JP2003234721A - Optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the variation of a loss between nodes to a minimum when distances between nodes are different in an optical communication system for supplying an optical carrier from a master station node to respective slave station nodes. <P>SOLUTION: A remote node is provided with an optical branching means for branching a plurality of optical carriers having different wavelengths to (m) outgoing optical fibers in a prescribed branching ratio and an optical coupling means for coupling wavelength multiplexed optical signals respectively arriving from (m) incoming optical fibers in a prescribed coupling ratio, and the (m) outgoing optical fibers and the incoming optical fibers are connected to a port in which the losses of the optical branching means and the optical coupling means are reduced as the distance becomes long. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system in which an optical carrier is supplied from a multi-wavelength light source of a master station node to each slave station node, the optical carrier is modulated at each slave station node and returned to the master station node. .

[0002]

2. Description of the Related Art In recent years, with the progress of multimedia services represented by the Internet, it has become necessary to increase the transfer capacity in backbone optical communication networks. As a technique for realizing this increase in transfer capacity, a WDM system that wavelength-multiplexes and transmits a plurality of optical signals having different wavelengths in one optical fiber is in a practical stage.

By the way, a wide area communication network is generally hierarchized. For example, a wavelength division multiplexed optical signal transmitted from an access node to a higher remote node is further multiplexed and transmitted to a higher node. Such an optical communication network is configured as shown in FIG. 7, for example. The access nodes 50-1 to 50-m include light sources 51 having wavelengths λ1 ′ to λn ′, n ′ optical modulators 52 that modulate the output light from each light source, and n ′ modulated light beams. It is composed of a multiplexer 53 that multiplexes signals.

The remote node 60 has m demultiplexers 61 for demultiplexing the wavelength division multiplexed optical signals transmitted from the access nodes 50-1 to 50-m, respectively, and optical signals of the respective wavelengths as electric signals. N (= n ′ × m) optical receivers 62 to be converted, light sources 63 having wavelengths λ1 to λn, and n optical modulators that modulate the output light from each light source with an electric signal output from the optical receiver 62. It is composed of an optical modulator 64 and a multiplexer 65 for multiplexing n modulated optical signals. The light source may be directly modulated without using the optical modulator.

On the other hand, considering the ease of maintenance,
Japanese Unexamined Patent Publication (Kokai) No. 53-41104 discloses an optical communication system in which an optical carrier generated in a master station is sent to a slave station, and the slave station modulates and returns the optical carrier. Further, an example in which this is applied to a ring-shaped optical communication system is disclosed in JP-A-7-231305. The latter master station has a multi-wavelength light source, and is configured to separate, modulate and transmit optical carriers of the wavelengths respectively assigned by the plurality of slave stations.

[0006]

In the wavelength division multiplexing optical communication network shown in FIG. 7, even when an optical signal is transmitted from the access node to the center node, the remote node converts the optical signal from each access node into an electrical signal. Further, it is necessary to convert the signals into optical signals having different wavelengths and perform wavelength multiplexing for transmission.

Further, in the optical communication system for supplying the optical carrier from the multi-wavelength light source of the master station node to each slave station node, the configuration is not considered in consideration of the case where the distance between nodes and the loss are different.

According to the present invention, in an optical communication system in which an optical carrier is supplied from a multi-wavelength light source of a master station node to each slave station node, variations in loss between nodes are minimized in consideration of the case where the distances between nodes are different. It is an object of the present invention to provide an optical communication system capable of efficiently distributing and combining while suppressing the above.

[0009]

According to the invention of claim 1, a plurality of optical carriers having different wavelengths are transmitted from a remote node.
Are supplied to a plurality of m access nodes via a plurality of downstream optical fibers, the access nodes demultiplex the optical carriers of a plurality of wavelengths respectively allocated from the plurality of optical carriers, and modulate and combine the optical carriers. An optical communication system in which the generated wavelength-multiplexed optical signal is transmitted to each remote node via a plurality of m upstream optical fibers, and the wavelength-multiplexed optical signal from each access node is combined at the remote node and transmitted to an upper node. The remote node divides a plurality of optical carriers having different wavelengths into m downstream optical fibers at a predetermined branching ratio and a wavelength-multiplexed optical signal respectively arriving from the upstream optical fibers by a predetermined coupling. The optical coupling means for coupling at a ratio, and the m number of the downstream optical fibers and the upstream optical fibers, the optical branching means and the optical A configuration in which the loss of the coupling means is connected to the small port.

According to a second aspect of the present invention, a plurality of optical carriers having different wavelengths are respectively supplied from a remote node to a plurality of m access nodes via one downlink optical fiber, and each access node outputs a plurality of optical carriers. Wavelength multiplexed optical signals generated by demultiplexing optical carriers of a plurality of allocated wavelengths, respectively modulating and multiplexing, and transmitting to a remote node via one upstream optical fiber, and each access node at the remote node In the optical communication system for transmitting the wavelength-division-multiplexed optical signal from the above to the upper node, each access node branches the plurality of optical carriers having different wavelengths from one downlink optical fiber at a predetermined branching ratio and takes in the optical branching. Means and an optical coupling means for coupling each wavelength-multiplexed optical signal into one upstream optical fiber at a predetermined coupling ratio, Toki means and the optical coupling means is a configuration in which the coupling ratio of binding to the branch ratio and uplink optical fiber branched from the downstream optical fiber according to the distance from the remote node is set differently.

Further, on the downstream side from the remote node to each access node, the configuration described in claim 1 is adopted,
The upstream side from each access node to the remote node may have the configuration described in claim 2 (claim 3).

Further, on the downstream side from the remote node to each access node, the configuration described in claim 2 is adopted,
The upstream side from each access node to the remote node may have the configuration described in claim 1 (claim 4).

Further, the optical branching means has a wavelength selectivity in which the transmission wavelength is different depending on the branching output port,
The optical coupling output may have a wavelength selectivity in which the transmission wavelength differs depending on the coupling input port (claim 5).

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows a first embodiment of the optical communication system of the present invention.

In the figure, in the remote node 10, a plurality of optical carriers (multi-wavelength light having wavelengths λ1 to λn) output from the multi-wavelength light source 11 and having different wavelengths are separated by the optical branching means 12.
It is branched and sent to m optical fibers 1-1 to 1-m.
At the other end of each optical fiber, access nodes 20-1 and 20-2 are provided.
0-m are respectively connected.

Each access node demultiplexes an optical demultiplexer 21 that demultiplexes the optical carriers of a plurality of wavelengths assigned among the multi-wavelength light of wavelengths λ1 to λn, and modulates the demultiplexed optical carriers of the wavelengths. It is composed of a plurality of optical modulators 22 and an optical multiplexer 23 that multiplexes the optical signals output from the respective optical modulators. The wavelength-multiplexed optical signal output from the optical multiplexer 23 of each access node is composed of m optical fibers 2-1.
~ 2-m. The wavelengths (wavelength groups) of a plurality of optical carriers demultiplexed at each access node are assigned differently at each access node. However, if the number of wavelengths demultiplexed at each access node is 2 or more, the number of wavelengths may be different from each other.

From each access node to the optical fibers 2-1 to 2-1.
The wavelength-multiplexed optical signal transmitted via 2-m is input to the optical coupling means 13 of the remote node 10 to be coupled, and is transmitted to an upper node (for example, a center node). In addition,
Optical amplifiers may be arranged at appropriate positions of the remote node 10 and the access nodes 20-1 to 20-m shown in FIG.

Here, the feature of this embodiment is that the optical branching means 12 and the optical coupling means 13 of the remote node 10 have the same branching ratio and the same coupling ratio. That is, the ones having different losses for each branch output port of the optical branching unit 12 and each coupling input port of the optical coupling unit 13 are used. Then, the longer the distance between the optical fibers 1-1 to 2-m and the optical fibers 2-1 to 2-m, the smaller the loss, and the smaller the loss is connected to the branch output port and the coupled input port. As a result, the levels of the multi-wavelength light reaching the access nodes can be made substantially equal, and the wavelength division multiplexed optical signals from the access nodes that are combined at the remote node can be combined almost evenly.

FIG. 2 shows a configuration example of the optical branching means 12 and the optical coupling means 13. Here, a 4-port type is shown. The optical branching unit 12 and the optical coupling unit 13 are realized by a configuration in which 1 × 2 optical couplers 31 for branching (coupling) light in a ratio of 1: 1 are connected in three stages. As a result, the branch ratio (coupling ratio) of the four ports can be set to 4: 2: 1: 1.

(Second Embodiment) FIG. 3 shows a second embodiment of the optical communication system of the present invention.

In the figure, a remote node 10 uses a single optical fiber 1 for a plurality of optical carriers (multi-wavelength light having wavelengths λ1 to λn) output from a multi-wavelength light source 11 and having different wavelengths.
Send to. The access nodes 20-1 to 20-m are connected to the optical fiber 1 in parallel, and the optical branching means 24 respectively.
The multi-wavelength light is branched and taken in at a predetermined branching ratio via.

Each access node has branched wavelengths λ1 to λ1.
Of the multi-wavelength light of λn, an optical demultiplexer 21 that demultiplexes the optical carriers of a plurality of wavelengths respectively assigned, a plurality of optical modulators 22 that modulates the demultiplexed optical carriers of the wavelengths, and an optical modulation of each Optical multiplexer 23 that multiplexes the optical signals output from the optical device
Composed of. The wavelength-multiplexed optical signal output from the optical multiplexer 23 of each access node is coupled (wavelength-multiplexed) to the optical fiber 2 via the optical coupling means 25 having a predetermined coupling ratio. The wavelengths (wavelength groups) of a plurality of optical carriers demultiplexed at each access node are assigned differently at each access node. However, if the number of wavelengths demultiplexed at each access node is 2 or more, the number of wavelengths may be different from each other.

The wavelength-multiplexed optical signal transmitted from each access node via the optical fiber 2 is transmitted via the remote node 10 to an upper node (for example, a center node). Optical amplifiers may be arranged at appropriate positions of the remote node 10 and the access nodes 20-1 to 20-m shown in FIG.

Here, the feature of this embodiment is that the optical branching means 24 and the optical coupling means 25 of the access nodes 20-1 to 20-m have different branching ratios and coupling ratios. For example, the branching ratio of the optical branching means 24 of the access node 20-1 closest to the remote node 10 is a: 1, and multi-wavelength light having a power of 1 / (a + 1) is taken in. The branching ratio of the optical branching means 24 of the next access node 20-2 is b: 1, and 1 / (b +
The multi-wavelength light having the power of 1) is taken in. At this time, a> b
By setting the access nodes 20-1 and 20-2
It is possible to make the power of the multi-wavelength light to be taken into the substantially uniform. The same applies to the optical coupling means 25.

(Third Embodiment) FIG. 4 shows a third embodiment of the optical communication system of the present invention.

In the figure, in the remote node 10, a plurality of optical carriers (multi-wavelength light having wavelengths λ1 to λn) output from the multi-wavelength light source 11 and having different wavelengths are separated by the optical branching means 12.
It is branched and sent to m optical fibers 1-1 to 1-m.
At the other end of each optical fiber, access nodes 20-1 and 20-2 are provided.
0-m are respectively connected.

Each access node demultiplexes the optical carriers of a plurality of wavelengths assigned respectively among the multi-wavelength lights of wavelengths λ1 to λn, and modulates the demultiplexed optical carriers of each wavelength. It is composed of a plurality of optical modulators 22 and an optical multiplexer 23 that multiplexes the optical signals output from the respective optical modulators. The wavelength-multiplexed optical signal output from the optical multiplexer 23 of each access node is coupled (wavelength-multiplexed) to the optical fiber 2 via the optical coupling means 25 having a predetermined coupling ratio. The wavelengths (wavelength groups) of a plurality of optical carriers demultiplexed at each access node are assigned differently at each access node. However, if the number of wavelengths demultiplexed at each access node is 2 or more, the number of wavelengths may be different from each other.

The wavelength-division-multiplexed optical signal transmitted from each access node via the optical fiber 2 is transmitted via the remote node 10 to an upper node (for example, a center node). Optical amplifiers may be arranged at appropriate positions of the remote node 10 and the access nodes 20-1 to 20-m shown in FIG.

Here, the feature of this embodiment is that the optical branching means 12 of the remote node 10 are those having unequal branching ratios, and the optical coupling means 25 of the access nodes 20-1 to 20-m are used as the coupling ratio. Are sequentially different.
That is, the downstream side from the remote node to each access node has the configuration of the first embodiment, and the upstream side from the access node to the remote node has the configuration of the second embodiment. As a result, the levels of the multi-wavelength light reaching the access nodes can be made substantially equal, and the wavelength-multiplexed optical signals from the access nodes reaching the remote nodes can be made almost equal.

(Fourth Embodiment) FIG. 5 shows a fourth embodiment of the optical communication system of the present invention.

In the figure, the remote node 10 uses a single optical fiber 1 for a plurality of optical carriers (multi-wavelength light having wavelengths λ1 to λn) output from the multi-wavelength light source 11 and having different wavelengths.
Send to. The access nodes 20-1 to 20-m are connected to the optical fiber 1 in parallel, and the optical branching means 24 respectively.
The multi-wavelength light is branched and taken in at a predetermined branching ratio via.

Each access node has branched wavelengths λ1 to λ1.
Of the multi-wavelength light of λn, an optical demultiplexer 21 that demultiplexes the optical carriers of a plurality of wavelengths respectively assigned, a plurality of optical modulators 22 that modulates the demultiplexed optical carriers of the wavelengths, and an optical modulation of each Optical multiplexer 23 that multiplexes the optical signals output from the optical device
Composed of. The wavelength-multiplexed optical signal output from the optical multiplexer 23 of each access node is sent to each of m optical fibers 2-1 to 2-m. The wavelengths (wavelength groups) of a plurality of optical carriers demultiplexed at each access node are assigned differently at each access node. However, if the number of wavelengths demultiplexed at each access node is 2 or more, the number of wavelengths may be different from each other.

Optical fibers 2-1 to 2-1 from each access node
The wavelength-multiplexed optical signal transmitted via 2-m is input to the optical coupling means 13 of the remote node 10 to be coupled, and is transmitted to an upper node (for example, a center node). In addition,
Optical amplifiers may be arranged at appropriate positions of the remote node 10 and the access nodes 20-1 to 20-m shown in FIG.

Here, the feature of this embodiment is that the optical branching means 24 of the access nodes 20-1 to 20-m have different branching ratios sequentially, and the optical coupling means 13 of the remote node 10 have different coupling ratios. Use one. That is, the downstream side from the remote node to each access node has the configuration of the second embodiment, and the upstream side from the access node to the remote node has the configuration of the first embodiment. As a result, the levels of the multi-wavelength light reaching the access nodes can be made substantially equal, and the wavelength-multiplexed optical signals from the access nodes can be almost evenly combined at the remote node.

(Fifth Embodiment) Of the multi-wavelength light of wavelengths λ1 to λn output from the multi-wavelength light source 10 of the remote node 10, the access nodes 20-1, 20-2, ...
A plurality of wavelengths of multi-wavelength light assigned to 0-m are assigned to the wavelength group 1,
The wavelength group 2 is referred to as a wavelength group m.

The optical branching means 12 and 24 and the optical coupling means 13 and 25 shown in the first to fourth embodiments have no wavelength dependence. Therefore, all the multi-wavelength lights having the wavelengths λ1 to λn are input to the access nodes 20-1 to 20-m. In the present embodiment, as the optical branching units 12 and 24 and the optical coupling units 13 and 25, those having a configuration of demultiplexing or multiplexing the wavelength group assigned to each access node are used. For example, when the three-stage combination of the 1 × 2 optical coupler 31 shown in FIG. 2 is used as the optical branching means 12 of the remote node 10, each is replaced with a 1 × 2 WDM coupler having wavelength selectivity. The first stage WDM coupler demultiplexes wavelength groups 1 to 3 and wavelength group 4, the second stage WDM coupler demultiplexes wavelength groups 1 and 2 and wavelength group 3, and the third stage WDM coupler The group 1 and the wavelength group 2 are demultiplexed. Further, the optical branching means 24 of the access node 20-1 of FIG. 3 demultiplexes the wavelength group 1 and the wavelength groups 2 to m, and the optical coupling means 25 couples the wavelength group 1 and the wavelength groups 2 to m.
Use a coupler.

FIG. 6 shows an example of the structure of a WDM coupler. In the figure, the WDM coupler includes a fiber grating 41 and an optical circulator 42 that reflect only a specific wavelength group.
Composed of. For example, as a WDM coupler that demultiplexes the wavelength groups 1 to 3 and the wavelength group 4, the light of the wavelength groups 1 to 4 is transmitted through the optical circulator 42 to the fiber grating 41.
The light of the wavelength group 4 reflected by the fiber grating 41 is output via the optical circulator 42. At this time, the light of the wavelength groups 1 to 3 is transmitted to the fiber grating 4
1 is transmitted. The WDM coupler can also be configured by using a dielectric multilayer filter that transmits a specific wavelength and reflects the other wavelengths.

[0038]

As described above, the optical communication system of the present invention efficiently minimizes variations in loss between nodes even when the distance between the remote node and each access node is different. It can be distributed and combined.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an optical communication system of the present invention.

FIG. 2 is a diagram showing a configuration example of an optical branching unit 12 and an optical coupling unit 13.

FIG. 3 is a block diagram showing a second embodiment of the optical communication system of the present invention.

FIG. 4 is a block diagram showing a third embodiment of the optical communication system of the present invention.

FIG. 5 is a block diagram showing a fourth embodiment of the optical communication system of the present invention.

FIG. 6 is a diagram showing a configuration example of a WDM coupler.

FIG. 7 is a diagram showing a configuration example of a conventional wavelength division multiplexing optical communication network.

[Explanation of symbols]

1 optical fiber (down) 2 optical fiber (up) 10 remote node 11 Multi-wavelength light source 12 Optical branching means 13 Optical coupling means 20 access nodes 21 Optical demultiplexer 22 Optical modulator 23 Optical multiplexer 24 Optical branching means 25 Optical coupling means 31 1 × 2 Optical coupler 41 Grating filter 42 Optical circulator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsumi Iwatsuki             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F term (reference) 5K002 AA01 AA06 BA04 BA05 CA14                       DA02 DA04 DA09 FA01

Claims (5)

[Claims] 1. A plurality of optical carriers having different wavelengths are transmitted from a remote node via a plurality of m downstream optical fibers.
A plurality of wavelength-division-multiplexed optical signals which are respectively supplied to the respective access nodes, the optical carriers having a plurality of wavelengths respectively allocated from the plurality of optical carriers are demultiplexed at the respective access nodes, and the wavelength-division-multiplexed optical signals generated by the modulation and the multiplexing are respectively generated by a plurality of In an optical communication system that transmits to each remote node via the upstream optical fiber of the book, and combines the wavelength-multiplexed optical signals from each access node at the remote node to transmit to the upper node, the remote node is An optical branching means for branching a plurality of different optical carriers into m downstream optical fibers at a predetermined branching ratio, and an optical coupling for coupling the WDM optical signals respectively arriving from the m upstream optical fibers at a predetermined coupling ratio. Means, the m down-link optical fibers and the up-link optical fibers, the longer the distance, the more the optical branching means and the optical coupling. An optical communication system characterized in that the optical communication system is configured to be connected to a port with low loss of means. 2. A plurality of optical carriers having different wavelengths are supplied from a remote node to a plurality of m access nodes via a single downstream optical fiber, and each access node is assigned from the plurality of optical carriers. Wavelength multiplex optical signals generated by demultiplexing optical carriers of multiple wavelengths and modulating / combining them are transmitted to the remote node via one upstream optical fiber, and the wavelength multiplexing from each access node is performed at the remote node. In the optical communication system for transmitting an optical signal to an upper node, each access node branches the plurality of optical carriers having different wavelengths from the one downlink optical fiber at a predetermined branching ratio and takes in the optical branching means. And an optical coupling unit that couples the wavelength multiplexed optical signals to the one upstream optical fiber at a predetermined coupling ratio. The optical branching means and the optical coupling means of the node are configured so that a branching ratio for branching from the downstream optical fiber and a coupling ratio for coupling to the upstream optical fiber differ depending on the distance from the remote node. Optical communication system. 3. The configuration according to claim 1 for the downstream side from the remote node to each of the access nodes, and the configuration according to claim 2 for the upstream side from each of the access nodes to the remote node. An optical communication system characterized by: 4. The configuration according to claim 2 is used for the downstream side from the remote node to each of the access nodes, and the configuration according to claim 1 is for the upstream side from the access nodes to the remote node. An optical communication system characterized by: 5. The optical communication system according to any one of claims 1 to 4, wherein the optical branching unit has a wavelength selectivity with different transmission wavelengths depending on branching output ports, and the optical coupling output includes: An optical communication system having a wavelength selectivity in which a transmission wavelength is different depending on a coupling input port.