JP2675615B2 - Optical shutdown method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical shutdown system applied to a star-bus type optical fiber transmission system using a 1 × N optical star coupler.

(Prior Art) FIG. 2 is a diagram showing a basic configuration of a star bus type optical fiber transmission system using a 1 × N optical star coupler. In FIG. 2, 1 is an optical transmitter / receiver arranged in the telephone station TEX, 2 is a 1xN optical star coupler arranged in a feeder line FDP, 3
-1 to 3-N are optical transceivers arranged in each subscriber SUB.

The 1xN optical star coupler 2 has one port on the telephone station TEX side and N ports on the subscriber SUB side, and is connected to the optical transceiver 1 of the telephone station TEX by one optical fiber 4.
Each port is an optical transmitter / receiver 3-1 to 3-1-of each subscriber SUB.
They are connected by N and N optical fibers 5-1 to 5-N, respectively. Further, the wavelength of the signal light transmitted and received is λ ₀
It is.

In such a configuration, the optical transceiver 1 of the telephone station TEX
After being propagated through the optical fiber 4, the signal light sent from is incident on the optical star coupler 2 and is branched into N. The respective N-branched signal lights are optical fibers 5-1 to 5-N.
Optical transmitter / receiver 3 on the subscriber SUB side
It is received by -1 to 3-N.

On the other hand, the signal light transmitted from the optical transceivers 3-1 to 3-N of the subscriber SUB is transmitted through the route opposite to the above. That is, after propagating through each of the optical fibers 5-1 to 5-N, they are incident on the optical star coupler 2 and merged. The combined signal lights propagate through the optical fiber 4 and are received by the optical transceiver 1 of the telephone station TEX. At this time, for example, a time division multiple access (TDMA) system is applied so that the combined signal lights do not collide with each other during propagation through the optical fiber 4.

In this way, the star bus type optical fiber transmission system using the optical star coupler transmits the same signal light to a plurality of subscriber SUs.
Since it can be distributed to B simultaneously, it is suitable for broadcast type optical communication networks such as CATV.

However, an unavoidable problem in this configuration is how to disconnect the subscriber SUB that is in breach of contract from the network, and how to disconnect the abnormal subscriber whose TDMA control is disabled.

 Next, these problems will be described.

First, let us consider the problem of, for example, CATV. In CATV, the same video is played to each subscriber SUB, but in this, pay-per-view (PP
There is a paid service called V). This service is
Only subscribers can receive it.

Specifically, the terminal adapter installed in the subscriber,
It is equipped with a so-called cryptanalysis circuit, and only the cryptanalysis circuit of the contracted subscriber can operate under the control of the telephone station TEX and receive the PPV service.
However, it is also conceivable that an uncontracted subscriber may make some modifications to the terminal adapter to activate the decryption circuit without contracting. Therefore, in this case, it is necessary to terminate the service for this subscriber.

Next, the problem of will be described. As described above, TDMA is one method of sharing one channel (for example, the optical fiber 4) among a plurality of signal lights while avoiding collision.

Specifically, each signal source or each subscriber is assigned a certain fixed time, and the signal light is transmitted to the channel only for the determined time. This operation is periodically performed between the signal lights. In this case, if an abnormality occurs in one signal source and the transmission timing of that signal is deviated,
Communication by other signal sources will also be lost. Therefore, in this case, it is necessary to stop and disconnect the service only to the subscriber in which the abnormality has occurred.

A good solution to these problems is to use an optical switch for turning on / off the signal light in the configuration of FIG.
Insert into each of the optical fibers 5-1 to 5-N on the SUB side,
The so-called optical shutdown method is adopted.

Conventionally, as optical switches applicable to this optical shutdown method, there have been optoelectric converter + electronic switch + electrooptical converter, mechanical optical switch, electrooptical optical switch, semiconductor optical switch, and the like.

(Problems to be Solved by the Invention) However, in each of the above optical switches, there is a drawback in that it is necessary to dispose the feeding circuit in the middle of the transmission path, and moreover, the coupling loss with the optical fiber forming the transmission path is large. Furthermore, because it has polarization dependence, a special circuit for maintaining polarization is required, which leads to an increase in the number of parts, and miniaturization is difficult, and high-density mounting and cost reduction are essential conditions. The subscriber system has a problem that it is not suitable.

The present invention has been made in view of such circumstances,
An object of the present invention is to provide an optical shutdown method capable of turning on / off a signal light with a small size and a simple structure capable of realizing high-density mounting, and further reducing the system cost of an optical fiber transmission system. is there.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, an optical star coupler having one port on one side and N on the other side (N = 2, 3, ...) Is used. In an optical shutdown system of a star-bus type optical fiber transmission system, in each transmission system of the other port side, a rare earth element-doped optical fiber amplifier whose gain changes according to the incident pumping light intensity is inserted, The pumping light intensity for each rare earth element-doped optical fiber amplifier is controlled individually.

(Operation) According to the present invention, the signal light propagated through the optical fiber transmission line and subjected to a certain attenuation action as it propagates through this optical fiber is transmitted to one port on one side of the optical star coupler. It is incident and is branched into N here. Here, the signal light undergoes optical branch loss. Next, each of the N branched signal lights is
The light is emitted from each of the N ports on the other side and is incident on the rare earth element-doped optical fiber amplifier.

At this time, when the pumping light is incident on the rare earth element-doped optical fiber amplifier with a predetermined intensity, the pumping light pumps the rare earth element doped in the optical fiber while propagating through the rare earth element-doped optical fiber amplifier. Along with this, the signal light is amplified with a predetermined gain, and the lowered intensity is recovered.

In this way, each signal light subjected to the amplification action is propagated through the N optical fiber transmission lines in the next stage after being emitted from the rare earth element-doped optical fiber amplifier.

On the other hand, the signal light propagated through the N optical fiber transmission lines is transmitted through a route opposite to the above, merged by the optical star coupler, and then propagated through one optical fiber transmission line.

Here, for example, in the case where some abnormality occurs in the subscribers of the transmission destinations of the N optical fiber transmission lines and the communication to this abnormal subscriber must be stopped and the system must be disconnected from the system, For example, the injection of the pumping light into the rare earth element-doped optical fiber amplifier is stopped. As a result, the signal light for the abnormal subscriber branched by the optical star coupler is absorbed by the optical fiber and attenuated, and does not reach the subscriber.

(Embodiment) FIG. 1 is a configuration diagram showing a first embodiment of an optical fiber transmission system adopting an optical shutdown system according to the present invention, and the same components as those of FIG. 2 showing a basic configuration are the same. It is represented by a sign. That is, TEX is a telephone station, FDP is a feeder point, SUB
Is a subscriber, 1 is an optical transmitter / receiver installed in the telephone station TEX, 2
1xN optical star coupler, 3-1 ~
3-N is an optical transmitter / receiver arranged in each subscriber SUB, 4 is a port on the telephone station TEX side of the optical star coupler 2 and a telephone station T
Optical fiber connected between the optical transceivers 1 of EX, 5-1 to 5
-N is a feeder FDP (N ports on the subscriber SUB side of the optical star coupler 2) and the optical transceivers 3-1 to 3-1 of each subscriber SUB.
An optical fiber connected to 3-N. The wavelength λ ₀ of the transmitted and received signal light is 1.53 to 1.56 μm.

Reference numerals 6-1 to 6-N denote excitation light sources arranged in the telephone station TEX, which are semiconductor lasers having an oscillation wavelength of 1.48 μm (λ ₁ ), for example, and emit excitation light that is unmodulated light (DC light) to a predetermined intensity. Emit at.

7-1 to 7-N are optical fibers for excitation light, and the excitation light emitted from each excitation light source 6-1 to 6-N is propagated.

Reference numerals 8-1 to 8-N denote optical multiplexers, which are respectively connected to N respective ports on the subscriber SUB side of the optical star coupler 2 and are branched into N by the optical star coupler 2 and respective pump light sources. 6
The excitation lights of -1 to 6-N are combined.

Reference numerals 9-1 to 9-N are rare earth element-doped optical fiber amplifiers (hereinafter referred to as optical fiber amplifiers), which are configured by adding a rare earth element such as erbium (hereinafter referred to as Er) to an optical fiber at a predetermined concentration. ing. These optical fiber amplifiers 9-1 to 9-N include optical multiplexers 8-1 to 8-
It is connected to the output side of the N multiplexed light, and when the pumping light is incident with a predetermined intensity, it amplifies the signal light with a predetermined gain (up to 25 dB), and its length is several meters to several tens of meters. Is set.

The wavelength with a gain, that is, the wavelength range in which the optical fiber amplifiers 9-1 to 9-N act as an ON / OFF optical switch, is the wavelength λ of the signal light when the added rare earth element is Er.
₀ is 1.53 to 1.56 μm (wavelength λ _{1 of} excitation light is 1.48 μm
m) (Reference: K.Hagimoto.et.al. “A 212 km
NON-REPEATED TRANSMISSION EXPERIMENT AT 1.8Gb / s
USING LD PUMPED Er ³⁺ −DOPED FIBER AMPLIFIERS IN AN
INDIRECT-DETECTION REPEATER SYSTEM ", OFC′89, Post
See Deadline Paper.PD15-1).

Reference numerals 10-1 to 10-N are pumping light removing filters, which are connected to the input / output ends of the optical fiber amplifiers 9-1 to 9-N on the subscriber SUB side. Cut off.

Next, the operation of the above configuration will be described. Note that only the communication operation of the signal destination from the telephone station TEX to the subscriber SUB will be described here.

The signal light transmitted from the optical transceiver 1 of the telephone station TEX is
It is propagated through the optical fiber 4. At this time, as the signal light propagates through the optical fiber 4, it undergoes a certain attenuation effect and enters the optical star coupler 2, where it is branched into N. Here, the signal light undergoes optical branch loss. Next, the respective N-branched signal lights are incident on the optical multiplexers 8-1 to 8-N.

At this time, the excitation light sources 6-1 to 6-1 arranged in the telephone station TEX
When the excitation light is emitted with a predetermined intensity by the 6-N, the excitation light propagates through the optical fibers 7-1 to 7-N,
The light is incident on the optical multiplexers 8-1 to 8-N. As a result, in the optical multiplexers 8-1 to 8-N, the signal light and the pump light are multiplexed, and the respective combined lights are incident on the optical fiber amplifiers 9-1 to 9-N, respectively. Of the combined lights incident on the optical fiber amplifiers 9-1 to 9-N, Er is excited by the excitation light,
Along with this, the signal light is amplified with a predetermined gain, and the intensity lowered during propagation through the optical fiber 4 and the optical branch loss by the optical star coupler 2 are compensated.

In this way, the signal light and the pump light that have been amplified are
Next, the light enters the filters 10-1 to 10-N, the signal light is transmitted as it is, and the excitation light is blocked. As a result, only the signal light is propagated through the respective optical fibers 5-1 to 5-N and received by the respective optical transceivers 3-1 to 3-N on the subscriber SUB side.

On the other hand, the signal light transmitted from the optical transceivers 3-1 to 3-N of the subscriber SUB is transmitted through the route opposite to the above. At this time, for example, the TDMA (time division multiple access) method is applied to the combined signal lights so that they do not collide with each other during propagation through the optical fiber 4.

Here, for example, the subscriber SUB including the optical transceiver 3-1
If any abnormality occurs in the system and the communication to the abnormal subscriber is stopped and the system needs to be disconnected from the system, the emission of the excitation light by the excitation light source 6-1 is stopped. As a result, the pumping light is not combined with the signal light for the optical transmitter / receiver 3-1 branched by the optical star coupler 2, and the signal light is absorbed and attenuated by the optical fiber amplifier 9-1. Do not reach

In this way, the optical fiber amplifiers 9-1 to 9-N function as ON / OFF optical switches by turning on / off the pumping light incident state on the optical fiber amplifiers 9-1 to 9-N. The signal light for communication is turned on / off.

As described above, according to the first embodiment, in the optical fiber transmission system using the 1xN optical star coupler 2, the signal is transmitted to the N port sides of the optical star coupler 2 according to the incident state of the pumping light. Since the Er-doped optical fiber amplifiers 9-1 to 9-N for turning on / off the light are connected, the optical fiber transmission line loses the intensity due to the optical loss and the optical star coupler 2 causes the optical branch loss (10LOG (N)). Can be compensated for, and the noise characteristics are good, so that good optical communication can be realized.
Furthermore, since the Er-doped optical fiber amplifiers 9-1 to 9-N can be set to the same structural parameters as the transmission line optical fiber, the coupling loss with the transmission line optical fiber can be reduced. Furthermore, since there is no polarization dependence, a special optical circuit for maintaining polarization is unnecessary, and since it can be used with a short optical fiber length, the signal light can be turned on / off with a simple configuration.
An optical fiber transmission system that can be turned off can be realized.

In the first embodiment, Er (erbium) is used as an example of the rare earth element added to the optical fiber, but the present invention is not limited to this, and an optical fiber amplifier added with another rare earth element is used. However, it goes without saying that the same effect as described above can be obtained. In this case, the wavelength of the excitation light is appropriately selected according to the rare earth element to be added.

Further, as a multiplexing means for multiplexing the signal light and the pumping light,
Of course, an optical coupler may be used instead of the optical light wave devices 8-1 to 8-N.

FIG. 3 is a configuration diagram showing a second embodiment of an optical fiber transmission system adopting the optical shutdown system according to the present invention. The difference between the second embodiment and the first embodiment is that
In the first embodiment, the signal light is propagated through the optical fiber 4,
After branching into N by the optical star coupler 2, the optical fiber 7
The pumping lights propagated through -1 to 7-N are multiplexed by the optical multiplexers 8-1 to 8-N arranged at the feeder FDP and supplied to the optical fiber amplifiers 9-1 to 9-N. In contrast to the configuration described above, the configuration is as follows.

That is, in the second embodiment, the optical wavelength division multiplexing system is adopted, and the pumping lights 6a-1 to 6a-N have different oscillation wavelengths (λ ₁ ≠ λ ₂ ≠, ..., ≠) in the 1.48 μm band. λ _N ) is configured to emit excitation light, and an optical multiplexer
By arranging 8a in the telephone station TEX, the pump light and the signal light from the optical transmitter / receiver 1 are combined by the optical multiplexer 8a, and then the combined light is propagated through the optical fiber 4 and further the optical star coupler. 2 N ports and each optical fiber amplifier 9
Filters for removing unnecessary excitation light that block unnecessary excitation light between the input / output end faces of the optical star couplers 2 side of -1 to 9-N
11-1 to 11-N (for example, the filter 11-1 transmits the excitation light of the wavelength λ ₁ and blocks the excitation light of other wavelengths).

With such a configuration, in addition to the effect of the first embodiment, the optical fibers connecting the telephone station TEX and the optical star coupler 2 can be integrated into one, and the cost of the optical fiber transmission system can be reduced. Can be reduced.

(Effects of the Invention) As described above, according to the present invention, the N-side ports of the optical star coupler in which the number of one port is 1 and the number of the other port is N (N = 2, 3, ...). A rare earth element-doped optical fiber amplifier whose gain changes according to the incident pumping light intensity is inserted into each transmission system, and the pumping light intensity for each rare earth element-doped optical fiber amplifier is controlled individually. Therefore, it is possible to compensate for the decrease in strength due to the optical loss in the optical fiber transmission line and the optical branch loss due to the optical star coupler, and since the noise characteristics are good, good optical communication can be realized.

Furthermore, since the rare earth element-doped optical fiber amplifier can be set to the same structural parameters as the transmission line optical fiber, the coupling loss with the transmission line optical fiber can be reduced. Furthermore, since there is no polarization dependence, no special optical circuit for maintaining polarization is required, and since it can be used with a short optical fiber length, it is possible to turn on / off the signal light with a compact and simple structure. Moreover, there is an advantage that it is possible to provide an optical shutdown method that can reduce the cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of an optical fiber transmission system adopting an optical shutdown system according to the present invention, and FIG. 2 is a star bus type optical fiber transmission system using a 1 × N optical star coupler. FIG. 3 is a diagram showing a basic configuration, and FIG. 3 is a configuration diagram showing a second embodiment of an optical fiber transmission system adopting the optical shutdown system according to the present invention. In the figure, 1 ... Telephone station TEX-side optical transceiver, 2 ... Optical star coupler, 3-1 to 3-N ... Subscriber SUB-side optical transceiver,
4,5-1 to 5-N ... Optical fiber for transmission line, 6-1 to 6
-N, 6a-1 to 6a-N ... Excitation light source, 7-1 to 7-N ...
Optical fiber for pumping light, 8-1 to 8-N, 8a ... Optical multiplexer,
9-1 to 9-N ... Er (rare earth element) -doped optical fiber amplifier, 10-1 to 10-N ... Pump light removal filter, 11-
1-11-N ... Filter for unnecessary excitation light.

Claims (1)

(57) [Claims] 1. The number of ports on one side is 1, and the number of ports on the other side is N.
A star using an optical star coupler with (N = 2,3, ...)
In an optical shutdown method of a bus type optical fiber transmission system, a rare earth element-doped optical fiber amplifier whose gain changes according to the incident pumping light intensity is inserted into each transmission system on the side of the other port. An optical shutdown method characterized by individually controlling the pumping light intensity for the element-doped optical fiber amplifier.