KR20080092897A - Reconfigurable optical add/drop multiplexer using tunable wavelength lasers - Google Patents

Abstract

A ROADM(Reconfigurable Optical Add/Drop Multiplexer) using a tunable laser and a method thereof are provided to help communication providers to improve infra networks by implementing all required functions without using expensive components, such as an NxN optical switch, a WSS(Wavelength Selective Switch), a wavelength blocker, etc. A ROADM consists of an optical drop unit and an optical add unit. The optical drop unit comprises an optical demultiplexer(551) and a plurality of optical receivers(502). The optical demultiplexer separates inputted optical signals having different wavelengths according to wavelength channels. The optical receivers, fixedly connected to arbitrary output ports of the optical demultiplexer respectively, receive optical signals of channels to drop among the separated channel-by-channel optical signals. The optical add unit comprises an optical multiplexer(552), a plurality of tunable transmitters(503), an Nx1 coupler(554), and a 2x1 coupler(553). The optical multiplexer multiplexes optical signals of channels to pass one among the separated channel-by-channel optical signals. The tunable transmitters create optical signals of channels to add. The tunable transmitters respectively are operated at preset different wavelengths which can be reset. The Nx1 coupler couples the tunable transmitters. The 2x1 coupler couples the output of the Nx1 coupler with the output of the optical multiplexer.

Description

Reconfigurable Optical Add / Drop Multiplexer using tunable wavelength lasers

The present invention relates to the configuration and structure of a reconfigurable optical add / drop multiplexer (ROADM) used in a reconfigurable optical add / drop multiplexing network (ROADM network).

ROADM means OADM equipment that can freely configure the circuit without software intervention. In other words, it refers to an OADM device that can freely connect a specific channel of a specific node with a specific channel of another specific node. OADM equipment prior to ROADM had to do all the work by hand to do this.

In recent years, as data traffic volume has increased rapidly, such as IPTV, and there is a lot of need to change the network structure according to the customer's demand, service providers are demanding easily reconfigurable branch-coupled multiplex (ROADM). . This ROADM is much more expensive than the existing OADM equipment, but it is expected to provide economic benefits over the existing OADM equipment because of the relatively small amount of time and manpower required to operate or reconfigure the network.

Therefore, much research is being conducted and reported on the effective ROADM device and device structure. If ROADM is largely classified, it can be divided into switch-based ROADM and wavelength-variable device-based ROADM. "Online Connection Provisioning in Metro Optical WDM Networks Using Reconfigurable OADMs," by Hongyue Zhu and Biswanath Mukherjee, J. Lightw . Technol ., Vol. 23, no. 10, pp. 2893-2901, Oct. 2005. ROADM having such a configuration is described.

ROADMs based on tunable devices are also called broadcast and select structures, and are co-authored by June-Koo Rhee, Ioannis Tomkos, and Ming-Jun Li, "A Broadcast-and-Select OADM Optical Network With Dedicated Optical-Channel Protection," J. . Lightw. Technol ., Vol. 21, no. 1, pp. 25-31, Jan. 2003.

Figure 1 illustrates a switch-based ROADM. The description of the operation is as follows. N different wavelength signals enter through the optical path 100. These signals are separated at each wavelength through a demultiplexer 102 made with an arrayed waveguide grating (AWG), fiber bragg grating (FBG), or thin film filter (TFF). Each of the separated wavelength signals is connected to the optical multiplexer 103 by the 2x2 optical switch 104 or to the NxN optical switch 105. If the wavelength signal does not need to be dropped, the 2x2 optical switch 104 becomes a bar-state so that the wavelength signal is transmitted to the optical multiplexer. On the other hand, if it is a signal that needs to branch, the 2x2 optical switch 104 becomes a cross-state and sends a wavelength signal to the NxN optical switch 105. The N × N optical switch 105 connects the wavelength signal to one of the receivers 107 according to a command of the ROADM device operator. For example, the receiver 107 may be connected to any of the outputs 1, 2, N of the multiplexer according to the combination and state of the 2x2 optical switch 104 and the NxN optical switch 105.

