JP2006020092A - Photodetector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a reliable and rapid search operation without increasing a deflection frequency in a biaxial light deflection means concerning a photodetector including the biaxial light deflection means such as a mirror to be able to control the deflection of a light beam, etc. <P>SOLUTION: Two periodical signals which are mutually different in frequency are generated by a DSP (digital signal processor) 3. A deflection operation in each axial direction is independently controlled in the biaxial deflection mirror 1. The search operation to retrieve the direction of a light emitting element for allowing the light beam to be made incident to the biaxial deflection mirror 1 is performed with the locus of an incident position in the two-dimensional PSD (position sensitive detector) element 2 of the light beam after passing the biaxial deflection mirror 1 as a Lissajous figure. The amplitude of a control signal is limited, and a direct current component is superimposed upon the control signal to thereby perform a search operation about a portion of an area where a search operation can be performed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photodetection device that detects the direction of a light-emitting element and enables automatic optical axis adjustment based on the detected direction of the light-emitting element, and is used, for example, in a light receiving and emitting module for optical wireless communication. is there.

  In recent years, optical wireless transmission technology using light has been proposed as a means for transmitting information signals. As such an optical wireless transmission technology, for example, a so-called “optical wireless LAN” for performing communication between a plurality of computers, a technology for transmitting video information and audio information to an AV (Audio-Visual) device, and the like have been proposed. Yes. Such optical wireless transmission is performed by transmitting and receiving a light beam modulated in accordance with digital information between devices configured by a light receiving and emitting device.

  In order to perform accurate information communication by such optical wireless transmission, it is necessary to match the optical axes between the light receiving and emitting devices, and the optical axis adjusting function in these light receiving and emitting devices is indispensable.

  Here, when the transmitted light beam of the light emitting element on the transmitting side does not have directivity, the optical axis adjustment may be performed only on the light receiving element on the receiving side, but when the light emitting element on the transmitting side has directivity. Needs to adjust the optical axis on both the transmitting and receiving sides. Further, when performing high-speed communication in the gigahertz band, it is necessary to reduce the diameter of the light beam used for communication in order to ensure the transmission SN ratio, and it is necessary to adjust the optical axis with high accuracy.

  As an optical axis adjustment mechanism for realizing such an optical axis adjustment function, as described in Patent Document 1, a light receiving / emitting element unit is supported by a biaxial drive mechanism, and the light receiving / emitting direction of the light receiving / emitting element unit is as follows. A mechanism has been proposed that can be deflected in two axial directions.

  Furthermore, in order to reduce the size of the communication system and increase the speed of optical axis adjustment, a mirror capable of biaxial deflection control is used, and a light beam is incident on the receiving light receiving element via this mirror. There has been proposed a photodetecting device including the angle control mechanism. In this photodetection device, the direction of the light emitting element on the transmitting side is searched by deflecting the mirror in two axes, and the optical axis between the light emitting element and the light receiving element is matched by controlling the angle of the mirror. Let

  In the search operation in the direction of the light emitting element on the transmission side in this photodetector, for example, while monitoring the amount of light received at the light receiving element on the reception side, the mirror is deflected according to preset conditions, and the amount of received light is maximized. The current mirror direction is stored, and after the mirror deflection operation, the mirror direction is set to the stored direction.

  In such a light detection device, in order to perform the optical axis control with higher accuracy, the light beam from the light emitting element on the transmission side passes through a mirror capable of controlling the deflection in the biaxial direction, and the two-dimensional optical position is controlled. The light is incident on the detection element. In this light detection device, the optical axis between the light emitting element and the light receiving element is controlled by feedback to the control of the deflection direction of the mirror based on the information on the incident position of the light beam in the two-dimensional light position detecting element. Is adjusted with high accuracy.

In addition, as a configuration for performing a search operation at high speed, the present inventors extract a spot component of incident light from the light emitting element on the transmission side based on image data of the two-dimensional imaging element, and perform this two-dimensional imaging. A device for detecting the direction of the other party from the spot position on the element has been proposed. In this apparatus, it is possible to roughly detect the direction of the counterpart light emitting element from the image data of the two-dimensional image sensor, and to drive and control the biaxial deflection mirror based on the detection result.
JP 2003-8515 A

  By the way, as described above, the closed loop control in the photodetecting device having the angle control mechanism using the mirror capable of deflection control and the two-dimensional optical position detecting element is performed by the light beam being incident on the two-dimensional optical position detecting element. This is possible only when the optical axis is off and the optical axis is greatly deviated and the light beam is not incident on the two-dimensional optical position detection element. Therefore, even in such a photodetection device, when the optical axis is greatly deviated, the search operation is first performed, and the light beam is incident on the two-dimensional optical position detection element, and then the servo lock is performed. It will be necessary.

  As a search operation in such a light detection device, a wide-range (wide angle) and high-speed (high-frequency) operation is required in order to reliably and promptly detect the direction of the light-emitting element on the transmission side. Is done. In other words, in this photodetection device, it is necessary to deflect the direction of the mirror capable of deflection control at a wide angle and at a high speed (high frequency).

  However, the speed (frequency) for deflecting the mirror is limited by the influence of mechanical frequency characteristics. Further, when the mirror is deflected at a high speed (high frequency), abnormal vibration may occur due to the influence of mechanical resonance, and an accurate search operation may not be performed. Such problems due to frequency characteristics and resonance become more prominent when the mirror deflection angle is widened.

  Therefore, in such a light detection device, the speed (frequency) for deflecting the mirror cannot be increased sufficiently, the time required for the search operation cannot be shortened, and the time required for optical axis adjustment is shortened. It has become difficult. In particular, when the diameter of the light beam from the light emitting unit on the transmission side is small, a high-density search operation is required, and there is a problem that the time required for the search operation becomes longer.

  Note that, in the apparatus that detects the direction of the counterpart light-emitting element roughly using the two-dimensional imaging element as described above, depending on the control accuracy of the biaxial deflecting mirror, after the control of the biaxial deflecting mirror, There is a possibility that the servo cannot be locked immediately. That is, it is considered that a search operation may be required even when the direction of the counterpart light emitting element is roughly detected using the two-dimensional imaging element.

  Therefore, the present invention has been proposed in view of the above-described circumstances, and is a photodetecting device having a biaxial light deflecting unit such as a mirror capable of controlling the deflection of an incident light beam. It is an object of the present invention to provide a photodetector that can realize a reliable and quick search operation without increasing the deflection frequency of the optical deflection means.

  In order to solve the above-described problems, a photodetector according to the present invention generates biaxial light deflecting means for deflecting a light beam incident from the outside in the biaxial direction, and generates a control signal, based on the control signal. Search control means for controlling the two-axis light deflection means, and two-dimensional light position detection means capable of two-dimensionally detecting the incident position of the light beam that has entered the two-axis light deflection means. A light detection device for detecting a direction of incidence of a light beam from the outside based on an incident position of the light beam detected by the two-dimensional light position detection means by performing a search operation by deflection of the biaxial light deflection means. The search control means generates two periodic signals having different frequencies as control signals, and the two periodic signals deflect the biaxial light deflecting means for each axis so that the locus of the incident position becomes a Lissajous figure. Independently Gosuru one, as well as limiting the amplitude of the control signal, by superimposing a DC component on the control signal, the deflection, is characterized in that control to perform for some it available space.

  In this light detection apparatus, the search control means uses a Lissajous figure as the locus of the incident position of the light beam that has passed through the biaxial light deflection means in the two-dimensional light position detection means, and the light beam is incident on the two-dimensional light position detection means. In performing a search operation for detecting the direction of the light emitting element that causes the light beam to enter the biaxial light deflecting means by detecting the position, the amplitude of the control signal is limited and a DC component is superimposed on the control signal. As a result, the search operation is performed on a part of the region where the search operation is possible, so that the direction of the light emitting element can be detected reliably and promptly.

  Here, a Lissajous figure (bowditch curve) means that particles moving on a plane perform harmonic motion in two orthogonal axes, and the ratio of their frequencies is a rational number (the quotient of two integers). This is a figure drawn by the particle. In the present invention, the Lissajous figure includes a case where the ratio of the frequencies in two orthogonal axial directions is an irrational number.

  In addition, the light detection device according to the present invention includes a biaxial light deflecting unit capable of deflecting and emitting a light beam incident from the outside in the biaxial direction, a control signal is generated, and the biaxial light is generated based on the control signal. A search control means for controlling the light deflection means, and a first two-dimensional light position detection means capable of two-dimensionally detecting the incident position of the light beam incident on the light beam having passed through the biaxial light deflection means. A light detecting device for detecting a direction of incidence of the light beam from outside based on an incident position of the light beam detected by the first two-dimensional light position detecting means by executing a search operation by deflection of the biaxial light deflecting means A second two-dimensional light position detecting means for receiving a light beam incident from the outside without passing through the biaxial light deflecting means and roughly detecting the incident direction of the light beam; , The frequency of each other as the control signal The two periodic signals are generated, and the two periodic signals are used to independently control the deflection of the biaxial light deflecting means for each axis so that the locus of the incident position becomes a Lissajous figure. The control signal is superposed with a direct current component based on the approximate incident direction of the light beam detected by the second two-dimensional optical position detection means, so that deflection can be applied to a part of the region where it is possible. It is characterized by controlling to perform.

  In this light detection apparatus, the search control means uses a Lissajous figure as the locus of the incident position of the light beam that has passed through the biaxial light deflection means in the two-dimensional light position detection means, and the light beam is incident on the two-dimensional light position detection means. In performing the search operation for detecting the direction of the light emitting element that makes the light beam incident on the biaxial light deflecting means by detecting the position, the amplitude of the control signal is limited, and the control signal is roughly By superimposing a direct current component based on the correct incident direction, the search operation is performed for a part of the region where the search operation is possible, so that the direction of the light emitting element can be detected reliably and rapidly.

  Further, according to the present invention, in the photodetection device, the search control unit superimposes the direct current component on the control signal so that the center position in a part of the region to be deflected is a position corresponding to the approximate incident direction. It is characterized by.

  In this photodetection device, in the search operation, a direct current component based on the approximate incident direction of the light beam is superimposed on the control signal. Therefore, the search operation is performed with the incident direction of the light beam as the center position, and the light emitting element The direction can be detected reliably and quickly.

  In the light detection apparatus according to the embodiment of the present invention, the search control means uses the Lissajous figure as the locus of the incident position of the light beam that has passed through the biaxial light deflection means in the two-dimensional light position detection means. In executing the search operation for detecting the direction of the light emitting element that makes the light beam incident on the biaxial light deflecting means by detecting the incident position of the light beam in the means, the amplitude of the control signal is limited, and the control signal By superimposing the direct current component on the part, the search operation is performed for a part of the region where the search operation is possible, so that the direction of the light emitting element can be detected reliably and rapidly.

  Further, in this light detection apparatus, the search control means uses the Lissajous figure as the locus of the incident position of the light beam that has passed through the biaxial light deflection means in the two-dimensional light position detection means, and the light beam in the two-dimensional light position detection means. In performing the search operation for detecting the direction of the light emitting element that makes the light beam incident on the biaxial light deflecting means by limiting the incident position of the light beam, the amplitude of the control signal is limited, and By superimposing a direct current component based on the approximate incident direction, the search operation is performed on a part of the region where the search operation is possible, so that the direction of the light emitting element can be detected reliably and rapidly.

  Further, in this optical detection device, in the search operation, a direct current component based on the approximate incident direction of the light beam is superimposed on the control signal, so that the search operation is performed with the approximate incident direction of the light beam as the central position. In other words, the direction of the light emitting element can be detected reliably and rapidly.

  That is, the present invention is a photodetection device having a biaxial light deflecting means such as a mirror capable of controlling the deflection of an incident light beam, and performing a search operation on a part of the searchable region. It is possible to provide a photodetector that can realize a reliable and quick search operation without increasing the deflection frequency in the biaxial light deflection means.

  Embodiments of the present invention will be described below with reference to the drawings.

  The light detection device according to the present invention is used, for example, in a light receiving and emitting module for optical wireless communication, detects the direction of the light emitting element, in other words, the incident direction of the light beam, and emits the optical axis of the light receiving element. This is a light detection device for always following the optical axis of the element.

  The photodetector in this embodiment is configured on the transmitting side of optical wireless communication, and is stable by adjusting the optical axis of the transmitting light emitting element based on the pilot reference light from the pilot emitting light element on the receiving side. It has a function for realizing communication.

[Configuration of First Embodiment]
(Configuration of photodetection device)
FIG. 1 is a block diagram showing a configuration of the photodetection device according to the first embodiment of the present invention.

  As shown in FIG. 1, a light detection apparatus according to the present invention includes a biaxial deflecting mirror 1 that is a biaxial light deflecting means capable of deflecting and emitting an incident light beam in two axial directions, and the biaxial beam. It has a two-dimensional PSD (Position Sensitive Detector) element 2 which is a two-dimensional light position detecting means capable of two-dimensionally detecting the incident position of the light beam reflected by the deflection mirror 1. is doing.

  Pilot reference light (PLB) from the pilot light emitting element on the receiving side, which is incident on the light detection device, is incident on the biaxial deflecting mirror 1 via a fisheye lens (concave lens) 14. The fish-eye lens 14 is for allowing the light beam to enter and exit the biaxial deflecting mirror 1 at a wider angle. The pilot reference light incident on the biaxial deflecting mirror 1 is reflected by the biaxial deflecting mirror 1, passes through the beam splitter 13 and the PSD condensing lens 10, and reaches the light receiving surface 2 a of the two-dimensional PSD element 2. Incident. The PSD condensing lens 10 condenses pilot reference light on the light receiving surface 2 a of the two-dimensional PSD element 2.

  This photodetecting device includes an LD (Laser Diode) light emitting element 12 for signal transmission. The LD light emitting element 12 emits a transmission light beam (LDB) that is optically modulated according to transmission data. The transmission light beam emitted from the LD light emitting element 12 is transmitted through the collimator lens 11 to become a parallel light beam, reflected by the beam splitter 13, deflected, and incident on the biaxial deflection mirror 1. The transmitting light beam incident on the biaxial deflecting mirror 1 is reflected by the biaxial deflecting mirror 1 and is emitted through a fisheye lens 14 toward a receiving side device having a pilot light emitting element that emits pilot reference light. The

  In the optical system of this photodetecting device, the pilot light beam (LDB) and the pilot reference light beam (PLB) are coaxial when the pilot reference light beam (PLB) is incident on the center of the light receiving surface 2a of the two-dimensional PSD element 2. It has been adjusted to be. That is, in this optical system, the center of the light receiving surface 2 a of the two-dimensional PSD element 2 and the light emitting point of the LD light emitting element 12 are in a conjugate position with respect to the reflecting surface of the beam splitter 13. Thus, in the state where the transmission light beam (LDB) and the pilot reference light (PLB) are coaxial, the transmission light beam (LDB) is applied to the light receiving element for signal reception of the device on the reception side. Can be accurately incident.

  FIG. 2 is a plan view showing the configuration of the biaxial deflection mirror 1.

  As shown in FIG. 2, the biaxial deflecting mirror 1 has a base 1a made of a material such as polyimide. Double circular voids 1b and 1c are formed in the base 1a by means such as pattern etching. The outer side and the inner side of the outer gap 1b are connected by two narrow Y-axis beam portions 1d and 1d. Further, the outer side and the inner side of the inner gap 1c are connected by two narrow X-axis beam portions 1e and 1e. The Y-axis beam portions 1d and 1d and the X-axis beam portions 1e and 1e are formed at positions of 180 ° around the center of the circle formed by the air gaps 1b and 1c, respectively, and 90 around each other. It is formed at the position where it becomes °. Therefore, the inner disk-shaped portion of the inner space 1c can be tilted in the X-axis direction indicated by the arrow X in FIG. 2 by twisting the X-axis beam portions 1e and 1e, and the Y-axis By twisting the beam portions 1d and 1d, it is possible to incline in the Y-axis direction indicated by the arrow Y in FIG.

  Thus, the disk-shaped part inside the inner space 1c that can be inclined in the X-axis direction and the Y-axis direction is a mirror reflecting portion 1f. The surface portion of the mirror reflection portion 1f becomes a mirror surface (reflection surface). An annular portion between the inner space 1c and the outer space 1b is an X-axis supporting gimbal portion 1g.

  FIG. 3 is an exploded perspective view showing the configuration of the biaxial deflecting mirror 1.

  As shown in FIG. 3, an X-axis drive magnetic core 1i and a Y-axis drive magnetic core 1j are disposed behind the base 1a. These X-axis drive magnetic core 1i and Y-axis drive magnetic core 1j are each formed in an annular shape (C-shape) with a part missing, and coils 1k and 1l are respectively provided on the opposite side of the lack part. It is wound and the missing part becomes the magnetic gap part 1m, 1m. The magnetic gap portions 1m and 1m of the X-axis driving magnetic core 1i and the Y-axis driving magnetic core 1j are arranged so as to form a magnetic field in the same space when fed to the coils 1k and 1l, In addition, the directions of the magnetic fields to be formed are orthogonal to each other.

  And the permanent magnet pin 1h is protrudingly provided in the back surface part of the mirror reflection part 1f. The permanent magnet pin 1h is attached substantially perpendicular to the mirror reflecting portion 1f. The tip side portion of the permanent magnet pin 1h is inserted into the magnetic gap portions 1m and 1m of the X-axis drive magnetic core 1i and the Y-axis drive magnetic core 1j. The X-axis drive magnetic core 1i, the Y-axis drive magnetic core 1j, and the base 1a are positioned with respect to each other such that the tip side portion of the permanent magnet pin 1h is located at the approximate center of each magnetic gap portion 1m, 1m. Has been placed.

  In the biaxial deflecting mirror 1 configured in this way, the magnetic field strength and direction (polarity) formed in the magnetic gap portion 1m of the X-axis driving magnetic core 1i and the magnetic gap portion 1m of the Y-axis driving magnetic core 1j. Accordingly, the tip side of the permanent magnet pin 1h is moved, and the mirror reflecting surface 1f is tilted in the biaxial direction.

  FIG. 4 is a front view showing the configuration of the two-dimensional PSD element 2.

  As shown in FIG. 4, the two-dimensional PSD element 2 on which the light beam that has passed through the biaxial deflecting mirror 1 is incident is an element that can detect the incident position of the light beam two-dimensionally. is there. The two-dimensional PSD element 2 is an element generally used in optical position measurement. The two-dimensional PSD element 2 outputs four PSD output signals corresponding to the incident positions in the light receiving surface 2a of the light beam 2b incident on the light receiving surface (position detecting unit) 2a, to four output terminals 2c, 2d, 2e. , 2f. The incident position of the light beam 2b in the light receiving surface 2a is expressed by the level of each PSD output signal.

  The two-dimensional light position detection means is not limited to the two-dimensional PSD element 2 and can be replaced with a four-division PD (Photo Ditecter), a C-MOSS sensor, or the like.

  As shown in FIG. 1, this photodetection device converts a DSP (Digital Signal Processor) 3 serving as search control means and X-axis numerical data SAX and Y-axis numerical data SAY output from the DSP 3 into analog data. And a D / A converter 4 for conversion and output. The DSP 3 is a processor capable of performing arithmetic processing for discrete-time signal processing at a high speed during a fixed sampling period, generates a control signal, and controls the biaxial deflection mirror 1 based on the control signal. To do.

  That is, the DSP 3 generates X-axis numerical data SAX and Y-axis numerical data SAY, which are two periodic signals having different frequencies as control signals. These X-axis numerical data SAX and Y-axis numerical data SAY are converted into analog data by the D / A converter 4 to become an X-axis control signal SSX and a Y-axis control signal SSY. Then, it is sent to the drive amplifier 6. The drive amplifier 6 is supplied with the X-axis control signal SSX and the Y-axis control signal SSY, amplifies the X-axis control signal SSX and the Y-axis control signal SSY, and responds to the X-axis control signal SSX and the Y-axis control signal SSY. The X-axis drive current SDX and the Y-axis drive current SDY are supplied to the coils 1k and 1l of the X-axis drive magnetic core 1i and the Y-axis drive magnetic core 1j of the biaxial deflection mirror 1, respectively.

  The DSP 3 and the D / A converter 4 operate based on the clock signal supplied from the clock generator 15. That is, the sampling signal (SCL) for synchronously controlling the interrupt operation in the DSP 3 and the conversion timing in the D / A converter 4 is generated based on the clock signal supplied from the clock generator 15. The period of the sampling signal (SCL) is preferably sufficiently higher than the frequency of the periodic signal generated in the DSP 3.

  The mirror reflecting portion 1f of the biaxial deflection mirror 1 is tilted in the X-axis direction according to the X-axis drive current SDX fed to the coil 1k of the X-axis drive magnetic core 1i, and is applied to the coil 11 of the Y-axis drive magnetic core 1j. It is tilted in the Y-axis direction according to the fed Y-axis drive current SDY. The inclination in the X-axis direction and the inclination in the Y-axis direction are performed independently of each other.

  Here, since the X-axis numerical data SAX and the Y-axis numerical data SAY are two periodic signals having different frequencies, the tilt direction of the mirror reflecting surface of the biaxial deflecting mirror 1 is determined as a Lissajous figure, Bowditch curve. ) Will change in the direction of drawing. That is, the locus of the incident position on the two-dimensional PSD element 2 of the light beam incident on the biaxial deflecting mirror 1 and reflected by the mirror reflecting portion 1a of the biaxial deflecting mirror 1 is a Lissajous figure.

  Here, a Lissajous figure is a particle that moves on a plane that performs harmonic motion in two orthogonal axial directions, and the ratio of its frequencies is a rational number (a number that can be expressed by the quotient of two integers). Sometimes a figure drawn by the particles.

  In this photodetection device, the biaxial deflection mirror 1 is controlled based on the control signal generated by the DSP 3 in this way, so that the incident position of the light beam in the two-dimensional PSD element 2 is detected. A search operation for detecting the direction of the light emitting element that causes the light beam to enter the deflection mirror 1 is executed.

  On the other hand, the four PSD output signals output from the two-dimensional PSD element 2 are sent to a PSD signal processing circuit 7 serving as servo error signal generation means. This PSD signal processing circuit 7 is based on the output from the two-dimensional PSD element 2 and generates an X-axis position signal SX and an X-axis position that are servo error signals corresponding to the light beam incident position on the two-dimensional PSD element 2. A signal SY is generated and supplied to a servo control circuit 8 serving as servo control means.

  The X-axis position signal SX and the Y-axis position signal SY generated by the PSD signal processing unit 7 are signals having levels proportional to the positions in the X-axis and Y-axis directions where the coordinate center O indicated by O in FIG. 4 is zero. It is. Since the levels of the X-axis position signal SX and the Y-axis position signal SY are proportional to the amount of displacement from the coordinate center O, they are called servo error signals from a servo standpoint.

  As shown in FIG. 1, the servo control circuit 8 controls the biaxial deflection mirror 1 based on the X axis position signal SX and the X axis position signal SY, and determines the incident position of the light beam on the two-dimensional PSD element 2. It is a predetermined position.

  That is, the servo control circuit 8 generates the X-axis servo control signal SCX and the Y-axis servo control signal SCY based on the X-axis position signal SX and the Y-axis position signal SY from the PSD signal processing unit 7, and these X-axis servos The control signal SCX and the Y-axis servo control signal SCY are sent to the two-axis deflection mirror 1 via the signal switching unit 5 and the drive amplifier 6, and the two-axis deflection mirror 1 is controlled in a closed loop, whereby the two-dimensional PSD element 2 is controlled. The incident position of the light beam is a coordinate center O in the two-dimensional PSD element 2.

  The servo control circuit 8 includes a phase compensation circuit for the dynamic characteristics of the biaxial deflection mirror 1.

  The PSD signal processing circuit 7 has a function of generating an incident light amount signal SB for monitoring the incident light amount as the servo error signal level. The PSD signal processing circuit 7 supplies the generated incident light amount signal SB to the servo error signal level detection circuit 9.

  The servo error signal level detection circuit 9 includes a comparator circuit and a logic circuit, generates a switching control signal SE based on the incident light amount signal SB sent from the PSD signal processing unit 7, and sends it to the signal switching unit 5. The servo error signal level detection circuit 9 switches the state of the signal switching unit 5 by the switching control signal SE when the incident light amount signal SB corresponds to a predetermined level.

  The signal switching unit 5 converts the signals input to the two-axis deflection mirror 1 into the X-axis servo control signal SCX and Y-axis servo control signal SCY from the servo control circuit 8, and the X-axis control signal SSX and Y-axis from the DSP 3. It is switched by the control signal SSY.

  That is, the signal switching unit 5 controls the X-axis control from the DSP 3 to the biaxial deflection mirror 1 by the switching control signal SE generated by the detection circuit 9 based on the level of the incident light quantity signal SB generated by the PSD signal processing unit 7. A search operation in which the signal SSX and the Y-axis control signal SSY are input via the drive amplifier 6, and the X-axis servo control signal SCX and the Y-axis servo control signal SCY from the servo control circuit 8 to the two-axis deflection mirror 1 are driven by the drive amplifier 6. The servo operation to be input via is switched.

[Operation in the First Embodiment]
(Operation of photodetection device)
Hereinafter, the operation of the photodetecting device will be described.

  In this photodetection device, as shown in FIG. 1, the biaxial deflection mirror 1 is arranged so that pilot reference light from the receiving device enters the coordinate center (O) of the light receiving surface 2a of the two-dimensional PSD element 2. Is controlled, the optical axis of the transmission light beam coincides with the optical axis of the pilot reference light, and stable signal transmission is possible.

  If the pilot reference light is incident on the light receiving area of the light receiving surface 2a of the two-dimensional PSD element 2, the pilot reference light is incident on the coordinate center (O) of the light receiving surface 2a by the operation of the servo control circuit 8. Thus, the biaxial deflection mirror 1 is controlled to adjust the optical axis.

  FIG. 5 is a block diagram showing a state in which the optical axis of the transmission light beam and the optical axis of the pilot reference light are greatly shifted in the photodetector according to the present invention.

  However, as shown in FIG. 5, in a state where the optical axis of the transmission light beam and the optical axis of the pilot reference light are greatly deviated, the pilot reference light does not enter the light receiving surface 2a of the two-dimensional PSD element 2. The optical axis cannot be adjusted by the operation of the servo control circuit 8. Such a state occurs when signal communication is started for the first time after installing the transceiver, or when the transceiver has moved for some reason.

  In this light detection apparatus, when the optical axis of the transmission light beam and the optical axis of the pilot reference light are greatly deviated as described above, the DSP 3 operates the biaxial deflection mirror 1 with a wide angle. A search operation for detecting the direction of the pilot reference light is performed by scanning within the range.

  At the time of a search operation in this photodetection device, the X-axis control signal SSX and the Y-axis control signal SSY of the biaxial deflection mirror 1 are converted into sine wave signals having different frequencies so that the mirror reflector of the biaxial deflection mirror 1 The locus of the incident position on the two-dimensional PSD element 2 of the light beam reflected by 1a draws a Lissajous figure.

  As described above, the optical system is adjusted so that the transmission light beam and the pilot reference light are coaxial when the pilot reference light is incident on the center of the light receiving surface 2a of the two-dimensional PSD element 2. A Lissajous figure is also drawn in the transmission direction of the transmission light beam.

  Then, when the transmission direction of the transmission light beam approaches the optical axis of the pilot reference light during the search operation, the pilot reference light enters the light receiving area of the light receiving surface 2a of the two-dimensional PSD element 2. At this time, the optical axis adjustment is performed by switching from the search operation to the servo operation (closed loop control operation) by the servo control circuit 8, and the search operation is completed.

(Characteristics of Lissajous figures)
In order to explain the Lissajous operation in the biaxial deflecting mirror 1, consider a trajectory drawn by the transmission light beam from the LD light emitting element 12 being deflected by driving the biaxial deflecting mirror 1. That is, the locus drawn by the transmission light beam coincides with the locus in the tilt direction in the search operation of the biaxial deflection mirror 1.

  Here, the ratio of the frequencies Fx and Fy with respect to the X axis and the Y axis is assumed to be m as shown in the following (Formula 1).

m = Fy / Fx (Formula 1)
FIG. 6 is a graph showing a Lissajous locus drawn by the biaxial deflecting mirror 1 per second when the frequency Fx about the X axis is 50 [Hz].

  (A) in FIG. 6 is a search locus when the frequency ratio m = 1 (both frequencies are the same). In this case, since the phase difference between the sine waves of the X axis and the Y axis is zero, the trajectory is a straight line and the search operation is not performed.

  (B) in FIG. 6 is a search locus when the frequency ratio m = 1.50 (integer ratio 2: 3). In this case, the search locus converges in two sine wave cycles, and the same locus is drawn every 40 msec. Further, the trajectory crosses the Y axis four times and the X axis six times, resulting in a trajectory with very low resolution.

  When the ratio of the frequency Fx for the X axis and the frequency Fy for the Y axis is a relatively prime set (x: y), the Lissajous trajectory is 2x times and 2y times for the x axis and the y axis, respectively. It becomes a crossing figure. Here, for this figure, the resolution for searching the incident position of the light beam is assumed to be 4xy as the product of the number of times of traversing the x-axis and y-axis, respectively. That is, the resolution in the figure shown in FIG.

  (C) in FIG. 6 is a search locus when the frequency ratio m = 1.10 (integer ratio 10:11). In this case, the search trajectory converges in 10 sine waves, and the same trajectory is drawn every 200 msec. Further, the trajectory crosses the Y axis 20 times and the X axis 22 times, so that the resolution is improved as compared with (b) in FIG. 6 and the search operation is performed in all directions. In this case, the resolution is 440.

  (D) in FIG. 6 is a search locus when the frequency ratio m = 1.003 (integer ratio 1000: 1003). In this case, the trajectory has not yet converged in 1 second, and it takes 20 seconds to search and converge in all directions, which is disadvantageous in terms of high-speed search. In this case, the resolution is 4012000.

  (E) in FIG. 6 is a search locus when the frequency ratio m = 1.18 (integer ratio 50:59). In this case, the search locus converges with 50 sine waves and the same locus is drawn every second. Further, the trajectory crosses the Y axis 100 times and the X axis 118 times, and an omnidirectional search with high resolution becomes possible. In this case, the resolution is 11800.

  (F) in FIG. 6 is a search locus when the frequency ratio m = √2 (non-integer ratio, irrational number). In this case, the search trajectory does not converge and the resolution becomes almost infinite with time.

  In order to increase the speed of the search operation, the frequency of the sine wave (Fx, Fy) may be increased, but it cannot be increased unnecessarily due to the mechanical vibration of the biaxial deflection mirror 1. Further, the smaller the value of the frequency ratio m, the more stable the operation.

  Therefore, for example, when the value (1.18) of the frequency ratio m as shown in (e) in FIG. 6 is taken, a Lissajous operation that enables an omnidirectional search with high resolution within a short time even if the frequency itself is low. It can be performed.

  Further, when the frequency ratio m is set to a value other than the integer ratio as shown in (f) in FIG. 6, the resolution can be almost infinite with time, so that the beam diameter of the pilot reference light is extremely small. Even so, a reliable search can be performed.

  The frequency and frequency ratio m of each sine wave can be optimized to achieve the target search time and detection resolution.

  Here, the frequency of each sine wave is preferably in the range of 10 to 1000 Hz. The frequency ratio m of each sine wave is preferably in the range of 1 to 1.5.

(About using triangular waves as control signals)
If a periodic signal including a high-frequency component such as a triangular wave is used as a control signal for controlling the search operation as described above, resonance easily occurs due to the vibration characteristics of the biaxial deflecting mirror 1 and is stable. There is a possibility that the operation cannot be performed. In particular, when the biaxial deflection mirror 1 is driven at a high speed in a wide angle range, the influence becomes remarkable.

  Therefore, the waveform of the control signal is preferably a sine waveform with the least high frequency components.

  However, it is also possible to use a triangular wave.

  FIG. 7 is a graph showing a locus drawn by the biaxial deflecting mirror when a triangular wave is used as the control signal.

  In the search operation, when a triangular wave is used as the control signal for both the X axis and the Y axis, as shown in FIG. 7A, the figure drawn by the deflection direction of the biaxial deflection mirror 1 is the X axis and It becomes a lattice figure composed of straight lines parallel to the Y axis and inclined straight lines.

  When a triangular wave is used as the control signal for the X axis and a sine wave is used for the Y axis, as shown in FIG. 7B, there is an asymmetric locus in the X axis direction and the Y axis direction. be painted. In the example shown in FIGS. 7A and 7B, the frequency ratio m for the X axis and the Y axis is 1.10, similar to that shown in FIG. 6C. Is.

  Thus, when a periodic signal such as a triangular wave is used, the periodic signal contains a lot of high-frequency components, and therefore it is necessary to suppress abnormal vibration of the biaxial deflection mirror 1 by using a low-pass filter or the like.

(Search area dividing operation)
In this photodetection device, the Lissajous figure drawing range in the search operation can be performed over a wide range by using the entire movable range of the biaxial deflection mirror 1.

  By the way, if the Lissajous figure has a fine trajectory, that is, if an attempt is made to increase the search resolution, it takes time to search. Therefore, in order to perform a high-speed search, the X-axis control signal SSX and the Y-axis control It is necessary to increase the frequency of the signal SSY. When a wide range search operation is to be performed at high speed, the frequency of the X-axis control signal SSX and the Y-axis control signal SSY may be increased. Stable operation cannot be performed due to the influence.

  On the other hand, if the drawing range of the Lissajous figure is reduced and the search operation is performed for a part of the search range, the driving angle of the biaxial deflection mirror 1 becomes small. Therefore, the X-axis control signal SSX and the Y-axis control signal SSY Stable operation is possible even at a high frequency.

  FIG. 8 is a search locus when the frequency ratio m = 1.01 (integer ratio 100: 101), FX = 400 Hz, and Fy = 404 Hz.

  In this case, the search trajectory converges with 100 cycles of the sine wave, and the same trajectory is drawn every 0.25 seconds. The trajectory crosses the Y axis 200 times and the X axis 202 times. In addition, since the amplitudes of the X-axis control signal SSX and the Y-axis control signal SSY are halved so that the drive angle of the biaxial deflection mirror 1 is reduced, in this case, the resolution is twice that of 40400, 80800, and in this region, a high-resolution search with high resolution is possible.

  FIG. 9 is an explanatory diagram of the operation when the search range is divided.

  Using this characteristic, as shown in FIG. 9, the search range is divided into a plurality of areas, and a search operation is performed on the divided area by drawing a Lissajous figure. By sequentially switching the regions, it is possible to search the entire movable range of the biaxial deflecting mirror 1.

  Specifically, the amplitudes of the X-axis control signal SSX and Y-axis control signal SSY, which are sine wave signals, are limited, and a DC component is superimposed on the X-axis control signal SSX and Y-axis control signal SSY to draw The drawing center position (angle) of the Lissajous figure, that is, the center position of the search area can be arbitrarily changed. The search range can be divided by optimally setting the amplitudes of the X-axis control signal SSX and the Y-axis control signal SSY. When the drawing range of the Lissajous figure is reduced in this way, the driving angle of the biaxial deflection mirror 1 is reduced, so that stable operation is possible even when the X-axis control signal SSX and the Y-axis control signal SSY are high. .

  At this time, the amplitudes of the X-axis control signal SSX and the Y-axis control signal SSY are set so that the divided areas can be covered by the search operation. In this case, since the amplitudes of the X-axis control signal SSX and the Y-axis control signal SSY are ½ of the amplitude that covers the search region SE at a time, the high resolution and high speed as shown in FIG. A search operation can be performed.

  9A, the search range is the search division region SDE1, and the X-axis control signal SSX and the Lissajous figure drawing center position are set to the XY coordinates (0.5, 0.5). A DC component of 0.5 is superimposed on the Y-axis search control code SSY. Further, waveforms of the X-axis control signal SSX and the Y-axis control signal SSY are shown.

  In FIG. 9B, the X-axis control signal SSX is set so that the search range is the search division region SDE2 and the drawing center position of the Lissajous figure is the XY coordinates (−0.5, 0.5). The DC component of −0.5 and 0.5 is superimposed on the Y-axis search control code SSY. Further, the waveforms of the X-axis control signal SSX and the Y-axis control signal SSY are shown.

  In (c) of FIG. 9, the X-axis control signal is such that the search range is the search division region SDE3 and the drawing center position of the Lissajous figure is the XY coordinates (−0.5, −0.5). A DC component of −0.5 is superimposed on the SSX and Y-axis control signal SSY. Further, waveforms of the X-axis control signal SSX and the Y-axis control signal SSY are shown.

  In (d) of FIG. 9, the search range is the search division region SDE4, and the X-axis control signal SSX is set so that the drawing center position of the Lissajous figure is the XY coordinates (0.5, -0.5). And a DC component of −0.5 are superimposed on the Y-axis control signal SSY. Further, waveforms of the X-axis control signal SSX and the Y-axis control signal SSY are shown.

  By sequentially repeating the search operations shown in (a) to (d) of FIG. 9, the search operation for the entire search region SE can be performed. As described above, the search operation for each of these divided regions converges in 0.25 seconds. Therefore, by switching the search operation for each region every 0.25 seconds, the search region SE in one second is totaled. A search operation for the entire area can be performed. As described above, the resolution at this time is 80800, and the search time is 1 second.

  By the way, when the search operation for the entire search SE is performed by drawing one Lissajous figure, if the search time is 1 second, as described above, the frequency FX of the search signal FX = 50 Hz, m = 1.18, and the resolution is 11800.

  Therefore, if the search area is divided and the search operation is performed sequentially for each divided area, the frequency of the control signal can be increased compared to the method of searching the entire search area by drawing one Lissajous figure, A high-resolution search operation can be performed quickly.

  Note that the number of divisions of the search area is not particularly limited, and similarly, the frequency ratio m and the frequency of the search signal are determined according to the mechanical characteristics of the biaxial deflection mirror 1 and the required search characteristics. Can do.

(Usefulness of DSP for Lissajous operation)
As means for generating the control signal as described above, signal generation by arithmetic processing using a DSP or the like is preferable.

  The reason will be described below.

  FIG. 10 is a graph showing a locus when an error occurs in the frequency ratio about the X axis and the Y axis.

  As shown in FIG. 6 (e), when the frequency ratio m = 1.18, Fx = 50 [Hz], Fy = 59 [Hz]. When an error of 1 [Hz] occurs, the frequency ratio m becomes 25:29 as shown in (b) of FIG. 10, or the frequency ratio 1n becomes 5 as shown in (C) of FIG. : 6, resulting in a completely different operation. In addition, (a) in FIG. 10 is a locus drawn when there is no error.

  Therefore, in order to perform such an operation, it is required to control the frequency with high accuracy at least with an error smaller than about 0.1 [Hz].

  In this photodetector, since the X-axis control signal SSX and the Y-axis control signal SSY generated by the arithmetic processing in the DSP 3 are used, the frequency ratio m between the X-axis control signal SSX and the Y-axis control signal SSY is set with high accuracy. The X axis control signal SSX and the Y axis control signal SSY can be used to control the inclination of each axis direction in the biaxial deflection mirror 1 to perform a search operation that draws a stable trajectory. Can do.

  When the X-axis control signal SSX and the Y-axis control signal SSY are generated by an analog circuit, it is difficult to set with high accuracy, and the frequency and frequency ratio change due to the influence of temperature drift, etc. Stable operation cannot be performed.

(About sin calculation method)
In the search operation, the DSP 3 calculates a variable φ that increases at a constant rate according to the sampling period, and continuously outputs the result to the D / A converter 4 that operates in synchronization with the sampling period. X-axis control signal SSX and Y-axis control signal SSY are generated.

  Hereinafter, an internal program operation of the DSP 3 will be described with respect to a method of generating the X-axis control signal SSX and the Y-axis control signal SSY by the DSP 3.

  FIG. 11 is a block diagram showing a configuration of the DSP 3 for calculating a sine wave.

  FIG. 11 represents the calculation function inside the DSP 3 as discrete signal processing. In the DSP 3, the Sin calculation block 20 is a block for calculating Sin (φ) of the input variable φ. As a specific calculation method, the Sin function provided by the compiler can be used as it is, but an approximate polynomial may be used in consideration of the balance between calculation accuracy and calculation speed.

  The sampling delay means 21 has a function of holding the numerical value of the input variable φ one sampling period before. Further, the adder 22 performs an addition operation on the input variable φ and the input variable φ one sampling period before held by the sampling delay unit 21, and sends it to the Sin calculation block 20 and the sampling delay unit 21.

  The constant C that determines the frequency of the sine wave in the DSP 3 is obtained by the following (Equation 2).

C = 2 · π · F0 · T (∵F0 is the frequency of the sine wave, T is the sampling period) (Equation 2)
The parts other than the Sin calculation block 20 perform the calculation shown in the following (Equation 3).

φ [n] = φ [n−1] + C (∵n is the current sampling count) (Equation 3)
This (Equation 3) means that φ [n] is increased at a constant rate C for each sampling period. Thus, by calculating Sin (φ [n]) in the Sin calculation block 20 for each sampling period, Sin calculation that changes for each sampling period is performed. Since φ [n] sequentially increases with the sampling period, when the condition of (φ [n]> 2π) is satisfied, the calculation of the following (Equation 4) is performed to prevent the divergence of the calculation.

φ [n] = φ [n−1] −2π (Formula 4)
FIG. 12 is a flowchart showing a sine wave calculation process in the DSP 3.

  Next, the flow of a program in the DSP 3 will be described with reference to the sine wave calculation flowchart shown in FIG.

  In S1, the input variable φ is initialized (φ = 0), and the process proceeds to S2.

  In S2, the constant C is calculated by the above (Formula 2), and the process proceeds to S3.

  In S3, a sampling (interrupt) signal from the clock generator 15 is waited. If there is an interrupt, the process proceeds to S4.

  In S4, a constant C is added to the input variable φ, and it is increased at a constant rate, and the process proceeds to S5.

  In S5, if the input variable φ is 2π or more, the process proceeds to S6, and if the input variable φ is less than 2π, the process proceeds to S7.

  In S6, 2π is subtracted from the input variable φ to prevent the input variable φ from diverging, and the process proceeds to S7.

  In S7, Sin (φ) is calculated and set to D, and the process proceeds to S8.

  In S8, D, which is Sin (φ), is multiplied by a constant W for controlling the amplitude of the Lissajous operation, and then a constant S for determining the DC component (constant S has a positive or negative value) is added.

  In S9, DD is multiplied by a constant A corresponding to the number of bits of the D / A converter 4 to obtain SD, and the process returns to S3.

  Further, in order to generate the X-axis control signal SSX and the Y-axis control signal SSY having different frequencies by such calculation processing, the DSP 3 performs the Sin calculation shown in the above (Equation 2) with two different constants C. You can use it.

  FIG. 13 is a flowchart showing a calculation process when the DSP 3 generates the X-axis control signal SSX and the Y-axis control signal SSY having different frequencies.

  That is, in FIG. 13, the frequency for the X axis and the Y axis in the biaxial deflection mirror 1 is Fx and Fy, respectively, and the constant corresponding to (Expression 2) for calculating the X axis Sin numerical data SAX is Cx. , The constant corresponding to (Expression 2) for calculating the Y-axis Sin numerical data SAY is represented by Cy.

  In S1, the input variables φx and φy are initialized (φx = 0, φy = 0), and the process proceeds to S2.

  In S2, the constants Cx and Cy are calculated by the above (Formula 2), and the process proceeds to S3.

  In S3, a sampling (interrupt) signal from the clock generator 15 is waited. If there is an interrupt, the process proceeds to S4.

  In S4, the constant Cx is added to the input variable φx, and the constant Cy is added to the input variable φy, which are increased at a constant rate, and the process proceeds to S5.

  In S5, if the input variable φx is 2π or more, the process proceeds to S6, and if the input variable φx is less than 2π, the process proceeds to S7.

  In S6, in order to prevent the divergence of the input variable φx, 2π is subtracted from φx, and the process proceeds to S7.

  In S7, if the input variable φy is 2π or more, the process proceeds to S8, and if the input variable φy is less than 2π, the process proceeds to S9.

  In S8, in order to prevent the divergence of the input variable φy, 2π is subtracted from φy, and the process proceeds to S9.

  In S9, Sin (φx) and Sin (φy) are calculated, respectively, and Dx and Dy are set, respectively, and the process proceeds to S10.

  In S10, Dx and Dy are multiplied by constants WX and WY for controlling the amplitude of the Lissajous operation, respectively, and then constants SX and SY (constants SX and SY have positive and negative values) for determining DC components are added. .

  In S11, DDX and DDY are multiplied by a constant A corresponding to the number of bits of the D / A converter 4 to obtain SDX and SDY, and the process returns to S3.

  Here, Dx is the X-axis Sin numerical data SAX, and Dy is the Y-axis Sin numerical data SAY.

  The X-axis Sin numerical data SAX and the Y-axis Sin numerical data SAY calculated in this way are D / A converted by the D / A converter 4 and current-amplified by the drive amplifier 6 to be X-axis driven magnetic cores 1i and Y. By supplying power to the coils 1k and 1l of the shaft driving magnetic core 1j, each axis of the biaxial deflection mirror 1 is driven in a sine wave. In addition, an operation of drawing a Lissajous figure centering on a specific direction is performed by the superimposed DC component.

(Regarding the search operation control method with divided areas)
In this photodetection device, as described above, the search operation for the entire search region SE can be performed by sequentially repeating the search operations shown in FIGS. 9A to 9D. Since such a search operation converges every 0.25 seconds as described above, the search operation for the entire region of the search region SE is performed in one second by switching the search operation for each region every 0.25 seconds. It can be performed.

  FIG. 14 is a flowchart of arithmetic processing control of the DSP 3 in the first embodiment of the light detection device according to the present invention.

  First, in order to search the search division area SDE1 shown in FIG. 9A, the DSP 3 sets the drawing center position of the Lissajous figure to the XY coordinates (0.5, 0.5) in S1 shown in FIG. Constants Sx and Sy are set so that The numerical values here are for explanation corresponding to the drawings, and have no numerical meaning.

  Next, a search operation for the search division region SDE1 is started in S2 of FIG. 14, the search time is monitored in S3, and if 0.25 seconds have elapsed, the process proceeds to S4.

  In S4 of FIG. 14, in order to search the search division area SDE2 shown in FIG. 9B, the constant Sx is set so that the drawing center position of the Lissajous figure becomes the XY coordinates (−0.5, 0.5). , Sy are set.

  Next, a search operation for the search division region SDE2 is started in S5 of FIG. 14, the search time is monitored in S6, and if 0.25 seconds have elapsed, the process proceeds to S7.

  In S7 of FIG. 14, in order to search the search division area SDE3 shown in FIG. 9C, constants are set so that the drawing center position of the Lissajous figure becomes the XY coordinates (−0.5, −0.5). Sx and Sy are set.

  Next, a search operation for the search division region SDE3 is started in S8 of FIG. 14, the search time is monitored in S9, and if 0.25 seconds have elapsed, the process proceeds to S10.

  In S10 of FIG. 14, in order to search the search division area SDE4 shown in FIG. 9D, the constant Sx is set so that the drawing center position of the Lissajous figure becomes the XY coordinates (0.5, −0.5). , Sy are set.

  Next, a search operation for the search division region SDE4 is started in S11 of FIG. 14, the search time is monitored in S12, and if 0.25 seconds have elapsed, the process returns to S1.

  According to the routine as described above, the search operation for the entire search area SE can be performed in one second.

  If the pilot reference light is incident on the light receiving surface 2a of the two-dimensional PSD element 2 during this routine, the search operation is completed. That is, when the pilot reference light enters the light receiving area of the light receiving surface 2a during the search operation, the servo error signal level detection circuit 9 determines the servo error signal level based on the incident light amount signal SB. Then, by the operation of the signal switching unit 5, the search operation is switched to the servo operation (closed loop control operation) by the servo control circuit 8, and the optical axis is adjusted.

(Switching operation between search operation and servo operation)
FIG. 15 is a waveform diagram showing output signal waveforms from the PSD signal processing circuit 7 and the servo error signal level detection circuit 9 during the search operation.

  During the search operation as described above, when pilot reference light is irradiated into the light receiving area of the light receiving surface 2a of the two-dimensional PSD element 2, the PSD signal processing circuit 7 is shown in FIG. As the level of the incident light amount signal (SB) from the signal increases, a servo error signal (X-axis position corresponding to the spot position of the pilot reference light from the PSD signal processing circuit 7 as shown in FIG. Signal (SX), Y-axis position signal (SY)) changes.

  In the servo error signal level detection circuit 9, for example, the incident light amount signal (SB) is equal to or higher than a specified level A, and the level of either the X-axis position signal (SX) or the Y-axis position signal (SY) is 0. At this time, as shown in FIG. 15C, the switching control signal (SE) is changed to control the signal switching unit 5, and the switching from the search operation to the servo operation (closed norape control operation) is performed. To adjust the optical axis.

  During the servo operation, as long as the pilot reference light is incident in the light receiving area of the light receiving surface 2a of the two-dimensional PSD element 2, the optical axis follows the direction of the pilot reference light by the biaxial deflection mirror 1. Is adjusted.

[Second Embodiment]
FIG. 16 is a flowchart showing a first example of arithmetic processing control of the DSP 3 in the second embodiment of the light detection device according to the present invention.

  In the second embodiment, as shown in FIG. 16, the DSP 3 starts the search operation in S1, and in S2, the first resolution (for example, (e in FIG. The frequency ratio m at which the resolution shown in (1) is 11800 is 1.18), and the search operation for the entire search region SE is executed.

  Next, in S3, it is determined whether or not the incidence of pilot reference light on the light receiving surface 2a of the two-dimensional PSD element 2 is detected within a predetermined time. If the pilot reference light is incident on the light receiving surface 2a of the two-dimensional PSD element 2 within the predetermined time, the process proceeds to S5, the search operation is terminated, and if it is not incident, the process proceeds to S4.

  In S4, the DSP 3 divides the search area SE into four, thereby setting the second resolution higher than the first resolution (for example, the frequency ratio m = 1.01 at which the resolution shown in the drawing is 80800), The search operation is executed until the incidence of pilot reference light on the light receiving surface 2a of the two-dimensional PSD element 2 is detected.

  As described above, the search operation at this time divides the search area SE and sequentially performs the search operation for each of the divided areas.

  When this search operation is completed, the process proceeds to S5 and the search operation is terminated.

  In this way, by starting the search operation at a relatively low resolution, if the incidence of pilot reference light on the light receiving surface 2a of the two-dimensional PSD element 2 is detected at this stage, the search operation can be completed quickly. it can. Further, even if the pilot reference light is not detected by the search operation at a relatively low resolution, the search operation at the high resolution is executed next, so that the pilot reference light can be reliably detected.

  FIG. 17 is a flowchart showing a second example of arithmetic processing control of the DSP 3 in the second embodiment of the light detection device according to the present invention.

  Furthermore, as shown in FIG. 17, the DSP 3 may repeatedly execute the search operation while sequentially increasing the resolution by sequentially increasing the number of divisions of the search area SE.

  That is, in this case, as shown in FIG. 17, the DSP 3 starts the search operation in S1, and in S2, the resolution is set to the first resolution (for example, (e in FIG. The search operation for the entire search region SE is executed at a frequency ratio l11 = 1.18) where the resolution shown in FIG.

  Next, in S3, it is determined whether or not the incidence of pilot reference light on the light receiving surface 2a of the two-dimensional PSD element 2 is detected within a predetermined time. If the pilot reference light is incident on the light receiving surface 2a of the two-dimensional PSD element 2 within the predetermined time, the process proceeds to S7, the search operation is terminated, and if it is not incident, the process proceeds to S4.

  In S4, the DSP 3 divides the search area SE into four, thereby setting the second resolution higher than the first resolution (for example, the frequency ratio m = 1.01 at which the resolution shown in the drawing is 80800), The search operation is executed until the incidence of pilot reference light on the light receiving surface 2a of the two-dimensional PSD element 2 is detected.

  As described above, the search operation at this time divides the search area SE and sequentially performs the search operation for each of the divided areas.

  Next, in S5, it is determined whether or not the incidence of pilot reference light on the light receiving surface 2a of the two-dimensional PSD element 2 is detected within a predetermined time. If the pilot reference light is incident on the light receiving surface 2a of the two-dimensional PSD element 2 within a predetermined time, the process proceeds to S7, the search operation is terminated, and if it is not incident, the process proceeds to S6.

  In S6, the DSP 3 divides the search area SE into 16 parts, so that the third resolution is higher than the second resolution (for example, twice the frequency ratio m = 1.01 at which the resolution shown in the figure is 80800). The search operation is executed until the incidence of pilot reference light on the light receiving surface 2a of the two-dimensional PSD element 2 is detected.

  As described above, the search operation at this time divides the search area SE and sequentially performs the search operation for each of the divided areas.

  When this search operation is completed, the process proceeds to S7 and the search operation is terminated.

  Although FIG. 17 shows the search operation with the first to third resolutions, the search is further performed while increasing the resolution sequentially, such as the fourth, fifth,... Resolutions. The operation may be repeatedly executed.

  In this way, by starting the search operation at a relatively low resolution, if the incidence of pilot reference light on the light receiving surface 2a of the two-dimensional PSD element 2 is detected at this stage, the search operation can be completed quickly. it can. Also, even if the pilot reference light is not detected by the search operation at a relatively low resolution, the search operation is repeatedly executed with the resolution being increased successively, so that the pilot reference light is reliably detected. be able to.

[Third Embodiment]
FIG. 18 is a block diagram showing the configuration of the photodetecting device according to the third embodiment of the present invention.

  As shown in FIG. 18, the photodetector in this embodiment includes the configuration of the photodetector in the first embodiment described above, and further serves as a second two-dimensional optical position detector. A two-dimensional optical position detector is provided.

    As shown in FIG. 18, the second two-dimensional light position detection unit does not require a CMOS sensor 18, a wide-angle lens 17 for condensing pilot reference light (PLB) from a wide range of directions on the CMOS sensor 18, and unnecessary. And a visible light blocking filter 19 for cutting light. The second two-dimensional light position detection unit is disposed integrally with the optical system and the biaxial deflection mirror 1 described above.

  Pilot reference light (PLB) emitted from the receiving device is diffused light that covers the entire communication area. Therefore, the pilot reference light (PLB) is always incident on the CMOS sensor 18, and a light beam spot is formed somewhere on the light receiving surface. Therefore, on the light receiving surface of the CMOS sensor 18, the position of the light beam spot changes depending on the incident direction of the pilot reference light (PLB).

  FIG. 19 is a plan view showing the relationship between the light receiving surface of the CMOS sensor of the photodetector and the irradiation light beam spot PLBs of the pilot reference light PLB.

  For example, the CMOS sensor 18 includes 90 × 90 pixels arranged in a matrix, and image information is output by converting light information of each pixel into an electrical signal.

  Image information output from the CMOS sensor 18 is input to the spot position information processing unit 20. The spot position information processing unit 20 calculates the center pixel position of the light beam spot PLBs by image processing such as the level of each pixel information and spot shape extraction processing.

  FIG. 20 is an example of a coordinate angle conversion table used in the spot position information processing unit of the light detection device.

  Further, as shown in FIG. 20, the spot position information processing unit 20 includes a coordinate angle conversion table for correcting image distortion caused by the wide-angle lens 17 and the influence of the relative positions of the biaxial deflection mirror 1 and the CMOS sensor. Are stored, and DC component data (x00, y00 to x89, y89) of the biaxial deflection mirror drive signal corresponding to each pixel is stored.

  The DC component data is sent to the DSP 3. In the DSP 3, a direct current component is generated from the direct current component data and is superimposed on the drive signal of the biaxial deflection mirror 1.

  By the method as described above, the approximate emission direction of the pilot reference light PLB becomes the center of the Lissajous search direction, that is, the search operation by the biaxial deflection mirror 1 is centered on the specified search direction. Thus, the biaxial deflection mirror 1 can be controlled.

(Operation of photodetection device)
Hereinafter, the operation of the photodetector in this embodiment will be described.

  In this photodetection device, as shown in FIG. 18, the biaxial deflecting mirror 1 is arranged so that pilot reference light from the receiving device enters the coordinate center (O) of the light receiving surface 2a of the two-dimensional PSD element 2. Is controlled, that is, in the servo operation state, the optical axis of the transmission light beam coincides with the optical axis of the pilot reference light, and stable signal transmission becomes possible.

  If the pilot reference light is incident on the light receiving area of the light receiving surface 2a of the two-dimensional PSD element 2, the pilot reference light is incident on the coordinate center (O) of the light receiving surface 2a by the operation of the servo control circuit 8. Thus, the biaxial deflection mirror 1 is controlled to adjust the optical axis.

  FIG. 21 is a block diagram showing a state in which the optical axis of the transmission light beam and the optical axis of the pilot reference light are greatly deviated in the photodetector according to the present invention.

  As shown in FIG. 21, in a state where the optical axis of the transmission light beam and the optical axis of the pilot reference light are greatly deviated, the pilot reference light does not enter the light receiving surface 2a of the two-dimensional PSD element 2, so that the servo The optical axis cannot be adjusted by the operation of the control circuit 8. Such a state occurs when signal communication is started for the first time after installing the transmitter / receiver, or when the transmitter / receiver moves for some reason.

  In this light detection apparatus, when the optical axis of the transmission light beam and the optical axis of the pilot reference light are greatly deviated as described above, the DSP 3 operates the biaxial deflection mirror 1 with a wide angle. A search operation for detecting the direction of the pilot reference light is performed by scanning within the range.

  In the search operation of the present invention, the X-axis control signal SSX and the Y-axis search control sign SSY of the biaxial deflecting mirror 1 are sine wave signals having different frequencies so that the direction of inclination of the mirror reflecting surface is a Lissajous figure. Draw.

  Since the optical system is adjusted so that the transmission light beam and the pilot reference light are coaxial when the pilot reference light is incident on the center of the light receiving surface 2a of the PSD 2, as described above, the transmission light beam The Lissajous figure is also drawn in the sending direction.

  Therefore, when the transmission light beam virtual transmission direction and the optical axis of the pilot reference light approach during the search operation, the pilot reference light enters the light receiving area of the light receiving surface 2a of the PSD 2, so that the servo control circuit 8 starts the search operation. The servo operation (closed loop control operation) is switched, the optical axis is adjusted, and the search operation ends.

  As in the first embodiment, the Lissajous drawing range can perform a wide range of search operations by using the entire movable range of the biaxial deflection mirror 1. Further, if the Lissajous figure is used as a fine trajectory and an attempt is made to increase the search resolution, it takes time for the search. Therefore, in order to perform a high-speed search, the frequency of the X-axis control signal SSX and the Y-axis control signal SSY. Need to be high.

(Search area limitation)
When a wide range search operation is to be performed at high speed, the frequency of the X-axis control signal SSX and the Y-axis control signal SSY may be increased. Stable operation cannot be performed due to the influence. Therefore, if the Lissajous figure drawing range is reduced, the drive angle of the biaxial deflecting mirror 1 is reduced, so that stable operation is possible even if the frequency of the X-axis control signal SSX and Y-axis control signal SSY is high.

