KR20040048467A - Ring-type WDM PON system - Google Patents

Abstract

PURPOSE: A ring type WDM(Wavelength Division Multiplexing) PON(Passive Optical Network) system is provided to implement the recovery function at each node without an active equipment by implementing a centrifugal bi-direction ring structure. CONSTITUTION: A CO(Central Office) generates an optical signal having N number of different wavelengths, multiplexes it to transmit it to an RN(Remote Node) through a single optical fiber, or demultiplexes the multiplexed signal received from the RN to detect data of each subscriber unit. The RN is connected to the CO through the single optical fiber and connected to multiple subscriber units through each optical fiber. A MUX1 multiplexes and transmits multiple wavelength signals to a WDM filter(201) of an optical splitting/coupling unit of each RN, or receives an optical signal with a wavelength reflected from the WDM filter(201). A MUX2 multiplexes and transmits multiple wavelength signals to a WDM filter(202) of an optical splitting/coupling unit of each RN, or receives an optical signal with a wavelength reflected from the WDM filter(202).

Description

Ring-type WDM PON system

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system employing Wavelength Division Multiplexing (WDM), and more particularly to a ring type WDM passive optical network (PON) system having a recovery function.

The demand for bandwidth is exploding with the rise of the Internet. In order to meet this expectation, communication methods using optical fibers have been actively studied. In particular, the WDM technology has been studied as a next-generation technology because it is a technology with excellent bandwidth / performance that can efficiently and flexibly transfer large amounts of data. Here, the WDM is a method in which a central base station (CO) allocates different wavelengths to each subscriber and transmits data at the same time. Each subscriber can always transmit / receive data using the assigned wavelength. This method not only transmits a large amount of data to each subscriber, but also secures communication and improves performance.

In addition, with the recent increase in the high-speed Internet, the traffic of the Internet is rapidly increasing. In order to efficiently provide Internet traffic to subscribers, optical communication must be established. Among them, research on PON using passive optical devices has been actively conducted.

Here, PON is a method of establishing an optical subscriber network, and a method of allowing a single optical line termination (OLT) to connect several optical network units (ONUs) to a optical cable using a passive distribution optical device (Passive Distribution Optical Device). In other words, PON is a network that connects the central office (CO), a provider of services, and subscribers (subscribers), using only passive optical devices, to connect multiplexed voice, data, or video services to optical signals. It is passively transmitted to subscribers through the optical fiber and optical splitter shared by the subscribers. In particular, the conventional optical access method is a one-to-one optical fiber connection from the CO to the subscriber, whereas the PON is transmitted from one CO to a local base station (Remote Node; RN) in one optical fiber and passive optical distribution element in the RN It is divided into and transmitted to each subscriber by optical fiber. In other words, the PON is a structure in which a single optical fiber is connected to a RN installed in a neighboring area of subscribers in a CO, and an independent optical fiber is connected to each subscriber in a RN, and an initial investment cost can be reduced. The cost of optical cables can be significantly reduced compared to the installation of optical cables.

Then, the WDM PON has a structure in which a plurality of ONUs are connected to the CO through a plurality of optical links using a WDM scheme for multiplexing wavelengths by subscriber or service. That is, in CO, optical signals having different wavelengths are generated, and in RN located between CO and ONU, signals are routed and multiplexed / demultiplexed using passive optical devices such as AWG (Array Waveguide Grating). / demultiplexing).

In addition, the physical topology selected in the design of the optical network is selected and applied according to its application such as a ring type, a bus type, and a star type. In other words, the physical topology and the symmetric concept are logical topologies, which are divided into rings, buses, and stars according to the state of the physical connection between the network members and the logical connection state. Among them, the ring network has been recognized for its reliability in the backbone for a long time because it can perform recovery (terms such as self-healing and restoration) even in system switching due to natural disasters or accidents.

It is in this context that the research on the recovery function of switching over is actively performed in the system using Ethernet, which occupies most of the network equipment market recently. However, there is no recovery on basic Ethernet. Therefore, a lot of researches have recently been conducted to overcome this problem, and there are many ongoing studies. While Ethernet is low cost, which is excellent in price / performance, it is in the spotlight in the metro section or subscribers, but there is no reliable reason why Ethernet is not yet available in the important network side such as the backbone. In other words, if a failure occurs in a subscriber network, the service life cannot be used, but if a failure occurs in a backbone network, thousands to tens of thousands of users are disabled.

The initial WDM ring structure is a unidirectional structure, and at least two core fibers are required to implement a bidirectional structure. In recent research, there have been studies of single fiber bi-directional ring networks (SFBDRN), which are implemented using a new type of Bidirectional Add-Drop Module (B-ADM). CHKim et al, "Bidirectional WDM Self-Healing Ring Network based on Simple Bidirectional Add / Drop Amplifier Modules", and Y. Zhao et al, "A Novel Bidirectional Add-Drop Module for Single Fiber Bidirectional Self-Healing Wavelength Division Multiplexed Ring Networks ").

In other words, the existing recovery system uses a two-core ring structure, and if the system is switched due to the fiber switching, the path is transferred to the recovery fiber at both ends of the transfer part using an active element. Bypassing, you can recover your system from a switchover.

However, the above-described single-sided bidirectional ring network using B-ADM is complicated in structure, expensive to implement, and requires a complicated and new type of optical device.

In addition, as described above, in recent years, a system using Ethernet can be implemented at a low cost, and is eroding most of the network structure due to compatibility with existing Internet traffic. On the backbone, there is a problem that Ethernet is not adopted because reliability is not yet verified.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a single-way bidirectional ring-type WDM PON system of the same wavelength up and down having a recovery function using an optical drop / add device. .

1 is a view illustrating a structure of a general optical splitter / combiner

2 is a view showing the structure of an optical splitter / combiner according to the present invention

3 is a view showing the structure of a ring-type WDM PON system of the present invention employing the optical splitter / coupler of FIG.

Explanation of symbols for main parts of the drawings

201,201: WDM filter for optical splitter / combiner

Single-way bidirectional ring-type WDM PON system according to the present invention for achieving the above object, the first multiplexing / demultiplexer for multiplexing / demultiplexing the steady-state signal, and the second multiplexing for multiplexing / demultiplexing the recovery signal / Demultiplexer, each multiplexer / demultiplexer generates an optical signal having N different multiple wavelengths and then multiplexed and transmitted to a local base station through a single optical fiber, or multiplexed from the local base station A central base station (CO) demultiplexing to detect data of each subscriber device; And a bidirectional optical splitter / combiner corresponding to each subscriber device to form a ring-shaped distribution network, wherein the optical splitter / combiner has a signal flow in a direction opposite to each other and has a first WDM filter for branching / combining steady-state signals. And a local base station comprising a second WDM filter for branching / combining a recovery signal.

The central base station uses the first multiplexer / demultiplexer in the same way up and down with respect to the steady state signal, and the second multiplexer / demultiplexer uses the same in the uplink and downlink for the recovery signal. It is done.

Each WDM filter of the bidirectional branch / combiner transmits N optical signals of different wavelengths through the input port to branch only the optical signals of the selected wavelength to the branch port through reflection and transmit them to the corresponding subscriber device, and the optical signals of the remaining wavelengths. Is passed through and output to the output port, and the optical signal of the selected wavelength of the corresponding subscriber device reversibly input to the branch port is reflected back to the input port and is output to the central base station.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings illustrating the configuration and operation of the embodiment of the present invention, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, By the technical spirit of the present invention described above and its core configuration and operation is not limited.

In general, when constructing a transmission network using a WDM PON system, a branch / addition must be essentially performed for each node of the transmission network. Branch / coupling devices for this purpose are typically used in WDM systems for wavelength signals of specific channels. ) And drop another signal of the same wavelength ( ') Is a device used to add and separate a specific channel in a WDM system.

FIG. 1 shows a basic configuration of a 4-port branch / combination element employing a conventional WDM thin film filter. Two elements can transmit a specific band signal and reflect a specific band signal, and are basically reversible. Has operating characteristics. This principle of operation is widely used to separate or combine signals of different wavelengths up and down on a single optical fiber in the existing WDM system (that is, the reflected side can be used as Tx and the transmitted side can be used as Rx). As described above, the conventional WDM-PON system uses different wavelengths for the uplink and downlink for each channel.

FIG. 2 illustrates the structure of the branch / coupling device of the present invention in a new form using the branch / coupling device of FIG. 1 described above to perform a recovery function in a WDM PON system.

Referring to FIG. 2, the structure of a four-port branch / combiner having two WDM thin film filters is used. However, each WDM thin film filter uses the same wavelength in the uplink and downlink channels. That is, since the same wavelength is used for link per channel, only one WDM filter can be implemented. In the past, two WDMs were required because different wavelengths were used up and down as shown in FIG. 1 when linking each channel. However, in the present invention, only one WDM filter is required for the same function. Can be reduced by half.

According to the present invention, two WDM filters having the same function are provided as shown in FIG. 2, so that one WDM filter 201 is used for a clockwise channel used for steady state, and the other WDM filter 202 Used for channel (counter clockwise) used for recovery. Here, the signal direction of the WDM filter used for the steady state and the signal direction of the WDM filter used for the recovery are opposite directions.

