JPH0342927A - Monitor system for optical amplifying and repeating transmission line - Google Patents

Abstract

PURPOSE:To miniaturize the system, to simplify the constitution, and to reduce the power consumption by sending a light signal back to a terminal station not through a movable part like a switch without converting the light signal into electricity at each repeater, and monitoring the repeating transmission line or locating a faulty repeater. CONSTITUTION:If a repeater gets out of order, the optical transmission part 2 of the terminal station A sends out a light pulse signal P1 for monitoring which has wavelength lambda1 so as to locate the faulty repeater. Consequently, a signal having the wavelength passes through a filter lambda1 of each repeater and the light signal is sent back to the terminal station. The terminal station A separate signals with lambda0 through a branching filter 10. At this time, light pulses arrive at the terminal station after the time corresponding to the length of an optical fiber. Consequently, if one repeater 5 deteriorates or breaks, a 3rd pulse decreases in amplitude or does not return. The transmission period of sent pulses need to be made much longer than the pulse sending-back time from the farthest repeater.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is a transmission system that uses optical fibers to exchange information between two points, and uses an optical direct amplifier to amplify optical signals that are attenuated on the way. The present invention relates to a monitoring system for constantly monitoring the status of a multi-relay transmission line and locating a failed repeater.

(Prior Art) FIG. 5 shows conventional transmission lines, including land transmission lines and submarine transmission lines. Since the optical signal transmitted from the terminal station is attenuated due to loss in the optical fiber, it is necessary to insert repeaters at certain intervals to amplify the optical signal. These amplifying devices include those using optical fibers and those using semiconductor lasers, which directly amplify input light and send out light having the same wavelength as the input light.

In Figure 5, the optical signal from the terminal station (A) is transmitted through the upstream transmission line via repeaters 5 (1 to n), and the signal from the terminal station (B) is relayed through the downstream transmission line. 5(n-1).

(Problem M to be Solved by the Invention) However, in a transmission line having such a configuration, since there is no return signal path at the repeater, it is not possible to monitor the operating state of each repeater. Another disadvantage is that when an optical direct amplifier fails, it is difficult to determine which repeater has failed. On the other hand, a method of converting light into electricity and signal processing within a repeater could be considered, but this would increase the circuit scale and power consumption. Points will not be utilized.

The present invention solves these shortcomings by returning the optical signal to the terminal station without converting the optical signal into electricity at each repeater and without moving parts such as switches, thereby achieving high reliability. The purpose of this invention is to provide a method for monitoring intermediate amplification repeater amplifiers for monitoring repeater transmission lines or locating faulty repeaters.

(Means for Solving the Problems) The present invention has a terminal station for transmitting and receiving optical signals;
A digital two-way relay transmission line equipped with optical fibers for upstream and downstream transmission lines that transmit this optical signal, and seven or more optical repeaters that directly amplify and send out the attenuated optical signal transmitted through the optical fiber. In the above, each repeater connects an optical amplifier for each transmission line and the output of the optical amplifier to extract a monitoring signal having a wavelength different from the wavelength of the main signal and close to the wavelength of the main signal, and then It has a filter that is applied to the input of the optical amplifier of the transmission line on the side, and when an optical pulse signal with a monitoring wavelength is sent from one terminal station to the optical fiber, the signal from the terminal station to each repeater is This is a monitoring method for optical amplification repeater transmission lines that locates a failed repeater from the amplitude of each pulse in a pulse train that returns to the terminal station with a propagation time corresponding to the distance.

Another feature of the present invention is that the repetition period of the monitoring optical pulse signal sent from the terminal station is set to be longer than the time it takes for the optical signal to travel back and forth between the repeater farthest from the terminal station and the terminal station, and each relay The pulse train that is returned by the transmitter and received by the terminal station is extracted and monitored for each repeater at the terminal station, and the results are used to constantly monitor the transmission characteristics of each repeater on the transmission path or to locate a faulty repeater. It is a monitoring method for optical amplification repeater transmission lines.

(Operation) The terminal station on the transmitting side inputs the wavelength. Along with the main signal, a monitoring signal with a wavelength λ□ close to the input 〇 is sent out. Each repeater is λ. and λ,
After amplifying the signal, only the wavelength λ for monitoring is extracted by a filter, and the signal is returned to the transmitting end station via a return optical fiber. Therefore, the transmitting terminal station receives the return pulse at a time according to the distance of each repeater from the transmitting terminal station. By observing this folded pulse, it is possible to locate a failure in a repeater or monitor a transmission path.

Therefore, the above-mentioned objectives of the invention are achieved.

(Example 1) Figure 1 shows an example of this monitoring system, and shows the case of a transmission line with three relays. (A) and the terminal station (B).The terminal station 1 (A) has an optical transmitter 2 having a light source with wavelengths λ0 and λ, and an optical receiver 3 capable of receiving light in this wavelength range. .The wavelength of the main signal in the optical transmitter 2 is assumed to be λ.

The wavelength λ is for monitoring purposes, and is set so that the wavelength side is slightly longer than the wavelength of the main signal, and the wavelength side is slightly shorter than the wavelength of the main signal, and within a band that can be amplified by an optical amplifier.

The optical signal sent from the optical transmitter 2 is transmitted through the optical fiber 4 (upstream transmission line) and reaches the repeater 5.The attenuated optical signal is amplified to its original amplitude by the optical direct amplifier 6. is transmitted again to the optical fiber 4, where each repeater 5 from 1 to 3 has an identical filter 7 for selecting the wavelength for monitoring.However, the transmission of the upstream and downstream filters The wavelengths must be set to be different. Also, these wavelengths must be set so that they are within the band of the optical direct amplifier. Figure 2 shows the gain band characteristics of the optical amplifier and the monitoring signal. An example of the wavelength of the light source set to .

Furthermore, in each repeater 5, an optical direct amplifier 6 on the upstream transmission line
One part of the main signal is sent to the transmission line as it is by the optical branching part 8, and the other part passes through a filter and is input to the optical amplifier 6 on the downstream transmission line via the optical coupling part 9. . Further, a demultiplexer may be used to separate the main signal of wavelength λ0 and the monitoring signal of wavelength λ1. Regarding the downstream transmission path, the other configurations are the same except that the wavelength for monitoring is λ'1.

Because of this configuration, the normal main signal is transmitted through the uplink and downlink lines without being looped back at the repeater.

First, the monitoring method according to claim (1) will be explained. When a repeater fails, in order to locate which repeater has failed, the optical transmitter 2 of the terminal station (A) sends a monitoring optical pulse signal P1 of wavelength λ1 as shown in FIG. Send to. In this way, the signal of this wavelength passes through the filter λ1 of each repeater, and the optical signal is returned to the terminal station. At the terminal station (A), the demultiplexer 10 outputs λ. Separate the wavelengths of and. At this time, the optical pulses arrive at the terminal station in a time corresponding to the length of the optical fiber, so if there are three repeaters, a train of three pulses S as shown in FIG. 3 is obtained.

For example, if the repeater (3) deteriorates or is disconnected, the amplitude of the third pulse will decrease or the third pulse will not be returned, as shown in the pulse train 82 in Figure 3. become. If repeater (2) fails, S
If the second and subsequent pulses as in pulse train 3 fail, and if repeater (1) fails, the first and subsequent pulses as in S4 will not be obtained, so which repeater is the failed one? You can find out if there is any, and what the degree of deterioration is. Note that the transmission period of the transmission pulse is
It is necessary to take a time that is sufficiently longer than the pulse return time from the farthest repeater.

Next, claim (2) will be explained. this is,
This method is more suitable for in-service monitoring of the transmission characteristics of a repeater section than for monitoring failures in the repeater itself. The transmission path has the same configuration as claimed in claim (1). As shown in FIG. 4, the monitoring pulse is set to have a cycle that is an integral multiple of the time it takes for the optical signal to return from the repeater farthest from the terminal station. In this way, the pulse obtained at the terminal station will be obtained repeatedly at the period of the pulse sent by the signal returned from each repeater, as shown at 91 in FIG.

In the case of Figure 3, it was only necessary to discover whether there was a failure in the repeater, so the transmission period of the monitoring pulse could have been large, but here we will measure the transmission characteristics of the repeater transmission line by measuring the bit error rate. Therefore, it is necessary to send out monitoring pulses at short intervals.

(For example, to obtain an error rate of 10-4,
It is necessary to transmit a pulse of about 0.08. ) Therefore, in order to make it possible to identify the pulses returned by each repeater, the monitoring pulses are transmitted based on the return time from the farthest repeater.

When this pulse train is divided by the time division device 11 shown in FIG. 1, it becomes q*, q3, . A Q4 pulse train is obtained.

q2 is only the signal returned from repeater (1), and Ql and q4 are signals returned from repeaters (2) and (3), respectively. The signal q21 thus obtained
From q31 to q4, transmission characteristics such as the bit error rate of signals for each repeater can be monitored all at once. The code error rate may be monitored by the same method as in the past, so there is nothing particularly new about the time division device 11. This monitoring is the main signal λ. It can also be done while transmitting the main signal λ. Although it is possible to do this without transmitting the main signal λ, it is preferable to use the main signal λ. There is an advantage to doing this while transmitting the data.

Similar operations can also be performed from the terminal station (B).

(Effects of the Invention) As explained above, it is possible to locate a failed repeater by returning the signal without converting the optical signal into electricity within the repeater and without having a mechanically moving part such as a switch. Since it is possible to constantly monitor operations and transmission paths, it is possible to reduce the power consumption of repeaters and realize a compact and highly reliable monitoring system.

[Brief explanation of drawings]

FIG. 1 is an embodiment of a monitoring system for an optical amplification repeater transmission line. FIG. 2 is a diagram showing an example of the gain band characteristics of an optical direct amplifier and the wavelength of a monitoring optical signal. FIG. FIG. 4 shows an example of a pulse train to explain the operation of the second embodiment of the present invention, and FIG. 5 shows a transmission line using a conventional optical direct amplifier. shows. 1: Terminal station (A) (B), 2: Optical transmitter, 3: Optical receiver, 4: Optical fiber (up and down), 5: Repeater (1 to n), 7: Filter, 9: Optical coupling Part 11: Time division device. 6: Optical direct amplifier, 8: Optical branching section, 10: Demultiplexer,

Claims (2)

[Claims] (1) Terminals for transmitting and receiving optical signals, optical fibers for upstream and downstream transmission lines that transmit this optical signal, and light that directly amplifies and transmits attenuated optical signals transmitted through optical fibers. In a digital bidirectional repeating transmission line with multiple repeaters installed, each repeater has an optical amplifier for each transmission line, and the output of the optical amplifier is coupled to the wavelength of the main signal, which is different from the wavelength of the main signal. It has a filter that extracts monitoring signals with adjacent wavelengths and applies them to the input of the optical amplifier on the opposite transmission line, and sends out an optical pulse signal with the monitoring wavelength from one end station to the optical fiber. The optical amplification relay is characterized in that the faulty repeater is located from the amplitude of each pulse of a pulse train that returns to the terminal station with a propagation time corresponding to the distance from the terminal station to each repeater. Transmission path monitoring method. (2) The repetition period of the monitoring optical pulse signal sent from the terminal station is set to be longer than the time it takes for the optical signal to travel back and forth between the repeater furthest from the terminal station and the The pulse train received at the station is extracted and monitored for each repeater at the end station, and the results are used to constantly monitor the transmission characteristics of each repeater on the transmission path or to locate a faulty repeater. A monitoring system for an optical amplification repeater transmission line according to claim 1.