JP2007300248A - Optical receiving unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical receiving unit having a simple structure, capable of promptly adjusting an optical axis even if optical axis deviation exists. <P>SOLUTION: A half mirror 12 divides a signal light beam 10 into two. One divided light 10a is made incident on a light receiving element 16 via lens 14. The light receiving element 16 is mounted to an XY stage 18. The other divided signal light beam 10b is incident on area sensors 26, 30 with mutually different optical lengths. A beam gravity center detection apparatus 32 detects the beam center (center of gravity) of the incident beam on the area sensors 26, 34. From the position output of the beam gravity center detection apparatuses 32, 34, a control unit 36 calculates an incident position (X0, Y0) on the XY stage 18 of the signal light beam 10a, and drives an X-axis actuator 20 and a Y-axis actuator 22 by means of an X-drive circuit 38 and a Y-drive circuit 40, respectively, so as to position the light receiving element 16 in the position (X0, Y0). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical receiver for spatial light transmission.

  In spatial light transmission, it is important how well the optical axes of the optical transmitter and the optical receiver are aligned. When the signal light beam is thin, the signal cannot be transmitted unless the optical axis is aligned.

Patent Documents 1 and 2 describe optical systems that guide an incident beam to a predetermined location by feedback-controlling a biaxial gimbal mirror. In particular, Patent Document 2 discloses, as an optical receiver that receives a signal beam from a moving counterpart station such as a communication satellite, a first closed-loop control system that performs feedback control of a communication biaxial gimbal mechanism, and an optical receiver. There is described a configuration in which a second closed loop control system for feedback control of a beam deflector arranged on the front surface is provided.
JP 2000-292541 A JP 2002-341006 A

  In the prior art described in Patent Document 1, it is assumed that the signal light beam hits the rotation center of the biaxial gimbal mirror, that is, the center of the mirror. The beam cannot be received correctly. That is, it can cope with the angular deviation of the incident beam, but cannot cope with the positional deviation.

  In the configuration described in Patent Document 2, by introducing a beam deflector, it becomes possible to capture and track a signal light beam not only for an angle shift but also for a position shift. However, two feedback systems are required, which increases the size of the device and increases the cost.

  For example, in high-speed spatial light transmission exceeding 1 Gbps, the light receiver must reduce the light receiving diameter of the light receiver in order to support high-speed modulation. For example, it becomes 200 μmφ or less. In such a small light receiver, not only the angle deviation of the signal light beam but also the deviation of the incident position greatly affects the reception quality.

  In consideration of mounting a spatial light transmission device on a mobile terminal such as a mobile phone, it is desired to reduce the load on the arithmetic processing device and to reduce the size of the device, and to reduce the feedback control system and / or the number of components. There is a request to do.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical receiver having a simpler configuration that can cope with an angle shift and a position shift of a signal light beam.

  An optical receiving apparatus according to the present invention includes a beam demultiplexer that divides a signal light beam into two and outputs first and second divided signal lights, and the beam demultiplexer of the second divided signal light. First and second beam centroid detection devices that detect beam centroids at different optical distances, a photoreceiver, an XY movement device that moves the photoreceiver in a two-dimensional direction within a predetermined plane, and the first And a control device that controls the XY moving device according to the detection result of the second beam centroid detecting device and moves the light receiver to a position where the first divided signal light is incident.

  An optical receiving apparatus according to the present invention includes a beam demultiplexer that divides a signal light beam into two and outputs first and second divided signal lights, and the beam demultiplexer of the second divided signal light. The first and second beam centroid detection devices that detect beam centroids at different optical distances, a light receiver, an optical axis adjustment device that adjusts the optical axis of the first divided signal light, and the first And a control device that controls the optical axis adjustment device according to the detection result of the second beam centroid detection device and causes the first split signal light output from the optical axis adjustment device to enter the light receiver. It is characterized by doing.