That is, the present invention divides the branch / combination element into clockwise and counterclockwise directions according to the transmission direction of the entire WDM channel signal. At this time, if the clockwise direction is normally used in the normal state, the counterclockwise direction is used for recovery during the transfer of the fiber due to the disaster. If one side works, the other side does not work. In addition, unlike the existing application, by applying the same wavelength up and down to the up and down channels, it is used to combine / branch the up and down signals in each coupling port and branch port. That is, the same wavelength is used up and down, and is separated and coupled to the transmission / reception module for the up / down optical signal through a 1 * 2 splitter with a single optical fiber.

Looking only at the WDM filter 201 in which the WDM channel signal proceeds in a clockwise direction, a signal of a corresponding band among the optical signals of a plurality of different wavelengths input through the first input port ( ) Selectively branches to the branch port through reflection, and transmits signals in the remaining bands. Reversibly, the signal of the corresponding band input from the branch port ( ) Is reflected back toward the first input port. That is, the transmission and reception wavelength of the same band is used for each channel.

Similarly, the WDM filter 202 in which the WDM channel signal proceeds in the counterclockwise direction uses the same transmission / reception wavelength of each channel. That is, the signals of the corresponding bands among the optical signals of different wavelengths input through the second input port ) Selectively branches through the reflection to the coupling port and transmits the signal in the remaining bands. Reversibly, the signal of the corresponding band input from the combining port ( ) Is reflected back towards the second input port.

As described above, the 4-port branch / coupling element of the present invention is a system in which one WDM filter 201 is reserved for a steady state and the other WDM filter 202 is reserved for one extra channel for recovery.

Therefore, since the present invention implements the ring network as a single core and has a recovery function, the fiber construction cost is reduced by half compared to the existing ring system, and the cost of the WDM filter is reduced due to the use of the same wavelength. It is reduced by half.

3 is a structure of a bidirectional centrifugal ring WDM PON system of the present invention employing the branching / coupling device of FIG. 2 described above, and generates an optical signal having N different wavelengths and then multiplexes through a multiplexer to form a single optical fiber A central office (CO) for detecting data of each subscriber station by transmitting to a local node (RN) through a demultiplexer or by demultiplexing a signal multiplexed and received from the RN through a demultiplexer; And RN connected through a single optical fiber and connected through a plurality of subscriber devices and each optical fiber.

At this time, the CO is provided with a 1 * 2 coupler and two WDM MUX. At this time, if MUX1 is used for the steady state, MUX2 is used for recovery. That is, the MUX1 multiplexes and transmits a plurality of wavelength signals to the WDM filter 201 of the optical splitter / combiner of each RN or receives an optical signal having a wavelength reflected from the WDM filter 201. Similarly, the MUX2 multiplexes and transmits a plurality of wavelength signals to the WDM filter 202 of the optical branch / combiner of each RN, or receives an optical signal having a wavelength reflected from the WDM filter 202.

The RN is located between the CO and each subscriber device to demultiplex and route multiple optical signals from the CO to each subscriber device using passive optical devices of WDM multiplexing / demultiplexing (MUX / DEMUX). On the contrary, each WDM channel destined for the CO in each subscriber device is multiplexed and delivered to the CO.

At this time, the RN is provided by the number of subscribers to form a bidirectional ring-shaped distribution network, each RN is provided with an optical branch / coupling device as shown in FIG.

At this time, each of the RN is assigned a unique wavelength of the node, and branched only the optical signal of the wavelength assigned among the plurality of wavelengths inputted using the branching / combining element as shown in FIG. The optical signal of wavelength passes. That is, each RN communicates with CO only with an optical signal of the assigned wavelength.

In the optical fiber ring as shown in FIG. 3, the signal transmission direction is divided into a clockwise direction and a counterclockwise direction.

At this time, in the normal state, only the WDM filter 201 that transmits the signal in the clockwise direction operates, and in the recovery state, only the WDM filter 202 that transmits the signal in the counterclockwise direction operates, thereby providing a centrifugal bidirectional WDM PON system having a recovery function. Can be implemented.

The present invention basically operates a clockwise channel having a function in normal operation, and puts a counterclockwise channel in a spare state for system recovery in case of a switchover due to a disaster.

First, in the case of the downlink at the time of the steady state operation, in the CO, the signal for each channel is coupled to the single-fiber optical fiber through a 1 * 2 coupler, and the signal for each channel is transmitted to the transmission optical fiber through the WDM MUX1. Delivered.

When the transmitted signal passes through the branch / combiner of each RN, the signal of the corresponding channel is reflected by the WDM filter 201 and branched out, and this signal enters the Rx receiving end of the subscriber (or ONU) through the 3dB coupler. Send a signal.

On the contrary, in the upward direction, a signal transmitted from each channel (subscriber or ONU) is coupled to the WDM filter 201 of the branch / combiner of the corresponding RN through a 1 * 2 coupler, and the combined signal is transmitted through a transmission fiber. Is sent to. The transmitted signal is reversibly separated for each channel through the WDM MUX1 and linked to the Rx terminal through a 1 * 2 coupler. That is, the CO detects data for each channel by demultiplexing the multiplexed optical signal again.