The addition of the wavelength signal is done in the same way. The transmitter 106 with the wavelength conversion function may vary the wavelength as commanded by the operator. After being varied to a specific wavelength, it can be connected to either of the 2x2 optical switches 104 via the NxN optical switch 104. At this time, the state of the connected 2x2 optical switch 104 is a cross-state. Thus, the 2x2 optical switch 104 and the two NxN optical switches 104 and 105 can freely connect and configure a signal of any wavelength.

However, the switch-based ROADM has the following disadvantages. ROADM is also basically a class of WDM (Wavelength Division Multiplexing) equipment. In general, WDM equipment is installed by using fewer channels at first installation and then gradually increasing the channels as traffic increases. However, in the case of the switch-based ROADM equipment shown in FIG. By the way, NxN optical switch is very expensive and technical improvement of reliability is calculated | required. The ROADM with this configuration is described in "Large-Capacity Strictly Nonblocking Optical Cross-Connects Based on Microelectrooptomechanical System (MEOMS) Switch Matrices: Reliability Performance Analysis," J. Lightw , co-authored by Lena Wosinska, Lars Thylen and Roger P. Holmstrom . Technol ., Vol. 19, no. 8, pp. 1065-1075, Aug. Found in 2001.

2 illustrates an ROADM of a broadcast and select structure. The description of the operation is as follows. When different wavelength signals enter through the optical path 200, some go to the wavelength blocker 204 and some go to the Wavelength Selective Switch (WSS) 205 through the optical coupler 202. The operating principle of the WSSs 205 and 206 is shown in FIG. The wavelength signals input to the port 300 are separated into respective wavelength signals through the wide multiplexer 302 and then input to the 1 × N optical switch 303. Each 1xN optical switch 303 may send each input wavelength signal to a desired output port 305. For this purpose, each 1xN optical switch 303 and an optical coupler 304 are connected as shown in FIG. 3 is intended to illustrate the basic principle of WSS, and is not actually made like FIG. The actual configuration of WSS is co-authored by Jui-che Tsai and Ming C. Wu, "A High Port-Count Wavelength-Selective Switch Using a Large Scan-Angle, High Fill-Factor, Two-Axis MEMS Scanner Array," J. Lightw . Technol ., Vol. 18, no. 13, pp. 1439-1441, JULY. 2006.

Since the WSS performs this operation, in FIG. 2, the receiver 207 may select and receive any wavelength signal as the operator manipulates the WSS 205.

Meanwhile, the wavelength tunable transmitter 208 may add an arbitrary wavelength signal to the optocoupler 203 through the WSS 206. Since the WSSs 205 and 206 are optical devices capable of reversing input and output, the input ports can be used as output ports or vice versa. The optocoupler 203 combines the wavelength signals from the optocoupler 202 through the wavelength blocker 204 and the signals from the wavelength variable transmitter 208 and outputs them to the optical path 201.

In this process, when the wavelength of the added signal and the pass-through signal match, an error occurs. Therefore, it is necessary to prevent the passing signal. This is done by the Wavelength blocker 204. . The wavelength blocker 204 is an optical device that passes or blocks a specific wavelength signal. The basic principle of the Wavelength Blocker 204 is shown in FIG. Wavelength signals coming into the input port 400 are separated by wavelengths by the multiplexer 401. Each wavelength signal is determined whether to be transmitted or blocked by the optical switch 402. The transmitted wavelength signals are combined by the optical coupler 403 and output to the output port 404.

ROADM of Broadcast and Select structure has the following disadvantages. This method has the advantages of lower initial cost and relatively simple device structure compared to switch-based ROADM, but has the disadvantage that the cost increases as channel expansion continues. The reason for this is that Wavelength Selective Switch (WSS), which is a core element of Broadcast and Select structure, is expensive, and 1xN (N = 8) WSS is commercially available, and the number of ports is relatively small. This means, for example, that 32/8 = 4 WSSs are needed to support 32 channel ROADM.

As described above, since both the switch-based ROADM and the broadcast and select ROADM are based on expensive optical devices, the initial installation cost of the ROADM is high, and the cost of expanding the channel is very burdensome. .