  An optical receiving apparatus according to the present invention includes a beam demultiplexer that divides a signal light beam into two and outputs first and second divided signal lights, and the beam demultiplexer of the second divided signal light. First and second beam centroid detection devices that detect beam centroids at different optical distances, a photoreceiver, an XY movement device that moves the photoreceiver in a two-dimensional direction within a predetermined plane, and the first The optical axis adjustment device that adjusts the optical axis of the divided signal light, and the XY movement device and the optical axis adjustment device are controlled according to the detection results of the first and second beam centroid detection devices, and the optical axis adjustment is performed. And a control device that causes the first split signal light output from the device to enter the light receiver.

  According to the present invention, it is possible to cope with the angular deviation and the positional deviation of the incident light beam, and the signal light can be received at a position where the received light intensity is sufficiently strong. As a result, even if an angle shift or a position shift occurs in the optical axis of the signal light due to camera shake or the like, data can be transmitted at high speed without causing a communication interruption.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration diagram of an embodiment of the present invention. In this embodiment, it is assumed that the signal light is a thin parallel beam. The signal light beam 10 is split into two by a half mirror 12, and one split light (data reception beam) 10 a is collected by a lens 14 and enters a light receiving element 16. The light receiving element 16 is placed on an XY stage 18 that can move in the X and Y directions within a plane perpendicular to the optical axis of the ideal signal light beam 10. The X-axis actuator 20 moves the XY stage 18 in the X direction within a plane perpendicular to the ideal optical axis of the signal light beam 10a, and the Y-axis actuator 22 moves the XY stage 18 in the Y direction. Thereby, the light receiving element 16 can move in the X direction and the Y direction in a plane perpendicular to the ideal optical axis of the signal light beam 10.

  The other divided signal light beam 10b (optical axis monitoring beam) from the half mirror 12 is further divided into two by the half mirror 24, one of the divided lights is incident on the area sensor 26, and the other divided light is mirrored. The light is reflected by 28 and enters the area sensor 30. The optical distances from the half mirror 12 to the area sensors 26 and 30 are different from each other. The area sensors 26 and 30 are so-called image sensors, and output electric signals having a charge amount corresponding to the incident light intensity for each pixel. The area sensors 26 and 30 can obtain intensity distribution information of the incident signal light in a plane perpendicular to the optical axis.

  The beam center of gravity detection device 32 detects the position (X1, Y1) of the beam center (center of gravity) from the beam intensity distribution information output from the area sensor 26. Similarly, the beam gravity center detection device 34 detects the position (X2, Y2) of the beam center (center of gravity) of the signal light beam incident on the area sensor 30 from the output of the area sensor 30.

  The control device 36 calculates the incident position (X0, Y0) of the signal light beam 10a on the XY stage 18 from the position outputs (X1, Y1), (X2, Y2) of the beam centroid detection devices 32, 34. The control device 36 controls the X drive circuit 38 and the Y drive circuit 40 so that the light receiving element 16 is positioned at the obtained position (X0, Y0), and drives the X axis actuator 20 and the Y axis actuator 22, respectively. Let As a result, the light receiving element 16 moves to the position (X0, Y0), and the signal light beam 10a correctly enters the light receiving element 16. The demodulating circuit 42 demodulates data carried by the signal light beam 10 from the output electric signal of the light receiving element 16.

FIG. 2 shows an equivalent optical system of the present embodiment. The calculation method will be described with reference to FIG. A solid line indicates an ideal optical axis of the signal light beam 10a, and a broken line indicates a shifted optical axis. The distance from the half mirror 12 to the light receiving element 16 is D0, the distance from the half mirror 12 to the area sensor 26 is D1, and the distance from the half mirror 12 to the area sensor 30 is D2. When the optical axis is shifted as indicated by the broken line, the incident position (X0, Y0) of the signal light beam on the XY stage 18 is the light receiving position (X1, Y1), (X2, Y2) of the area sensors 26, 30. And the distances D0, D1, and D2, the following formula is used. That is,
X0 = X1- (D1-D0) (X2-X1) / (D2-D1)
Y0 = Y1- (D1-D0) (Y2-Y1) / (D2-D1)
The control device 36 performs the calculation of the above formula, drives the X actuator 20 and the Y actuator 22 by the X drive circuit 38 and the Y drive circuit 40, respectively, and moves the light receiving element 16 to the position (X0, Y0). By this position control, the signal light beam 10 can be correctly incident on the light receiving element 16 even if its optical axis is deviated from the ideal position / angle, and the light receiving device of this embodiment can transmit the data carried by the signal light beam 10. Can be received.

  It is clear that the calculation of the control device 36 for determining the position (X0, Y0) can be simply replaced with a lookup table.

  In the present embodiment, since the position of the light receiving element 16 for receiving the signal light beam 10 is determined from the incident beams of the two area sensors 26 and 30, signals can be received quickly with a simple configuration.

  When a human tries to align the optical axis while holding the portable terminal in his / her hand, an angle shift and a position shift due to camera shake always occur. Shake due to camera shake is 1 to 5 Hz in frequency. If the optical axis correction is performed in real time, the angular deviation and the positional deviation must be detected and corrected at a response speed sufficiently faster than this. Examples of the X-axis actuator 20 and the Y-axis actuator 22 include stepping motor actuators, voice coil motor actuators, and piezoelectric actuators. Among these, the response speed of the voice coil motor is generally 1 msec, and the response speed of the piezoelectric actuator is 0.01 msec, which can ensure a response speed sufficiently higher than the camera shake frequency of 1 to 5 Hz. From the viewpoint of position accuracy, it is 0.1 μm in the case of a voice coil motor and 0.01 μm in the case of a piezoelectric actuator, and sufficiently accurate control is possible even when compared with the light receiving diameter of the light receiving element 16 of 200 μmφ. is there.

  In order to take advantage of the response speed of the actuators 20 and 22, it is preferable that the frame rate of the area sensors 26 and 30 is large. As the area sensors 26 and 30, CCD (Charge Coupled Device) sensors are generally employed. The CCD sensor has a high frame rate of 1000 frames / sec, which is 100 times or more the frequency of shaking due to camera shake. The combination of the XY stage with actuator 18 and the area sensors 26 and 30 can sense the angular deviation and the positional deviation due to camera shake at a sufficient response speed, and control the light receiving element 16 to the signal light incident position.

  As the area sensors 26 and 30, a two-dimensional PSD (Position Sensitive Detector) element can also be used. When light enters the two-dimensional PSD element, a charge proportional to the amount of incident light is generated at the incident position. This electric charge passes through the resistance layer of the PSD element as a photocurrent and is taken out from the electrode at the end of the light receiving surface. Since this photocurrent is divided in inverse proportion to the distance to the electrodes on both ends, the incident position of light can be specified from the photocurrent extracted from the electrodes. The beam centroid detection device 32 detects the X position of the centroid from the photocurrents from the two end electrodes in the X direction, and detects the Y position of the centroid from the photocurrents from the two end electrodes in the Y direction.

  When the beam diameter of the signal light 10 output from the optical transmitter is large or diffused, an optical system for reducing the beam diameter or an optical system for making a parallel thin beam may be disposed in front of the half mirror 12. good. Of course, a condenser such as a condenser lens may be disposed in front of the area sensors 26 and 30 as appropriate.

  In the first embodiment, the light receiving element 16 is moved in the XY plane for receiving the signal light 10, but the light receiving element 16 may be stopped and the lens 14 may be moved in the XY plane. FIG. 3 shows a schematic configuration diagram of the second embodiment thus modified.

  In this embodiment, the lens 14 is equipped with an X-axis actuator 50 and a Y-axis actuator 52, and the lens 14 is moved in the X-axis direction and the Y-axis direction in a plane perpendicular to the ideal optical axis of the beam 10a. Is possible. The light receiving element 16 is stationary. The control device 54 drives the X-axis actuator 50 by the X-axis drive circuit 56 so that the beam incident on the position (X0, Y0) of the previous calculation formula is incident on the light receiving element 16 by the lens 14, and drives the Y-axis. The Y-axis actuator 52 is driven by the circuit 58. In other words, the control device 54 controls the position of the lens 14 so as to cancel the positional deviation and the angular deviation of the signal light beam 10.

  In the above embodiment, both the light receiving element 16 and the lens 14 may be moved in the XY plane.

  The split signal light 10a may be deflected according to the optical axis deviation of the incident signal light 10 so that the signal light 10a is always incident on the light receiving element 16. FIG. 4 shows a schematic configuration diagram of the embodiment.

  In this embodiment, a deflecting device 60 capable of deflecting the direction of the light beam is disposed between the half mirror 12 and the lens 14. The light receiving element 16 is stationary. The control device 62 controls the deflection device 60 so that the beam which is about to enter the position (X0, Y0) of the previous calculation formula is deflected by the deflection device 60 and enters the light receiving element 16. In other words, the control device 62 deflects the optical axis of the signal light beam 10 a by the deflecting device 60 so as to cancel the positional deviation and the angular deviation of the signal light beam 10. Such a deflection device 60 can be realized by, for example, a variable apex angle prism.

  The first embodiment and the third embodiment may be combined. FIG. 5 shows a schematic block diagram of the modified embodiment. The control device 64 controls the deflection of the deflection device 60 according to the detection results of the beam centroid detection devices 32 and 34 and controls the position of the light receiving element 16 by the XY stage 18.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a schematic block diagram of one Example of this invention. It is a schematic diagram of the equivalent optical system of a present Example. It is a schematic block diagram of Example 2 of this invention. It is a schematic block diagram of Example 3 of this invention. It is a schematic block diagram of Example 4 of this invention.

Explanation of symbols

10: Signal light beam 12: Half mirror 10a: Divided signal light (data receiving beam)
10b: Split signal light (optical axis monitor beam)
14: Lens 16: Light receiving element 18: XY stage 20: X axis actuator 22: Y axis actuator 24: Half mirror 26: Area sensor 28: Mirror 30: Area sensor 32: Beam centroid detection device 34: Beam centroid detection device 36: Control device 38: X drive circuit 40: Y drive circuit 42: Demodulation circuit 50: X axis actuator 52: Y axis actuator 54: Control device 56: X drive circuit 58: Y drive circuit 60: Deflection device 62: Control device 64: Control device

Claims (3)

A beam splitter (12) for splitting the signal light beam into two and outputting first and second split signal lights;
First and second beam centroid detectors (26, 30, 32, 34) for detecting beam centroids of the second split signal light at different optical distances from the beam splitter;
A light receiver (16);
An XY moving device (18, 20, 22) for moving the light receiver (16) in a two-dimensional direction within a predetermined plane;
A control device (36) for controlling the XY moving device according to the detection results of the first and second beam centroid detecting devices and moving the light receiver (16) to a position where the first divided signal light is incident.
An optical receiver characterized by comprising: A beam splitter (12) for splitting the signal light beam into two and outputting first and second split signal lights;
First and second beam centroid detectors (26, 30, 32, 34) for detecting beam centroids of the second split signal light at different optical distances from the beam splitter;
A light receiver (16);
An optical axis adjustment device (14, 60) for adjusting the optical axis of the first divided signal light;
The optical axis adjustment device is controlled according to the detection results of the first and second beam centroid detection devices, and the first divided signal light output from the optical axis adjustment device is incident on the light receiver (16). Control device (54, 60)
An optical receiver characterized by comprising: A beam splitter (12) for splitting the signal light beam into two and outputting first and second split signal lights;
First and second beam centroid detectors (26, 30, 32, 34) for detecting beam centroids of the second split signal light at different optical distances from the beam splitter;
A light receiver (16);
An XY moving device (18, 20, 22) for moving the light receiver (16) in a two-dimensional direction within a predetermined plane;
An optical axis adjustment device (14, 60) for adjusting the optical axis of the first divided signal light;
According to the detection results of the first and second beam centroid detection devices, the XY movement device and the optical axis adjustment device are controlled, and the first split signal light output from the optical axis adjustment device is used as the light receiver. Control device (64) for incidence on (16)
An optical receiver characterized by comprising:

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