JP2008160349A - Optical signal transmission device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical signal transmission device capable of more stably transmitting data in consideration of the waveform variance due to operations of a quickly driven deflecting optical system in the optical signal transmission device which transmits a data signal and a control signal one over the other and separates a data signal and a control signal from a received signal. <P>SOLUTION: A data signal D is modulated using a modulation system for modulation into a signal having no DC components, and a control signal S for controlling the deflecting optical system of the optical signal transmission device on a reception side is superposed on the modulated signal, so that the spectrum of the control signal S and the operation control band A of the deflecting optical system are present in a frequency band lower than that of the data signal D. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical signal transmission apparatus that performs data transmission by transmitting and receiving an optical signal modulated by a data signal or the like.

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

  In such an optical signal transmission device, an LED (light emitting diode) or an LD (laser diode) is used as a light emitting element on the transmission side for transmitting an optical signal. When an LED is used as the light emitting element, the light beam from the LED has a wide directivity, and this light beam must be collected by a focusing lens. However, since there is a limit to condensing light with a focusing lens, in an apparatus using an LED as a light emitting element, when an optical signal is transmitted over a long distance, the beam diameter is expanded, and the received power is reduced. End up.

  On the other hand, when an LD is used as the light emitting element, the directivity of the outgoing light beam can be made narrower, and an optical signal can be transmitted over a long distance. However, in this case, the light beam with a narrow directivity must be accurately applied to the light receiving unit of the device to be transmitted. Therefore, for example, as described in Patent Literature 1, Patent Literature 2, and Patent Literature 3, using a deflection optical system having a movable mirror, optical axis adjustment between a transmission-side device and a reception-side device is performed. Has been done.

  That is, in the transmission / reception unit of such an optical signal transmission device, a control signal (pilot signal) is superimposed on the data signal supplied from the external interface 101 by the data supply unit 102 as shown in FIG. Based on the above, the light emission intensity of the light emitting element 103 is modulated. The light beam emitted from the light emitting element 103 is converted into a parallel light beam by the collimator lens 104, passes through the beam splitters 105 and 106, and enters the deflection optical system 107. The deflection optical system 107 is configured to include a reflection mirror that can control deflection, and reflects the light beam transmitted through the beam splitters 105 and 106. The light beam reflected by the reflecting mirror is emitted from the optical signal transmission device.

  On the other hand, the light beam transmitted from the optical signal transmission device that is the communication partner is reflected by the deflection optical system 107, partially reflected by the beam splitters 106 and 105, and condensed by the condenser lenses 108 and 109, respectively. The light receiving elements 110 and 111 receive the light.

  The light detection signal output from the light receiving element 110 for data reception is subjected to waveform shaping and digital data by the reception signal processing unit 112 and supplied to the external interface 113. The light detection signal output from the control light receiving element 111 is subjected to signal processing for controlling the deflection optical system 107 in the deflection angle control signal supply unit 114. The deflection angle control signal supply unit 114 controls the deflection optical system 107 based on the light detection signal output from the control light receiving element 111, and transmits the optical signal of the light beam to be transmitted / received as a communication partner. Match the optical axis of the device.

JP-A-6-152541 Japanese Patent Laid-Open No. 2001-77760 JP 2001-77762 A

  As described above, in the optical signal transmission device, the data supply unit 102 supplies the light emitting element 103 with a signal in which the data signal and the control signal are superimposed. The data signal supplied from the external interface 101 has a wide spectrum including a direct current (DC) component, as shown in FIG. As a control signal, a signal having a specific frequency (fps) is used so as not to be affected by background light.

  As shown in FIG. 8B, the transmitted optical signal has a waveform in which a control signal of a specific frequency is superimposed on the data signal, and there is a possibility that it is difficult to receive stable data. It was.

  Here, in order not to be affected by the background light, it is also conceivable to remove the direct current component from the received signal in the optical signal transmission device on the receiving side. However, as described above, since the spectrum of the data signal includes a direct current component, if the direct current component is removed from the received signal, the data signal cannot be accurately demodulated.

  In the conventional optical signal transmission apparatus, as described in Patent Document 2 and Patent Document 3 described above, in the optical signal transmission apparatus on the reception side, control is performed from the received signal shown in FIG. 9 is separated, and a signal having a polarity opposite to that of the separated control signal shown in (b) of FIG. 9 is added to the received signal, as shown in (c) of FIG. The waveform shaping of the data signal was performed.

  However, in such a conventional optical signal transmission device, the waveform change due to the movement of the deflection optical system that is driven at high speed is not taken into consideration, and there is a possibility that communication during movement becomes difficult.

  In the data supply unit 102 of the conventional optical signal transmission apparatus, as shown in FIG. 10, a data signal on which a control signal is superimposed is input, and a driving current corresponding to the data signal is generated by the modulation current generator 115. And supplied to the light emitting element 103. On the other hand, a constant bias current is generated by the bias current (DC) generator 116 and supplied to the light emitting element 103 via the low-pass filter 117 so as not to affect the data signal.

  Therefore, the present invention has been proposed in view of the above-described circumstances, and transmits a data signal and a control signal superimposed on each other and separates the data signal and the control signal from the received signal. It is an object of the present invention to provide an optical signal transmission device that enables more stable data transmission in consideration of waveform changes due to the movement of a deflection optical system that is driven at high speed.

  In order to solve the above-described problem, an optical signal transmission device according to the present invention has the following configuration.

[Configuration 1]
In an optical signal transmission device that transmits an optical signal modulated based on a data signal and receives and demodulates an optical signal modulated based on the data signal, the optical signal is modulated to a signal having no DC component Modulation based on an optical signal modulated based on a data signal modulated using a modulation method and a control signal for controlling the deflection optical system of another optical signal transmission apparatus that receives the optical signal via the deflection optical system A transmission unit that superimposes and transmits the optical signal, and the operation control band of the deflection optical system of another optical signal transmission device is f1, and the carrier frequency of the control signal for controlling this deflection optical system is f2, When the low frequency limit frequency of the optical signal for data transmission is f3,
100 · f1 <10 · f2 <f3
A data emission control unit that supplies a drive current corresponding to a signal modulated based on a data signal to a light emitting element that modulates based on the data signal and emits an optical signal, and a light emitting element Connected via a low-pass filter to control the direct-current light emission amount of the light-emitting element, and connected to the light-emitting element via a low-pass filter for modulation based on the control signal and for controlling the light-emitting element And a control light emission control unit that supplies a drive current corresponding to the signal modulated based on the signal.

  In this optical signal transmission device, the spectrum of a control signal that modulates the data signal to be transmitted into a signal having no DC component and controls the deflection optical system of another optical signal transmission device in a frequency band lower than this signal. In addition, since the operation control band of the deflection optical system exists, the control signal can be stably received even during the operation of the deflection optical system. Further, the data signal and the control signal can be easily separated by the frequency filter.

  Further, in this optical signal transmission device, the modulated light emission according to the signal obtained by superimposing the data signal and the control signal is performed by one light emitting element, so that the configuration of the transmission unit can be simplified.

  In an optical signal transmission device according to an embodiment of the present invention, a data signal to be transmitted is modulated into a signal having no DC component, and a deflection optical system of another optical signal transmission device is provided in a frequency band lower than the optical signal. A spectrum of a control signal to be controlled and an operation control band of the deflection optical system are present.

  Therefore, in this optical signal transmission device, stable control signal reception can be realized even during operation of the deflection optical system, and data signals and control can be performed even during operation of the deflection optical system capable of high-speed operation. It becomes possible to superimpose and transmit the signal for use. Further, the data signal and the control signal can be easily separated by a frequency filter.

  Further, in this optical signal transmission device, the modulated light emission according to the signal obtained by superimposing the data signal and the control signal is performed by one light emitting element, so that the configuration of the transmission unit can be simplified.

  In other words, the present invention relates to the movement of a deflection optical system that is driven at high speed in an optical signal transmission apparatus that superimposes a data signal and a control signal for transmission and separates the data signal and the control signal from the received signal. In consideration of the waveform change due to the above, it is possible to provide an optical signal transmission device capable of more stable data transmission.

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

  The optical signal transmission device according to the present invention detects the direction of the optical signal transmission device that is the counterpart of communication, in other words, the incident direction of the light beam, and the optical axis of the light emitting element is set to the optical axis of the light receiving element. This is an optical signal transmission device having a function of always following.

[Configuration in Embodiment of Optical Signal Transmission Device]
FIG. 1 is a side view showing a configuration in an embodiment of an optical signal transmission apparatus according to the present invention.

  In the optical signal transmission device according to the present invention, as shown in FIG. 1, a control signal (pilot signal) is superimposed on the data signal supplied from the external interface 1 by the data supply unit 2, and based on this signal, The light emission intensity of the light emitting element 3 is modulated. That is, the light emission intensity in the light emitting element 3 is an optical signal in which an optical signal modulated based on the data signal and an optical signal modulated based on the control signal are superimposed. For example, a laser diode is used as the light emitting element 3.

  As will be described later, the data signal supplied from the external interface 1 is modulated using a modulation method that modulates the signal to have no DC component. The control signal is a signal having a specific frequency.

  The light beam emitted from the light emitting element 3 is converted into a parallel light beam by the collimator lens 4, passes through the beam splitters 5 and 6, and enters the deflection optical system 7. The deflection optical system 7 includes a reflection mirror that can be controlled to be deflected in two axial directions by an electromagnetic drive mechanism, for example. The deflecting optical system 7 can reflect the light beam that has passed through the beam splitters 5 and 6 and deflect the incident light beam in the biaxial direction for emission. The light beam reflected by the reflecting mirror is emitted from the optical signal transmission device.

  And this optical signal transmission apparatus receives the light beam transmitted from the other optical signal transmission apparatus used as a communicating party. This received light beam is an optical signal modulated based on a signal in which a data signal and a control signal (pilot signal) are superimposed, similarly to the light beam transmitted from the optical signal transmission device.

  A received light beam transmitted and received from another optical signal transmission device as a communication partner is reflected by the deflecting optical system 7 and partially reflected by the beam splitters 6 and 5, respectively. The light is collected and received by the first and second light receiving elements 10 and 11 serving as a receiving unit.

  The photodetection signal output from the first light receiving element 10 for data reception is subjected to waveform shaping and digital data by the reception signal processing unit 12 and supplied to the external interface 13. The light detection signal output from the control second light receiving element 11 is subjected to signal processing for controlling the deflection optical system 7 in the deflection angle control signal supply unit 14. The deflection angle control signal supply unit 14 controls the deflection optical system 7 on the basis of the light detection signal output from the control light receiving element 11, and transmits the optical signal of the light beam to be transmitted / received as a communication partner. Match the optical axis of the device.

  The optical system of this optical signal transmission device includes a light beam to be transmitted in a state where a reception light beam transmitted from another optical signal transmission device that is a communication partner is incident on the center of the light receiving surface of the second light receiving element 11. The receiving light beam is adjusted to be coaxial. That is, in this optical system, the center of the light receiving surface of the second light receiving element 11 and the light emitting point of the light emitting element 3 are in a conjugate position with respect to the reflecting surface of the beam splitter 5. In such a state where the transmitted light beam and the received light beam are coaxial, the transmitted light beam is accurately incident on the light receiving element for signal reception of the optical signal transmission device on the receiving side. Can do.

  FIG. 2 is a front view showing the configuration of the second light receiving element 11.

  As shown in FIG. 2, the second light receiving element 11 is a two-dimensional PSD (Position Sensitive Detector) element capable of two-dimensionally detecting the incident position of the incident light beam. It is a quadrant PD (Photo Detector) divided into four areas radially from the center. The second light receiving element 11 is an element generally used in optical position measurement. The second light receiving element 11 outputs four output signals corresponding to the four light receiving regions according to the incident positions in the light receiving surface 11a of the light beam incident on the light receiving surface (position detecting unit) 11a. Output from the terminal. The level of each of these output signals represents the incident position of the light beam in the light receiving surface 11a.

  The light beam received by the second light receiving element 11 is received on the light receiving surface 11 a by the optical axis of the light beam transmitted via the deflection optical system 7 and the received light beam received via the deflection optical system 7. A light spot is formed at a position corresponding to the deviation from the optical axis.

  Note that the second light receiving element 11 is not limited to the four-divided PD, and can be replaced with, for example, a C-MOSS sensor.

  FIG. 3A is a block diagram illustrating a configuration of the deflection angle control signal supply unit 14.

  Output signals SIG-A, SIG-B, SIG-C, and SIG-D from the respective light receiving regions PD-A, PD-B, PD-C, and PD-D of the second light receiving element 11 are shown in FIG. 3A. As described above, the signals are amplified by the AGC amplifiers 21, 22, 23, and 24 that are independent variable gain amplifier circuits. The amplified signal is converted into a direct current (DC) voltage corresponding to the amount of light received in each of the light receiving regions PD-A, PD-B, PD-C, and PD-D by the detection / rectifier circuits 25, 26, 27, and 28. Converted. The DC voltage corresponding to the amount of received light is sent to the arithmetic processing unit 29. The arithmetic processing unit 29 determines the deflection angle of the reflecting mirror of the deflection optical system 7 and the light receiving light quantity in each light receiving area PD-A, PD-B, PD-C, PD-D of the second light receiving element 11 and A signal for appropriately controlling the deflection direction is generated.

  The reflection mirror of the deflection optical system 7 is controlled to be deflected by the signal generated by the arithmetic processing unit 29, so that the optical axis of the light beam transmitted via the deflection optical system 7 and the reception via the deflection optical system 7 are received. The optical axis of the received light beam is matched. At this time, the light beam received by the second light receiving element 11 forms a light spot at the center of the light receiving surface 11a.

  In the deflection angle control signal supply unit 14, the gain settings of the AGC amplifiers 21, 22, 23, and 24 are set to the same gain by the variable gain setting unit 30. The variable gain setting unit 30 receives the signals amplified by the AGC amplifiers 21, 22, 23, and 24, and the sum of the signals amplified by the AGC amplifiers 21, 22, 23, and 24 is constant. The gain of each AGC amplifier 21, 22, 23, 24 is set.

  As a result, the change in the output signal from the second light receiving element 11 due to the deviation of the optical axis between the transmitted light beam and the received light beam, and the output signal due to the gain fluctuation in each AGC amplifier 21, 22, 23, 24 It becomes possible to separate changes.

  FIG. 3B is a block diagram illustrating another example of the configuration of the deflection angle control signal supply unit 14.

  In the deflection angle control signal supply unit 14, the variable gain setting unit 30 for setting the gains of the AGC amplifiers 21, 22, 23, and 24 includes detection / rectification circuits 25, 26, 27 and 28 outputs may be input.

  Also in this case, the variable gain setting unit 30 sets the gains of the AGC amplifiers 21, 22, 23, and 24 to the same gain, and is amplified and detected by the AGC amplifiers 21, 22, 23, and 24. Each AGC amplifier 21, 22, 23, 24 is input so that the signals that have passed through the rectifier circuits 25, 26, 27, 28 are input and the sum of the signals that have passed through the detector / rectifier circuits 25, 26, 27, 28 is constant. Set the gain.

  FIG. 4 is a graph showing a spectrum of a modulation signal in the signal modulation method.

  The data signal from the external interface 1 is modulated by using a modulation method that modulates the signal without a DC component. As such a modulation method, as shown in FIG. 4, “8B10B modulation” (a modulation method for converting an arbitrary 8-bit signal into a 10-bit signal having an equal positive / negative ratio) and the like can be mentioned.

  In other words, the optical signal transmission apparatus according to the present invention has a sufficient optical signal transmission compared to a conventional optical signal transmission apparatus that employs a modulation method that is modulated to a signal having a DC component, such as “NRZ modulation”. Using the characteristics having a transmission band, the data is modulated into a signal having no DC component by “8B10B modulation” or the like, and used as transmission data.

  Therefore, in the conventional optical signal transmission apparatus, signal processing such as waveform shaping is required for the received signal, whereas in the optical signal transmission apparatus according to the present invention, a spectrum in a low frequency band that is not used. Can be obtained by separating the control signal and the data signal stably with a simple configuration such as a frequency filter.

  In high-speed data transmission, using a modulation method that does not have a DC component is effective in improving transmission performance. The absence of a direct current component means that the direct current (DC) balance performance is high, and the number of 0s and 1s of modulation codes that are balanced in DC are substantially equal in all periods of length N. For example, in the “Manchester code”, logic 1 is expressed as 10 and logic 0 is expressed as 01, so that complete DC balance is realized. The “8B10B code” improves the DC balance by converting an 8-bit code into a 10-bit code. Furthermore, since the amplifier of the light receiving circuit can be AC-coupled, the variable gain amplifier circuit (AGC) can be easily designed. In the present invention, the “modulation method having no DC component” is not limited to the above two types.

  FIG. 5 is a graph showing the spectrum of the data signal and the control signal in this optical signal transmission apparatus.

  In this optical signal transmission device, as shown in FIG. 5, the control signal is between the spectrum of the data signal D modulated into a signal having no DC component and the control band A in which the deflection optical system 7 operates. Set so that S spectrum exists.

  The frequency f1 of the control band A in which the deflection optical system 7 operates is at most about 1 kHz. When the frequency of the gain intersection of the control band A and the control signal S is set to 1 kHz, the center frequency f2 of the control signal S needs to be 10 times or more. Further, considering the operation of the detection circuit and the like, the center frequency f2 of the control signal S is preferably 20 times or more the frequency f1 of the control band A, and is 20 kHz or more. Note that the modulation method of the control signal S is not particularly limited, such as FM modulation, AM modulation, and PSK modulation.

  Furthermore, if the frequency band f3 of the data signal D is set to 10 times or more the center frequency f2 of the control signal S, the data signal D and the control signal S can be separated by a simple frequency filter. That is, the data signal D can be separated by, for example, removing a signal of 200 kHz or less by the HPF. As a configuration of the HPF, HPF characteristics can also be obtained by making the light receiving circuit an amplifier configuration using AC coupling. Furthermore, the HPF characteristic of the AC coupling amplifier can be adjusted also by the element area of the light receiving element.

  The frequency characteristics of the variable gain in the AGC amplifiers 21, 22, 23 and 24 for the control signal S are sufficient if the frequency f 1 of the control band A in which the deflection optical system 7 operates is sufficient.

From such examination, in the optical signal transmission device according to the present invention, the control signal S and the data signal can be obtained with a small circuit configuration by establishing the following relationship with respect to the frequency spectrum distribution of each signal. It is possible to configure an optical signal transmission apparatus that performs transmission and reception by superimposing D and controls the optical axes of transmission light and reception light.
100 · f1 <10 · f2 <f3

When a digital control system is used to control the deflection optical system 7, sampling of control signals (A / D) is required. Sampling becomes a phase lag element in the control loop. The transfer function based on the zero-order hold is expressed by the following equation by the sampling period T.
(1-e- ^Ts ) / s

  From this equation, it can be seen that the phase lag at the desired gain intersection frequency varies with the sampling period T. Therefore, a sufficiently high sampling frequency is required. By setting the sampling frequency to 10 times or more with respect to the gain crossover frequency, the phase delay can be set to several degrees, so that the center frequency f2 of the control signal S is set to the frequency f1 of the control band A of the deflection optical system 7. The numerical value of 10 times as large as can be used as a guideline at the time of design even when a digital control system is used.

  FIG. 6 is a circuit diagram showing the configuration of the data supply unit in this optical signal transmission apparatus.

  In the data supply unit 2 of the optical signal transmission device, as shown in FIG. 6, a data signal is input, and a drive current corresponding to the data signal is generated by a modulation current generator 15 serving as a data emission control unit, The light is supplied to the light emitting element 3. In other words, the modulation current generator 15 performs modulation based on the data signal, and supplies a drive current corresponding to the signal modulated based on the data signal to the light emitting element 3.

  On the other hand, a constant bias current is generated by a bias current (DC) generator 16 serving as a direct current light emission control unit, and is supplied to the light emitting element 3 via a low-pass filter 17 so as not to affect the data signal. . The bias current generator 16 is connected to the light emitting element 3 via a low-pass filter 17 and controls the amount of DC light emission of the light emitting element 3.

  Further, a control signal generator 18 serving as a control signal light emission control unit is connected to the light emitting element 3 via a low pass filter 17. The control signal generator 18 performs modulation based on the control signal and supplies the light emitting element 3 with a drive current corresponding to the signal modulated based on the control signal.

  In the data supply unit 2, the bias current and the drive current corresponding to the signal modulated based on the control signal are added and supplied to the light emitting element 3 through the low-pass filter 17. The characteristic of the low-pass filter 17 is that the drive current corresponding to the control signal is passed and the signal in the band of the data signal is not passed, and the quality of the data signal is maintained and the response is made according to the control signal. It is possible to superimpose the drive current.

  In this optical signal transmission device, the low-pass filter 17 can be easily configured because the distribution of the frequency spectrum of the data signal and the control signal satisfies the above-described relationship.

It is a side view which shows the structure in embodiment of the optical signal transmission apparatus which concerns on this invention. It is a front view which shows the structure of the 2nd light receiving element in the said optical signal transmission apparatus. It is a block diagram which shows the structure of the deflection angle control signal supply part in the said optical signal transmission apparatus. It is a block diagram which shows the other example of a structure of the deflection angle control signal supply part in the said optical signal transmission apparatus. It is a graph which shows the spectrum of the modulation signal in the signal modulation system used in the said optical signal transmission apparatus. It is a graph which shows the spectrum of the data signal and control signal in the said optical signal transmission apparatus. It is a circuit diagram which shows the structure of the data supply part in the said optical signal transmission apparatus. It is a side view which shows the structure of the conventional optical signal transmission apparatus. It is a figure which shows the conventional data signal and the signal for control. It is the figure which showed the separation method of the conventional data signal and the signal for control. It is a circuit diagram which shows the structure of the data supply part in the conventional optical signal transmission apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 External interface 2 Data supply part 3 Light emitting element 4 Collimator lens 5,6 Beam splitter 7 Deflection optical system 8,9 Condensing lens 10 1st light receiving element 11 2nd light receiving element 13 External interface 14 Deflection angle control signal supply part DESCRIPTION OF SYMBOLS 15 Modulation current generator 16 Bias current generator 17 Low pass filter 18 Control signal generator 21, 22, 23, 24 AGC amplifier 25, 26, 27, 28 Detection / rectification circuit 29 Arithmetic processing part 30 Variable gain setting part A Operation Control band S Signal band for control D Data signal band

Claims (1)

In an optical signal transmission apparatus that transmits data by transmitting an optical signal modulated based on a data signal and receiving and demodulating the optical signal modulated based on the data signal,
An optical signal modulated based on a data signal modulated using a modulation method that modulates a signal having no DC component, and the deflection optical system of another optical signal transmission apparatus that receives the optical signal via the deflection optical system A transmission unit that superimposes and transmits an optical signal modulated based on a control signal for controlling
The operation control band of the deflection optical system of the other optical signal transmission apparatus is set to f1, the carrier frequency of the control signal for controlling this deflection optical system is set to f2, and the low frequency limit frequency of the optical signal for data transmission is set to f3. When
100 · f1 <10 · f2 <f3
The relationship is established,
A data emission control unit that performs modulation based on the data signal and supplies a driving current corresponding to the signal modulated based on the data signal to the light emitting element that emits the optical signal;
A direct current light emission control unit that is connected to the light emitting element via a low-pass filter and controls the direct current light emission amount of the light emitting element;
Connected to the light emitting element through the low-pass filter, performs modulation based on the control signal, and supplies a drive current corresponding to the signal modulated based on the control signal to the light emitting element. An optical signal transmission device comprising: a control signal light emission control unit.

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