JPH0685753A - Optical multiplex communication equipment - Google Patents

Abstract

PURPOSE:To secure an optimum S/N for each line even when the number of lines is changed by correcting a signal level of an information signal based on the result of detection of the lines. CONSTITUTION:The equipment is provided with information signal generating circuits 10A-10D, 28, 32A-32C, 34 which set freely the line number of an input signal as required, convert the input signal into modulation signals S5, S6, multiplex them and generate an information signals S1 and with line number detection circuits 50A-50D, 54A-54C detecting number of the line of the input signal and output line number detection results K1, K2. Thus, the amplitude of the information signal S1 resulting from multiplexing the input signal is kept to a prescribed value by correcting the signal level of the information signal S1 based on the line number detection results K1, K2 in the signal level compensating circuit 28 and 34.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Technology Problem to be Solved by the Invention Means for Solving the Problem (FIG. 2) Action (FIG. 2) Example (1) Configuration of Example (FIGS. 1 to 5) (2) Effects of Examples (3) Other Examples Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multiplex communication device,
For example, the present invention can be applied to an optical space transmission device that transmits / receives a video signal to / from a transmission signal through a light beam that transmits space.

[0003]

2. Description of the Related Art Conventionally, in this type of optical space transmission device, a portion of a transmission light beam sent to a transmission object is folded back and received, whereby the irradiation position of the transmission light beam can be easily detected on the transmission side. The one that is designed to be obtained is proposed (Japanese Patent Application No. 63-138120).

That is, in this type of optical space transmission device, a laser diode is driven by a predetermined information signal, and a transmission light beam having a predetermined plane of polarization is emitted from the laser diode. As a result, in the optical space transmission device, the transmission light beam is sent to the transmission target via the predetermined optical system, and the information signal is transmitted via the transmission light beam.

Further, in the optical space transmission device, the received light beam coming from the transmission object is received by the light receiving element, and the output signal of this light receiving element is processed by a predetermined signal processing circuit.
As a result, in the optical space transmission device, the information signal to be transmitted is received via this reception light beam.

Further, in the optical space transmission device, a part of the transmission light beam is separated and folded back in parallel with the optical axis of the transmission light beam, and the folded back transmission light beam is imaged together with the scenery of the transmission target. With this, in the optical space transmission device, the irradiation position of the transmission light beam can be detected as a bright luminescent spot in the captured image by capturing an image of the transmission object, which can simplify the installation work, and can be carried outdoors, for example. It is designed so that a video signal picked up by a television camera can be easily relayed.

[0007]

By the way, in such an optical space transmission apparatus that can be easily carried and installed, it is possible to transmit and receive a video signal in a desired form by switching the channels for transmission and reception as required. If possible, it would be convenient and useful.

In this case, for example, a slot of 4 channels may be formed in the body of the optical space transmission device so that each card-shaped board can be housed, and the board for transmission or the board for reception can be housed in the slot in a replaceable manner. Conceivable.

That is, in the optical space transmission device, this 4
A connector is arranged in one slot, and the board inserted in each slot is connected to this connector. On the other hand, in each transmission board, a connector for inputting a video signal and an FM modulation circuit for frequency-modulating the video signal are mounted,
Each receiving board is equipped with an FM demodulation circuit that demodulates an FM modulated signal to reproduce a video signal and a connector that outputs the reproduced video signal.

Correspondingly, in the body of the optical free space transmission apparatus, the output signals of the respective connectors are input to the adder circuit, and when the transmitting substrate is accommodated in the slot, the FM modulated signals are frequency-multiplexed and the laser is transmitted. Drive the diode. Further, in the optical free space transmission apparatus main body, the received signal is band-separated and output to each slot.

As a result, in the optical free space transmission apparatus, it is possible to replace the transmission substrate and the reception substrate as needed to secure the transmission and reception channels within the range of maximum 4 channels. Therefore, the user can exchange the board as needed and freely set the transmission / reception channel within a range of up to 4 channels, thereby improving the usability by setting the transmission / reception channel according to the purpose of use. .

By the way, in an optical communication system for driving a laser diode to transmit an information signal, the laser diode is driven so as to avoid a non-linear region of the laser diode and obtain a sufficient light quantity ratio. Cross-modulation is prevented in advance, and a practically sufficient SN ratio is ensured.

On the other hand, if the transmission / reception channels can be freely set in this way, the number of lines in the transmission channel changes, and the maximum amplitude of the frequency-multiplexed signal changes in accordance with the change in the number of lines. Therefore, in the laser diode, the maximum amplitude of the drive signal changes according to the number of transmission channel lines.

In this case, when the number of lines decreases, it becomes impossible to effectively use the linear region of the laser diode to transmit the information signal. On the other hand, when the number of lines increases, the operating region may reach the non-linear region. There is. That is, if the transmission / reception channels can be freely set in this way, there is a problem that the optimum SN ratio cannot be secured for each channel.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose an optical multiplex communication apparatus capable of ensuring an optimum SN ratio for each line even when the number of lines changes. .

[0016]

In order to solve such a problem, according to the present invention, a laser diode 4 is driven by a predetermined information signal S1 and a transmission light beam L1 emitted from the laser diode 4 is transmitted to a transmission object. In the optical multiplex communication apparatus 1 for transmitting the information signal S1 to the transmission object, the number of lines of the input signal can be freely set as needed, and the input signal is converted into the modulated signals S5 and S6 and then multiplexed to obtain the information signal. S
Information signal generating circuits 10A to 10D, 28, which generate 1
32A to 32C and 34, and a line number detection circuit 5 that detects the number of lines of the input signal and outputs the line number detection results K1 and K2.
0A to 50D, 54A to 54C, and the number of lines detection result K
Signal level correction circuits 28 and 34 for holding the amplitude of the information signal (S1) obtained by multiplexing the input signal at a predetermined value by correcting the signal level of the information signal (S1) based on 1 and K2. To do so.

Further, in the present invention, the input signals are the first and second input signals of different types, and the signal level correction circuits 28 and 34 change the modulation signals S5 and S6 of the first and second input signals. The signal levels of the modulated signals S5 and S6 are corrected so that the amplitude ratio R is maintained at a constant value.

Further, in the present invention, the first input signal and the second input signal are audio signals for communication between the video signal and the transmission object.

Further, in the present invention, by transmitting the transmission light beam L1 to the space through the predetermined optical system 6, the input signal is transmitted to the transmission target through the space.

[0020]

By correcting the signal level of the information signal (S1) based on the detection results K1 and K2 of the number of lines, if the amplitude of the information signal (S1) obtained by multiplexing the input signal is held at a predetermined value, Even if the number changes, the optimum SN ratio can be secured.

At this time, if the amplitude ratio R of the modulated signals S5 and S6 of the first and second input signals is held at a constant value,
It is possible to secure the optimum transmission state according to the input signal.

In particular, by applying it to a video signal and an audio signal for communication between a transmission target and the image signal, it is possible to prevent the image quality of the image signal from deteriorating, and at the same time, the clarity of the communication line can be secured.

Further, it can be applied to an optical space transmission device to improve usability.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

(1) Configuration of Embodiment In FIG. 1, reference numeral 1 denotes an optical space transmission device as a whole,
The laser diode (LD) drive signal S1 is input to the laser diode (LD) drive circuit 2, and the LD drive circuit 2 drives the laser diode 4 accordingly. As a result, in the optical space transmission device 1, the laser diode 4 generates the transmission light beam L1 having a predetermined polarization plane, and the transmission light beam L1 is sent to the transmission target via the optical system such as the lens 6.
The information signal composed of the LD drive signal S1 can be transmitted to a predetermined transmission target.

This optical space transmission device 1 is designed so that a card substrate can be exchangeably accommodated in a predetermined slot, whereby a transmission substrate and a reception substrate can be accommodated in this slot as required, and a desired substrate can be accommodated. It is designed to secure the transmission and reception channels. In the case of this embodiment, in the optical free space transmission apparatus 1, four transmission substrates are inserted in each slot so that a 4-channel line can be secured for transmission of a video signal, and further transmission target It is designed to secure a 3-channel line for communication between the two.

That is, as shown in FIG. 2, in the optical space transmission device 1, the video transmission circuits 10A to 10D are formed on the transmission substrates, respectively, and the video transmission circuit 10A is formed.
Input video signals to 10D. As shown in FIG. 3, in the video transmission circuits 10A to 10D, after the input video signal S2 is processed by a predetermined signal processing circuit, the varicap diode 12 and the resonance coil 14 connected to the oscillation circuit 16 are used. Is input to the tank circuit 18 and the frequency modulation signal S held at a predetermined amplitude is thereby obtained.
4 is generated.

Further, in the video transmission circuits 10A to 10D, after the frequency modulation signal S4 is amplified by the amplification circuit 20, the mixer 22 multiplies the output signal of the local oscillation circuit 24 and the output signal of the mixer 22 is bandpassed. It is output via a filter circuit (BPF) 26. As a result, in the video transmission circuits 10A to 10D, the transmission circuits 10A to 10D
The video signal S2 is converted into the frequency modulation signal S5 in the frequency band assigned to 10D, and the frequency modulation signal S5 is output to the optical space transmission apparatus main body.

In the video transmission circuits 10A to 10D, the signal processing circuit preliminarily superimposes the audio signal on the video signal S2 to generate the frequency modulation signal S5, whereby not only the video signal but also the audio signal is generated. It can be transmitted at the same time.

In the optical free space transmission apparatus 1, the frequency modulation signal S5 output from each of the video transmission circuits 10A to 10D is output to the level control circuit 28, and the frequency modulation signal S5 is added here to obtain the frequency. Modulation signal S5
Is frequency-multiplexed and output to the adder circuit 30. Further, in the optical space transmission device 1, the communication transmission circuits 32A to 32A
Input the audio signal for communication to 2C, and send the video transmission circuit 10
Similar to A to 10D, this audio signal is frequency-modulated to generate a frequency-modulated signal S6 having a predetermined amplitude.

Further, in the optical free space transmission apparatus 1, the frequency modulation signal S6 output from each of the communication transmission circuits 32A to 32C is input to the level control circuit 34, and is added here to add the frequency modulation signal S6 to the frequency. Multiplex. The adder circuit 30 adds the output signals of the level control circuits 28 and 34 to generate and output the frequency multiplexed signal S8.

As a result, in the optical space transmission device 1,
The level control circuit 36 corrects the signal level of the frequency multiplexed signal S8 to generate the information signal S1. As a result, in the transmission target, the transmission light beam L
1 is received by a predetermined light receiving element, and the output signal of this light receiving element is band-divided and demodulated so that a video signal of 4 channels and a communication voice signal of 3 channels can be received.

That is, as shown in FIG. 4, in the transmission object, after the band-divided output signal S8 of the light-receiving element is band-limited by the bandpass filter circuit (BPF) 40, the output signal S8 of the oscillation circuit 44 is output by the mixer 42. The frequency is converted by multiplication. Further, in the transmission target, the output signal of the mixer 42 is detected by the FM detection circuit 46, and the detection signal obtained as a result is output via the amplification circuit 48. As a result, in the transmission object, it is possible to set the demodulation circuits as many as the number of lines and receive the video signals of 4 channels and the communication voice signals of 3 channels.

On the other hand, the level detection circuits 50A-50
D is connected to the input terminal of the frequency modulation signal S5 formed in each slot, and the frequency modulation signal S5 is connected to this input terminal.
The line detection result K in which the signal level rises when is input
1 is output to the control circuit 52. As a result, in the optical free space transmission apparatus 1, the control circuit 52 can detect the number of lines of the video signal set by the user.

Similarly, the level detection circuits 54A to 54C are
The line detection result K2, which is connected to the input terminal of the frequency modulation signal S6 output from the communication transmission circuits 32A to 32C and whose signal level rises when the frequency modulation signal S6 is input to this input terminal, is output to the control circuit 52. . As a result, in the free-space optical transmission apparatus 1, the number of communication lines set by the user can be detected by the control circuit 52, as in the case of the video signal.

The control circuit 52 corrects the signal level of the frequency-multiplexed signal in the level control circuits 28 and 34 based on the line detection results K1 and K2, so that the predetermined maximum amplitude is maintained even when the number of lines is changed. The laser diode 4 is driven.

That is, there are p and q (in this case, 4 and 3 in this case) generation sources for the frequency-modulated signals S5 and S6, respectively.
When 5 and S6 are multiplexed to drive the laser diode, it is considered that the correlation is low in the frequency modulation signals S5 and S6. Therefore, the amplitude of the drive signal that drives the laser diode is the amplitude of the frequency modulation signals S5 and S6. Can be seen as a probability density function.

At this time, the probability density function approaches a Gaussian distribution, and eventually the amplitude of the drive signal is the frequency modulation signal S.
It can be considered as the sum of the electric powers of 5 and S6.

On the other hand, the optical modulation degree m of the transmission light beam L1 is expressed by the following equation using the modulation amplitude Ps of the transmission light beam L1 and the center level Po at the time of modulation.

[Equation 1] When driving a laser diode by combining uncorrelated N-channel signals, the amplitude mt of the combined drive signal is

[Equation 2] Can be expressed as

As a result, when the amplitudes of the frequency modulated signals S5 and S6 are set to mp and mq, respectively, for the frequency multiplexed signals of the frequency modulated signals S5 and S6, the amplitudes mtp and mtq are calculated as follows.

[Equation 3]

[Equation 4] The amplitude mt of the output signal of the adder circuit 30 can be expressed as

[Equation 5] Can be expressed as

That is, it can be seen that when the number of lines changes, the amplitude of the drive signal for driving the laser diode changes according to the relationship of equation (5). As a result, the center level of the drive signal is held at a constant value, and if the amplitudes of the modulation signals S5 and S6 are corrected so that the amplitude mt is held at a constant value in this state, the preset linear region is effectively used. Thus, the laser diode can be driven, and the SN ratio of each line can be optimally maintained even when the number of lines changes.

That is, the amplitude ratio R of the frequency modulation signals S5 and S6 is given by

[Equation 6] By modifying the equation (5), the following equation can be obtained.

[Equation 7]

[Equation 8] The relational expression of can be obtained.

As a result, the control circuit 52 executes the arithmetic processing of equations (7) and (8) based on the line detection results K1 and K2, and controls the level control circuits 28 and 34 based on the arithmetic processing results. It outputs voltages C1 and C2. As shown in FIG. 5, the level control circuits 28 and 34 connect the control voltage C to the grounded pin diode 58 via the resistor 56.
1 and C2, thereby switching the resistance value of the pin diode 58 according to the voltages of the control voltages C1 and C2.

Further, the level control circuits 28 and 34 input / output the frequency-multiplexed signal via the coupling capacitors 60 and 62 to the connection midpoint of the resistor 56 and the pin diode 58, and thereby the voltage of the control voltages C1 and C2. Accordingly, the signal level of the frequency multiplexed signal is corrected and the amplitude of this frequency multiplexed signal is held at the value determined by the equations (7) and (8).

As a result, in the optical space transmission device 1,
Even if the number of lines changes, the optimum SN ratio can be secured,
As a result, it is possible to switch the transmission and reception channels according to the needs of the user and secure a good communication line.

Further, at this time, the amplitude of the frequency multiplexed signal is corrected to the amplitude determined by the equations (7) and (8) so that the relational expression of the equation (6) is satisfied between the video signal and the communication voice signal. In the space optical transmission apparatus 1, the amplitude ratio of the frequency modulation signals S5 and S6 can be held at a constant value. As a result, in the space optical transmission apparatus 1, the SN
The communication line for which clarity is prioritized over the ratio and the line for video signal transmission over which the SN ratio is prioritized are designed to hold the amplitude ratios of the frequency-modulated signals S5 and S6 at constant values. It is designed to ensure the required characteristics.

Further, the control circuit 52 outputs the control voltage C3 to the level control circuit 36 based on the temperature detection result of the predetermined temperature detection sensor, and when the ambient temperature is changed by this and the characteristics of the laser diode are changed, The amplitude and / or center level of the drive signal is corrected by following the change in this characteristic.

(2) Effects of the Embodiments According to the above configuration, the amplitude of the frequency-multiplexed signal is corrected based on the detection result of the number of lines and the amplitude of the drive signal for driving the laser diode is held at a predetermined value. As a result, even if the number of lines changes, the optimum SN ratio can be obtained for each line.

(3) Other Embodiments In the above-described embodiments, the case where the line of 4 channels is set for the video signal and the line of 3 channels for communication is described, but the present invention is not limited to this, and is not necessary. You can freely set the number of lines accordingly.

Further, in the above-mentioned embodiment, the case where the video signal on which the audio signal is superimposed and the communication audio signal are transmitted has been described, but the present invention is not limited to this, and it is possible to transmit various signals. It can be widely applied.

Further, in the above-mentioned embodiments, the case where the present invention is applied to the optical space transmission device is described, but the present invention is not limited to this, and a laser diode is driven to transmit a desired information signal to a transmission object. It can be widely applied when

[0052]

As described above, according to the present invention, when an input signal having a desired number of lines is multiplexed to generate an information signal and the information signal is transmitted, based on the detection result of the number of lines. By correcting the signal level of the information signal, the amplitude of the information signal can be maintained at a predetermined value, and even if the number of lines changes, the optimum SN for each line can be obtained.
It is possible to obtain an optical multiplex communication device that can secure the ratio.

[Brief description of drawings]

FIG. 1 is a block diagram showing an optical space transmission device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing its detailed configuration.

FIG. 3 is a block diagram showing the video transmission circuit.

FIG. 4 is a block diagram showing the demodulation circuit.

FIG. 5 is a block diagram showing a level control circuit.

[Explanation of symbols]

1 ... Optical space transmission device, 2 ... LD drive circuit, 4 ... Laser diode, 10A-10D ... Video signal transmission circuit, 28, 34, 36 ... Level control circuit, 32A-3
2C ... Transmission circuit for communication, 50A to 50D, 54A to 5
4C: level detection circuit, 52: control circuit.

Claims (4)

[Claims] 1. An optical multiplex communication device for driving a laser diode with a predetermined information signal, transmitting a transmission light beam emitted from the laser diode to a transmission target, and transmitting the information signal to the transmission target. The number of lines of the input signal can be freely set, the information signal generating circuit for generating the information signal by converting the input signal into a modulated signal and then multiplexing, and detecting the number of lines of the input signal. A line number detection circuit that outputs a line number detection result, and based on the line number detection result, corrects the signal level of the information signal to set the amplitude of the information signal obtained by multiplexing the input signal to a predetermined value. An optical multiplex communication device, comprising: a signal level correction circuit that holds the signal level correction circuit. 2. The input signal comprises first and second input signals of different types, and the signal level correction circuit keeps the amplitude ratio of the modulated signals of the first and second input signals constant. The optical multiplex communication apparatus according to claim 1, wherein the signal level of each of the modulated signals is corrected so as to hold the value. 3. The optical multiplex according to claim 2, wherein the first input signal and the second input signal are audio signals for communication between a video signal and the transmission target. Communication device. 4. The input signal is transmitted to the transmission target through the space by transmitting the transmission light beam to the space through a predetermined optical system. The optical multiplex communication device according to claim 2 or 3.