JPS58175329A - Light source switching system of optical repeater - Google Patents

Abstract

PURPOSE:To ensure an optical digital transmission system of high reliability, by detecting the deterioration of a light source from a code error factor of a transmission line and then switching the deteriorated light source to a normal spare one. CONSTITUTION:The error detecting signal which is transmitted to a repeater from an end office device is converted into an electric signal by a light-electricity converting circuit 14. Then the reproduced output signal obtained from a discriminating/reproducing circuit 16 is sent to an error factor measuring circuit E to detect an error pulse. When error pulses more than a fixed number are detected, a signal is delivered from an error detecting signal generating circuit 20. This detecting signal is transmitted to a repeater preceding by one repeating section. Then a deteriorated light source is switched to a normal spare one with a light source LD and via a light source switching circuit S.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light source switching method in a light source redundant configuration that is applied to increase the reliability of a semiconductor laser that is a light source of an optical repeater.

Conventionally, in optical fiber relay transmission systems, multiple light sources are installed in an optical repeater to monitor the threshold current of a current temperature-stabilized semiconductor laser, and when the threshold current rises above a predetermined threshold current, A known method is to assume that the laser has deteriorated and switch to a backup light source. Although an increase in threshold current is one factor for determining deterioration of a light source, an increase in threshold current does not necessarily correspond to deterioration in optical transmission characteristics in an optical fiber transmission line. For example, when the optical spectrum of a light source widens, in a transmission system that uses a single mode optical fiber as a transmission medium, the influence of wavelength dispersion of the optical fiber appears, degrading the transmission characteristics. There is generally no correlation between the deterioration of the spectral characteristics of the semiconductor laser and the increase in the threshold of the light source. Therefore, in conventional methods, the light source cannot be switched even though the characteristics of the transmission path have deteriorated due to the broadening of the spectral characteristics of the semiconductor laser. will not be carried out. On the other hand, for example, if the leakage current of a semiconductor laser increases and the threshold current rises to a certain extent, but it still functions as a normal light source, the conventional method would switch to a backup light source as an over-prevention measure. There is a fear.

An object of the present invention is to measure the code error rate of the transmission line in the opposing optical repeater, and detect a part that generates an error signal when the error rate exceeds a predetermined error rate, and a backup light source using an error detection signal, in order to avoid the above problems. By connecting the repeaters of both parties with a medium that transmits error detection signals, deterioration of the light source can be determined from the transmission line code error rate characteristics based on the error detection signal train from the optical terminal equipment, and It is an object of the present invention to provide a system for switching a working light source of a transmitting section in a relay section with a high code error rate to a standby standby light source. Regarding the monitoring of the bit error rate of a transmission line, the terminal equipment locates one optical repeater among multiple optical repeaters, returns the signal at the optical repeater under test, and transmits the signal via an intervening line or downlink transmission line. A method for measuring the error rate has been known for some time, but it requires a remote control signal for locating the optical repeater and controlling the return of the signal for each optical repeater. Since the rate measurements are performed sequentially, there is a drawback that a long measurement time is required in a transmission system having a large number of optical repeaters, such as a long-distance optical submarine cable system.

With the configuration of the present invention, only one signal sequence is required for the bit error rate, and since each optical repeater has a built-in error-side constant circuit, temporally parallel measurements are possible, and the measurement time is significantly reduced. Since it is shortened, the above problem is solved.

The present invention will be described in detail below using the drawings.

FIG. 1 is a diagram showing the principle of a conventional phase detection method used to determine code errors on the vehicle side, and this method is used to measure the code error rate. The principle of the phase detection method will be explained below with reference to FIG. In the phase detection method, when a binary code sequence passes through a conversion circuit on the transmitting side and an inverse conversion circuit on the receiving side, it becomes the original positive code sequence or its complementary code sequence. Take advantage of the fact that they alternate. Applying this principle, a code string whose mark rate is not 7 can be repeated at a constant repetition period (
1/2f, ), performs complementary code conversion, that is, mark rate modulation, and sends it to the transmission path after being glycoded.・Reception 9111 O
De°-' output 91 plus sign 1/complementary sign 1
An output in which the columns are alternated is obtained, and the output signal is mark rate modulated, so the DC component of the signal deviates with a period f, and after passing through a low-frequency f wave generator, the repetition period becomes 1/2f1. A signal waveform of is obtained. When an error pulse occurs on the transmission path, the code sequence of the decoder output is inverted, and the phase of the signal that has passed through the low-frequency f-wave generator is inverted, so it can be determined whether or not an error has occurred.

