JPS60182827A - Optical loop transmission system - Google Patents

Abstract

PURPOSE:To simplify the circuit by bringing an output of a photocoupler of an intermediate relay station of a ring form optical fiber line to a low level received by an adjacent relay station only and increasing the output to a level reaching an adjacent next relay station with skipping at fault. CONSTITUTION:Plural relay stations are provided at the midpoint of a line where an optical fiber 40 is formed in a ring. Each relay station comprises a photocoupler 30 including a half mirror 31, an optical signal from the upper stream is reflected on the half mirror 31, photoelectrically converted (32) and enters a processing circuit 34, where the signal is subjected to processing, the result is electrooptically converted (33), enters the half mirror 31 of the coupler 30 and is transmitted to the down stream. The output level is kept to a level to be received by the next relay station only. If any of the relay stations is faulty, the optical signal does not circulate the loop, an output of the relay station of the upper stream of a faulty relay station is increased and the faulty relay station is skipped. Thus, no optical switch is required and the system with high reliability is constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background and Objectives of the Invention] The present invention relates to a loop transmission system using optical fibers.

FIG. 1 shows an example of the configuration of a conventionally known loop transmission system, where 1o is an optical fiber and constitutes a loop-shaped transmission line.

Reference numeral 11 denotes a plurality of node stations arranged at predetermined positions on this optical fiber transmission line, and signals circulate within this transmission line.

The node station 11 controls the exchange of signals with a computer or data terminal 12.

That is, one computer or data terminal, e.g. 12a and another computer or data terminal 12b.
When transmitting and receiving signals between the node station 11a and the computer or data terminal 12a,
The node station 11b receives a signal and sends it to the optical fiber transmission line 10, and upon receiving the signal, the node station 11b sends the signal to a computer or data terminal 12b.

By the way, in this system, all data from computers or terminals passes through a common optical fiber transmission line, and is therefore multiplexed in an appropriate manner on the time axis on this transmission line.

Furthermore, optical fiber transmission lines are generally duplicated to ensure reliability.

Next, FIG. 2 shows the configuration of a conventional node station.

The signal coming in from the optical fiber 20a is sent to the optical receiver 21.
The signal is returned to an electrical signal and enters the processing circuit 23.

On the other hand, the signal output from the processing circuit 23 is converted into light by the optical transmitter 22 and output again to the optical fiber transmission line 20b.

Reference numeral 24 denotes a bypass optical switch, which is provided to bypass this node station when the power to this node station is cut off.

In the conventional loop transmission system described above, all transmitted signals are once converted back to electrical signals at the node station and then optically transmitted again. It was necessary to prepare a bypass using an optical switch in case of an emergency.

However, this bypass optical switch had a complicated structure and configuration, was not reliable enough, and was expensive.

An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a highly reliable loop transmission system without using a bypass optical switch.

[Summary of the Invention] In other words, the gist of the present invention is to provide a plurality of optical receiving couplers at predetermined positions of a loop-shaped optical fiber line, and to connect a processing circuit of a node station via the couplers. However, in a loop transmission system that communicates with each other, the minimum light receiving level of the optical receiving circuit of each node station is set to a predetermined value, and when a node station transmits a signal, it always The signal level is set so that only the node station receives an optical signal higher than the minimum light reception level, and the signal is relayed to adjacent node stations one after another.If a node station fails, the transmitting node The station sequentially issues commands to increase the transmission output of normal node stations adjacent to the failed node station, skipping the failed node station, and allowing the signal to reach the adjacent node station. The optical loop transmission system is characterized by:

Embodiment 1 of the Invention FIG. 3 shows an embodiment of a node station used in the present invention.

That is, about half of the energy of the signal arriving at this station from the optical fiber 35 is reflected by the half mirror 31 of the coupler 30 and enters the optical receiver 32.

The remaining energy passes through the half mirror 31 and exits to the optical fiber transmission line 36.

On the other hand, the signal that has entered this station is returned to an electrical signal by the optical receiver 32 and enters the processing circuit 34, where it is processed and then converted back to an optical signal by the optical transmitter 33.
The light is made incident on the half mirror 31 of the coupler.

The signal is reflected here and goes out into optical fiber 36.

The big advantage of this method is that the coupler is just a half mirror, so even if a power outage occurs at the node station, the optical signal can still pass through this station via optical fiber 35 → half mirror 31 → optical fiber 36. It's in the point of gaining.

Next, an embodiment of the system of the present invention is shown in FIG.

FIG. 4 simply shows the node stations shown in FIG. 3 connected in a loop through an optical fiber 4o.

However, the configuration shown in FIG. 4 does not function as a loop transmission system as it is.

Firstly, if the loss of the half mirror in the coupler 3° in Fig. 4 is ideally low, the optical signal emitted from one of the stations will go around the loop many times. There was a problem that unless this attenuation converged, other stations would not be able to send out signals.

In this case, a problem arises in that a signal emitted from a certain station is received by multiple stations almost simultaneously, resulting in duplication and confusion in reception processing.

Second, if the loss of the half mirror in the coupler is too large, there is a problem that the optical signal cannot go around the loop.

