Optical wavefront measuring device and optical wavefront correction device

Abstract

This technology provides the ability to measure the wavefront shape of light with high temporal resolution while keeping costs down. [Solution] The optical wavefront measuring device comprises a lens array 31, a light receiving sensor 33, and a wavefront shape calculation unit. The lens array 31 focuses the measurement light into regions of the wavefront W. The light receiving sensor 33 receives multiple light spots S focused by the lens array 31 and outputs an electrical signal indicating the direction of increase or decrease in the amount of light received and the time when the amount of light received changed for each pixel. The wavefront shape calculation unit calculates the wavefront shape of the measurement light based on the electrical signals output from the light receiving sensor 33. The amount of information output by the light receiving sensor 33 is small compared to outputting information for all pixels. Therefore, the light receiving sensor 33 can output information regarding the displacement of the light spots S with high temporal resolution. Thus, the wavefront shape of the measurement light can be measured with high temporal resolution based on the information output from the light receiving sensor 33.

Description

Technical Field

[0001] The present disclosure relates to a technique for measuring the wavefront of light that has passed through the atmosphere.

Background Art

[0002] Conventionally, satellite communication technology for communicating information by radio waves between artificial satellites and ground stations is known. However, since radio waves have a limited available frequency band, there is a limit to the communication volume of information. Therefore, in recent years, "optical satellite communication" that uses light instead of radio waves for communication between artificial satellites and ground stations has been expected.

[0003] However, the light emitted from an artificial satellite reaches a ground station through the atmosphere that covers the surface of the earth. Therefore, in optical satellite communication, there is a problem that the wavefront of light is disturbed according to the state of the atmosphere. In addition, the wavefront aberration of light generated by an optical system may affect information transmission. Therefore, a wavefront compensation technique for measuring the wavefront shape of light and correcting a disturbed wavefront to a flat state is required.

[0004] As a wavefront sensor for measuring the wavefront shape of light, a Shack-Hartmann wavefront sensor has been conventionally known. The Shack-Hartmann wavefront sensor converges measurement light by a plurality of microlenses, and detects the wavefront shape of light based on the positions of a plurality of light spots detected by a light sensor. Such a conventional wavefront sensor for light is described in, for example, Patent Document 1.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Therefore, this disclosure aims to provide a technology that can measure the wavefront shape of light with high temporal resolution while keeping costs down. [Means for solving the problem]

[0008] The first disclosure is an optical wavefront measuring device for measuring the wavefront of a measurement light that has passed through the atmosphere, comprising: a lens array that focuses the measurement light into each wavefront region; a light receiving sensor that receives a plurality of light spots focused by the lens array and outputs an electrical signal indicating the direction of increase or decrease in the amount of light received and the time when the amount of light received changed for each pixel; and a wavefront shape calculation unit that calculates the wavefront shape of the measurement light based on the electrical signal output from the light receiving sensor.

[0009] The second disclosure is a wavefront measuring device of the first disclosure, used to correct the wavefront shape of communication light transmitted and received for communication between an artificial satellite and a ground station, wherein the measurement light is the communication light.

[0010] The third disclosure is a wavefront measuring device of the first disclosure, used to correct the wavefront shape of communication light transmitted and received for communication between an artificial satellite and a ground station, wherein the measuring light is a guide light with a different wavelength from the communication light.

[0011] The fourth disclosure is a wavefront measuring device of the third disclosure, wherein the measuring light is the light of a guide star created by exciting sodium atoms present in the upper atmosphere with laser light.

[0012] The fifth disclosure is an optical wavefront correction device for correcting the wavefront shape of communication light transmitted and received for communication between an artificial satellite and a ground station, comprising: an optical wavefront measuring device disclosed in any one of the second to fourth disclosures; a two-dimensional optical phase modulator for correcting the wavefront shape of the communication light; a correction value calculation unit for calculating a correction value for flattening the wavefront based on the wavefront shape calculated by the wavefront shape calculation unit; and a control unit for controlling the two-dimensional optical phase modulator based on the correction value calculated by the correction value calculation unit.

[0013] The sixth disclosure is an optical wavefront correction device of the fifth disclosure, wherein the two-dimensional optical phase modulator has a plurality of mirrors that can be driven for each wavefront region, the wavefront shape calculation unit calculates a polynomial representing the wavefront shape by fitting based on the displacement of a plurality of light spots measured by the light receiving sensor, and the correction value calculation unit calculates a correction value for driving each mirror of the two-dimensional optical phase modulator based on the polynomial.

[0014] The seventh disclosure is an optical wavefront correction device of the fifth or sixth disclosure, further comprising a beam splitter downstream of the two-dimensional optical phase modulator in the optical path for splitting communication light into two rays, wherein one of the two rays split by the beam splitter is incident on the lens array, and the other of the two rays split by the beam splitter is incident on an optical fiber for reading information. [Effects of the Invention]

[0015] According to the first to seventh disclosures, the amount of information output can be reduced compared to outputting information from all pixels of the light-receiving sensor. As a result, the light-receiving sensor can output information about the displacement of the light spot with high temporal resolution. Therefore, based on the information output from the light-receiving sensor, the wavefront shape of the measured light can be measured with high temporal resolution.

[0016] In particular, according to the second disclosure, the wavefront shape of the communication light itself can be measured with high temporal resolution.

[0017] Particularly, according to the third disclosure, even when the light receiving sensor cannot receive the wavelength of the communication light itself, the wavefront shape of the communication light can be estimated by measuring the wavefront shapes of the guide lights with different wavelengths.

[0018] Particularly, according to the fifth disclosure, based on the wavefront shape measured with high time resolution, by controlling the two-dimensional optical phase modulator, the wavefront shape of the communication light can be corrected with high time resolution.

[0019] Particularly, according to the sixth disclosure, even when the number of regions of the wavefront divided by the lens array is different from the number of regions of the wavefront corrected by each mirror of the two-dimensional optical phase modulator, by once approximating the wavefront shape with a polynomial, the wavefront shape of the communication light can be appropriately corrected for each region.

[0020] Particularly, according to the seventh disclosure, the wavefront shape of the communication light is measured on the downstream side of the optical path from the two-dimensional optical phase modulator. Thereby, the wavefront shape of the communication light can be measured at a position closer to the optical fiber.

Brief Description of the Drawings

[0021] [Figure 1] It is a diagram showing the configuration of an optical satellite communication system. [Figure 2] It is a schematic diagram of a two-dimensional optical phase modulator. [Figure 3] It is a schematic diagram of an optical wavefront sensor. [Figure 4] It is a block diagram conceptually showing the functions realized by a computer. [Figure 5] It is a flowchart showing the flow of processes executed by a wavefront shape calculation unit, a correction value calculation unit, and a control unit. [Figure 6] It is a diagram showing the configuration of an optical satellite communication system according to a modification example.

Modes for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0023] <1. Optical satellite communication system> Figure 1 shows the configuration of an optical satellite communication system 100 including an optical wavefront correction device 1 according to one embodiment. The optical satellite communication system 100 is a system that communicates information between an artificial satellite 101 and a ground station 102 using light. The ground station 102 is located on the surface of the Earth. The artificial satellite 101 is located in outer space, outside the atmosphere that covers the surface of the Earth. Hereinafter, the light transmitted and received between the artificial satellite 101 and the ground station 102 for communication will be referred to as "communication light L1".

[0024] Satellite 101 emits communication light L1 toward ground station 102. Communication light L1 is an infrared light beam with a beam diameter of, for example, about 0.5 meters or more than 1 meter. Communication light L1 transmits information by modulating its intensity, frequency, or phase. Communication light L1 can be modulated at a higher speed than radio waves. Therefore, by using communication light L1, a larger amount of information can be transmitted and received than when using radio waves.

[0025] As shown in Figure 1, the ground station 102 includes a telescope 91, a reflecting mirror 92, a reduction optical system 93, an optical wavefront correction device 1, an aspherical lens 94, an optical fiber 95, and an information reading unit 96.

[0026] The communication light L1 emitted from the satellite 101 passes through the Earth's atmosphere and enters the telescope 91. After passing through the telescope 91, the communication light L1 is reflected by a reflective mirror 92 and enters the optical wavefront correction device 1 through a reduction optical system 93 composed of multiple lenses. The beam diameter of the communication light L1 is reduced to approximately 5 to 10 millimeters after passing through the telescope 91 and the reduction optical system 93.

[0027] As the communication light L1 passes through the atmosphere, its wavefront is distorted depending on the atmospheric conditions. The optical wavefront correction device 1 measures the wavefront shape of the communication light L1, including this distortion, and automatically corrects the wavefront shape of the communication light L1 based on the measurement results. The communication light L1, whose wavefront has been corrected by the optical wavefront correction device 1, is focused by the aspherical lens 94 and incident on the optical fiber 95. Then, the information reading unit 96 reads information from the communication light L1 transmitted through the optical fiber 95.

[0028] <2. Optical wavefront correction device> Next, the detailed configuration of the optical wavefront correction device 1 will be described. As shown in Figure 1, the optical wavefront correction device 1 includes a two-dimensional optical phase modulator 10, a beam splitter 20, an optical wavefront sensor 30, and a computer 40.

[0029] The two-dimensional optical phase modulator 10 is an optical instrument for correcting the wavefront shape of the communication light L1. Figure 2 is a schematic diagram of the two-dimensional optical phase modulator 10. For example, a Planar Light Valve (PLV) is used in the two-dimensional optical phase modulator 10. The PLV is a micro-electromechanical system (MEMS) having multiple micromirrors 11 arranged in a grid. The communication light L1 is reflected by the surfaces of the multiple micromirrors 11.

[0030] A micromirror 11 is an example of a "mirror". The size of one micromirror 11 is sufficiently smaller than the beam diameter of the communication light L1 incident on the two-dimensional optical phase modulator 10. The shape of the micromirror 11 is, for example, rectangular, as shown in Figure 2. The number of micromirrors 11 in the two-dimensional optical phase modulator 10 is, for example, 128 × 128, but is not limited to this. Multiple micromirrors 11 correspond to each region into which the wavefront of the communication light L1 is divided into multiple regions.

[0031] The two-dimensional optical phase modulator 10 individually drives multiple micromirrors 11 based on electrical signals input from the computer 40, causing minute variations in the height of each micromirror 11. The height of each micromirror 11 can be varied in multiple steps (e.g., four steps), for example, by a few nanometers at a time. This modulates the phase of the communication light L1 in each region. As a result, the wavefront shape of the communication light L1 reflected by the two-dimensional optical phase modulator 10 can be corrected in each region.

[0032] The beam splitter 20 is positioned downstream of the two-dimensional optical phase modulator 10 in the optical path. The beam splitter 20 splits the communication light L1 reflected by the two-dimensional optical phase modulator 10 into two beams. The two communication light beams L1 split by the beam splitter 20 have the same wavefront. One of the communication light beams L1 is incident on the optical wavefront sensor 30. The other communication light beam L1 is incident on the optical fiber 95 via the aspherical lens 94.

[0033] The wavefront sensor 30 is a sensor that measures the wavefront shape of the communication light L1. In this embodiment, the communication light L1 itself is used as the measurement light. For example, a Shack-Hartmann wavefront sensor is used for the wavefront sensor 30. Figure 3 is a schematic diagram of the wavefront sensor 30. As shown in Figure 3, the wavefront sensor 30 has a lens array 31 and a light receiving sensor 33.

[0034] The lens array 31 is positioned perpendicular to the optical axis of the communication light L1. The lens array 31 has a plurality of microlenses 32 arranged in a grid. The size of the microlenses 32 is, for example, about 50 to 500 microns. It is desirable that the number of microlenses 32 in the lens array 31 be 2 × 2 or more. The plurality of microlenses 32 correspond to each region into which the wavefront W of the communication light L1 is divided into multiple regions.

[0035] The lens array 31 focuses the communication light L1 into regions of the wavefront W. As a result, the same number of light spots S as the microlenses 32 are incident on the light receiving sensor 33. If the wavefront W of the communication light L1 is a plane perpendicular to the optical axis, the multiple light spots S are imaged on the central axis Z of each microlens 32. However, if the wavefront W of the communication light L1 is distorted, each light spot S is imaged at a position offset from the central axis Z of the microlens 32.

[0036] The light-receiving sensor 33 is a two-dimensional image sensor that captures multiple light spots S. For example, an event-based camera can be used as the light-receiving sensor 33. Unlike a typical frame-based camera used for video recording, an event-based camera captures only changes in brightness. A frame-based camera outputs video data in which frame images, each containing brightness value information for a large number of pixels, are arranged in a time series. In contrast, an event-based camera outputs information only for pixels whose brightness value has changed.

[0037] The light receiving sensor 33 receives light from multiple light spots S and outputs an electrical signal to the computer 40 indicating the direction of the increase or decrease in the amount of light received and the time when the amount of light received changed, only for pixels where the change in the amount of light received exceeds a threshold. The light receiving sensor 33 does not output an electrical signal for pixels where the amount of light received does not change. For this reason, the amount of information in the electrical signal output from the light receiving sensor 33 is smaller than the amount of information in the electrical signal output from the frame-based camera.

[0038] Therefore, by using an event-based camera as the light-receiving sensor 33, brightness changes can be detected and electrical signals can be output at a faster speed than when using a frame-based camera. Specifically, while a typical frame-based camera has a frame rate of 100fps or less, an event-based camera can output the above-mentioned electrical signals with a time resolution of more than 10kHz.

[0039] Furthermore, the modulation of the intensity, frequency, or phase of the communication light L1 to represent the communication information is at a frequency of 1 GHz or higher, which is even finer than the time resolution of the light receiving sensor 33, which is an event-based camera. For this reason, the modulation of the communication light L1 to represent the communication information is not detected by the light receiving sensor 33.

[0040] Returning to Figure 1, the computer 40 is a unit that controls the two-dimensional optical phase modulator 10 based on the electrical signal output from the light receiving sensor 33. The computer 40 has a processor 41 such as a CPU (Central Processing Unit), memory 42 such as RAM (Random Access Memory), and a storage unit 43 such as a hard disk drive. The storage unit 43 stores the computer program P.

[0041] Figure 4 is a block diagram conceptually illustrating the functions implemented by the computer 40. As shown in Figure 4, the computer 40 includes a wavefront shape calculation unit 44, a correction value calculation unit 45, and a control unit 46. The functions of the wavefront shape calculation unit 44, the correction value calculation unit 45, and the control unit 46 are implemented by the operation of the processor 41 according to the computer program P.

[0042] Figure 5 is a flowchart showing the processing flow performed by the wavefront shape calculation unit 44, the correction value calculation unit 45, and the control unit 46. The functions of the wavefront shape calculation unit 44, the correction value calculation unit 45, and the control unit 46 will be described below with reference to Figures 4 and 5.

[0043] The wavefront shape calculation unit 44 is a processing unit that calculates the wavefront shape of the communication light L1 based on the electrical signal output from the light receiving sensor 33. The lens array 31, the light receiving sensor 33, and the wavefront shape calculation unit 44 constitute an "optical wavefront measuring device" that measures the wavefront shape of the communication light L1, which is the light to be measured.

[0044] The wavefront shape calculation unit 44 first calculates the light-receiving area of ​​the light spot S from the detection result of the light-receiving sensor 33 (step ST1). The light-receiving sensor 33 outputs information only for pixels where the amount of light received has changed. Therefore, the wavefront shape calculation unit 44 changes the light-receiving area of ​​the light spot S for pixels where the amount of light received has changed, but does not change it for other pixels. The wavefront shape calculation unit 44 updates this light-receiving area each time an electrical signal is input from the light-receiving sensor 33. This allows the light-receiving area of ​​the light spot S to be identified in real time.

[0045] Next, the wavefront shape calculation unit 44 calculates the centroid position of each of the multiple light spots S (step ST2). The centroid position of a light spot S is, for example, the center position of the light-receiving area of ​​each light spot S. Then, the wavefront shape calculation unit 44 calculates the displacement amount dy of the centroid position of each light spot S (step ST3). Specifically, it calculates how much the centroid position calculated in step ST2 has been displaced in a direction perpendicular to the central axis Z from the position where it coincides with the central axis Z of the microlens 32, for each light spot S.

[0046] As shown in Figure 3, the centroid displacement dy calculated in step ST3 reflects the inclination of the wavefront W of the communication light L1 in each region. That is, when the wavefront W is perpendicular to the central axis Z of the microlens 32, the centroid displacement dy is 0. As the inclination of the wavefront W with respect to the central axis Z increases, the centroid displacement dy also increases. Furthermore, the direction in which the centroid of the light spot S is displaced from the central axis Z of the microlens 32 reflects the direction of the inclination of the wavefront W.

[0047] The wavefront shape calculation unit 44 calculates the wavefront incidence angle α shown in Figure 2 for each light spot S based on the displacement amount dy of the centroid position calculated in step ST3 (step ST4). The wavefront incidence angle α can be geometrically calculated, for example, by the following formula (1), where F is the length in the optical axis direction from the microlens 32 to the light receiving sensor 33. α = tan -1 (δy / F) (1)

[0048] The wavefront shape calculation unit 44 calculates the overall wavefront shape of the communication light L1 based on the displacement amount dy or wavefront incidence angle α for each light spot S (step ST5). Here, the wavefront shape calculation unit 44 calculates a polynomial representing the shape of the wavefront W by performing polynomial fitting based on the distribution of the displacement amount dy or wavefront incidence angle α of the light spots S. This expresses the continuous wavefront shape of the entire communication light L1. This polynomial fitting can preferably be performed using, for example, Zernike polynomials.

[0049] The correction value calculation unit 45 is a processing unit that calculates a correction value for flattening the wavefront W based on the wavefront shape calculated by the wavefront shape calculation unit 44. The correction value calculation unit 45 calculates a correction value for each region of each micromirror 11 of the two-dimensional optical phase modulator 10 based on the polynomial calculated in step ST5 (step ST6).

[0050] The correction value calculation unit 45 calculates a correction value to inversely correct the distortion of the wavefront W measured by the optical wavefront sensor 30. For example, in a region where the phase of light is lagging, it calculates a correction value to drive the micromirror 11 to advance the phase. Also, in a region where the phase of light is leading, it calculates a correction value to drive the micromirror 11 to delay the phase.

[0051] The control unit 46 is a processing unit that controls the driving of the two-dimensional optical phase modulator 10. Based on the correction value calculated by the correction value calculation unit 45, the control unit 46 drives each micromirror 11 of the two-dimensional optical phase modulator 10 (step ST7). As a result, the phase of the communication light L1 reflected by the two-dimensional optical phase modulator 10 is corrected for each region. Consequently, the wavefront W of the communication light L1 is flattened.

[0052] As described above, this optical wavefront correction device 1 uses an event-based camera as the light receiving sensor 33 of the optical wavefront sensor 30. The event-based camera does not output information for pixels whose light reception amount does not change. Therefore, the light receiving sensor 33 can output information regarding the displacement of the light spot S with high temporal resolution. Consequently, the wavefront shape of the communication light L1 can be measured with high temporal resolution based on the information output from the light receiving sensor 33. Then, by controlling the two-dimensional optical phase modulator 10 based on the measured wavefront shape, the wavefront shape of the communication light L1 can be corrected with high temporal resolution. In other words, by using this optical wavefront correction device 1, high-speed wavefront compensation required for optical communication can be achieved.

[0053] Furthermore, by using an event-based camera, measurements with high temporal resolution can be achieved without using expensive and large high-speed cameras. Therefore, compared to using a high-speed camera, the cost of the optical wavefront correction device 1 can be significantly reduced, and the size of the optical wavefront correction device 1 can also be significantly reduced.

[0054] In particular, in this embodiment, the communication light L1 emitted from the artificial satellite 101 is used as the measurement light for the optical wavefront sensor 30. Therefore, the wavefront shape of the communication light L1 itself can be measured with high temporal resolution, and the wavefront of the communication light L1 can be corrected with high accuracy.

[0055] Furthermore, in this embodiment, in step ST5, the wavefront shape calculation unit 44 calculates a polynomial representing the wavefront shape based on the displacement of the multiple light spots S. Therefore, even if the number of wavefront regions divided by the lens array 31 of the optical wavefront sensor 30 and the number of wavefront regions divided by the multiple micromirrors 11 of the two-dimensional optical phase modulator 10 are different, the wavefront of the communication light L1 can be appropriately corrected for each region based on the wavefront shape continuously represented by the polynomial.

[0056] Furthermore, in this embodiment, the wavefront shape of the communication light L1 is measured downstream of the two-dimensional optical phase modulator 10 in the optical path. Therefore, the wavefront shape of the communication light L1 can be measured at a position closer to the optical fiber 95 than when the wavefront shape of the communication light L1 is measured upstream of the two-dimensional optical phase modulator 10 in the optical path.

[0057] <3. Variant> Although one embodiment has been described above, this disclosure is not limited to the above embodiment. Below, various modifications will be described, focusing on the differences from the above embodiment.

[0058] <3-1. First variation> Figure 6 shows the configuration of an optical satellite communication system 100 including an optical wavefront correction device 1 according to the first modified example. The example in Figure 6 assumes that the light receiving sensor 33 cannot receive the wavelength of the communication light L1 itself. For example, it assumes that the communication light L1 is infrared, and the event-based camera, which is the light receiving sensor 33, is using a silicon sensor that cannot receive infrared light.

[0059] In the example shown in Figure 6, the wavefront correction device 1 is equipped with a laser light source 50. The laser light source 50 emits laser light L2 towards the sodium layer in the upper atmosphere. The wavelength of the laser light L2 is set to a wavelength between 500 and 600 nm, which is capable of exciting sodium atoms. When the laser light L2 irradiates the sodium atoms in the sodium layer, the sodium atoms are excited by the laser light L2 and emit light. This creates a guide star G in the sodium layer. Note that the above method for creating the guide star G is just one example, and the wavelength of the laser light used to create the guide star G is not limited to that described above.

[0060] The guide star G is preferably created on or near the optical path of the communication light L1 emitted from the artificial satellite 101. The guide star G emits guide light L3 of a visible wavelength that can be received by the light receiving sensor 33. In this case, the guide light L3 emitted from the guide star G passes through the telescope 91, the reflecting mirror 92, and the reduction optical system 93 and enters the two-dimensional optical phase modulator 10. The guide light L3 reflected by the two-dimensional optical phase modulator 10 then enters the optical wavefront sensor 30 via the beam splitter 20. Therefore, the wavefront shape calculation unit 44 can calculate the wavefront shape of the guide light L3 based on the electrical signal output from the optical wavefront sensor 30.

[0061] In this way, even if the light receiving sensor 33 cannot receive the wavelength of the communication light L1 itself, the wavefront shape of the guide light L3, which has a different wavelength from the communication light L1, can be measured. It is assumed that the wavefronts of both the communication light L1 and the guide light L3 are similarly distorted by the atmosphere. Therefore, the computer 40 can estimate the wavefront shape of the communication light L1 based on the wavefront shape of the guide light L3. Then, the computer 40 can correct the wavefront shape of the communication light L1 based on the estimated wavefront shape.

[0062] However, the amount of wavefront distortion is inversely proportional to the wavelength of light. For this reason, it is necessary to convert the amount of wavefront distortion measured by the guide light L3 to match the wavelength of the communication light L1 that you want to correct. Specifically, let the wavelength of the communication light L1 be λ1, the amount of wavefront distortion of the communication light L1 be W1, the wavelength of the guide light L3 be λ2, and the amount of wavefront distortion of the guide light L3 be W2. Then, calculate the amount of wavefront distortion W1 of the communication light L1 using the following conversion formula (2). W1 = W2 × λ1 / λ2 (2)

[0063] <3-2. Other variations> In the above embodiment, an event-based camera was given as an example of the light-receiving sensor 33. However, the light-receiving sensor 33 is not limited to a so-called event-based camera. Other sensors that can output electrical signals indicating the direction of increase or decrease in the amount of light received and the time when the amount of light received changed for pixels where the amount of light received has changed, and that can output electrical signals with a higher temporal resolution than a frame-based high-speed camera, may also be used.

[0064] Furthermore, in the above embodiment, a PLV was given as an example of the two-dimensional optical phase modulator 10. However, the two-dimensional optical phase modulator 10 may be a device other than a PLV. For example, the two-dimensional optical phase modulator 10 may be a DMD (Digital Mirror Device). Alternatively, the two-dimensional optical phase modulator 10 may be a device that modulates the phase in each region while transmitting light rather than reflecting it (for example, an LCOS (Liquid Crystal On Silicon)).

[0065] Furthermore, the above embodiment described the case in which communication light L1 emitted from the artificial satellite 101 is received by the ground station 102. For this reason, in the above embodiment, the optical wavefront correction device 1 was installed at the ground station 102. However, when the communication light L1 emitted from the ground station 102 is received by the artificial satellite 101, the wavefront of the communication light L1 may be measured and corrected in the same manner as in the above embodiment. In that case, the optical wavefront correction device 1 should be installed at the artificial satellite 101.

[0066] Furthermore, the elements that appear in the above embodiments and modifications may be combined or some may be omitted as appropriate, to the extent that no contradictions arise. [Explanation of Symbols]

[0067] 1: Optical wavefront correction device 10: Two-dimensional optical phase modulator 11: Micromirror 20: Beam Splitter 30: Optical wavefront sensor 31: Lens Array 32: Microlens 33: Light receiving sensor 40: Computer 44: Wavefront shape calculation section 45: Correction value calculation unit 46: Control Unit 50: Laser light source 91: Telescope 92: Reflective mirror 93:Reducing optical system 94: Aspherical lenses 95: Optical fiber 96: Information Reading Unit 100: Optical satellite communication system 101:Artificial satellite 102: Ground station G: Guide star L1: Communication Optical Fiber L2: Laser light L3: Guide light S: Light spot W: wavefront Z: Center axis dy: Displacement α: Wavefront incidence angle

Claims

1. A wavefront measuring device for measuring the wavefront of light that has passed through the atmosphere, A lens array that focuses the measurement light into each wavefront region, A light receiving sensor that receives multiple light spots focused by the lens array and outputs an electrical signal indicating the direction of increase or decrease in the amount of light received and the time when the amount of light received changed for each pixel, A wavefront shape calculation unit calculates the wavefront shape of the measured light based on the electrical signal output from the light receiving sensor, A wavefront measuring device equipped with the following features.

2. A wavefront measuring device according to claim 1, It is used to correct the wavefront shape of communication light transmitted and received for communication between artificial satellites and ground stations. The measurement light is the communication light, and the device is an optical wavefront measuring device.

3. A wavefront measuring device according to claim 1, It is used to correct the wavefront shape of communication light transmitted and received for communication between artificial satellites and ground stations. The optical wavefront measuring device wherein the measurement light is a guide light with a different wavelength from the communication light.

4. A wavefront measuring device according to claim 3, The aforementioned measurement light is the light from a guide star, which is created by exciting sodium atoms present in the upper atmosphere with laser light; this is an optical wavefront measurement device.

5. An optical wavefront correction device for correcting the wavefront shape of communication light transmitted and received between an artificial satellite and a ground station for communication, A wavefront measuring device according to any one of claims 2 to 4, A two-dimensional optical phase modulator for correcting the wavefront shape of the communication light, A correction value calculation unit calculates a correction value for flattening the wavefront based on the wavefront shape calculated by the wavefront shape calculation unit, Based on the correction value calculated by the correction value calculation unit, a control unit controls the two-dimensional optical phase modulator, A wavefront correction device equipped with the following features.

6. A wavefront correction device according to claim 5, The two-dimensional optical phase modulator has a plurality of mirrors that can be driven for each wavefront region, The wavefront shape calculation unit calculates a polynomial representing the wavefront shape by performing fitting based on the displacement of multiple light spots measured by the light receiving sensor. The correction value calculation unit calculates a correction value for driving each mirror of the two-dimensional optical phase modulator based on the polynomial, and is an optical wavefront correction device.

7. A wavefront correction device according to claim 5, A beam splitter located downstream of the two-dimensional optical phase modulator in the optical path splits the communication light into two beams. Furthermore, One of the two light rays split by the beam splitter enters the lens array. A wavefront correction device in which the other of the two light rays split by the beam splitter is incident on an optical fiber for reading information.

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