JPS6011132A - Detector for optical fiber line - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical fiber line detection device used for optical loop transmission in which multiple information such as still images, facsimile, voice, data signals, etc. is wavelength-multiplexed transmitted over a single optical fiber. Regarding.

Conventional configuration and its problems The biggest bottleneck in optical loop networks is that even a single failure on the loop, including the station, can be fatal. As shown in Figure 1, each station shore 1 is provided with an optical bypass loop 2 to isolate the faulty station from the loop 3.

1. In case of a line failure, as shown in FIG. 2, a backup loop 5 running in the opposite direction to the current loop 4 is prepared, and the station is provided with a loopback function 6. Therefore, in the event of a line failure, a loopback 6 is performed between the working loop 4 and the backup loop 5 to create a new loop.

For this purpose, it is necessary to obtain a signal at each station 1 that constantly monitors whether or not the original fiber line has been cut.

As one method for this, the method shown in FIG. 3 is used.

4a-f are timing charts for explaining the block diagram shown in FIG. 3; FIG. In Figure 3, 6 is the original data input terminal, 7 is the encoder, and 8 is Elo
(Electro-optical) conversion circuit, 9 is an optical fiber cable,
1o is a 0/E (optical-electrical) conversion circuit, 11 is a decoder, 12 is a data output terminal, 13 (d filter (LPF)
, 14 is a binary level converter, 15 is an optical fiber breakage detection signal output terminal, and 16 is a control section.

The operation shown in FIG. 3 will be explained using FIG. 4. At each station, an encoder 7 is applied to the original data so that even if the original data a remains at L level or H level for a long time, the signal does not become a unidirectional level in the transmission path of the optical fiber cable 9. A signal that constantly changes between H and L is transmitted by the E/○ conversion circuit 8 through the E/○ conversion circuit 8. In the receiving section where the optical fiber cable 9 is connected,
A/E conversion circuit 10 converts the signal into an electrical signal, and the encoded signal is decoded into original data C by a encoder 11. When the line of the optical fiber cable 9 is disconnected, the output signal d of the O/E conversion circuit 10 directly connected to the optical fiber 9 is outputted from the output signal e through the filter (LPF) 13, and then the signal e is
The value level conversion circuit 14 performs binarization at a certain slice level, detects line breakage of the optical fiber cable, and supplies this detection signal f to the control unit 16 to perform loopback.

However, due to optical deterioration, shortcuts, breaks in optical fiber cables, or poor line conditions at the transmitting station, erroneous information sometimes occurs in the data at the receiving station, and conventional methods cannot transmit The amount of light α sent from the station is detected, and the output of this detection determines whether the optical fiber cable is disconnected and loopback is performed. Therefore, in the above-mentioned state, detection is impossible and the terminal The one thing that caused a problem,
It used fiber optic lines, which were deteriorating.

Purpose of the Invention In view of the above, the present invention provides a system that supplies a detection signal to a control unit to perform a loopback when the optical fiber cable is disconnected, the light deteriorates at the transmitting station, or the line is unstable. The purpose of the present invention is to provide a stable and accurate optical fiber line detection device that can perform the following steps.

Structure of the Invention In order to achieve such an object, the present invention converts an analog signal of a photoelectric conversion circuit coupled to an optical fiber cable into a digital signal, and uses this digital signal to fully operate a monostable multivib break. This Hino I
・A device that is activated by a signal indicating an error, counts the total number of bit errors that have occurred within a set timer, and outputs each output signal by turning on and outputting a means for determining that the line is unstable based on the result. It is.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described in detail below. FIG. 6 is a block diagram of an optical fiber line detection device which is an embodiment of the present invention. 5 is a timing chart illustrating the operation of the embodiment. 6th
In the figure, 17 is an optical fiber cable connected to the transmitting station, 10 is a photoelectric conversion circuit that converts an optical signal into an electrical signal, 18 is an amplifier, and 19 is an AGC circuit that keeps the amplitude of the photoelectrically converted electrical signal constant. , 2o is a retrigger type monostable multipipe rake, 21 is a comparator that slices the output of the AGC circuit 19 with a constant amplitude at a constant level and converts it into a binary value, and 22 is the binary output of the comparator 21. A digital filter with a spectrum within the range of the transmission bit frequency Δf; 23 is a digital PLL that generates a continuous clock pulse of the transmission bit frequency phase-synchronized with the encoded data; 11 is the encoder; A decoder 24 decodes the encoded data into the original data, and an error detection unit 24 detects an error location from the encoded data using the outputs of the decoder 11 and digital PLL 23 and generates an error detection pulse. 12 is a decoded original data output terminal, 26 is a clock pulse output terminal, 26 is a timer that generates a long gate pulse in response to the error detection pulse of the error detection circuit 24, and 27 is a circuit for the error detection circuit 24 and the timer 26. A gate circuit that allows only the error signal that occurs within the set timer period to pass through, depending on the output.
28 is a frequency divider that counts the output signal of the gate circuit 27;
29 indicates an abnormality (hereinafter NG) from each frequency dividing terminal of the frequency divider 28.
7 lip-flops are connected to the output terminal (denoted as ) and operate with the output (the output of the frequency dividing terminal changes depending on the count number), 3o is the OFF circuit, and 31 is used when the optical fiber line is unstable (when the optical fiber cable is about to break, The output terminal of the flip-flop 29 is a flip-flop 29 which is used to repair a broken optical fiber cable and return the determination circuit 33 to its initial state when the line is restored to normal. 34 is an optical fiber line detection output terminal,
The determination circuit 33 uses the timer 26. Gate circuit 272 frequency divider 28. It is composed of a flip-flop 29.

Next, the operation of this device will be explained using the timing chart shown in FIG.

Signal A is an encoded analog signal sent from the transmitting station via the optical fiber cable 17, subjected to photoelectric conversion by the photoelectric conversion circuit 1o, and obtained at the output of the amplifier 18.
This is a diagram showing the state when it is cut out.

Optical fiber cable 17° photoelectric conversion circuit 10. Amplifier 1a, AGC circuit 19° comparator 21. This is a diagram illustrating an error state caused by the optical line being cut or the line condition with respect to the encoded signal sent from the transmitting station at the output of the digital filter 22, obtained through the digital filter 22, Signal E is the signal waveform when the signal is normal, and signal waveform when the signal is NG.

The signals to signals A and E are the same in time series. First, detection when the optical fiber cable 17 is cut will be explained.

The encoded analog signal A obtained at the output of the amplifier 18 is passed through the AGC circuit 19 to obtain a signal whose amplitude is constant at the output even if the amplitude of the input signal changes slightly.

The output of the AC7C circuit 19 is output by the comparator 21.
Slice at a constant level to obtain a binary signal called signal C. The output signal C is converted into a binary signal at a constant level by the comparator 21, and the noise component is removed by the digital filter 22, which cuts unnecessary frequency bands.
Input to re-trigger type metastable multi-by-break 2°. If the time constant of the retrigger type metastable multivibrator 2o is set to operate for a time longer than the transmission frequency of encoded data, in the state of the output signal from the digital filter 22, As shown in signal 2, the H level continues, and when the output signal from the digital filter 22 disappears, it becomes the L level after the time constant set by the metastable multi-vib break 20.

Therefore, depending on the presence or absence of a signal obtained through the optical fiber cable, it is possible to detect a break in the original fiber cable or a deterioration of the light source of the transmitting station.

Next, we will explain how to detect when an optical fiber cable is about to break or when the line condition is poor. The output of the digital filter 22 is changed to a digital PLL.
23, the decoder 11 and the error detection circuit 24 are manually input. The digital PLL 23 generates a continuous clock pulse at the transmission focus frequency that is phase-synchronized with the encoded data, and the decoder 11 and the error detection circuit 24 are operated by this clock pulse. Decoder 1
1, the signal H or H is decoded into the original data before being encoded according to the encoding rules at the transmitting station, and its output is sent to the original data output terminal 12 and the error detection circuit 24.
supplied to Depending on the state of the optical transmission path, the data encoded according to the encoding rules at the transmitting station may contain NG portions that do not conform to the encoding rules as shown in FIG. The error detection circuit 24 detects that the encoding rule is not met based on the output of the digital PLL 23 and the encoded data of the digital filter 22, and an error detection pulse is output at the NG location. The output of the error detection circuit 24 is sent to the timer 26. Gate circuit 2722 frequency divider 28.
The signal is supplied to a timer 26 and a gate circuit 27 of a determination circuit 33 consisting of a flip-flop 29.

The timer 26 is provided to monitor the error state over a long period of time, and the timer 26 is provided to monitor the error state for a long time.
・As a Riga, generates a long pulse. The output of the timer 26 is supplied to a gate circuit 27 and a frequency divider 28. The gate circuit 27 obtains a signal in which only error detection pulses generated within the long period of pulses obtained by the timer 26 are passed. The gated output signal is input to the frequency divider 28, and if the number of errors exceeds the minimum allowable number within the time period generated by the timer 26, the divided output signal of the frequency divider 28 is determined to be NG (for example, ,
If the number of errors is 4 or more and it is set as NG, the frequency divider 23
If the 2 frequency divider terminal is used, when 4 error detection pulses are input, the 23 frequency divider terminal changes. )7il-input to flip-flop 29; The frequency divider 28 is the timer 26
It will be cleared after the time set in , and error detection will start again.

The output power of the flip-flop 29 is held at a one-way level at the beginning of the change output level (rising edge) of the output of the frequency divider 28 that is determined to be NG. The output of the flip-flop 29 is supplied to the optical line instability detection output terminal 26 and the output circuit 30. The output signal from the retrigger monostable multi-by-break 20 and the output signal from the flip-flop 29 are input to the output circuit 30, and either one of them (same time)
If the result is NG, NG ff is output to the optical fiber line detection output terminal 34. The output of this optical fiber line detection output terminal 34 is supplied to a control section that performs loopback.

If the reset terminal 32 is NG, the flip-flop 2
9 is held at a one-way level, so from the control unit etc.
This is an input terminal for returning to the initial state.

Detection based only on the number of error detections can be used to determine whether light is coming from the transmitting station when the receiving station is powered on (the optical fiber cable is broken or the transmitting side is off), or whether the optical fiber cable is disconnected during transmission. Sometimes, the error detection pulse becomes a one-way level, and the frequency divider 28 set as NG loses its count.
It becomes difficult to detect breaks in the optical fiber cable.

Therefore, to detect a break in an optical fiber cable, the photoelectrically converted data is binarized, a retrigger type monostable multi-vibration break is operated, and the determination is made based on the output. It's a reed.
To detect an unstable state of the line (when the optical fiber cable is about to break or when the line condition is poor), we count the errors that have occurred, encode the NGs, and convert the transmitted optical signal into an electrical signal using electrical conversion means. It was then converted into a binary value using a binary conversion means, and the binary signal was used to operate a re-trigger type monostable multivibrator tray to detect a break in the optical fiber cable and to obtain a total count of bit errors that occurred when decoding the received data. Then, by detecting the unstable state of the optical line obtained by the NG determined by the count number, it is possible to stably and highly accurately detect an abnormality in the optical fiber line without detecting the amount of light source sent from the transmitting station. can do.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram explaining the optical bypass performed in the event of a station failure, Figure 2 is a circuit diagram illustrating the loopback performed in the event of a line failure, and Figure 3 is the conventional method for loopback performed in the event of a line failure in Figure 2. FIG. 4 is a timing chart for explaining the operation of FIG. 3; FIG. 5 is a block diagram of an optical fiber line detection device according to an embodiment of the present invention; FIG. FIG. 6 is a timing chart for explaining the operation of the optical fiber line detection device in FIG. 10...Photoelectric conversion circuit, 11...Decoder, 17...Optical fiber cable, 18...Mark amplifier, 19...A G 'C circuit , 2o・
・Group/retrigger monostable multi, 21...Comparator, 22...Digital filter, 23...
... Digital PLL, 24 ... Error detection circuit, 26 ... Timer, 27 ... Gate circuit, 28 ... Frequency divider, 29. ...Frinopfronov, 30...Owa Circuit, 33...
...Judgment circuit.

Claims (1)

[Scope of Claims] (1) A photoelectric conversion means for converting an optical signal coupled to an optical fiber into an electrical signal, a binary conversion means for converting the output signal of the photoelectric conversion means into a binary signal and a bell signal; Clock pulse generation means for generating continuous clock pulses synchronized with data from the output signal of the binary conversion means; and decoding means for decoding data from the output signal of the binary conversion means and the output signal of the clock pulse generation means. and an error detection means for detecting a bit error from the output signal of the binary conversion means based on the output signal of the binary conversion means and the output signal of the clock pulse generation means, and the number of times the error detection means detects a bit error. a determining means for determining line abnormality of the optical fiber; a monostable multivibrator circuit operating on the output signal of the binary converting means; and a monostable multivibrator circuit for synthesizing the output signal of the determining means and the output signal of the stable multivibrator circuit. An optical fiber line detection device characterized by comprising a circuit. (3) The determining means includes a timer means for generating a constant gate pulse from the first bit error detected by the error detecting means, and a gate means for passing a signal indicating a bit error occurring within the time of the timer means. and abnormal signal output means for counting the number of bit errors from the output of the gate means and outputting a signal at a constant level according to the count number and the time of the timer means. The optical fiber line detection device according to item 1).