Spatial optical transmission apparatus

Optical transmission apparatuses are disclosed. An example apparatus includes: a circulator that receives and provides a first signal at a first port and at a second port respectively, and receives and provides a second signal at the second port and at a third port respectively; a projecting lens movable perpendicular to an optical axis of a signal through the second port; a receiving lens movable perpendicular to an optical axis of a signal through the third port; a spectroscope that splits a signal through the receiving lens into transmitted light and reflected light; a sensor that detects an optical axis position of either the transmitted light or reflected light; and a controller that adjusts a position of the receiving lens and/or the projecting lens based on the optical axis position, and adjusts the optical axis to cause the other of the transmitted light or reflected light to enter a cable.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a U.S. National Stage filing under 35 U.S.C. § 371 of PCT Application No. PCT/JP2021/007875, filed Mar. 2, 2021, which claims priority to Japanese Application No. 2020-106236, filed Jun. 19, 2020, which are incorporated herein by reference, in their entirety, for any purpose.

TECHNICAL FIELD

The present invention relates to a spatial optical transmission apparatus capable of automatically controlling optical axis adjustment for a wide range of optical axis deviation.

BACKGROUND ART

There is a technology of spatial optical transmission as one of means for non-contact communication between two points. This spatial optical transmission is optical data communication, and thus is a technology allowing high-speed and high-capacity transfer. In order to reliably perform communication between two distant points, it is necessary to use an optical signal having high directivity, and it is necessary to accurately perform optical axis alignment.

For example, Patent Literature 1 discloses a spatial optical transmission apparatus.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2018-170647 A

SUMMARY OF INVENTION

Technical Problem

The spatial optical transmission apparatus described in Patent Literature 1 can automatically control optical axis adjustment for a wide range of optical axis deviation. The apparatus requires a transmission-side apparatus used for transmission and a reception-side apparatus used for reception, and there is no problem with unidirectional data transmission. However, in order to realize bidirectional data communication, it is necessary to prepare two optical axes for data communication. If two optical axes are prepared, it is difficult to adopt the movement of the roll for control at the time of optical axis alignment, and as a result, there is a problem that the difficulty of optical axis alignment increases.

The present invention has been made in view of the above problem, and it is an object of the present invention to provide a spatial optical transmission apparatus capable of transmission and reception on one optical axis in common between transmission and reception.

Solution to Problem

A spatial optical transmission apparatus according to the present invention is a spatial optical transmission apparatus that transmits an optical signal emitted from a transmission optical fiber cable to a counterpart side, receives an optical signal from the counterpart side and causes the optical signal to enter a reception optical fiber cable, and realizes communication by spatial optical transmission, the spatial optical transmission apparatus including: an optical circulator configured to output and project an optical signal emitted from the transmission optical fiber cable and input to a first port, from a second port to a counterpart side, and output an optical signal input from the counterpart side to the second port, from a third port; at least one or more light projecting movable lenses positionally adjustable in a plane substantially perpendicular to an optical axis of an optical signal passing through the second port outside the second port of the optical circulator; at least one or more light receiving movable lenses positionally adjustable in a plane substantially perpendicular to an optical axis of an optical signal passing through the third port outside the third port of the optical circulator; at least one or more spectroscopes configured to split an optical signal having passed through the light receiving movable lens to transmitted light and reflected light; at least one or more position sensors configured to detect a position of an optical axis using either one of the transmitted light or reflected light from the spectroscope; and a control unit configured to perform position adjustment of the light receiving movable lens and/or the light projecting movable lens on the basis of the optical axis position detected by the position sensor, and control optical axis adjustment so that the other of the transmitted light or reflected light from the spectroscope is appropriately incident on the reception optical fiber cable.

In the spatial optical transmission apparatus according to the present invention, the light projecting movable lens is controlled so that a drive amount of the light projecting movable lens is the same as a drive amount of the receiving movable lens closest to the optical circulator on an optical signal path through which an optical signal output from the third port is incident on the reception optical fiber cable, whereby the light projecting movable lens and the receiving movable lens are driven in conjunction with each other.

In the spatial optical transmission apparatus according to the present invention, a first receiving movable lens, a first spectroscope, a second receiving movable lens, and a second spectroscope are sequentially provided on an optical signal path through which an optical signal output from the third port is incident on the reception optical fiber cable, and light branched from the path by the first spectroscope is input to a first position sensor, and light branched from the path by the second spectroscope is input to a second position sensor, and the control unit performs first PID control to perform PID control on the first receiving movable lens based on the optical axis position detected by the first position sensor, and performs second PID control to perform PID control on the second receiving movable lens based on the optical axis position detected by the second position sensor.

In the spatial optical transmission apparatus according to the present invention, a single control amount of the movable lens with respect to a shift amount from a center of the optical axis position detected by the position sensor is set to be different between the first PID control and the second PID control.

The spatial optical transmission apparatus according to the present invention further includes: a laser light source configured to transmit beacon light to a counterpart side; a high-speed camera configured to detect beacon light transmitted from the counterpart side; and an electronic platform that is disposed in a lower portion of a housing and is positionally adjustable by moving the entire housing within a predetermined range, and the control unit calculates optical barycentric coordinates of the beacon light detected by the high-speed camera, and controls the electronic platform such that an imaging axis of the high-speed camera is positioned at a center of the optical barycentric coordinates.

A spatial optical transmission apparatus according to the present invention is a spatial optical transmission apparatus that transmits an optical signal emitted from a transmission optical fiber cable to a counterpart side, receives an optical signal from the counterpart side and causes the optical signal to enter a reception optical fiber cable, and realizes communication by spatial optical transmission, the spatial optical transmission apparatus including: an optical circulator configured to output and project an optical signal input to a first port and emitted from the transmission optical fiber cable, from a second port to a counterpart side, and output an optical signal input from the counterpart side to the second port, from a third port; at least one or more light projecting movable lenses positionally adjustable in a plane substantially perpendicular to an optical axis of an optical signal passing through the second port outside the second port of the optical circulator; at least one or more light receiving movable lenses positionally adjustable in a plane substantially perpendicular to an optical axis of an optical signal passing through the third port outside the third port of the optical circulator; at least one or more spectroscopes configured to split an optical signal having passed through the light receiving movable lens to transmitted light and reflected light; an optical power detector configured to measure optical reception intensity of communication light incident on the reception optical fiber cable; and a control unit configured to measure light reception intensity by the optical power detector at a current control position of the light receiving movable lens to be controlled and at one or more measurement positions of the light receiving movable lens driven by a predetermined control amount from the current control position, and control the light receiving movable lens to be located at the measurement position with the highest light reception intensity.

Advantageous Effects of Invention

According to the present invention, the optical circulator is adopted to make the light projecting optical axis and the light receiving optical axis uniaxial, so that it is possible to reduce the difficulty of optical axis alignment in the case of performing bidirectional spatial optical transmission. The control of the light projecting movable lens is performed in conjunction with the control of the receiving movable lens, so that it is possible to simultaneously realize the control of the light receiving axis and the control of the light projecting axis. The two lenses of the first receiving movable lens and the second receiving movable lens are provided in the light receiving optical axis path to perform the first PID control and the second PID control in two stages, thereby enhancing the accuracy of optical axis alignment. In addition, by controlling the electronic platform according to the optical barycentric position of the beacon light, the accuracy of optical axis alignment is further improved.

The shift of the optical axis from the center can be grasped by the beacon light in a situation where the optical axis may be shifted, such as communication with a mobile body, thereby, enhancing tracking capability for returning the optical axis to the original position even if a change occurs in the direction in which the optical axis is shifted.

In addition, according to the present invention, the light reception intensity in the reception optical fiber cable is measured by the optical power detector at the current control position of the light receiving movable lens to be controlled and at one or more measurement positions of the light receiving movable lens driven by the predetermined control amount from the current control position, and the light receiving movable lens is controlled so as to be located at the measurement position with the highest light reception intensity. Therefore, it is possible to perform control so as to maximize the actual light reception intensity.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, an example of a spatial optical transmission apparatus will be described with reference to the drawings.FIG.1is an explanatory diagram illustrating an example of a configuration of a spatial optical transmission apparatus100according to the present invention. Referring toFIG.1, description will be provided on the assumption that bidirectional spatial optical transmission communication is performed between a spatial optical transmission apparatus100A and a spatial optical transmission apparatus100B. The spatial optical transmission apparatus100A and the spatial optical transmission apparatus100B will be described as two apparatuses having the same performance as an example. Thus, functions with the same reference signs are the same functions unless otherwise described as distinguished from each other.

The spatial optical transmission apparatus100includes a housing10and an electronic platform11supporting the housing. Various configurations are stored inside the housing10. A transmission optical fiber cable12is for propagating an optical signal for transmission. A reception optical fiber cable13is for propagating an optical signal for reception. An optical antenna lens14is configured to first receive light from a counterpart side. A light projecting movable lens15is a movable lens whose position is adjustable in a plane substantially perpendicular to the optical axis of an optical signal, and is used to adjust the light projecting axis. An optical circulator16is an optical device configured to output an optical signal emitted from the transmission optical fiber cable12input to a first port from a second port and project the optical signal to the counterpart side, and output an optical signal from the counterpart side input to the second port from a third port. A lens17is a lens for collecting an optical signal emitted from the transmission optical fiber cable12. A first light receiving movable lens13is a movable lens whose position is adjustable in a plane substantially perpendicular to a light receiving optical axis of an optical signal, and is used to adjust the light receiving optical axis. A spectroscope19is configured to split the optical signal having passed through the first light receiving movable lens18into transmitted light and reflected light. For example, a beam splitter or the like is used as the spectroscope19. A lens20is a lens for condensing the reflected light from the spectroscope19. A first position sensor21is configured to detect the position of the optical axis using the reflected light from the spectroscope19. For example, a quadrant photodetector (QPD) or the like is used as the first position sensor21. A second light receiving movable lens22is a movable lens whose position is adjustable in a plane substantially perpendicular to the light receiving optical axis of an optical signal, and is used to adjust the light receiving optical axis. A spectroscope23is configured to split the optical signal having passed through the second light receiving movable lens22into transmitted light and reflected light. For example, a beam splitter or the like is used as the spectroscope23. A lens24is a lens for condensing reflected light from the spectroscope23. A second position sensor25is configured to detect the position of the optical axis using the reflected light from the spectroscope23. For example, a quadrant photodetector (QPD) or the like is used as the second position sensor25. A lens26is a lens for condensing an optical signal to be incident on the reception optical fiber cable13. A laser light source27is configured to transmit beacon light. A high-speed camera28is configured to detect beacon light from the counterpart side. A control unit29is configured to execute various types of control necessary in the spatial optical transmission apparatus100. Referring toFIG.1, as an image of region setting with QPDs employed as the first position sensor21and the second position sensor25, regions A to D are set in four corresponding regions of a circle. As illustrated inFIG.1, in two spatial optical transmission apparatuses100A and100B which are communication partners, setting the four regions to be mirror images of each other produces an effect of stabilizing control that is performed based on the same control program.

