JPWO2002025850A1 - Add / drop filter, packet switch, wavelength multiplexing device, communication device, and communication network - Google Patents

Abstract

Provided is an add / drop filter that can be manufactured at low cost and can perform bidirectional transmission. An optical signal having eight wavelengths λ1 to λ8, which has passed through the optical fiber 3a, is converted into parallel light by the lens 4a and applied to the dielectric filter 2. The light of λ1 is reflected at right angles, and the optical signals of other wavelengths (λ2 to λ8) are transmitted. As a result, the reflected light of λ1 is guided to the optical fiber 3b via the lens 4b. The transmitted light of λ2 to λ8 is guided to the optical fiber 3c via the lens 4c. The light of λ1 that has passed through the optical fiber 3b is guided to the optical fiber 3a via the lens 4b, the dielectric filter 2, and the lens 4a. That is, the optical signal of λ1 is bidirectionally transmitted between the optical fiber 3a and the optical fiber 3b. The same add / drop operation is realized for the optical signals of λ1 to λ8 that have passed through the optical fiber 3c.

Description

TECHNICAL FIELD The present invention relates to optical fiber communication, and more particularly to an add / drop filter for adding or removing an optical signal optical fiber of a specific wavelength in wavelength multiplexed optical fiber communication, a packet switch for optical fiber communication, and an optical fiber communication network. .
BACKGROUND ART Conventionally, an add / drop filter as shown in FIG. 12 has been known. This is an add-drop filter including a structure 100 in which a fiber Bragg grating is coupled as a Michelson type interference system. In this filter, of the light of different wavelengths λ1 to λ8 incident from the terminal 101, light of only the wavelength λ1 goes to the terminal 102, and the remaining light of the wavelengths λ2 to λ8 goes to the terminal 104. Although not shown, the light path is opposite to that of FIG. 12 and light of wavelengths λ2 to λ8 is applied to the terminal 104 and light of wavelength λ1 is applied to the terminal 102. I do. Since light of a specific wavelength can be added to or dropped from light of many other wavelengths in this manner, it is called an add-drop (Add-Drop) filter.
FIG. 13 shows a conventional example of a wavelength division multiplexing optical communication network using the above-described add / drop filter. The two trunk base stations 111 and 112 are connected by two optical fibers 113 and 114. The optical fibers 113 and 114 have a unidirectional light path. Each local station 121 to 124 is provided with two add / drop filters. For example, the local station 121 is provided with add / drop filters 131 and 141, and the light of the wavelength λ1 is added or extracted. Similarly, the local station 122 is provided with add-drop filters 132 and 142 for adding or extracting light of the wavelength λ2. Further, the local station 123 is provided with add-drop filters 133 and 143, and the light of the wavelength λ3 is added or extracted. The local station 124 is provided with add / drop filters 134 and 144 for adding or extracting light of wavelength λ4.
DISCLOSURE OF THE INVENTION The conventional method of configuring a fiber Bragg grating as a Michelson-type interference system has a drawback that it is difficult and expensive to manufacture. An object of the present invention is to realize an inexpensive add / drop filter which can be easily manufactured.
Further, in the conventional optical communication network using the add / drop filter, since the transmission is performed by one-way transmission, there is a disadvantage that the transmission capacity of the optical fiber is small. SUMMARY OF THE INVENTION An object of the present invention is to perform transmission of a larger capacity by applying add-drop to bidirectional optical communication.
In order to solve the above-mentioned problems, an add-drop filter according to the present invention is characterized in that a dielectric filter and a lens are combined to extract light of a specific wavelength in two directions. Therefore, it can be easily manufactured and a low price can be realized.
Further, the communication network of the present invention is characterized in that light of the same wavelength sent from two directions (left direction and right direction) is dropped from the optical fiber by the optical fiber. For this reason, the utilization efficiency of the optical fiber can be improved. Furthermore, in the communication network of the present invention, since the packet switch having the function of distributing the communication load in two directions (left direction and right direction) is used, the utilization efficiency of the communication network can be improved.
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
[First embodiment]
FIG. 1 shows a top view of an embodiment of the add / drop filter 1 of the present invention. The add / drop filter 1 reflects a specific wavelength (here, λ1) and transmits other wavelengths (λ2 to λ8), a dielectric filter 2, four optical fibers 3a to 3d, and four lenses 4a to 4d. Consists of
An optical signal having eight wavelengths λ1 to λ8, which has passed through the optical fiber 3a, is converted into parallel light by the lens 4a and applied to the dielectric filter 2. The light of λ1 is reflected at right angles, and the optical signals of other wavelengths (λ2 to λ8) are transmitted. As a result, the reflected light of λ1 is guided to the optical fiber 3b via the lens 4b. The transmitted light of λ2 to λ8 is guided to the optical fiber 3c via the lens 4c.
The light of λ1 that has passed through the optical fiber 3b is guided to the optical fiber 3a via the lens 4b, the dielectric filter 2, and the lens 4a. That is, the optical signal of λ1 is transmitted bidirectionally between the optical fiber 3a and the optical fiber 3b.
The optical signals of λ1 to λ8 that have passed through the optical fiber 3c are converted into parallel light by the lens 4c and applied to the dielectric filter 2. The light of λ1 is reflected at right angles, and the optical signals of other wavelengths (λ2 to λ8) are transmitted. As a result, the reflected light of λ1 is guided to the optical fiber 3d via the lens 4d. The transmitted light of λ2 to λ8 is guided to the optical fiber 3a through the lens 4a.
The light of λ1 having passed through the optical fiber 3d is guided to the optical fiber 3c via the lens 4d, the dielectric filter 2, and the lens 4c. That is, the optical signal of λ1 is transmitted bidirectionally between the optical fiber 3c and the optical fiber 3d.
Although the case where the dielectric filter 2 that reflects λ1 is used has been described above, an arbitrary wavelength can be added and dropped by changing the dielectric filter. In addition, for the sake of simplicity, the case where the dielectric filter reflects a specific wavelength (for example, λ1) at a right angle has been described. However, the angle of reflection is not limited to a right angle, and may be any angle. The design of such filter characteristics can be realized according to a known dielectric filter design method. Also, the case where there are eight types of optical signals having different wavelengths has been described as an example, but it is needless to say that the above-described function can be realized for any number of wavelengths without limitation to the number of wavelengths.
Alternatively, an add-drop filter can be constructed by using a dielectric filter that transmits only λ1 and reflects other wavelengths (λ2−λ8), contrary to the above embodiment. In this case, the relationship between 3b and 3c with respect to the optical fiber 3a is switched. That is, the optical signal of λ1 from the optical fiber 3a is guided to the optical fiber 3c, and another optical signal (λ2-λ8) from the optical fiber 3a is guided to the optical fiber 3b.
Since the add-drop filter of the present invention is configured by combining a dielectric filter and a lens, the add-drop filter can be realized with inexpensive components.
[Second embodiment]
An embodiment of a communication network using an add / drop filter will be described with reference to FIGS. FIG. 2 is a diagram showing a main part of the communication network of the present invention. FIG. 3 is a diagram showing the entire communication network.
In FIG. 2, the main base stations 11a and 11b are connected by an optical fiber 18. A multiplexed optical signal of eight wavelengths is transmitted to the optical fiber 18 in both directions. Local stations 15a to 15d are provided on the optical fiber 18. The local stations 15a to 15d are provided with add / drop filters 12a to 12d, respectively, and λ1 to λ4 are respectively added and dropped. As the add / drop filter, both the add / drop filter shown in FIG. 1 and the conventional add / drop filter can be used. The local stations 15a to 15d are provided with packet switches 13a to 13d, respectively. Client station groups 14a to 14d are connected to the packet switches 13a to 13d, respectively.
The conventional add / drop filter shown in FIG. 12 and the add / drop filter shown in FIG. 1 are collectively called a two-way type 4-port add / drop filter. In addition to the one shown in FIG. 12, there is a unidirectional three-port add / drop filter. Usually, when referred to as an add-drop filter, it often refers to this unidirectional three-port add-drop.
In the example of FIG. 2, the wavelengths λ5 to λ8 are reserved for direct communication between the trunk base stations 11a and 11b or for future expansion. In addition to communicating with the trunk line base stations 11a and 11b using the wavelengths λ5 to λ8, it is also possible to communicate via the packet switches by the relay function of the packet switches 13a to 13d as described later.
The wavelength for the direct communication (core communication) between the trunk base stations uses a high-density wavelength multiplexing with a narrow wavelength interval, and the wavelength for the communication (access communication) between the trunk base station and the local station is a wavelength. Widely spaced low-density wavelength multiplexing can also be used. As shown in FIG. 4, wavelengths [lambda] 1 to [lambda] 6 are used for access communication, and optical signals composed of a large number of wavelengths of dense wavelength division multiplexing (DWDM) are used for core communication. Dense wavelength multiplexing has a large communication capacity but is expensive. Access communication has a relatively small communication volume, but demands for cost reduction are severe. Therefore, there is a problem that the use of high-density wavelength multiplexing for access communication is not well balanced in terms of cost. Therefore, this cost balance can be improved by using low-cost low-density wavelength multiplexing for access communication. In addition, a band shortage can be dealt with by using high-density wavelength multiplexing for core communication having a large traffic. With the above configuration, both access communication and core communication can be covered by the same optical fiber, which is economical.
In the base station 11, a wavelength multiplexing device 60 as shown in FIG. 5 is provided. The wavelength multiplexing device 60 includes a low-density wavelength multiplexing device 61, a high-density wavelength multiplexing device 62, and a wavelength multiplexing device 63. The access communication signal from the packet switch 64 is transmitted to the low-density wavelength multiplexing device 61. , The core communication signal is multiplexed to one optical fiber 18 via the high-density wavelength multiplexing device 62.
FIG. 3 is a diagram showing the entire communication network of the present invention. Trunk base stations 11a to 11f are connected in a ring. In order to correspond to FIG. 2, four local stations 15a to 15d are provided between the trunk base stations 11a and 11b. Although not shown for the sake of explanation, many similar local stations are provided between other trunk base stations. The client 14 is connected to the local station 15a. Although not shown in the figure for the sake of explanation, many clients are connected to each local station. In the above description, a network constructed by connecting trunk base stations in a ring shape is called a backbone network.
Data centers 16a and 16b are connected to the trunk base stations 11d and 11e, respectively. The data centers 16a and 16b are provided with a server cluster (not shown) including a large number of servers, and provide various services. Now, consider a case where the client 14 connected to the local station 15a accesses the data center 16a. There are two routes 17L (counterclockwise) and 17R (clockwise) from the client 14 to the data center 16a. In the communication network of the present invention, communication is performed using these two routes. A packet switch provided in each local station or trunk communication station performs dynamic routing so that the traffic of the entire communication network is balanced clockwise and counterclockwise.
Although the optical fiber 18 is one, since the bidirectional transmission is performed, the communication network of FIGS. 2 and 3 is effectively a double ring type network. For this reason, if a failure occurs somewhere in the ring-shaped network, it is possible to perform communication while avoiding the failure location by performing return transmission.
[Third embodiment]
The structure and behavior of the packet switch of the present invention will be described with reference to FIGS. FIG. 6 is a diagram showing the behavior of the packet switch of the present invention, FIG. 7 is a diagram showing the structure of the engine portion 30 of the packet switch, FIG. 8 is a diagram showing the internal structure of the various components shown in FIG. FIG. 3 is a diagram showing a structure of a packet switch.
FIG. 6A shows the flow of a packet from the port group 22 connected to the client to the ports 21L (for counterclockwise) to 21R (clockwise) connected to the trunk line (backbone network). Packets from the port group 22 are allocated to the ports 21L to 21R so that the load is distributed. Normally, the packet is assigned to the destination that is the shortest distance to the final destination of the packet. However, when network traffic is congested, a distant route may be selected.
FIG. 6B shows the flow of a packet from the main network to the client. When the destination among the packets sent through the ports 21L to 21R is any of the clients connected to the port group 22, the packets are switched as shown in FIG. 6B.
FIG. 6C shows the processing of traffic inside the port group 22 and the case of relaying between the ports 21L and 21R (or bypassing the packet switch 13). Packets exchanged between clients connected to the port group 22 are subjected to the same processing as that of a normal packet switch, as shown in FIG. If the destination of the packet transmitted from the port 21L to the port 21R is not any of the clients connected to the port group 22, the packet is transmitted from the port 21L to the port 21R or in the opposite direction. This can be called a relay function or a bypass function.
Returning to FIG. 2, the effect of this relay function (bypass function) will be described. For example, the wavelength λ1 is assigned to the packet switch 13a, and is normally used for communication between the trunk base stations 11a to 11b and the client group 14a. However, there may be a case where there is not much communication demand in the client group 14a due to traffic fluctuation. In such a case, the trunk line base station 11a and the trunk line base station 11b can exchange packets on other routes using the relay function (bypass function) of the packet switch 13a. In this way, the relay function (bypass function) can be used to make full use of the vacant line.
FIG. 6D shows the failure recovery operation of the packet switch 13. For example, it is assumed that a trouble (such as a broken cable) occurs in the network connected to the port 21R. In this case, a packet sent from the port 21L and not addressed to the client group connected to the port group 22 is sent back to the port 21L (return function). It works similarly to the known foldback function in a dual ring communication network.
FIG. 7 is a block diagram showing the internal configuration of the engine unit 30 of the packet switch 13. Network interface card (NIC) array 31, crossbar switch interface card (CIC) array 32, crossbar switch 34, crossbar switch control circuit 33, crossbar switch interface card (CIC) array 35, network interface card (NIC) array It consists of 36.
FIG. 8A shows the structure of the network interface card 31a. It comprises an optical transceiver 41, a serial / parallel converter (SERDES) 42, and a medium control chip (MAC) 43. A serial optical signal input from an optical fiber cable (not shown) is converted into a serial electric signal by an optical transceiver 41 and then converted into a parallel signal by a serial / parallel converter (SERDES). This parallel signal is interpreted for each packet by the media control chip (MAC) 43 and sent to the crossbar switch interface card 32a. The signal in packet units sent from the crossbar switch interface card 32a is converted into a parallel signal by a medium control chip (MAC) 43, converted into a serial electric signal by a serial / parallel converter (SERDES) 42, and further converted into an optical signal. The signal is converted into an optical serial signal by the transceiver 41 and transmitted to an optical fiber cable (not shown). The network interface card 36a has the same structure as the network interface card 31a.
Note that a packet is a unit of information transmission, and includes a destination address, a source address, and the like in addition to an information entity. The transmission unit of this information may be called a cell, but these two are almost synonymous.
In the above description, the medium control chip (MAC) 43 has a function of identifying a packet and a non-packet part (idle signal). Further, the medium control chip (MAC) 43 can identify a source address and a destination address for each packet. By combining this function of the medium control chip (MAC) 43 with the function of the crossbar switch, various packet switch operations shown in FIG. 6 can be realized.
By using the crossbar switch method, it is possible to construct a packet switch that functions for a transmission channel having a higher transmission rate than other methods, for example, a shared memory method.
FIG. 8B shows the structure of the crossbar switch interface card 32a. It comprises a first-in first-out memory (FIFO) 44, a medium control chip (MAC) 43, a serial / parallel converter (SERDES) 42, and a copper wire transceiver 46. The packet unit signal sent from the network interface card 31a is stored in a first-in first-out memory (FIFO) 44, sent to a medium control chip (MAC) 43 and converted into a parallel signal, and further converted into a serial-parallel converter (SERDES). The signal is converted into a serial signal by 42, further converted by a copper wire transceiver 46 into a serial electric signal that can be transmitted several meters over a copper wire, and sent to the crossbar switch 34. The amount of memory stored in the first-in first-out memory (FIFO) 44 is sent to the crossbar switch control circuit 33 via a signal line 45. The serial electric signal transmitted from the crossbar switch 34 is transmitted through the copper wire transceiver 46, the serial / parallel converter (SERDES) 42, and the medium control chip (MAC) 43 in the opposite direction to the above, and the first-in first-out memory (FIFO) ) 44. The signal in packet units stored in the first-in first-out memory (FIFO) 44 is sent to the network interface card 31a. The crossbar switch interface card 35a has the same structure as the crossbar switch interface card 32a.