Therefore, the initial installation cost of ROADM is low, and the cost increase is not great even when the channel is expanded. Therefore, it is important to develop a realistic ROADM structure that the service provider can actually accommodate.

The present invention is intended to devise a structure of a ROADM device that satisfies the characteristics generally required for ROADM equipment without using expensive NxN optical switches, WSSs, or Wavelength Blockers, which are widely applied in ROADM equipment. It is.

For this purpose, tunable laser diodes and wavelength fixed filters are used, and 2N wavelengths are used to form N channels.

The present invention relates to a ROADM device and method that does not use a Wavelength Selective Switch, Wavelength Blocker, NxN Optical Switch, or the like. When transmitting, a wavelength variable transmitter is used, a fixed wavelength multiplexer is used at a receiving end, and a wavelength that is twice as large as the number of channels can be used to freely configure channel-to-node channels.

According to the present invention, a ROADM device can be configured at low cost by using a wavelength tunable transmitter, using a fixed wavelength multiplexer at a receiving end, and using twice as many wavelengths as the number of channels. In addition, the WSS, Wavelength Blocker, NxN switch, etc. based on the mechanical movement is not used to increase the durability and reliability of the device. In addition, it can do all the functions required for ROADM devices without using expensive WSS, Wavelength Blocker, and NxN switches, which can greatly contribute to improving the infrastructure network of the carriers.

The present invention is to realize the above object.

The present invention provides an optical splitting multiplexing device for splitting an optical signal of an arbitrary wavelength or combining and transmitting an optical signal of an arbitrary wavelength in an optical signal of different wavelengths transmitted to an optical path, having a different wavelength input from an optical path. An optical multiplexer for splitting an optical signal for each wavelength channel, a plurality of optical receivers for receiving optical signals of a plurality of channels that branch among the separated optical signals for each wavelength channel, and an optical signal for each of the separated wavelength channels An optical multiplexer for multiplexing optical signals of a channel, a plurality of wavelength variable transmitters for generating optical signals of a channel to be combined, an Nx1 coupler (N ≥ number of wavelength variable transmitters) for combining a plurality of wavelength variable transmitters, A 2x1 coupler for combining the output of an Nx1 coupler with the output of the multiplexer,

Here, the plurality of optical receivers are each fixedly connected to any output port of the wide multiplexer, and the plurality of wavelength variable transmitters operate at different wavelengths set by the user, respectively, The other wavelength is for a Reconfigurable Optical Add Drop Multiplxer (ROADM) with a reset function, which can be reset by the user.

In another aspect of the present invention, the optical multiplexer or optical multiplexer in the optical coupling device multiplexing device is replaced with a combination of interleavers composed of multiple stages, the Nx1 coupler is a combination of Mx1 coupler (M <N) and 2x1 coupler An optical coupling branch multiplexer with a reset function is characterized by being replaced.

According to another aspect of the present invention, in an annular network composed of a plurality of optical branch coupling nodes, the optical branch coupling node including the optical branch coupling multiplexing device and the specific output port of the optical multiplexer of the optical branch coupling multiplexing device are fixed. And an optical receiver of the optical branch coupling multiplexing device connected to each other to receive only an optical signal of a specific wavelength, and another optical receiver existing in the annular network, so as not to receive an optical signal of the specific wavelength. The present invention relates to an annular network composed of an optical coupling branch multiplexing device having a reset function, which is transmitted to only an optical receiver of the optical coupling node multiplexing device.

5 shows a specific embodiment of the present invention. 5 shows only one direction. In order to construct the annular network, there should be another one as shown in FIG. 5 operating in the opposite direction.

Looking at the configuration of the common unit 550, there is a wide multiplexer 551 that separates the various wavelength signals coming from the input optical line 500 for each channel. The channel to be dropped is connected to the receiver 502 as shown in FIG.

In the present embodiment, the two channel optical signals are split and transmitted to the optical receiver 502. The connection between the optical receiver 502 and the wide multiplexer 551 has a passive and fixed connection structure that cannot be automatically reset.

The channel to pass except for the branched channel is connected to the corresponding output port of the demultiplexer and the corresponding input port of the optical multiplexer 552. The channel to pass is multiplexed by the optical multiplexer 552 and transmitted to the 2x1 optocoupler. The optical multiplexer 552 and the global multiplexer 551 may use an arrayed waveguide grating (AWG).

This embodiment shows a configuration in which two channels are combined. Multiple channel combinations can be provided as needed. The channel to be added is a 2x1 optocoupler (2x1 optocoupler) in order to vary the wavelength of the tunable transmitter 503 to a desired position and then combine it with a signal passed after wavelength multiplexing at an Nx1 optocoupler (N &gt; 553). The two optocouplers 553 and 554 are common optocoupler devices where each port has no wavelength dependence. If necessary, an AWG and a wavelength filter may be used, and an optical amplifier may be used when the attenuation of the Nx1 optocoupler is excessive.

As shown in FIG. 5, the present invention does not use an expensive WSS, Wavelength Blocker, or NxN optical switch. However, the tunable transmitter 503 is as essential as in other ROADMs.

6A shows how the ROADM of the present invention operates. FIG. 6A shows an example of a reflection network using four optical branch coupling nodes (Node-1, Node-2, Node-3, and Node-4). Each node is composed of the ROADM of FIG. 5, and each node has a configuration of branching one optical signal channel and combining one optical signal channel. When configuring an annular network as shown in Fig. 6A, each node is assigned a specific wavelength, and the receivers 605, 606, 607, and 608 of each node receive only the optical fan of the wavelength assigned to each node. That is, in one annular network, a receiver for receiving an optical signal of a specific wavelength is specified in advance, and other receivers except for the specified receiver do not receive the optical signal of the corresponding wavelength.

For the purpose of clarity, the number of channels in the ROADM network is limited to two. In the present invention, four wavelengths are used to support two channels. In general terms, 2N wavelengths are used to support N channels.

FIG. 6A assumes an ROADM network having a ring network in which one channel is formed between Node-1 and Node-3 and one channel is formed between Node-2 and Node-4.

In order to transmit from Node-1 to Node-3, since the receiver 607 in Node-3 can only receive l3, the wavelength variable transmitter 601 in Node-1 changes the wavelength to λ3 and then Send it. On the other hand, in order to transmit from Node-3 to Node-1, since the receiver 605 in Node-1 is connected to receive only λ1, if the transmitter 603 of Node-3 transmits with the wavelength of λ1 One channel is formed between Node-1 and Node-3.

The same is true for the channel between Node-2 and Node-4. The transmitter 602 of the Node-2 may be tuned to the wavelength of? 4, and the transmitter of the Node-4 may be changed to? 2 and then transmitted. At this time, the receivers of the Node-2 and the Node-4 receive optical signals of λ2 and λ4, respectively.

ROADM must be able to freely change the channel configuration without having to change the optical connection directly. In FIG. 6A, the transmitters 601, 602, 603, and 604 in each node may change wavelengths according to a user's control command.

Now assume that we are working to change the configuration of FIG. 6A. The channel formed between Node-1 and Node-3 is cut off, and a channel is formed between Node-1 and Node-2. In addition, the channel formed between Node-2 and Node-4 is cut off, and a channel is formed between Node-3 and Node-4. In order to remove the existing channel and configure a new channel, the present invention changes the wavelengths of the transmitters 601, 602, 603, 604 of each node. The newly formed channel is shown in Figure 6b.

Referring to FIG. 6B, it can be seen that one channel is formed between Node-1 and Node-2. The transmitter 601 of the Node-1 may change the wavelength to l2, and the Transmitter 602 of the Node-2 may change the wavelength to λ1. Channel formation between Node-3 and Node-4 is also possible on the same principle. Thus, in the present invention, it is possible to provide reconfiguration capability required for ROADM equipment without using expensive WSS, Wavelength Blocker, NxN switch, and the like.

On the other hand, a disadvantage of the present invention is that general WDM devices or ROADM equipments other than the present invention use only N wavelengths to configure N channels, whereas the present invention uses twice as many 2N wavelengths. However, the problem can be solved by using a wavelength interval corresponding to half of the wavelength interval used in conventional WDM or other ROADM equipment. For example, if the conventional WDM or other ROADM equipment uses a wavelength interval of 100 GHz and supports 32 channels, the present invention may support the same 32 channels using a 50 GHz wavelength interval.

5 simply illustrates the structure of the present invention. When the present invention is actually implemented, it can have various structures. 7 shows an embodiment. 7 shows that the structure of the present invention can be divided into several stages. When multiple wavelength signals are input through the input optical line 500, first, the wavelength having the odd number and the wavelength having the even number may be divided into the interleaver 560. Since many channels are not required at the beginning of the system installation, only the multiplexer 551 and the optical multiplexer 552 are used at the beginning of the installation, and the wide multiplexer 558 and the optical multiplexer 559 do not need to be installed. If more channels are needed, then installing them is economical. The device 561 that combines odd and even numbers may use an interleaver or a 1 × 2 optocoupler. The device 560 that divided the light may also use a 1x2 optocoupler. When the device 560 that divides the light is used as a 1x2 optical coupler, the demultiplexers 551 and 552 demultiplex and output the optical signal of the operating region wavelength, and block the wavelength of the remaining band.

In addition to the wavelength signal (add) side by using the small 1xM optocouplers (555, 556, 557) step by step, not only the initial installation burden, but also the connection between the system self can be simplified.

The illustrated embodiments are intended to illustrate but not limit the invention. It will be apparent to those skilled in the art that various changes, modifications, or adjustments to the above embodiments can be made without departing from the spirit of the invention. Therefore, the protection scope of the present invention will be limited only by the appended claims, and should be construed as including all such changes, modifications or adjustments.

1 is a switch-based ROADM structure

2 is a broadcast and select based ROADM structure

3 is the basic principle of WSS

4 is a basic principle of the Wavelength Blocker

5 is a structure of a ROADM device according to an embodiment of the present invention

6A is an operation example of the present invention

6B is an operation example of the present invention.

Figure 7 is another embodiment of the present invention

Claims (7)

In the annular network comprising an optical branch coupling node composed of an optical branch coupling multiplexing device, The optical branch coupling multiplexing apparatus comprises: an optical branching apparatus for branching and receiving optical signals having a wavelength specifically assigned to each optical branch coupling node; And an optical coupling device for coupling optical signals having a wavelength assigned to the selected multiple optical coupling nodes to transmit optical signals to the selected multiple optical coupling nodes. The wavelength of the branched optical signals is predetermined The wavelength of the combined optical signals is such that when the selected nodes change, combining the optical signals of the wavelengths assigned to the changed nodes. An annular network comprising a resettable optical coupling node The method of claim 1, The optical branch device An optical multiplexer for separating input optical signals having different wavelengths for each wavelength channel; And a plurality of optical receivers for receiving optical signals of a plurality of channels to be split among the separated optical signals for each wavelength channel. An annular network comprising a resettable optical coupling node The method of claim 2, The optical coupling device An optical multiplexer for multiplexing optical signals of channels to be passed among the separated optical signals for each wavelength channel; It consists of a plurality of wavelength variable transmitter for generating an optical signal of the channel to be coupled An annular network comprising a resettable optical coupling node The method of claim 3, An N × 1 coupler (N ≧ number of tunable transmitters) for coupling a plurality of tunable transmitters; And a 2x1 coupler for coupling the output of the Nx1 coupler and the output of the multiplexer. An annular network comprising a resettable optical coupling node The method according to claim 3 or 4, The plurality of optical receivers are each fixedly connected to any output port of the wide multiplexer, The plurality of wavelength tunable transmitters operate at different wavelengths set by the user, respectively, and the set different wavelengths can be reset by the user. An annular network comprising a resettable optical coupling node The method according to claim 3 or 4, The wide multiplexer or the optical multiplexer is replaced with a combination of multi-stage interleavers, The Nx1 coupler is replaced by a combination of Mx1 coupler (M <N) and 2x1 coupler An annular network comprising a resettable optical coupling node The method of claim 5, The wide multiplexer or the optical multiplexer is replaced with a combination of multi-stage interleavers, The Nx1 coupler is replaced by a combination of Mx1 coupler (M <N) and 2x1 coupler An annular network comprising a resettable optical coupling node

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