  As described above, a search locus when the frequency ratio m = 1.01 (integer ratio 100: 101), FX = 400 Hz, and Fy = 404 Hz is considered. In this case, the search trajectory converges with 100 cycles of the sine wave, and the same trajectory is drawn every 0.25 seconds. The trajectory crosses the Y axis 200 times and the X axis 202 times. Further, if the amplitude of the Lissajous drawing is halved so that the drive angle of the biaxial deflecting mirror 1 becomes small, the resolution can be considered to be twice that of 40400, 80800. In this region, the resolution is High-speed and stable high-speed search is possible.

  Using this characteristic, in this embodiment, the direction of the receiving device is specified in a roughly narrow region from the information obtained by the second two-dimensional light position detector based on the position information of the pilot reference light. The search operation is performed by drawing the Lissajous figure so that the search operation is performed at high speed and with high resolution in the region.

(Description of specific search method using CMOS sensor)
In order to set the center coordinates of the search operation, the DSP 3 first determines the pixel having the highest imaging level as the pilot reference light in the CMOS sensor 18 of the second two-dimensional light position detection unit, and specifies the irradiation position.

  Here, as described above, the spot position information processing unit 20 stores a control information table corresponding to each pixel of the CMOS sensor 18. By referring to this control information table, it is possible to generate an optimum DC component such that the center of the search operation is the incident direction of the pilot reference light.

  FIG. 22 is a flowchart showing the search operation according to the present invention.

  In S1, an image is captured by the CMOS sensor, and the process proceeds to S2.

  In S2, the spot position information processing unit 20 performs image processing for extracting a beam spot, and the process proceeds to S3.

  In S3, it is determined whether or not there is a beam spot in the captured image. If there is a beam spot, the process proceeds to S4. If not, the process returns to S1.

  In S4, with reference to the coordinate angle conversion table, the DC component data of the biaxial deflection mirror drive signal corresponding to each pixel is output, and the process proceeds to S5.

  In S5, the DSP 3 drives the biaxial deflection mirror 1 so that the direct current component is superimposed on the drive signal and the Lissajous search of a limited area is performed, and the process proceeds to S6.

  In S6, it is determined whether the servo is locked. If the servo is locked, the search operation is terminated.

  FIG. 23 is an explanatory diagram of the operation when the search range is limited.

  FIG. 23 shows a case where the center position of the search operation is set to XY coordinates (−0.3, 0.3). As shown in FIG. 23, the X-axis control signal SSX and the Y-axis control signal SSY are direct currents for specifying the center position (direction) of the Lissajous figure in the sine wave drive signal for drawing the Lissajous figure. It becomes a waveform with superimposed components.

  Specifically, as shown in FIG. 23, by superimposing a DC component on the X-axis control signal SSX and the Y-axis control signal SSY, the center position (angle) of the Lissajous figure, that is, the center of the area where the search operation is performed. The search range is controlled by arbitrarily changing the position and further optimally setting the drawing amplitude of the Lissajous figure.

  These operations are the same as those in the first and second embodiments described above.

  The superimposition of the DC component on the X-axis control signal SSX and the Y-axis control signal SSY in the DSP 3 is obtained from the control information table with respect to the X-axis control signal SSX and the Y-axis control signal SSY obtained as a calculation result. This can be realized by adding constants.

It is a block diagram which shows the structure of the photon detection apparatus which concerns on 1st Embodiment of this invention. It is a top view which shows the structure of the biaxial deflection | deviation mirror of the said photon detection apparatus. It is a disassembled perspective view which shows the structure of the biaxial deflection | deviation mirror of the said photon detection apparatus. It is a front view which shows the structure of the two-dimensional PSD element 2 of the said photon detection apparatus. FIG. 3 is a block diagram showing a state in which the optical axis of a transmission light beam and the optical axis of pilot reference light are greatly shifted in the photodetector. It is a graph which shows the Lissajous locus drawn in 1 second when the frequency about the X-axis is 50 [Hz] in the biaxial deflection mirror of the photodetection device. It is a graph which shows the Lissajous figure drawn with a biaxial deflection | deviation mirror, when the triangular wave is used as a control signal in the said photon detection apparatus. In the said photon detection apparatus, it is a graph which shows the search locus | trajectory when frequency ratio m is 1.01, FX is 400 Hz, and Fy is 404 Hz. 6 is a graph illustrating an operation when a search range is divided in the photodetection device. It is a graph which shows a Lissajous locus | trajectory when an error arises in the frequency ratio about X-axis and Y-axis in the biaxial deflecting mirror of the photodetection device. It is a block diagram which shows the structure of DSP for calculating a sine wave in the said photon detection apparatus. It is a flowchart which shows the calculation process of the sine wave in the said DSP. 4 is a flowchart showing a calculation process when an X-axis control signal SSX and a Y-axis control signal SSY having different frequencies are generated in the DSP. It is a flowchart of the arithmetic processing control of DSP in 1st Embodiment of the photon detection apparatus which concerns on this invention. FIG. 5 is a waveform diagram showing output signal waveforms from a PSD signal processing circuit and a servo error signal level detection circuit during a search operation. It is a flowchart which shows the 1st example of the arithmetic processing control of DSP in 2nd Embodiment of the photon detection apparatus which concerns on this invention. It is a flowchart which shows the 2nd example of arithmetic processing control of DSP in 2nd Embodiment of the photon detection apparatus which concerns on this invention. It is a block diagram which shows the structure of the photon detection apparatus which concerns on 3rd Embodiment of this invention. It is a top view which shows the relationship between the CMOS sensor light-receiving surface of the said photon detection apparatus, and the irradiation light beam spot PLBs of pilot reference light PLB. It is an example of the coordinate angle conversion table used by the spot position information processing part of the said photon detection apparatus. FIG. 3 is a block diagram showing a state in which the optical axis of a transmission light beam and the optical axis of pilot reference light are greatly shifted in the photodetector. It is a flowchart which shows the search operation | movement of the said photon detection apparatus. It is a graph which shows the example which made the center of the search range arbitrary positions in the biaxial deflection | deviation mirror of the said photon detection apparatus.

Explanation of symbols

1 Biaxial deflection mirror 2 Two-dimensional PSD element 2a Light receiving surface 3 DSP (Digital Signal Processor)
4 D / A converter 5 Signal switching unit 6 Drive amplifier 7 PSD signal processing circuit 8 Servo control circuit 9 Servo error signal level detection circuit 10 Condensing lens for PSD 11 Collimator lens 12 LD light emitting element 13 Beam splitter 14 Fisheye lens 15 Clock generation 16 A / D converter 17 Wide angle lens 18 CMOS sensor 19 Visible light blocking filter 20 Spot position information processing unit

Claims (3)

A biaxial light deflecting means for deflecting and emitting a light beam incident from the outside in the biaxial direction;
Search control means for generating a control signal and controlling the biaxial light deflection means based on the control signal;
A light beam that has passed through the two-axis light deflecting means is incident, and two-dimensional light position detecting means capable of two-dimensionally detecting the incident position of the light beam,
A photodetecting device for detecting a direction of incidence of the light beam from the outside based on the incident position of the light beam detected by the two-dimensional light position detecting means by executing a search operation by deflection of the biaxial light deflecting means Because
The search control means generates two periodic signals having different frequencies as control signals, and the biaxial light deflecting means deflects each axis so that the locus of the incident position becomes a Lissajous figure by the two periodic signals. While independently controlling each time, the amplitude of the control signal is limited, and a direct current component is superimposed on the control signal, and the deflection is controlled so as to be performed on a part of a region where the deflection is possible. And a light detection device. Biaxial light deflecting means capable of deflecting and emitting a light beam incident from the outside in the biaxial direction;
Search control means for generating a control signal and controlling the biaxial light deflection means based on the control signal;
A first two-dimensional light position detecting means capable of two-dimensionally detecting an incident position of the light beam incident on the light beam having passed through the two-axis light deflecting means;
With
A search operation by deflection of the biaxial light deflecting means is executed to detect the incident direction of the light beam from the outside based on the incident position of the light beam detected by the first two-dimensional light position detecting means. A light detection device comprising:
A light beam incident from the outside is received without passing through the biaxial light deflecting means, and a second two-dimensional light position detecting means for detecting the incident direction of the light beam is provided.
The search control means generates two periodic signals having different frequencies as control signals, and the biaxial light deflecting means deflects each axis so that the locus of the incident position becomes a Lissajous figure by the two periodic signals. While controlling independently each time, while limiting the amplitude of the control signal, a direct current component based on the approximate incident direction of the light beam detected by the second two-dimensional light position detecting means in the control signal And controlling so that the deflection is performed on a part of a region where the deflection is possible. The light detection device according to claim 2,
The search control means superimposes the direct current component on the control signal so that a center position in a part of the region to be deflected is a position corresponding to the approximate incident direction. apparatus.

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