JP2560647B2 - Optical intermediate repeater - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical intermediate repeater,
For example, the present invention relates to an optical intermediate repeater used in an optical video communication system for transmitting a video signal and an audio signal.

[0002]

2. Description of the Related Art In the field of optical communication, transmission of a video signal having a large amount of data is sometimes performed by an analog transmission method because the occupied frequency bandwidth of the transmission path is small and the device configuration can be simplified. The analog transmission in optical communication is performed by changing the intensity of light according to the change in the amplitude of a signal to be transmitted. At that time, if the video signal is converted into the light intensity as it is, if the amplitude change of the signal is slow, the light intensity must be changed correspondingly. The condition of linearity becomes severe. Therefore, in the usual case, before converting a video signal into an optical signal, the video signal to be transmitted is modulated in advance so that the linearity condition required for the light emitting element is relaxed and then converted into the optical signal. The modulation method is adopted.

FIG. 3 shows an example of a pre-modulation method used in such optical communication. If the original signal of the transmitted video signal is a signal as shown in FIG. 3A, if this is converted into a change in the light intensity as it is, the light intensity must also be changed gently, and the linearity of the light emitting element is increased. Must be kept strict, which makes control difficult. On the other hand, FIG. 2B shows a signal that is frequency-modulated (FM) so that the frequency is proportional to the amplitude of the original signal. By performing the pre-modulation in this way, the linearity required for the light emitting element is relaxed. Further, FIG. 6C shows a signal which is pulse frequency modulated (PFM) so that the pulse repetition frequency is proportional to the amplitude of the original signal, and FIG. 7D is a frequency modulated signal using a square wave (SW). FM) signal. When the original signal is pre-modulated like the latter two, when converted into an optical signal, the light intensity is converted into a binary value of high level and low level. Therefore, the video signal can be transmitted with almost no influence of the non-linearity of the light emitting element.

The video signal thus premodulated and transmitted may include an audio signal. Before pre-modulating the video signal, a carrier having a frequency different from the frequency band occupied by the video signal is prepared, modulated with an audio signal, and the modulated wave is superposed on the video signal.
By pre-modulating a video signal containing such an audio signal and converting it into an optical signal, the audio signal can be transmitted simultaneously with the video signal.

In the optical video communication system for transmitting the video signal and the audio signal thus performed, the transmitted signal does not have an inherent timing frequency. Therefore, the optical intermediate repeater used is 2R without the timing extraction function.
A repeater is sufficient and the configuration is simple.

By the way, when a failure occurs at one point of such an optical video communication system and the optical input is interrupted at one of the optical intermediate repeaters, the same applies to the repeaters and receivers arranged downstream. Disability occurs. Despite the fact that the failure occurred at one point, it spilled over and the failure occurred at one point.
It is not possible to identify whether a failure has occurred at multiple points, which complicates the location of the failure point. Therefore, there is a possibility that the return to normal communication may be delayed. Therefore, in order to avoid such a situation, the optical intermediate repeater newly generates the pre-modulated carrier wave used for transmitting the video signal when the disconnection of the optical input is detected, and this is used for another downstream relay. It has a function to send to the receiver and receiver. This prevents the spread of obstacles and facilitates the location of obstacles.

FIG. 4 shows an example of the configuration of a conventional intermediate repeater. In this example, an intermediate repeater is shown in the case where optical communication is performed by a pre-modulation analog transmission method using SWFM, which transmits a square wave frequency-modulated video signal. The optical signal 11 input to the optical intermediate repeater is received by the light receiving element 12 and converted into an electric signal 13. The preamplifier 14 amplifies this electric signal 13, and the limiter amplifier 15 amplifies the output signal of the preamplifier 14 so that the amplitude becomes constant. The output signal 16 of the limiter amplifier is branched into three.