FIG.2is an explanatory diagram illustrating a mechanism of an optical circulator. As illustrated inFIG.2(a), as a path at the time of transmission, transmission light of non-polarized light input to the first port is split by a polarizing beam splitter into two polarized light beams, P-polarized light beam and S-polarized light beam orthogonal to each other, and these beams are rotated by 45° each in the same direction, 90° in total, by a Faraday rotator and a ½ wavelength plate, such that the P-polarized light beam is converted into S-polarized light beam and the S-polarized light beam is converted into P-polarized light beam, then multiplexed by another polarizing beam splitter, and output from a second port. Further, as illustrated in2(b), as a path at the time of reception, the transmission light of non-polarized light input to the first port is split into two polarized light beams, P-polarized light beam and S-polarized light beam orthogonal to each other by the polarization beam splitter, and these beams are rotated by 45° by the ½ wavelength plate and are rotated by 45° in the opposite direction by the Faraday rotator and returned to the original state due to the irreciprocity of the Faraday rotator, so that a change of the P-polarized light and the S-polarized light does not occur. Therefore, when multiplexed by the polarization beam splitter, the transmission light is output to a third port instead of the first port. By using the optical circulator of such a mechanism, the communication light of the transmission light and the reception light is uniaxial at the time of spatial optical transmission, but it is possible to selectively use the transmission port and the reception port inside the spatial optical transmission apparatus100. The optical circulator does not need to be based on the principle illustrated inFIG.2as long as the optical circulator functions similarly.

FIG.3is a block diagram illustrating an example of PID control. The light projecting movable lens15, the first light receiving movable lens18, and the second light receiving movable lens22in the spatial optical transmission apparatus100are used to perform optical axis adjustment by their respective control methods. As one of these control methods, it is conceivable to perform Proportional-Integral-Differential Controller (PID) control. As illustrated inFIG.2, first, a target value for the optical axis is input. Specifically, when it is assumed that the path of the reception light or the transmission light is optimal in a case where the position of the optical axis detected by the corresponding position sensor is the center, the coordinate position with the optical axis on the center of the position sensor is set as “0” as the target value.

Next, at a summing point30, a difference between the information on the optical axis position detected by the immediately preceding position sensor (feedback from a pick-off point35) and the target value is calculated and input to a PID controller31. The PID controller31performs PID control based on three elements of the difference (deviation) from the target value, an integral thereof, and a derivative thereof, thereby to determine a control amount for the movable lens. On the basis of this control amount, the movable lens is driven by a control controller33to bring the optical axis position closer to the center. However, in actuality, since there is an influence of disturbance, the displacement amount of the optical axis due to the disturbance from a disturbance circuit36is added at a summing point34to the optical axis position after being driven by the control controller33, and the actual optical axis position is determined.

As a problem of the feedback control, since the control is started after the optical axis position is shifted due to the influence of disturbance (displacement of the optical axis position detected by the position sensor), there is a point where a time delay occurs until the shift is corrected. Therefore, at the stage of detecting the influence of the disturbance, a control amount correction calculation unit37calculates the direction of the positional displacement and the moving distance with respect to the optical axis due to the influence of the disturbance, predicts the next position per unit time, calculates the correction value of the control amount in the direction of canceling the displacement, and adds the correction value from the control amount correction calculation unit37to the control amount from the PID controller31at the addition point32to determine the actual control amount. This makes it possible to immediately reflect the influence of the disturbance in the control amount although the correction value is a minute value.

The light projecting movable lens15, the first light receiving movable lens18, and the second light receiving movable lens22may be subjected to independent PID control. However, for example, the light projecting movable lens15may be controlled by the same drive amount as the drive amount of the first light receiving movable lens18such that the light projecting movable lens15and the first light receiving movable lens18are driven in conjunction with each other. In addition, first PID control related to the driving of the first light receiving movable lens18and second PID control related to the driving of the second light receiving movable lens22may be alternately executed.

FIG.4is a flowchart illustrating an example of a process flow of two-stage PID control. First, a flowchart of light projecting axis control illustrated on the upper side ofFIG.4will be described. The light projecting axis control is first started by the control unit29setting the light projecting movable lens to the initial position (step S101). Next, the control unit29determines whether PID control has been started (step S102). As long as the PID control is not started (S102—N), the control unit29maintains the light projecting movable lens at the initial position. When the PID control has been started (S102—Y), the control unit29drives the light projecting movable lens in conjunction with the drive amount of the first light receiving movable lens (step3103).

Thereafter, as long as the PID control continues to be executed (3102—Y), the control unit29maintains the process of driving the light projecting movable lens in conjunction with the drive amount of the first light receiving movable lens (step S103).

A flowchart of light receiving axis control illustrated on the lower side ofFIG.4will be described. In the light receiving axis control, first, the control unit29determines whether the first PID control has been started (step S201). When the first PID control has been started (S201—Y), the control unit29fetches optical axis position data acquired by the first position sensor (first QPD) (step3202). Next, the control unit29determines whether the acquired optical axis position is located at the center of an optical spot position (step S203). When the acquired optical axis position is located at the center of the optical spot position (S203—Y), the control unit29returns to step S202to acquire the optical axis position data by the first position sensor again without executing the drive control. When the acquired optical axis position is deviated from the center of the optical spot position (S203—N), the control unit29determines the drive amount of the first light receiving movable lens so that the optical axis position moves to the center as specific processing of the first PID control, and executes the drive control (step3204). Next, the control unit29determines whether the second PID control has been started (step S205). When the second PID control has been started (3205-Y), the control unit29fetches optical axis position data acquired by the second position sensor (second QPD) (step S206). Next, the control unit29determines whether the acquired optical axis position is located at the center of an optical spot position (step S207). When the acquired optical axis position is located at the center of the optical spot position (S207—Y), the control unit29returns to step S206to acquire the optical axis position data by the second position sensor again without executing the drive control. When the acquired optical axis position is out of the center of the optical spot position (S207—N), the control unit29determines the drive amount of the second light receiving movable lens so that the optical axis position moves to the center as specific processing of the second PID control, and executes the drive control (step3208). When the drive control of the second light receiving movable lens has completed, the control unit29returns to step S201and repeatedly executes the light receiving axis control from the beginning.

By alternately executing the first PID control and the second PID control as illustrated inFIG.4and driving the light projecting movable lens in conjunction with the drive amount of the first light receiving movable lens determined by the first PID control, it is possible to reliably converge the optical axis alignment. In addition, by setting the control width to be different between the first PID control and the second PID control, for example, setting the first PID control to perform rough control and setting the second PID control to perform fine control, it is possible to expect a reduction in time until convergence.

FIG.5is a flowchart illustrating an example of a process flow of electronic platform control using beacon light. The optical axis position can be detected by the first position sensor21and the second position sensor25in a case where the communication light from the counterpart side can be captured by the optical antenna lens14. If the optical axis is shifted to such an extent that the communication light cannot be captured at all, another optical axis position adjustment unit is required. Therefore, as illustrated inFIG.1, the spatial optical transmission apparatus100may be provided with the laser light source27and the high-speed camera28to realize more rough optical axis position adjustment by driving and controlling the electronic platform11on the basis of the shift amount from the center when the high-speed camera28receives beacon light generated mutually by the laser light source27and the counterpart side. As also illustrated inFIG.1, it is necessary to set the optical axis such that, when the beacon light from the counterpart side is captured at the center of the high-speed camera28, the beacon light transmitted by the own apparatus is captured at the center of the high-speed camera28at the counterpart side. Here, the communication light needs to be an optical signal having high directivity, but the beacon light used only for optical axis adjustment can be picked up at the counterpart side with higher probability by being emitted at a wide angle.

As illustrated inFIG.5, the light reception control of the beacon light is started by the control unit29initiating detection of the beacon light (step S301). When the beacon light has been detected by the high-speed camera28(S301—Y), the control unit29takes in optical barycentric coordinates of the detected beacon light (specifies by calculation) (step S302). Specifically, by calculating the light intensity of the beacon light of each pixel in the captured image having been successfully captured by the high-speed camera28, a pixel (or region) having the strongest light intensity in the captured image can be specified. When a pixel (or region) having the strongest light intensity in the captured image is considered as the optical barycentric coordinates of the beacon light, the optical barycentric coordinates can be estimated as a place where the beacon light has traveled straight, that is, a place where the center optical axis of the laser light source27has collided with the captured image plane. Next, the control unit29determines whether the optical barycentric coordinates of the beacon light are located at the center of the imaging range of the high-speed camera (step S303). If the optical barycentric coordinates of the beacon light are located at the center of the imaging range of the high-speed camera28(S303—Y), it is not necessary to adjust the optical axis. Therefore, the control unit29returns to step S302and takes in the optical barycentric coordinates of the beacon light again without executing the drive control of the electronic platform11. If the optical barycentric coordinates of the beacon light are out of the center of the imaging range of the high-speed camera28(S303—N), the control unit29determines the drive amount of the electronic platform11such that the optical barycentric coordinates of the beacon light move to the center, and executes the drive control (step S304). When the drive control of the electronic platform11has completed, the control unit29returns to step S301and repeatedly executes the light reception control of the beacon light from the beginning.

As described above, by providing both wider optical axis alignment using beacon light and optical axis alignment to move the optical axis position detected by the position sensor to the center by PID control, it is possible to reliably perform optical axis alignment, and it is possible to easily align the optical axis again even in a situation where the aligned optical axis has been shifted due to an irregular change.

The control target may be switched according to the state such that the optical axis adjustment is performed by the electronic platform11when the shift amount of the optical barycentric coordinates of the beacon light from the imaging center is equal to or greater than a predetermined value, and the optical axis adjustment is performed by the movable lens without controlling the electronic platform11when the shift amount is within the predetermined value.

As described above, according to the spatial optical transmission apparatus100of the present invention, the optical circulator is adopted to make the light projecting optical axis and the light receiving optical axis uniaxial, so that it is possible to reduce the difficulty of optical axis alignment in the case of performing bidirectional spatial optical transmission. The control of the light projecting movable lens is performed in conjunction with the control of the receiving movable lens, so that it is possible to simultaneously realize the control of the light receiving axis and the control of the light projecting axis. The two lenses of the first receiving movable lens and the second receiving movable lens are provided in the light receiving optical axis path to perform the first PID control and the second PID control in two stages, thereby enhancing the accuracy of optical axis alignment. In addition, by controlling the electronic platform according to the optical barycentric position of the beacon light, the accuracy of optical axis alignment is further improved.

The shift of the optical axis from the center can be grasped by the beacon light in a situation where the optical axis may be shifted, such as communication with a mobile body, thereby, enhancing tracking capability for returning the optical axis to the original position even if a change occurs in the direction in which the optical axis is shifted.

The above embodiment, has been described on the assumption that the movable lens is structured to be positionally adjustable at least in a plane (X-Y plane) substantially perpendicular to the optical axis of the optical signal. Furthermore, the movable lens may be further positionally adjustable in the optical axis direction (Z-axis direction). By providing the movable lens with an adjustment function in the optical axis direction, it is possible to perform fine adjustment in the Z-axis direction of the movable lens while observing the reception intensity in the reception optical fiber cable13, and set the movable lens to a position where the maximum reception intensity can be obtained.

Second Embodiment

FIG.6is an explanatory diagram illustrating an example of a configuration of a spatial optical transmission apparatus100according to the present invention. The example illustrated inFIG.6is a configuration for performing bidirectional spatial optical transmission on the same optical axis between spatial optical transmission apparatuses100C and100D having the same configuration. The spatial optical transmission apparatuses100C and100D described below measure the optical reception intensity of an optical signal received by an optical power detector and control a light receiving movable lens on the basis of the measurement result to adjust a light reception optical axis. The detailed configuration of the optical apparatuses is not limited to the example illustrated inFIG.6.

In the spatial optical transmission apparatuses100C and100D, various configurations are stored inside the housing10. A transmission optical fiber cable12is for propagating an optical signal for transmission. A reception optical fiber cable13is for propagating an optical signal for reception. An optical antenna lens14is configured to first receive light from a counterpart side. A light projecting movable lens15is a movable lens whose position is adjustable in a plane substantially perpendicular to the optical axis of an optical signal, and is used to adjust the light projecting axis. An optical circulator16is an optical device configured to output an optical signal emitted from the transmission optical fiber cable12input to a first port from a second port and project the optical signal to the counterpart side, and output an optical signal from the counterpart side input to the second port from a third port. A lens17is a lens for collecting an optical signal emitted from the transmission optical fiber cable12. The lens17may also be a movable lens. A spectroscope19is configured to split the optical signal output from the third port of the optical circulator16into transmitted light and reflected light. For example, a beam splitter or the like is used as the spectroscope19. A lens20is a lens for condensing the reflected light from the spectroscope19. A first position sensor21is configured to detect the position of the optical axis using the reflected light from the spectroscope19. For example, a quadrant photodetector (QPD) or the like is used as the first position sensor21. A control unit29is configured to execute various types of control necessary in the spatial optical transmission apparatus100. A retroreflector38is configured to reflect incident light in a direction parallel to and opposite to an incident direction. The retroreflector38is provided in front of the optical antenna lens14so that insertion and extraction can be arbitrarily performed. An optical power detector39is configured to measure the optical reception intensity of an optical signal incident on the reception optical fiber cable13. A light receiving movable lens40is a movable lens whose position is adjustable in a plane substantially perpendicular to the light receiving optical axis of an optical signal, and is used to adjust the light receiving optical axis. An optical axis adjustment platform41is configured to change the posture of the entire optical apparatus system for optical axis adjustment in housing10.

Optical axis adjustment in the spatial optical transmission apparatuses100C and100D illustrated inFIG.6will be described. First, at the places where the spatial optical transmission apparatus100C and the spatial optical transmission apparatus100D are installed, the installation positions of the entire housings10are adjusted so that an optical signal is emitted to a position where the optical antenna lens14on the counterpart side is located. Next, the retroreflector3S of the spatial optical transmission apparatus100D on the counter side is inserted in front of the optical antenna lens14. Then, an optical signal is output from the transmission optical fiber cable12of the spatial optical transmission apparatus100C on the side where the optical axis adjustment is to be performed, and is emitted to the spatial optical transmission apparatus100D on the counterpart side. When the emitted optical signal is incident on the light receiving range of the retroreflector38on the counterpart side, the optical signal is reflected and returned from the retroreflector38and returned. However, when the emitted optical signal is not incident on the light receiving range of the retroreflector38on the counterpart side, the optical signal never returns. When the optical signal is reflected and returned, the optical signal can be received by the first position sensor21via the optical antenna lens14to the spectroscope19. That is, the installation position of the entire housing10is adjusted by searching for the position where the optical signal is to be received by the first position sensor21. In addition, the emission direction of the optical signal may be adjusted by the optical axis adjustment platform41provided inside the housing so as to receive the reflected light from the retroreflector33on the counterpart side.

Then, when the optical axis adjustment related to the emission of the optical signal from one side has completed, the optical axis adjustment related to the emission of an optical signal from the other side is similarly executed. When the optical axis adjustment on both of the sides has completed in this manner, the axes are substantially overlapped, but further fine adjustment is required. As fine adjustment of the optical axis as the initial setting, the optical axis adjustment is also executed for the light projecting movable lens15, the lens17in the case of adopting the movable lens, and the like. In the optical axis adjustment as the initial setting, the adjustment may be performed using the light reception intensity detected by the optical power detector39as a guide.

After the optical axis adjustment using the retroreflectors38, actual bidirectional communication becomes possible. During the actual bidirectional communication, as described in the first embodiment, the position of the light projecting movable lens15is controlled by performing PID control so that the light receiving position of the optical signal approaches the center based on the reception position of the optical signal detected by the first position sensor21.

Furthermore, the spatial optical transmission apparatuses100C and100D according to the second embodiment are each characterized in that the position adjustment of the light receiving movable lens40is controlled on the basis of the measurement result of the light reception intensity by the optical power detector39.

FIG.7is a flowchart illustrating an example of a flow of position control processing of the light receiving movable lens40based on light reception intensity. As illustrated inFIG.7, the position control process is started by the control unit29acquiring the current control position information of the light receiving movable lens40(step S501). Next, the control unit29measures the optical reception intensity of the reception optical fiber cable13by the optical power detector39at the current control position and a plurality of positions obtained by moving the movable lens by a predetermined control amount from the current control position (step S502). Then, the control unit29performs control to move the light receiving movable lens40to a position where the light reception intensity is the highest (step3503), and ends the processing. It is conceivable that the position control process illustrated inFIG.7is executed, for example, at regular time intervals or in a case where the light reception intensity of the reception optical fiber cable13detected by the optical power detector39changes by a predetermined value or more.

FIG.8is an explanatory diagram illustrating an example of a measurement position of light reception intensity. InFIG.8, the magnitude of the light reception intensity is expressed by the size of a circle, and the light reception intensity at the current position of the light receiving movable lens40is mainly displayed. The plurality of positions where to measure the light reception intensity may be set in any manner. In the example ofFIG.8, total nine points of combinations including any of three patterns of movement of each of the X axis and the Y axis in a + direction from the center position by a predetermined drive amount, no movement, and movement in a − direction by a predetermined drive amount (including the current position of the light receiving movable lens40) are set at the measurement positions of light reception strength in an X-Y plane where the drive control of the light receiving movable lens40is performed. As a result of measuring the optical reception intensity at the nine points, the example illustrated inFIG.8indicates that the light reception intensity was the highest at a position moved by a predetermined drive amount in the negative direction only with regard to the X axis. That is, in a case where the measurement results of the light reception intensity as illustrated inFIG.8are obtained, control of moving the light receiving movable lens40by a predetermined driving amount in the negative direction is executed. Such control makes it possible to control the light receiving movable lens40so that the light reception intensity of the reception optical fiber cable13becomes higher.

As described above, according to the spatial optical transmission apparatus of the second embodiment of the present invention, the light reception intensity is measured by the optical power detector at the current control position of the light receiving movable lens to be controlled and at one or more measurement positions of the light receiving movable lens driven by the predetermined control amount from the current control position, and the light receiving movable lens is controlled so as to be located at the measurement position with the highest light reception intensity. Therefore, it is possible to perform control so as to maximize the actual light reception intensity.

The drive control of the light receiving movable lens40by the optical power detector39in the second embodiment has been described assuming that the control is adjusted in the X-Y plane (plane perpendicular to the communication optical axis), but the present invention is not limited thereto. Control may be performed so as to be adjusted also in the Z direction (communication optical axis direction). In this case, the control in the X-Y plane and the control in the Z axis may be separately executed, or the control in the X-Y plane and the control in the Z axis may be simultaneously executed, that is, the light reception intensities at a plurality of measurement positions in the XYZ space may be compared.

In addition, in relation to the second embodiment, the object to be controlled by the measurement of the light reception intensity by the optical power detector39has been described as the light receiving movable lens40, but the present invention is not limited thereto. For example, at the stage of the optical axis adjustment as the initial setting, the control may be performed such that the positions of the projecting movable lens15, the lens17in the case of adopting the movable lens, the optical axis adjustment platform41, and the like are adjusted to positions with higher optical reception intensities based on the measurement of the optical reception intensity by the optical power detector39.

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