Optical adjustment method and apparatus in a spatial transmission optical communication system

Abstract

This invention provides a new optical adjustment method and apparatus that enables faster, more precise, and easier optical adjustment in spatial optical communication. [Solution] The optical adjustment device uses communication light (L S ) and guide light (L) on the same optical axis (AX) G The system includes a variable focus optical system (103) that focuses the light at a focal position between the transmitter and the receiver to illuminate a wider area than the light-receiving unit (T) in the receiver; an imaging unit (104) that images a portion of a predetermined pattern (P1-P4) provided around the light-receiving unit that is illuminated by the guide light; and a control unit (110) that adjusts at least one of the focal position and optical axis of the variable focus optical system so that the imaged portion of the pattern coincides with a predetermined portion of the predetermined pattern.

Description

[Technical Field]

[0001] This invention relates to an optical adjustment technique for precisely irradiating a light beam from a transmitter to a receiver. [Background technology]

[0002] When transmitting information spatially using light, it is necessary for the light emitted from the transmitting side to accurately illuminate the light-receiving unit on the receiving side. For this reason, many optical adjustment techniques have been proposed to adjust the size and position of the illumination spot at the light-receiving unit.

[0003] For example, according to the spatial optical communication system disclosed in Patent Document 1, a communication station transmits a transmission laser beam to a receiving station, monitors the received intensity of the reflected laser beam that has been reflected back by the receiving station, and adjusts the intensity, divergence angle, and emission direction of the transmission laser beam based on the monitoring results. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-159032 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in spatial optical communication between two spatially separated points, it is extremely difficult to perform optical adjustments such as the divergence angle and emission direction of the transmitted laser beam at high speed and with high precision based on changes in received light intensity or the distribution of received light intensity.

[0006] Therefore, the object of the present invention is to provide a new optical adjustment method and apparatus that can perform optical adjustment in spatial optical communication at a faster speed, with higher precision and ease. [Means for solving the problem]

[0007] An optical adjustment device according to one aspect of the present invention is an optical adjustment device in a spatial optical communication system that transmits communication light from a transmitter to a receiver, and includes: a variable focus optical system that focuses guide light on the same optical axis as the communication light at a focal position between the transmitter and the receiver to illuminate a wider area than the light receiving unit in the receiver; an imaging unit that images a portion of a predetermined pattern provided around the light receiving unit that is illuminated by the guide light; and a control unit that adjusts at least one of the focal position and optical axis of the variable focus optical system so that the imaged portion of the pattern coincides with a predetermined portion of the predetermined pattern. An optical adjustment method according to one aspect of the present invention is an optical adjustment method for a spatial optical communication system that transmits communication light from a transmitter to a receiver, wherein a predetermined pattern is prepared around a light-receiving unit in the receiver, a variable focus optical system focuses guide light on the same optical axis as the communication light at a focal position between the transmitter and the receiver to illuminate a wider area than the light-receiving unit, an imaging unit images a portion of the predetermined pattern illuminated by the guide light, and a control unit adjusts at least one of the focal position and optical axis of the variable focus optical system so that the imaged portion of the predetermined pattern coincides with a predetermined portion of the predetermined pattern. A program according to one aspect of the present invention is a program that causes a computer to function as an optical adjustment device in a spatial optical communication system that transmits communication light from a transmitter to a receiver, wherein the optical adjustment device includes a variable focus optical system that focuses guide light on the same optical axis as the communication light at a focal position between the transmitter and the receiver to illuminate a light-receiving surface including a light-receiving part of the receiver over a wider area than the light-receiving part, and an imaging unit that images a portion of a predetermined pattern formed around the light-receiving part that is illuminated by the guide light, wherein the computer has the function of identifying the portion of the pattern from the imaging data of the imaging unit by irradiating the guide light and performing pattern matching between the portion of the pattern and the predetermined pattern, and the function of adjusting at least one of the focal position and optical axis of the variable focus optical system so that the portion of the pattern matches a predetermined portion of the predetermined pattern. [Effects of the Invention]

[0008] According to the present invention, optical adjustment in spatial optical communication can be achieved more quickly, with higher precision, and more easily. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a diagram showing an example of an optical adjustment system employing an optical adjustment device according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic block diagram showing an example of the variable focus lens section in Figure 1. [Figure 3] Figure 3 shows an example of a predetermined pattern in Figure 1. [Figure 4] Figure 4 is a schematic diagram showing an example of the optimal irradiation size and irradiation position of guide light in a predetermined pattern illustrated in Figure 3. [Figure 5] Figure 5 is a block diagram illustrating the configuration of a transmitter employing an optical adjustment device according to one embodiment of the present invention. [Figure 6] Figure 6 is a schematic diagram illustrating the focus shift of guide light using the predetermined pattern shown in Figure 3. [Figure 7] Figure 7 is a schematic diagram illustrating the optical axis misalignment of guide light using the predetermined pattern shown in Figure 3. [Figure 8] Figure 8 shows coordinate axes for generally representing the beam focus misalignment and optical axis misalignment of the optical adjustment device according to this embodiment. [Figure 9] Figure 9 is a flowchart illustrating the optical adjustment method of the optical adjustment device according to this embodiment. [Figure 10] Figure 10 is a block diagram showing an example of a transmitter for a quantum key distribution system to which the optical adjustment device according to this embodiment is applied. [Modes for carrying out the invention]

[0010] <Overview of Embodiments> According to an embodiment of the present invention, a variable focus optical system focuses guide light coaxial with the communication light at a focal position to illuminate a wide area of ​​the light-receiving surface, including the light-receiving unit on the communication partner side. A predetermined pattern is provided around the light-receiving unit, and a portion of this pattern illuminated by the guide light is imaged by a camera. The imaged portion of the pattern changes according to the change in the focal position and / or optical axis of the variable focus optical system. Therefore, by adjusting the variable focus optical system so that the portion of the pattern illuminated by the guide light coincides with a predetermined portion of the predetermined pattern, the communication light coaxial with the guide light can be accurately irradiated onto the light-receiving unit of the receiver, and high-speed and high-precision optical adjustment can be easily achieved.

[0011] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the components described in the following embodiments and examples are merely illustrative and are not intended to limit the technical scope of the present invention to them alone.

[0012] 1. One Embodiment <System Configuration> As illustrated in Figure 1, the optical adjustment device according to this embodiment is applied to a spatial optical communication system. The spatial optical communication system consists of a transmitter 100 and a receiver 200, which are optically connected via free space 300. Free space 300 is a space free from obstacles that hinder the straight-line propagation of electromagnetic waves, including light, and can be in the atmosphere or a vacuum. Hereinafter, the guide light L in the transmitter 100... G Or communication optical L S The optical axis AX is represented by the Z axis, and the plane perpendicular to the optical axis AX is represented by the X axis and Y axis.

[0013] The transmitter 100 includes an optical fiber 101, a collimator 102, a variable focus optical system 103, a camera 104, and an optical adjustment control unit 110. The optical fiber 101, collimator 102, and variable focus optical system 103 are arranged on the same optical axis. Guide light L is emitted from the optical fiber 101. G Or communication optical L S The light becomes parallel light due to the collimator 102 and enters the variable focus optical system 103. In this embodiment, the guide light LG Let the wavelength of the guide light L be λg and the wavelength of the communication light L S be λs, and assume that the wavelength λg is shorter than the wavelength λs (λg < λs).

[0014] The variable-focus optical system 103 is a focusing optical system including an optical element having a refractive surface. The variable-focus optical system 103 can form a beam waist at the focal position between the incident parallel light and the receiver 200 and irradiate the light receiving surface 201 of the receiver 200.

[0015] As is well known, the refractive index increases as the wavelength decreases. Therefore, the focal length f(λg) of the guide light L G is shorter than the focal length f(λs) of the communication light L S . Thus, the guide light L G irradiates the light receiving surface 201 with a wider beam diameter than the communication light L S . Since the guide light L G and the communication light L S have the same optical axis, the irradiation range and irradiation position of the communication light L G on the light receiving surface 201 can be determined by detecting the irradiation range and irradiation position of the guide light L S . That is, the focus shift and optical axis shift of the communication light L G can be detected from the irradiation range and irradiation position of the guide light L S .

[0016] A collimator 202 is provided at a predetermined position on the light receiving surface 201, and the aperture of the collimator 202 serves as the light receiving portion T of the communication light L S . If the communication light L S arriving from the transmitter 100 irradiates the light receiving portion T at a predetermined position along the optical axis AX with a predetermined beam diameter, the communication light L S is focused by the collimator 202 and enters the light receiving end of the optical fiber 203.

[0017] On the light receiving surface 201, a predetermined pattern (P1 - P4) is arranged around the light receiving portion T by printing or pasting or other methods. The guide light L G is on the light receiving surface 201 where the communication light L SBecause it has a wider beam diameter, it can illuminate not only the light-receiving section T but also a portion of the predetermined pattern (P1-P4) around it.

[0018] The predetermined pattern (P1-P4) consists of multiple reflective regions that radiate outward from the light-receiving section T, and it is desirable to use a reflective material (retroreflective material) that reflects incident light as each reflective region. The predetermined pattern (P1-P4) is guide light L G Any pattern that can detect the irradiation range and irradiation position is acceptable, and for example, a configuration in which multiple reflection regions are arranged in the X-axis direction and the Y-axis direction, respectively, is acceptable. Specific examples of predetermined patterns will be described later.

[0019] The camera 104 provided on the transmitter 100 is an imaging means (two-dimensional sensor) that selectively receives light of wavelength λg, and can image a wide area including the light-receiving surface 201 of the receiver 200. Therefore, the camera 104 receives guide light L of wavelength λg. G This allows for the acquisition of an image of the illuminated light-receiving surface 201, i.e., a portion (partial pattern) of a predetermined pattern (P1-P4). Therefore, it is possible to acquire a partial pattern without aligning the camera 104 with the optical axis of the light-receiving unit 202.

[0020] The optical adjustment control unit 110 receives the image captured by the camera 104 and, as will be described later, can identify which part of a predetermined pattern (P1-P4) the partial pattern belongs to using techniques such as pattern recognition. Therefore, the optical adjustment control unit 110 can adjust the focal position and / or optical axis position of the variable focus optical system 103 to match the captured partial pattern with the central pattern of the predetermined pattern (P1-P4) centered on the light-receiving part T. That is, guide light L G By aligning the partial pattern imaged by the illumination with the central pattern of a predetermined pattern, the guide light L G and the same optical axis as the communication optical L S This allows for accurate illumination of the light-receiving section T. The variable focus optical system 103 will be described in detail below.

[0021] <Variable Focus Optical System> As illustrated in Figure 2, the variable focus optical system 103 can be constructed by a combination of a convex lens L1 and a concave lens L2. The convex lens L1 and the concave lens L2 are positioned at a distance d in the direction of the optical axis AX (Z direction), and the distance d can be changed.

[0022] If the focal lengths of convex lens L1 and concave lens L2 are f1 and f2, respectively, then the combined focal length f of the variable focus optical system 103 is f = f1·f2 / (f1 + f2 - d) Therefore, by adjusting the distance d between the convex lens L1 and the concave lens L2, the combined focal length f can be moved along the optical axis AX (Z axis). In addition, by moving the variable focus optical system 103 along the XY plane, the optical axis AX can be moved in the X-axis direction and / or the Y-axis direction.

[0023] As mentioned above, guide light L G The wavelength λg is the communication light L S Since it is shorter than the wavelength λs, the guide light L G The focal length f(λg) when transmitted is the communication light L S The focal length becomes shorter than the focal length f(λs) when light is transmitted. Note that the variable focus optical system 103 can use not only a combination of a convex lens L1 and a concave lens L2, but also a liquid lens that can change the focal length.

[0024] <Predetermined pattern> As illustrated in Figure 3, the predetermined pattern provided on the light-receiving surface 201 of the receiver 200 consists of pattern regions P2 and P4 in the X-axis direction and pattern regions P1 and P3 in the Y-axis direction, centered on the light-receiving section T. In each pattern region, multiple reflection regions are sequentially arranged radially around the light-receiving section T. More specifically, in pattern region P1, reflection region P11 is located closest to the light-receiving section T, and reflection regions P12 and P13 are located at predetermined intervals in the direction away from the light-receiving section T. Similarly, in pattern region P2, reflection regions P21, P22, and P23 are located at predetermined intervals in the direction away from the light-receiving section T; in pattern region P3, reflection regions P31, P32, and P33 are located at predetermined intervals in the direction away from the light-receiving section T; and in pattern region P4, reflection regions P41, P42, and P43 are located at predetermined intervals in the direction away from the light-receiving section T.

[0025] <Optimal irradiation conditions> As illustrated in Figure 4, the communication optical L S When the light receiving portion T of the light receiving surface 201 is illuminated in an optimal state without excess or deficiency, the communication light L S Guide light L on the same optical axis AX G It shall illuminate the reflection regions up to the second from the inside of each pattern region. That is, the communication light L S When the light receiving unit T is illuminated with the same beam diameter, the guide light L G The system shall irradiate reflection regions P21, P22, P41, and P42 in the X-axis direction, and reflection regions P11, P12, P31, and P32 in the Y-axis direction.

[0026] In this optimal illumination state, the communication light L on the same optical axis AX S and guide light L G This means that the beams are focused at a reference focal point (beam waist) between the transmitter 100 and the receiver 200, respectively, and illuminate the light-receiving surface 201.

[0027] Based on this optimal irradiation state, the guide light L G If the irradiation beam diameter deviates from the standard, the guide light L GThe reflective region illuminated by the guide light L changes in the X and Y directions. G The camera 104 detects the pattern of the reflective region illuminated by the communication light L, i.e., a partial pattern of a predetermined pattern. S It can detect the presence or absence of focus misalignment and the amount of focus misalignment.

[0028] Also, guide light L G If the optical axis AX deviates from the reference, the guide light L G The reflective region illuminated by the guide light L changes in the X and / or Y directions. G By detecting the partial pattern of the reflective region illuminated by the camera 104, the communication light L S It can detect the presence or absence of optical axis misalignment and the amount of optical axis misalignment.

[0029] In the example in Figure 4, three reflection regions are arranged in each pattern region, but this is not the only example. Depending on the number of reflection regions in each pattern region, the width in the radiation direction, and the spacing, the communication light L S The amount of focus shift and optical axis misalignment can be measured with a desired granularity. The optical adjustment control unit 110 measures the amount of focus shift and optical axis misalignment and adjusts the focal position and optical axis position of the variable focus optical system 103 to eliminate these misalignments.

[0030] Thus, according to this embodiment, by utilizing pattern recognition, rapid optical adjustment, i.e., focus adjustment and optical axis adjustment, becomes possible. Furthermore, the communication optical L S Guide light L, which is on the same optical axis but has a different wavelength. G By using this method, the difference in refractive index can be utilized to illuminate a wide area of ​​the light-receiving surface 201 with guide light. Therefore, without the need for a special optical system for guide light, rapid and highly accurate optical adjustment can be performed with a simple configuration.

[0031] The configuration and operation of an optical adjustment device according to one embodiment of the present invention will be described in detail below with reference to Figures 5 to 9. However, the same reference numerals will be used for components that are the same as those in the above-described embodiment (Figure 1), and the explanation will be simplified.

[0032] 2. One Example 2.1) Configuration As illustrated in Figure 5, the transmitter 100 includes the optical fiber 101, collimator 102, variable focus optical system 103, and camera 104 described above. The variable focus optical system 103 has the lens configuration illustrated in Figure 2, and the movement mechanism 105 can move the combined focal length f along the Z axis and the optical axis AX along the X axis and / or Y axis. For example, the movement mechanism 105 may include a first movement mechanism that changes the distance (d) between lens holders holding the convex lens L1 and the concave lens L2, respectively, and a second movement mechanism that moves the entire variable focus optical system 103 along the X axis and / or Y axis.

[0033] Furthermore, the transmitter 100 emits a guide light L with wavelength λg. G A laser light source 107 that outputs light, and a communication light L with an infrared wavelength λs. S The system includes a laser light source 108 that outputs a guide light L and a dichroic mirror 106. In this embodiment, the guide light L G The wavelength λg is 650nm, and the communication light L S The wavelength λs is 1550 nm.

[0034] The dichroic mirror 106 uses guide light L with wavelength λg. G It reflects and the communication light L of wavelength λs. S It has the property of transmitting light. Guide light L of wavelength λg G The light is reflected by the dichroic mirror 106 and incident on the optical fiber 101, and the communication light L has a wavelength of λs. S The laser light passes through the dichroic mirror 106 and enters the optical fiber 101. The laser light sources 107 and 108 and the dichroic mirror 106 are guide light L that enters the optical fiber 101. G and communication optical L S They are arranged so that they are on the same optical axis.

[0035] Furthermore, the transmitter 100 has a processor 120 and a program memory 130. The processor 120 can realize the functions of the optical adjustment control unit 110 described above by executing a program stored in the program memory 130.

[0036] The optical adjustment control unit 110 has functions consisting of a pattern recognition unit 111 and a focus / optical axis adjustment unit 112. The pattern recognition unit 111 receives imaging data D from the camera 104. IMG Enter the image data D IMG From guide light L G The light extracts a partial pattern from the illuminated reflective region. Furthermore, the pattern recognition unit 111 performs pattern matching between the partial pattern and a predetermined pattern held in advance to recognize which part of the predetermined pattern the partial pattern matches.

[0037] The focus / optical axis adjustment unit 112 adjusts the focal position and / or optical axis of the variable focus optical system 103 using the movement mechanism 105 so that the partial pattern matches the pattern in a predetermined range at the center of a predetermined pattern (see Figure 4) based on the recognition result of the pattern recognition unit 111. As described above, by moving the focal position in the Z-axis direction, the guide light L G The illumination beam diameter on the light-receiving surface 201 can be adjusted, and by moving the optical axis of the variable focus optical system 103 along the XY plane, a guide light L G The optical axis of the illumination beam on the light-receiving surface 201 can be adjusted in this way. G By adjusting using this method, the communication light L on the same optical axis can be adjusted. S Adjustment is possible. Below, an example of the optical adjustment method according to this embodiment will be described with reference to Figures 6-8.

[0038] 2.2) Operation First, as illustrated in Figures 6 and 7, when the focal position of the variable focus optical system 103 is at the optimal position, the guide light L GThe reflective regions P11-P12, P21-P22, P31-P32, and P41-P42 of a predetermined pattern are irradiated (see Figure 4). In this case, the partial pattern obtained from the imaging data of camera 104 is the partial pattern image FP0.

[0039] <Focus position adjustment> In Figure 6, when the focal position of the variable focus optical system 103 is deviated from the optimal position toward the receiver 200, the guide light L G This illuminates a predetermined pattern on the light-receiving surface 201 in a range narrower than the optimal range, in this case the reflection regions P11, P21, P31, and P41 of the predetermined pattern. In this case, the partial pattern obtained from the imaging data of the camera 104 is the partial pattern image FP1.

[0040] Conversely, if the focal position of the variable focus optical system 103 is deviated from the optimal position toward the transmitter 100, the guide light L G This illuminates a predetermined pattern on the light-receiving surface 201 over a wider range than the optimal range, in this case the reflection regions P11-P13, P21-P23, P31-P33, and P41-P43 of the predetermined pattern. In this case, the partial pattern obtained from the imaging data of the camera 104 is the partial pattern image FP2.

[0041] In this way, the amount of the focal position shift of the variable focus optical system 103 can be estimated by determining which range of the reflection region of a predetermined pattern the partial pattern image includes. The focus / optical axis adjustment unit 112 moves the focal position of the variable focus optical system 103 in the Z-axis direction to eliminate the amount of the focal position shift.

[0042] <Optical axis position adjustment> In Figure 7, if the optical axis of the variable focus optical system 103 is deviated from the optimal position in the Y-axis direction of the light-receiving surface 201, for example, guide light L G This illuminates the range of the light-receiving surface 201 that is shifted in the negative direction of the Y-axis from the optimal range of a predetermined pattern, in this case the reflection regions P11, P21-P22, P31-P33, and P41-P42 of the predetermined pattern. In this case, the partial pattern obtained from the imaging data of the camera 104 is the partial pattern image FP3.

[0043] Furthermore, if the optical axis of the variable focus optical system 103 is deviated from the optimal position in the X and Y axis directions of the light-receiving surface 201, for example, if the guide light L G This illuminates the range of the light-receiving surface 201 that is shifted from the optimal range in the negative X-axis direction and the positive Y-axis direction, in this case the reflection regions P11-P13, P21-P23, P31 and P41 of the predetermined pattern. In this case, the partial pattern obtained from the imaging data of the camera 104 is the partial pattern image FP4.

[0044] By performing pattern recognition on the acquired partial pattern image, it is possible to determine which part of a predetermined pattern the captured partial pattern corresponds to, thereby estimating the amount of misalignment of the optical axis AX of the variable focus optical system 103. The focus / optical axis adjustment unit 112 moves the variable focus optical system 103 in the X and / or Y directions to eliminate the misalignment of the optical axis.

[0045] <Optical adjustment> By performing at least one of the above-described focus position adjustment and optical axis adjustment, the guide light L G The light can be irradiated onto a predetermined position and range of a predetermined pattern on the light-receiving surface 201. As a result, the guide light L G and the same optical axis as the communication optical L S This makes it possible to illuminate the light-receiving portion T of the light-receiving surface 201 in an optimal state. The optical adjustment operation according to this embodiment will be described below with reference to Figures 8 and 9.

[0046] As illustrated in Figure 8, the amount of optical axis misalignment Δ in the X-axis direction X Δ, the amount of optical axis misalignment in the Y-axis direction Y and the amount of focus shift Δ Z Assume that an optical shift Δ occurs. According to this embodiment, the guide light L G This eliminates the detected optical misalignment Δ, allowing the guide light to be optically adjusted to the optimal illumination position (effectively zero misalignment).

[0047] In Figure 9, the processor 120 determines whether or not it is the image analysis timing (operation 301). If it is the image analysis timing (YES in operation 301), the processor 120 drives the laser light source 107 to emit guide light L G The light is then irradiated. Next, the processor 120 drives the camera 104 to emit guide light L G The light-receiving surface illuminated by the device is imaged, and a partial pattern image is obtained from the image data (operation 302).

[0048] Next, the processor 120 determines, by pattern matching, which part of a predetermined pattern corresponds to the partial pattern of the captured partial pattern image, and thereby determines the amount of deviation (Δ) of the optical axis AX of the variable focus optical system 103. X ,Δ Y The processor 120 then controls the movement mechanism 105 to drive the variable focus optical system 103 and detects the amount of displacement (Δ). X ,Δ Y Adjust the position of the optical axis AX so that ) is canceled (operation 303).

[0049] Once the optical axis adjustment is complete, the processor 120 determines the amount of focal position shift Δ depending on which range of the predetermined pattern's reflection region the captured partial pattern image includes. Z The processor 120 then controls the movement mechanism 105 to drive the variable focus optical system 103, and the displacement amount Δ Z The focal position of the variable focus optical system 103 is adjusted so that the effect is canceled (operation 304).

[0050] By utilizing pattern recognition in this way, optical axis adjustment and focus adjustment can be performed at high speed. Furthermore, the communication optical L S Guide light L, which is on the same optical axis but has a different wavelength. G By using this, the difference in refractive index is utilized to create a guide light L G This allows for illumination over a wide area of ​​the light-receiving surface 201. Therefore, without the need for a special optical system for guide light, rapid and highly accurate optical adjustment is possible with a simple configuration.

[0051] The above operations 302 to 304 are repeated at each image analysis timing, but are not executed when it is not an image analysis timing (NO in operation 301). The processor 120 may also re-execute operations 302 to 304 after adjusting the variable focus optical system 103 to eliminate the misalignment, to check whether the misalignment has been sufficiently reduced. If the misalignment exceeds a predetermined threshold, the adjustment operations of operation 303 and / or operation 304 may be repeated.

[0052] Furthermore, the image analysis timing in operation 301 can be set according to the optical system to which the optical axis adjustment device according to this embodiment is applied. For example, in an optical communication system using quantum light, precise alignment of the communication light beam is required between the transmitting and receiving sides. Also, if the amount of light incident on the receiving side fluctuates due to vibration of the communication device, shortening the interval of the image analysis timing makes it possible to adjust the focus and optical axis in near real-time.

[0053] 3. Examples of application The following describes an example of applying the optical adjustment device according to the above embodiment to a quantum key distribution (QKD) system. However, blocks having the same function as the transmitter 100 illustrated in Figure 5 are given the same reference number and their explanation is omitted.

[0054] As illustrated in Figure 10, the quantum cryptography communication system consists of a communication device 100A including a transmitter (Alice) and a communication device (not shown) including a receiver (Bob). The communication device 100A includes the functions of the transmitter 100 illustrated in Figure 5.

[0055] Furthermore, the communication device 100A includes a non-polarized beam splitter (BS) 401 and a polarized beam splitter (PBS) 402, a mirror 403, a half-wave plate 404, an attenuator 405, a phase modulator 406, a mirror 407, and a processor 408. Here, the input port of the non-polarized beam splitter 401 is connected to the output port of the laser light source 108, and the output port of the polarized beam splitter 402 is connected to the optical fiber 101 through the dichroic mirror 106.

[0056] The laser light source 108 of the communication device 100A outputs an optical pulse P of linearly polarized light with a wavelength λs to the input port of the non-polarizing beam splitter 401. The optical pulse P is split by the non-polarizing beam splitter 401, and one optical pulse travels along the path R on the reference light side LO and the other optical pulse travels along the path R on the signal light side Q and are respectively sent out.

[0057] The optical pulse on the reference light side path R LO passes through the polarization beam splitter 402 as it is, and passes through the dichroic mirror 106 as a reference optical pulse P with normal intensity having no quantum state LO and enters the optical fiber 101. The optical pulse on the signal light side path R Q is reflected by the polarization beam splitter 402 through the mirror 403, the half-wave plate 404, the attenuator 405, the phase modulator 406 and the mirror 407, and passes through the dichroic mirror 106 as a weak signal optical pulse P having a quantum state Q and enters the optical fiber 101. More specifically, the half-wave plate 404 rotates the polarization of the optical pulse on the path R Q by 90 degrees, the attenuator 405 attenuates the optical pulse to weak light having a quantum state, and the phase modulator 406 phase-modulates the weak optical pulse to generate the signal optical pulse P Q . Note that the attenuator 405 and the phase modulator 406 may be arranged in the reverse order with respect to the traveling direction of the optical pulse.

[0058] Here, the path R on the signal light side Q has a longer optical path than the path R on the reference light side LO . The difference in the optical path lengths between the path R Q and the path R LO , the half-wave plate 404, and the non-polarizing beam splitter 401 and the polarization beam splitter 402 cause the reference optical pulse P LO and the signal optical pulse P Q whose polarizations are orthogonal to each other and are temporally separated from one optical pulse P to be generated as the communication optical light L S described above. Note that when the non-polarizing beam splitter 401 is used as a polarization beam splitter, the half-wave plate 404 may not be used.

[0059] The processor 408 controls the communication device 100A, and in addition to the key generation control unit for generating encryption keys, it also has the function of the optical adjustment control unit 110 described above. That is, before performing key generation, the processor 408 uses guide light L G The optical axis and focal position adjustment (optical adjustment) of the variable focus optical system 103 described above is performed using this method.

[0060] Once optical adjustment is complete, the processor 408 controls the laser light source 108, the attenuator 405, and the phase modulator 406, driving the phase modulator 406 in four phases (0°, 90°, 180°, 270°) according to the original random number of the encryption key. This causes the phase modulator 406 to phase modulate the weak light pulse output from the attenuator 405 according to the key information, thereby generating a signal light pulse P Q This generates a reference light pulse P of normal intensity. LO and a phase-modulated signal light pulse P Q The pulse train is the communication light L S The light is then shone onto the light-receiving surface 201 of the receiver (Bob) described above through the dichroic mirror 106, optical fiber 101, collimator 102, and variable focus optical system 103. The variable focus optical system 103 is used to shone the guide light L G Since it has been optically calibrated in advance using the guide light L G Reference light pulse P on the same optical axis LO and signal light pulse P Q (Communication light L S The light is precisely incident on the light-receiving section T of the receiver 200.

[0061] The receiver 200 receives the reference light pulse P received through free space 300. LO and signal light pulse P QAn interferometer is configured to cause interference, and the transmitted signal is detected by homodyne detection, but this is not essential to the present invention, so the explanation is omitted. In a QKD system using spatial optical transmission, a weak signal light having a quantum state is transmitted through free space 300, so it is particularly important to accurately irradiate the light receiving section T of the receiver 200 with communication light Ls. By applying the optical adjustment device according to this embodiment, a highly reliable QKD system can be constructed.

[0062] 4. Addendum Some or all of the embodiments and examples described above may also be described as follows, but are not limited to these. (Note 1) An optical adjustment device in a spatial optical communication system that transmits communication light from a transmitter to a receiver, A variable focus optical system that focuses a guide light on the same optical axis as the communication light at a focal position between the transmitter and the receiver to illuminate a wider area than the light receiving unit in the receiver, An imaging unit that captures a portion of a predetermined pattern provided around the light-receiving unit that is illuminated by the guide light, A control unit that adjusts at least one of the focal position and optical axis of the variable focus optical system so that the captured partial pattern matches a predetermined portion of the predetermined pattern, Optical adjustment device including (Note 2) The optical adjustment device according to Appendix 1, wherein the variable focus optical system includes a lens having a plurality of refractive surfaces, and the focal positions differ between the communication light and the guide light. (Note 3) The optical adjustment device described in Appendix 2, wherein the wavelength of the guide light is shorter than the wavelength of the communication light. (Note 4) An optical adjustment device according to Appendix 2, wherein the refractive index for the guide light is greater than the refractive index for the communication light. (Note 5) The optical adjustment device according to any one of the appendices 1-4, wherein the predetermined pattern comprises a plurality of reflective regions that radiate outward from the light-receiving portion. (Note 6) The optical adjustment device according to Appendix 5, wherein the plurality of reflection regions are arranged at predetermined intervals on two orthogonal axes centered on the light receiving unit. (Note 7) The optical adjustment device according to Appendix 5 or 6, wherein the plurality of reflective regions are made of retroreflective material. (Note 8) The optical adjustment device according to any one of the appendices 5-7, wherein the imaging unit selectively images reflected light of the wavelength of the guide light. (Note 9) An optical adjustment method in a spatial optical communication system that transmits communication light from a transmitter to a receiver, A predetermined pattern is prepared around the light-receiving section of the receiver, The variable focus optical system focuses guide light, which is on the same optical axis as the communication light, at a focal position between the transmitter and the receiver, thereby illuminating a wider area than the light receiving unit. The imaging unit captures a portion of the predetermined pattern illuminated by the guide light, The control unit adjusts at least one of the focal position and optical axis of the variable focus optical system so that the captured partial pattern coincides with a predetermined portion of the predetermined pattern. Optical adjustment method. (Note 10) The optical adjustment method according to Appendix 9, wherein the variable focus optical system includes a lens having a plurality of refractive surfaces, and the focal positions of the communication light and the guide light are different. (Note 11) The optical adjustment method described in Appendix 10, wherein the wavelength of the guide light is shorter than the wavelength of the communication light. (Note 12) The optical adjustment method described in Appendix 10, wherein the refractive index for the guide light is greater than the refractive index for the communication light. (Note 13) The optical adjustment method according to any one of the items in Appendix 9 or 12, wherein the predetermined pattern consists of a plurality of reflection regions that radiate outward from the light receiving portion. (Note 14) The optical adjustment method according to Appendix 13, wherein the plurality of reflection regions are arranged at predetermined intervals on two orthogonal axes centered on the light receiving portion. (Note 15) The optical adjustment method according to Appendix 13 or 14, wherein the plurality of reflective regions consist of retroreflective material. (Note 16) The optical adjustment method according to any one of the appendices 13-15, wherein the imaging unit selectively images reflected light of the wavelength of the guide light. (Note 17) A transmitter including an optical adjustment device as described in any one of the items 1-8 of the appendix, A transmitter that performs spatial optical communication using the signal light after the control unit has adjusted at least one of the focal position and the optical axis of the variable focus optical system using the guide light. (Note 18) The spatial optical signal system is a quantum key distribution system, and the transmitter according to Appendix 17 includes weak light having a quantum state. (Note 19) A program that causes a computer to function as an optical adjustment device in a spatial optical communication system that transmits communication light from a transmitter to a receiver, The optical adjustment device includes a variable focus optical system that focuses guide light on the same optical axis as the communication light at a focal position between the transmitter and the receiver to illuminate the light-receiving surface, including the light-receiving part of the receiver, over a wider area than the light-receiving part, and an imaging unit that images a portion of a predetermined pattern formed around the light-receiving part that is illuminated by the guide light. The aforementioned computer, The function includes identifying the partial pattern from the imaging data of the imaging unit by irradiating it with the guide light, and performing pattern matching between the partial pattern and the predetermined pattern, A function to adjust at least one of the focal position and optical axis of the variable focus optical system so that the partial pattern coincides with a predetermined portion of the predetermined pattern, A program that achieves this. [Industrial applicability]

[0063] This invention can be used in communication devices for optical communication systems that require optical adjustment. [Explanation of Symbols]

[0064] 100 Transmitters 101 Optical Fiber 102 Collimator 103 Variable focus optical system 104 Camera 105 Moving mechanism 106 Dichroic Mirror 107 Laser light source (wavelength λg) 108 Laser light source (wavelength λs) 110 Optical adjustment control unit 111 Pattern Recognition Unit 112 Focus / optical axis adjustment section 120 processors 130 Program Memory 200 receivers 201 Photosensitive surface 202 Collimator 203 Optical Fiber L G Guide light L S Optical communication T Light receiving section P1-P4 predetermined pattern FP0-FP4 Partial Pattern Image 300 free space

Claims

1. An optical adjustment device in a spatial optical communication system that transmits communication light from a transmitter to a receiver, A variable focus optical system that focuses a guide light on the same optical axis as the communication light at a focal position between the transmitter and the receiver to illuminate a wider area than the light receiving unit in the receiver, An imaging unit that captures a portion of a predetermined pattern provided around the light-receiving unit that is illuminated by the guide light, A control unit that adjusts at least one of the focal position and optical axis of the variable focus optical system so that the captured partial pattern matches a predetermined portion of the predetermined pattern, Optical adjustment device including

2. The optical adjustment device according to claim 1, wherein the variable focus optical system includes a lens having a plurality of refractive surfaces, and the focal positions of the communication light and the guide light are different.

3. The optical adjustment device according to claim 2, wherein the wavelength of the guide light is shorter than the wavelength of the communication light.

4. The optical adjustment device according to any one of claims 1 to 3, wherein the predetermined pattern comprises a plurality of reflective regions that spread radially from the light receiving unit.

5. The optical adjustment device according to claim 4, wherein the plurality of reflection regions are arranged at predetermined intervals on two orthogonal axes centered on the light receiving unit.

6. An optical adjustment method in a spatial optical communication system that transmits communication light from a transmitter to a receiver, A predetermined pattern is prepared around the light-receiving section of the receiver, The variable focus optical system focuses guide light, which is on the same optical axis as the communication light, at a focal position between the transmitter and the receiver, thereby illuminating a wider area than the light receiving unit. The imaging unit captures a portion of the predetermined pattern illuminated by the guide light, The control unit adjusts at least one of the focal position and optical axis of the variable focus optical system so that the captured partial pattern coincides with a predetermined portion of the predetermined pattern. Optical adjustment method.

7. The optical adjustment method according to claim 6, wherein the variable focus optical system includes a lens having a plurality of refractive surfaces, and the focal positions of the communication light and the guide light are different.

8. A transmitter including an optical adjustment device according to any one of claims 1 to 3, A transmitter that performs spatial optical communication using the signal light after the control unit has adjusted at least one of the focal position and the optical axis of the variable focus optical system using the guide light.

9. The transmitter according to claim 8, wherein the spatial optical signal system is a quantum key distribution system, and the signal light includes weak light having a quantum state.

10. A program that causes a computer to function as an optical adjustment device in a spatial optical communication system that transmits communication light from a transmitter to a receiver, The optical adjustment device includes a variable focus optical system that focuses guide light on the same optical axis as the communication light at a focal position between the transmitter and the receiver to illuminate the light-receiving surface, including the light-receiving part of the receiver, over a wider area than the light-receiving part, and an imaging unit that images a portion of a predetermined pattern formed around the light-receiving part that is illuminated by the guide light. The aforementioned computer, The function includes identifying the partial pattern from the imaging data of the imaging unit by irradiating it with the guide light, and performing pattern matching between the partial pattern and the predetermined pattern, A function to adjust at least one of the focal position and optical axis of the variable focus optical system so that the partial pattern coincides with a predetermined portion of the predetermined pattern, A program that achieves this.

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