The first branch signal 16 ₁ passes through a band pass filter 17 and a SWFM carrier 18 which is a premodulation carrier is extracted. The detector 19 detects the strength of the extracted SWFM carrier 18 and outputs a potential 20 according to the strength. This potential 20 is 1 of the comparison input terminal of the comparator 21.
One of the reference potentials is input to another comparison input terminal via the variable resistor 22 and compared with a predetermined reference potential. Relay 24
Drives the contact 25 in accordance with the output signal 23 of the comparator 21.

The second branch signal 16 ₂ can be input to the laser drive circuit 26 via the contact 25. The laser driving circuit 26 is connected to the laser diode module 27 and converts an input signal into an optical signal 28. The voice carrier generation circuit 29 also generates a voice carrier 30 that carries a voice signal. The SWFM modulator 31 SWFM-modulates the input voice carrier 30 and outputs it. The SWFM modulated wave 32 output from the SWFM modulator 31 can be input to the laser drive circuit 26 when the contact 25 is closed to the side b.

The third branch signal 16 ₃ is input to the monostable multivibrator (monomulti) 33. The monostable multivibrator 33 converts the input branch signal 16 ₃ into a signal 34 having a constant pulse width. The low pass filter 35 cuts high frequency components from the signal 34 and extracts a baseband signal 36. The baseband signal 36 is input to the video amplifier 37. A video signal is output from the output terminal 38 of the video amplifier 37.

In the optical intermediate repeater having such a structure, first,
The operation of the optical intermediate repeater when the optical signal is normally input will be described. An optical signal 11 sent from a transmitter or a repeater (not shown) upstream of the intermediate repeater is converted into an electric signal 13 by the light receiving element 12. The converted electric signal 13 is amplified by the preamplifier 14 and further amplified by the limiter amplifier 15 so that the amplitude becomes constant. As a result, the waveform-shaped signal 16 is output.

S extracted from the first branch signal 16 ₁ of the waveform-shaped signal by the bandpass filter 17
The intensity of the WFM carrier 18 is detected by the detector 18, and the potential 20 corresponding to the intensity is output. When the optical signal is normally input, the potential 20 is higher than the reference potential. Therefore, the comparator 21 outputs a high level signal to the relay 24. As a result, the relay 24 closes the contact 25 to the side a shown in the figure. As a result, the signal 16 waveform-shaped by the limiter amplifier 15 is input to the laser diode drive circuit 25, converted into an optical signal 28 by the laser diode of the laser diode module 26, and transmitted.

Next, the operation of the optical intermediate repeater when the optical input is disconnected will be described. When the light input is cut off, the potential 20 according to the intensity of the SWFM carrier detected by the detector 19 becomes smaller than the reference potential. As a result, the output signal 23 of the comparator 21 becomes low level, and the relay 24 switches the contact 25 to the b side shown in the figure. The SWFM modulator and the voice carrier generator connected to the terminal on the b side constantly generate the SWFM carrier and the voice carrier, and the SWFM modulated wave 32 modulated by the voice carrier 30 is passed through the contact 25 to the laser drive circuit. 26 is input. Then, it is converted into an optical signal 28 and sent to an optical intermediate repeater or an optical receiver (not shown) downstream.

As described above, even when the input optical signal 11 is disconnected, the SWFM carrier and the voice carrier are sent to an optical receiver (not shown) located downstream. As a result, the stable operation of the receiver, which was operating until the optical input was cut off, is maintained, and it is shown that the optical intermediate repeater is operating normally and the location of the input cutoff source can be located. Also, this SW
Since the FM modulated wave is modulated by the voice carrier, noise is prevented from occurring in the voice processing circuit arranged in the subsequent stage due to the interruption of the voice carrier.

[0015]

In the optical intermediate repeater having such a structure, the pre-modulation carrier generator and the voice carrier generator such as the SWFM modulator are always operated in preparation for the interruption of the input of the optical signal. . However, depending on the usage of the optical video communication system, only video may be transmitted and audio may not be transmitted. In such a case, in the configuration of the conventional optical intermediate repeater, the voice carrier generator operates regardless of whether or not the voice signal is transmitted, and power consumption is wasted.

Of course, if a voice signal is not transmitted, it is possible to construct a line by using an optical intermediate repeater that does not handle voice. However, if a voice signal is transmitted later,
Not only the exchange of terminal stations such as optical transmitters and optical receivers but also the exchange of many optical intermediate repeaters in the transmission line must be exchanged, and the versatility of the line is lacking.

Therefore, an object of the present invention is to provide an optical intermediate repeater capable of supporting both optical video communication systems in the case where a video signal to be transmitted includes an audio signal and not including the audio signal, and reducing power consumption. Is to provide.

[0018]

According to a first aspect of the present invention, (a) an opto-electric conversion means for converting an optical signal into an electric signal, and (b) an electric signal output from the opto-electric conversion means is an optical signal. And (d) a video carrier extracting means for extracting a video carrier carrying a video signal from the electric signal output from the opto-electric converting means, and (d) a video carrier extracting means. Video carrier level detecting means for detecting the level of the video carrier, (e) audio carrier generating means for generating an audio carrier to be superimposed on the video signal, and (f) modulation by an audio carrier output from the audio carrier generating means. When the level of the image carrier detected by the (g) image carrier level detecting means for generating the image carrier and (g) image carrier level detecting means is smaller than a predetermined value Switching means for inputting the video carrier wave output from the video carrier wave generating means to the electro-optical converting means in place of the converted electric signal, and (h) an audio signal is carried from the electric signal output from the opto-electric converting means. An audio carrier wave extracting means for extracting an audio carrier wave, (i) an audio carrier wave level detecting means for detecting the level of the audio carrier wave extracted by the audio carrier wave extracting means, and (e) an audio carrier wave detected by the audio carrier wave level detecting means. Power supply blocking means for blocking the supply of power to the voice carrier generation means when the level of is less than a predetermined value, and (l) the level of the voice carrier detected by the voice carrier level detecting means is greater than a predetermined value. Power supply control means for prohibiting the operation of the power supply blocking means to continue the supply of power to the voice carrier generation means when Thereby and means to light intermediate repeaters.

That is, according to the first aspect of the invention, the strength of the voice carrier that carries the voice signal is detected by the voice carrier level detecting means. When this intensity is lower than a predetermined level, the power supply blocking means does not supply power to the voice carrier generation means. Only when it is detected that the strength of the voice carrier is higher than a predetermined level, the power of the voice carrier generating means is supplied. Therefore, when the audio signal is not included, the power consumption of the optical intermediate repeater is reduced.

According to a second aspect of the invention, (a) an opto-electric conversion means for converting an optical signal into an electric signal, and (b) an electro-optic conversion for converting an electric signal output from the opto-electric conversion means into an optical signal. Means, (c) a video carrier wave extracting means for extracting a video carrier wave carrying the video signal from the electric signal outputted from the photoelectric conversion means, and (d) detecting the level of the video carrier wave extracted by the video carrier wave extracting means. Video carrier level detection means, (e) audio carrier generation means for generating an audio carrier to be superimposed on the video signal, and (f) video for generating a video carrier modulated by the audio carrier output from the audio carrier generation means. Carrier wave generating means,
(G) When the level of the image carrier detected by the image carrier level detecting means is smaller than a predetermined level, the image carrier generated by the image carrier generating means is replaced with the electrical signal converted by the photoelectric conversion means. Switching means for inputting to the optical conversion means, and (h) power supply means for supplying power to the video carrier generation means when the level of the video carrier detected by the video carrier level detection means is smaller than a predetermined value, (B) audio carrier extraction means for extracting an audio carrier that carries an audio signal from the electrical signal output from the opto-electric conversion means, and (n) an audio carrier level for detecting the level of the audio carrier extracted by the audio carrier extraction means. If the level of the sound carrier detected by the detecting means and (le) sound carrier level detecting means is smaller than a predetermined value. Power supply blocking means for blocking power supply to the voice carrier generation means, and (2) power supply means when the level of the voice carrier detected by the voice carrier level detection means is larger than a predetermined value. The optical intermediate repeater is provided with a power supply control means for prohibiting the operation of the power supply blocking means and continuing the power supply to the audio carrier generation means when the power is supplied to the video carrier generation means.

That is, according to the second aspect of the present invention, the strengths of the video carrier and the audio carrier are detected by the video carrier level detecting means and the audio carrier level detecting means, respectively. When the sound carrier level detecting means detects the sound carrier at a predetermined level, and the picture carrier level detecting means detects that the level of the picture carrier is smaller than the predetermined level, the power supplying means and the power supply are provided for the first time. The control means supplies power to the video carrier generation means and the audio carrier generation means, respectively. Therefore, power is not supplied to the video carrier generation means and the audio carrier generation means when the optical signal is normally input, and power consumption is reduced. On the other hand, no audio signal is being transmitted,
The power supply blocking means does not supply power to the voice carrier generation means as long as the voice carrier is detected to be smaller than the predetermined level by the voice carrier level detection means. Therefore, when the audio signal is not included in the signals to be transmitted, the electric power is not supplied to the audio carrier wave generation means regardless of whether or not the optical input is interrupted, so that the power consumption is further reduced.

According to the third aspect of the present invention, the inhibition of the operation performed by the power supply control means on the power supply blocking means is initialized by the initialization means after the power is turned on. That is,
By turning the power on again, it is possible to return to the initial state in which the power supply to the audio carrier generation means is blocked. Therefore,
It is possible to change the line that was transmitting the voice signal to the line that does not transmit the voice signal while reducing the power consumption, thus increasing the versatility of the line.

According to the fourth aspect of the invention, the power supply blocking means and the power supply control means are collectively controlled by a holding type relay. As a result, the power supplied to the sound carrier generation means can be controlled, and the power consumption can be reduced.

According to the fifth aspect of the invention, the control of the power supply means for supplying the power to the image carrier generation means is performed by the relay together with the switching means. Therefore, power consumption can be reduced.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows in principle the structure of an optical intermediate repeater according to an embodiment of the present invention. The optical intermediate repeater of the present embodiment is one in the case where optical communication is performed by the pre-modulation analog transmission system by SWFM. An optical signal 11 input to the optical intermediate repeater is received by a light receiving element 12 such as an avalanche photodiode,
It is converted into an electric signal 13. The preamplifier 14 amplifies this electric signal 13, and the limiter amplifier 15
Is for amplifying the output signal of the preamplifier 14 so that the amplitude is constant. The output signal 16 of the limiter amplifier is branched into three.

The band pass filter 17 is a limiter amplifier 1
The SWFM carrier 18, which is a premodulation carrier, is extracted from the output signal 16 of No. 5. The detector 19 is the extracted SWF
The strength of the M carrier 18 is detected, and the potential 20 corresponding to the strength is detected.
Is output. This potential 20 is input to one of the comparison input terminals of the comparator 21. A predetermined reference potential is input to the other comparison input terminal of the comparator 21 via the variable resistor 22. The comparator 21 compares the potentials of the two,
When the output potential 20 of the detector 19 is higher than the reference potential, a high level signal 23 is output, and when it is low, a low level signal 23 is output. The relay 24 is the comparator 21.
The contact point 25 and the contact point 43 are driven according to the output signal 23. When the contact 25 is connected to the side a shown in the figure,
The contact 43 is opened, and when the contact 25 is connected to the side b, the contact 43 is closed.

The output signal 16 of the limiter amplifier or the SWF is connected to the laser drive circuit 26 depending on the connection state of the contact 25.
The output 32 of the M modulator 31 is input.
The laser drive circuit 26 oscillates the laser diode in the laser diode module 27 according to the input signal, and sends the optical signal 28 to a downstream receiver (not shown). The voice carrier generation circuit 29 also generates a voice carrier 30 that carries a voice signal. The SWFM modulator 31 SWFM-modulates the input voice carrier 30 and outputs it.

The monostable multivibrator (monomulti) 33 has an input signal 1 with a duty ratio of 50%.
6 is converted into a signal 34 having a constant pulse width. A DC component appears in the signal 34 due to the change of the duty ratio. This signal 34 is input to a low-pass filter 35 and a voice carrier extraction circuit 41 for extracting a voice carrier. The low pass filter 35 cuts high frequency components from the signal 34 and extracts a baseband signal 36. The baseband signal 36 is input to the video amplifier 37. A video signal is output from the output terminal 38 of the video amplifier 37. Mainly for maintenance of the optical intermediate repeater,
The video signal can be monitored.

FIG. 2 specifically shows the voice carrier extraction circuit of this embodiment. In the voice carrier extraction circuit 41, the band pass filter 44 outputs the voice carrier 4 from the output signal 34 of the monostable multivibrator 33.
5 are extracted. The detector 46 detects the intensity of the extracted voice carrier 45 and outputs a potential 47 according to the intensity. The potential 47 is input to one input terminal of the comparator 48. A predetermined reference potential is input to the other input terminal of the comparator 48 via the variable resistor 49. The comparator 48 compares the output potential 47 of the detector 46 with the reference potential. Output 50 of comparator 48
Is input to the holding type relay 51. Holding type relay 51
Controls the contact 42 connected to the power supply terminal to the voice carrier generator. Contact 4 as the initial state
2 is in the open state, and the holding relay 51 closes the contact 42 by the signal output from the comparator 48 when the voice carrier is detected higher than the reference potential. After that, the state is maintained regardless of whether or not the voice carrier is detected.
The power-on reset circuit 52 outputs a signal 53 for returning the holding type relay 51 to the initial state, that is, the state where the contact 42 is opened, to the holding type relay 51 when the power is turned on after the installation of the intermediate relay. Is.

In the optical intermediate repeater having such a configuration, first,
The operation when this optical intermediate repeater is installed in the optical communication system in which the video signal and the audio signal are simultaneously transmitted from the upstream communication device will be described.

When the power of the intermediate repeater is turned on after the optical intermediate repeater is installed, the power-on reset circuit 52 operates in the voice carrier extraction circuit 41 to initialize the holding type relay 51. Is output. This signal 53
In response, the holding type relay 51 opens the contact 42. After that, when communication is started, the voice carrier extraction circuit 41 determines whether or not a voice carrier is detected. Audio carrier 4 extracted by bandpass filter 44
When 5 is detected with a constant intensity corresponding to the reference potential, the output signal 50 of the comparator 48 changes from low level to high level. As a result, the holding type relay 51 closes the contact 42, and then the state of the contact 42 is maintained unless the signal 53 for initialization is received from the power-on reset circuit 52.

On the other hand, the SWFM carrier detector 19 determines whether or not the SWFM carrier is detected. When the voltage is normally detected and is higher than the intensity corresponding to the reference voltage, a high level signal is output from the comparator 21, and the relay 24
Closes contact 25 to side a. Therefore, the signal 16 output from the limiter amplifier is converted into an optical signal and emitted from the laser diode module 27 via the laser drive circuit. At the same time, the relay 24 has a contact 43
open. Therefore, the voice carrier generation circuit 29 connected to the SWFM modulator 31 via the closed contact 42.
The power supply to and is cut off.

The operation of the optical intermediate repeater when the optical signal input to the optical intermediate repeater is disconnected in this state will be described. When the optical signal is disconnected, the SWFM carrier is no longer extracted, and the output 23 of the comparator 21 changes from high level to low level. The relay 24 receiving the low-level signal connects the contact 25 to the side b, and at the same time, closes the contact 43. On the other hand, the contact 42 is held in a closed state by the holding type relay 51. That is, the relay 51 does not open the contact 42 even though the voice carrier is no longer extracted due to the interruption of the optical input. As a result, power is supplied to the SWFM modulator 31 and the voice carrier generator 29. Since the contact 42 does not open, the operation of blocking the power supply to the voice carrier generator 29 is prohibited, and thereafter, the power supply to only the voice carrier generator 29 is not blocked. Therefore, the voice carrier 30 generated by the voice carrier generation circuit 29 is SWFM modulated by the SWFM modulator 31, and this SWFM modulated wave 32 is generated.
Input to the laser diode drive circuit 26 via the contact 25. The laser diode drive circuit 26 converts the SWFM modulated wave 32 into an optical signal 28 and sends it out. In this way, when the optical signal is cut off, the SWFM is connected to the downstream device.
The carrier and voice carrier are output.

Next, the operation of the optical intermediate repeater when the optical intermediate repeater is installed in the optical communication system in which only the video signal is transmitted from the upstream communication device will be described.

In this case, since the voice carrier has not been transmitted, the output 50 of the comparator 48 in the voice carrier extraction circuit 41 remains at the low level. The holding relay 51 that receives a low-level signal does not operate while being initialized by the power-on reset circuit 51 when the power is turned on, and does not close the contact 42. At this time, if the optical input is cut off, the SWFM carrier is not detected by the detector 19, and the contact 43 is closed by the relay 24. But,
Since the contact 42 remains open, the power supply to the voice carrier generator 29 is blocked and only the SWFM modulator 31 is supplied with power. Therefore, SW is installed in the downstream device.
Only the SWFM carrier output from the FM modulator 31 is converted into an optical signal and output.

When no voice signal is transmitted from the upstream communication device, the optical intermediate repeater does not always supply power to the voice carrier generator 29 regardless of whether or not the optical input is interrupted. Can be reduced. Also, SWFM
Since the power supply to the modulator 31 is performed only when the input of the optical signal is interrupted, the power consumption can be further reduced.

In the embodiment described above, the SWFM pre-modulation method is used as the pre-modulation method, but the PFM pre-modulation method may be used. In this case, the SWFM modulator 31
Serves as a PFM modulator and generates a pulse modulated by the voice carrier 30 output from the voice carrier generation circuit 29.

[0039]

According to the first aspect of the present invention, when used in an optical video communication system in which an audio signal is not transmitted from an upstream transmitter, an audio carrier wave generation circuit is provided before and after disconnection of an optical input. Power is not supplied to the. Therefore, the power consumption of the optical intermediate repeater is reduced, and an unnecessary voice carrier for signal processing is not sent to the repeater or receiver in the subsequent stage.

According to the second aspect of the present invention, when the optical signal is normally input, the power is not supplied to the circuit for generating the video carrier and the audio carrier, so that the power consumption of the optical intermediate repeater can be reduced. . Moreover, when the voice signal is not transmitted from the upstream transmitter, the power is not always supplied to the voice carrier generator regardless of the interruption of the optical input, so that the power consumption is further reduced.

According to the third aspect of the invention, the optical intermediate repeater is initialized by turning on the power again. Therefore, even when the line provided with the optical intermediate repeater is used in an optical video communication system that transmits an audio signal and then used in an optical video communication system that does not transmit an audio signal, And it can be driven in a state of low power consumption as described in claim 2. That is, the power consumption can be reduced while the versatility of the line in which the optical intermediate repeater is laid is improved against the change of the optical video communication system.

Further, according to the invention described in claim 4, since the control for supplying the electric power to the sound carrier generating means is performed by the holding type relay, the electric power can be controlled with a simple structure.

According to the invention described in claim 5, since the switching means and the video carrier generation means are controlled by one relay, the switching operation can be performed reliably and the arrangement of parts can be improved. You can save space.

[Brief description of drawings]

FIG. 1 is a block diagram showing in principle the configuration of an optical intermediate repeater in an embodiment of the present invention.

FIG. 2 is a circuit diagram specifically showing a voice carrier extraction circuit according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a state of pre-modulation.

FIG. 4 is a block diagram showing a configuration of a conventional optical intermediate repeater.

[Explanation of symbols]

12 light receiving element 14 preamplifier 15 limiter amplifier 17, 44 bandpass filter 19, 46 detector 21, 48 comparator 24 relay 25, 42, 43 contacts 26 laser diode (LD) drive circuit 27 laser diode module 29 voice carrier generator 31 SWFM modulator 33 Monostable multivibrator (monomulti) 35 Low-pass filter 37 Video amplifier 51 Holding type relay 52 Power-on reset circuit

Claims (5)

(57) [Claims] 1. An opto-electrical conversion means for converting an optical signal into an electric signal, an electro-optical conversion means for converting an electric signal output from the opto-electrical conversion means into an optical signal, and an opto-electrical conversion means. Video carrier extracting means for extracting a video carrier carrying the video signal from the electric signal, video carrier level detecting means for detecting the level of the video carrier extracted by the video carrier extracting means, and an audio carrier superimposed on the video signal And a video carrier generation unit for generating a video carrier modulated by the sound carrier output from the sound carrier generation unit, and a level of the video carrier detected by the video carrier level detection unit. When it is smaller than a predetermined value, the image carrier wave is generated instead of the electric signal converted by the photoelectric conversion means. Switching means for inputting the video carrier output from the means to the electro-optical converting means, audio carrier extracting means for extracting an audio carrier carrying an audio signal from the electrical signal output from the opto-electric converting means, Audio carrier level detecting means for detecting the level of the audio carrier extracted by the carrier extracting means, and power to the audio carrier generating means when the level of the audio carrier detected by the audio carrier level detecting means is smaller than a predetermined value. Power supply blocking means for blocking the supply of the voice signal, and when the level of the voice carrier detected by the voice carrier level detecting means is detected to be larger than a predetermined value, the operation of the power source blocking means is prohibited and the voice And an electric power supply control means for continuing the supply of electric power to the carrier wave generation means. Repeater. 2. An opto-electrical conversion means for converting an optical signal into an electric signal, an electro-optical conversion means for converting an electric signal output from the opto-electrical conversion means into an optical signal, and an opto-electrical conversion means. Video carrier extracting means for extracting a video carrier carrying the video signal from the electric signal, video carrier level detecting means for detecting the level of the video carrier extracted by the video carrier extracting means, and an audio carrier superimposed on the video signal And a video carrier generation unit for generating a video carrier modulated by the sound carrier output from the sound carrier generation unit, and a level of the video carrier detected by the video carrier level detection unit. When it is lower than a predetermined level, the video carrier is replaced with the electric signal converted by the photoelectric conversion means. Switching means for inputting the video carrier wave output from the generating means to the electro-optical converting means; and to the video carrier wave generating means when the level of the video carrier wave detected by the video carrier level detecting means is smaller than a predetermined value. Power supply means for supplying power, audio carrier extraction means for extracting an audio carrier that carries an audio signal from the electrical signal output from the photoelectric conversion means, and level of the audio carrier extracted by the audio carrier extraction means A voice carrier level detecting means for detecting the power supply, and a power supply blocking means for blocking power supply to the voice carrier generating means when the level of the voice carrier detected by the voice carrier level detecting means is smaller than a predetermined value, The level of the voice carrier detected by the voice carrier level detecting means is larger than a predetermined value. When the power supply means supplies power to the video carrier generation means when it is detected, a power supply for prohibiting the operation of the power supply blocking means and continuing supply of power to the audio carrier generation means An optical intermediate repeater comprising: a control unit. 3. The method according to claim 1, further comprising an initialization unit that initializes prohibition of an operation performed by the power supply control unit with respect to the power supply blocking unit when the power is turned on. Optical intermediate repeater. 4. The power supply blocking means and the power supply control means are holding-type relays, which are excited when the level of the voice carrier detected by the voice carrier level detecting means exceeds a predetermined value. The contact is connected to maintain this state.
The optical intermediate repeater described in 3. 5. The switching of the signal input to the electro-optical conversion means performed by the switching means and the switching of the power supply on / off performed by the power supply means are performed by one.
5. The optical intermediate repeater according to claim 2, wherein the relays are simultaneously operated by using different contacts of the two relays.