Returning to FIG. 7, the operation of the packet switch engine 30 will be described. The signals from the six channels of ports 22x and ports 21x (21L and 21R) are sent to a crossbar switch 34 via a network interface card (NIC) array 31 and a crossbar switch interface card (CIC) array 32. The state of the information (packet) stored in each crossbar switch interface card (CIC) is sent from the crossbar switch interface card (CIC) array 32 to the crossbar switch control circuit 33. The crossbar switch control circuit 33 changes the connection pattern of the crossbar switch 34 according to the state of information (packets) stored in each crossbar switch interface card (CIC). The change of the connection pattern of the crossbar switch 34 is performed for each packet described above. Note that the packet length is not always a fixed value. Extraction of a packet (removal of an idle signal) and detection of a source address and a destination address are performed by a medium control chip (MAC) 43. The detection result of the medium control chip (MAC) 43 is sent to the crossbar switch control circuit 33, and the connection pattern of the crossbar switch 34 is changed. Thus, the various switch patterns shown in FIG. 6 are realized.
FIG. 9 is a diagram showing the structure of the packet switch 13. The corresponding ports of the input port group 22x and the output port group 22y of the packet switch engine 30 are connected to each other by an optical coupler group 37 to realize bidirectional optical communication. Similarly, corresponding ports of the input port group 21x and the output port group 21y are connected by the optical coupler group 38.
[Fourth embodiment]
FIG. 10 shows another embodiment of the packet switch and the optical communication network of the present invention. In FIG. 10, two optical fibers 18a and 18b are connected to the trunk base stations 51a and 51b. Multiplexed optical signals of eight wavelengths are transmitted bidirectionally to the optical fibers 18a and 18b. Local stations 55a to 55d are provided on the optical fiber 18. Each of the local stations 55a to 55d is provided with two add / drop filters. For example, the local station 15a is provided with add / drop filters 12a1 to 12a2. The local stations 15a to 15d are provided with packet switches 53a to 53d, respectively. The client station groups 14a to 14d are connected to the packet switches 53a to 53d, respectively.
In this embodiment, two optical fibers and two clockwise counterclockwise paths are routed to the packet switch. Therefore, if the transmission speed of a single line is the same, a line capacity twice that of the embodiment shown in FIG. 2 can be obtained. Further, even when one of the two optical fibers 18a and 18b is disconnected, communication can be performed through the other optical fiber, so that higher reliability can be realized.
In the above embodiment, two optical fibers are provided. However, more optical fibers may be provided, or a plurality of wavelengths may be added and dropped from one optical fiber. Furthermore, it goes without saying that these can be combined to increase the line capacity.
When a large number of trunk lines are provided in the packet switch 53, "statistical multiplexing" as described in International Patent Application No. PCT / JP01 / 04346 (Japanese Patent Application No. 2000-155739) by the present applicant can be realized.
[Fifth embodiment]
The packet switch 13 is effective when combined with an add / drop filter, but can be used alone. By connecting packet switches as shown in FIG. 11, a ring communication network can be realized without performing wavelength multiplexing and without using an add / drop filter.
INDUSTRIAL APPLICABILITY According to the present invention, an inexpensive add / drop filter having a simple structure can be realized. Further, according to the present invention, it is possible to provide a communication network capable of performing efficient communication by combining a two-way 4-port add / drop filter and a packet switch.
[Brief description of the drawings]
FIG. 1 is a top view of one embodiment of the add / drop filter of the first embodiment of the present invention.
FIG. 2 is a diagram showing a main part of a communication network according to a second embodiment of the present invention.
FIG. 3 is a diagram showing the entire communication network according to the second embodiment of the present invention.
FIG. 4 is a diagram illustrating the coexistence of low-density wavelength multiplexing and high-density wavelength multiplexing.
FIG. 5 is a diagram illustrating a wavelength multiplexing device and a packet switch provided in the trunk base station 11.
FIG. 6 is a diagram showing the behavior of the packet switch according to the third embodiment of the present invention.
FIG. 7 is a diagram showing the structure of the engine part 30 of the packet switch according to the third embodiment of the present invention.
FIG. 8 is a diagram showing the internal structure of the various components shown in FIG.
FIG. 9 is a diagram showing the structure of the packet switch according to the third embodiment of the present invention.
FIG. 10 is a diagram illustrating another embodiment (fourth example) of the packet switch and the optical communication network.
FIG. 11 is a diagram illustrating a ring communication network configured by directly connecting packet switches.
FIG. 12 is a diagram showing the structure of a conventional drop filter.
FIG. 13 is a diagram illustrating a conventional optical communication network configured using an add / drop filter.

Claims (13)

A first to a fourth optical fiber, a first to a fourth lens, and a dielectric filter, wherein the dielectric filter has a characteristic of reflecting only a specific wavelength and transmitting other wavelengths,
The light from the first optical fiber is converted into parallel light by the first lens and guided to the dielectric filter, and the light of the specific wavelength reflected from the dielectric filter passes through the second lens to the second lens. And the other wavelength light transmitted through the dielectric filter is guided to the third optical fiber through the third lens,
The light from the third optical fiber is converted into parallel light by the third lens and guided to the dielectric filter, and the light of the specific wavelength reflected from the dielectric filter passes through the fourth lens to the fourth lens. An add / drop filter, which is guided to an optical fiber. A first to a fourth optical fiber, a first to a fourth lens, and a dielectric filter, wherein the dielectric filter has a property of transmitting only a specific wavelength and reflecting other wavelengths,
The light from the first optical fiber is converted into parallel light by the first lens and guided to the dielectric filter, and the light of the specific wavelength transmitted through the dielectric filter passes through the second lens to the second lens. The other wavelength light guided to the optical fiber and reflected by the dielectric filter is guided to the third optical fiber via the third lens,
The light from the third optical fiber is converted into parallel light by the third lens and guided to the dielectric filter, and the light of the specific wavelength transmitted through the dielectric filter passes through the fourth lens to the fourth lens. An add / drop filter which is guided to an optical fiber. A packet switch having a plurality of local ports prepared to be connected to a local station and at least one pair of backbone ports prepared to be connected to a backbone network,
A packet switch having a switch function of sending a packet sent from a local station to a backbone network to one of at least one pair of backbone ports in a load-balanced manner. 4. The packet switch according to claim 3, further comprising at least one 4-port add / drop filter, wherein two of the ports of the add / drop filter are connected to the two backbone ports forming a pair of the packet switch. A packet switch characterized by being performed. 4. The packet switch according to claim 3, wherein a packet not addressed to a local station connected to said packet switch is relayed between said pair of backbone ports. The packet switch according to claim 5, further comprising at least one 4-port add / drop filter, wherein two of the ports of the add / drop filter and the two backbone ports forming a pair of the packet switch are provided. A packet switch, which is connected. An optical fiber, a plurality of packet switches according to claim 3, and two trunk base stations, wherein the packet switch group is provided between the trunk base stations, and the trunk base station and the packet switch group are provided. The optical fiber is connected to the optical fiber, and optical signals of a plurality of wavelengths are transmitted in a wavelength multiplexed manner in the optical fiber, and the packet switch receives the same identification signal transmitted between the trunk base stations on both sides. A communication network wherein an optical signal of a wavelength is dropped. 8. The communication network according to claim 7, wherein an optical signal of at least one wavelength is exclusively allocated for communication between two trunk base stations. A communication network, wherein the networks according to claim 7 are connected in a ring shape. 10. The communication network according to claim 9, wherein control is performed to balance a counterclockwise communication load and a clockwise communication load. 9. The network according to claim 8, wherein the communication between the two trunk base stations uses an optical signal that has been subjected to high-density wavelength multiplexing with a narrow wavelength interval. A communication network, characterized in that an optical signal subjected to low-density wavelength multiplexing with a wide wavelength interval is used for the communication. A first wavelength multiplexing mechanism having a wide wavelength interval and a second wavelength multiplexing mechanism having a narrow wavelength interval are provided, and the first wavelength multiplexing mechanism and the second wavelength multiplexing mechanism are further wavelength-multiplexed. A wavelength multiplexing device comprising a mechanism. A packet switch having a mechanism for switching between access communication and core communication, and a wavelength multiplexing device according to claim 12, wherein access communication is performed through a first wavelength multiplexing mechanism of the wavelength multiplexing device. The communication device, wherein the core communication is performed through a second wavelength multiplexing mechanism of the wavelength multiplexing device.

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