Movable mirror device and communication device

Abstract

To realize a mirror capable of receiving high-energy-density laser light for precise tracking in optical wireless communication. [Solution] The movable mirror device (1) comprises a mirror (1_1) that receives laser light in optical wireless communication, a drive unit (1_2) that drives the mirror (1_1), a substrate (1_3) on which the drive unit (1_2) is mounted, a package (1_5) that contains the mirror (1_1), the drive unit (1_2), and the substrate (1_3) inside, and a cooling element (1_4) that is arranged to conduct heat to the substrate (1_3).

Description

Technical Field

[0001] The present disclosure relates to a movable mirror device and a communication device.

Background Art

[0002] A technique for performing optical wireless communication by performing fine tracking that drives the optical axis of a mirror that receives laser light to align with the laser light is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Means for Solving the Problems

[0004] A movable mirror device according to an aspect of the present disclosure includes a mirror that receives laser light in optical wireless communication, a driving unit that drives the mirror, a substrate on which the driving unit is mounted, a package that internally includes the mirror, the driving unit, and the substrate, and a cooling element that is disposed so as to be thermally conductive with respect to the substrate.

Brief Description of the Drawings

[0005] [Figure 1] It is a schematic cross-sectional view of a movable mirror device according to the present disclosure. [Figure 2] It is a block diagram showing an example of control of a Peltier element according to the present disclosure. [Figure 3] It is a diagram schematically showing the configuration of a movable mirror device according to the present disclosure. <从这里开始,后面的内容与前面的翻译内容重复,按照要求,重复内容应完整保留,所以继续翻译如下:]] [Figure 4] It is a schematic cross-sectional view of a movable mirror device according to the present disclosure. [Figure 5] It is a diagram schematically showing the configuration of a movable mirror device according to the present disclosure. [Figure 6]This is a schematic cross-sectional view of the communication device related to this disclosure. [Figure 7] This is a schematic front view of the communication device related to this disclosure. [Figure 8] This is a block diagram schematically showing the configuration of the communication device related to this disclosure. [Figure 9] This figure shows an example of the configuration of the communication system related to this disclosure. [Modes for carrying out the invention]

[0006] <Embodiment 1> Hereinafter, one embodiment of this disclosure will be described in detail with reference to the drawings. For ease of understanding, the background and challenges of this disclosure will be described first, followed by a detailed description of the disclosure.

[0007] <Mirrors used for precise tracking in optical wireless communication> Communication devices that perform optical wireless communication perform coarse tracking, which involves directing a mirror towards the communication partner's location to receive the laser beam, and fine tracking, which involves driving the mirror to align the mirror's optical axis with the laser beam. For example, in coarse tracking, the communication device drives a galvanometer mirror to direct it towards the communication partner's location. In fine tracking, the communication device uses a micro-electro-mechanical system (MEMS) or an ultrasonic motor to drive a high-speed mirror such as a MEMS mirror or a VCM (Voice Coil Mirror) to align the mirror's optical axis with the laser beam.

[0008] In precise tracking of optical wireless communication, mirrors need to be driven at high speed to compensate for laser beam deviations caused by high-speed vibrations and atmospheric turbulence. Therefore, small-area mirrors are used in precise tracking to increase the driving speed. However, when the mirror area is small, it becomes necessary to concentrate the laser beam received by the mirror, resulting in a high energy density of the received laser beam. Mirrors that receive high-energy-density laser beams can burn out. Therefore, there is a need for mirrors capable of receiving high-energy-density laser beams in precise tracking of optical wireless communication.

[0009] <Overview of the movable mirror device 1> The movable mirror device 1 according to this embodiment is a device that performs precise tracking in optical wireless communication by driving the mirror 1_1 at high speed to align the optical axis of the mirror 1_1 with the received laser light. For example, the movable mirror device 1 is implemented in a communication device that performs optical wireless communication and is located in the stratosphere or outside the atmosphere. For example, the movable mirror device 1 is implemented in a HAPS (High Altitude Platform Station) in the stratosphere or a LEO (Low Earth Orbit) outside the atmosphere.

[0010] <Configuration of the movable mirror device 1> The detailed configuration of the movable mirror device 1 will be described with reference to Figure 1. Figure 1 is a schematic cross-sectional view of the movable mirror device 1. In this disclosure, a coordinate system is set up such that the right side of the x-axis in the horizontal direction is positive, the far side of the horizontal plane of the paper is positive for the y-axis, and the upward side of the vertical direction is positive for the z-axis.

[0011] The movable mirror device 1 comprises a mirror 1_1 that receives laser light in optical wireless communication, a drive unit 1_2 that drives the mirror 1_1, a substrate 1_3 on which the drive unit 1_2 is mounted, a package 1_5 that contains the mirror 1_1, the drive unit 1_2, and the substrate 1_3, and a cooling element 1_4 that is arranged to conduct heat to the substrate 1_3.

[0012] In the movable mirror device 1, even when the mirror 1_1 receives laser light with a high energy density and the temperature of the mirror 1_1 rises, the substrate 1_3 is cooled by the cooling element 1_4, and the entire interior of the package 1_5 including the mirror 1_1 is cooled. Therefore, in the movable mirror device 1, it is possible to suppress the temperature of the mirror 1_1 from rising and burning when the mirror 1_1 receives laser light with a high energy density. That is, in the movable mirror device 1, the mirror 1_1 can receive laser light with a high energy density in fine tracking in optical wireless communication.

[0013] <Mirror 1_1> The mirror 1_1 is a mirror that receives laser light in optical wireless communication. More specifically, the mirror 1_1 is a mirror used in fine tracking to align the optical axis with the laser light, and is a high-speed drive mirror driven by the drive unit 1_2. The mirror 1_1 receives laser light traveling from the positive side to the negative side of the z-axis in FIG. 1. Examples of the mirror 1_1 include a MEMS mirror and a VCM.

[0014] <Drive unit 1_2> The drive unit 1_2 drives the mirror 1_1 to align the optical axis of the mirror 1_1 with the laser light based on a control signal according to the position detection result of the laser light. As an example, the control signal is supplied from a photodetector (not shown in FIG. 1) that detects the laser light. As an example, the drive unit 1_2 drives the mirror 1_1 by a microelectromechanical system (MEMS) method. With this configuration, the movable mirror device 1 can be miniaturized, and the mirror 1_1 can be driven at high speed.

[0015] The position where the drive unit 1_2 is arranged is not particularly limited, and it may be arranged at a position that does not prevent the mirror 1_1 from receiving laser light. As an example, as shown in FIG. 1, it is arranged between the mirror 1_1 and the substrate 1_3 in the z-axis direction.

[0016] <Substrate 1_3> The substrate 1_3 is mounted with the drive unit 1_2. As an example, the substrate 1_3 is a PCB (Printed Circuit Board). As an example, the substrate 1_3 supplies a control signal supplied from a photodetector (not shown in FIG. 1) that detects laser light to the drive unit 1_2.

[0017] The position where the substrate 1_3 is disposed is not particularly limited, and it may be disposed at a position that does not prevent the mirror 1_1 from receiving the laser light. As an example, as shown in FIG. 1, it is disposed so as to contact the package 1_5 on the surface opposite to the surface on which the drive unit 1_2 is mounted in the z-axis direction.

[0018] <Cooling element 1_4> The cooling element 1_4 is disposed so as to be thermally conductive with respect to the substrate 1_3. In other words, the cooling element 1_4 is disposed in direct or indirect contact with the substrate 1_3. In FIG. 1, the cooling element 1_4 is disposed in indirect contact with the substrate 1_3 via the package 1_5. That is, in FIG. 1, the cooling element 1_4 is disposed in contact with the package 1_5 outside the package 1_5. With this configuration, the movable mirror device 1 can dispose the cooling element 1_4 at an appropriate position according to the installation environment of the movable mirror device 1.

[0019] The cooling element 1_4 is not particularly limited as long as it is an element that cools (absorbs heat). As an example, the cooling element 1_4 is a Peltier element. When the cooling element 1_4 is a Peltier element, in FIG. 1, the Peltier element 1_4 is disposed so that the package 1_5 side (positive z-axis side) is cooled (heat absorption) in the z-axis direction and the side opposite to the package 1_5 (negative z-axis side) is heated (heat generation) in the z-axis direction. The control when the cooling element 1_4 is a Peltier element will be described later with reference to a different drawing.

[0020] <Package 1_5> Package 1_5 is a packaging component that protects the interior from the surroundings and provides contacts for inputting and outputting electrical signals to and from the outside. As shown in Figure 1, Package 1_5 contains a mirror 1_1, a drive unit 1_2, and a substrate 1_3. Also, as shown in Figure 1, Package 1_5 has a light-receiving window 1_6 formed on the positive z-axis side of the mirror 1_1 so that the mirror 1_1 can receive laser light.

[0021] Package 1_5 is packaged after its interior is purged with gas. As an example, package 1_5 is filled with helium. By filling the package with helium, which has high thermal conductivity, the movable mirror device 1 can suitably cool the inside of the package using the cooling element 1_4.

[0022] <Control method for Peltier element 1_4> The process of controlling a Peltier element when the cooling element 1_4 is a Peltier element will be explained with reference to Figure 2. Figure 2 is a block diagram showing an example of Peltier element control according to this embodiment. As an example of a configuration for controlling a Peltier element, as shown in Figure 2, a control device 330 is connected to the Peltier element 1_4, and an EDFA (Erbium Doped Fiber Amplifier) ​​320 is connected to the control device 330.

[0023] The EDFA320 is an optical amplifier. The EDFA320 amplifies the laser light incident on mirror 1_1 and supplies the amplified laser light to the control device 330.

[0024] The control device 330 supplies current and voltage to the Peltier element 1_4 based on the intensity of the laser light supplied from the EDFA 320. For example, the control device 330 supplies current and voltage to the Peltier element 1_4 that are proportional to the intensity of the laser light supplied from the EDFA 320. In other words, the control device 330 supplies current and voltage according to the intensity of the laser light received by the mirror 1_1.

[0025] The amount of heat input to mirror 1_1 is directly proportional to the intensity of the laser light received by mirror 1_1. Therefore, by connecting a control device 330 that supplies current and voltage according to the intensity of the laser light received by mirror 1_1 to the Peltier element 1_4, the temperature rise of mirror 1_1 can be effectively suppressed. Furthermore, in this configuration, it is not necessary to maintain the temperature of mirror 1_1 at a constant temperature; it is sufficient to prevent mirror 1_1 from burning out, so feedback control is unnecessary.

[0026] <Effects of the movable mirror device 1> Thus, the movable mirror device 1 comprises a mirror 1_1 that receives laser light in optical wireless communication, a drive unit 1_2 that drives the mirror 1_1, a substrate 1_3 on which the drive unit 1_2 is mounted, a package 1_5 that contains the mirror 1_1, the drive unit 1_2, and the substrate 1_3, and a cooling element 1_4 that is arranged to conduct heat to the substrate 1_3.

[0027] In the movable mirror device 1, even if the temperature of the mirror 1_1 rises due to the mirror 1_1 receiving high-energy-density laser light, the substrate 1_3 is cooled by the cooling element 1_4, and the entire interior of the package 1_5, including the mirror 1_1, is cooled. Therefore, in the movable mirror device 1, the temperature of the mirror 1_1 rises and burning due to the mirror 1_1 receiving high-energy-density laser light can be suppressed. In other words, in the movable mirror device 1, the mirror 1_1 can receive high-energy-density laser light for precise tracking in optical wireless communication.

[0028] Furthermore, even when the movable mirror device 1 is located in the stratosphere or outside the atmosphere where heat dissipation is difficult due to thin or no atmosphere, the cooling element 1_4 can cool the inside of the package 1_5. Therefore, even when the movable mirror device 1 is located in LEO or HAPS, the mirror 1_1 can receive laser light with high energy density during precise tracking.

[0029] <Example 1> A modified example of the movable mirror device 1, the movable mirror device 1A, will be described with reference to Figure 3. Figure 3 is a diagram showing the configuration of the movable mirror device 1A according to this modified example. The upper part of Figure 3 is a schematic cross-sectional view of the movable mirror device 1A, and the lower part of Figure 3 is a view taken in the direction of arrow A in the upper part of Figure 3.

[0030] The movable mirror device 1A includes fins 1_7 with high thermal conductivity in addition to the configuration of the movable mirror device 1. More specifically, as shown in Figure 3, the movable mirror device 1 includes fins 1_7 inside the package 1_5. The position where fins 1_7 are placed is not particularly limited, and they should be placed in a position that does not hinder the cooling of the inside of the package 1_5 by the cooling element 1_4 and does not hinder the mirror 1_1 from receiving laser light. Fins 1_7 may be placed in contact with the package 1_5. Alternatively, fins 1_7 may be placed in contact with the substrate 1_3.

[0031] Thus, the movable mirror device 1A can suitably lower the temperature inside the package 1_5 by providing fins 1_7 with high thermal conductivity inside the package 1_5. Furthermore, with this configuration, the movable mirror device 1 can efficiently lower the temperature inside the package 1_5 even when placed in a high vacuum space such as outside the atmosphere.

[0032] <Embodiment 2> Other embodiments of this disclosure will be described in detail below with reference to the drawings. For the sake of clarity, components having the same function as those described in the above embodiments will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0033] <Configuration of movable mirror device 1B> The movable mirror device 1B according to this embodiment is a device that performs precise tracking, similar to the movable mirror device 1 described above. An example of the configuration of the movable mirror device 1B will be described with reference to Figure 4. Figure 4 is a schematic cross-sectional view of the movable mirror device 1B according to this embodiment.

[0034] As shown in Figure 4, the movable mirror device 1B, like the movable mirror device 1, includes a mirror 1_1, a drive unit 1_2, a substrate 1_3, a cooling element 1_4, and a package 1_5. As shown in Figure 4, the arrangement of the mirror 1_1 and the drive unit 1_2 is also the same as that of the movable mirror device 1.

[0035] Unlike the movable mirror device 1, the cooling element 1_4 in the movable mirror device 1B is located inside the package 1_5. The position of the cooling element 1_4 is not particularly limited; it should be located in a position that allows the inside of the package 1_5 to be cooled and does not obstruct the mirror 1_1 from receiving laser light. For example, as shown in Figure 4, the cooling element 1_4 is located between the package 1_5 and the substrate 1_3. More specifically, the cooling element 1_4 is located between the package 1_5 and the substrate 1_3 in the z-axis direction inside the package 1_5.

[0036] If the cooling element 1_4 is a Peltier element, as shown in Figure 4, the Peltier element 1_4 is positioned such that the substrate 1_3 side (positive z-axis side) is cooled (heat absorbed) and the package 1_5 side (negative z-axis side) is heated (heat generated) in the z-axis direction. In other words, the Peltier element 1_4 is positioned so that the inside of the package 1_5 is cooled.

[0037] <Effects of movable mirror device 1B> Thus, in the movable mirror device 1B, the cooling element 1_4 is positioned between the package 1_5 and the substrate 1_3. Therefore, even if the specific heat of the package 1_5 is low and the temperature inside the package 1_5 is not easily released to the outside, the movable mirror device 1B cools the inside of the package 1_5, so that the mirror 1_1 can receive laser light with a high energy density.