FIG. 2 shows an embodiment of a system for counting code error pulses using the phase detection method used in the present invention. To explain the operation of FIG. 2, FIG. 3 shows the waveform of the second section. The operation when measuring the bit error rate using . In addition, the symbols for I~ shown in each part of Fig. 2 are the same as I~ in Fig. 3.
This shows where each waveform exists. The output from the binary number sequence generation circuit 1 as shown in FIG. The exclusive OR circuit 4 performs mark rate modulation as shown at the beginning of FIG. 3, and the precoder 5 performs code conversion, and its output becomes a signal sequence with a mark rate i. When a received signal is converted into an optical signal, passes through an optical transmission line, and is converted back into an electrical signal, when a loss occurs in the decoder 6 corresponding to the T-flip-flop, the positive sign and complementary sign are inverted, and the received signal becomes low. The output waveform that has passed through the frequency range f wave generator 7 and the Schmitt circuit 8 is the third waveform.
As shown in Figure E, this output and the time t-1/9
9 with the waveform passed through delay i$9 with a delay of 2f1
The output of the NOR circuit is as shown in FIG. 3, and in response to the occurrence of an error pulse, <Rus is obtained. At time T when the error detection signal is being transmitted, the low-band r-wave generator 7 outputs
Since a signal with a frequency component of fl is generated, it is distinguished from the signal sequence during service, and this is extracted by the r-wave circuit 11 tuned to the frequency f, and this output opens gate 2, and the negative OR circuit The counting circuit 13 starts counting the error detection pulses output from the gate circuit 10.The gate circuit 12 counts the number of occurrences of error pulses during the time period T during which the error detection signal is being transmitted, and counts the number of error pulses that the signal has generated. When the signal is disconnected, the output of the r-wave circuit 11 becomes zero, the gate circuit 12 is closed, and the counting circuit 13 is reset.The counting circuit output (Qo, Ql, Q2.
-”, QN-1), the error rate is measured by
This output is used to determine whether the error rate is equal to or higher than a predetermined error rate.

FIG. 4 is a block diagram showing an example of the configuration of an optical repeater reproducing circuit and an error measuring circuit used in the present invention. optical/electrical conversion circuits, including automatic gain control) circuits;
15 is a waveform equalization circuit, 16 is an identification/reproduction circuit, 17 is a timing extraction circuit, 18 is a signal disconnection detection circuit, 19 is a light source drive circuit, E is a code error rate measurement circuit, and 21 is an error detection signal generation circuit. is an AND circuit.

Next, the operating principle will be explained. When the error detection signal is transmitted from the terminal equipment and reaches repeater R, it is converted into an electrical signal by 14 optical-to-electrical conversion circuits, and the reproduced output signal obtained by 16 identification and reproduction circuits is used to measure the error rate of E. When an error pulse is detected by the circuit, and a certain number of error pulses or more are detected, a signal is output from an additional error detection signal generation circuit, and a signal is output from the relay section one relay section earlier via the medium that transmits the error detection signal. The light is transmitted to the light source, and is used by the light source LD to switch between the backup light source and the backup light source via the light source switching circuit S.

In order to prevent the code error from propagating to the optical repeater in the subsequent stage after the optical repeater that detected the error and generate an error detection signal, the output of the additional error detection signal generation circuit is added to the AND circuit 21. Either stop transmitting the signal to the optical repeater in the next stage, or transmit a signal containing an error pulse to the optical repeater in the subsequent stage, and output the error detection signal transmitted from the optical repeater after one repeating interval. By comparing the outputs of the additional error detection signal generation circuits, it is sufficient to prevent the light source switching error.

Figures 5a, b, and c are diagrams showing transmission systems necessary to explain the principles of three types of systems for transmitting error information to an optical repeater one relay section before in the present invention. ,M,r
x4' is the terminal equipment, R,, I......lRo is the optical repeater, 'II + """ + Rlk-1+ R
lk + “”” + Rln is the outgoing optical repeater circuit,
R21,...+ R2 -1+ R2k'・
..., R2n is an optical repeater circuit on the return path, l is an optical fiber transmission line, 1 and C are code error rate measuring circuits on the outgoing path, and S is a light source switching circuit.

Next, three types of methods will be sequentially explained. Figure 5a is
An error detection signal is transmitted from terminal M, and optical repeater R'l
k, the error rate measuring circuit of E counts the error pulses, and when the number exceeds a predetermined value, an error detection signal is generated, and l
', and drives the light source switching circuit of the optical repeater R1k-1 one relay section before. FIG. 5 shows how the error detection signal generated in the optical repeater RIk is transmitted to the modulation circuit Md.
The optical repeater R1 is modulated with a natural frequency for locating the signal, and is transmitted via the return transmission path where the signal is disconnected. Yotsu, optical repeater R1
The arrival of the signal from k is detected, and the light source switching circuit of S is driven. FIG. 5C shows different wavelengths λ1. It is a bidirectional transmission system using λ2, and the signal from the terminal station M has a wavelength of λ2, for example.
, the signal is transmitted via an optical fiber transmission line via a multiplexer/demultiplexer MX, and the return signal is transmitted at wavelength λ2. The error detection signal is transmitted from the terminal equipment using the wavelength λ1. Errors are detected at the repeater R1k. When the number of errors exceeds a predetermined number, the wavelength λ1 built in the optical repeater at R1 is transmitted. R,
The signal is transmitted to the optical repeater 1-1, and the light source switching circuit S is driven.

The method using the intervening line shown in Figure 5a does not require a particular circuit to switch the transmission line signal from the main signal to the error detection signal, compared to the method using the main signal transmission line to send the error detection signal. Therefore, there is an advantage that the electric circuit is not complicated. In the method shown in FIG. 5, since the main signal transmission line in the opposite direction is used, no other special purpose transmission line is required, so that the transmission line can be made more economical. Furthermore, since the method shown in FIG. 5C requires only one transmission line, further economicalization can be achieved when the transmission line cost is high, such as in a single mode optical fiber cable.

FIG. 6 is a diagram showing an example of an implementation circuit of the light source switching circuit according to the present invention.

From the terminal A, a transmission line signal pulse drives a CML (current switching logic) circuit composed of transistors ql + q2 and resistor r1, and Ll! R21...
・, Among the N semiconductor lasers of LN, the transistor Q
4 + Q2 +...+QN is turned on and one semiconductor laser is operated for switching. B is a terminal to which a semiconductor laser switching control signal is applied, and in the present invention, an error detection signal is used. F is a shift register, and A7. A2.・
・・・・・・．

ZN17)! Zener diode for pressure bell adjustment,
The transistors Q, , Q, . . . IQN are sequentially turned on via the resistors R,', R+; , . . . R'N, and the semiconductor laser L,.

L2p..., LN switching is performed. A...
A2. ..., AN is a photodetection element, and each photodetection element corresponds to, R2゜..., detects the rear output signal light of the semiconductor laser of LN, and detects the rear output signal light of the semiconductor laser of C, and the It is integrated by the differential amplifier of A, the resistance of r, and the capacitance of C' through the resistance of capacitor r6, and is compared with the reference voltage of VE through the resistance of r, the resistance of r8, and the buffer of q3. Through the resistor of the transistor r, D, , D2
．． ..., from the i-th diode that is turned on among the diodes of DN, the first transistor Q+
The bias current of the i-th semiconductor laser is controlled by the pace N current, and the output light is stabilized. The threshold current of a semiconductor laser differs depending on the individual element, so R8°R
2. The control width of the stabilization control current is initialized in advance using the +-RN resistor, and the control width of the stabilization control current is made small when switching is performed. (The output light of each semiconductor laser is are collected into one optical fiber transmission line.

The above describes the method of detecting deterioration of the light source based on the bit error rate of the transmission path and switching to a spare normal light source, the bit error rate measurement and error detection circuit, the bit error rate detection signal transmission method, and and the light source switching circuit. According to the present invention, it is possible to prevent the deterioration of the spectral characteristics of the semiconductor laser or the excessive switching of the light source, which was impossible with the conventional semiconductor laser deterioration detection method, so that a highly reliable optical digital transmission system can be realized. It has the effect of being configurable.

[Brief explanation of drawings]

Figure 1 is a principle diagram of code error rate measurement, Figure 2 is a code error pulse counting circuit according to the present invention, and Figure 3 is a diagram of the code error rate measurement.
2 is an explanatory diagram of the operation of the circuit, FIG. 4 is an optical repeater regeneration circuit according to the present invention, FIGS. It is a circuit. Patent applicant International Telegraph and Telephone Co., Ltd. Patent application agent Megumi Yamamoto −

Claims (1)

[Claims] In a light source switching method for an optical repeater that has active and backup light sources and relays up and down transmission lines, the optical repeater measures the code error rate of the transmission line, and when the error rate reaches a predetermined error rate, A light source switching method for an optical repeater, characterized in that the optical repeater sends an error signal to an adjacent transmitting-side optical repeater, and the optical repeater that receives the error signal switches from the active light source to the backup light source. .