COMMUNICATION DEVICE, OPTICAL AXIS DIRECTION ADJUSTMENT METHOD, AND COMMUNICATION SYSTEM

Abstract

To provide a communication device equipped with a lens for condensing signal light so as to facilitate both fine optical axis direction adjustment and coarse optical axis direction adjustment, a communication system, and an optical axis direction adjusting method.SOLUTION: A communication device 1 is equipped with a zoom lens 11 that condenses signal light. By setting focal length of a zoom lens short (widening angle of view) by a focal length adjustment mechanism 14, coarse optical axis direction adjustment can be easily performed. By setting the focal length of the zoom lens long (narrowing angle of view), fine optical axis direction adjustment is easily performed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a communication device and a communication system that communicates using light, and also to a method for adjusting an optical axis direction in such a communication device. [Background technology]

[0002] Expectations for high-speed wireless communication, such as 5th generation wireless communication, are rising. In addition, attention is being paid to technology that will realize part of a high-speed wireless communication network using wireless communication using light (wavelength 1mm or less) instead of wireless communication using radio waves (wavelength 1mm or more). Wireless communication using light is not restricted by the Radio Law, unlike wireless communication using radio waves. In addition, light has a high tendency to travel in a straight line and is not emitted in all directions like radio waves, so it is advantageous from the perspective of security. In particular, wireless communication using visible light is considered to have a low risk of unexpected eavesdropping. Wireless communication using light is not suitable for communication with mobile stations such as mobile phone terminals, but is suitable for communication between fixed stations such as base stations and relay stations.

[0003] Incidentally, when performing wireless communication using light, it is necessary to adjust the optical axis direction of the optical system in the receiving communication device so that it coincides with the direction of the transmitting communication device as seen from the receiving communication device. Examples of documents disclosing techniques for adjusting the optical axis direction of the optical system in the receiving communication device include Patent Documents 1 to 3. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-163041 [Patent Document 2] JP2004-15135A [Patent Document 3] JP2005-86392A Summary of the Invention [Problem to be solved by the invention]

[0005] However, a communication device (receiving communication device) equipped with a lens for concentrating signal light has the following problems. That is, when a lens with a short focal length (wide angle of view) is used as a lens for concentrating signal light, it is easy to perform a rough optical axis direction adjustment to fit the light source of the signal light (transmitting communication device) into the angle of view, but it is difficult to perform a fine optical axis direction adjustment to match the center of the light source of the signal light with the center of the angle of view. On the other hand, when a lens with a long focal length (narrow angle of view) is used as a lens for concentrating signal light, it is easy to perform a fine optical axis direction adjustment to match the light source of the signal light with the center of the angle of view, but it is difficult to perform a rough optical axis direction adjustment to fit the light source of the signal light into the angle of view.

[0006] One aspect of the present invention has been made in consideration of the above problems, and aims to facilitate both fine and coarse optical axis direction adjustment in a communication device equipped with a lens for concentrating signal light. [Means for solving the problem]

[0007] A communication device according to one aspect of the present invention is characterized in that it includes a zoom lens with a variable focal length as a lens for converging signal light. Effect of the Invention

[0008] According to one aspect of the present invention, by setting the focal length of the zoom lens short (wide angle of view), coarse adjustment of the optical axis direction can be easily performed, and by setting the focal length of the zoom lens long (narrow angle of view), fine adjustment of the optical axis direction can be easily performed. [Brief description of the drawings]

[0009] [Figure 1] 1 is a side view showing a configuration of a communication device according to an embodiment of the present invention; [Diagram 2] 4 is a flowchart showing the flow of an optical axis direction adjustment method in the communication device of FIG. [Diagram 3]2 is a transition diagram showing a transition of an image represented by an output signal of a signal light detector included in the communication device of FIG. 1. [Figure 4] 2 is a diagram showing a configuration of a communication system including the communication device of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 1.Communication Device Configuration The configuration of a communication device 1 according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a side view showing the configuration of the communication device 1.

[0011] The communication device 1 is a device for receiving signal light SL, and includes a zoom lens 11, a receiving circuit 12, and an optical fiber 13, as shown in FIG. 1. The zoom lens 11 is a lens with a variable focal length for collecting the signal light SL. The receiving circuit 12 is a circuit for converting the signal light SL collected by the zoom lens 11 into an electric signal. In this embodiment, the light collected by the zoom lens 11 is guided to the receiving circuit 12 by the optical fiber 13. The signal light SL may be visible light having a wavelength of 360 nm or more and less than 760 nm, or infrared light having a wavelength of 760 nm or more and 1 mm or less. If the wavelength of the signal light SL is 1000 nm or more and 1650 nm or less (more preferably 1290 nm or more and 1610 nm or less), it becomes easy to generate the signal light SL using a light source for optical communication, such as a YAG laser.

[0012] In this embodiment, an optical system consisting of a focus group 11a, a magnification group 11b, a correction group 11c, and an imaging group 11d is used as the zoom lens 11. Here, the focus group 11a, the correction group 11c, and the imaging group 11d each consist of one or more lenses and have a positive refractive index. The magnification group 11b consists of one or more lenses and has a negative refractive index. However, the configuration of the zoom lens 11 is arbitrary, and the present invention is not limited to this. For example, the zoom lens 11 may include an anti-vibration group (not shown). In this case, it is possible to suppress the fluctuation of the focal position of the signal light SL that may occur when the zoom lens 11 vibrates.

[0013] 1, the communication device 1 further includes a focal length adjustment mechanism 14 and an optical axis direction adjustment mechanism 15. The focal length adjustment mechanism 14 is a mechanism for adjusting the focal length of the zoom lens 11. The optical axis direction adjustment mechanism 15 is a mechanism for adjusting the optical axis direction of the zoom lens 11.

[0014] In this embodiment, a mechanism (e.g., a cam mechanism) that adjusts the focal length of the zoom lens 11 by moving the magnification variable group 11b and the correction group 11c in the optical axis direction is used as the focal length adjustment mechanism 14. Also, in this embodiment, a mechanism (e.g., a camera platform) that adjusts the optical axis direction of the zoom lens 11 by changing the elevation angle and azimuth angle of a lens barrel that houses the zoom lens 11 is used as the optical axis direction adjustment mechanism 15. However, the configurations of the focal length adjustment mechanism 14 and the optical axis direction adjustment mechanism 15 are arbitrary, and the present invention is not limited thereto.

[0015] As shown in FIG. 1, the communication device 1 further includes a half mirror 16, a signal light detector 17, and a control circuit 18. The half mirror 16 is an optical element for splitting the signal light SL transmitted through the zoom lens 11 into transmitted light and reflected light. The signal light detector 17 is a detector for detecting the reflected light reflected by the half mirror 16 from the signal light SL transmitted through the zoom lens 11. The control circuit 18 is a circuit for specifying the light source direction of the signal light SL by referring to the output signal of the signal light detector 17, and for controlling the focal length adjustment mechanism 14 and the optical axis direction adjustment mechanism 15 based on the specified light source direction. Here, the light source direction of the signal light SL refers to the direction in which the light source of the signal light SL (for example, the communication device on the transmitting side) exists as viewed from the communication device 1. It should be noted that the transmitted light transmitted through the half mirror 16 from the signal light SL transmitted through the zoom lens 11 is input to the receiving circuit 12 via the optical fiber 13.

[0016] In this embodiment, a two-dimensional image sensor such as a CCD (Charge Coupled Device) is used as the signal light detector 17. Therefore, the output signal of the signal light detector 17 is an image including the light source of the signal light SL (the communication device that transmits the signal light SL) as a subject. When the focal length of the zoom lens 11 is changed by the focal length adjustment mechanism 14, the angle of view of this image changes. However, the configuration of the signal light detector 17 is arbitrary, and the present invention is not limited to this. For example, a set of photodiodes arranged in a matrix may be used as the signal light detector 17. Furthermore, when an anti-vibration group is included in the optical system (for example, the zoom lens 11) included in the communication device 1, it is possible to specify the light source direction of the signal light SL by the position and / or direction of the anti-vibration group. In this case, instead of specifying the light source direction of the signal light SL by referring to the output signal of the signal light detector 17, the light source direction may be specified by referring to a signal indicating the position and / or direction of the anti-vibration group.

[0017] In this embodiment, the control circuit 18 uses a circuit including a processor (arithmetic device) such as a CPU (Central Processing Unit), a main memory (main storage device) such as a semiconductor RAM (Random Access Memory), and an auxiliary memory (auxiliary storage device) such as an HDD (Hard Disk Drive). The processor loads a program stored in the auxiliary memory onto the memory, and controls the focal length adjustment mechanism 14 and the optical axis direction adjustment mechanism 15 by executing instructions included in the program loaded onto the memory. However, the configuration of the control circuit 18 is arbitrary, and the present invention is not limited thereto.

[0018] In this embodiment, the communication device 1 has a function of adjusting the optical axis direction before starting communication. This optical axis direction adjustment is realized by controlling the focal length adjustment mechanism 14 so that the focal length of the zoom lens 11 becomes shorter than the focal length during communication, and then controlling the optical axis direction adjustment mechanism 15 so that the optical axis direction of the zoom lens 11 approaches the light source direction of the signal light SL. Details of the optical axis direction adjustment method S1 in the communication device 1, which is realized by the control of the control circuit 18, will be described later with reference to the drawings.

[0019] 2. Flow of optical axis direction adjustment method The flow of the optical axis direction adjustment method S1 in the communication device 1 will be described with reference to Fig. 2. Fig. 2 is a flowchart showing the flow of the optical axis direction adjustment method S1 in the communication device 1.

[0020] The optical axis direction adjustment method S1 includes steps S101 to S113 which will be described below.

[0021] Steps S101 to S105 are steps for setting the optical axis direction of the zoom lens 11 so that the light source of the signal light SL (hereinafter referred to as the "signal light source") is included in the angle of view when the focal length f of the zoom lens 11 is at its minimum (the angle of view is at its maximum).

[0022] Step S101 is a step in which the control circuit 18 controls the focal length adjustment mechanism 14 so that the focal length f of the zoom lens 11 becomes the minimum value fmin. Step S102 is a step in which the control circuit 18 judges whether or not the signal light source is included in the angle of view by referring to the output signal of the signal light detector 17. Step S103 is a step in which the control circuit 18 controls the optical axis direction adjustment mechanism 15 so that the optical axis direction of the zoom lens 11 changes by a predetermined angle. This step S103 is executed when the previous step S102 is judged as "NO". Step S104 is a step in which the control circuit 18 judges whether or not the optical axis direction of the zoom lens 11 covers the movable range. Step S105 is a step in which the control circuit 18 outputs an error message indicating that the signal light source cannot be included in the angle of view. This step S105 is executed when the previous step S104 is judged as "YES".

[0023] Steps S106 to S110 are steps for gradually increasing the focal length f of the zoom lens 11 (gradually decreasing the angle of view) while gradually moving the optical axis direction of the zoom lens 11 closer to the light source direction of the signal light SL.

[0024] Step S106 is a step in which the control circuit 18 specifies the position P of the signal light source in the angle of view (more precisely, the position P of the center of the image of the signal light source in the image represented by the output signal of the signal light detector 17) by referring to the output signal of the signal light detector 17. The position of the signal light source in the angle of view represents the direction in which the signal light source is present as seen from the communication device 1. Step S107 is a step in which the control circuit 18 determines whether the position P of the signal light source is included in a predetermined area A1 including the center of the angle of view. Step S108 is a step in which the control circuit 18 controls the optical axis direction adjustment mechanism 15 so that the optical axis direction of the zoom lens 11 is changed by a predetermined angle. This step S108 is executed when the previous step S107 is determined as "NO". Note that the amount of change in the optical axis direction of the zoom lens 11 in this step S108 is set to be smaller than the amount of change in the optical axis direction of the zoom lens 11 in the above-mentioned step S103. Step S109 is a step in which the control circuit 18 controls the focal length adjustment mechanism 14 so that the focal length f of the zoom lens 11 increases by a predetermined increment Δf. This step S109 is executed when the previous step S107 is judged as "YES". Step S110 is a step in which the control circuit 18 judges whether the focal length f of the zoom lens 11 coincides with the maximum value fmax. Steps S106 to S109 are repeated until the step S110 is judged as "YES".

[0025] Steps S111 to S113 are steps for moving the optical axis direction of the zoom lens 11 closer to the light source direction of the signal light SL when the focal length f of the zoom lens 11 is at its maximum (when the angle of view is at its minimum).

[0026] Step S111 is a step in which the control circuit 18 specifies the position P of the signal light source in the angle of view by referring to the output signal of the signal light detector 17. Step S112 is a step in which the control circuit 18 judges whether the position P of the signal light source is included in a predetermined area A2 including the center of the angle of view. The area A2 referred to in this step S112 is an area smaller than the area A1 referred to in the above-mentioned step S107. Step S113 is a step in which the control circuit 18 controls the optical axis direction adjustment mechanism 15 so that the optical axis direction of the zoom lens 11 changes by a predetermined angle. This step S1113 is executed when the previous step S112 is judged as "NO". The amount of change in the optical axis direction of the zoom lens 11 in this step S113 is set to be smaller than the amount of change in the optical axis direction of the zoom lens 11 in the above-mentioned step S108. Steps S111 and S113 are repeated until the judgment in step S112 is "YES".

[0027] After carrying out the optical axis direction adjustment method S1 described above, the communication device 1 performs data communication with a transmitting communication device, which is a signal light source, in a state in which the focal length f of the zoom lens 11 is at its maximum.

[0028] In this embodiment, the optical axis direction adjustment mechanism 15 is used for the optical axis direction adjustment in step S108 (optical axis direction adjustment before minimizing the angle of view) and the optical axis direction adjustment in step S113 (optical axis direction adjustment after minimizing the angle of view). However, the present invention is not limited to this. For example, the optical axis direction adjustment mechanism 15 (e.g., a camera platform, etc.) may be used for the optical axis direction adjustment in step S108, and a tracking mechanism (e.g., an anti-vibration group, etc.) capable of faster and finer adjustment than the optical axis direction adjustment mechanism 15 may be used for the optical axis direction adjustment in step S113.

[0029] 3. Example of how to adjust the optical axis direction An example of the optical axis direction adjustment method S1 will be described with reference to Fig. 3. Fig. 3 is a transition diagram of an image (hereinafter, referred to as a "detected image") represented by an output signal of the signal light detector 17. In this example, the minimum value fmin of the focal length f of the zoom lens 11 is set to 18 mm, and the maximum value fmax is set to 55 mm.

[0030] The detected image Img1 is an image obtained when it is determined in step S102 that the signal light source is included in the angle of view after step S101 of setting the focal length f of the zoom lens 11 to 18 mm is executed and then step S103 of changing the optical axis of the zoom lens 11 is repeated. At this time, the optical axis direction of the zoom lens 11 approaches the light source direction of the signal light SL to such an extent that the signal light source is included in the angle of view when the focal length f is 18 mm.

[0031] The detected image Img2 is an image obtained when step S108 for changing the optical axis direction of the zoom lens 11 is repeated and it is determined in step S107 that the position P of the signal light source is included in the region A1. At this time, the optical axis direction of the zoom lens 11 approaches the light source direction of the signal light SL to such an extent that the signal light source is included in the region A1 when the focal length f is 18 mm.