[0038] <Modification 2> A modified example of the movable mirror device 1B, the movable mirror device 1C, will be described with reference to Figure 5. Figure 5 is a diagram showing the configuration of the movable mirror device 1C according to this modified example. The upper part of Figure 5 is a schematic cross-sectional view of the movable mirror device 1C, and the lower part of Figure 5 is a view taken in the direction of arrow B in the upper part of Figure 5.

[0039] The movable mirror device 1C includes, in addition to the configuration of the movable mirror device 1B, fins 1_7 with high thermal conductivity. More specifically, as shown in Figure 5, the movable mirror device 1C further includes fins 1_7 positioned on the outside of the package 1_5 so as to contact the package 1_5. Preferably, the fins 1_7 are positioned so as to contact the entire package 1_5 in at least one of the x-axis, y-axis, and z-axis directions.

[0040] Thus, the movable mirror device 1C is equipped with fins 1_7 with high thermal conductivity that contact the package 1_5 on the outside of the package 1_5. In this configuration, if the cooling element 1_4 is a Peltier element, the movable mirror device 1C can suitably lower the temperature of the package 1_5 heated by the Peltier element 1_4. Therefore, the movable mirror device 1C can prevent the temperature inside the package 1_5 from rising due to the package 1_5 being heated by the Peltier element 1_4.

[0041] <Configuration of communication device 500> An example of a communication device 500 equipped with at least one of the movable mirror devices 1 to 1C described above will be explained. The communication device 500 is, as an example, an optical wireless communication device that communicates by propagating a communication laser beam in a vacuum or atmosphere via a flying object or artificial satellite. The configuration of the communication device 500 will be explained with reference to Figures 6 to 8. Figure 6 is a schematic cross-sectional view of the communication device 500, and Figure 7 is a schematic front view of the communication device 500. For the sake of explanation, in Figures 6 and 7, a coordinate system is set up so that the right side of the x-axis is positive in the horizontal direction, the back of the paper in the horizontal direction is positive in the y-axis, and the top of the vertical direction is positive in the z-axis.

[0042] As shown in Figure 7, the communication device 500 comprises a main mirror section 10, a support section 20, and a base section 30. Also, as shown in Figure 7, the communication device 500 is • A first hollow shaft 41 connects the main mirror section 10 to the support section 20 so that it can rotate around the x-axis (first axis), and • A second hollow shaft 42 connects the support portion 20 to the base portion 30 so that it can rotate around the z-axis (second axis), which is non-parallel to the x-axis (first axis). The device is equipped with the following. Here, the x-axis and the y-axis perpendicular to the x-axis are given as examples of the first and second axes, respectively, but this does not limit this embodiment, and the first and second axes do not need to be parallel. Also, the number of hollow axes provided by the communication device 500 is not limited to the above example, and may be one or three or more.

[0043] <Main mirror section 10> As shown in Figure 7, the main mirror section 10 is equipped with a light-receiving window 11 on its front side. Here, the term "light-receiving window 11" is not limited to this embodiment and may also be called a light-transmitting window, light-transmitting window, etc. The light-receiving window 11 is not particularly limited as long as it transmits the communication laser light transmitted and received by the communication device 500. Furthermore, the light-receiving window 11 may also function as a lens that refracts the communication laser light.

[0044] Figure 6 is a cross-sectional view obtained by cutting the communication device 500 through a section including the optical path LP of the communication laser light in the communication device 500. As shown in Figure 6, the main mirror section 10 includes a main mirror M11 and a secondary mirror M12. The main mirror M11 is a concave mirror as an example, and the secondary mirror M12 is a convex mirror as an example, but is not limited to these. For convenience, the following description will be given in accordance with the propagation order of the laser light when the communication device 500 receives the communication laser light, but this is not limited to this embodiment. More specifically, as will be described later, the communication device 500 also functions as a device that transmits (sends out) the communication laser light.

[0045] The communication laser light incident on the primary mirror section 10 from the front side (the near side of the paper in Figure 7, the negative side of the y-axis) is reflected by the primary mirror M11, which is located on the back side of the primary mirror section 10 and has its mirror surface facing the front side, and is focused by the secondary mirror M12, which is located in front of the primary mirror M11. For example, the mirror surface of the secondary mirror M12 is oriented such that the normal vector of the mirror surface points at 45° from the positive side of the x-axis on the xy-plane (so that the normal vector of the mirror surface on the xy-plane is (1,1)). As a result, the communication laser light incident on the secondary mirror M12 from the primary mirror M11 is guided toward the positive side of the x-axis in Figure 7.

[0046] In Figure 6, the communication laser beam emitted from the secondary mirror M12 is denoted by the symbol LP. The communication laser beam LP is sometimes simply referred to as laser beam LP. Furthermore, the upper end (the end with a larger z-coordinate) of the communication laser beam LP in the primary mirror 10 is denoted by the symbol L1, and the lower end (the end with a smaller z-coordinate) of the communication laser beam LP in the primary mirror 10 is denoted by the symbol L2. Unless otherwise specified, the optical path through which the communication laser beam LP propagates within the communication device 500 is also sometimes referred to as optical path LP using the same symbol LP. Therefore, symbols L1 and L2 can also be considered as symbols that define the ends (edges) of the optical path LP.

[0047] <First hollow shaft 41> The first hollow shaft 41 connects the main mirror 10 to the support 20 so that it can rotate around the x-axis (first axis). As shown in Figure 6, the communication laser beam LP directed by the secondary mirror M12 penetrates the hollow portion 41v formed in the first hollow shaft 41. Here, as shown in Figure 6, the hollow portion 41v is a hollow region defined by the inner wall 41a of the first hollow shaft 41. As an example, when the communication device 500 is located on the Earth's surface or in the atmosphere, the hollow portion 41v is filled with air or with gas filled inside the communication device 500. As another example, when the communication device 500 is located in outer space, the hollow portion 41v is a vacuum or filled with gas filled inside the communication device 500. However, these examples are not limiting to this embodiment.

[0048] The specific configuration of the first hollow shaft 41 is not limited to this embodiment, but as an example, it can be configured to include a bearing and a shaft that is rotatably supported by the bearing and has the hollow portion 41v formed on it. In this configuration, the hollow portion 41v is defined by an inner wall 41a formed to penetrate the shaft.

[0049] Furthermore, the first hollow shaft 41 is equipped with a drive motor for rotating the main mirror section 10 relative to the support section 20. In other words, it is equipped with a drive motor for driving the first hollow shaft 41. Here, this drive motor is controlled, for example, by a receiving section 31 or a transmitting section 32, which will be described later.

[0050] <Support part 20> The support portion 20 supports the main mirror portion 10 relative to the base portion 30. The designation of the support portion 20 is not limited to this embodiment, and it may also be called a support frame or gimbal frame, etc.

[0051] As shown in Figure 6, for example, the support portion 20 has a cavity formed inside, and the laser light LP is guided through this cavity. Here, as shown in Figure 7, the support portion 20 is equipped with a plurality of mirrors M21, M22, and M23 for directing the communication laser light LP. For example, mirror M21 is oriented to guide the laser light LP incident from the secondary mirror M12 of the main mirror portion 10 along the x-axis to the negative side in the z-axis direction. Similarly, mirror M22 is oriented to guide the laser light LP incident from mirror M21 along the z-axis to the negative side in the x-axis direction. Furthermore, mirror M23 is oriented to guide the laser light LP incident from mirror M22 along the x-axis to the negative side in the z-axis direction.

[0052] Furthermore, when the communication device 500 is located on the Earth's surface or in the atmosphere, the cavity in the support section 20 through which the laser beam LP is guided is filled with air or with a gas filled inside the communication device 500. As another example, when the communication device 500 is located in outer space, the cavity is either a vacuum or filled with a gas filled inside the communication device 500. However, these examples do not limit this embodiment.

[0053] In the above example, the case in which the cavity through which the laser light LP is guided is formed inside the support portion 20 was described, but this is not limited to this embodiment. As will be described later, the support portion 20 may be configured to separately include a frame portion that supports the main mirror portion 10 relative to the base portion 30 and a housing for shielding the optical path of the communication laser light LP from the outside world.

[0054] <Second hollow shaft 42> The second hollow shaft 42 connects the support portion 20 to the base portion 30 so that it can rotate around the z-axis (second axis). As shown in Figure 6, the communication laser beam LP, directed by the mirror M23 of the support portion 20, penetrates the hollow portion 42v formed in the second hollow shaft 42. Here, as shown in Figure 6, the hollow portion 42v is a hollow region defined by the inner wall 42a of the second hollow shaft 42. As an example, when the communication device 500 is located on the Earth's surface or in the atmosphere, the hollow portion 42v is filled with air or with gas filled inside the communication device 500. As another example, when the communication device 500 is located in outer space, the hollow portion 42v is a vacuum or filled with gas filled inside the communication device 500. However, these examples are not limiting to this embodiment.

[0055] The specific configuration of the second hollow shaft 42 is not limited to this embodiment, but as an example, it can be configured to include a bearing and a shaft that is rotatably supported by the bearing and has the hollow portion 42v formed on it. In this configuration, the hollow portion 42v is defined by an inner wall 42a formed to penetrate the shaft.

[0056] Furthermore, the second hollow shaft 42 is equipped with a drive motor for rotating the support portion 20 relative to the base portion 30. In other words, it is equipped with a drive motor for driving the second hollow shaft 42. Here, this drive motor is controlled, for example, by a receiving unit 31 or a transmitting unit 32, which will be described later.

[0057] <Base 30> The base 30 is configured to support and drive the main mirror 10 via the support 20. The base 30 also includes a receiving unit for receiving laser light LP, a transmitting unit for transmitting laser light LP, and a modem connected to the receiving unit and the transmitting unit. Here, the receiving unit includes, for example, a collimator (coupler) for coupling the received laser light LP to an optical fiber, and the transmitting unit includes a collimator (coupler) for forming the laser light LP for transmission from the optical signal propagating through the optical fiber.