On the other hand, in the case of a spare channel for use when switching is performed in the same process, in this case, the signal flow is made in the opposite direction to the above-mentioned steady state, and also the WDM filter 202 of the MUX2 of CO and the branch / combiner of each RN. ) Only works.

Basically, each node needs two Tx / Rx modules corresponding to the wavelength of each channel.

Such a network structure logically has a bus shape in clockwise and counterclockwise directions, respectively. Therefore, this structure can be applied to the Ethernet system as the basic structure of Ethernet. In other words, an Ethernet system having a recovery function can be implemented by employing two bus structures in Ethernet.

Thus, the ring-shaped WDM PON system of the present invention can effectively save fiber laying costs when the distances of the subscriber's locations are far apart.

In addition, in the case of the conventional centrifugal bidirectional up and down channels use different wavelengths, the up and down multiplexing / demultiplexers are required separately, but the present invention uses the same wavelength up and down, so the multiplexing / demultiplexing of CO is reversible. The same downward availability can significantly reduce the cost of implementing the system. In this case, two multiplexing / demultiplexing systems of CO in the present invention are required for use separately for steady state and recovery. For example, in the case of using only the steady state, the multiplexer / demultiplexer is required for the up and down, respectively, but only one is needed in the present invention.

That is, the conventional centrifugal bidirectional WDM filter requires two WDM filters to detect a signal at the receiving end (subscriber site). However, the present invention uses the same wavelength in both the up and down directions. Multiplexing / demultiplexing can be implemented with only one WDM device, thereby reducing the cost of multiplexing / demultiplexing in half compared to a conventional WDM system.

In addition, since the optical branch coupler provided for each RN can be used not only in the up-and-down channel, but also in both the steady state signal and the channel used for recovery, the system implementation cost can be significantly reduced.

Therefore, the present invention enables a modular module of lower cost and implements a system having high stability.

As described above, according to the single-center bidirectional ring-type WDM PON system according to the present invention, a centrifugal bidirectional ring structure having a recovery function is realized by applying a branching / combiner having the same wavelength up and down without using a complicated optical device, thereby active at each node. The recovery function can be implemented without equipment, thereby reducing the maintenance, management, maintenance, and implementation costs that are characteristic of the PON structure.

In addition, by using the same wavelength up and down for each WDM channel, since the WDM-based devices can be used reversibly, the system implementation cost can be significantly reduced compared to the conventional.

In addition, by implementing a single-sided bidirectional ring-type WDM PON system of the same wavelength up and down with a recovery function, Ethernet technology can be employed, so that low-cost network equipment can be used. In particular, the optical subscriber network as well as the Met Ethernet in the MAN section can be implemented with high reliability.

In addition, by adopting a ring structure in the metro Ethernet section where the subscribers are not located at one place, the fiber laying cost (centrifugal) can be drastically reduced, thereby reducing the inexpensive metro system and optical subscriber network (FTTH). Can be implemented.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (4)

A wavelength division multiplexing (WDM) passive optical subscriber network (PON) comprising a central base station (CO) and a local base station (RN) connected to the central base station via a single optical fiber and connected to a plurality of subscriber devices via respective optical fibers. ) In the system, A first multiplexer / demultiplexer for multiplexing / demultiplexing a steady state signal and a second multiplexer / demultiplexer for multiplexing / demultiplexing a recovery signal, each of which has N different wavelengths; A central base station (CO) for generating an optical signal having a multiplexing signal and transmitting the multiplexed signal to a local base station through a single optical fiber or demultiplexing a signal multiplexed and received from the local base station to detect data of each subscriber device; And And a bidirectional optical splitter / combiner corresponding to each subscriber device to form a ring distribution network, wherein the optical splitter / combiner has a signal flow in a direction opposite to each other and a first WDM filter for branching / coupling a steady state signal; A ring type WDM PON system, comprising: a local base station comprising a second WDM filter for branching / combining a recovery signal. The method of claim 1, wherein the central base station Ring-type WDM PON system, characterized in that for using the first multiplexer / demultiplexer in the same way up and down for the steady state signal. The method of claim 1, wherein the central base station Ring-type WDM PON system, characterized in that for using the second multiplexer / demultiplexer for the recovery signal in the same way up and down. The method of claim 1, Each WDM filter of the bidirectional branch / combiner transmits N optical signals of different wavelengths through the input port to branch only the optical signals of the selected wavelength to the branch port through reflection and transmit them to the corresponding subscriber device, and the optical signals of the remaining wavelengths. Is passed through and output to the output port, the ring-type WDM PON system characterized in that the optical signal of the selected wavelength of the subscriber station reversibly input to the branch port is reflected back to the input port and output to the central base station.