frequency comb LC1 to a visible wavelength range or ultraviolet wavelength range other than the near-infrared wavelength range when the optical frequency comb LC1, whose spectral distribution is included in the near-infrared wavelength range, is incident on it. The configuration of the wavelength conversion unit 70 may be changed as appropriate. However, the phase φ of each optical pulse LPn in the optical frequency comb LC1 emitted from the wavelength conversion unit 70 n The relationship is maintained. In the wavefront control device 11 of the first embodiment, by further including a wavefront conversion unit 70, wavefront control and adaptive optics of ultrashort light pulses from the deep ultraviolet wavelength range to the terahertz (THz) range can be realized.

[0059] In the wavefront control device 11 of the first embodiment, the wavefront combining unit 22 includes an MPC optical system (resonator structure) 60 having a concave mirror 62 and a plane mirror 64 (a pair of mirrors) arranged opposite each other. The reflective surface 62a of the concave mirror 62 specularly reflects almost the entire incident optical frequency comb LCp. The reflective surface 64a of the plane mirror (one of the mirrors) 64 reflects a portion of the incident optical frequency comb LCp and transmits at least a portion of the remainder. The distance L between the reflective surfaces L of the concave mirror 62a and the reflective surface L of the plane mirror 64 is expressed by equation (1) (i.e., equation (6)), and the repetition frequency f of the optical frequency comb LC1 rep It is controlled by [something].

[0060] According to the wavefront control device 11 of the first embodiment, the optical frequency comb LC1 incident on the passive optical system MPC optical system 60 is moved back and forth between the reflective surfaces 62a and 64a, and optical frequency combs LCp2 with different numbers n of optical pulses LPn are emitted from the reflective surface 64a at the same time and position in the direction of propagation. In the wavefront control device 11 of the first embodiment, the multiple optical pulses LPn of the optical frequency comb LC1 are phased φ between the emission surface 64b of the plane mirror 64 and the plane 66b of the plano-convex lens 66 without mechanical drive. n They can be distributed to different locations depending on the situation.

[0061] The wavefront control device 11 of the first embodiment includes an adjustment mechanism 146. The adjustment mechanism 146 adjusts the incidence angle of the optical frequency comb LC1 incident on the reflective surface 64a of the plane mirror 64 (at least one of the mirrors) among the concave mirror 62 and the plane mirror 64 (a pair of mirrors). By adjusting the angle of the reflective surface 46a of the plane mirror 46 using the adjustment mechanism 146, the angle of the optical frequency comb LC1 incident on the plane mirror 64 can be changed, and the composite wavefront WP can be controlled.

[0062] In the wavefront control device 11 of the first embodiment, the reflective surface 62a of the concave mirror 62 is a concave surface relative to the flat reflective surface 64a of the plane mirror 64 and the plane 66b of the plano-convex lens 66. As a result, the optical frequency comb LC1 emitted from the optical frequency comb generation unit 21 is incident on the MPC optical system 60 so as to be substantially perpendicular to the reflective surface 64a. In the wavefront control device 11 of the first embodiment, the optical frequency comb LCp resonates between the concave mirror 62 and the plane mirror 64, and focuses from the reflective surface 62a toward the reflective surface 64a. According to the wavefront control device 11 of the first embodiment, the focusing region R of the reflective surface 64b 64 In this configuration, multiple optical pulses LPn can be distributed at appropriate intervals and arrangements that suitably form a composite wavefront WP.

[0063] According to the wavefront control device 11 of the first embodiment, by using a free-space type MPC optical system 60, multiple optical pulses LPn are phased φ at the exit surface 64b of the plane mirror 64. n They can be distributed to different locations depending on the situation.

[0064] In the wavefront control device 11 of the first embodiment, the resonator length of the MPC optical system 60, i.e., the distance L between reflective surfaces, is the repetition frequency f of the optical frequency comb LC1. rep It depends on the repetition frequency f of the generated optical frequency comb. For example, in a fiber laser equipped with an erbium (Er) doped fiber with an excitation wavelength of about 1550 nm, a ytterbium (Yb) doped fiber with an excitation wavelength of about 1050 nm, or a thulium (Tm) doped fiber with an excitation wavelength of about 2000 nm, the repetition frequency f of the generated optical frequency comb rep The frequency range is approximately 10 MHz to 1000 MHz. When a fiber laser equipped with an impurity-doped fiber whose excitation wavelength is in the near-infrared wavelength range is used as the optical frequency comb generator 30, the distance L between the reflective surfaces of the MPC optical system 60 is approximately several tens of centimeters to 1 m. When a micro-resonator with a resonant wavelength of approximately 1550 nm is used as the optical frequency comb generator 30, The repetition frequency f of the generated optical frequency comb rep The frequency range is approximately 10 GHz to 100 GHz. In this case, the distance L between the reflective surfaces of the MPC optical system 60 can be kept to a few centimeters to about 10 centimeters. The repetition frequency f is set as the optical frequency comb generator 30. rep By using a high-performance optical comb source, the MPC optical system 60 and the wavelength control device 11 can be miniaturized, making it possible to realize a wavelength control device that can fit in the palm of your hand, for example.

[0065] [Second Embodiment] As shown in Figure 5, the adaptive optics apparatus 12 of the second embodiment of the present invention comprises the wavefront control device 11 of the first embodiment and the imaging optical system 13. In the following description of the second embodiment and subsequent embodiments, components common to the configuration of the wavefront control device 11 of the first embodiment will be denoted by the same reference numerals as those of the wavefront control device 11 of the first embodiment. In the description of the second embodiment and subsequent embodiments, the description of content common to the description of the wavefront control device 11 of the first embodiment will be omitted.

[0066] Figure 5 shows a schematic configuration of only the output surface 64b of the plane mirror 64 of the wavefront combining unit 22 of the wavefront control device 11. The imaging optical system 13 is positioned in front of the propagation direction D3 of the light wave LL formed from the output surface 64b. The imaging optical system 13 includes a beam splitter 102, focusing lenses 104 and 106, and an imaging camera 110. The adaptive optics system 12 measures the wavefront using the imaging camera 110 and captures a clear image of the object S to be measured once wavefront compensation is achieved. Wavefront measurement may be performed using a device other than the adaptive optics system 12 exemplified in Figure 5, and the wavefront-compensated image may be captured with the imaging camera 110.

[0067] In the adaptive optics system 12, the object to be measured S is positioned in front of the direction of propagation D3 of the light wave LL from the emission surface 64b. The beam splitter 102 and the focusing lens 104 are sequentially positioned between the plane mirror 64 and the object to be measured S in the direction of propagation D3. The focusing lens 104 is positioned between the beam splitter 102 and the object to be measured S in the direction of propagation D3. The beam splitter 102 transmits the light wave LL emitted from the emission surface 64b and incident along the direction of propagation D3. The focusing lens 104 is positioned behind the measurement position PX on the surface or inside the object to be measured S by a distance equal to the focal length in the direction of propagation D3.

[0068] The beam splitter 102 has a reflective surface 102a. The reflective surface 102a transmits light waves LL incident from the direction of travel D3. The reflective surface 102a specularly reflects light waves LW incident from approximately parallel to and opposite to the direction of travel D3, and reflects them toward the direction of travel D4, which intersects the direction of travel D3. A focusing lens 106 and an imaging camera 110 are sequentially arranged in front of the beam splitter 102 in the direction of travel D4.

[0069] In the adaptive optics system 12, the optical wave LL emitted from the emission surface 64b of the plane mirror 64 passes through the beam splitter 102 and propagates along the direction of propagation D3. The wavefront WP1 of the optical wave LL in the imaging optical system 13 is the same wavefront WP0 that propagates and arrives at the imaging optical system 13, which is the same wavefront WP0 that is generated by the synthesis of multiple optical pulses LPn emitted from each of the optical antennas on the emission surface 64b. The optical wave LL that has passed through the beam splitter 102 is focused at the measurement position PX by the focusing lens 104. The optical wave LW reflected from the measurement position PX contains information about the optical wave LL and information about the object under measurement S. That is, the wavefront WP2 of the optical wave LW is the wavefront that has been changed by the optical properties of the object under measurement S acting on the wavefront WP1. If the wavefront WP1 is an ideal plane wave, the wavefront WP2 is scattered by the object under measurement S and becomes a distorted wavefront, and a distorted image is captured by the imaging camera 110. If a known wavefront is generated by the wavefront control device 11 and the wavefront WP2 is captured as a reflected image, the optical properties of the object S to be measured can be identified. If a wavefront WP1 that compensates for the optical properties is generated by the wavefront control device 11, the wavefront WP2, which is the object light, is aligned, and the image of the object S to be measured obtained by the imaging camera 110 becomes clear. The light wave LW reflected from the object S to be measured is incident on the focusing lens 104, collimated, and propagates in a direction approximately parallel to and opposite to the direction of propagation D3. The light wave LW is incident on the beam splitter 102 in a direction approximately parallel to and opposite to the direction of propagation D3, and is specularly reflected by the reflecting surface 102a in the direction of propagation D4. The light wave LW reflected by the reflecting surface 102a propagates along the direction of propagation D4, is focused by the focusing lens 106, and is received by the imaging camera 110.

[0070] In the adaptive optics apparatus 12 shown in Figure 5, for example, when the wavefront WP2 of the optical wave LW, which reflects the optical characteristics of the object S being measured, travels in a direction approximately parallel to and opposite to the direction of propagation D3, the phase control unit 50 of the wavefront control device 11 controls the repetition frequency f of the optical frequency comb LC1 so that a wavefront approximately perpendicular to the direction of propagation D3 and approximately flat is obtained. rep and offset frequency f ceo It is controlled.

[0071] The adaptive optics apparatus 12 of the second embodiment described above comprises the wavefront control device 11 of the first embodiment and the imaging optical system 13. The imaging optical system 13 is configured to irradiate the object to be measured S with light waves LL emitted from the wavefront control device 11, and to receive light waves LW reflected or transmitted from the object to be measured S. According to the adaptive optics apparatus 12 of the second embodiment, the phase control unit 50 of the wavefront control device 11 controls two control parameters of the optical frequency comb LC1; repetition frequency f rep and offset frequency f ceo By controlling only this, the wavefront WP1 of the light wave LL irradiated onto the object S to be measured can be freely controlled. According to the adaptive optics apparatus 12 of the second embodiment, the wavefront WP2 can be freely controlled. In the adaptive optics apparatus 12 of the second embodiment, the repetition frequency f of the optical frequency comb LC1 controlled by the phase control unit 50 and the information acquired from the light wave LW received in the imaging optical system 13 rep and offset frequency f ceo Based on this relationship, the optical properties of the object S being measured at the measurement position PX can be measured.

[0072] In the adaptive optics apparatus 12 of the second embodiment, for example, the phase control unit 50 of the wavefront control device 11 controls two control parameters of the optical frequency comb LC1; repetition frequency f, so that the wavefront WP2 of the light wave LW reflected or transmitted (reflected in Figure 5) from the object S to be measured becomes a flat wavefront perpendicular to the optical axis. rep and offset frequency f ceo Only the phase φ of multiple lights can be controlled. This means that, for example, due to the influence of air fluctuations or heat in the imaging optical system 13, disturbances that are not causally related to the optical properties at the measurement position PX of the object S under measurement may occur in the wavefront WP1 of the optical wave LL and the wavefront WP2 of the optical wave LW. In such cases, the wavefront WP2 can be flattened, and a high-contrast image and highly accurate measurement data can be acquired by the imaging camera 110. n These are emitted from multiple positions POn that function as optical antennas, forming a wavefront WP0. According to the adaptive optics apparatus 12 of the second embodiment, multiple light phases φ are formed, as in the conventional method. nIt is not necessary to control each of them individually. According to the adaptive optics apparatus 12 of the second embodiment, the wavefront WP2 of the optical wave LW can be compensated.

[0073] In the adaptive optics apparatus 12 of the second embodiment, a wavelength conversion unit 70 is provided in the optical frequency comb generation unit 21 of the wavefront control device 11, thereby enabling wavelength conversion of the optical frequency comb LC1 prior to the installation position of the wavelength conversion unit 70. This makes it possible to realize adaptive optics with ultrashort pulses from the deep ultraviolet wavelength range to the THz range, for example, regardless of the wavelength of the optical frequency comb LC1 prior to the installation position of the wavelength conversion unit 70. Adaptive optics using the adaptive optics apparatus 12 of the second embodiment enables, for example, the realization of more efficient direct fluorescence measurement than conventional methods, or application to multiphoton absorption measurement and multiphoton microscopy.

[0074] The adaptive optics apparatus 12 of the second embodiment can be used not only for the purpose of realizing adaptive optics as described above, but also for the purpose of evaluating the transverse mode characteristics of light waves. In the configuration shown in Figure 5, the light emission section of a complex optical system constituting an optical communication system or optical functional device (not shown) may be placed in place of the object to be measured S, and the emitted light may be measured. In the configuration shown in Figure 5, the emitted light and the wavefront generated by the wavefront control device 11 may be interfered with. As shown in the upper part of Figure 6, the light wave LL emitted from the emission surface 64b of the plane mirror 64 at position P1 is controlled by the phase control device 50 to control the repetition frequency f in a two-dimensional plane intersecting the optical axis. rep and offset frequency f ceo Phase φ controlled by n A corresponding wavefront distribution is formed. The lower panel of Figure 6 shows several 2D wavefront distributions: WD1, WD2, ..., WD n As shown in Figure 6, an example of the pattern is given, and the repetition frequency f is controlled by the phase control unit 50. rep and offset frequency f ceoWhen this is controlled and changed, the two-dimensional wavefront distribution of the wavefront WP0, i.e., the composite wavefront WP, of the optical wave LL emitted from the emission surface 64b of the plane mirror 64 changes, and the light intensity of the optical wave LL changes. Based on this, by receiving the optical wave LW reflected or transmitted from the light emission part of a complex optical system without compensating for the wavefront and measuring the light intensity of the optical wave LW, it is possible to understand how the original optical wave LL was affected by the complex optical system. From this, it is possible to understand what kind of simple combination of wavefronts generated the optical wave LW, and to accurately evaluate the transverse mode characteristics of the complex optical system, etc. Two-dimensional wavefront distribution WD1,WD2,···,WD n When these waves are generated sequentially and interfere sequentially with the wavefront emitted from the output section of a complex optical system, the degree to which each transverse mode is present can be determined by the interference intensity.

[0075] The adaptive optics apparatus 12 of the second embodiment functions suitably as a wavefront analyzer or two-dimensional spectrometer for evaluating transverse modes.

[0076] [Third Embodiment] As shown in Figure 7, in the wavefront control device 15 of the third embodiment of the present invention, a feedback mechanism 150 is provided in the wavefront control device 11 of the first embodiment. The feedback mechanism 150 comprises a beam splitter 152 and a photodiode (PD) 154. The beam splitter 152 is positioned in the region through which the optical frequency comb LCp2 passes between the plane mirror 64 and the plano-convex lens 66 of the wavefront combining unit 22, and is positioned on the central axis AX between the plane mirror 64 and the plano-convex lens 66. The beam splitter 152 has a reflective surface 152a.

[0077] In the wavefront control device 15, the optical frequency comb LCp2, which has passed through the reflective surface 64a of the plane mirror 64 and is emitted from the exit surface 64b, is incident on the beam splitter 152. A portion of the optical frequency comb LCp2 incident on the beam splitter 152 is specularly reflected by the reflective surface 152a in the direction of travel D3, which is substantially perpendicular to the forward direction D1 and the return direction D2. At least a portion of the remaining optical frequency comb LCp2 incident on the beam splitter 152 passes through the reflective surface 152a and is incident on the plano-convex lens 66. At the exit surface 64b of the plane mirror 64, multiple optical pulses LPn are in phase φ n Depending on the position PO n It is distributed to the following. An optical wave LL having a composite wavefront WP is emitted from the emission surface 64b of the plane mirror 64.

[0078] The photodiode 154 receives the optical frequency comb LCp2 reflected in the direction of propagation D3 by the reflective surface 152a of the beam splitter 152. The photodiode 154 and the phase control unit 50 of the optical frequency comb generation unit 21 are electrically connected by wire or wireless. The photodiode 154 outputs an electrical signal to the phase control unit 50 in real time, corresponding to the amount of light from the received optical frequency comb LCp2.

[0079] Figure 7 shows only the repetition frequency control unit 161, the offset frequency control unit 162, the frequency dividers 165 and 166, and the mixer 170 of the optical frequency comb generation unit 21 of the wavefront control device 15. The repetition frequency control unit 161 receives the electrical signal obtained by the feedback mechanism 150 and the phase control unit 50, and synchronizes with the inter-reflection surface distance L of the MPC optical system 60 to set the repetition frequency f of the optical frequency comb LC1. rep The offset frequency control unit 162 controls the offset frequency f of the optical frequency comb LC1. ceo The repetition frequency f is controlled by the repetition frequency control unit 161. repThe signal is input to frequency divider 165 and divided to (1 / α). The output from offset frequency control unit 162 is input to frequency divider 166 and divided to (1 / β). The outputs from frequency dividers 165 and 166 are input to mixer 170, and the mixer 170 is recursively input to offset frequency control unit 162. The offset frequency control unit 162 adjusts the offset frequency f according to the recursively input signal. ceo The offset frequency control unit 162 controls the repetition frequency f to stabilize the MPC optical system 60. rep The phase control unit 50 controls the repetition frequency f rep For the offset frequency f ceo If it operates to control the repetition frequency f according to equation (10), rep and offset frequency f ceo The frequency ratio can be controlled.

[0080]

number

[0081] An optical frequency comb LC1 satisfying the relationship in equation (10) is emitted from the optical frequency comb generation unit 21 of the wavefront control device 15. Figure 8 shows the results of numerical calculation of the phase distribution of multiple optical pulses LPn distributed on the emission surface 64b of the plane mirror 64 of the wavefront combining unit 22. The X and Y axes in Figure 8 represent two mutually orthogonal directions included in the emission surface 64b, with the origin being the position where the emission surface 64b intersects the central axis AX. The vertical axis in Figure 8 represents the phase φ n This represents the following. As shown in Figure 8, a phase distribution is formed on the exit surface 64b along the circumferential direction centered on the central axis AX. Multiple phases φ of the phase distribution formed around the central axis AX n The surface continuously increases and decreases in the circumferential direction, forming a virtual inclined surface. The light wave LL generated from the light pulse LPn is emitted in a direction approximately perpendicular to the inclined surface.

[0082] The phase control unit 50 controls the repetition frequency f of the optical frequency comb LC1. rep and offset frequency f ceoBy controlling this, the phase distribution of multiple optical pulses LPn at the output surface 64b can be freely and rapidly controlled. The phase control unit 50 controls at least the repetition frequency f of the optical frequency comb LC1. rep By controlling the ratio parameter (α / β) in equation (10), multiple phases φ n By controlling these parameters collectively, the gradient of the phase distribution of multiple optical pulses LPn at the emission surface 64b and the emission direction of the optical wave LL can be freely and accurately set.

[0083] In the wavefront control device 15 of the third embodiment, similar to the wavefront control device 11 of the first embodiment, multiple optical pulses LPn are distributed by the MPC optical system 60 having a concave mirror 62 and a plane mirror 64, so that a phase distribution is formed in the circumferential direction around the central axis AX at the exit surface 64b. By controlling (α / β) using the phase control unit 50, the radius of the phase distribution of multiple optical pulses LPn around the central axis AX at the exit surface 64b can be controlled.

[0084] The wavefront control device 15 of the third embodiment includes a feedback mechanism 150. The feedback mechanism 150 is located between the plane mirror 64 and the plano-convex lens 66 of the MPC optical system 60 of the wavefront combining unit 22, and the phase φ emitted from the plane mirror 64 and at the emission surface 64b. n Multiple optical frequency combs LCp2 optical pulses LP distributed to different positions accordingly n The intensity information is fed back to the phase control unit 50 of the optical frequency comb generation unit 21. The phase control unit 50 receives the optical pulses LP of the multiple optical frequency combs LCp2. n Intensity information and pre-known optical frequency comb LC1 optical pulse LP n The intensity information is compared with that. By using the phase control unit 50, for example, the optical pulse LP of the optical frequency comb LCp2 due to environmental changes such as air fluctuations is compared. n It is possible to check in real time whether there are any fluctuations or disturbances in the phase distribution. Optical pulse LP of optical frequency comb LCp2 nWhen it is determined that there is fluctuation or disturbance in the phase distribution, the phase control unit 50 is used to control the two parameters of the optical frequency comb LC1 in the optical frequency comb generation unit 21; repetition frequency f rep and offset frequency f ceo By controlling only this, fluctuations and disturbances in the phase distribution can be eliminated. According to the wavefront control device 15 of the third embodiment, the repetition frequency f of the optical frequency comb LC1 is set to the resonator length of the MPC optical system 60. rep By synchronizing them, the optical antenna can be stabilized.

[0085] Environmental instability of various optical antennas, including the MPC optics 60, is controlled by the repetition frequency f of the optical comb. rep and offset frequency f ceo By providing feedback, the stability to the environment can be increased to the same level as that of an atomic clock, enabling extremely robust wavefront control.

[0086] The wavefront control device 15 of the third embodiment can be applied to ultra-precise three-dimensional measurement by focusing point scanning on a plane intersecting the propagation direction of the optical wave LL and the central axis AX. The wavefront control device 15 of the third embodiment can be applied to ultra-precise three-dimensional measurement by absolute distance measurement in the depth direction substantially parallel to the propagation direction of the optical wave LL and the central axis AX. For example, using the wavefront control device 15 of the third embodiment, a three-dimensional scan of an object S to be measured having a spherical surface can be performed, and the shortest distance to the sphere can be calculated by surface measurement. From the results, for example, Avogadro's constant can be determined by shape measurement of a silicon sphere. For example, by performing depth direction measurement simultaneously with focusing point scanning using the wavefront control device 15 of the third embodiment, three-dimensional LiDAR can be realized.

[0087] In the wavefront control device 15 of the third embodiment, the beam splitter 152 of the feedback mechanism 150 is positioned between the plane mirror 64 and the plano-convex lens 66 of the MPC optical system 60. The beam splitter 152 may be positioned in the region through which the optical frequency comb LCp reflected by the reflective surface 64a of the plane mirror 64 passes, for example, as shown by the dashed line in Figure 7.

[0088] In the wavefront control device 15 of the third embodiment, an MPC optical system 60 having a concave mirror 62 and a plane mirror 64 is used, so the phase components of the multiple optical pulses LPn change circumferentially with respect to time in the circumferential direction around the central axis AX at the exit surface 64b of the plane mirror 64. To stop the circumferential change, a population inversion distribution is applied to the phase distribution of the multiple optical pulses LPn, which is an inversion of the phase distribution of the multiple optical pulses LPn.

[0089] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to any particular embodiment. Various modifications and changes to the embodiments of the present invention are possible within the scope of the gist of the present invention as described in the claims. The contents of the first to third embodiments can be combined as appropriate. For example, the adaptive optics apparatus 12 of the second embodiment may be equipped with the wavefront control device 15 of the third embodiment instead of the wavefront control device 11 of the first embodiment.

[0090] For example, the wavefront combining section of the wavefront control device according to the present invention may include a passive optical antenna structure other than the MPC optical system. First and second modified examples of the wavefront control device according to the present invention include the wavefront control device 17 shown in Figure 9 and the wavefront control device 18 shown in Figure 10.

[0091] As shown in Figure 9, the optical frequency comb generation unit 21 of the wavefront control device 17 comprises an optical frequency comb generator 30, a phase control unit 50, an optical fiber 42, and an optical fiber coupler 180. The wavefront combining unit 22 of the wavefront control device 17 replaces the MPC optical system 60 of the wavefront control devices 11 and 15 with a plurality of output waveguides 182. The incident end of the optical fiber coupler 180 is connected to the exit end of the optical fiber 42. The exit end of the optical fiber coupler 180 is connected to the incident end of the plurality of output waveguides 182. The plurality of output waveguides 182 are composed of output waveguides with different optical path lengths. The difference in optical path length between the output waveguides 182 corresponds to the optical pulses LP adjacent to each other on the time axis of the optical frequency comb LC1. n LP n+1This is equal to the difference in optical path length when the light propagates through the output waveguide 182. At position P1 where the exit ends of multiple output waveguides 182 are located, optical frequency combs LC1 with optical pulse LPn numbers shifted from each other are emitted at the same time. In the wavefront control device 17 of the first modified example, similar to the wavefront control devices 11 and 15, the multiple optical pulses LPn of the optical frequency comb LC1 are phased φ without mechanical drive. n Depending on the situation, the output can be distributed to the exit ends of multiple output waveguides 182 located at different positions. The wavefront control device 17 of the first modified example can achieve the same effects as the wavefront control devices 11 and 15.

[0092] As shown in Figure 10, the optical frequency comb generation unit 21 of the wavefront control device 18 comprises an optical frequency comb generator 30, a phase control unit 50, and an optical fiber 42. The wavefront combining unit 22 of the wavefront control device 18 comprises an arrayed-waveguide grating (AWG) 190 instead of the MPC optical system 60 of the wavefront control devices 11 and 15. The arrayed-waveguide grating 190 comprises an input waveguide 191 connected to the output end of the optical fiber 42, an input-side slab waveguide 192, an arrayed waveguide group 193, an output-side slab waveguide 194, and a plurality of output waveguides 195. The optical frequency comb LC1 emitted from the optical fiber 42 is diffracted by the input-side slab waveguide 192 via the input waveguide 191, incident on the arrayed waveguide group 193, and propagates through an independent optical path for each waveguide of the arrayed waveguide group 193. The difference in optical path length between each waveguide in the array waveguide group 193 is the difference between adjacent optical pulses LP on the time axis of the optical frequency comb LC1. n LP n+1 This depends on the optical path length difference as it propagates through the output waveguide 182. The optical frequency combs LC1 emitted from the array waveguide group 193 undergo multiple interference in the output-side slab waveguide 194 and are focused at different incident ends of the output waveguides 195 for each wavelength. At position P1 where the exit ends of multiple output waveguides 195 are located, optical frequency combs LC1 with optical pulse LPn numbers n shifted at the same time are emitted. In the wavefront control device 18 of the second modified example, similar to the wavefront control devices 11 and 15, the multiple optical pulses LPn of the optical frequency comb LC1 are phased φ without mechanical drive.n The output can be distributed to the exit ends of multiple output waveguides 195 located at different positions accordingly. The wavefront control device 18 of the second modification can achieve the same effects as the wavefront control devices 11 and 15.

[0093] A third modified example of the wavefront control device according to the present invention is the wavefront control device 81 shown in Figure 11. As shown in Figure 11, in the wavefront control device 81, an intensity modulator (IM) 160 is provided in the wavefront control device 15 of the third embodiment. The intensity modulator 160 is positioned on the path of the optical frequency comb LC1 between the optical frequency comb generator 30 and the fiber collimator 44, and is located in the middle of the optical fiber 42 of the optical frequency comb generation unit 21. The intensity modulator 160 thins out a predetermined number of optical pulses LPn of the optical frequency comb LC1 that are emitted from the optical frequency comb generator 30 and then incident through the optical fiber 42. In Figure 11, as an example, the intensity modulator 160 thins out some of the optical pulses LC of the optical frequency comb LC1. n+1 ~LC n+8 Among the optical pulse LC n+3 LC n+6 LC n+7 Some of the light pulses are thinned out. When a predetermined number of light pulses LPn from the optical frequency comb LC1 are thinned out by the intensity modulator 160, the relative arrangement of the light pulses at the output surface 64b of the wavefront combining unit 22 changes, as shown in Figure 12. When a predetermined number of light pulses from the optical frequency comb LC1 are thinned out by the intensity modulator 160, the phase distribution formed on the output surface 64b of the plane mirror 64 is different from the phase distribution formed by the optical frequency comb LC1 in which the predetermined number of light pulses have not been thinned out, based on the principle explained with reference to Figure 8. The light wave LL generated from the optical frequency comb LC1 is emitted in a direction substantially perpendicular to the inclined plane of the phase distribution formed on the output surface 64b. By thinning out a predetermined number of light pulses from the optical frequency comb LC1 by the intensity modulator 160, a new light wave LL is generated that is different from the light wave LL generated by the optical frequency comb LC1 in which the predetermined number of light pulses have not been thinned out.

[0094] In the wavefront control device 81 of the third modified example, a composite wavefront WP is emitted from the plane 66b of the plano-convex lens 66 in the wavefront combining unit 22, formed by the interference of multiple optical pulses LPn that remain after a predetermined optical pulse from the optical frequency comb LC1 has been thinned out. For example, as shown in Figure 11, the intensity modulator 160 controls the optical pulse LC n+3 LC n+6 LC n+7 If the quantification occurs, the optical pulse LC is emitted from the plane 66b of the plano-convex lens 66. n+1 LC n+2 LC n+4 LC n+5 LC n+8 The combined wavefront WP generated by the interference is emitted. The two-dimensional wavefront distribution of the wavefront WP0 of the optical wave LL, i.e., the combined wavefront WP, is based on the optical pulses that remain after a predetermined number of optical pulses have been thinned out. The predetermined number of optical pulses thinned out by the intensity modulator 160 is calculated from the combined wavefront WP output from the wavefront combining unit 22 and set as appropriate. Thus, in order to obtain the combined wavefront WP and the two-dimensional wavefront distribution which are specific transverse modes, the intensity modulator 160 thins out predetermined optical pulses corresponding to a specific transverse mode among the multiple optical pulses LPn of the incident optical frequency comb LC1.

[0095] As described above, the wavefront control device 81 of the third modified example includes an intensity modulator 160 that emits some of the optical pulses LCn of the optical frequency comb LC1 emitted from the optical frequency comb generation unit 21 toward the wavefront combining unit 22. The some optical pulses emitted from the intensity modulator 160 are determined by working backward from the desired transverse mode of the composite wavefront WP generated in the wavefront combining unit 22. According to the wavefront control device 81 of the third modified example, higher-order transverse modes can be generated and utilized from a phase distribution with a high degree of controllability. In the wavefront control device 81 of the third modified example, a phase distribution that gives rise to higher-order transverse modes can be calculated and the phase distribution can be controlled using the intensity modulator 160. In the wavefront control device 81 of the third modified example, multiple phases φ emitted from multiple positions POn that function as optical antennas nThe correspondence between these can be appropriately determined. Furthermore, by interfering not only the composite wavefront WP formed by the thinned pulse train with another composite wavefront WP formed subsequently, more complex higher-order transverse modes can be formed. In that case, although not shown in the figure, a resonator having the same resonator length as the MPC optical system 60 is placed ahead of the plano-convex lens 66 in the direction of propagation of the composite wavefront WP, and pulse stacking is performed using this resonator to form the complex higher-order transverse modes as described above. The resonator placed ahead of the MPC optical system 60 may be a spatial optical system like the MPC optical system 60, or it may be composed of an array of waveguides or a bundle of multiple fibers. [Explanation of symbols]

[0096] 11,15...Wavefront control device 12...Adaptive optics device 13. Imaging Optics 21. Optical frequency comb generation unit 22...Wavefront synthesis section

Claims

1. An optical frequency comb generation unit that emits an optical frequency comb having multiple optical pulses arranged in numerical order on the time axis, A wavefront combining unit distributes each of the plurality of optical pulses incident from the optical frequency comb generation unit to different positions on a plane intersecting the propagation direction of the optical frequency comb, according to their relative phase with respect to the first optical pulse, and generates a combined wavefront of the optical pulses emitted from these different positions. Equipped with, The optical frequency comb generation unit includes a phase control unit that controls the repetition frequency and offset frequency of the optical frequency comb. Wavefront control device.

2. The wavefront combining section comprises a resonator structure having a pair of mirrors arranged opposite each other, The reflective surface of one of the pair of mirrors reflects a portion of the incident optical frequency comb and transmits at least a portion of the remainder. The distance L between the reflective surfaces of the pair of mirrors is expressed by the following equation (1): The wavefront control device according to claim 1. [Math 1] In equation (1), L ｒｅｐ represents the pulse-to-pulse distance of the optical frequency comb, c represents the speed of light, and f ｒｅｐ This represents the repetition frequency of the optical frequency comb.

3. The system includes an adjustment mechanism for adjusting the incident angle of the optical frequency comb that is incident on at least one of the pair of mirrors. The wavefront control device according to claim 2.

4. The optical frequency comb generation unit includes a wavelength conversion unit that converts the wavelength of the optical frequency comb. A wavefront control device according to any one of claims 1 to 3.

5. The system includes a feedback mechanism that feeds back the intensity information of the light wave having the composite wavefront to the phase control unit. A wavefront control device according to any one of claims 1 to 4.

6. The phase control unit sets the ratio of the repetition frequency to the offset frequency to a predetermined value. A wavefront control device according to any one of claims 1 to 5.

7. The system includes an intensity modulator that directs some of the multiple optical pulses emitted from the optical frequency comb generation unit toward the wavefront synthesis unit. A wavefront control device according to any one of claims 1 to 6.

8. A wavefront control device according to any one of claims 1 to 7, Imaging optical system, Equipped with, The imaging optical system is configured to emit light waves having the combined wavefront from the wavefront combining unit of the wavefront control device and to irradiate the object to be measured with light waves, and is configured to receive light waves reflected or transmitted from the object to be measured. Adaptive optics device.

Images