[0058] As an example, as shown in Figure 6, the base unit 30 is configured to include a dichroic mirror M3, a receiving unit 31, a transmitting unit 32, and a modem 33. The dichroic mirror M3 transmits light in a specific wavelength range and reflects light outside that specific wavelength range. In the example shown in Figure 6, the dichroic mirror M3 is • A laser beam LP in a specific wavelength range, which is transmitted through the laser beam LP received by the communication device 500. • The laser light LP is outside the specific wavelength range and is configured to reflect the laser light LP transmitted by the communication device 500.

[0059] As a result, the dichroic mirror M3 guides the laser light LP received by the main mirror section 10 to the receiving section 31, while guiding the laser light LP for transmission provided by the transmitting section 32 to the support section 20. The receiving section and transmitting section will be described later with reference to different drawings.

[0060] <Beam size in optical path LP> Furthermore, in the above-described configuration, regarding the beam size (beam diameter) of the laser light LP, the beam size W of the received laser light LP immediately after reflection by the sub-mirror M12 and the beam size Wr of the received laser light LP immediately before it enters the receiving unit 31 are as follows: Design Example 1: W=Wr The mirror surfaces of the primary mirror M11, secondary mirror M12, and mirrors M21-M23 may be designed in such a way. Design Example 2: W>Wr The mirror surfaces of the primary mirror M11, secondary mirror M12, and mirrors M21-M23 may be designed accordingly. In design example 2, the received laser light LP received by the primary mirror 10 is gradually focused along the optical path from the primary mirror 10 to the base 30 and guided to the receiving unit 31. In this way, a configuration in which the received laser light LP is focused at a longer focal length may be used compared to a configuration in which it is focused within the primary mirror 10. Note that in design example 1, the beam size Wt of the transmitted laser light LP immediately after it is emitted from the transmitting unit 32 and the beam size W of the transmitted laser light LP immediately before it is reflected by the secondary mirror M12 are, W=Wt The following conditions are met, and in the case of design example 2, W>Wt This will satisfy the condition. Note that the specific value of W mentioned above is not limited to this embodiment, but as an example, it may be a few millimeters to several tens of millimeters, or it may be a value exceeding 100 mm.

[0061] <Detailed configuration of communication device 500> Next, the detailed configuration of the communication device 500 will be described with reference to Figure 8. Figure 8 is a schematic block diagram showing the configuration of the communication device 500. In Figure 8, the received laser light LP is denoted by the code Lr, and the transmitted laser light is denoted by the code Lt. In addition, the drive unit that drives the first hollow shaft 41 is denoted by the code 23, and the drive unit that drives the second hollow shaft 42 is denoted by the code 24.

[0062] The drive unit 23 includes, for example, an encoder that encodes the control signal SC1 supplied from the receiving unit 31, and a drive motor driven by the control signal SC1 encoded by the encoder. Similarly, the drive unit 24 includes, for example, an encoder that encodes the control signal SC2 supplied from the receiving unit 31, and a drive motor driven by the control signal SC2 encoded by the encoder.

[0063] As shown in Figure 8, the received laser light Lr received by the main mirror 10 is guided to the dichroic mirror M3 via the hollow section 41v formed in the first hollow shaft 41 and the hollow section 42v formed in the second hollow shaft 42. Also, as shown in Figure 8, the transmitted laser light Lt emitted from the dichroic mirror M3 is guided to the main mirror 10 via the hollow section 41v formed in the first hollow shaft 41 and the hollow section 42v formed in the second hollow shaft 42.

[0064] <Receiver 31> As shown in Figure 8, the receiving unit 31 includes a first beam splitter 311, a first photodetector 312, a high-speed steering mirror 313 (corresponding to movable mirror devices 1 to 1C), a second beam splitter 314, a second photodetector 315, and a collimator 316. Here, the first beam splitter 311 and the first photodetector 312, together with the drive units 23 and 24, constitute a coarse tracking mechanism for coarsely tracking the received laser light Lr. The high-speed steering mirror 313, the second beam splitter 314, and the second photodetector 315 constitute a precise tracking mechanism for precisely tracking the received laser light Lr. The coarse tracking mechanism and the precise tracking mechanism together are also referred to as the tracking mechanism 310.

[0065] <Coarse tracking mechanism> The first beam splitter 311 receives the received laser light Lr reflected by the dichroic mirror M3. The first beam splitter 311 splits the received laser light Lr into two laser beams, guiding one of them to the first photodetector 312 and the other to the high-speed steering mirror 313.

[0066] The first photodetector 312 detects the position of the laser light incident from the first beam splitter 311 and generates control signals SC1 and SC2 according to the detection result. Here, control signal SC1 is a coarse tracking control signal around the x-axis (elevation direction) supplied to the drive unit 23 that drives the first hollow shaft 41. On the other hand, control signal SC2 is a coarse tracking control signal around the z-axis (azimuth direction) supplied to the drive unit 24 that drives the second hollow shaft 42. The specific configuration of the first photodetector 312 is not limited to this embodiment, but as an example, a four-quadrant detection element, a CCD (Charge Coupled Device) sensor, or a CMOS (Complementary Metal Oxide Semiconductor) sensor can be used.

[0067] The receiving unit 31 controls the drive units 23 and 24 with control signals SC1 and SC2, respectively, so that the main mirror unit 10 can roughly track the received laser light Lr around the x-axis (elevation direction) and the z-axis (azimuth direction), respectively.

[0068] <Precise tracking mechanism> Laser light that has passed through the first beam splitter 311 is incident on the high-speed steering mirror 313. The high-speed steering mirror 313 changes the path of the laser light incident on it at high speed and with high precision according to the control signal SF from the second photodetector 315, which will be described later. More specifically, in the movable mirror devices 1 to 1C, the drive unit 1_2 drives the mirror 1_1 based on the control signal SF from the second photodetector 315.

[0069] The second beam splitter 314 splits the laser light incident from the high-speed steering mirror 313 into two laser beams, guiding one of the laser beams to the second photodetector 315 and the other laser beam to the collimator 316.

[0070] The second photodetector 315 detects the position of the laser light incident from the second beam splitter 314 and generates a control signal SF according to the detection result. Here, the control signal SF is a precision tracking control signal supplied to the high-speed steering mirror 313, and as an example, includes a precision tracking control signal around the x-axis (elevation direction) and a precision tracking control signal around the z-axis (azimuth direction).

[0071] The second photodetector 315 supplies the control signal SF to the high-speed steering mirror 313, thereby forming a closed-loop system with the high-speed steering mirror 313, the second beam splitter 314, and the second photodetector 315. By supplying the control signal SF to the high-speed steering mirror 313, the receiving unit 31 can precisely track the received laser light Lr.

[0072] <Collimator 316> The collimator 316 collimates the laser light that has passed through the second beam splitter 314 and couples it to the optical fiber F31. The optical fiber F31 is connected to the modem 33.

[0073] The receiving unit 31, configured as described above, can coarsely and precisely track the received laser light Lr received by the main mirror unit 10, couple it to the optical fiber F31, and supply it to the modem 33.

[0074] <Transmitter 32> As shown in Figure 8, the transmitting unit 32 is equipped with a collimator 321. The collimator 321 forms a transmitted laser beam Lt from the optical signal for transmission supplied from the modem 33 via the optical fiber F32. As shown in Figure 8, the transmitted laser beam Lt formed by the transmitting unit 32 passes through the dichroic mirror M3, penetrates the second hollow axis 42 and the first hollow axis 41, and is supplied to the main mirror unit 10. It is then reflected by the secondary mirror M12 and the main mirror M11 and emitted from the main mirror unit 10 to the outside world (transmission destination).

[0075] <Modem 33> The modem 33 acquires transmission data from a communication device (not shown) and supplies received data to the same communication device. For example, the modem 33 converts the optical signal indicated by the received laser light Lr supplied from the receiving unit 31 via the optical fiber F31 into a digital signal and supplies the digital signal as received data to the communication device. The modem 33 also converts the transmission data acquired from the communication device into an optical signal for transmission and supplies it to the transmitting unit 32 via the optical fiber F32.

[0076] (Communication system 100) Next, with reference to Figure 9, a communication system 100 including one or more communication devices having a configuration similar to that of the communication device 500 will be described. Figure 9 is a diagram showing an example configuration of the communication system 100 according to this embodiment. The communication system 100 is an optical wireless communication system that performs communication by propagating laser light for communication in a vacuum or in the atmosphere.

[0077] In the example shown in Figure 9, the communication system 100 includes a first communication device 500a, a second communication device 500b, a communication device 511 located on the flying object 51, and a communication device 512 located on the flying object 52. Here, the first communication device 500a, the second communication device 500b, the communication device 511, and the communication device 512 have a configuration similar to that of the communication device 500 described above, as an example.

[0078] As shown in Figure 9, the first communication device 500a performs optical wireless communication with the communication device 511 located on the flying object 51 via laser beam LA1. The communication device 511 located on the flying object 51 then performs optical wireless communication with the communication device 512 located on the flying object 52 via laser beam LA2. The communication device 512 located on the flying object 52 then performs optical wireless communication with the second communication device 500b via laser beam LA3.

[0079] As described above, the communication system 100 illustrated in Figure 9 is an optical wireless communication system that performs communication by propagating a communication laser beam through a vacuum or the atmosphere via one or more flying objects. The configuration of the communication system 100 is not limited to the above example; for example, it may also be configured to perform communication via communication devices located on one or more artificial satellites.

[0080] Furthermore, while Figure 9 shows a balloon-type flying body equipped with a propulsion system as an example of the flying bodies 51 and 52, this is not an example that limits the invention to this one. For example, the flying bodies 51 and 52 may be drones equipped with multiple propellers or airplanes equipped with wings. These flying bodies may be piloted by humans or automatically piloted by a predetermined algorithm. For example, the flying bodies 51 and 52 may be LEOs or HAPSs. These flying bodies equipped with a communication device having a configuration similar to that of the communication device 500 are also included in the invention described herein. <Summary> This disclosure includes at least the following aspects:

[0081] A movable mirror device according to Embodiment 1 of the present disclosure comprises a mirror for receiving laser light in optical wireless communication, a drive unit for driving the mirror, a substrate on which the drive unit is mounted, a package containing the mirror, the drive unit, and the substrate, and a cooling element arranged to conduct heat to the substrate.

[0082] According to the above configuration, the movable mirror device according to Embodiment 1 of this disclosure can receive laser light with a high energy density.

[0083] In the movable mirror device according to Embodiment 2 of the present disclosure, the cooling element in Embodiment 1 is a Peltier element, and the Peltier element is connected to a control device that supplies current and voltage according to the intensity of the laser light received by the mirror.

[0084] According to the above configuration, the movable mirror device according to Embodiment 2 of the present disclosure can suitably suppress the rise in the temperature of the mirror.

[0085] In the movable mirror device according to embodiment 3 of this disclosure, the package in embodiment 1 or 2 is filled with helium.

[0086] According to the above configuration, the movable mirror device according to embodiment 3 of the present disclosure can suitably cool the inside of the package using a cooling element.

[0087] In the movable mirror device according to Embodiment 4 of the present disclosure, the cooling element in any of Embodiments 1 to 3 is arranged on the outside of the package in contact with the package.

[0088] According to the above configuration, the movable mirror device according to embodiment 4 of this disclosure can position the cooling element in an appropriate location depending on the installation environment.

[0089] The movable mirror device according to aspect 5 of this disclosure comprises fins inside the package in aspect 4.

[0090] According to the above configuration, the movable mirror device according to aspect 5 of this disclosure can efficiently lower the temperature inside the package even when it is placed in a high-vacuum space such as outside the atmosphere.

[0091] In the movable mirror device according to embodiment 6 of the present disclosure, the cooling element in any of embodiments 1 to 3 is arranged between the package and the substrate.

[0092] According to the above configuration, the movable mirror device according to embodiment 6 of this disclosure can cool the inside of the package even if the configuration makes it difficult for the temperature inside the package to be released to the outside of the package.

[0093] The movable mirror device according to embodiment 7 of the present disclosure further comprises, in embodiment 6, fins arranged on the outside of the package so as to be in contact with the package.

[0094] According to the above configuration, the movable mirror device according to embodiment 7 of the present disclosure can suppress the rise in temperature inside the package due to the package being heated by the cooling element.

[0095] In the movable mirror device according to aspect 8 of the present disclosure, the drive unit in any of aspects 1 to 7 drives the mirror using a micro-electromechanical system.

[0096] According to the above configuration, the movable mirror device according to embodiment 8 of this disclosure can be miniaturized and the mirror can be driven at high speed.

[0097] The movable mirror device according to aspect 9 of this disclosure is located in the stratosphere or outside the atmosphere in any of aspects 1 to 8.

[0098] According to the above configuration, the movable mirror device according to aspect 9 of this disclosure can receive laser light with a high energy density during precise tracking, even when it is placed in LEO or HAPS.

[0099] A communication device according to aspect 10 of this disclosure is equipped with a movable mirror device as described in any of aspects 1 to 9.

[0100] According to the above configuration, the communication device according to aspect 10 of this disclosure can realize a communication device that achieves the same effects as the movable mirror device described above.

[0101] (Additional notes) This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure.

[0102] Furthermore, the present invention enables miniaturization of the mirror used in precise tracking in optical wireless communication. Therefore, the present invention improves tracking performance and serves as an innovative technological foundation in the telecommunications business, thereby contributing to the achievement of Sustainable Development Goal (SDG) 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation." [Explanation of Symbols]

[0103] 1, 1A, 1B, 1C Movable mirror device 1_1 Mirror 1_2 Drive Unit 1_3 Circuit board 1_4 Cooling element (Peltier element) 1_5 Package 1_6 Light-receiving window 1_7 Finn 320 EDFA 330 Control device

Claims

1. A mirror that receives laser light in optical wireless communication, A drive unit for driving the aforementioned mirror, A circuit board on which the aforementioned drive unit is mounted, A package containing the mirror, the drive unit, and the substrate inside, A cooling element arranged to conduct heat with respect to the substrate, A movable mirror device equipped with a mirror.

2. The cooling element is a Peltier element, The Peltier element is connected to a control device that supplies current and voltage according to the intensity of the laser light received by the mirror. The movable mirror device according to claim 1.

3. The package is filled with helium. The movable mirror device according to claim 1 or 2.

4. The cooling element is positioned on the outside of the package and in contact with the package. The movable mirror device according to claim 1 or 2.

5. The package has fins inside, The movable mirror device according to claim 4.

6. The cooling element is disposed between the package and the substrate. The movable mirror device according to claim 1 or 2.

7. The package further comprises fins positioned on the outside of the package so as to be in contact with the package. The movable mirror device according to claim 6.

8. The drive unit drives the mirror using a micro-electromechanical system. The movable mirror device according to claim 1 or 2.

9. The movable mirror device is located in the stratosphere or outside the atmosphere. The movable mirror device according to claim 1 or 2.

10. A communication device comprising the movable mirror device described in claim 1 or 2.

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