JP3104046B2 - Optical space transmission apparatus and optical space transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for transmitting information such as video and audio in an optical space.

[0002]

2. Description of the Related Art For example, when video and audio signals are transmitted between a video reproducing apparatus and a television, information space is transmitted using light in order to improve the degree of freedom in the layout of the video reproducing apparatus and the television. An optical space transmission device that performs transmission may be used. By the way, in an optical space transmission device using laser light as light for information transmission, it is necessary to always direct the laser light to the receiving side device.
Japanese Patent Application Laid-Open No. 62-274837 discloses a method of correcting and controlling the transmission direction of a laser beam for information transmission using a half mirror and an imaging device.

Further, Japanese Patent Laid-Open Publication No. Hei 3-235438 discloses a method of detecting the orientation of a device by a mirror arranged on a focal plane of a transmitting or receiving lens.
Japanese Patent Application Laid-Open No. 3-236640 discloses a method of detecting fluctuations in the vertical and horizontal directions of a laser beam using an inclinometer or an accelerometer, and correcting the irradiation position of the laser beam based on the results.

[0004]

However, in the method disclosed in Japanese Patent Application Laid-Open No. Sho 62-274837, a part of the laser beam for information transmission is used for detecting the sending direction of the laser beam. The output of the signal transmitted to the side decreases, and it takes time for image processing and the like, so that the response of the correction of the transmission direction is delayed. Further, if the half mirror is not irradiated with the laser light at the time of the initial setting, it is not possible to detect the sending direction of the laser light, and to perform the indirect correction for aligning the receiving device with the laser light on the half mirror. There was a problem of becoming.

On the other hand, the method disclosed in Japanese Patent Application Laid-Open No. 3-235438 is a complete manual correction, and it is impossible to correct the optical axis by following a change in the relative position between the transmitting side and the receiving side during communication. There was a problem that is. Further, Japanese Unexamined Patent Publication No.
The method disclosed in Japanese Patent Publication No. 236640 has a problem that it can follow the position fluctuation on the transmitting side but cannot follow the position fluctuation on the receiving side.

[0006] The present invention solves the above problems,
An object of the present invention is to provide an optical space transmission device capable of correcting an optical axis shift in a wide range.

[0007]

In order to solve the above-mentioned problems, a space optical transmission apparatus according to the present invention comprises a transmitting unit for outputting a light beam modulated based on a predetermined information signal, and a light receiving unit for receiving the light beam. And a demodulating and receiving unit, wherein the receiving unit is provided with a light source that outputs infrared light toward the transmitting unit and a transmitter that outputs radio waves toward the transmitting unit. , The transmitting unit includes a light detecting module having four light detecting elements, and a differential amplifier for comparing outputs of left, right, upper and lower light detecting elements, and an irradiation position for detecting an irradiation position of the infrared light. Detection means, reception intensity detection means for receiving the radio wave and detecting the reception intensity of the radio wave, and irradiating the light beam based on the detection results of the irradiation position detection means and the reception intensity detection means Correcting means for correcting the direction of the light beam, when at least one output of the differential amplifier becomes larger than a first predetermined value, and when the output of the reception intensity detecting means becomes smaller than a predetermined value. Security means for stopping the output and outputting a light beam when the output of the differential amplifier becomes smaller than a second predetermined value smaller than the first predetermined value.

[0008]

According to the optical space transmission apparatus of the present invention, the deviation of the light beam for information transmission in the optical axis direction is roughly corrected over a wide range based on the reception intensity of the radio wave output from the receiving unit. Since the deviation of the light beam in the optical axis direction is precisely corrected based on the irradiation position of the infrared light output from the receiving unit side, the deviation of the light beam in the optical axis direction can be corrected over a wide range.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a transmission unit of a free-space optical transmission apparatus according to one embodiment of the present invention in a partial block, FIG. FIG. 3B is a perspective view illustrating a main part of the transmission unit and the reception unit illustrated in FIGS. 1 and 2.

In the transmission unit 1 shown in FIG. 1, for example, an analog signal such as a video signal is converted into a frequency pre-modulation unit (PFM-M
D) 11, and a digital signal such as an audio signal passes through an encoding unit (CMI-CODEC) 12 and a laser driver (LD drive) of an electric-optical conversion unit (E / O) 13
er) 131. The laser driver 131 outputs a laser output from the laser diode 132 based on a signal sent from the frequency pre-modulation unit 11 or the encoding unit 12.
The laser beam (light beam) LB is modulated, and the modulated laser beam LB is shaped into a parallel light beam by the collimator lens 133 and transmitted to space.

The laser beam LB output from the laser diode 132 is received by a photodetector 134, and a signal corresponding to the amount of the received light, that is, a signal corresponding to the laser power, is sent from the photodetector 134 to an auto power controller (APC). 13
5 is input. And the auto power controller 1
35 is based on a detection signal from the light detection element 134,
Feedback control is performed via the laser driver 131 so as to stabilize the laser power of the laser light LB output from the laser diode 132.

Reference numeral 14 in FIG. 1 denotes an actuator (ACT) for changing the directivity of the laser beam LB output from the laser diode 132. As shown in FIG. 1, a rotary table 141 rotatable in the horizontal direction, a support frame 142 provided on the rotary table 141, and a laser diode 132 shown in FIG. And a cylindrical body 143 in which the collimating lens 133 is accommodated, and is placed on the bottom case B and covered with a cover C. The actuator 14 is driven by a drive control signal from a servo circuit 15 (see FIG. 1) mounted on the board A.

Reference numeral 16 in FIG. 1 designates four light detection elements 161 to 164, which are irradiated with infrared light RB emitted from a light emitting diode (LED) 31 of the receiving unit 3 described later. Light detection module (Q
UARD-PD), and is attached to the upper part of the cylindrical body 143 in the direction in which the laser light from the laser diode 132 is directed, as shown in FIG. Further, reference numerals 171 and 172 in FIG.
61, 162, 163 and 164. The outputs of the differential amplifiers 171 and 172 are, as shown in FIG. 1, the shift (PITCH) of the laser light LB output from the laser diode 132 in the left-right direction.
And a signal indicating a vertical shift (YAW).

On the other hand, reference numeral 181 in FIG. 1 denotes a receiving antenna for receiving a radio wave transmitted into the air from a transmitting antenna 362 of the receiving unit 3 to be described later.
As shown in (1), the laser light LB from the laser diode 132 is attached to the upper part of the photodetection module 16 in the direction of direction. Reference numeral 182 in FIG. 1 denotes an RF circuit that demodulates a radio wave received by the reception antenna 181. A signal obtained by demodulating the radio wave from the RF circuit 182 corresponds to the reception intensity of the radio wave. The level is output to the servo circuit 15. Then, the servo circuit 15 controls the drive of the actuator 14 based on the outputs of the differential amplifiers 171 and 172 and the RF circuit 182.

Further, in FIG. 1, reference numeral 19 denotes an action to the auto power controller 135 when at least one of the outputs of the differential amplifiers 171 and 172 exceeds a predetermined value and when the output of the RF circuit 182 falls below a predetermined value. The security circuit stops the output of the laser beam LB from the laser diode 132 via the laser driver 131.
In this embodiment, the actuator 14 and the servo circuit 15 correspond to a correction unit, the light detection module 16 and the differential amplifiers 171 and 172 correspond to an irradiation position detection unit,
The receiving antenna 181 and the RF circuit 182 correspond to a receiving intensity detecting unit.

On the other hand, in the receiving unit 3 shown in FIG. 2, the laser beam LB output from the laser diode 132 of the transmitting unit 1 is transmitted to the filter 32 which functions as both a filter for cutting disturbance light and a condenser lens. Through this, the light enters the light receiving element 331 of the photoelectric conversion unit (O / E) 33. Ray
A signal output from the light receiving element 331 in response to the incidence of the light LB is amplified by an amplifier (IV) 332 and input to an auto gain controller (AGC) 333, where the signal level is adjusted to be constant.

Further, thereafter, a band-pass filter (B
PF) 334 cuts out frequency components other than the predetermined frequency band, analog signal components such as video signals pass through a frequency demodulation unit (PFM-DEM) 34, and digital signal components such as audio signals are decoded by a decoding unit (CMI). −CODEC) 35 to be output.

In the receiving unit 3 shown in FIG. 2, separately, the laser light LB output from the laser diode 132 of the transmitting unit 1 and the light receiving element 331 are aligned first. As described above, the light emitting diode 31 for transmitting the infrared light RB, the transmitter 361 for transmitting the weak radio wave by the FM wave, and the transmitting antenna 362 are provided.

The light emitting diode 31 and the transmitting antenna 362 are, as shown in FIG.
Of the laser diode 13
The laser beam LB output from the light receiving element 2 is directed to the incident direction of the laser light LB incident on the light receiving element 331.

Next, the infrared light RB transmitted from the light emitting diode 31 and the F transmitted from the transmitting antenna 362 are transmitted.
The directivity relationship with the M wave will be described with reference to FIG. 4 showing the correlation. In this embodiment, as shown in FIG. 4, the emission angle θ2 of the FM wave is larger than the emission angle θ1 of the infrared light RB by θ2 >> θ1 (for example, θ1 = 15 deg, θ2 = 1).
30 deg).

This is because when adjusting the optical axis of the laser beam LB with infrared light having a large radiation angle, if the distance between transmission and reception exceeds 7 m, the reliability of the signal with respect to disturbance noise cannot be ensured (low S). / N), it is necessary to narrow the emission angle of the infrared light, and as shown in FIG.
The infrared light RB sent from the light emitting diode 31 is focused by the focusing lens D so that the above relationship is obtained. By narrowing the radiation angle of the infrared light RB, a high angle detection resolution can be ensured (0.
5 deg or less).

On the other hand, for example, the FM used in this embodiment
For radio waves such as waves, if there are no obstacles,
It is possible to determine the position up to about 00 m. However, the angle detection resolution is extremely poor (at most 1
0 deg), it is impossible to adjust the optical axis of the laser light using radio waves alone. Therefore, in the optical space transmission apparatus of the present embodiment, by combining the respective advantages of the infrared light and the radio wave, a high angle detection resolution is secured in a wide range.

Next, the operation of adjusting the optical axis of the laser beam LB output from the laser diode 132 of the transmission unit 1 will be described with reference to FIG. First, it is assumed that the optical axis of the laser beam LB from the transmitting unit 1 passes through the point X in FIG. 5, and the receiving unit 3 outputs an FM wave, and outputs a signal corresponding to the receiving intensity from the RF circuit 182. Servo circuit 15
And the actuator 14 is driven based on this. When the infrared light RB sent from the light emitting diode 31 starts to be irradiated on the light detection module 16 with the driving of the actuator 14, the differential amplifiers 171 and 172
Signal value of the output signal decreases.

Therefore, the signal values of the difference signals output from the differential amplifiers 171 and 172 shown in the third column from the top in FIG. 6 are set to predetermined values (threshold 1 and first predetermined value).
Below the value), the laser beam LB to a location shown in FIG. 5 Y point
Is adjusted, the input to the servo circuit 15 is switched from the RF circuit 182 to the light detection module 16. Note that the servo gain is adjusted at this time in the transmission unit 1 of the present embodiment, and when the input to the servo circuit 15 is switched to the light detection module 16, the drive of the actuator 14 is decelerated.

Thereafter, the optical axis of the laser beam LB is
31 when approaching a position suitable for the differential amplifier 171,
172, the signal value of the difference signal further decreases, and another prescribed value (threshold 2 , first predetermined value) set in advance in the vicinity of the optical axis of the laser beam LB coincides with the light receiving element 331.
At a point in time when the value falls below a (second predetermined value smaller than the value) , a signal of light emission permission is transmitted from the servo circuit 15 to the security circuit 19, and the laser light LB is output from the laser diode 132. On the other hand, when the laser beam LB is received by the light receiving element 331 of the receiving unit 3, the gain of the auto gain controller 333 decreases accordingly.
Transmits a signal to stop the output to the light emitting diode 31 and the transmitter 361, and stops the output of the infrared light RB and the FM wave. Thereafter, the servo circuit 15 always controls the alignment state between the optical axis of the laser beam LB and the light receiving element 331, and the laser beam LB is transmitted in a good state.

As described above, according to the free-space optical transmission apparatus of the present embodiment, the rough adjustment of the laser light LB in the optical axis direction is performed by the FM wave transmitted from the transmitter 361 of the receiving unit 3. After that, the light emitting diode 31 of the receiving unit 3
The laser beam LB is accurately adjusted in the direction of the optical axis by the infrared light RB sent from the device, so that the displacement of the light beam in the direction of the optical axis can be corrected with high accuracy over a wide range.

In this embodiment, FM waves are used as radio waves, but other band waves may be used. Further, in the present embodiment, on the transmission unit 1 side, a signal obtained by demodulating the FM wave received by the receiving antenna 181 by the RF circuit 182 is converted into a signal at a level corresponding to the reception intensity of the FM wave.
5 and the servo circuit 15 controls the driving of the actuator 14 based on the reception intensity of the FM wave. However, a configuration as shown in FIGS. 7 and 8 may be used.

FIG. 7 is a block diagram showing a transmission unit of an optical free space transmission apparatus according to another embodiment of the present invention in a partial block.
FIG. 8 is a perspective view showing a main part of the transmission unit shown in FIG. The transmitting unit 5 shown in FIGS. 7 and 8 has substantially the same configuration as the transmitting unit 1 of the embodiment shown in FIGS. 1 and 3 (a), and includes the receiving antennas 183, 184 and the RF circuit. 185, 186 are a receiving system of the space diversity system in which two are provided respectively, and a differential amplifier 187 obtains a difference between demodulated signals received by the two RF circuits 185, 186 by a differential amplifier 187. Fifteen
Is different from the configuration of the transmission unit 1 of the previous embodiment.

Therefore, although the basic principle is the same,
There is no need to mount an antenna directly on the actuator 14, and thus the weight of the drive unit of the actuator 14 can be reduced. In the present embodiment, the receiving antennas 183 and 184, the RF circuits 185 and 186, and the differential amplifier 187 correspond to a reception intensity detecting unit. The receiving antennas 183 and 184 are erected on the structures 201 and 202 which protrude on both sides of the cover C.
RF circuits 185 and 186 are built in 01 and 202, respectively.

[0030]

As described above, according to the present invention, the optical axis direction of the light beam for information transmission is roughly corrected over a wide range based on the reception intensity of the radio wave output from the receiving unit. Since the displacement of the light beam in the optical axis direction is precisely corrected based on the irradiation position of the infrared light output from the unit side, the displacement of the light beam in the optical axis direction can be corrected over a wide range.

Further, since the spread angle of the infrared rays is made sufficiently smaller than that of the above-mentioned embodiment by using together with the radio wave, and the aperture is narrowed down, it is practically acceptable. It is possible to reach infrared rays up to.

Further, since information transmission of the light beam is stopped when the laser diode emits light, internal interference (noise, beat) generated in the photoelectric conversion unit, frequency demodulation unit and decoding unit on the receiving side can be prevented. A high S / N signal transmission system can be constructed.

Further, it is possible to prevent a decrease in the output of the signal and a delay in the correction response as in the above-described conventional technique, and to perform a reliable correction of the optical axis by a direct correction. The optical axis can be corrected following the change in the position of only the unit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a transmission unit of an optical free space transmission apparatus according to one embodiment of the present invention, which is shown in partial blocks.

FIG. 2 is a block diagram illustrating a receiving unit of the free-space optical transmission apparatus according to one embodiment of the present invention, with partial blocks.

3A and 3B are diagrams showing main parts of a transmission unit and a reception unit shown in FIGS. 1 and 2, wherein FIG. 3A is a perspective view of main parts of the transmission unit, and FIG. 3B is a main part of the reception unit; It is a perspective view.

4 is a diagram showing infrared light transmitted from a light emitting diode of the receiving unit shown in FIG. 2 and FM transmitted from a transmitting antenna;
It is a correlation diagram which shows the directivity relationship with a wave.

FIG. 5 is an explanatory diagram illustrating an adjustment operation of the laser unit in the optical axis direction by the transmission unit of FIG. 1;

FIG. 6 is a time chart showing changes over time in various states in the transmission and reception units of FIGS. 1 and 2;

FIG. 7 is a block diagram showing a transmission unit of a free space optical transmission apparatus according to another embodiment of the present invention, in partial blocks.

FIG. 8 is a perspective view showing a main part of the transmission unit shown in FIG. 7;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Transmitting unit 3 Receiving unit 11 Frequency premodulation part 12 Encoding part 13 Electric-optical conversion part 14 Actuator (correction means) 15 Servo circuit (correction means) 16 Light detection module (irradiation position detection means) 19 Security circuit 31 Light emitting diode (Light source) 32 filter 33 photoelectric conversion unit 34 frequency demodulation unit 35 decoding unit 131 laser driver 132 laser diode 133 collimating lens 134 photodetector 135 auto power controller 141 rotation table 142 support frame 143 cylinder 161 to 164 photodetector 171 , 172 Differential amplifier (irradiation position detecting means) 181, 183, 184 Receiving antenna (receiving intensity detecting means) 182, 185, 186 RF circuit (receiving intensity detecting means) 187 Differential amplifier (receiving intensity detecting means) 201 202 structure 331 receiving element 332 amplifier 333 automatic gain controller 334 band-pass filter 361 transmitter 362 transmitting antenna LB laser beam RB infrared light A board B bottom case C Cover D focusing lens

Claims (2)

(57) [Claims] 1. An optical space transmission apparatus comprising: a transmission unit that outputs a light beam modulated based on a predetermined information signal; and a reception unit that receives and demodulates the light beam. A light source that outputs infrared light toward the transmission unit; and a transmitter that outputs radio waves to the transmission unit. The transmission unit includes: a light detection module having four light detection elements; An irradiation position detecting means for detecting an irradiation position of the infrared light, and a reception intensity detection device for receiving the radio wave and detecting a reception intensity of the radio wave. Means, correction means for correcting the irradiation direction of the light beam based on detection results of the irradiation position detection means and the reception intensity detection means, and at least one output of the differential amplifier is 1 and when the output of the reception intensity detecting means is smaller than a predetermined value, the output of the light beam is stopped, and the output of the differential amplifier is smaller than the first predetermined value. And a security means for outputting a light beam when the light beam becomes smaller than a second predetermined value. 2. An optical space transmission apparatus comprising: a transmitting unit that outputs a light beam modulated based on a predetermined information signal; and a receiving unit that receives and demodulates the light beam. A light source that outputs infrared light toward the transmission unit; and a transmitter that outputs radio waves to the transmission unit. The transmission unit includes: a light detection module having four light detection elements; An irradiation position detecting means for detecting an irradiation position of the infrared light, and a reception intensity detection device for receiving the radio wave and detecting a reception intensity of the radio wave. Means, correction means for correcting the irradiation direction of the light beam based on detection results of the irradiation position detection means and the reception intensity detection means, and at least one output of the differential amplifier is 1 and when the output of the reception intensity detecting means is smaller than a predetermined value, the output of the light beam is stopped, and the output of the differential amplifier is smaller than the first predetermined value. Using a spatial light transmission device provided with a security means for outputting a light beam when the light intensity becomes smaller than a second predetermined value, a radio wave is output from a transmitter of the reception unit, and a reception intensity detection means of the transmission unit Detecting the reception intensity of the radio wave, correcting the irradiation direction of the light beam by the correction means according to the detection result, and the signal value of the differential signal output from the differential amplifier is lower than a first predetermined value. And the correction means corrects the irradiation direction of the light beam according to the detection result of the irradiation position detection means, and further sets a signal value of the differential amplifier to a second predetermined value smaller than the first predetermined value. When it falls below The security means to allow the output of the light beam, the optical space transmission method characterized in that the output from the transmitter and a light source of the receiving unit has to be stopped.