JP2705625B2 - Optical fiber cable break detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber cable disconnection detection system for detecting when an optical fiber cable is disconnected.

[0002] In an optical communication system, an optical fiber cable is used to transmit an optical signal. If the optical fiber cable is disconnected for any reason, communication cannot be performed. It is necessary to detect the disconnection of the cable quickly and reliably.

It is desirable that such an optical fiber cable disconnection detection system can reliably detect an optical fiber cable disconnection without performing special encoding on an optical signal.

[0004]

2. Description of the Related Art As an example (1) of a conventional optical fiber cable disconnection detecting method, there is an optical signal input disconnection detecting apparatus described in Japanese Patent Application Laid-Open No. 3-40538.

In this known optical signal input disconnection detecting device, a received optical signal is converted into an electric signal by a photoelectric conversion circuit.
The clock extraction circuit extracts the clock from the received signal,
The identification circuit identifies the received signal based on the extracted clock and outputs data, and the optical input disconnection determination circuit determines disconnection of the optical input.

At this time, in the optical input interruption determining circuit, the average voltage of the output data is calculated by the average voltage calculating circuit, and the output is compared with the reference voltage by the comparing circuit to determine the output of the optical input disconnection. Occurs.

Further, as an example (2) of the conventional optical fiber cable disconnection detecting method, there is an optical input signal disconnection detecting method described in Japanese Patent Application Laid-Open No. Hei 2-17744.

In this known optical input signal disconnection detection method, a violation bit detector detects a periodic output from the optical / electrical conversion element, which violates a certain code rule contained in the received output. The detected output is temporarily stored by the comparison detection means at the time of detection of the violation bit, and the output value is compared with a predetermined detection level, thereby detecting the disconnection of the optical input signal. Occurs.

[0009]

In the conventional method (1) of the optical fiber cable disconnection detection method, after an optical signal is converted into an electric signal, a timing component is extracted from the signal waveform to extract a clock. In an optical signal, it is necessary to perform encoding such that the number of change points increases, and a transmitting circuit requires an encoding circuit that performs such encoding, and a receiving circuit requires a decoding circuit that decodes such a signal. At the same time, when "0" continues in the optical signal, there is a problem that the optical fiber cable disconnection is erroneously detected on the receiving side.

In the conventional method (2) of the optical fiber cable disconnection detection method, encoding is performed so that the violation signal is included in the optical signal at a fixed period, and the receiving side can detect such violation bit. In addition to the necessity, when "0" continues in the optical signal, there is a problem that the receiving side erroneously detects disconnection of the optical fiber cable.

An object of the present invention is to solve such a problem of the prior art. The transmitting side inverts the polarity of a transmitting signal at a fixed period and transmits the signal, and the receiving side transmits the received signal at the same period. Reproduce the transmission signal by inverting the polarity, and detect the disconnection of the optical fiber cable and output an alarm even if "0" continues in the transmission signal when the optical signal is not encoded. The purpose is to be able to.

[0012]

According to the present invention, the above-mentioned object is achieved by adopting the following constitution.

(1) The transmission side is provided with a selector 11, and the transmission data (S) and the inverted transmission data (S ^* ) obtained by inverting the transmission data are alternately switched according to a logic switching timing signal, and the transmission data (S) is inverted. The received signal is converted into a signal and transmitted through the optical fiber cable 3, and a selector 21 is provided on the receiving side, and output data (R) obtained by identifying the received optical signal and inverted output data (R ^* ) obtained by inverting the output data ^. ) Is alternately switched according to a logic switching timing signal to generate reception data, and
The disconnection of the optical fiber cable is detected by continuing the non-output state for a period exceeding the logic switching timing signal cycle.

(2) In the case of (1), the logical switching timing signal on the receiving side is sent from the transmitting side via the optical fiber cable 3 and another cable.

[0015]

(1) On the transmitting side, the transmission data (S) and the inverted transmission data (S ^* ) are alternately switched by the selector 11 in accordance with the logical switching timing signal, and are converted into optical signals to be converted into optical signals. 3 and the receiving side alternately switches output data (R) and inverted output data (R ^* ) obtained by identifying an optical signal in accordance with a logic switching timing signal to generate reception data. .

At this time, if the optical fiber cable 3 is normal, in the reception identification output, the non-output state does not continue for a period exceeding the logic switching timing signal cycle, but the optical fiber cable 3 is disconnected. In such a case, in the reception identification output, the non-output state continues for a period exceeding the logic switching timing signal cycle. Therefore, by determining this state, it is possible to detect disconnection of the optical fiber cable between the transmission circuit and the reception circuit. Can be.

(2) As the logical switching timing signal on the receiving side, a logical switching timing signal on the transmitting side which is sent from the transmitting side via a cable different from the optical fiber cable 3 can be used. .

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention, in which a transmitting circuit 1 and a receiving circuit 2 are shown in a block diagram.

In the transmission circuit 1, the selector 11
The transmission data S and its inverted transmission data S ^* (
^{* Indicates} an inverted signal), and alternately outputs a signal at a constant period ΔT corresponding to N (N is an arbitrary integer) bits in accordance with the logic switching timing signal K. The light emitting element drive circuit 12 drives the light emitting element 13 according to the output of the selector 11, and the light emitting element 13 outputs an optical signal from the transmission circuit 1 to the optical fiber cable 3.

In the receiving circuit 2, the light receiving element 21 converts the received optical signal into an electric signal, the preamplifier 22 amplifies the electric signal by DC, and the identification circuit 23 identifies the output of the preamplifier and determines the logic level. . The inversion circuit 24 outputs the output data R of the same waveform and the inverted output data R ^{* obtained} by inverting the output data R of the logic level output from the identification circuit 23 ^.
And generate. The selector 25 alternately switches the output data R and the inverted output data R ^* at the same constant period ΔT as the transmission side in accordance with the logical switching timing signal K sent from the transmission side by another cable.
The transmission data is reproduced and the reception data is output.

The 0-continuation detecting circuit 26 detects a cable disconnection alarm A by detecting, at the output of the discriminating circuit 23, a time longer than the time during which the selector 11 switches two or more times, that is, the continuation of "0" of N + 1 bits. Is output.

2A and 2B show output signal waveforms of various parts of the embodiment. FIG. 2A shows a signal in a normal case.
(B) shows a signal when the optical fiber cable is disconnected.

In FIG. 2A, on the transmission side, transmission data S as shown and inverted transmission data S
^{Suppose *} is entered. The selector is initially positive logic and selects the transmission data S in response to the logic switching timing signal K, but at time T = t ₁ ,
The logic becomes negative logic, and the inverted transmission data S ^* is selected.
= T ₂ , the logic becomes positive again, and the transmission data S is selected. Thereby, the transmission data S and the inverted transmission data S
^* And is selected alternately with N bits (= [Delta] T) period, it generates an optical signal output.

On the receiving side, the output of the discrimination circuit has the same logic as the output of the selector, because the output of the discrimination circuit is obtained by DC amplification of the optical signal input and discriminating the logic level. The selector alternately switches output data R having the same waveform as the output of the discrimination circuit and inverted output data R ^* obtained by inverting the output data R in the same cycle as that of the transmission side according to the logic switching timing signal K. Outputs the received data with the same waveform as the data. The cable break alarm A output from the 0 consecutive detection circuit becomes “L” at time T = t ₀ because the output of the identification circuit is “1”. Since then also it has a "1" to the identification circuit output between times T = t ₁ and T = t _2, the cable loss alarm A is followed by "L".

In FIG. 2B, if the same transmission data is input, the output up to the selector is the same, but since the optical fiber cable is disconnected, the optical signal input is ^.
0 "continues. Therefore, the output of the discriminating circuit also continues as" 0 ".

Now, it is assumed that the optical fiber cable is connected until immediately before time T = t ₀ , and the cable break alarm A, which is the output of the 0 continuous detection circuit, is “L”. Time T
= T _{0, and} at time T = t ₂ when N + 1 bits have elapsed, “0” continues to the output of the discrimination circuit. Therefore, at the next time T = t ₃ , the cable break alarm A
Output “H”.

If the optical fiber cable is not disconnected, but data such that "0" continues for a time longer than 2ΔT is input to the selector output, the receiving side once generates a cable disconnection alarm, and the receiving side To the transmitting side, the transmitting side inputs data such that “0” continues to the input of the selector for a time longer than 2ΔT, thereby confirming whether the optical fiber cable is disconnected. I do. As a result of this processing, when the cable disconnection alarm is detected again, it is definitely determined that the optical fiber cable is disconnected. If the cable disconnection alarm is not detected as a result of this processing, it is determined to be erroneous detection and a sufficiently long time (for example, 2000ΔT) for 2ΔT is determined.
Only in T), the cable disconnection alarm is masked and ignored.

[0028]

As described above, according to the present invention, the transmission side alternately selects the logic of "1" and "0" of transmission data at a fixed period and transmits the same, and the reception side has the same operation as the transmission side. In a cycle,
The logic of "1" and "0" of the reception identification output is alternately selected to reproduce the transmission data, and the disconnection of the reception identification output for a certain period or more determines the disconnection of the optical fiber cable. Without special encoding,
An optical fiber cable break can be reliably detected.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

2A and 2B are diagrams showing output signal waveforms of respective parts of the embodiment. FIG. 2A shows a signal in a normal case, and FIG.
Indicates a signal when the optical fiber cable is disconnected.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmission circuit 11 Selector 12 Light emitting element drive circuit 13 Light emitting element 2 Receiving circuit 21 Light receiving element 22 Preamplifier 23 Identification circuit 24 Selector 25 0 Continuous detection circuit 3 Optical fiber cable

Claims (3)

(57) [Claims] 1. A transmission side comprising a selector, transmission data (S) and inverted transmission data (S) obtained by inverting the transmission data (S).
^* ) Is alternately switched according to the logic switching timing signal, converted to an optical signal, transmitted via an optical fiber cable, and provided with a selector on the receiving side, and output data obtained by identifying the received optical signal. (R) and inverted output data (R ^* ) obtained by inverting the output data are alternately switched according to the logic switching timing signal to generate reception data, and the logic switching timing signal cycle in the identification output is changed. An optical fiber cable disconnection detection method, wherein the disconnection of the optical fiber cable is detected by continuing the non-output state for a period longer than the above. 2. The optical fiber cable disconnection detection method according to claim 1, wherein the logical switching timing signal on the receiving side is transmitted from the transmitting side via the optical fiber cable. 3. The optical fiber cable disconnection according to claim 1, wherein the logical switching timing signal on the receiving side is transmitted from the transmitting side via a cable different from the optical fiber cable. Detection method.