JP4668124B2 - Ring-type wavelength division multiplexing transmission system, control method thereof, and optical transmission apparatus - Google Patents

Description

  The present invention relates to a ring-type wavelength multiplex transmission system in which a plurality of optical transmission devices for branching and inserting optical signals of arbitrary wavelengths are connected in a ring shape through an optical transmission line, a control method therefor, and an optical transmission device.

  In the ring-type wavelength multiplexing transmission system, a transparent optical path using an OADM (Optical Add / Drop Multiplexer) device, that is, a system in which conversion to an electric signal within the ring is suppressed as much as possible has become the mainstream. As a switching (redundancy) method in this ring-type wavelength division multiplexing transmission system, Och occupancy switching (O-UPSR) in which an optical signal is split into two and transmitted to both clockwise and counterclockwise rings has become common ( Non-patent document 1).

  In a ring network that can have a redundant system in one system, the optical path connecting the start and end devices is transmitted both clockwise and counterclockwise, and the total transmission distance is Although it is equal to one round of the ring, there are cases where each transmission distance is extremely different. This is shown in FIG. The optical transmission devices 1 to 8 are ring-connected. Here, the optical path connecting the optical transmission apparatus 4 and the optical transmission apparatus 5 includes a clockwise path W1 and a counterclockwise path P1, but the clockwise path W1 is counterclockwise with respect to one span. The surrounding path P1 has 7 spans. In the optical transmission device 4, the optical signal is branched into two and distributed to each path, and the optical transmission device 5 receives the same optical signal from both sides and selects one of them.

FIG. 6 illustrates a configuration example of each transmission unit of the optical transmission apparatuses 1 to 8.
In the figure, the optical signal transmission units 61-1 to 61-3 convert the transmission signals into optical signals having predetermined wavelengths, respectively, and output them. The optical signal of each wavelength is bifurcated by the optical branching devices 62-1 to 62-3, and the branching / inserting unit 64 that replaces the optical signals branched by the wavelength demultiplexers 63-1, 63-2. The group transmitted to the counterclockwise path via -1 and 64-2 is input to the wavelength multiplexer 65-1, and the group transmitted to the clockwise path is input to the wavelength multiplexer 65-2. Entered. The optical signal of each wavelength input to the wavelength multiplexer 65-1 is wavelength-multiplexed with the optical signal passing through the branch / insertion unit 64-1, and is sent out to the counterclockwise path. The optical signal of each wavelength input to the wavelength multiplexer 65-2 is wavelength-multiplexed with the optical signal passing through the branching / insertion unit 64-2, and is transmitted to the clockwise path.

  In the figure, the system for receiving the optical signal branched by the branch / insertion units 64-1 and 64-2 is omitted.

By the way, conventionally, the advantage that the transmission / reception circuit can be easily configured and the intensity modulation have been emphasized by the optical amplifying relay, but a transmission method using phase modulation that is strong for long-distance transmission has attracted attention due to the improvement of the reception sensitivity. Furthermore, in high-speed transmission such as 40 Gbps, a four-value or higher multi-value transmission method, particularly a differential four-phase phase modulation method (DQPSK) is used as a modulation / demodulation method having a narrow-band optical spectrum (non-patent document). 2).
Optical Network, 2nd ed., Morgan Kaufmann Publishers, pp. 567-569, 2001 Wree et al., "RZ-DQPSK format with high spectral efficiency and high robustness towards fiber nonlinearities", Proceeding of ECOC2002, paper 9.6.6, 2002

  In a ring network, considering the distance for transmitting signals and the number of wavelength multiplexers / demultiplexers (optical filters) of the optical transmission device that passes along the way, in the case of high-speed transmission such as 40 Gbps, the clockwise rotation shown in FIG. An optical path with a shorter transmission distance (usually the active system) such as the path W1 of FIG. 5 can be transmitted, but an optical path with a longer transmission distance (usually the standby system) such as the counterclockwise path P1 is Transmission may become impossible due to signal quality degradation due to nonlinear optical effects in the optical transmission line. In such a case, there is a method in which the optical path with the longer transmission distance is divided into a plurality of low-speed optical paths for transmission, but the wavelength use efficiency is reduced, and the wavelengths with different speeds are managed together. It was cumbersome to do.

  The present invention takes into account the chirp characteristics corresponding to the lengths of the clockwise route and the counterclockwise route in a ring network, and can suppress the signal quality degradation and increase the ring length in any route. An object of the present invention is to provide a ring-type wavelength division multiplexing transmission system, a control method therefor, and an optical transmission apparatus.

According to a first aspect of the present invention, a plurality of optical transmission devices for branching / inserting an optical signal of an arbitrary wavelength are connected in a ring shape through an optical transmission line, and light is transmitted from the first optical transmission device to the second optical transmission device. In a ring-type wavelength division multiplexing transmission system in which a redundant system is configured by a clockwise path and a counterclockwise path when transmitting a signal, each of the plurality of optical transmission devices has a clock with respect to the optical transmission device that is the transmission destination of the optical signal. The chirp amount corresponding to the wavelength of the optical signal transmitted to each path is calculated according to at least one of the transmission distance of each path in the clockwise and counterclockwise directions or the number of optical transmission devices through which the optical signal passes on each path. The apparatus includes a chirp amount calculating unit and a chirp applying unit that applies a chirp corresponding to the chirp amount calculated by the chirp amount calculating unit to an optical signal transmitted to at least a path having a longer transmission distance.

According to a second aspect of the present invention, a plurality of optical transmission devices for branching / inserting an optical signal of an arbitrary wavelength are connected in a ring shape through an optical transmission line, and light is transmitted from the first optical transmission device to the second optical transmission device. In a method for controlling a ring-type wavelength division multiplexing transmission system in which a redundant system is configured by a clockwise path and a counterclockwise path when transmitting a signal, a transmission distance of each clockwise and counterclockwise path or an optical transmission device The chirp amount corresponding to the wavelength of the optical signal transmitted to each path is calculated according to at least one of the numbers , and at least according to the chirp amount calculated for the optical signal transmitted to the path with the longer transmission distance Grant chirp.

According to a third aspect of the present invention, a plurality of optical transmission devices for branching / inserting an optical signal having an arbitrary wavelength are connected in a ring shape through an optical transmission line, and light is transmitted from the first optical transmission device to the second optical transmission device. When transmitting a signal, in the optical transmission device of a ring-type wavelength division multiplexing transmission system that forms a redundant system with a clockwise path and a counterclockwise path, the transmission distance or each path of each clockwise and counterclockwise path The determination means for determining at least one of the number of optical transmission devices through which the optical signal passes above, and the transmission to each path according to at least one of the transmission distance of each path or the number of optical transmission apparatuses determined by the determination means Chirp amount calculation means for calculating the chirp amount corresponding to the wavelength of the optical signal, and at least chirp corresponding to the chirp amount calculated by the chirp amount calculation means is applied to the optical signal transmitted to the path with the longer transmission distance The And a chirp applying means.

  According to the present invention, the chirp characteristic of an optical signal can be set for each wavelength in accordance with the transmission distance and the number of devices of a start point optical transmission device and an end point optical transmission device. As a result, even if the optical signal passes through many optical transmission devices between the start point and the end point and the transmission distance becomes long, deterioration of the quality of the optical signal reaching the end point optical transmission device can be suppressed, and long distance transmission is possible. Is possible. Therefore, in a ring network, even if the transmission distance and the number of optical transmission devices are unbalanced in the clockwise route and the counterclockwise route, the optical signal quality in both directions can be made uniform. It becomes easy to arrange the optical transmission apparatus.

FIG. 1 shows a configuration example of an optical transmission device of a ring type wavelength division multiplexing transmission system of the present invention.
In the figure, optical signal transmitters 11-1 to 11-3 each convert a transmission signal to be inserted into a ring-type wavelength multiplexing transmission system into an optical signal having a predetermined wavelength and output the optical signal. The optical signals of each wavelength are bifurcated by optical splitters 12-1 to 12-3, respectively, and chirping units 13-1, 13-2, 13-3, 13-4, 13-5, 13-6, respectively. Is input. The chirp control unit 14 determines the transmission distance of the clockwise and counterclockwise paths with respect to the transmission destination optical transmission apparatus and / or the optical transmission apparatus through which the optical signal passes on each path according to the routing information of the optical signal ( The chirp amount to compensate for signal quality degradation caused by the nonlinear optical effect is calculated according to the number of optical multiplexers / demultiplexers) and the wavelength of the optical signal transmitted to each path, and the chirp amount corresponding to each chirp amount is calculated. Set in the assigning units 13-1 to 13-6. Each chirp imparting unit is configured to be able to variably set a designated chirp amount, and is composed of, for example, a phase modulator or a dispersion compensation module.

  An optical signal of each wavelength output from each of the chirp applying units 13-1 to 13-6 is replaced with an optical signal branched by the wavelength demultiplexers 15-1 and 15-2. 1 and 16-2, the group sent to the counterclockwise path is input to the wavelength multiplexer 17-1, and the group sent to the clockwise path is input to the wavelength multiplexer 17-2. Is done. The optical signal of each wavelength input to the wavelength multiplexer 17-1 is wavelength-multiplexed with the optical signal that passes through the branching / insertion unit 16-1, and is sent to the counterclockwise path. The optical signal of each wavelength input to the wavelength multiplexer 17-2 is wavelength-multiplexed with the optical signal that passes through the branching / insertion unit 16-2, and is sent to the clockwise path.

  In the figure, the system for receiving the optical signal branched by the branch / insertion units 16-1 and 16-2 is omitted.

  FIG. 2 shows an example of optical path arrangement in the ring-type wavelength division multiplexing transmission system of the present invention. Here, a case where an optical path starting from the optical transmission device 4 and ending at the optical transmission device 5 is set as an example. Note that the present invention can be applied not only to an O-UPSR that prepares a redundant system when setting an optical path, but also to a system that sets a backup optical path after a failure.

  In the figure, when the wavelength setting of the optical path connecting the optical transmission device 4 and the optical transmission device 5 is instructed, the chirp control unit 14 shown in FIG. 1 performs the topology for each opposing device of the optical transmission device 4 shown in FIG. Search the information and check the connection relationship. Then, based on the clockwise route information and the counterclockwise route information from the optical transmission device 4 to the optical transmission device 5, the optical wavelength and the chirp amount to be added are determined. In this example, in the topology table of FIG. 3, the short path (working) 4 → 5 in the clockwise direction is 53 km in one span, so the chirp amount α to be added is determined to be 0 and the corresponding chirping unit Set to. On the other hand, the counterclockwise 4 → 3 →... → 5, which is a long path (preliminary), is 275 km in 7 spans, so the chirp amount α to be added is determined to be, for example, +2.0, and the corresponding chirp imparting unit Set to.

  As described above, the optical signal chirped from the optical transmission device 4 and transmitted counterclockwise passes through the optical transmission devices 3, 2, 1, 8, 7, and 6 and is branched by the optical transmission device 5. Received. An optical signal transmitted clockwise from the optical transmission device 4 is branched and received by the optical transmission device 5. The optical transmission device 5 selectively receives one of these two optical signals, but both the chirped optical signal and the unchirped optical signal can be received by the same receiver, for example, amplitude modulation (intensity modulation) Modulation), direct detection, and differential phase modulation, differential detection. Note that the chirped optical signal is suppressed from nonlinear optical effects due to long-distance transmission and can be received well.

  In the configuration of FIG. 1, chirp imparting units 13-1 to 13-3 may be arranged in front of the optical branching units 12-1 to 12-3, respectively, so that the number of chirp imparting units is halved. In this case, the chirp amount α of each chirp imparting unit is set according to the longer path. Therefore, more than necessary (or unnecessary) chirp is set for the short path, but the influence is small because the path is short.

  FIG. 4 shows the relationship between the number of optical filters through which an optical signal passes and signal quality degradation. The optical filter includes a wavelength demultiplexer for demultiplexing into an optical signal of each wavelength, an optical signal to pass through, and an optical signal to be inserted in order to select an optical signal branched from the wavelength multiplexed optical signal in each optical transmission device. These are wavelength multiplexers for multiplexing, and two are arranged for each optical transmission device. Here, the transmission path between the optical filters is connected by a 40 km dispersion-shifted fiber, and the modulation system is the DQPSK system. The amount of chirp added to the transmitted optical signal is indicated by a chirp parameter α.

  In this example, assuming that a penalty of 1 dB can be allowed, if no chirp is given (α = 0), it can pass through 16 optical filters, but if chirp is given and α = 2. 18 optical filters can be passed. Therefore, one optical transmission device can be added, and the ring length can be increased by 40 km.

The figure which shows embodiment of the optical transmission apparatus of the ring-type wavelength division multiplexing transmission system of this invention. The figure which shows the example of an optical path arrangement | positioning of the ring-type wavelength division multiplexing transmission system of this invention. FIG. 6 is a diagram showing an example of topology information for determining the chirp amount set in the optical transmission device 4; The figure which shows the relationship between the number of the optical filters which an optical signal passes, and signal quality degradation. The figure which shows the example of optical path arrangement | positioning of O-UPSR switching. The figure which shows the structural example of the optical transmission apparatus of the conventional ring-type wavelength division multiplexing transmission system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1-8 Optical transmission apparatus 11 Optical signal transmission part 12 Optical branching device 13 Chirp imparting part 14 Chirp control part 15 Wavelength demultiplexer 16 Branching / insertion part 17 Wavelength multiplexer 61 Optical signal transmission part 62 Optical branching unit 63 Wavelength division Wave multiplexer 64 Branch / insertion unit 65 Wavelength multiplexer

Claims (3)

When transmitting optical signals from the first optical transmission device to the second optical transmission device by connecting a plurality of optical transmission devices for branching / inserting an optical signal of an arbitrary wavelength in a ring shape through an optical transmission line In a ring-type wavelength multiplex transmission system that forms a redundant system by a clockwise route and a counterclockwise route,
Said plurality of optical transmission devices, the number of each optical transmission device transmission distance or the optical signal on each path of the clockwise and the counterclockwise each path for the optical transmission apparatus of the transmission destination of the optical signal passes the A chirp amount calculating means for calculating a chirp amount corresponding to the wavelength of an optical signal transmitted to each path according to at least one of the above, and the chirp amount calculating means for an optical signal transmitted to a path having a longer transmission distance. ring type wavelength division multiplexing transmission system, characterized in that a configuration in which a chirp applying means for applying a chirp corresponding to the calculated chirp amount in. When transmitting optical signals from the first optical transmission device to the second optical transmission device by connecting a plurality of optical transmission devices for branching / inserting an optical signal of an arbitrary wavelength in a ring shape through an optical transmission line In a ring-type wavelength multiplex transmission system that forms a redundant system by a clockwise route and a counterclockwise route,
The chirp amount corresponding to the wavelength of the optical signal transmitted to each path is calculated according to at least one of the transmission distance or the number of optical transmission devices in each of the clockwise and counterclockwise paths, and at least the transmission distance is long. A control method for a ring-type wavelength division multiplexing transmission system, wherein a chirp corresponding to the calculated chirp amount is added to an optical signal transmitted to the other path. When transmitting optical signals from the first optical transmission device to the second optical transmission device by connecting a plurality of optical transmission devices for branching / inserting an optical signal of an arbitrary wavelength in a ring shape through an optical transmission line In the optical transmission device of the ring-type wavelength division multiplexing transmission system that forms a redundant system by a clockwise route and a counterclockwise route,
A determination means for determining at least one of a transmission distance of each of the clockwise and counterclockwise paths or the number of optical transmission devices through which the optical signal passes on each path;
A chirp amount calculating means for calculating a chirp amount corresponding to the wavelength of the optical signal transmitted to each path according to at least one of the transmission distance or the number of optical transmission devices of each path determined by the determining means;
An optical transmission apparatus comprising: a chirp applying unit that applies a chirp according to the chirp amount calculated by the chirp amount calculating unit to an optical signal transmitted to at least a path having a longer transmission distance.

Images