JPH06303215A - Optical transmission equipment - Google Patents

Abstract

PURPOSE:To effectively avoid the deterioration in transmission quality, to frequency-multiplex and transmit the information signals of plural channels by setting carrier frequencies so that the interval of the adjacent carrier frequencies becomes a specified one. CONSTITUTION:In a frequency multiplexing circuit, transmission substrates stored in slots 12A-12D generate the modulation signals of the carrier frequencies which are previously set in accordance with the slots 12A-12-D. The carrier frequencies are set so that the intervals DF1-DFn-1 of the adjacent carrier frequencies become uniform. The addition value of the interval DF1 between the adjacent carrier frequencies, which is the narrowest, and the interval DF2 which is the narrowest next to the interval DF1 is set so that it becomes larger than the interval DFn-1 which is the largest. A wave-synthesizing circuit 13 adds the output signals of the transmission substrates, frequency-multiplexes the modulation signal generated in the respective transmission substrates and generates an information signal S1.

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 Problems to be Solved by the Invention Means for Solving the Problems (FIGS. 1, 2 and 7) Operation (FIGS. 1, 2 and 8) Embodiment (1) Overall Configuration (Fig. 1) (2) Slot connection (Figs. 2 and 3) (3) Transmission substrate (Fig. 4) (4) Reception substrate (Fig. 5) (5) Frequency allocation (Figs. 7 and 8) (6) Effects of Examples (7) Other Examples Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical space transmission device,
In particular, it can be applied to the case of transmitting and receiving a desired information signal to and from a transmission target through a light beam propagating in 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 out to the transmission target via the predetermined optical system, and the information signal is transmitted via the transmission light beam L1.

Further, in the optical free space transmission apparatus, the received light beam coming from the transmission object is received by a predetermined 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. As a result, 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 of the transmission target, 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, the optical communication system of this type is characterized in that it can secure a large frequency band for transmission as compared with a normal micro line or the like. Therefore, in this type of optical space transmission device, it is considered that the information signals of a plurality of channels can be efficiently transmitted by frequency-multiplexing and transmitting, for example, a video signal and an audio signal.

In this case, for example, by frequency-modulating the audio signals of a plurality of channels, a frequency-modulated signal in which carrier frequencies are set so that the frequency intervals are equal is generated, and the frequency-modulated signals are frequency-multiplexed and transmitted. There are possible ways to do this.

However, a laser diode used for this kind of optical communication is characterized by non-linear distortion. Especially, in a laser diode used for an optical space transmission device, a high output laser diode is used. The characteristic of this non-linear distortion is large. Therefore, when transmitting a plurality of channels of audio signals or the like, in this type of optical space transmission device, it is unavoidable to generate second-order distortion and third-order distortion. Therefore, the frequency-modulated signals are frequency-multiplexed in this way. However, there is a problem in that the channels affect each other and the transmission quality of the audio signal deteriorates.

To solve this problem, a method of using a laser diode having good linearity is conceivable. However, this method has a problem that a high output laser diode cannot be freely selected, which is still a practically insufficient problem. There is

The present invention has been made in consideration of the above points, and proposes an optical space transmission apparatus capable of frequency-multiplexing and transmitting information signals of a plurality of channels while effectively avoiding deterioration of transmission quality. Is what you are trying to do.

[0012]

In order to solve such a problem, according to the present invention, a plurality of information signals S4 and S5 of a plurality of channels CH1 to CHF are respectively modulated at predetermined carrier frequencies to correspond to a plurality of channels CH1 to CHF. Frequency modulation circuits 13, 16 for generating a frequency-multiplexed signal S1 by frequency-multiplexing the plurality of modulated signals, and a laser for generating a transmission light beam L1 modulated by the frequency-multiplexed signal S1. A diode 3 and transmission optical systems 3, 5, 6, 7 for transmitting a transmission light beam L1 emitted from the laser diode 3 to a transmission target,
The frequency multiplexing circuits 13 and 16 set the carrier frequencies so that the intervals DF1, DF2, ..., DFn-1 between the adjacent carrier frequencies become non-uniform, and the first carrier with the smallest interval between the adjacent carrier frequencies is set. Carrier frequency spacing DF
1 and the interval DF2 of the second carrier frequency where the interval of the adjacent carrier frequencies is the narrowest following the interval of the first carrier frequency is the third carrier frequency where the interval of the adjacent carrier frequencies is the widest. The carrier frequency is set to be larger than the interval DFn-1 of.

Further, in the present invention, the optical space transmission device 1
Is a plurality of slots 1 each accommodating the transmission board 16.
2A to 12D, the frequency multiplexing circuits 13 and 16 are
The transmission board 16 housed in the slots 12A to 12D generates a modulation signal having a carrier frequency preset corresponding to the slots 12A to 12D housing the transmission board 16.

[0014]

Operation: Intervals DF1 and DF between adjacent carrier frequencies
2, ..., so that DFn-1 becomes non-uniform, the interval between the first carrier frequencies is DF1 which is the narrowest interval between the adjacent carrier frequencies, and the adjacent carrier frequency is adjacent to the interval between the first carrier frequencies. If the carrier frequency is set so that the added value with the interval DF2 of the second carrier frequencies with the smallest interval of is larger than the interval DFn-1 of the third carrier frequencies with the largest interval of the adjacent carrier frequencies, It is possible to effectively prevent the signal component generated by the third-order distortion from being mixed into any of the plurality of channels.

[0015]

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

(1) Overall Configuration In FIG. 1, reference numeral 1 denotes an optical space transmission device as a whole,
The driver 2 drives the laser diode 3, which causes the laser diode 3 to emit a transmission light beam L1 having a predetermined polarization plane.

Further, in the optical space transmission apparatus 1, after the transmission light beam L1 is converted into parallel rays by the lens 4, it passes through the deflecting beam splitter 5 and is guided to the lenses 6 and 7.
Thereby, the transmission light beam L1 is transmitted in a predetermined beam shape. As a result, in the optical space transmission device 1, the transmission light beam L1 is sent to the transmission target, and the transmission light beam L1 is transmitted.
The desired information signal S1 is transmitted via the.

Further, in the optical space transmission device 1, after the received light beam L2 coming from the transmission object is received by the lens 7, it is guided to the deflection beam splitter 5 via the lens 6. Here, the reception light beam L2 is transmitted from the transmission target so that the plane of polarization is orthogonal to that of the transmission light beam L1, so that in the optical space transmission device 1, the reception light beam L2 is transmitted by the deflection beam splitter 5. It is reflected and guided to the lens 8. Here, the lens 8 focuses the received light beam L2 on the light receiving element 9, and the light receiving element 9 outputs the output signal, which is the light receiving result, to the demultiplexing circuit 11 via the AGC circuit 10.

Further, in this embodiment, the optical space transmission device 1 has first to fourth slots 12A to 12D adapted to accommodate card-shaped substrates, respectively, and accommodated in the slots 12A to 12D. The output signals of the transmission boards are added by the multiplexing circuit 13 having the addition circuit configuration, whereby the modulation signals generated by the respective transmission boards are frequency-multiplexed to generate the information signal S1. Further, in the free-space optical transmission device 1, in addition to this transmission substrate, the modulation signal generated by the intercom circuit 14 is frequency-multiplexed by the multiplexing circuit 13, whereby various signals for communication can be transmitted toward the transmission target. It is done like this.

Further, in the optical free space transmission apparatus 1, the demultiplexing circuit 11 band-separates the information signal S2 and outputs the information signal S2 to the first to fourth slots 12A to 12D and the intercom circuit 14, instead of the transmission substrate. By inserting the receiving board into the desired slots 12A to 12D, the audio signal coming from the transmission object can be processed, and the communication signal sent from the transmission object via the intercom circuit 14 is demodulated. It is designed to get you.

As a result, in the optical space transmission device 1,
If necessary, a transmission board or a reception board may be inserted into the first to fourth slots 12A to 12D to secure a desired transmission / reception channel.

(2) Slot Connection Here, as shown in FIG. 2, in each of the slots 12A to 12D, the card-shaped substrate is connected to the mother substrate through a predetermined connector, and in the optical space transmission device 1. The multiplexing circuit 13, the demultiplexing circuit 11, and the income circuit 14 are formed on this mother substrate.

That is, in the mother board, when the transmitting boards 16A and 16B are housed in the respective slots by connecting the respective connectors to the multiplexing circuit 13 and the demultiplexing circuit 11, the transmitting boards 16A and 16B output the signals. While the modulated signals SMA to SMD to be output are output to the multiplexing circuit 13, when the receiving boards 17C and 17D are inserted in the slot instead of the transmitting board, the output signal SDA of the demultiplexing circuit 11 is output.
~ SDD can be supplied to the receiving boards 17C and 17D.

At this time, the system control circuit 18 outputs the control data DA to DD assigned to the respective slots 12A to 12D to the connectors of the respective slots 12A to 12D, so that the transmission data inserted in the respective slots. Set the operating frequency of the board and the receiving board to each slot 1
The frequencies assigned to 2A to 12D are set. On the other hand, the transmission board 16 and the reception board 1
7 is configured to modulate and demodulate a 1-channel video signal and a 2-channel audio signal, respectively, and the system control circuit 18 is configured to set the center frequency of each video signal and audio signal in correspondence with the slot. ing.

Of these, as shown in FIG. 3, in the optical space transmission device 1, the first slot 12A receives the first audio signal.
And 7th channels CH1 and CH7 are assigned to the second slot 12B, and second and eighth channels CH2 and CH8 of the audio signal are assigned to the second slot 12B. Similarly, the third and fourth slots 12C and 12D are assigned to the audio signals respectively. 3, 9th channel CH3, CH9 and 4th,
The tenth channel CH4 and CH10 are assigned.

In the case of this embodiment, the optical space transmission device 1
In consideration of future expandability, the fifth and sixth slots can be formed, and the fifth and sixth slots CH5, CH11 and CH11 of the audio signal are respectively provided to the fifth and sixth slots. 6, 12th Channel C
H6 and CH12 are assigned.

As a result, the first and second slots 12A
When the transmission boards 16A and 16B are housed in 12B and 12B, the transmission boards 16A and 16B frequency-modulate the audio signals of the 2nd channel, respectively, and the 1st, 7th channels CH1, CH7 and the 2nd, 8th channels CH2,
The modulated signal of the center frequency assigned to CH8 is output to the multiplexing circuit 13.

On the other hand, the third and fourth slots 12
When the receiving boards 17C and 17D are housed in C and 12D, the receiving boards 17C and 17D set the center frequencies of the demodulation circuit to the frequencies of the third and ninth channels CH3 and CH9 and the fourth and tenth channels CH3 and CH10, respectively. Set to.

Therefore, in the optical space transmission device 1, the first and second optical space transmission devices 1B to be transmitted are
By accommodating the receiving boards 17A and 17B in the first and second slots 12A and 12B so as to correspond to the slots 12A and 12B, respectively, the first and the seventh channels CH1 from the optical space transmission device 1 to the transmission object 1B. , CH7 and the second and eighth channels CH2 and CH8, the frequency-modulated audio signal can be transmitted.

Further, the optical free space transmission apparatus 1 accommodates the transmission boards 16C and 16D in the third and fourth slots 12C and 12D to be transmitted so as to correspond to the third and fourth slots 12C and 12D. As a result, the third and ninth channels CH3 and CH sent from the transmission target 1B
The audio signals frequency-modulated via the ninth, fourth, and tenth channels CH4 and CH10 can be received by the receiving boards 17C and 17D.

Thus, in the optical free space transmission apparatus 1, a plurality of substrate storage positions are formed so that the transmission substrate and the reception substrate can be selectively stored, and the operating frequency of this substrate is set for each substrate storage position. By setting the frequency,
The transmission / reception channels can be set only by selectively housing a desired transmission substrate or reception substrate so as to correspond to the transmission target, and at this time, the frequency of each channel can be easily set. At this time, in the optical free space transmission apparatus 1, since the four slots are shared by the transmitting board and the receiving board, the entire shape can be downsized and the transmission / reception channel can be set easily.

Further, in the system control circuit 18,
Each bit of a predetermined input port is connected to each slot 12A-12
The connector D is assigned to each connector, and the connection line of this connector is connected to the power source in the transmission board 16, while the connection line of this connector is grounded to the ground in the reception board 17. There is.
Thus, in the system control circuit 18, it is determined whether any of the transmission substrate 16 or the reception substrate 17 is housed in each of the slots 12A to 12D, and the transmission and reception frequencies of the intercom circuit 14 are determined based on the determination result. To set.

That is, in the system control circuit 18, when the transmission board 16 is housed in the first slot 12A, the intercom circuit among the first to sixth intercom channels CHA to CHF assigned for the intercom circuit is used. The 14 transmit channels and the receive channels are set to the first to third income channels CHA to CHC and the fourth to sixth income channels CHD to CHF, respectively. On the contrary, in the system control circuit 18, when the receiving board 17 is housed in the first slot 12A, the transmitting channel and the receiving channel of the intercom circuit 14 are set to the fourth to sixth income channels CHD, respectively.
~ CHF and first to third income channels CHA ~
Set to CHC.

As a result, in the optical space transmission device 1,
The frequency of the intercom circuit 14 is set according to the type of the substrate accommodated in the first slot 12A, whereby the communication line can be secured without impairing the compatibility.

Further, in the optical space transmission device 1, the first
When the transmitting board 16 and the receiving board 17 are not housed in the slot 12A, the board housed in the second slot 12B is detected, and when the transmitting board 16 is housed in the second slot 12B. , The first to third income channels CHA to CHC and the fourth to sixth reception channels of the income circuit 14, respectively.
Set to the income channel CHD to CHF. On the other hand, when the transmitting board 16 and the receiving board 17 are not housed in the first slot 12A and the receiving board 17 is housed in the subsequent second slot 12B, the transmitting channel and the receiving channel of the intercom circuit 14 are received. The channels are set to the fourth to sixth income channels CHD to CHF and the first to third income channels CHA to CHC, respectively.

Further, in the optical space transmission device 1, the first
When neither the transmitting board 16 nor the receiving board 17 is housed in the second slot 12A and the second slot 12B, the board housed in the subsequent third slot 12C is detected and transmitted to the third slot 12C, respectively. When the board 16 or the receiving board 17 is housed, the transmission / reception channels of the income circuit 14 are set to the first to third income channels CHA to CHC and the fourth to sixth income channels CHD to CHF, respectively.

Similarly, in the optical space transmission device 1, the first
~ When none of the substrates is accommodated in the third slots 12A to 12C, the transmission / reception channel of the intercom circuit 14 is set according to the substrate accommodated in the subsequent fourth slot 12D. In addition, the optical space transmission device 1 uses each slot 1 for the video signal as in the case of the audio signal described above.
Channels are assigned to 2A to 12D.

(3) Transmitter board As shown in FIG. 4, when the transmitter board 16 is housed in each of the slots 12A to 12D, a video signal input from a predetermined connector arranged in the housing and Among the audio signals, the video signal of 1 channel and the audio signal of 2 channels are input through the connectors of the slots 12A to 12D, and the video signals and audio signals are frequency-modulated and output. Among them, the transmission board 16 is configured to receive the audio signals S4 and S5 of 2 channels.
Are input to voltage controlled oscillators (VCOs) 20 and 21, respectively, where a frequency modulation signal whose oscillation frequency is displaced according to the signal levels of the audio signals S4 and S5 is generated, and this frequency modulation signal is combined with the multiplexing circuit 13 Output to.

At this time, the transmission board 16 inputs the frequency modulation signals output from the voltage controlled oscillators 20 and 21 to the counters 22 and 23, respectively, and detects the frequency of the frequency modulation signal. Ie counters 22 and 23
Is control data D output from the system control circuit 18.
It is formed by a ring counter adapted to switch the operation based on A to DD, and thereby the control data DA to
The frequency-modulated signal is frequency-divided and output at a frequency division ratio determined by DD.

The phase comparators 24 and 25 output the result of phase comparison between the frequency division result and a predetermined reference signal S3, whereas the amplifier circuits 26 and 27 amplify the result of phase comparison, respectively, and then include it. To the voltage-controlled oscillators 20 and 21 via the low-pass filter.

As a result, each of the transmission substrates 16 has an AF
A C loop is formed to frequency modulate the audio signals S4 and S5. At this time, control data DA to D
Based on D, the carrier frequency of the frequency modulation signal can be switched. Incidentally, for the video signal, the carrier frequency can be similarly switched to generate the frequency modulation signal.

(4) Receiving Substrate On the other hand, in the receiving substrate 17, as shown in FIG. 5, the output signals SDA (SDB to SDF) of the demultiplexing circuit 11 are outputted.
Is band-limited and applied to the video demodulator 30, where the video signal SV is demodulated and output. Further, the reception board 17 outputs the output signal SDA (SDB to SDF) of the demultiplexing circuit 11 via the bandpass filter circuit (BPF) 31 to the amplification circuit 3
2 and amplifies and outputs to the mixer 33.

The mixer 33 converts the output signal SDA (SDB to SDF) into the low frequency band by multiplying the output signal of the amplifier circuit 32 and the local oscillation signal of the local oscillation circuit 34, and then the band pass filter 35 is applied. Output through. Further, the receiving board 17 outputs the output signal of the band pass filter 35 to the mixers 36 and 37, where it is multiplied with the local oscillation signals of the local oscillation circuits 38 and 39, respectively, and converted into an intermediate frequency signal. , Bandpass Filter 4
Output via 0 and 41.

Thus, the receiving board 17 can demodulate the audio signal by demodulating the output signals of the band pass filters 40 and 41 by the wave detectors 42 and 43. At this time, the local oscillator circuits 38 and 39
Is formed so as to switch the oscillation frequency based on the control data output from the system control circuit 18, whereby a local oscillation signal having a frequency corresponding to each of the slots 12A to 12D is generated.

As a result, in the optical space transmission device 1,
Even when the receiving board 17 is housed in place of the transmitting board 16, the audio signal and the video signal can be demodulated for the channels assigned to the slots 12A to 12D, whereby the transmitting and receiving channels can be set easily and surely. It is designed to get you. By the way, the intercom circuit 14 is designed to be capable of inputting and outputting a voice signal of an operator, a relay manager, etc. to and from a transmission target via a microphone jack and an ear on jack provided on the housing operation surface. This voice signal is transmitted and received as a signal to and from the transmission target. The income circuit 14 is formed so that the reception frequency and the transmission frequency can be switched similarly to the transmission board 16 and the reception board 17, so that the income circuit 14 corresponds to the boards housed in the first to fourth slots 12A to 12D. The system control circuit 18 can set a transmission / reception channel.

(5) Frequency allocation In setting the transmission / reception frequency of the transmission board 16, the reception board 17, and the intercom circuit 14 to the frequency assigned to each of the slots 12A to 12D in this way, in the optical space transmission device 1, The center frequency of the bandpass filters 40 and 41 is selected to a frequency of 10.7 [MHz], and the oscillation frequencies of the local oscillator circuits 38 and 39 are selected so as to correspond to this. Similarly, in the optical free space transmission apparatus 1, the intermediate frequency of the intercom circuit 14 is selected to be 10.7 [MHz].

In this state, the optical free space transmission apparatus 1 sets the frequencies of the audio channels CA1 to CH12 and the income channels CHA to CHF as shown in FIG. 6, so that the frequency band twice the frequency of 10.7 [MHz] is set.
Within 21.4 [MHz], audio channels CA1 to CH1
2 and the frequencies of the income channels CHA to CHF are set to effectively avoid deterioration of transmission quality due to image interference.

Further, the optical free space transmission apparatus 1 uses the band pass filter 40 to mix the adjoining channels within a practically sufficient range.
And 41, as can be prevented by audio channel C
A1 to CH12 and income channel CHA to CHF
Among them, audio channels CA1 to CH1 are arranged so that adjacent channels are separated by a frequency of 600 [kHz] or more.
2 and the frequencies of the income channels CHA to CHF are set.

Further, as shown in FIG. 7, the optical space transmission device 1
In order to effectively avoid the deterioration of transmission quality due to second-order distortion and third-order distortion, audio channels CA1 to CH1
2 and the income channels CHA to CHF, the sum frequency of the frequency interval DF1 having the narrowest carrier frequency interval between adjacent channels and the frequency interval DF2 having the narrowest carrier frequency interval between adjacent channels is the carrier between adjacent channels. Widest frequency spacing DFn-
To be larger than 1, Audio Channel CA1
~ CH12 and the income channels CHA to CHF are set.

That is, if this relationship is expressed by an equation,

[Equation 1] , And as shown in FIG. 8, frequency intervals DF1, DF1, ..., DFn-2, DF between successive channels.
It can be seen that, with the same value of the frequency difference DF of n−1, mixing of other channels of the signal component caused by the third-order distortion can be prevented. Here, by transforming the equation (1), the following equation is obtained.

[Equation 2] And replace this inequality sign with an equal sign and set it as DF1L.

[Equation 3] The relational expression of can be obtained.

On the other hand, the frequency intervals DF1, DF1,
The sum of DFn-2 and DFn-1 needs to be smaller than the used bandwidth BW.

[Equation 4] Can be obtained, where DF is replaced by DF
Substituting 1L and rearranging, the following formula

[Equation 5] The relational expression of can be obtained.

By substituting the relationships of the expressions (2) and (4) into the expression (5) and rearranging, the following expression is obtained.

[Equation 6] It is possible to obtain the relational expression of, and after selecting Df, the value of DF1 is selected so as to satisfy the expressions (2) and (5), and the mutual interference due to the third-order distortion is effectively avoided. You know you will get.

By the way, audio channels C1 to C
By selecting the frequencies of the H12 and the income channels CHA to CHF in this way, mutual interference between the channels due to second-order distortion can be effectively avoided. Further, in the mutual interference between the channels due to the distortion of the fourth or higher order, its influence on the transmission quality is extremely small and can be practically ignored.

In other words, in this embodiment, the optical space transmission apparatus 1 has an audio channel and an income channel in which the channel number n is 18 channels.
Use bandwidth BW of 20 [MHz], frequency 605 to 625 [MH
z] and select from equation (5)

[Equation 7] The frequency difference Df can be obtained, and the frequency difference Df is selected to 50 [kHz].

Further, by substituting the difference Df of the frequency intervals into the expressions (2) and (5), the following expression can be obtained for the narrowest frequency interval DF1.

[Equation 8]

[Equation 9] Can be obtained, and the narrowest frequency interval DF1 is selected as the frequency 760 [kHz]. If this frequency is selected, the adjacent channels will be
[KHz] or more can be spaced apart.

(6) Effects of the Embodiments According to the above configuration, the sum frequency of the frequency interval DF1 having the smallest carrier frequency interval between the adjacent channels and the frequency interval DF2 having the smallest carrier frequency interval is obtained. By setting the frequencies of the audio channels CA1 to CH12 and the income channels CHA to CHF such that the carrier frequency interval between adjacent channels is larger than the widest frequency interval DFn-1.
Mutual interference between channels due to second-order distortion and third-order distortion can be effectively avoided, whereby deterioration of transmission quality can be effectively avoided, and audio signals of a plurality of channels can be frequency-multiplexed and transmitted.

(7) Other Embodiments In the above embodiments, the case where the frequency modulation signal is directly generated has been described, but the present invention is not limited to this.
It can be widely applied to the case where the intermediate frequency signal is once generated to generate the frequency modulation signal.

Further, in the above-mentioned embodiment, the case where the channels are set for the four slots and the income circuit has been described, but the present invention is not limited to this, and various channel numbers can be selected as necessary. The intercom circuit may be omitted.

Further, in the above embodiment, the case of transmitting the video signal and the audio signal has been described.
The present invention is not limited to this, and can be widely applied to an optical space transmission device that transmits various information signals.

[0060]

As described above, according to the present invention, the sum frequency of the frequency interval in which the carrier frequency is the narrowest between adjacent channels and the frequency interval in which the carrier frequency is next narrow is the adjacent frequency. So that the carrier frequency spacing is greater than the widest frequency spacing,
By setting the carrier frequency of the modulation signal, mutual interference between channels due to second-order distortion and third-order distortion can be effectively avoided, thereby effectively avoiding deterioration of transmission quality and transmitting information signals of multiple channels. An optical space transmission device capable of frequency-multiplexing and transmitting can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an optical free space transmission apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the connection of the slots.

FIG. 3 is a schematic diagram for explaining channel assignment.

FIG. 4 is a block diagram showing a transmission board.

FIG. 5 is a block diagram showing a receiving board.

FIG. 6 is a chart showing frequency allocation.

FIG. 7 is a schematic diagram used for the description.

FIG. 8 is a schematic diagram for explaining a difference in frequency interval.

[Explanation of symbols]

1, 1B ... Optical space transmission device, 3 ... Laser diode, 4, 5, 6, 7, 8 ... Lens, 12A-12D ...
... slot, 11 ... demultiplexing circuit, 13 ... multiplexing circuit, 14
...... Incom circuit, 16 ...... Transmission board, 17 ...... Reception board, 18 ...... System control circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04J 1/04 8949-5K

Claims (2)

[Claims] 1. An information signal of a plurality of channels is modulated at a predetermined carrier frequency to generate a plurality of modulated signals corresponding to the plurality of channels, and then the plurality of modulated signals are frequency-multiplexed to form a frequency-multiplexed signal. A frequency multiplexing circuit for generating, a laser diode for generating a transmission light beam modulated by the frequency multiplexing signal, and a transmission optical system for transmitting the transmission light beam emitted from the laser diode to a transmission target, The frequency multiplexing circuit sets the carrier frequencies so that the intervals of the adjacent carrier frequencies become non-uniform, and the interval of the first carrier frequency having the smallest interval between the adjacent carrier frequencies and the interval of the adjacent carrier frequencies. The carrier frequency interval is the narrowest following the first carrier frequency interval and the second carrier frequency interval. Added value of, so that the distance between adjacent said carrier frequency is greater than the spacing of the widest third carrier frequency, the optical space transmission apparatus characterized by setting the above carrier frequency. 2. The optical space transmission device has a plurality of slots for accommodating transmission boards, respectively, and the frequency multiplexing circuit is a transmission board accommodated in the slots and corresponds to the slot accommodating the transmission boards. The optical space transmission device according to claim 1, wherein the modulated signal having a carrier frequency set in advance is generated.