JP2017181038A - Wavefront sensor - Google Patents

Abstract

A laser beam wavefront sensor having a simple structure and a large measurement angle range is provided.
A wavefront sensor includes an angle selection filter having a different reflectance according to an incident angle, and a photodetector that receives light arriving through the angle selection filter.
[Selection] Figure 1

Description

  The present invention relates to a wavefront sensor that is used in particular for measuring the wavefront shape of laser light. The present invention further relates to an optical space communication device including such a wavefront sensor.

  In recent years, with the increasing demand for ground observation from the sky using artificial satellites and aircraft, the volume of measurement data output from measuring instruments mounted on them has increased. For this reason, it is inevitable that communication capacity between artificial satellites and airplanes and the ground should be increased. However, it is difficult to greatly increase the transmission capacity in the future in the conventional microwave communication with restrictions on frequency resources, and the appearance of a new technology is strongly desired.

  The optical space communication technology is one of the technologies expected to greatly increase the wireless transmission capacity. This technique uses a transmitter that emits modulated signal light to free space and a receiver that collects and receives the propagated signal light. In order to realize high-speed optical space communication, the use of optical transmission technology cultivated in terrestrial optical fiber communication systems, such as low-noise optical amplification technology and high-sensitivity reception technology using coherent detection, is particularly It is valid. Since these technologies are based on the premise that signal light is in a single-mode optical fiber, in order to use these technologies in optical space communication, signal light that has propagated through free space in a receiver is transmitted to a single-mode optical fiber. It is necessary to bind to.

  The core diameter of the single mode optical fiber is as small as about 10 microns. For this reason, in order to combine the received signal light with high efficiency, it is necessary to align the beam spot obtained by condensing the laser light, which is the signal light, with the core portion of the optical fiber with high accuracy. Here, when the receiver is installed on the ground, the propagation direction and wavefront shape of the laser light change from moment to moment due to the atmosphere near the ground surface, which causes a serious instability of communication, fading due to so-called atmospheric fluctuations. Problems arise. The change in the propagation direction becomes a cause for the position of the beam spot that condenses the laser light to be displaced from the core of the optical fiber. In addition, the change in the wavefront shape deteriorates the light condensing property of the beam spot, and becomes a factor of reducing the coupling efficiency between the laser beam and the single mode optical fiber.

  As one measure for solving such a problem, the direction of the laser beam and the distortion of the wavefront are corrected by using a plane mirror that is driven at high speed and a deformable mirror that can arbitrarily change the shape of the reflecting surface. , There is a technique called adaptive optics (AO, applied optics). This AO system uses a wavefront sensor that measures the wavefront shape of a laser beam in order to determine a control amount of a mirror that corrects the wavefront of the laser beam. Here, a case where the AO system is used in an optical space communication apparatus using an optical fiber will be described. The inclination of the wavefront of the laser beam, which is the signal light, is removed by controlling the directing direction with a plane mirror, and the converging position of the beam spot is adjusted with high accuracy to the core of the optical fiber. Higher-order wavefront distortion that cannot be corrected by a flat mirror is corrected by a deformable mirror whose reflection surface has been deformed so as to cancel out the distortion. Improve.

  As a conventional wavefront sensor, there is a Shack-Hartmann wavefront sensor (for example, Non-Patent Document 1 “Hect Optics I—Basic and Geometric Optics”, Eugene Hecht, Ozaki / Asakura translation, pp.343-348). The Shack-Hartmann wavefront sensor includes a microlens array and an area sensor array in which the sections are divided so as to correspond to the respective microlenses. The laser light incident on the wavefront sensor is divided into a plurality of light beams by the microlens array, and then condensed on a plurality of beam spots on the area sensor array installed on the focal plane of the microlens. If the wavefront of the laser beam is an ideal plane, the plurality of beam spots are collected at the center of each area sensor. On the other hand, when the wavefront is inclined within the aperture of the microlens, a “shift” from the center occurs at the spot position on the area sensor. From the ratio of the deviation amount and the focal length of the microlens, the amount of inclination of the wavefront within the microlens aperture range can be detected. Similarly, the wavefront shape of the entire laser beam can be measured from the distribution of beam spots on the area sensor array formed by the two-dimensionally arranged microlens array.

  As a wavefront sensor other than the Shack-Hartmann wavefront sensor proposed as means for measuring the wavefront shape, for example, there is a wavefront detection device described in Patent Document 1. This wavefront detection apparatus includes a plurality of double mode waveguides formed on a substrate and means for detecting the asymmetry of light installed at the exit end of each double mode waveguide. Two mode light beams are excited in the plurality of double mode waveguides in accordance with the phase asymmetry due to the inclination of the incident wavefront. For this reason, the detection means detects the inclination of the wavefront at the position of each double mode waveguide.

JP 2000-65646 A

Hector Optics I (Original: OPTICS, 4th Edition, Eugene Hecht, translated by Ozaki and Asakura) pp.343-348

  The following analysis is given by the present invention. It should be noted that the entire disclosure of each of the above prior art documents is incorporated herein by reference.

  The Shack-Hartmann wavefront sensor has the following problems because it uses a microlens array. The first is that the measurable wavefront shape is limited. When the wavefront inclination increases, the amount of displacement of the beam spot increases, and it may span adjacent area sensors. At this time, the area sensor cannot determine which microlens is the focused beam spot, and cannot measure the wavefront shape. The spatial resolution for measuring the wavefront is determined by the number of microlens arrays. As described above, in the Shack-Hartmann wavefront sensor, the detectable amount of wavefront inclination and spatial resolution are limited by the optical characteristics of the microlens array. Secondly, since it is necessary to manufacture the microlens array and the entire optical system with high accuracy, the structure is complicated and expensive.

  The wavefront detection device described in Patent Document 1 can measure a two-dimensional distribution of wavefront shapes with a simple structure, but has the following problems. First, in order to obtain spatial resolution, it is necessary to form a large number of double-mode waveguides on the substrate, and a detection device corresponding only to that is required. Second, since the opening area of the waveguide is small relative to the area of the wavefront to be detected, the measurable energy is small.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a laser beam wavefront sensor having a simple structure and a large measurement angle range.

  According to a first aspect of the present invention, there is provided a wavefront sensor including an angle selection filter having a different reflectance according to an incident angle, and a photodetector that receives light arriving through the angle selection filter.

  According to the second aspect of the present invention, the movable mirror that controls the propagation direction of the incident light, the deformable mirror that controls the wavefront shape of the incident light, and the light coming from the movable mirror or the deformable mirror are divided. An optical space communication device is provided that includes a beam splitter that receives the light beam and the wavefront sensor of the present invention that receives one of the light beams divided by the beam splitter.

  According to the third aspect of the present invention, a movable mirror that controls the propagation direction of incident light, a deformable mirror that controls the wavefront shape of incident light, and an angle selection that separates incident light depending on the incident angle. And a method of controlling the optical space communication device including the filter, the external light from the external space incident on the space optical communication device and arriving through the movable mirror and the deformable mirror by the angle selection filter Separating, obtaining signal intensities of a plurality of separated lights separated by the angle selection filter, based on optical characteristics (stored in advance) of the angle selection filter and the signal intensities of the plurality of separated lights. There is provided a control method including determining a control amount of the movable mirror and the deformable mirror, and changing a directivity direction of the movable mirror and a reflecting surface shape of the deformable mirror based on the control amount.

  According to a fourth aspect of the present invention, the method includes separating incident light into a plurality of separated lights by an angle selection filter that separates light depending on an incident angle, and comparing signal strengths of the plurality of separated lights. A method for determining the wavefront shape of incident light is provided.

  According to a fifth aspect of the present invention, a movable mirror that controls the propagation direction of incident light, a deformable mirror that controls the wavefront shape of incident light, and an angle selection that separates incident light depending on the incident angle. And a filter for correcting a wavefront of external light from an external space incident on an optical space communication device, the external light entering the optical space communication device and arriving via the movable mirror and the deformable mirror Separating external light from the space with the angle selection filter, obtaining signal intensities of a plurality of separated lights separated by the angle selection filter, optical characteristics (stored in advance) of the angle selection filter, and There is provided a correction method including changing a directivity direction of the movable mirror and a reflecting surface shape of the deformable mirror based on signal intensities of a plurality of separated lights.

  According to the first aspect of the present invention, a wavefront sensor having a simple measurement structure and a large measurement angle range can be provided. Furthermore, according to the second aspect of the present invention, it is possible to provide an optical space communication device that enables stable large-capacity communication even when the wavefront of signal light is inclined or distorted.

It is a schematic diagram of the wavefront sensor by 1st Embodiment. It is a graph which shows the incident angle dependence of the reflectance of an example of an angle selection filter. It is a graph which shows typically the measurement result of the plane wave by the wavefront sensor by a 1st embodiment using the photodetector which has spatial resolution. It is a graph which shows typically the measurement result of the spherical wave by the wavefront sensor by a 1st embodiment using the photodetector which has spatial resolution. It is a graph which shows typically the measurement result of the higher order wavefront fluctuation by the wavefront sensor by a 1st embodiment using the photodetector which has spatial resolution. It is a graph which shows typically the measurement result of the wavefront which has energy distribution by the wavefront sensor by a 1st embodiment using the photodetector which has spatial resolution. It is a graph which shows typically the difference in the spatial resolution of the wave front by the wave front sensor by a 1st embodiment using the photodetector which has spatial resolution. It is a schematic diagram of the wavefront sensor by 2nd Embodiment. It is the schematic diagram which looked at a part of wavefront sensor of FIG. 8 from the angle different from FIG. It is a schematic diagram of an example of the optical space communication apparatus containing the wavefront sensor of 2nd Embodiment.

  An outline of a basic embodiment of the present invention will be described. It should be noted that the reference numerals of the drawings attached to the outline are only for the purpose of assisting understanding, and are not intended to limit the present invention to the illustrated embodiment.

  The wavefront sensor according to the basic embodiment of the present invention includes an angle selection filter that receives light incident on the wavefront sensor, and a photodetector that receives light arriving via the angle selection filter. In this document, “light” particularly means “laser light”, but is not limited thereto. In addition, in this document, “laser light” is merely an example of light that can cause tilt or distortion in the wavefront.

  This angle selection filter has different reflectivity depending on the incident angle, and has, for example, the dependency of the reflectivity shown in FIG. 2 on the incident angle (hereinafter also referred to as “reflectance incident angle characteristic”). The angle selection filter in FIG. 2 transmits all light with an incident angle of 44 degrees or less, reflects all light with an angle of 46 degrees or more, and transmits light from 44 degrees to 46 degrees as a transmission component according to the incident angle. Separation is performed with a separation ratio that continuously changes to the reflection component.

  Further, for example, as shown in FIG. 1, photodetectors 30 and 31 for receiving the transmission component 100 and the reflection component 101 of the light 10 incident on the angle selection filter 20 are disposed after the angle selection filter 20. The angle selection filter 20 having the characteristics shown in FIG. 2 is used as the angle selection filter 20, and the angle selection filter 20 is oriented so that light with no wavefront tilt is incident on the angle selection filter 20 at an angle of 45 degrees. . The signals of the photodetectors 30 and 31 that have received the light separated by the angle selection filter 20 are compared. The inclination of the wavefront of the incident light 10 can be determined by the magnitude relationship between these signal intensities. Also, the absolute value of this slope can be determined from the ratio of these signal intensities. Thus, the wavefront shape of the incident light 10 can be obtained. In this document, the incident angle at which the transmission component and the reflection component are separated by 1: 1 by the angle selection filter is also referred to as an “ideal angle”. For example, in the case of an angle selection filter having the characteristics of FIG. 2, the “ideal angle” is 45 degrees. In addition, light that is incident on the angle selection filter at an ideal angle and has no wavefront tilt (including laser light) is also referred to as “ideal light”. The inclination with respect to the ideal angle is also referred to as “wavefront inclination”. Further, “after A is placed on B” means that A is arranged downstream of B with respect to the traveling direction of light, and “A is placed before B” is related with the traveling direction of light. , A is arranged upstream of B.

  Further, for example, in the wavefront sensor shown in FIG. 1, for example, the angle selection filter having the reflectance incident angle characteristic shown in FIG. 2 is used as the angle selection filter 20, and the angle selection filter 20 is, for example, the optical axis of the incident light 10. It is also possible to configure to be rotatable around. Then, by rotating the angle selection filter by 180 degrees around its rotation axis, even if one of the photodetectors 30 and 31 is omitted, that is, only one photodetector is assigned to one angle selection filter, the incident light is incident. The wavefront shape of the light 10 can be obtained. For example, in the state shown in FIG. 1, the inclination of the wavefront of the incident light 10 is α. When the angle selection filter 20 is rotated 180 degrees around its rotation axis, the normal direction of the reflection surface of the angle selection filter is rotated 90 degrees in the incident plane. Therefore, the inclination of the wavefront is −α, and the transmission component of the angle selection filter 20 in this orientation state corresponds to the reflection component of the angle selection filter 20 in the orientation state of FIG. Therefore, the wavefront shape of the incident light 10 can be obtained by receiving the transmitted component of the angle selection filter 20 before and after the rotation by the photodetector 30 and comparing these signals. Therefore, the wavefront shape of the incident light 10 can be obtained even if the photodetector 31 is omitted, that is, only the photodetector 30 is assigned to the angle selection filter 20. Alternatively, one photodetector can be assigned to one angle selective filter, for example by allowing one photodetector to move between two positions for the photodetectors 30 and 31 shown in FIG. Only the wavefront shape of the incident light can be obtained.

  Note that the slope of the wavefront of the incident light 10 and the absolute value thereof can be determined by the calculation unit 40 (see FIG. 1). The calculation unit 40 can be provided in the wavefront sensor itself. Alternatively, a wavefront sensor unit including the wavefront sensor and the calculation unit 40 can be configured. Or it is also possible to comprise the wavefront sensor system which combined the wavefront sensor and the control apparatus etc. which contain the calculating part 40 as the component or the function.

  Thus, according to the basic embodiment of the present invention, the light used for obtaining the wavefront shape of the incident light is received by the photodetector through the angle selection filter, thereby using the microlens array. Compared with a Shack-Hartmann wavefront sensor or the like, the wavefront shape of incident light can be obtained with a simple structure and a large measurement angle range.

  Specific embodiments of the present invention will be described below in detail with reference to the drawings. Note that the reference numerals of the drawings attached to the following embodiments are only for helping understanding, and are not intended to limit the present invention to the illustrated embodiments.

[First Embodiment]
FIG. 1 is a schematic diagram of a wavefront sensor according to the first embodiment. This wavefront sensor includes an angle selection filter 20 that receives a laser beam 10 incident on the wavefront sensor, and two photodetectors 30 and 31 that receive a laser beam arriving via the angle selection filter 20.

  The angle selection filter 20 is oriented such that an ideal laser beam is incident on the angle selection filter 20 at an angle of 45 degrees. The angle selection filter 20 and the transmission component 100 correspond to the incident angle of the laser beam 10 (or its wavefront). The reflection component 101 is separated. The transmission component 100 is received by the photodetector 30, and the reflection component 101 is received by the photodetector 31. The calculation unit 40 receives the measurement data of the photodetectors 30 and 31. The computing unit 40 calculates the inclination of the wavefront of the laser light based on these measurement data.

  The angle selection filter 20 that supplies light to the photodetectors 30 and 31 further has the reflectance incident angle characteristic shown in FIG.

  FIG. 2 shows the reflectance incident angle characteristic of the angle selection filter 20 of the first embodiment, that is, the relationship between the incident angle of light incident on the angle selection filter 20 and the reflectance of the angle selection filter 20. In FIG. 2, the horizontal axis indicates the incident angle of light with respect to the angle selection filter 20, and the vertical axis indicates the reflectance.

  As shown in FIG. 2, the angle selection filter 20 transmits all light with an incident angle of 44 degrees or less, reflects all light with an angle of 46 degrees or more, and reflects light with an angle greater than 44 degrees and less than 46 degrees. In accordance with the above, separation is performed with a separation ratio that continuously changes into a transmission component and a reflection component.

  The transmission component 100 and the reflection component 101 separated by the angle selection filter 20 are received by the corresponding photodetectors 30 and 31, respectively. The photodetectors 30 and 31 convert the received light energy into an electrical signal and transmit it to the arithmetic unit 40. In addition, there exists PD (Photodiode) etc. as an element which performs such photoelectric conversion.

  When the incident angle of the incident light (or its wavefront) is greater than 44 degrees and less than 46 degrees, the calculation unit 40 compares the signals obtained from the photodetectors 30 and 31, and based on the magnitude of these signal intensities, The direction of the inclination is determined, and the absolute value of the inclination is determined from the ratio of these signal intensities. On the other hand, even if the incident angle of incident light (or its wavefront) is 44 degrees or less or 46 degrees or more, if the incident light is within the effective range of the angle selection filter and the photodetector, the calculation unit 40 Although the absolute value cannot be determined, the direction of the wavefront inclination can be determined by which photodetector is receiving light. For this reason, the wavefront sensor of the present invention not only can measure the inclination of the wavefront in a large range with a simple structure, but also assists the wavefront sensor in which the amount of wavefront inclination that can be measured is limited, such as the Shack-Hartmann wavefront sensor. Can also play a role.

[Angle selection filter]
The angle selection filter 20 can accurately separate the transmission component and the reflection component in accordance with the incident angle of the wavefront in the entire region where the laser light is incident, and the coating area has scalability. When the incident area of the laser beam is increased, the energy density is lowered, so that a photodetector with high detection sensitivity is required. However, this makes it possible to realize a wavefront sensor with a large aperture area. The light absorption by the dielectric multilayer film is as small as about 1%, although it depends on the total number of coating films. For this reason, a highly efficient wavefront sensor with little energy loss is realizable by using the angle selection filter which has a dielectric multilayer.

  As a means for realizing the optical characteristic of separating the transmission component and the reflection component with respect to the incident angle, such as the angle selection filter 20, for example, a dielectric multilayer film or a fine periodic structure of nano to micro order on the substrate surface is used. There is a diffractive optical element formed.

  In the wavefront sensor of the present invention, the homogeneity of the in-plane optical characteristics of the region where the laser light is incident is an important parameter. In this regard, when an optical filter is coated with a dielectric multilayer film, a technique for forming a uniform coating over a wide range by using a vacuum deposition method or a sputtering method has been put into practical use.

  The optical characteristics shown in FIG. 2 are set so that the angle selection width is 2 degrees and the incident angle dependency is linear for easy understanding. However, the optical characteristics of the optical filter can be finely adjusted by the design of the film. For example, a steep incident angle dependency for detecting a minute change in the incident angle of the wavefront of the laser beam can be realized. Thus, the wavefront sensor of the present invention allows customization of the angle selective filter design according to the optical characteristics required for each application.

  Further, the angle selection filter is not limited to the illustrated parallel plate as long as the same effect as described above can be obtained. Therefore, the angle selection filter can be configured as, for example, a prism formed by bonding two triangular prisms.

  Furthermore, the angle selection width of the angle selection filter is not limited to 2 degrees shown in FIG. 2, and the ideal angle with respect to the angle selection filter is not limited to 45 degrees shown in FIG.

[Photodetector]
The photodetector can also be configured as an area sensor having spatial resolution, for example, a CCD (Charge Coupled Device).

  Hereinafter, results obtained when the photodetector of the wavefront sensor according to the first embodiment shown in FIG. 1 has spatial resolution will be described with reference to specific examples of wavefront shapes. Here, the precautions regarding the handling of the spatial distribution of energy measured by the photodetector will be described. Since the laser beam received by the photodetector 31 is a reflection component of the angle selection filter, the spatial distribution of the wavefront is inverted in the direction of the incident surface. Therefore, in order to arrange the photodetectors 30 and 31 in the same axial direction with respect to the propagation direction of the laser light received, and to calculate the inclination of the wavefront within the range of the photodetector resolution, the photodetectors 30 and 31 are used. It is necessary to invert the spatial distribution of one of the photodetectors in the direction of the incident surface of the angle selection filter 20 instead of comparing the same pixels. Here, in order to facilitate understanding, the result of reversing the spatial distribution of the photodetector 31 in the direction parallel to the paper surface, which is the direction of the incident surface, is illustrated.

(1) Plane wave whose wavefront is inclined The case where the wavefront of a laser beam is a flat surface without unevenness, but the wavefront is inclined with respect to an ideal angle will be described. FIG. 3 is a schematic diagram showing measurement data of a plane wave photodetector having a wavefront tilt and a calculation result of the tilt of the wavefront of the laser beam. The broken line in the figure showing the inclination of the wavefront of the laser beam indicates an ideal angle, and the shape of the laser beam is determined from the difference between this broken line and the solid line of the measurement result. Since the inclination of the wavefront of the laser light incident on the angle selection filter is equal throughout the angle selection filter, the energy distribution received by the photodetectors 30 and 31 is constant. However, since the energy of the transmission component and the reflection component are separated according to the incident angle dependency of the angle selection filter, the inclination of the wavefront of the laser beam can be detected by calculating the intensity ratio of the photodetector.

(2) Divergence or convergent spherical wave with curvature When the wavefront of laser light has a curvature, the laser light is either a divergent wave or a convergent wave, and is distinguished by the sign of curvature. FIG. 4 is a schematic view showing the measurement data of the photodetector and the result of calculating the inclination of the wavefront of the laser beam when the wavefront is a spherical wave having a curvature. The broken line in the figure showing the inclination of the wavefront of the laser beam indicates an ideal angle, and the shape of the laser beam is determined from the difference between this broken line and the solid line of the measurement result. When a wavefront having a curvature is incident on the angle selection filter, the incident angle is continuously converted in a region where the laser light is incident. Accordingly, the ratio of separation between the transmission component and the reflection component changes spatially continuously, and the energy distribution detected by the photodetector simply increases or decreases. The amount of inclination depends on the magnitude of the curvature of the wavefront. When the inclination is large, the curvature is large, and when the inclination is small, it is closer to a plane wave. The direction of curvature, that is, whether the wave is a divergent wave or a convergent wave, can be determined from the sign of the slope of the spatial distribution of the photodetector.

(3) Wavefront shape including irregularities Even if the wavefront of the laser beam has a spatially complex shape, the direction of the wavefront inclination in the minute region and the absolute value can be obtained because the photodetector has spatial resolution. The value can be detected. FIG. 5 is a schematic view showing the measurement data of the photodetector and the result of calculating the inclination of the wavefront of the laser light when the wavefront has a wavefront distortion including irregularities. The broken line in the figure showing the inclination of the wavefront of the laser beam indicates an ideal angle, and the shape of the laser beam is determined from the difference between this broken line and the solid line of the measurement result.

(4) Wavefront having energy distribution The calculation results of the wavefront slopes of (1) to (3) above are based on the assumption that the energy distribution of the laser beam is constant. For this reason, the spatial distribution of either detector and the incident angle of the wave front are the same distribution, and there appears to be no merit of using two detectors. However, in the actual use situation, the in-plane energy distribution of the laser beam may not be constant. FIG. 6 is a schematic diagram showing the measurement data obtained when a spherical divergent wave having a normal energy distribution is incident and the result of calculating the inclination of the wavefront of the laser beam. The broken line in the figure showing the inclination of the wavefront of the laser beam indicates an ideal angle, and the shape of the laser beam is determined from the difference between this broken line and the solid line of the measurement result. In the photodetectors 30 and 31, it can be seen that the influence of the energy distribution of the laser beam is superimposed on the spatial distribution characteristic by the spherical wave. For this reason, even if the wavefront shape is calculated by the photodetector 30 alone, it cannot be determined to be spherical. As a reference, when the measurement data of the photodetectors 30 and 31 are added together, a normal distribution that is the energy distribution of the laser light is obtained. As described above, in the wavefront sensor of the present invention, even when the energy distribution of the laser beam is not constant, the wavefront shape is calculated correctly by measuring both the transmission component and the reflection component of the angle selection filter and calculating the wavefront shape. It is possible to measure. Therefore, even if the surface of the laser beam becomes non-uniform due to the influence of the atmosphere, it is possible to measure the wavefront shape with high accuracy.

(5) Adjustment of spatial resolution of wavefront shape calculation In the present invention, the spatial resolution when calculating the wavefront can be changed according to the spatial resolution of the wavefront required for the wavefront sensor. FIG. 7 is a schematic diagram showing the difference in the wavefront shape measurement result according to the spatial resolution of the spatial distribution of the wavefront shape. The broken line in the figure showing the inclination of the wavefront of the laser beam indicates an ideal angle, and the shape of the laser beam is determined from the difference between this broken line and the solid line that is the measurement result. Also, the solid line is the calculation result of the wavefront inclination with high resolution, and the alternate long and short dash line is the calculation result of the wavefront inclination with low resolution. By setting an appropriate resolution with respect to the change of the wavefront shape in the region where the wavefront is measured, an excessive load on the calculation process can be avoided. The simplest way to detect the inclination of the entire wavefront of the laser light is to compare the total energy received by the photodetector, so that the wavefront calculation process in the computing unit is compared with the case of calculating the spatial distribution of the wavefront shape. Thus, the wavefront inclination can be measured at high speed. When the wavefront shape needs to be measured in more detail, a high-definition wavefront shape can be obtained by dividing the measurement result of the photodetector more finely and calculating the wavefront in the calculation unit. As described above, the wavefront sensor of the present invention can obtain a wide range of wavefront measurement characteristics according to application requirements while having a simple configuration.

[Control of polarization of laser light incident on wavefront sensor]
In the wavefront sensor of the first embodiment, a polarization control unit can be placed in front of the angle selection filter. The polarization control unit can make the polarization of the laser light coincide with the polarization of the angle selection filter at the time of design.

  In general, an optical filter of a dielectric multilayer film has polarization dependency. Therefore, by limiting the polarization of incident laser light, the incident angle dependency of reflectance can be designed with higher accuracy.

[Second Embodiment]
FIG. 8 is a schematic diagram of a wavefront sensor according to the second embodiment.

  The wavefront sensor according to the second embodiment is assigned to the beam splitter 50, the first angle selection filter 21 and the second angle selection filter 22 that are disposed behind the beam splitter 50, and the first angle selection filter 21. It has two photodetectors 32 and 33 and two photodetectors 34 and 35 assigned to the second angle selection filter 22. As the first and second angle selection filters 21 and 22 and the photodetectors 32, 33, 34, and 35, the angle selection filter and the photodetector described in the first embodiment can be used. The first angle selection filter 21 and / or the second angle selection filter 22 can be preceded by the polarization control unit described in the first embodiment.

  The laser beam 10 incident on the wavefront sensor is divided into a transmission component 102 and a reflection component 103 by the beam splitter 50. The transmission component 102 of the beam splitter 50 is separated into a transmission component 104 and a reflection component 105 by the first angle selection filter 21. The reflection component 103 of the beam splitter 50 is separated into a transmission component 106 and a reflection component 107 by the second angle selection filter 22. The transmission component 104 and the reflection component 105 separated by the first angle selection filter 21 are received by the photodetectors 32 and 33, respectively. The transmission component 106 and the reflection component 107 separated by the second angle selection filter 22 are received by the photodetectors 34 and 35, respectively. The calculation unit 40 receives the measurement data of the photodetectors 32, 33, 34, and 35. The computing unit 40 determines the amount of inclination of the wavefront of the laser light 10 based on these measurement data.

  The beam splitter 50 is oriented so that the ideal laser beam 10 is incident on the beam splitter 50 at an angle of 45 degrees. Further, the beam splitter 50 divides only energy without affecting the wavefront shape of the laser beam 10, and functions as a so-called half mirror when the division ratio is 50:50.

  The first angle selection filter 21 is oriented so that the ideal transmitted light 102 of the beam splitter 50 is incident on the first angle selection filter 21 at an angle of 45 degrees. The second angle selection filter 22 is oriented so that the ideal reflected light 103 of the beam splitter 50 is incident on the second angle selection filter 22 at an angle of 45 degrees. The first and second angle selection filters 21 and 22 have reflectance incident angle characteristics shown in FIG.

  The first angle selection filter 21 and the second angle selection filter 22 are further in two directions in which the inclination of the wavefront of the laser beam 10 is orthogonal (for example, a direction perpendicular to a direction parallel to the paper surface of FIG. 8). In order to be detectable, these incident surfaces are arranged so as to be oriented in a direction crossing each other. This arrangement is particularly important when the first angle selection filter 21 and the second angle selection filter 22 have their entrance surfaces oriented parallel to each other. Any one of the filters 22 can be realized by rotating 90 degrees around the optical axis of the ideal light incident thereon. For example, in FIG. 8, the incident surface of the first angle selection filter 21 is oriented parallel to the incident surface of the beam splitter 50, and the incident surface of the second angle selection filter 22 is parallel to the incident surface of the beam splitter 50. The second angle selection filter 22 is rotated 90 degrees clockwise around the optical axis of the ideal reflected light 103 of the beam splitter 50. In this sense, it can be understood that the first angle selection filter 21 (or its incident surface) and the second angle selection filter 22 (or its incident surface) are orthogonal. In addition, in order to clarify the positional relationship of the beam splitter 50, the 2nd angle selection filter 22, and the photodetectors 34 and 35, the schematic diagram which looked at a part of wavefront sensor of FIG. 8 from the angle different from FIG. Is shown in FIG.

  Thus, the first angle selection filter 21 separates the transmission component 102 of the beam splitter 50 into the transmission component 104 and the reflection component 105 according to the inclination of the wavefront in the direction parallel to the paper surface of FIG. Similarly, the second angle selection filter 22 separates the reflection component 103 of the beam splitter 50 into a transmission component 106 and a reflection component 107 according to the inclination of the wavefront perpendicular to the paper surface of FIG.

  The calculation unit 40 receives the measurement data of the photodetectors 32, 33, 34, and 35. The arithmetic unit 40 compares the measurement data of the photodetectors 32 and 33 to determine the inclination of the wavefront in the direction parallel to the paper surface, and compares the measurement data of the photodetectors 34 and 35 to be perpendicular to the paper surface. Determine the slope of the wavefront in any direction.

  As described above, the wavefront sensor of the second embodiment can detect the inclination of the wavefront of the laser beam 10 in two directions orthogonal to each other (for example, a direction perpendicular to a direction parallel to the paper surface of FIG. 8). Therefore, the inclination of the wavefront of the laser beam can be measured with higher accuracy.

  Further, the configurations of the first angle selection filter 21 and the photodetectors 32 and 33 coincide with the configurations of the second angle selection filter 22 and the photodetectors 34 and 35 when rotated by 90 degrees about the optical axis. The optical characteristics required for the first angle selection filter 21 and the second angle selection filter 22 are also the same. For this reason, an increase in cost due to an increase in the types of components can be avoided.

  Furthermore, also in the second embodiment, as described in the basic embodiment, the angle selection filter can be configured to be rotatable around its rotation axis. Then, by rotating the angle selection filter by 180 degrees around the rotation axis, a desired result can be obtained only by assigning one photodetector to one angle selection filter.

  Further, when the angle selection filter configured to be rotatable around the rotation axis is rotated 90 degrees around the rotation axis and the transmission component and the reflection component are detected, the angle selection filter is perpendicular to the direction of the wavefront inclination before the rotation. Can determine the slope of the wavefront in any direction. For example, in FIG. 8, the first angle selection filter 21 and the photodetector 33 are rotated by 90 degrees while maintaining their relative positional relationship, or the photodetector 33 should be rotated. This can be realized by providing an additional photodetector at the position and rotating only the first angle selection filter 21. As a result, in FIG. 8, the second angle selection filter 22 and the two photodetectors 33 and 35 can be omitted. Thus, by using only one angle selection filter, the inclination of the wavefront of the laser light 10 is detected in each of two directions orthogonal to each other, thereby measuring the inclination of the wavefront of the laser light with higher accuracy. Can do.

[Third Embodiment]
FIG. 10 is a schematic diagram of an optical space communication device equipped with the wavefront sensor of the second embodiment. The wavefront sensor is not limited to the wavefront sensor of the second embodiment, and for example, the wavefront sensor of the first embodiment can be used.

  The space optical communication apparatus of the third embodiment arrives from a movable mirror 2 that controls the propagation direction of incident light, a deformable mirror 3 that controls the wavefront shape of incident light, and the movable mirror 2 or the deformable mirror 3. A beam splitter 4 that splits the light to be transmitted, and a wavefront sensor 6 that receives one of the lights split by the beam splitter 4. The optical space communication apparatus further includes an optical antenna 1 that receives signal light that propagates in free space and reaches the optical space communication apparatus, and an optical receiver 5 that receives the other of the lights divided by the beam splitter 4. . In FIG. 10, the deformable mirror 3 is placed behind the movable mirror 2, but the movable mirror 2 may be placed behind the deformable mirror 3.

  The wavefront sensor 6 includes the beam splitter 50, the first angle selection filter 21 and the second angle selection filter 22 that are disposed behind the beam splitter 50, and two light detections assigned to the first angle selection filter 21. And 32 photo detectors 34 and 35 assigned to the second angle selection filter 22. In FIG. 10, the wavefront sensor 6 or the optical space communication device includes a calculation unit 40 as a component or a function thereof. However, the arithmetic unit 40 can be included as a component or a function thereof in, for example, a control device outside the optical space communication device.

  Laser light 10 that is signal light that has propagated through free space and reached the optical space communication device is received by the optical antenna 1, and then the beam diameter is reduced in accordance with the effective diameter of the optical system inside the device. 11 is converted. After the laser beam 11 is reflected by the movable mirror 2 and the deformable mirror 3, the laser beam 11 is divided into a component received by the beam splitter 4 as signal light and a component whose wavefront shape is measured by the wavefront sensor 6. Is done. The optical receiver 5 couples signal light to an optical fiber communication system that receives signal light with high sensitivity. The computing unit 40 determines the control amount of the deflection angle of the movable mirror 2 and the reflection surface shape of the deformable mirror 3 based on the measured wavefront shape, and transmits a control signal to the movable mirror 2 and the deformable mirror 3. The movable mirror 2 and the deformable mirror 3 can correct the propagation direction of the laser light 11 and the distortion of the wavefront by changing the deflection angle and the reflection surface shape based on the control signal from the calculation unit 40, respectively. The corrected signal light 13 is supplied to the optical receiver 5.

  When signal light having a distorted wavefront is incident on the optical space communication apparatus configured as described above, a part 12 of the signal light is reflected by the beam splitter 4 and enters the wavefront sensor 6. After the divided laser light 12 is further divided by the beam splitter 50, as shown in the second embodiment, the energy distribution of the laser light and two directions orthogonal to each other (for example, parallel to the paper surface of FIG. 10). Wavefront shape in a direction perpendicular to the direction) is measured. The calculation unit 40 generates a control signal for correcting the wavefront of the laser light 11 to a substantially flat surface so that the light reception energy of the light receiving unit 5 is maximized from the measurement result of the wavefront shape of the laser light 12. The signal is transmitted to the movable mirror 2 and the deformable mirror 3.

  The control amount of the movable mirror 2 having a flat reflecting surface is such that the deflection angle in the direction parallel to the paper surface in FIG. 10 (rotation angle with respect to the rotation axis perpendicular to the paper surface) and the deflection angle in the vertical direction (rotation with respect to the rotation axis parallel to the paper surface). Angle). The amount of inclination of the wavefront in the parallel direction is obtained by comparing the total amount of energy received by the photodetectors 32 and 33 (or its signal intensity) by comparing the reflectance incident angle characteristics stored in the first angle selection filter 21 in advance. The amount of inclination of the wavefront in the vertical direction, which is obtained from the data, is calculated by comparing the total amount of energy received by the photodetectors 34 and 35 (or the signal intensity thereof), thereby comparing the pre-stored reflection of the second angle selection filter 22. It is obtained from the data of the rate incident angle characteristic. Then, the control amount of the movable mirror 2 is determined so that these obtained tilt amounts are canceled out. The deformable mirror 3 changes the shape of the reflecting surface by a control signal calculated by the calculation unit 40 so as to cancel out the distortion of the higher-order wavefront that cannot be removed by the movable mirror 2. The wavefront of the laser beam 13 reflected by the deformable mirror 3 whose reflection surface shape is changed in this way is corrected to a plane, and is supplied to the optical receiver 5 as a plane wave 13. Such wavefront measurement and wavefront correction processes are continuously executed while the communication system is operating.

  As described above, the optical space communication apparatus according to the third embodiment sequentially corrects the inclination and distortion of the wavefront measured by the wavefront sensor 6, so that the light reception energy in the optical receiver 5 is stabilized. Therefore, even in a communication system that uses laser light 10 propagated in the atmosphere as signal light, stable large-capacity communication can be performed by using this optical space communication device.

In the following, preferred forms relating to the present invention disclosed in the present specification and drawings are appended.
[Form 1]
An angle selection filter with different reflectivity according to the incident angle;
A photodetector for receiving light coming through the angle selection filter;
Including wavefront sensor.
[Form 2]
The photodetector is configured as a plurality of photodetectors that receive light separated by the angle selection filter.
The wavefront sensor according to aspect 1.
[Form 3]
A beam splitter placed in front of the angle selection filter;
The angle selection filter is configured as a first angle selection filter that receives light transmitted through the beam splitter and a second angle selection filter that receives light reflected from the beam splitter,
The plurality of photodetectors include a first photodetector that receives the light separated by the first angle selection filter and a second light detection that receives the light separated by the second angle selection filter. As a container
The first angle selection filter and the second angle selection filter are arranged so that the incident surface of the first angle selection filter and the incident surface of the second angle selection filter are oriented in a direction crossing each other. To be
The wavefront sensor according to the second aspect.
[Form 4]
The first photodetector is configured as a plurality of photodetectors that receive the light separated by the first angle selection filter, and
The second photodetector is configured as a plurality of photodetectors that receive the light separated by the second angle selection filter.
The wavefront sensor according to the third aspect.
[Form 5]
The photodetector has spatial resolution;
5. The wavefront sensor according to any one of forms 1 to 4.
[Form 6]
A polarization control element that converts the polarization of light incident on the angle selection filter into a specific polarization state;
6. The wavefront sensor according to any one of forms 1 to 5.
[Form 7]
The angle selection filter is configured to be rotatable about an optical axis of light incident on the angle selection filter, in particular, to be rotatable by 90 degrees and / or 180 degrees.
The wavefront sensor according to any one of Forms 1 to 6.
[Form 8]
The wavefront sensor according to any one of Embodiments 1 to 7, further including an arithmetic unit that obtains a wavefront shape of light incident on the wavefront sensor based on measurement data of the photodetector.
[Form 9]
The calculation unit compares a plurality of measurement data obtained from the same angle selection filter in order to obtain the wavefront shape.
The wavefront sensor according to aspect 8.
[Mode 10]
The plurality of measurement data obtained from the same angle selection filter are the signal intensity of the photodetector that has received the transmission component of the angle selection filter and the signal intensity of the photodetector that has received the reflection component of the angle selection filter.
The wavefront sensor according to the ninth aspect.
[Form 11]
The calculation unit determines the inclination of the wavefront of the incident light of the wavefront sensor according to the magnitude relationship between the signal intensity of the photodetector that receives the transmission component and the signal intensity of the photodetector that receives the reflection component, and these Determining the absolute value of the slope from the ratio of the signal strengths of
The wavefront sensor according to Form 10.
[Form 12]
A movable mirror that controls the propagation direction of incident light;
A deformable mirror that controls the wavefront shape of the incident light; and
A beam splitter for splitting light coming from the movable mirror or the deformable mirror;
The wavefront sensor according to any one of Embodiments 1 to 7, which receives one of the lights divided by the beam splitter;
including,
Optical space communication device.
[Form 13]
Based on optical characteristics (stored in advance) of the angle selection filter of the wavefront sensor and a plurality of measurement data of the photodetector of the wavefront sensor, the pointing direction of the movable mirror and the shape of the reflecting surface of the deformable mirror are controlled. Including the arithmetic unit,
The optical space communication apparatus according to Form 12.
[Form 14]
The plurality of measurement data of the photodetector is a plurality of measurement data obtained from the same angle selection filter.
The optical space communication apparatus according to Form 13.
[Form 15]
The plurality of measurement data obtained from the same angle selection filter are the signal intensity of the photodetector that has received the transmission component of the angle selection filter and the signal intensity of the photodetector that has received the reflection component of the angle selection filter.
The optical space communication apparatus according to Form 14.
[Form 16]
The inclination of the wavefront of the incident light of the wavefront sensor is determined by the magnitude relationship between the signal intensity of the photodetector that has received the transmission component and the signal intensity of the photodetector that has received the reflection component, and the ratio of these signal intensities The absolute value of the slope is determined from
The optical space communication apparatus according to Form 15.
[Form 17]
Including an optical antenna that receives light incident on the optical space communication device and supplies the light to the movable mirror or the deformable mirror;
The optical space communication apparatus according to any one of Forms 12 to 16.
[Form 18]
Including an optical receiver for coupling the signal light to an optical fiber communication system;
The optical space communication apparatus according to any one of Forms 12 to 17.
[Form 19]
An optical space communication device including a movable mirror that controls a propagation direction of incident light, a deformable mirror that controls a wavefront shape of incident light, and an angle selection filter that separates incident light depending on an incident angle. Control method,
Separating the external light from the external space incident on the optical space communication device and arriving through the movable mirror and the deformable mirror with the angle selection filter;
Obtaining signal intensities of a plurality of separated lights separated by the angle selection filter;
Obtaining control amounts of the movable mirror and the deformable mirror based on optical characteristics (stored in advance) of the angle selection filter and signal intensity of the plurality of separated lights;
Changing the directivity direction of the movable mirror and the reflecting surface of the deformable mirror based on the control amount.
[Mode 20]
The control amount of the movable mirror is such that the inclination of the wavefront of the external light obtained by comparing the optical characteristics (prestored) of the angle selection filter and the signal intensity of the plurality of separated lights is canceled out. Asked to change the orientation of
The control amount of the deformable mirror is required to change the reflection surface shape of the deformable mirror so as to cancel the distortion of the wavefront of the external light that is not removed by changing the directivity direction of the movable mirror.
The control method according to the nineteenth aspect.
[Form 21]
The plurality of separated lights are a transmission component and a reflection component of the angle selection filter,
The control method according to Form 19 or 20.
[Form 22]
Separating the incident light into a plurality of separated lights by an angle selection filter that separates the light depending on the incident angle;
Comparing the signal intensities of the plurality of separated lights,
A method for determining the wavefront shape of incident light.
[Form 23]
The method according to claim 22, wherein the slope of the wavefront of the incident light is determined based on the magnitude relationship between the signal intensities of the plurality of separated lights, and the absolute value of the slope is determined from the ratio of these signal intensities.
[Form 24]
The plurality of separated lights are a transmission component and a reflection component of the angle selection filter,
The method according to form 22 or 23.
[Form 25]
An optical space communication device including a movable mirror that controls a propagation direction of incident light, a deformable mirror that controls a wavefront shape of incident light, and an angle selection filter that separates incident light depending on an incident angle. A method for correcting the wavefront of external light from external space incident on
Separating the external light from the external space incident on the optical space communication device and arriving through the movable mirror and the deformable mirror with the angle selection filter;
Obtaining signal intensities of a plurality of separated lights separated by the angle selection filter;
Changing the pointing direction of the movable mirror and the reflecting surface of the deformable mirror based on the optical characteristics (prestored) of the angle selection filter and the signal intensity of the plurality of separated lights .
[Form 26]
The directivity direction of the movable mirror is changed so as to cancel the inclination of the wavefront of the external light obtained by comparing the optical characteristics (prestored) of the angle selection filter and the signal intensity of the plurality of separated lights,
The shape of the reflecting surface of the deformable mirror is changed so as to cancel the distortion of the wavefront of the external light that is not removed by changing the direction of the movable mirror.
The correction method according to Form 25.
[Form 27]
The plurality of separated lights are a transmission component and a reflection component of the angle selection filter,
The correction method according to Form 25 or 26.

  Within the scope of the entire disclosure (including claims and drawings) of the present invention, the embodiments can be changed and adjusted based on the basic technical concept. Various combinations or selections of various disclosed elements (including each element of each claim, each element of each embodiment, each element of each drawing, etc.) are possible within the scope of the claims of the present invention. is there. That is, the present invention naturally includes various modifications and changes that could be made by those skilled in the art according to the entire disclosure including the claims and the drawings, and the technical idea. In particular, with respect to the numerical ranges described in this document, any numerical value or small range included in the range should be construed as being specifically described even if there is no specific description.

DESCRIPTION OF SYMBOLS 1 Optical antenna 2 Movable mirror 3 Deformable mirror 4 Beam splitter 5 Optical receiver 6 Wavefront sensor 10 Laser beam coming from the outside 11 Laser beam reduced in diameter by the optical antenna 1 12 Reflected by the beam splitter 4 of the laser beam 11 Component 13 Laser beam with corrected wavefront 20 Angle selection filter 21 First angle selection filter 22 Second angle selection filter 30 Photo detector 31 Photo detector 32 Photo detector 33 Photo detector 34 Photo detector 35 Photo detection 40 Calculation unit 50 Beam splitter 100 Transmission component of angle selection filter 20 101 Reflection component of angle selection filter 20 102 Transmission component of beam splitter 50 103 Reflection component of beam splitter 50 104 Transmission component of first angle selection filter 21 Reflection component 10 of the angle selection filter 21 Transmitted component of the second angle selective filter 22 107 reflection component of the second angle selective filter 22

Claims (10)

An angle selection filter with different reflectivity according to the incident angle;
A photodetector for receiving light coming through the angle selection filter;
Including wavefront sensor. The photodetector is configured as a plurality of photodetectors that receive light separated by the angle selection filter.
The wavefront sensor according to claim 1. A beam splitter placed in front of the angle selection filter;
The angle selection filter is configured as a first angle selection filter that receives light transmitted through the beam splitter and a second angle selection filter that receives light reflected from the beam splitter,
The plurality of photodetectors include a first photodetector that receives the light separated by the first angle selection filter and a second light detection that receives the light separated by the second angle selection filter. As a container
The first angle selection filter and the second angle selection filter are arranged so that the incident surface of the first angle selection filter and the incident surface of the second angle selection filter are oriented in a direction crossing each other. To be
The wavefront sensor according to claim 2. The first photodetector is configured as a plurality of photodetectors that receive the light separated by the first angle selection filter, and
The second photodetector is configured as a plurality of photodetectors that receive the light separated by the second angle selection filter.
The wavefront sensor according to claim 3. The photodetector has spatial resolution;
The wavefront sensor according to any one of claims 1 to 4. A polarization control element that converts the polarization of light incident on the angle selection filter into a specific polarization state;
The wavefront sensor according to claim 1. A calculation unit for obtaining a wavefront shape of light incident on the wavefront sensor based on measurement data of the photodetector;
The wavefront sensor according to claim 1. The calculation unit compares a plurality of measurement data obtained from the same angle selection filter in order to obtain the wavefront shape.
The wavefront sensor according to claim 7. A movable mirror that controls the propagation direction of incident light;
A deformable mirror that controls the wavefront shape of the incident light; and
A beam splitter for splitting light coming from the movable mirror or the deformable mirror;
The wavefront sensor according to any one of claims 1 to 6, which receives one of the lights divided by the beam splitter;
including,
Optical space communication device. An arithmetic unit that controls a directivity direction of the movable mirror and a reflection surface shape of the deformable mirror based on optical characteristics of the angle selection filter of the wavefront sensor and a plurality of measurement data of a photodetector of the wavefront sensor;
The optical space communication apparatus according to claim 9.

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