Therefore, in order to operate this system, the following measures are necessary.

That is, first, an optical signal emitted from a certain node station is transmitted to the immediately adjacent node station, but is prevented from being transmitted to the next adjacent (ie, second) node station.

If this is done, the signals emitted from a certain node station will be sequentially relayed and propagated, and will then loop back to the accident station.

For this purpose, it is sufficient to appropriately increase the loss of the coupler.

Figure 5 is a level diagram showing how the signal emitted from station ■ is attenuated, and the horizontal axis shows the distance.
The vertical axis indicates the optical signal level, and J0AC is the loss of the coupler. For simplicity, the loss in this coupler is assumed to be the same for both reflection and transmission (direct).

Further, Af means fiber loss.

The condition that the signal emitted from station ■ is transmitted to station ■, but not to station ■, is that the minimum light reception level of the station is Prm1n (with Pt as the transmission level) Pt -3AC-2/M < Prm1n < Pt
-2AC-Af is satisfied.

For example, Pt = -17dBm, Ac =6dB,
Af = 2dB (fiber loss is 4d8/I,
If the distance between stations is 500m), -39
6BH< P rmin< -31dBm, and P
It is sufficient to set ra+in=-35 dBm.

This can be easily accomplished.

In another example, P t =-17 dBm, A c
= 10dBI++.

Af=odB Toshichi 476Ba+ < P rln
< -37dBm, so p r+++in=
It is sufficient to set it to -42 dBm.

Next, we will explain what to do when one node station fails and no longer shows the same response.

This involves the following steps.

(1) When a signal is sent from a certain station' (hereinafter referred to as a transmitting station), if the signal does not return to that station after a predetermined period of time, it is determined to be a failure state J.

(2) The transmitting station sequentially issues a command to specific stations to increase their transmission level.

The station that received the command increases its transmission level and
This will allow the signal to reach stations connected to 111Ijl.

This is shown in broken lines in FIG.

(3) By doing this, signals that were previously only relayed to each adjacent station will now be relayed one at a time, making it possible to skip a faulty station and perform transmission. I can do it.

(4) The station to be powered up, that is, the station next to the faulty station, cannot be known from the transmitting station immediately after the fault, and can only be learned through trial and error.

(5) In this case, some problems may occur during this trial and error process.

In other words, as shown in Figure 6 (1), there is no problem if the station to be powered up happens to be selected the first time, but as shown in Figure 6 (2), both the adjacent ■ and the adjacent adjacent ■ When a specific normal station ■ receives a command to power up, the signal sent from it will be received by both ■ and ■, which means that ■ and ■ will send out signals at the same time. It's inconvenient. (Since the signal propagation time between stations is sufficiently short compared to the transmission data length, the signals sent simultaneously from station ■■ will overlap at downstream stations below ■.) (6) To remedy this, do the following: Must be based on one of the following.

B. Stations whose received light level is higher than the specified value do not relay signals.

When specifying a station to be powered up from the source/transmission station, the station one station ahead is instructed not to relay signals at In] time.

In this way, the signals overlap on the transmission line and T l,
It never turns.

(7) If (6) above is configured, the transmitting station will be able to determine that the station one ahead of it has failed because the signal has gone through the loop only when a particular station powers up. This is something that can be done.

[Effects of the Invention] As explained above, the system of the present invention has the following effects, and has great industrial value.

(1) A highly reliable loop transmission system can be configured without using optical switches.

(2) Reliability is high because only optical fibers and couplers, that is, passive elements are lined up on the loop transmission path.

(3) A practical system can be constructed using the current couplers with relatively large losses.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the configuration of a conventionally known loop transmission system, Fig. 2 is an explanatory diagram showing the configuration of its node station section, and Fig. 3 is the configuration of a node station using a half-mirror coupler. FIG. 4 is an explanatory diagram showing one embodiment of the system of the present invention, and FIG.
The figure is an explanatory diagram showing the signal level die V, Fig. 6 (1)
, (2) is an explanatory diagram showing the operation of the node station. 10, 20.35.36.40: Optical fiber 11:
Node station 12: Computer or data terminal 21.33: Optical transmitter 22.32 + optical receiver 23.34: Processing circuit 24: Optical switch 30
:Coupler 31:Half mirror-◇:Transmitting station ◎:Station commanded to power up ・:Failure station 1 Eye box 4 Eye u Brother 6 day view 2 Eye 5 Figure Stage 1 No. 1

Claims (1)

[Claims] (1) In a loop transmission system in which a plurality of optical receiving couplers are provided at predetermined positions on a loop-shaped optical fiber line, and processing circuits of node stations communicate with each other via the couplers. “C1 The minimum light receiving level of the optical receiving circuit of each node station is set to a predetermined value, and when a certain node station transmits a signal,
Normally, the signal level is set so that only the adjacent node station receives an optical signal higher than the minimum light reception level, and the signal is relayed to the adjacent node station one after another.If a node station fails, In this case, the transmitting node station sequentially issues commands to increase the transmission output of the normal node stations adjacent to the failed node station, skipping the failed node station, and allowing the signal to reach the adjacent node station. An optical loop transmission system characterized by: