JP3288859B2 - Optical WDM Network System - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength division multiplexing network system using an optical fiber ring system.

[0002]

2. Description of the Related Art As shown in FIG. 15, a conventional optical wavelength-division multiplexing network system using an optical fiber ring system has a structure as shown in FIG.
An optical fiber cable is connected in a loop between the optical input / output terminals of the central node CN to form an optical fiber ring FR, and n terminal nodes LN # 1 to LN # are provided at arbitrary positions on the optical fiber ring FR. n.

Each of the terminal nodes LN # 1 to LN # n has an optical wavelength demultiplexer DEMUX for separating optical signals of wavelengths λ1 to λn from the optical fiber ring FR, and an optical wavelength multiplexing device for multiplexing optical signals of wavelengths λ1 to λn. And an optical receiver RX for extracting and receiving an optical signal of an individually assigned wavelength from the optical wavelength demultiplexer DEMUX, and an optical transmitter for sending the optical signal of the assigned wavelength to the optical wavelength multiplexer MUX. Device TX.

[0004] The central node CN separates optical signals of wavelengths λ1 to λn sent from the terminal nodes LN # 1 to LN # n through the optical fiber ring FR by an optical wavelength separator DEMUX. After conversion into an electric signal by / E, the signal is exchanged for each node destination by the N × N exchange switch SW. Then, the signal is converted into an optical signal having a wavelength assigned to the destination node by the electric-optical converter E / O, multiplexed by the optical wavelength multiplexer MUX, and transmitted to the optical fiber ring FR.
With the above configuration, an optical signal can be transmitted from any terminal node to any terminal node.

However, in the conventional optical wavelength division multiplexing network system as described above, each terminal node has a light source having a preset wavelength, and each node needs a light source having a different wavelength. For this reason, the following problems have arisen.

First, it is difficult to control the oscillation wavelength of the laser by the current manufacturing technology of the laser diode used for the light source, so that a large number of lasers are manufactured, and the respective wavelengths are measured and required. Only lasers that match the wavelength must be selected and used.

Second, since the laser oscillation wavelength shifts due to aging and environmental fluctuations, it is necessary to perform control for stabilizing the absolute wavelength of the laser and the wavelength interval between the lasers. In this case, there is also a problem that the lasers are physically separated from each other and it is difficult to control the wavelength of light already modulated with data. Although the above problem can be solved by using a variable wavelength light source or a variable wavelength optical filter, a highly reliable one has not been realized yet.

[0008]

As described above, in the conventional optical wavelength-division multiplexing network system using the optical fiber ring system, each terminal node has a light source of a preset wavelength, and each node has a light source having a different wavelength. Need to select and use only the laser that matches the required wavelength for each terminal node. Control is required for each terminal node to stabilize the absolute laser wavelength and the wavelength interval between lasers. There is a problem that it is difficult to control the wavelength of light already modulated by data because the lasers are physically separated from each other.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is possible to reduce the number of light sources required in a terminal node and to easily control stabilization of light sources by using an optical wavelength multiplexing method using an optical fiber ring system. The purpose is to provide a network system.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a wavelength multiplexing system between optical input / output terminals of a central node.
An optical fiber that transmits light in one direction is connected in a loop to form an optical fiber ring, a plurality of terminal nodes are interposed at arbitrary positions of the optical fiber ring, and an arbitrary terminal is connected through a central node. In an optical wavelength-division multiplexing network system that performs communication between nodes,
The wavelength included in the wavelength multiplexed light includes the transmission wavelength and the reception wavelength.
A network to which the long light wavelengths are exclusively assigned
A chromatography click, the central node, and the multi-wavelength light source for generating light of a transmission wavelength assigned to each of the plurality of end nodes, multiplexed with the optical fiber light of each generated in the light source wavelength First optical wavelength multiplexing means for transmitting to a ring, optical wavelength separating means for inputting an optical signal from the optical fiber ring and separating the signals for each wavelength, optical signal of each wavelength separated by the optical wavelength separating means Each destination terminal node
A replacement means for wavelength conversion on the reception wavelength of the optical signal whose wavelength is converted, respectively the exchanging means for multiplexing a second optical wavelength multiplexing means for sending to the optical fiber ring, the plurality of terminal nodes , Of the transmission wavelength assigned to itself
The light and the optical signal of the received wavelength are transmitted through the optical fiber.
An optical wavelength separating means for separating the transmitted wavelength multiplexed light, an optical receiver for receiving an optical signal of a receiving wavelength separated by the optical wavelength separating means, and a light of a transmitting wavelength separated by the optical wavelength separating means. Is modulated by a transmission signal to generate and output an optical signal.
And an optical wavelength multiplexing means for multiplexing an optical signal output from the optical modulator with light and an optical signal not separated by the optical wavelength separating means and sending the multiplexed optical signal to the optical fiber ring. It is characterized by the following.

[0011]

In the optical wavelength division multiplexing network system having the above-described configuration, the transmission wavelength and the reception wavelength of each terminal node are divided, and all the light having the required wavelengths at each terminal node are generated on the central node side and centrally managed at one place. In this way, the light source required for each terminal node is eliminated, and the light source stabilization control is facilitated.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of an optical wavelength division multiplexing network system according to the present invention. In FIG. 1, CN is a central node, FR is an optical fiber ring, and LN # 1 to LN # n are terminal nodes.

The k-th terminal node LN # k (k is 1 to n
Are the wavelengths λ1 + λ1 ′, λ2 + λ2 ′,..., Λk + λk ′,.
An optical wavelength separator DE for separating n sets of optical signals of n + λn '
MUX and the wavelength λ from the separated optical signal of λk + λk ′
wavelength splitter WDM for separating an optical signal of wavelength k and wavelength λk '
, An optical receiver RX for receiving the separated optical signal of wavelength λk ′, an optical modulator MOD for modulating the separated light of wavelength λk according to the transmission signal, a modulated transmission optical signal and an optical wavelength separator An optical wavelength multiplexer MUX for multiplexing optical signals other than λk and λk ′ from the DEMUX and transmitting the multiplexed optical signal to the optical fiber ring FR.

On the other hand, the central node CN is an optical wavelength separator DEM that separates the optical signals of the wavelengths λ1 to λn modulated by the terminal nodes LN # 1 to LN # n from the optical fiber ring FR.
UX, an optical-electrical converter O / E for receiving the separated optical signals of wavelengths λ1 to λn and converting them into electric signals,
An N × N exchange switch SW for exchanging each electric signal for each node destination, and an electric / optical converter E / for converting the exchanged electric signals into optical signals of wavelengths λ1 ′ to λn ′ assigned to the respective destination nodes. O, and an optical wavelength multiplexer MUX1 for multiplexing the converted optical signal and sending the multiplexed optical signal to the optical fiber ring FR, and further comprising terminal nodes LN # 1 to LN
A light source λ of wavelengths λ <b> 1 to λn, which is a light source of #n, and an optical wavelength multiplexer MUX <b> 2 that multiplexes optical signals of a plurality of wavelengths of these light sources OG and sends them to the optical fiber ring FR.

As described above, the k-th terminal node LN #
k can be received at wavelength λk 'and transmitted at wavelength λk. There are several methods for assigning transmission and reception wavelengths. For example, as shown in FIG.
k and the reception wavelength λk ′ are adjacent to each other, and the transmission wavelength λk and the reception wavelength λk ′ of the same node constitute an optical wavelength demultiplexer DEMUX and an optical wavelength multiplexer MUX as shown in FIG. An FSR method in which the filter is separated by an integer multiple (l × FSR) of the free spectral range (FSR) of the filter is conceivable. Here, it is assumed that the wavelength characteristic of the filter is repeated within a certain range. An optical separator WDM is provided as another filter for separating a transmission signal and a reception signal.

Recently, an optical add / drop wavelength multiplexing / demultiplexing filter (ADM filter) has been developed in the acousto-optic technique or the optical waveguide technique. In such a four-port filter, it becomes possible to draw in or insert only light of a certain wavelength. Light of other wavelengths passes through the filter.

For example, in the case of the acousto-optic filter shown in FIG. 3, the insertion and pull-in wavelengths are determined by the acoustic drive frequency. However, to pull in multiple wavelengths simultaneously,
It is necessary to drive the filter with acoustic signals of multiple frequencies simultaneously. FIG. 4 shows the wavelength versus transmission amount characteristic between the A and B terminals.
FIG. 4A shows the wavelength vs. transmission amount characteristics between the A and D terminals.
It is shown in (b).

In the case of the waveguide type lattice (grating) filter shown in FIG. 5, the transfer characteristic is repeated in the wavelength region. The width of this repetition is called FSR.
Depending on the filter design, one or more wavelengths can be pulled into the FSR. FIG. 6A shows the wavelength vs. transmission amount characteristics between the A and B terminals, and FIG. 6B shows the wavelength vs. transmission amount characteristics between the A and D terminals.

In the above embodiment, the terminal node LN # 1
Wavelength multiplexer MUX and optical wavelength demultiplexer DEM of LN # n
By implementing UX with one ADM filter, the node configuration can be simplified. The configuration is shown in FIG. 7, and a description will be given using the k-th terminal node LN # k as an example.

In FIG. 7, an optical signal from an optical fiber ring FR is input to an ADM filter 11, and only optical signals having wavelengths λk and λk ′ are guided to an optical wavelength separator (WDM) 12. In the WDM 12, the optical signals of λk and λk 'are separated. The optical signal of λk 'is guided to an optical receiver (RX) 13 and received and output. The optical signal of λk is guided to an optical modulator (MOD) 14, modulated by a transmission signal, and then transmitted to the optical fiber ring FR via the ADM filter 11 together with optical signals of other wavelengths.

Here, when the transmission system of the network adopts the interlace allocation system, the WDM1
2 has a filter characteristic as shown in FIG.
When the SR method is adopted, the WDM 12
What is necessary is just to have a filter characteristic as shown in (b).

However, in the case of using an ADM filter as described above, the isolation between the two output terminals of the filter may be incomplete, and the transmission signal may be considerably deteriorated. In particular, when the isolation is about 30 dB or less, the continuous wave light transmitted from the central node CN is not completely drawn in at the node to which the wavelength of the light is assigned, and only a part of the continuous wave light is optical fiber. It remains on the ring. For this reason, the signal interferes with the modulated light having the same wavelength to cause signal degradation. This is called interference noise.

In order to deal with such a problem, 30
Although a filter having an isolation of dB or more may be manufactured, its realization is very difficult with the current technology. For this reason, it is necessary to consider another method for suppressing the interference noise.

A generally conceivable method is a delay method as shown in FIG. This method simply connects two ADM filters 1 and 2 in series.

For example, as shown in the figure, an optical signal of λ1 and an optical signal of another wavelength are separated by an ADM filter 1 in the first stage,
After the k optical signal is modulated by the transmission signal by the optical modulator (MOD) 14, both signals are multiplexed by the ADM filter 2 in the next stage. Further, the ADM filter 2 separates the optical signal of λk 'from the optical signal of another wavelength, receives the optical signal of λk' by the optical receiver (RX), and converts the optical signal of other wavelength into the optical fiber ring FR. To send to.

The filter characteristics of the ADM filters 1 and 2 are as shown in FIG. 10A in the case of the interlace assignment system, and FIG. 10B in the case of the FSR assignment system.
What is necessary is just to set as shown in FIG.

As another method for suppressing the interference noise, a scrambler method using a modulator having a high-speed polarization scrambling function or a phase scrambling function can be considered.

In this scrambler system, as shown in FIG. 11, before an output of an optical modulator (MOD) 14 is sent out to an optical fiber ring FR by an ADM filter 11, a polarization or phase scrambler (SCR) 15 is used. To scramble the polarization or phase so that the average degree of polarization or phase coherency is zero in time units of one bit of data. According to this method, there is an advantage that interference noise can be removed by an electric filter on the receiving side with a simple configuration.

Alternatively, a method of suppressing interference noise in the time domain can be considered. In this case, a light source that generates a multi-wavelength pulse is used as the light source of the central node CN instead of generating a multi-wavelength continuous signal. Then, at a specific terminal node, the pulse light is drawn and modulated, and then the modulated light is inserted between the pulses coming from the central node CN.

This can be realized by interposing an optical delay 16 between the optical modulator 14 and the ADM filter 11, as shown in FIG. 12 (a) or (b). FIG.
12A shows a case where the cycle of the optical pulse train is the same as the data bit cycle, and FIG. 12B shows a case where the duty is 50% or less and the optical pulse width is the same as the width of a plurality of data bits. In any case, no interference occurs because the modulation pulse is inserted between the optical pulses from the central node CN.

By the way, in order to improve the reliability of the optical communication network, there is a case where the redundancy switching is performed, but this redundancy switching can be applied to the system according to the present invention. FIG. 13 shows the configuration. 13, the same parts as those in FIG. 1 are denoted by the same reference numerals, and only different parts will be described here.

In this embodiment, the optical fiber ring FR is duplicated, and the redundant changeover switch PSW for selectively connecting the optical fiber rings FR1 and FR2 is provided at the input / output section of each node CN and LN # 1 to LN # n. It is configured. The connection method of each redundant changeover switch PSW is shown in FIG.
4 (a) to (c), there are three types.

That is, by connecting each of the redundant changeover switches PSW to each other as shown in FIG. 14A, the operation can be performed in exactly the same manner as in FIG. 1 using the optical fiber ring FR1.

When one of the optical fiber rings FR1 and FR2 is broken, the redundant changeover switches PSW at both ends of the declared location are crossed and connected as shown in FIG. The communication process can be executed as it is, avoiding the disconnection point.

Further, the optical fiber rings FR1, FR2
When both are disconnected at the same location, the redundant changeover switches PSW at both ends of the disconnected location are short-circuited between the rings FR1 and FR2 as shown in FIG. Processing can be performed.

With the redundant configuration as described above, when the optical fiber ring FR is disconnected or the node itself breaks down, the redundant changeover switches at both ends of each node are switched and set, so that the network can be switched. The communication state can be maintained, and the reliability can be improved. It should be noted that the present invention is not limited to the above embodiment, and it goes without saying that the present invention can be implemented in various modifications without departing from the scope of the present invention.

[0037]

As described in detail above, according to the present invention,
It is possible to provide an optical wavelength multiplexing network system using an optical fiber ring system, which can reduce the number of light sources required at a terminal node and can easily perform stabilization control of light sources.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a configuration of one embodiment of an optical wavelength division multiplexing network system according to the present invention.

FIGS. 2A and 2B are diagrams showing an interface assignment method and an FSR assignment method as an assignment method of transmission and reception wavelengths in the embodiment.

FIG. 3 is a diagram showing a configuration of an acousto-optic filter used as an ADM filter.

FIG. 4 is a characteristic diagram showing a filter characteristic of FIG. 3;

FIG. 5 is a diagram illustrating a configuration of a waveguide lattice filter used as an ADM filter.

FIG. 6 is a characteristic diagram showing a filter characteristic of FIG. 5;

FIG. 7 is a block circuit diagram showing a configuration of a terminal node using the ADM filter in the embodiment.

8A and 8B are characteristic diagrams showing filter characteristics given to the WDM having the terminal node configuration of FIG. 7 in the case of the interface assignment method and FIG. 8B, respectively, in the case of the FSR assignment method.

FIG. 9 is a block circuit diagram showing a configuration of a terminal node using the ADM filter to eliminate interference noise in the embodiment.

10A and 10B are characteristic diagrams showing filter characteristics given to each ADM filter having the terminal node configuration of FIG. 9 in the case of the interface assignment method and FIG. 10B, respectively, in the case of the FSR assignment method.

FIG. 11 is a block circuit diagram showing a configuration of a terminal node when a polarization or phase scrambler is used to eliminate interference noise in the embodiment.

FIG. 12 shows a configuration in a case where a transmission optical signal is pulsed as another method for eliminating interference noise in the embodiment, and (a) shows a case where the period of an optical pulse train is the same as the data bit period. In this case, (b) is a duty of 50% or less,
FIG. 4 is a block circuit diagram illustrating a case where an optical pulse width is the same as a width of a plurality of data bits.

FIG. 13 is a block circuit diagram showing a configuration when redundancy switching is applied as another embodiment according to the present invention.

FIG. 14 is a diagram illustrating a connection method of a redundant changeover switch used for each node in FIG. 13;

FIG. 15 is a block circuit diagram showing a configuration of a conventional optical wavelength division multiplexing network system.

[Explanation of symbols]

CN: Central node, FR, FR1, FR2: Optical fiber ring, LN # 1 to LN # n: Terminal node, DEMUX
... optical wavelength separator, WDM ... optical wavelength separator, RX ... optical receiver, TX ... optical transmitter, MOD ... optical modulator, MUX, MU
X1, MUX2: optical wavelength multiplexer, O / E: optical-electrical converter, SW: N × N exchange switch, E / O: electric / optical converter, OG: multi-wavelength light source, PSW: redundant changeover switch,
1, 2, 11 ... ADM filter, 12 ... optical wavelength separator,
13: optical receiver, 14: optical modulator, 15: SCR (polarization or phase scrambler), 16: optical delay unit.

Continuation of the front page (56) References JP-A-4-213941 (JP, A) JP-A-58-105643 (JP, A) JP-A-4-336829 (JP, A) JP-A-49-120510 (JP, A) JP-A-6-317770 (JP, A) JP-A-2-36621 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 H04J 1/00 G02F 1/00

Claims (7)

(57) [Claims] 1. A wavelength division multiplexing device between optical input / output terminals of a central node.
An optical fiber that transmits light in one direction is connected in a loop to form an optical fiber ring, a plurality of terminal nodes are interposed at arbitrary positions of the optical fiber ring, and an arbitrary terminal is connected through a central node. In an optical wavelength division multiplexing network system that performs communication between nodes, the transmission wavelength and the reception wavelength at each terminal node are
The wavelengths of the wavelength light included in the wavelength multiplexed light are exclusively
A central node , wherein the central node includes: a multi-wavelength light source that generates light of a transmission wavelength allocated to each of the plurality of terminal nodes; and a light that multiplexes light of each wavelength generated by the light source. A first optical wavelength multiplexing means for sending out to the fiber ring; an optical wavelength separating means for inputting an optical signal from the optical fiber ring and separating for each wavelength; and a light of each wavelength separated by the optical wavelength separating means. signal, and exchange means for wavelength conversion to the reception wavelength of the destination terminal node, respectively, and a second optical wavelength multiplexing means for transmitting an optical signal whose wavelength is converted, respectively in this exchange means in the optical fiber ring multiplexes The plurality of terminal nodes, the optical signal of the transmission wavelength and the optical signal of the reception wavelength allocated to itself
From the wavelength multiplexed light transmitted through the optical fiber
An optical wavelength demultiplexing means for separating a light receiver for receiving the optical signal of the separated received wavelength the light wavelength separating unit modulates the light of the light wavelength separating means separate the transmission wavelength by transmission signal An optical modulator that generates and outputs an optical signal; and an optical wavelength multiplexing unit that multiplexes an optical signal output from the optical modulator with light and an optical signal that are not separated by the optical wavelength separating unit and sends the multiplexed optical signal to the optical fiber ring. An optical wavelength-division multiplexing network system using an optical fiber ring system, comprising: 2. The central node further comprises pulsing means for pulsing light of a transmission wavelength of each terminal node generated by the multi-wavelength light source at a predetermined period, wherein the plurality of terminal nodes each include 2. The optical device according to claim 1, further comprising a delay unit that delays the optical pulse modulated by the modulator, sends the delayed optical pulse to the optical wavelength multiplexing unit, and multiplexes the optical pulse from the central node. WDM network system. 3. The plurality of terminal nodes each include a scrambler for scrambling at least one of polarization and phase of the light modulated by the optical modulator and transmitting the scrambled light to the optical wavelength multiplexing means. 2. The optical wavelength division multiplexing network system according to claim 1, wherein: 4. The optical wavelength division multiplexing network system according to claim 3, wherein when the scrambling means scrambles the polarization, the average degree of polarization becomes zero in the bit time. 5. The optical wavelength-division multiplexing network system according to claim 3, wherein when the scrambling means performs phase scrambling, phase coherency becomes zero at a bit time. 6. A wavelength multiplexing device between optical input / output terminals of a central node.
An optical fiber for transmitting light in one direction is connected in a loop to form an optical fiber ring, and the wavelength multiplex as a transmission wavelength and a reception wavelength is provided at an arbitrary position of the optical fiber ring.
Wavelengths of light included in heavy light are exclusively assigned
The central node used in an optical wavelength division multiplexing network system for performing communication between arbitrary terminal nodes via a central node with a plurality of terminal nodes interposed therebetween, wherein the central node is assigned to each of the plurality of terminal nodes. A multi-wavelength light source that generates light of a given transmission wavelength, first optical wavelength multiplexing means for multiplexing light of each wavelength generated by the light source and sending the multiplexed light to the optical fiber ring, an optical wavelength demultiplexing means for separating each wavelength to input optical signals, an exchange means for converting the wavelength of optical signals of respective wavelengths separated by the light wavelength separating means to receive the wavelength of the destination terminal node respectively, this exchange A second optical wavelength multiplexing means for multiplexing the optical signals, each of which has been wavelength-converted by the means, and transmitting the multiplexed optical signal to the optical fiber ring. 7. A wavelength multiplexing device between optical input / output terminals of a central node.
An optical fiber for transmitting light in one direction is connected in a loop to form an optical fiber ring, and the wavelength multiplex as a transmission wavelength and a reception wavelength is provided at an arbitrary position of the optical fiber ring.
Wavelengths of light included in heavy light are exclusively assigned
Interposed a plurality of terminal nodes Terra, a said terminal node to be used in the optical wavelength multiplexing network system for performing communication between any terminal node via the central node, the transmission wavelength assigned to itself Light and the optical signal of the receiving wavelength
From the wavelength multiplexed light transmitted through the optical fiber
An optical wavelength demultiplexing means for separating, modulates an optical receiver for receiving the optical signal of the separated received wavelength optical wavelength separation means, the optical signal of the separated transmission wavelength in the light wavelength separating means by the transmission signal An optical modulator for generating and outputting an optical signal, and an optical wavelength multiplexing means for multiplexing an optical signal output from the optical modulator with light and an optical signal not separated by the optical wavelength separating means and sending the multiplexed optical signal to the optical fiber ring. A terminal node comprising: