JPH06237221A - Optical receiver for optical catv - Google Patents

Abstract

PURPOSE:To output a backup signal at the time when a demodulating signal does not reach a prescribed level by switching to a main signal and a backup signal in accordance with a demodulating signal level by an output of an amplifier. CONSTITUTION:In the case an optical signal is not inputted, a signal is not outputted either from a photodiode 9, therefore, a voltage level after passing through a detector 21 becomes an L level. Accordingly, a comparator 17 detects abnormality, transistor 18 is turned on, and a relay 11 is energized. As a result, from the signal output 15, a backup signal inputted from a coaxial signal input 19 is outputted. In the case there is no input to an optical transmitter 6 due to a fact that an input cable is detached, etc., although a optical signal is inputted, and even in the case of a fault of a high frequency signal amplifier 14, a voltage level of an output of the detector becomes L, and finally, the relay 11 is energized and the backup signal is outputted automatically from the output 15. In such a way, a stagnant wave caused by a fault, etc., can also be backed up as a system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical CATV receiver of an optical fiber backbone system, among devices for transmitting images using an optical fiber.

[0002]

2. Description of the Related Art In recent years, along with the expansion of CATV networks, there has been a demand for system reliability and high quality transmission lines. For this reason, high-quality optical CATV has attracted attention even in long-distance transmission. Under such circumstances, in order to further improve system reliability, an optical fiber backbone system is considered in which when the optical signal stops, another backup coaxial signal is placed and automatically switched to it.

FIG. 3 shows an example of this system. The signal sent from the head end 2 of the CATV center 1 is distributed to the home 3 near the center via the coaxial transmission line 4. On the other hand, to the home 5 at a long distance from the center, the light is normally sent by the optical transmitter 6 and sent to the optical receiver 8 by the optical fiber 7. Here, it is demodulated into an electric signal by the photodiode 9 and distributed using the coaxial transmission line 10.
When the optical transmitter 6 fails or the optical fiber 7 is broken, the optical receiver 8 detects the down of the signal and automatically switches the relay 11 to the coaxial transmission line side so that the subsequent signals of the optical receiver 8 are detected. It is designed to prevent the wave from stopping. This system not only improves the reliability of the system by backing up, but also makes use of the high image quality transmission of the optical system to achieve S / S even when the signal is transmitted from the center to the home 5 at a long distance.
There is an advantage that N is not deteriorated.

The conventional optical receiver 8 is constructed as shown in FIG. The optical signal input from the optical input 12 is converted into an electric signal by the photodiode 9, and is amplified by the high frequency signal amplifier 14 via the capacitor 13,
It is output from the output 15 via the relay 11. When an optical signal is input, a current flows through the photodiode 9 and the potential at the one end P of the resistor 16 rises. If the potential Vs at one end P is equal to or higher than the set level Vo, the output of the comparator 17 becomes L level, the collector-emitter of the transistor 18 is in the off state, and the relay 11 is not excited. As described above, when the optical signal output from the signal output 15 through the relay 11 is not input as described above, no current flows in the photodiode 9, the output of the comparator is inverted to the H level, and The collector-emitter 18 is turned on, the relay 11 is excited, and the signal output 15 is switched to the signal input from the coaxial signal input 19. In this way, even when the optical signal is stopped, the coaxial signal is automatically switched to prevent the wave from stopping.

[0005]

SUMMARY OF THE INVENTION With such a configuration,
The criterion for switching to the backup signal is that the light receiving current of the photodiode 9 is monitored, and when it falls below a certain level, a transmission error is detected and the relay 11 switches to the backup signal. It is effective when the light emitting element 6 is damaged or the optical fiber 7 is broken, but when the high frequency signal amplifier 14 of the electric signal is damaged or the optical transmitter 6 is normal, the input to the optical transmitter 6 When there is no input due to the cable being disconnected, etc., the backup was not possible due to the switching by the relay 11 and the wave was stopped, although the signal actually needed was lost.

It is an object of the present invention to provide an optical CATV optical receiver capable of switching to a backup signal even when the input cable to the optical transmitter 6 is disconnected or the high frequency signal amplifier 14 is damaged. .

[0007]

An optical CAT according to claim 1
The optical receiver for V receives the video signal output from the optical transmitter through an optical fiber, converts it into an electric signal, and further selects a main signal amplified by an amplifier and a backup signal by a switching circuit. In the optical CATV optical receiver for output, a comparator for comparing the demodulated signal level at the output of the amplifier with a specified level is provided, and the switching circuit is switched by the output of the comparator to bring the demodulated signal level to the specified level. It is characterized in that the main signal is output in the reached state and the backup signal is output when the demodulated signal level does not reach the specified level.

An optical receiver for an optical CATV according to claim 2,
Optical receiving for optical CATV, in which a video signal output from an optical transmitter is received via an optical fiber, converted into an electrical signal, and a main signal amplified by an amplifier and a backup signal are selected by a switching circuit and output. A detector for detecting the presence or absence of a specific frequency component generated in the output of the amplifier, and the switching circuit is switched by the output of the detector to output a main signal when the specific frequency component is detected, It is characterized in that the backup signal is output without detecting the frequency component.

[0009]

According to the structure of the present invention, the switching circuit is switched in accordance with the demodulated signal level at the output of the amplifier to switch between the main signal and the backup signal. Even if there is, the wave of the video signal can be prevented.

According to the second aspect of the invention, the switching circuit is switched to switch between the main signal and the backup signal depending on the presence or absence of the specific frequency component generated in the output of the amplifier, so that an abnormality occurs in the amplifier and the stage preceding the amplifier. Even in such a case, the wave stop of the video signal can be prevented.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Each embodiment of the present invention will be described below with reference to FIGS. It should be noted that components having the same operations as those of the conventional example shown in FIGS.

FIG. 1 shows a first embodiment. The optical signal input from the optical input 12 is converted into an electric signal by the photodiode 9, amplified by the high frequency signal amplifier 14 via the capacitor 13, and output 1 via the relay 11.
It is output from 5. The output of the amplifier 14 is provided with a branching device, and the signal branched by the branching device 20 is converted into a DC voltage level by the detector 21. The converted voltage is applied to the comparator 17, and outputs L level when the signal level is normal. As a result,
The relay 11 is not excited. Therefore, the signal that is input from the optical input 12 and is amplified in a normal state is output from the signal output 15.

In an abnormal state, for example, when no optical signal is input, no signal is output from the photodiode 9, so the voltage level after passing through the detector 21 becomes L level. Therefore, the comparator 17 detects an abnormality, turns on the transistor 18, and excites the relay 11. As a result, the signal output 15 outputs the backup signal input from the coaxial signal input 19.

Although the optical signal is input, the voltage level of the output of the detector is also detected when the optical transmitter 6 loses its input due to disconnection of the input cable or when the high-frequency signal amplifier 14 fails. Becomes L, and finally the relay 11 is excited and a backup signal is automatically output from the signal output 15.

In the above-described first embodiment, the output signal of the amplifier 14 is detected by the detector 21, the signal level is judged by the comparator 17, and the relay 11 is switched.
It can also be realized by the configuration as in the second embodiment shown in FIG.

In the second embodiment, a detector 22 for detecting the presence or absence of a specific frequency component generated in the output of the amplifier 14 is provided, and the relay 11 is switched by the output of this detector 22. Specifically, the SAW filter 23 is interposed between the branching device 20 and the detector 21 of the first embodiment. If the optical signal input to the optical input 12 is an RF multiplex optical transmission system for CATV, an AM-modulated video signal carrier "73 MHz" and a pilot signal "451.25 MHz" are usually included. In the SAW filter 23, “451.25M” is output from the output signal of the amplifier 14.
The pilot signal of "Hz" is extracted, and the signal level Vs detected by the wave detector 21 and the set level Vo are compared by the comparator 1.
7, when the pilot signal which is the specific frequency component is included in the output signal of the amplifier 14, the signal of the optical fiber system is output from the signal output 15 via the relay 11, and the output of the amplifier 14 is output. When the signal does not include the pilot signal, the backup signal input to the coaxial signal input 19 is output from the signal output 15 via the relay 11.

Although the pilot signal is used as the specific frequency component in the second embodiment, it is also possible to extract and determine other specific frequency components. In each of the above embodiments, the high frequency switching relay 11 is used as the switching circuit for selecting the main signal and the backup signal, but other switching means may be adopted.

[0018]

According to the first aspect of the present invention, since the switching circuit is switched to switch between the main signal and the backup signal according to the demodulated signal level at the output of the amplifier, the optical element of the transceiver is broken or the fiber is broken. In addition to the case where the optical system is down, the system can be backed up not only when the electric signal is input to the optical transmitter or when the wave is stopped due to a failure of the signal amplification circuit in the receiver.

According to the second aspect of the invention, the switching circuit is switched depending on the presence or absence of the specific frequency component generated in the output of the amplifier to switch between the main signal and the backup signal, so that the optical element of the transmitter / receiver is destroyed and the fiber is disconnected. In addition to the case where the optical system goes down, the system can be backed up not only when the electric signal is input to the optical transmitter, but also when the wave is stopped due to a failure of the signal amplification circuit in the receiver.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of an optical receiver for an optical CATV of the present invention.

FIG. 2 is a configuration diagram of a second embodiment.

FIG. 3 is a configuration diagram of an optical fiber backbone system.

FIG. 4 is a configuration diagram of a conventional optical receiver for optical CATV.

[Explanation of symbols]

 6 Optical Transmitter 7 Optical Fiber 8 Optical Receiver 9 Photodiode 11 Relay [Switching Circuit] 12 Optical Input 14 High Frequency Signal Amplifier 15 Signal Output 17 Comparator 19 Coaxial Signal Input 20 Brancher 21 Detector 22 Detecting Section 23 SAW Filter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04B 10/02

Claims (2)

[Claims] 1. A video signal output from an optical transmitter is received via an optical fiber, converted into an electrical signal, and further, a main signal amplified by an amplifier and a backup signal are selected and output by a switching circuit. In the optical receiver for optical CATV, a comparator for comparing the demodulated signal level at the output of the amplifier with a specified level is provided, and the switching circuit is switched by the output of the comparator, and the demodulated signal level reaches the specified level. An optical receiver for an optical CATV that outputs a main signal in a state and outputs a backup signal when the demodulated signal level does not reach a specified level. 2. A video signal output from an optical transmitter is received through an optical fiber, converted into an electrical signal, and further, a main signal amplified by an amplifier and a backup signal are selected and output by a switching circuit. In the optical CATV optical receiver, a detection unit that detects the presence or absence of a specific frequency component generated in the output of the amplifier and the switching circuit are switched by the output of the detection unit, and the main signal is detected when the specific frequency component is detected. , An optical CATV optical receiver that outputs a backup signal without detecting a specific frequency component.