[0032] The detected image Img3 is an image obtained after step S109 is executed to change the focal length f of the zoom lens 11 to 30 mm. It can be seen that the position P of the signal light source is moved out of the area A1 due to the focal length f of the zoom lens 11 becoming shorter (the angle of view becoming narrower).

[0033] The detected image Img4 is an image obtained when step S108 for changing the optical axis direction of the zoom lens 11 is repeated and it is determined in step S107 that the position P of the signal light source is included in the region A1. At this time, the optical axis direction of the zoom lens 11 approaches the light source direction of the signal light SL to such an extent that the signal light source is included in the region A1 when the focal length f is 30 mm.

[0034] The detected image Img5 is an image obtained after step S109 is executed to change the focal length f of the zoom lens 11 to 42 mm. It can be seen that the position P of the signal light source is moved out of the area A1 due to the focal length f of the zoom lens 11 becoming shorter (the angle of view becoming narrower).

[0035] The detected image Img6 is an image obtained when step S108 for changing the optical axis direction of the zoom lens 11 is repeated and it is determined in step S107 that the position P of the signal light source is included in the region A1. At this time, the optical axis direction of the zoom lens 11 approaches the light source direction of the signal light SL to such an extent that the signal light source is included in the region A1 when the focal length f is 42 mm.

[0036] The detected image Img7 is an image obtained after step S109 is executed to change the focal length f of the zoom lens 11 to 55 mm. It can be seen that the position P of the signal light source is moved out of the area A2 due to the focal length f of the zoom lens 11 becoming shorter (the angle of view becoming narrower).

[0037] Thereafter, step S1113 for changing the optical axis direction of the zoom lens 11 is repeated, and the detected image Img8 is an image obtained when it is determined in step S112 that the position P of the signal light source is included in the region A2. At this time, the optical axis direction of the zoom lens 11 approaches the light source direction of the signal light SL to such an extent that the signal light source is included in the region A2 when the focal length f is 55 mm.

[0038] 4.Communication System Configuration The configuration of a communication system 5 including the communication device 1 will be described with reference to Fig. 4. Fig. 4 is a diagram showing the configuration of the communication system 5.

[0039] 4, the communication system 5 includes a communication device 1 and a communication device 2. As described above, the communication device 1 is a device that receives signal light SL. The communication device 2 is a device that transmits signal light SL.

[0040] The communication device 2 is configured to transmit a signal light SL, which is a diverging light, before starting data communication with the communication device 1. Therefore, if the communication device 1 is present within the light cone of the signal light SL, the optical axis direction of the zoom lens 11 can be brought closer to the light source direction of the signal light SL, that is, the direction in which the communication device 2 is present as viewed from the communication device 1, by performing the optical axis direction adjustment method S1 described above. Examples of timings for performing such optical axis direction adjustment include (1) when one or both of the communication devices 1 and 2 are newly installed or reinstalled, or (2) when one or both of the communication devices 1 and 2 are maintained. It is also effective to adopt a configuration in which such optical axis direction adjustment is performed periodically or automatically when the communication quality is degraded, thereby maintaining the accuracy of the optical axis direction adjustment at a certain level or higher.

[0041] The communication device 1 may have a transmission function similar to that of the communication device 2. The communication device 2 may have a reception function similar to that of the communication device 1. In this case, two-way communication can be realized between the communication device 1 and the communication device 2.

[0042] In addition, in the communication system 5, the signal light SL used when adjusting the optical axis direction and the signal light SL used when communicating may be signal light of the same wavelength or signal light of different wavelengths. In this case, in the communication device 1, the optical path of the signal light used when adjusting the optical axis direction may be different from the optical path of the signal light used when communicating. Such an optical system can be easily realized by using a prism with a different refraction angle depending on the wavelength, or a half mirror with a different transmittance and reflectance depending on the wavelength. In this case, the signal light SL used when adjusting the optical axis direction in the atmosphere is preferably light with a wavelength of 800 nm or more, and from the viewpoint of eye safety, it is particularly preferable that the wavelength is 1400 nm or more. In addition, the signal light SL used when communicating in the atmosphere is preferably light with a wavelength of 1000 nm or more and 1650 nm or less. This allows the optical axis direction adjustment to be performed while communicating, so that it is possible to deal with, for example, a deviation in the optical axis direction that occurs during communication. When the communication system 5 is installed on the seabed, it is preferable to use light belonging to a wavelength band of 400 nm to 550 nm as the signal light SL. In this case, the wavelength band of 400 nm to 550 nm may be divided into two wavelength bands, and one wavelength band may be used when adjusting the optical axis direction, and the other wavelength band may be used when performing communication.

[0043] 5. Features and Effects of the Communication Device, Optical Axis Direction Adjustment Method, and Communication System As described above, the communication device 1 according to this embodiment includes the zoom lens 11 with a variable focal length as a lens for collecting the signal light SL.

[0044] Therefore, by lengthening the focal length of the zoom lens 11 (narrowing the angle of view), it becomes easy to make fine adjustments to the optical axis direction of the lens, which was difficult in a communication device equipped with a wide-angle lens with a short focal length. Also, by shortening the focal length of the zoom lens 11 (widening the angle of view), it becomes easy to make rough adjustments to the optical axis direction of the lens, which was difficult in a communication device equipped with a telephoto lens with a long focal length.

[0045] In addition, the communication device 1 of this embodiment further includes a focal length adjustment mechanism 14 that adjusts the focal length of the zoom lens 11, an optical axis direction adjustment mechanism 15 that adjusts the optical axis direction of the zoom lens, and a control circuit 18 that controls the focal length adjustment mechanism 14 so that the focal length of the zoom lens 11 during optical axis direction adjustment is shorter than the focal length during communication, and then controls the optical axis direction adjustment mechanism 15 so that the optical axis direction of the zoom lens 11 approaches the light source direction of the signal light SL.

[0046] Therefore, even if the signal light source is located at a position that is not included in the angle of view when the focal length of the zoom lens 11 is the same as the focal length during communication, the optical axis direction of the zoom lens 11 can be automatically moved closer to the light source direction of the signal light SL.

[0047] In addition, the communication device 1 of this embodiment further includes a signal light detector 17 that detects the signal light SL that has passed through the zoom lens 11, and the control circuit 18 identifies the light source direction of the signal light SL by referring to the output signal of the signal light detector 17.

[0048] Therefore, the light source direction of the signal light SL can be easily identified.

[0049] In the communication device 1 according to this embodiment, the signal light SL is visible light or infrared light.

[0050] Therefore, unlike communication devices using radio waves, the communication device 1 can be used without being restricted by the Radio Law. Also, since optical components for cameras (visible light cameras or infrared cameras) can be reused, it is easy to reduce the manufacturing cost of the communication device 1. Furthermore, particularly when the signal light SL is visible light, the risk of unexpected communication interception can be reduced compared to communication devices using light that does not belong to the visible light range.

[0051] The optical axis direction adjustment method S1 according to this embodiment is an optical axis direction adjustment method for adjusting the optical axis direction of the zoom lens 11 in the communication device 1 including the zoom lens 11 that collects the signal light SL. The optical axis direction adjustment method S1 according to this embodiment includes step S101 for shortening the focal length of the zoom lens 11 during the optical axis direction adjustment to be shorter than the focal length during communication, and step S103 for moving the optical axis direction of the zoom lens 11 closer to the light source direction of the signal light SL after performing step S101.

[0052] Therefore, even if the light source of the signal light SL is located at a position that is not included in the angle of view when the focal length of the zoom lens 11 is the same as the focal length during communication, the optical axis direction of the zoom lens 11 can be automatically moved closer to the direction of the light source of the signal light SL.

[0053] Moreover, the communication system 5 according to this embodiment includes a first communication device that receives the signal light SL and a second communication device that transmits the signal light SL, and the first communication device is the communication device 1 described above.

[0054] Therefore, by lengthening the focal length of the zoom lens 11 (narrowing the angle of view), it becomes easy to make fine adjustments in the optical axis direction of the lens (the zoom lens 11 in this embodiment), which was difficult in a communication device equipped with a wide-angle lens with a short focal length. Also, by shortening the focal length of the zoom lens 11 (widening the angle of view), it becomes easy to make rough adjustments in the optical axis direction of the lens (the zoom lens 11 in this embodiment), which was difficult in a communication device equipped with a telephoto lens with a long focal length.

[0055] 5. Additional Notes The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Other embodiments obtained by appropriately combining the technical means disclosed in the above-described embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0056] 1. Communications equipment 11 Zoom Lens 12 Receiving circuit 13. Optical Fiber 14 Focal length adjustment mechanism 15 Optical axis direction adjustment mechanism 16 Half Mirror 17 Signal Photodetector 18 Control circuit

Claims

1. A variable focal length zoom lens as a lens for converging the signal light; a focal length adjustment mechanism for adjusting the focal length of the zoom lens; an optical axis direction adjustment mechanism for adjusting the optical axis direction of the zoom lens; a control circuit for controlling the focal length adjustment mechanism so that a focal length during adjustment of the optical axis direction of the zoom lens is shorter than a focal length during communication, and then controlling the optical axis direction of the zoom lens to approach a light source direction of the signal light, which is divergent light, transmitted during the optical axis direction adjustment, and then, when the focal length during adjustment of the optical axis direction is less than a maximum focal length, controlling the optical axis direction adjustment mechanism so that the optical axis direction of the zoom lens is approached stepwise to the light source direction of the signal light, which is divergent light, while increasing the focal length stepwise so that the position of the light source of the signal light is included in a predetermined first region including the center of an angle of view at each step, and controlling the optical axis direction adjustment mechanism so that the optical axis direction of the zoom lens is approached stepwise to the light source direction of the signal light, which is divergent light, so that the position of the light source of the signal light is included in a predetermined second region including the center of the angle of view and smaller than the first region when the focal length is maximum; Equipped with A communication device comprising:

2. a signal light detector for detecting a signal light transmitted through the zoom lens, the control circuit refers to an output signal of the signal light detector to specify a light source direction of the signal light; 2. The communication device according to claim 1 .

3. The signal light is visible light or infrared light.

3. The communication device according to claim 1 or 2.

4. 1. A method for adjusting an optical axis direction of a zoom lens in a communication device that receives a diverging signal light and adjusts the optical axis direction of the zoom lens, the method comprising: a step of making a focal length of the zoom lens during optical axis direction adjustment shorter than a focal length during communication; and after performing the step, moving an optical axis direction of the zoom lens toward a light source direction of the signal light, an optical axis direction adjustment method for adjusting a focal length of the zoom lens, the optical axis direction of the zoom lens being increased stepwise while gradually approaching a direction of a light source of the signal light, which is a diverging light, so that a position of the light source of the signal light is included in a predetermined first region including a center of an angle of view at each step when the focal length of the zoom lens is less than a maximum focal length, and when the focal length is at a maximum, the optical axis direction of the zoom lens being increased stepwise while gradually approaching a direction of a light source of the signal light, which is a diverging light, so that a position of the light source of the signal light is included in a predetermined second region including the center of an angle of view and which is smaller than the first region.

5. a first communication device that receives a signal light; and a second communication device that transmits the signal light, which is a divergent light when the optical axis direction is adjusted, The first communication device is a communication device according to any one of claims 1 to 3. A communication system comprising:

Images