JP2000031910A - Optical space transmitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the disconnection of a line even when frost, etc., takes place by allowing a transmitting end to grasp the light received result of a light receiving end of a light beam and transmitting an information signal at an appropriate transmission rate. SOLUTION: A central processing unit 31 controls the operation of this entire optical space transmitting device and carries out prescribed processing procedures according to control data DC inputted from a network interface circuit 29. The unit 31 controls the operation of an actuator driving circuit 38 based on positional deviation information inputted from an analog to digital conversion circuit 37. That is, when a receiving light beam L2 is made incident from a device that is a speech communication object at the time of installation, a transmission light beam L1 is emitted in the incoming direction of the beam L1 and a line is set up. Also, when the line is set up, similarly, the operation of the circuit 38 is controlled according to the positional deviation information and consequently, the line is maintained even if the whole is vibrated owing to wind, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical space transmission apparatus, and more particularly to an apparatus for transmitting / receiving desired information via a light beam propagating in space. The present invention can prevent disconnection of a line even when fog or the like occurs, by grasping a light receiving result on a light receiving side of a light beam on a transmitting side and transmitting an information signal at an appropriate transmission rate. To do.

[0002]

2. Description of the Related Art Conventionally, an optical space transmission apparatus irradiates a light beam between the same kind of equipment arranged on a rooftop of a building or the like, for example, so that desired information is transmitted through a light beam transmitted through space. Is transmitted and received.

Such an optical space transmission apparatus can transmit an information signal over a wide band by transmitting and receiving an information signal by modulating a laser beam, and is a highly confidential communication without being restricted by the Radio Law. Can be performed.

[0004]

By the way, in this type of optical space transmission apparatus, B で Pth ² between the transmission rate B and the minimum received light quantity (the received light quantity that can secure a predetermined S / N ratio) Pth. There is a relationship. As a result, in the conventional optical space transmission device, when the attenuation of the transmission path increases due to fog, rain, etc., the S / N ratio deteriorates and bit errors frequently occur,
At last, there was a problem that the line was practically interrupted.

The present invention has been made in view of the above points, and it is an object of the present invention to propose an optical space transmission apparatus capable of preventing disconnection of a line even when fog or the like occurs. .

[0006]

According to the present invention, a transmission rate of an information signal is varied in accordance with information on a light receiving amount of a transmission light beam.

If the transmission rate of the information signal is varied in accordance with the information on the amount of received light of the transmission light beam, the information signal can be transmitted at a transmission rate that can secure a predetermined S / N ratio with the amount of received light in the transmitting / receiving device. By preventing frequent occurrence of errors, it is possible to prevent substantial disconnection of the line.

[0008]

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

(1) First Embodiment (1-1) Configuration of First Embodiment FIG. 2 shows an optical space transmission to which an optical space transmission apparatus according to a first embodiment of the present invention is applied. It is a schematic diagram showing a system.
In this space optical transmission system, the space optical transmission device 1
Are disposed on the rooftop of a building or the like so as to face the optical space transmission apparatus 1A having the same configuration (hereinafter referred to as a communication target device),
A light beam (hereinafter referred to as a transmission light beam) L1 is transmitted to the communication target device, and a light beam (hereinafter referred to as a reception light beam) L transmitted from the communication target device is transmitted.
2, various information signals are transmitted to and received from the communication target device.

In this embodiment, the optical space transmission device 1 and the communication target device 1A are connected to the first and second networks A and B via bridges, respectively. Input and output Ethernet signals. Optical space transmission device 1 and communication target device 1A
Transmits and receives an information signal based on the Ethernet signal.

FIG. 3 is a side view showing a cross section of the optical space transmission device 1. As shown in FIG. The optical space transmission device 1 is formed by housing the whole in a housing 2. Further, the optical space transmission device 1 is supplied with power via a connector 3 arranged on the back of the housing 2, and inputs and outputs information signals to be transmitted via the connector 3. Here, the information signal is an Ethernet signal.

The housing 2 has an opening formed on the front surface, and the opening is covered with a transparent cover glass 4. The optical space transmission device 1 emits the transmission light beam L1 through the cover glass 4 and receives the reception light beam L2. Here, the cover glass 4 is arranged so that the downward direction is inclined inward, thereby reducing the amount of dust, dust, water droplets, and the like attached to the surface, and the transmission light beam L1 and the reception light beam L2 due to the dust and the like. The loss is reduced.

The housing 2 is internally divided into two regions.
The circuit board 5 of the space optical transmission device 1 is arranged in the rear area. The housing 2 has an optical system 6 disposed in a front area.

The optical system 6 sends the transmission light beam L1 to the device to be talked to, receives the received light beam L2 arriving from the talk target, and outputs the light reception result. Optical system 6
Is formed so that after a lens barrel having a substantially circular cross section extends from the rear side of the cover glass 4 to the rear side (hereinafter, this portion is referred to as a front end portion), it is bent at 90 degrees and rises (hereinafter, rises at 90 degrees). A portion is called an optical module portion), and the optical module portion is formed so as to extend along a diagonal line of the housing 2 when viewed from the cover glass 4 side (a sectional view taken along line AA). 5) Thereby, the optical space transmission device 1 can be made smaller in size by effectively utilizing the internal space of the housing 2.

FIG. 4 is a cross-sectional view taken along a plane passing through the optical axis of the lens barrel bent at 90 degrees as described above (FIG. 4 is a cross-sectional view taken along the line AA of FIG. 3 and FIG. 4 is a cross-sectional view taken along the line BB). ), The optical system 6 is formed by attaching an interchangeable lens 8 to a lens barrel body 7 at the tip end.

Here, the interchangeable lens 8 is configured so that it can be attached to the tip of the lens barrel main body 7 so that it can be replaced according to the distance to the device to be talked.
The side faces abut the block (FIG. 3) and are held by the housing 2. As a result, the lens barrel body 7 is replaced with the heavy interchangeable lens 8.
Even if attached, it is made not to be deformed.

The interchangeable lens 8 constitutes a condensing optical system in which a plurality of lenses 8B are arranged on a holder 8A.
Has a concave lens 9 disposed behind the interchangeable lens 8. Accordingly, the interchangeable lens 8 and the concave lens 9 constitute a beam expander, emit the transmission light beam L1 toward the device to be talked with a desired spread, and substantially convert the reception light beam L2 incident from the device to talk. Convert to parallel rays.

The optical axis correcting section 10 reflects the transmission light beam L1 incident from the optical module portion by the mirror 11 at the root portion of the lens barrel main body 7 which is bent in an L-shape, thereby forming the transmission light beam L1. The optical path is bent by about 90 degrees and emitted to the front end side part, and the received light beam L2 incident from the front end side part is similarly reflected by the mirror 11 so that the optical path of the received light beam L2 is about 90 degrees.
It is bent once and emitted to the optical module.

The optical axis correcting unit 10 rotates the mirror 11 by a predetermined electromagnetic actuator about two rotation axes orthogonal to each other within the reflection surface of the mirror 11 to rotate the mirror 11 to a desired position. Is configured to be able to be tilted in the direction of. Accordingly, the optical axis correction unit 10 displaces the optical axis of the transmission light beam L1 that is incident on the optical module portion substantially from the optical axis of the lens barrel body 7 and emits it to the distal end portion, Even when L2 is incident on the optical path of the transmission light beam L1 by displacing the optical path of the transmission light beam L1 in reverse from the optical axis of the lens barrel body 7, the optical axis of the reception light beam L2 is made substantially coincident with the optical axis of the lens barrel body 7. The light is emitted to the module.

The optical axis correction unit 10 is configured so that the mirror 11 rotates within a predetermined range around the reference position, and the inclination of the mirror 11 from the reference position can be detected by a skew sensor (not shown). Has been made.

As shown in FIG. 5 by taking a cross section along the line AA, the optical module includes a light receiving block 13 for receiving the received light beam L2, a laser diode block 14 for emitting the transmitted light beam L1, Receive light beam L
2, a position detection block 15 for outputting a light reception result necessary for driving the optical axis correction unit 10, and a reception light beam L2 distributed to the light reception block 13 and the position detection block 15 and emitted from the laser diode block 14. Prism 16 for guiding the transmitted transmission light beam L1 to the optical axis correction unit 10.
It is composed of

Here, the prism 16 is different from the large right-angled triangular prism 16A with respect to the right-angled triangular prism 16A.
A small right-angled triangular prism 16 on two orthogonal surfaces of A
B is formed by bonding the inclined surfaces, and these two bonded surfaces are arranged so as to form an angle of approximately 45 degrees with the optical axis of the lens barrel when viewed from the cover glass 4 side. Further, the prism 16 has a vapor-deposited film formed on the surface on the optical axis correction unit 10 side of the two bonded surfaces, and selectively reflects a laser beam having a predetermined polarization plane by the bonded surfaces. The laser beam having a plane of polarization orthogonal to this is selectively transmitted. Thus, the prism 16 is configured such that a polarization beam splitter is formed on the optical axis correction unit 10 side and a half mirror is formed on the remaining bonding surface.

The laser diode block 14 directs the transmission light beam L1 to the optical axis correction unit 10 by making the transmission light beam L1 incident on and reflected by the polarization beam splitter formed on the optical axis correction unit 10 side. Emit. Here, the laser diode block 14 drives the laser diode 20 having a high modulatable frequency with the information signal, thereby generating the transmission light beam L1 having a predetermined polarization plane modulated by the laser diode 20 with the information signal. In the laser diode block 14, the laser diode 20 is arranged at a predetermined angle with respect to the optical axis such that the transmission light beam L1 is reflected by the polarization beam splitter in the prism 16. The laser diode block 14 converts the transmission light beam L1 emitted from the laser diode 20 into substantially parallel light beams by a converging optical system constituted by a plurality of lenses 21 and converts the transmission light beam L1 into prism beams.
Emitted to 6.

Thus, in the optical free space transmission apparatus 1, after the transmission light beam L1 modulated by the information signal is generated by the laser diode 20, the prism 16, the optical axis correction section 1
The light is emitted toward the device to be talked via the lens 0, the concave lens 9, and the lens 8.

In the optical space transmission device 1, the transmission light beam L1 transmitted to the space to be addressed to the communication target device in this manner is
The prism 16 and the like are configured such that the polarization plane is inclined at an angle of 45 degrees from the vertical direction. Accordingly, in the optical space transmission device 1, since the device to be talked has the same configuration, the device to be talked is arranged so as to face the device to be talked, and the polarization plane is orthogonal to the transmission light beam L1. Thus, the receiving light beam L2 is incident. Thereby, in the optical space transmission device 1, the receiving light beam L1 is selectively transmitted and guided to the bonding surface forming the half mirror on the bonding surface forming the polarization beam splitter of the prism 16, and the bonding surface is formed. Is configured to separate the reception light beam L2 into two light beams.

The laser diode 20 outputs a monitor signal of the amount of emitted light to a laser diode (LD) drive circuit 32 (FIG. 6) by a so-called rear monitor method.

The position detection block 15 makes the received light beam L2 reflected by the half mirror out of the two light beams incident on the filter 22, where the wavelength component of the received light beam L2 is selectively transmitted. The position detection block 15 converts the received light beam L2 transmitted through the filter 22 into a convergent light beam by a converging optical system constituted by a plurality of lenses 23, and condenses the light beam on the light receiving surface of the position detecting element 24.

Here, the position detecting element (PSD: Posit)
ion Sensitive Device) 24
A light receiving surface is formed in a substantially rectangular shape, and an electrode is formed on each side of the light receiving surface. The position detecting element 24 is configured to photoelectrically convert the light beam condensed on the light receiving surface and output the result of the photoelectric conversion from each electrode. The output ratio of the output photoelectric conversion result is configured to change.

Thus, the position detecting element 24 determines the position of the light beam condensed on the light receiving surface by two based on the output ratio of the photoelectric conversion result output from the electrode arranged to face the light receiving surface. It is formed so as to be detectable by a dimensional coordinate system, and the amount of light beam can be detected by adding the photoelectric conversion results output from the respective electrodes. The position detection element 24 is arranged such that the coordinate axes in the two-dimensional coordinate system correspond to the two rotation axes in the optical axis correction unit 10. Thereby, the optical space transmission apparatus 1 can detect the direction in which the received light beam L2 arrives in accordance with the optical axis correction direction in the optical axis correction unit 10 based on the light reception result of the position detection element 24. I have.

The light receiving block 13 makes the received light beam L2 transmitted through the half mirror of the prism 16 enter the filter 26, and selectively transmits the wavelength component of the received light beam L2. The light receiving block 13 converts the received light beam L2 transmitted through the filter 26 into a convergent light beam by a converging optical system constituted by a plurality of lenses 27, and focuses the light beam on a light receiving surface of a light receiving element 28.

Here, the light receiving element 28 is constituted by an avalanche photodiode, and outputs a light receiving result whose signal level changes in accordance with the amount of the received light beam L2.

FIG. 6 is a block diagram showing the configuration of the optical space transmission apparatus 1 together with the main part of the optical system 6 described above. In the optical space transmission device 1, the network interface (I / F) circuit 29 accumulates and holds the information signal S1 input from the bridge via the connector 3 (FIG. 2) in a predetermined buffer, and outputs the information signal S1 to the clock CK. Output synchronously. Network interface circuit 2
Conversely, the information signal S6 is input from the demodulation circuit 34 in synchronization with the clock CK from the device of the partner device, and is transmitted to the network via the bridge.

Network interface circuit 2
9 is warning information D from the central processing unit (CPU) 31.
When a frame based on M, status data D1, D2, and the like is input, the frame is temporarily stored in an internal memory and transmitted to the network in the same manner as the information signal S6. Conversely, predetermined information such as control data DC among frames input from the network is sent to the central processing unit 31.

Thus, in the optical free space transmission apparatus 1, the operation mode and the like can be set from the terminal connected to the network, and the control program and the like can be updated as needed. Also, the terminal can be notified of the abnormality of the transmission path by e-mail.

The clock generation circuit 29A generates and outputs various reference signals required for the operation of the optical free space transmission device 1. The clock generation circuit 29A includes, among these reference signals, a clock CK that defines the transmission rate of the information signal S1 transmitted from the optical space transmission device 1 to the communication target device, and the information signal S6 transmitted from the communication target. The frequency of the clock CK used for demodulation of the information signal S6 is switched under the control of the central processing unit 31 in accordance with the transmission rate of. Thereby, this optical space transmission device 1
Then, if necessary, transmission speed 1 [GHz], 100 [M
Hz] or 10 [MHz], the information signals S1 and S6
Is transmitted and received.

As shown in FIG. 7, the modulation circuit 30 modulates the information signal S1 input from the network interface circuit 29 with a carrier signal S2 having a predetermined frequency fm to generate a modulation signal S3 having a frequency band of 1000 [MHz]. I do.

Further, the modulation circuit 30 adds a synchronization pattern or the like to the status data D1 output from the central processing unit 31, and then modulates it with a carrier signal S4 having a frequency of 6 [MHz] at a transmission speed of 38.4 [bps]. The modulation signal obtained as a result is added to the modulation signal S3 of the information signal S1 to generate a drive signal. Thereby, the modulation circuit 30
Generates a drive signal by frequency-multiplexing the information signal S1 and the status data D1.

Laser diode (LD) drive circuit 32
Drives the laser diode 20 according to the signal level of the drive signal, thereby causing the laser diode 20 to emit a transmission light beam L1 whose light amount changes according to the signal level of the drive signal. At this time, the laser diode drive circuit 32 drives the laser diode 20 based on the monitor signal of the light amount output from the laser diode 20 so that the peak light amount of the transmission light beam L1 becomes the light amount instructed by the central processing unit 31. . Further, at this time, the laser diode driving circuit 32 notifies the central processing unit 31 of the driving current of the laser diode 20 required for emitting the light amount specified by the central processing unit 31 in this way. Also, the monitoring result of the light amount output from the laser diode 20 is similarly notified to the central processing unit 31.

Photodiode (PD) light receiving circuit 33
Converts the light receiving result of the light receiving element (PD) 28 into a current-to-voltage conversion and then amplifies the current with a predetermined gain. The photodiode light receiving circuit 33 equalizes the waveform of the amplification result and outputs the result to the demodulation circuit 34.

The demodulation circuit 34 receives the output signal of the photodiode light receiving circuit 33, separates this output signal into bands and identifies each of the two values, thereby obtaining an information signal S6 and a status data D2 transmitted from the communication target device. Is demodulated. The demodulation circuit 34 buffers this information signal S6 and outputs it from the connector 3 to an external device, and outputs status data D2 to the central processing unit 31.

The PSD light receiving circuit 36 includes a position detecting element (P
SD) A current-voltage conversion process is performed on the light reception result of 24, and a matrix operation process is performed, whereby two-dimensional displacement signals xθ and yθ indicating the arrival direction of the reception light beam L2 and the light amount indicating the light reception amount of the reception light beam L2 are obtained. The detection signal P0 is output.

Analog-to-digital conversion circuit (A / D) 3
7 indicates the position shift signals xθ, yθ and the light amount detection signal P
0 is subjected to analog-to-digital conversion processing, and the processing result, that is, positional deviation information and light amount detection information
Output to Digital-to-analog conversion circuit (D / A) 3
Reference numeral 8 latches and holds the light amount control data output from the central processing unit 31, and converts the light amount control data into an analog signal. Digital-to-analog conversion circuit 40
Outputs the analog signal to the laser diode drive circuit 32 as a control signal indicating the peak light amount of the transmission light beam L1.

The actuator drive circuit 38 operates the optical axis correction unit 10 under the control of the central processing unit 31 so that the condensing position of the received light beam L2 formed on the light receiving surface of the position detecting element 24 becomes a predetermined position. Thus, even when the optical space transmission apparatus 1 vibrates due to wind or the like, the transmission light beam L1 is correctly transmitted in the arrival direction of the reception light beam L2 so that the line can always be maintained.

The skew sensor angle detection circuit 39 performs signal processing on the output signal of the skew sensor disposed in the optical axis correction unit 10 and notifies the central processing unit 31 as tilt information of the mirror 11.

The central processing unit 31 constitutes a system control circuit for controlling the operation of the entire optical free space transmission apparatus 1 and executes a predetermined processing procedure in accordance with control data DC inputted from the network interface circuit 29. It controls the overall operation and updates this procedure as needed.

In controlling the entire operation, the central processing unit 31 controls the operation of the actuator driving circuit 38 based on the positional deviation information input from the analog-to-digital conversion circuit 37, so that the communication target When the receiving light beam L2 is incident from the device (1), the transmitting light beam L1 is emitted in the arrival direction of the receiving light beam L2, thereby opening a line. When the line is established in this way, the operation of the actuator drive circuit 38 is similarly controlled in accordance with the positional deviation information, so that the line is maintained even if the whole vibrates due to wind or the like.

In this control, the central processing unit 31
Controls the operation of the actuator drive circuit 38 in accordance with the tilt information of the mirror 11 output from the skew sensor angle detection circuit 39 so as not to deviate from the range in which the mirror 11 can move normally. To prevent failure.

The central processing unit 31 takes in the mirror tilt information at predetermined time intervals, and performs a moving average of the taken tilt information, thereby calculating the tilt of the movable center of the mirror 11. The central processing unit 31
When the inclination of the movable center changes by a predetermined value or more from the center value, it is determined that the movable range of the mirror 11 is likely to deviate from the range in which the mirror 11 can move normally, and the electronic mail based on the warning information DM is sent to the registered notification destination. Issue an email. This makes it difficult for the central processing unit 31 to perform correction by the optical axis correction unit 10 and to maintain a line even when, for example, a change occurs in the installation location of the optical space transmission device 1 due to a temporal change or the like. Before they become, they can take necessary measures.

Similarly, the central processing unit 31 fetches information of the drive current output from the laser diode drive circuit 32 at regular time intervals and performs moving averaging.
Further, the central processing unit 31 similarly issues an e-mail when the moving averaged drive current value exceeds a reference current value required for emitting a predetermined amount of light. Thereby, the central processing unit 31 detects the deterioration of the laser diode 20 by the drive current, and notifies the notification destination set in advance when the degree of the deterioration progresses by a certain value or more,
Necessary countermeasures can be taken.

The central processing unit 31 includes the mirror 1
By generating the status data D1 from the tilt of the movable center of 1 and the driving current value obtained by moving average and outputting the status data D1 to the modulation circuit 30, the information is also notified to the communication target device. Thereby, the central processing unit 31 can notify the deterioration of the laser diode 20 and the like as necessary even through the device to be talked.

FIG. 8 is a schematic diagram showing the status data D1 generated by the central processing unit 31 in this manner. The central processing unit 31 sets the first 8 bits
The number of bytes of the status data D1 is set, and a command indicating the type of data is set in the subsequent 8 bits. Further, the central processing unit 31 assigns data contents to the subsequent 8 × n bits, and assigns the tilt information of the movable center or the drive current value to this. In the case of the drive current value, if necessary, the power of the corresponding transmission light beam L1 is also adjusted to 8
Allocate to an area of × n bits. Further, the central processing unit 31 assigns a check sum for error correction to the subsequent 8 bits.

Further, the central processing unit 31 executes the processing procedure shown in FIG. 9 at a cycle of, for example, 10 [msec] with reference to the time measurement value of the timer, so that the information of the received light amount is obtained as one of the status data D1. Notify the call target. That is, when the processing start time is reached by the timer, the central processing unit 31 proceeds from step SP1 to step SP2, inputs the received light amount detection result P0 of the received light beam L2 via the analog-to-digital conversion circuit 37, and executes a loop on a memory (not shown). The received light amount detection result P0 is recorded in the buffer.

Subsequently, the central processing unit 31 proceeds to step SP3, where the past one stored in the loop buffer is stored.
A moving average is calculated from the detection result P0 of the received light amount of 00 times. Subsequently, the central processing unit 31 proceeds to step SP4 and, based on the counter value COUNT1 for time measurement, notifies the device of the call target of the received light amount, and then determines whether or not the number of times of calculation of the moving average has been repeated 100 times continuously. to decide.
If a negative result is obtained here, the central processing unit 31 proceeds to step SP5, where the counter value COUNT is set.
After incrementing “1” by “1”, the process proceeds to step SP6, and this processing procedure ends.

The central processing unit 31 thereby executes the steps SP1-SP2-SP3-SP4-SP5-SP6
Is repeated 99 times, and at the 100th time, a positive result is obtained in step SP4 and step SP7
Move on to Here, the central processing unit 31 executes step SP
The status data D1 described above with reference to FIG. 7 is created from the received light amount detection result based on the moving average calculated in step 3, and the status data D1 is output to the modulation circuit 30. Thus, the central processing unit 31 has a one-second cycle,
The average value of the amounts of the received light beams received is notified to the communication target device.

The central processing unit 31 subsequently proceeds to step SP8, resets the counter value COUNT1 for time measurement to a value of 0, and thereafter proceeds to step SP6 to end this processing procedure.

Thus, in the free-space optical transmission device 1, the driving current of the laser diode, which is the information on the operation state related to the transmission of the transmission light beam L1, the amount of received light, the information on the operation state related to the reception of the received light beam, Are mutually notified together with the information signal S1.

The central processing unit 31 stores the status data D1 and D2 in a predetermined memory as history information so that the status data D1 and D2 can be used for maintenance. Is transmitted via a network interface circuit 29 in response to a request from a terminal via a network.

The central processing unit 31 receives from the demodulation circuit 34 the status data D2 sent together with the information signal S6 from the device to be talked to, and among these status data D2, the drive current of the laser diode and the inclination of the mirror. The information is determined in the same manner as in the own device, and an e-mail is issued as necessary.

On the other hand, when the status data D2 is the amount of received light, the processing procedure shown in FIGS.
Thus, the transmission rate of the information signal S1 is changed based on the amount of received light on the communication target side.

That is, the central processing unit 31 proceeds from step SP10 to step SP11 and, upon receiving the status data D2 from the demodulation circuit 34,
In step 12, the user can confirm the format of the received data by transmitting control data or the like set by the user. Here, when the format of the received data is different from the data of the amount of received light, the central processing unit 31 proceeds to step SP13
The processing proceeds to step SP14, where the received data is ignored and the processing proceeds to step SP14 to end the processing procedure.

On the other hand, if the format of the received data is correct, a positive result is obtained in step SP12, and the central processing unit 31 proceeds to step SP15. Here, the central processing unit 31
Extracts information on the amount of received light assigned to the status (FIG. 7) from the received data and records it in the memory.

Subsequently, the central processing unit 31 proceeds to step SP16, in which the amount of received light P1 is equal to a predetermined threshold value P
It is determined whether it is less than th1. Here, this threshold value Pth
Reference numeral 1 denotes an amount of received light necessary for receiving a transmission light beam L1 transmitted from the optical space transmission device 1 by a communication target device and demodulating the information signal S1 at a current transmission rate below a predetermined bit error rate. It is.

That is, in the optical space transmission apparatus 1 according to the present embodiment, a transmission system between the optical communication apparatus and a communication target device can be represented as shown in FIG. In such a transmission system, light source noise Ng is superimposed on the information signal when emitting the transmission light beam L1, and noise Pb due to background light is mixed in when receiving the transmission light beam L1. Furthermore, shot noise Ns is mixed when photoelectric conversion is performed by the light receiving element, and thermal noise Nt is mixed when processing is performed by the light receiving circuit (FIG. 11A).

As a result, with respect to the power waveform Pg · g (t) of the transmission light beam L1 sent out by the intensity modulation, the waveform shape of the power waveform Pg · g (t) deteriorates, Finally, binary identification is performed (FIG. 11B). Note that in FIG.
R (t) is a received light power waveform received at the communication target, i1 (t) is a signal waveform of a light-receiving result obtained by photoelectric conversion,
i2 (t) is a signal waveform after current-voltage conversion, and S (t) is a signal waveform immediately before demodulation. In this transmission system, the power waveform P
The waveform shape of g · g (t) is degraded, and the binary waveform is finally identified by the waveform on which noise is superimposed.

Further, symbols Pg · g (f), Pr · r
(F), i1 (f), i2 (f), and S (f) are Fourier transforms of the corresponding signal waveforms (FIG. 11C).
0 ^a · HL (f) (a = −α / 10) is a transfer function of the spatial transmission path (FIG. 11D). Further, ηe / hν × M is a quantum effect which is a transfer function of the light receiving element, and is about 0.55 [A / W] in the case of a photodetector. Also H
(F) is a transfer function of the signal processing system, which is a transfer function Hp (f) of the light receiving circuit and a transfer function Heq of another signal processing circuit.
(F).

In such a model, there is no need to equalize the received waveform, and the noise figure of the amplifier circuit is constant N (f) =
If N0 and the frequency characteristic Hp (f) of the light receiving circuit is 1, the SNR of the impulse response in this transmission system is expressed by the following equation.

[0067]

(Equation 1)

Here, M represents the current multiplication effect of the avalanche photodiode (APD) as the light receiving element. In the avalanche photodiode, the signal is also multiplied and the shot noise is also multiplied. x is an excess noise figure. In Si-APD, x is about 0.3 and Ge-A
In PD, x is almost 1. If a Pin-photodiode having no current multiplication effect is used for the light receiving element, M is naturally 1 and x is also 1.

K is Boltzmann's constant (1.38 × 10
^-23 J / N), R is load resistance, T is absolute temperature, ζ is quantum efficiency (A / W), and Pb is the amount of background light. Where (1)
In the equation, the first term of the denominator indicates shot noise, and the second term
The term indicates thermal noise. In the model represented by the equation (1), the modulation degree m where g (t) = (1 + ma cos ω ₀ t) is satisfied.
If the analog amplitude modulation of a is applied, equation (1) can be transformed into the following equation. Here, APr is the average received light power.

[0070]

(Equation 2)

Here, assuming that the SN (SPP / Nrms) at which the bit error becomes 10 −9 or less is 14 dB, the Boltzmann constant k = 1.38E-23, the absolute temperature T = 300, the electron charge e = 1. 60E-19, quantum efficiency ζ = 0.55,
By substituting into the equation (2) with the modulation factor ma = 1, the load resistance R = 200Ω, the noise factor of the amplifier N0 = 5 dB, and the multiplication factor M = 50, the average received light power in the noise band 1000 [MHz] is obtained. APr = −43 [dBm], and in a noise band of 100 [MHz], the average received light power AP
When r = −48 [dBm] and the noise band is 10 [MHz], the average received light power APr = −53 [dBm] can be obtained.

The central processing unit 31 calculates the average received light power A corresponding to the transmission rate of the information signal S1 currently being transmitted.
The value corresponding to Pr is set to the threshold value Pth1. As a result, the central processing unit 31
When the amount of received light in the communication target device becomes equal to or less than a predetermined threshold value determined by the transmission rate, a positive result is obtained in step SP16, and the process proceeds to step SP17.

Here, the central processing unit 31 determines whether or not the operation mode of the optical space transmission apparatus 1 is set to the automatic rate switching mode via the network. Here, the automatic rate switching mode is an operation mode in which the spatial optical transmission device 1 automatically switches the transmission rate in response to a change in the spatial transmission path.

If a negative result is obtained here, the central processing unit 31 proceeds to step SP18, and it is becoming difficult to transmit the information signal S1 at a predetermined bit error rate or less due to a decrease in the received light amount. Notify the terminal via the network. Subsequently, the central processing unit 31
Moves to step SP19, and determines whether or not an instruction to switch the transmission rate has been input from the terminal in response to this notification. Here, if the switching instruction is not input even after the predetermined time has elapsed, or if control data indicating that switching is not to be performed is input, the central processing unit 31 proceeds to step SP1.
Then, the procedure goes to 4 to end this processing procedure. On the other hand, if the terminal instructs to switch the transmission rate, the process moves from step SP19 to step SP20 to prepare for reduction of the transmission rate.

On the other hand, if the automatic rate switching mode is set, the central processing unit 31 proceeds directly from step SP17 to step SP20, prepares for a reduction in the transmission rate, and proceeds to step SP21 (FIG. 10). Also, in the other device, the amount of received light is equal to the threshold Pth
Even if it is not lower than 1, the central processing unit 31 proceeds to step SP21 because a negative result is obtained in step SP16.

The central processing unit 31 executes this step S
In P21, the amount of received light P1 reaches a predetermined threshold value Pth
It is determined whether it is 2 or more. Here, this threshold value Pth2
Is an amount of light that can secure the amount of received light necessary to demodulate the information signal S1 at or below the predetermined bit error rate even when the transmission rate of the information signal S1 is increased;
This is the amount of light with a predetermined margin set for the average received light power APr described above.

If a positive result is obtained here, the central processing unit 31 proceeds to step SP22, and determines whether or not the operation mode of the optical space transmission device 1 is set to the automatic rate switching mode. If a negative result is obtained here, the central processing unit 31 proceeds to step SP23 and notifies the terminal that the transmission rate of the information signal S1 can be improved by increasing the received light amount. Subsequently, the central processing unit 31 proceeds to step SP24, and determines whether or not a transmission rate switching instruction has been input from the terminal in response to the notification. Here, if the switching instruction is not input after a predetermined time has elapsed, or if control data indicating that switching is not to be performed is input, the central processing unit 31 proceeds to step S
The process moves to P14 and the processing procedure ends. On the other hand, when the terminal instructs to switch the transmission rate, the process proceeds from step SP24 to step SP25, and after preparing for an increase in the transmission rate, the process proceeds to step SP26.

On the other hand, if the automatic rate switching mode is set, the central processing unit 31 proceeds directly from step SP22 to step SP25, prepares for an increase in the transmission rate, and then proceeds to step SP26. Also in the case where the amount of received light is not greater than the threshold value Pth2 in the partner device, the central processing unit 31 proceeds directly to step SP26 because a negative result is obtained in step SP21.

When the central processing unit 31 proceeds to step SP26 in this way, it sends status data D1 to the communication target device, notifies the transmission rate at which the information signal S1 will be transmitted in the future, and then proceeds to step SP27. Here, the central processing unit 31 determines whether or not a response approving the switching of the rate has been input from the device to be called,
Here, if a negative result is obtained, the process moves to step SP14 and ends this processing procedure. Step SP
If a positive result is obtained in step 27, the central processing unit 31 proceeds to step SP28, where the clock generation circuit 2
After instructing the switching of the clock to 9A to instruct the switching of the transmission rate, the process proceeds to step SP14 to end this processing procedure.

Further, the central processing unit 31 responds to the notification of the input transmission rate by executing this processing procedure in the communication target device, and sends out status data D1 for approving the switching of the transmission rate as necessary. . If the automatic rate switching mode is not set at this time, the terminal receives instructions from the terminal and executes necessary response processing.

Further, when the transmission rate of the information signal S1 is changed by the mutual communication executed in this manner, the central processing unit 31 substantially changes the transmission rate of the information signal S6 transmitted from the communication target device. The transmission rate is changed according to the synchronized timing.

(1-2) Operation of First Embodiment In the above configuration, the optical free space transmission apparatus 1 is arranged, for example, on the roof of a building so as to face a device to be talked to by the same apparatus. (FIGS. 2 and 6), the transmission light beam L1 emitted from the laser diode 20 is sequentially reflected by the polarization beam splitter of the prism 16 and the optical axis correction unit 10, and then spreads through the concave lens 9 and the lens group 8B to a predetermined extent. Thus, the light is emitted toward the communication target device. Similarly, a receiving light beam L2 is emitted from the communication target device toward the optical space transmission device 1.

When the reception light beam L2 transmitted from the communication target device enters the lens group 8B, the reception light beam L2 is converted into substantially parallel light by the lens group 8B and the concave lens 9, and then the optical axis correction unit 10. The light is sequentially reflected by the half mirror of the prism 16 and condensed on the position detecting element 24. Here, the reception light beam L2 is
The light receiving result of No. 4 is processed by the PSD light receiving circuit 36, so that the light condensing position on the light receiving surface of the position detecting element 24 is detected, and the central processing unit 31 determines the arrival direction of the received light beam L2 from the light condensing position. Is detected. Further, the central processing unit 31 tilts the mirror 11 (FIG. 4) of the optical axis correction unit 10 so that the condensing position of the received light beam L2 is at a predetermined position.
The emission direction of the transmission light beam L1 is set such that the transmission light beam L1 is emitted in the direction of arrival of the second light beam.

As a result, a state in which the communication target device can receive the transmission light beam L1 is formed, and the optical space transmission apparatus 1 forms a line with the communication target device.

When the line is formed as described above, the optical space transmission apparatus 1 generates a drive signal by modulating the information signal S1 based on the Ethernet signal input from the external device by the modulation circuit 30, and generates the drive signal. The transmission light beam L1 is modulated so that the amount of light changes according to the signal level of the communication signal, and the information signal S1 is transmitted to the communication target device via the transmission light beam L1. Similarly, the received light beam L2 modulated and transmitted by the information signal from the communication target device is received by the light receiving element 28, and the light receiving result is processed by the PD light receiving circuit 33 and the demodulation circuit 34, and the information signal S6 is output. Is received.

When transmitting and receiving the information signals S1 and S6 in this manner, as in the case of the line connection, the optical space transmission apparatus 1
The position detection element 24 detects the arrival direction of the reception light beam L2, and the central processing unit 31 controls the inclination of the mirror 11 in the optical axis correction unit 10 based on the detection result. Thereby, in the optical space transmission device 1, a servo loop is formed to correct the emission direction of the transmission light beam L1, and the line is maintained so as not to be interrupted even in the case of vibration or the like.

In this control, the optical space transmission apparatus 1
The inclination of the mirror 11 is detected by the skew sensor angle detection circuit 39, and the inclination of the mirror 11 is controlled so as not to exceed a predetermined movable range. The moving average of the inclination of the mirror 11 is calculated by the central processing unit 31, and when the inclination changes by a predetermined reference value or more, the registered object is notified by e-mail. Accordingly, the optical space transmission apparatus 1 can take necessary countermeasures before it becomes difficult to correct the optical axis correction unit 10 due to a change with time and maintenance of the line becomes difficult.

The drive current of the laser diode 20 is monitored by the central processing unit 31, and when the average value of the drive current exceeds the reference current value, an electronic mail is issued in the same manner. As a result, the optical space transmission device 1 detects the deterioration of the laser diode 20 by the drive current, and can take necessary countermeasures when the degree of deterioration progresses by a certain value or more.

Further, the optical free space transmission apparatus 1 has the position detecting element 24 for detecting the arrival direction of the received light beam L2.
The light amount of the received light beam L2 is detected from the result of the light reception, and a moving average value of this light amount is calculated (FIG. 9). Further, the calculated light amount is used as the status signal D1 as the information signal S.
1 (FIG. 7), and is notified to the communication target device.

Similarly, the transmission light beam L transmitted by being frequency-multiplexed and transmitted with the information signal S6 from the device to be talked to is transmitted.
1 is demodulated by the demodulation circuit 34, and in the central processing unit 31, when the received light quantity changes beyond a certain range, the transmission rates of the information signals S1 and S6 are changed (FIGS. 9 and 10). .

As a result, as shown in FIG. 12, in the optical space transmission device 1, when the loss of the transmission path increases due to fog, rain, etc. and the amount of received light decreases, a predetermined bit error rate is also determined by the amount of received light. The information signals S1 and S6 are transmitted and received at a transmission rate that allows transmission. Thus, disconnection of the line can be prevented even when fog or the like occurs.

Further, in addition to the amount of received light, the tilt of the mirror 11 and the drive current of the laser diode 20 are also notified as status data to be transmitted and received to and from the communication target. Even if it is difficult to notify the inclination of the mirror 11 and the drive current of the laser diode 20 by issuing an e-mail from the transmission device 1,
The notification can be made via the device to be called. In addition, by recording these status data in the record,
The history can be easily confirmed and can be used for maintenance.

(1-3) Effect of First Embodiment According to the above configuration, the result of light reception on the light receiving side of the light beam is grasped on the transmitting side, and the information signal S is transmitted at an appropriate transmission rate.
By transmitting 1, it is possible to prevent disconnection of the line even when fog or the like occurs.

(2) Second Embodiment (2-1) Configuration of Second Embodiment FIG. 13 is a diagram showing the relationship between the amount of received light in a central processing unit and the space optical transmission apparatus according to the second embodiment. It is a flowchart which shows a processing procedure. In this embodiment,
When the central processing unit executes the processing procedure of the received light amount and increases the light amount of the transmission light beam L1 and / or the reception light beam L2, the central processing unit cannot transmit and receive the information signals S1 and S6 at a predetermined bit error rate or less. 9 and FIG. 10, the transmission rate of the information signals S1 and S6 is reduced by performing the same processing procedure as that described above with reference to FIG. Conversely, when the amount of received light increases while the transmission rate is once reduced, the same processing procedure as the processing procedure described above with reference to FIGS. 9 and 10 is executed to reduce the transmission rates of the information signals S1 and S6. After the increase, this processing procedure is executed to reduce the light amount of the light beam. Note that, in this optical space transmission apparatus, the first procedure is the same except that the processing procedure of the central processing unit is different.
Since the configuration is the same as that of the first embodiment, the same reference numerals are given to the same configuration, and the duplicated description will be omitted.

That is, the central processing unit executes step S
The process proceeds from P30 to step SP31, and receives the status data D2 from the demodulation circuit 34.
Then, the format of the received data is confirmed. Here, when the format of the received data is different from the received light amount data, the central processing unit proceeds to step SP33, and ignores the received data in step SP34 for this received light amount processing.
To end the processing procedure.

On the other hand, if the format of the received data is correct, a positive result is obtained in step SP32, and the central processing unit proceeds to step SP35. Here, the central processing unit extracts information on the amount of received light assigned to the status from the received data and records the information in the memory.

Subsequently, the central processing unit proceeds to step SP
36, the received light amount P1 is set to a predetermined threshold value Pth.
It is determined whether it is 3 or less. If a positive result is obtained here, the process proceeds to step SP37, and the light amount of the transmission light beam L1 is set to 20 or less.
In step SP3, a variable PLDCONT defining the light amount of the transmission light beam L1 is set so as to increase [%].
Move to 8. On the other hand, if a negative result is obtained in step SP36, the process directly proceeds to step SP38.

Here, the threshold value Pth3 is determined based on information transmitted at a transmission rate of 1 [GHz] below a predetermined bit error rate when the transmission light beam L1 transmitted from the optical space transmission apparatus 1 is received by a communication target device. This is the amount of received light required to demodulate the signal S1.

Thus, the central processing unit sets the received light amount in the communication target device to be equal to or more than the predetermined light amount.
The information signal is transmitted by controlling the light amount of the transmission light beam L1 and securing a predetermined bit error rate.

The central processing unit proceeds to the next step SP3
At 8, it is determined whether or not the amount of received light P1 is equal to or greater than a predetermined threshold value Pth4.
A variable PLDCONT defining the light amount of the transmission light beam L1 is set so as to go down, and the routine goes to step SP40 (FIG. 9). On the other hand, if a negative result is obtained in step SP38, the process directly proceeds to step SP40.

Here, the threshold value Pth4 is used to demodulate the information signal S1 at a transmission rate of 1 [GHz] below a predetermined bit error rate even when the light amount of the transmission light beam L1 is reduced by 20 [%]. This is the amount of light that can secure the required amount of received light.

Thus, the central processing unit reduces the light amount of the transmission light beam L1 when a sufficient light amount is secured in the communication target device, thereby reducing the burden on the laser diode 20.

In the following step SP40 (FIG. 9)
The central processing unit sets the variable P thus set.
It is determined whether or not the light amount of the transmission light beam L1 specified by LDCONT is equal to or smaller than a predetermined threshold value Pth5. If a positive result is obtained here, the process proceeds to step SP41, and the light amount of the transmission light beam L1 is reduced to the threshold value Pth5. As you set
Variable PLDCONT defining the light amount of transmission light beam L1
Is set again, and the routine goes to step SP42. On the other hand, if a negative result is obtained in step SP40, the process directly proceeds to step SP42.

Here, the threshold value Pth5 is a light amount corresponding to a transition point in the laser diode 20, at which the relationship between the drive current and the emitted light amount changes from a non-linear characteristic to a linear characteristic. Thereby, the central processing unit controls the operation of the laser diode 20 so as to emit the transmission light beam L1 using only the region having excellent linearity when the transmission light beam L1 is amplitude-modulated.

On the other hand, in the following step SP42, the central processing unit determines whether or not the light quantity of the transmission light beam L1 specified by the variable PLDCONT thus set is equal to or more than a predetermined threshold value Pth6. When a positive result is obtained in step SP43, the process proceeds to step SP43, in which the variable PLDCO defining the light amount of the transmission light beam L1 is set so that the light amount of the transmission light beam L1 is set to the threshold value Pth6.
NT is set again, and the routine goes to Step SP44. On the other hand, if a negative result is obtained in step SP42, the process directly proceeds to step SP44.

Here, the threshold value Pth6 is a set value corresponding to the maximum standard of the laser diode, so that the central processing unit does not emit the transmission light beam L1 beyond a preset limit. , The operation of the laser diode 20 is controlled.

In step SP44, the central processing unit sets the variable PLDCONT in the digital-to-analog conversion circuit 40 and instructs the laser diode drive circuit 32 to change the light amount.
The process moves to P34 and the procedure ends.

Further, the central processing unit relates to the control of the light amount of the transmission light beam L1 performed in this manner,
Based on the result of monitoring the transmission light beam L1 output from the laser diode driving circuit 32, the carrier signal S2
Of the transmission light beam L1 emitted from the laser diode 20, the transmission light beam L1 is emitted with a constant modulation degree.

(2-2) Operation of the Second Embodiment In the above configuration, the optical space transmission apparatus receives the transmission light beam L1 which is frequency-multiplexed and transmitted with the information signal S6 from the communication target device. The light amount is demodulated by the demodulation circuit 34, and the central processing unit 31 controls the light amount of the transmission light beam L1 so that the received light amount is maintained in a constant range (FIGS. 13 and 14). Similarly, the light amount of the received light beam L2 is controlled so that the light amount notified from the optical space transmission device 1 is maintained in a certain range also in the communication target.

As a result, as shown in FIG. 15, in the optical space transmission device 1, when the loss of the transmission line increases due to fog, rain, etc., the light amount of the transmission light beam L1 is increased to compensate for the increase. . Therefore, when the loss of the transmission path is small, the light amount of the transmission light beam L1 can be reduced correspondingly, and the burden on the laser diode 20 can be reduced. Therefore, it is possible to transmit the transmission light beam with an appropriate amount of light by grasping the reception result of the spectral beam on the reception side on the transmission side,
This makes it possible to reduce the frequency of replacing the light emitting elements with a simple configuration.

When the information signal S1 cannot be transmitted below a predetermined bit error rate even if the light amount of the transmission light beam L1 is increased in this way, the transmission rate is reduced, thereby preventing disconnection of the line. .

In the same way, the light quantity of the received light beam L2 can be controlled in the same manner in the communication target, and the frequency of replacement of the light emitting elements can be reduced with a simple configuration.

Further, at this time, the transmission side grasps the amount of received light in the communication object and controls the light beam amount so that even when the conditions of the transmission path differ between the optical space transmission apparatus 1 and the communication object. In addition, the light amount of the light beam can be appropriately and reliably controlled so that a desired information signal can be reliably transmitted and received.

That is, as shown in FIG. 16, in the spatial transmission line connecting the optical spatial transmission devices 1 and 1A, the air is dense due to the terrain (ponds, grassland, roads, etc.) on the ground of the spatial transmission line. . When the light beams L1 and L2 emitted from the optical space transmission devices 1 and 1A pass through a region where the air density is higher than, for example, other portions generated in this way, the light beams L1 and L2 are refracted by this region. Become.

In this area, even when the two light beams L1 and L2 are refracted by the same degree, if this area is close to the optical space transmission device 1A, the light beams are respectively transmitted by the optical space transmission devices 1 and 1A. The spreads W1 and W2 of L1 and L2 are different. Thus, as in this embodiment, by controlling the amount of light beam by grasping the amount of received light in the call target on the transmitting side,
Even when the conditions of the transmission path are different between the optical space transmission device 1 and the communication target, the light amount of the light beam can be appropriately and reliably controlled so that a desired information signal can be reliably transmitted and received. .

In the control of the transmission light beam L1, in the optical space transmission device 1, the light amount of the transmission light beam L1 is controlled within a range not exceeding a predetermined upper limit value, thereby protecting the laser diode 20. In addition, the light amount of the transmission light beam L1 is controlled within a range not exceeding a predetermined lower limit so that the transmission light beam L1 can be modulated in a region having good linearity, thereby ensuring communication quality.

In the optical free space transmission apparatus 1, the signal level of the carrier signal S2 used for modulating the information signal S1 is controlled with the light amount of the transmission light beam L1 set in this way, and the modulation of the information signal S1 is performed. The degree is switched. As a result, even when the light amount of the transmission light beam L1 is switched, the modulation degree of the transmission light beam L1 is maintained at a constant value, and the communication quality is maintained.

(2-3) Effects of the Second Embodiment According to the above configuration, the result of light reception on the light receiving side of the light beam is grasped on the transmitting side, and the transmitted light amount of the light beam is also controlled. Accordingly, the burden on the laser diode can be reduced, and in addition to the effects of the first embodiment, the frequency of replacing the light emitting elements can be reduced with a simple configuration.

(3) Other Embodiments In the above-described embodiment, a case has been described in which the amount of received light is transmitted by frequency multiplexing. However, the present invention is not limited to this, and transmission is performed by time division multiplexing. May be.

Further, in the above-described embodiment, the case where the transmission speed of the information signal is simultaneously switched with the communication target device has been described. However, the present invention is not limited to this, and the sensitivity and the like differ between the devices. Because of this, one information signal may be transmitted at a higher transfer rate than the other information signal, if necessary.

Further, in the above-described embodiment, the case where the drive current of the laser diode, the light receiving result, and the inclination of the mirror are transmitted as the information of the operation state has been described. However, the present invention is not limited to this, and in addition thereto. For example, a bit error rate or the like may be transmitted.

Further, in the above-described embodiment, the case where the amount of received light is directly detected and notified is described.
The present invention is not limited to this, and may notify various parameters that change according to the amount of received light, and thereby indirectly notify the amount of received light. By the way,
In this case, A provided in the signal processing circuit for processing the reception result
It is conceivable to notify the gain of the GC circuit and further the bit error rate.

In the above-described embodiment, the case where the information signal which is an Ethernet signal is transmitted and received has been described. However, the present invention is not limited to this.
It can be widely applied when transmitting and receiving various information signals.

[0124]

As described above, according to the present invention, the fog or the like is generated by grasping the light receiving result on the light receiving side of the light beam on the transmitting side and transmitting the information signal at an appropriate transmission rate. However, disconnection of the line can be prevented.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a processing procedure of a central processing unit of a free-space optical transmission device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating an optical space transmission system using the optical space transmission apparatus according to the first embodiment of the present invention.

FIG. 3 is a side view showing the optical space transmission apparatus of FIG. 2;

FIG. 4 is a sectional view showing the optical system of FIG. 3;

FIG. 5 is a cross-sectional view of the optical system shown in FIG. 3 by cutting along line AA.

FIG. 6 is a block diagram of the free-space optical transmission apparatus of FIG. 3;

FIG. 7 is a characteristic curve diagram for explaining the operation of the modulation circuit of the free-space optical transmission device of FIG. 6;

FIG. 8 is a schematic diagram for explaining status data.

FIG. 9 is a flowchart for explaining a process of a received light amount.

FIG. 10 is a flowchart showing a processing procedure following FIG. 1;

FIG. 11 is a schematic diagram for explaining transmission characteristics in this type of transmission system.

FIG. 12 is a time chart showing a change in a transmission rate.

FIG. 13 is a flowchart illustrating a processing procedure of the free-space optical transmission apparatus according to the second embodiment.

FIG. 14 is a flowchart showing a processing procedure following FIG. 13;

FIG. 15 is a time chart showing a change in a transmission rate.

FIG. 16 is a schematic diagram for explaining conditions of a transmission path.

[Explanation of symbols]

1, 41 ... optical space transmission device, 10 ... optical axis correction unit, 2
0: laser diode, 24: position detecting element, 2
8 light receiving element, 30, 43 modulation circuit, 31 central processing unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H04B 10/18 F term (Reference) 2H043 AA02 AB05 AB09 AD02 BC01 CD02 5K002 AA05 BA13 CA00 CA02 CA09 DA02 DA03 DA04 DA05 FA03 GA04

Claims (4)

[Claims] 1. A transmission light beam modulated by a predetermined information signal is transmitted to a transmission / reception device arranged at a predetermined distance, and the transmission light beam is transmitted from the transmission / reception device by receiving the reception light beam transmitted from the transmission / reception device. An optical space transmission device that transmits the information signal to the transmission / reception device via a light beam and receives a predetermined information signal transmitted from the transmission / reception device via the reception light beam; An optical space transmission device, wherein information on the light amount is transmitted to the transmission / reception device, and the transmission rate of the information signal is varied according to the information on the received light amount of the transmission light beam transmitted from the transmission / reception device. 2. The information of the amount of received light is frequency-multiplexed with the information signal and transmitted.
Optical space transmission device according to claim 1. 3. The information on the amount of received light is time-division multiplexed with the information signal and transmitted.
Optical space transmission device according to claim 1. 4. The optical space transmission apparatus according to claim 1, wherein the information signal is an Ethernet signal.