Optical network

Abstract

A medium-scale IP telecommunications network is configured in a low-cost optical network with good reliability and expandability. A physical configuration example has a center node 2 - 1 and eight local nodes 2 - 11 through 2 - 18 connected in one OADM ring 2 - 21/2 - 22. The logical configuration is a star configuration with the central node 2 - 1 at its origin with all traffic passing through the center node 2 - 1. The local nodes 2 - 11 through 2 - 18 are connected to the central node 2 - 1 by wavelength-unit optical channels or optical paths λ 1 through λ 8. Channels are added as required. Initially, for example, the center node 2 - 1 and the local node 2 - 5 are connected by λ 5, but λ 13 can added when the need arises. Since the logical star network is limited to approximately two add/drop optical channels at local nodes, costs are reduced by using inexpensive filters (e.g., dielectric interference film filters or fiber Bragg reflectors) that are capable of extracting only the specific wavelength of the optical channel. High reliability is provided through the use of optical switches for correction of fiber transmission path failures.

What is claimed is:  
     
         1 . A wavelength division multiplexing optical network, comprising: 
 a client;    a plurality of redundant optical paths including a working path and a protection path; and    a plurality of network nodes redundantly connected through said optical paths in a predetermined configuration, at least one of said network nodes being connected to said client, said network nodes transmitting and receiving optical signals with each other at a set of wavelengths, each of said network nodes further comprising;    an optical add/drop multiplexer unit for converting a client optical signal at a first channel frequency from said client to a second channel frequency at one of said wavelengths to generate a converted client optical signal, said add/drop multiplexer unit splitting the converted client optical signal into split and converted redundant client optical signals for said optical paths, said add/drop multiplexer unit selectively multiplexing the split and converted redundant client optical signals to generate a wavelength division multiplexed optical signal, said add/drop multiplexer unit selectively demultiplexing the wavelength division multiplexed optical signal to generate a wavelength division demultiplexed optical signal;    an optical signal failure detector connected to each of said optical paths for detecting a failure in the wavelength division demultiplexed optical signal to generate an optical path failure signal; and    an optical switch unit connected to said optical paths in response to the optical path failure signal and having a first optical switch for switching from one of said optical paths to another of said optical paths.    
     
     
         2 . The wavelength division multiplexing optical network according to    claim 1    wherein the predetermined configuration is a ring structure.  
     
     
         3 . The wavelength division multiplexing optical network according to    claim 1    wherein the predetermined configuration is a liner structure.  
     
     
         4 . The wavelength division multiplexing optical network according to    claim 1    further comprises at least one main node and at least two local nodes.  
     
     
         5 . The wavelength division multiplexing optical network according to    claim 4    wherein said local nodes directly transmit the optical signals with each other without said main node.  
     
     
         6 . The wavelength division multiplexing optical network according to    claim 4    wherein said main node receives every one of the optical signals at one of said wavelengths from one of said local nodes and transmits the optical signals at a different one of said wavelengths to another of said local nodes.  
     
     
         7 . The wavelength division multiplexing optical network according to    claim 4    wherein said main node receives every one of the optical signals at one of said wavelengths from one of said local nodes and transmits optical signals at the same one of said wavelengths to the same one of said local nodes.  
     
     
         8 . The wavelength division multiplexing optical network according to    claim 1    wherein a number of the set of the wavelengths at each of said network node is flexibly modified.  
     
     
         9 . The wavelength division multiplexing optical network according to    claim 1    wherein said optical add/drop multiplexer unit further comprises: 
 a transponder for converting the client optical signal at the first channel frequency from said client to the second channel frequency at one of said wavelengths to generate the converted client optical signal;  
 an optical splitter connected said transponder to for splitting the converted client optical signal into the splitted and converted redundant client optical signals for said optical paths;  
 a wavelength division multiplexer connected to each of said optical paths of said optical splitter for selectively multiplexing the splitted and converted redundant client optical signals to generate the wavelength division multiplexed optical signal; and  
 a wavelength division demultiplexer connected to each of said optical paths of the wavelength division multiplexing optical network for selectively demultiplexing the wavelength division multiplexed optical signal to generate the wavelength division demultiplexed optical signal.  
 
     
     
         10 . The wavelength division multiplexing optical network according to    claim 9    wherein said optical add/drop multiplexer unit adds and drops a single channel frequency.  
     
     
         11 . The wavelength division multiplexing optical network according to    claim 9    wherein said optical switch unit further comprises a second optical switch and a third optical switch connected in series to said wavelength division demultiplexer for selectively connecting to said first optical switch to establish a drop route and to said wavelength division multiplexer to establish a through route.  
     
     
         12 . The wavelength division multiplexing optical network according to    claim 9    wherein said optical switch unit further comprises an optical coupler connected to said wavelength division demultiplexer for splitting the wavelength division demultiplexed optical signal and a fourth optical switch connected to said optical coupler for selectively connecting to said first optical switch to establish a drop route and to said wavelength division multiplexer to establish a through route.  
     
     
         13 . The wavelength division multiplexing optical network according to    claim 9    further comprises an optical amplifier connected to said wavelength division multiplexer for amplifying the wavelength division multiplexed optical signal.  
     
     
         14 . A wavelength division multiplexing optical network, comprising: 
 a client;    a plurality of optical paths; and    a plurality of network nodes connected through said optical paths in a predetermined configuration, at least one of said network nodes being connected to said client, said network nodes transmitting and receiving a plurality of optical signals with each other at a set of wavelengths;    a router connected to each of said network nodes for selecting one of said optical paths for transmitting one of the optical signals; and    an optical signal failure detector connected to each of said optical paths and said router for detecting a failure in the optical signal to generate an optical path failure signal for a particular one of said optical paths, wherein said router in response to the optical path failure signal switching from the particular one of said optical paths to another of said optical paths for transmitting the one of the optical signals.    
     
     
         15 . The wavelength division multiplexing optical network according to    claim 14    wherein the predetermined configuration is a ring structure.  
     
     
         16 . The wavelength division multiplexing optical network according to    claim 15    wherein said optical paths include dispersion shifted fibers with their chromatic dispersion at a wavelength near 1552 nm.  
     
     
         17 . The wavelength division multiplexing optical network according to    claim 16    wherein said dispersion shifted fibers transmit optical input signals being multiplexed at 200 GHz interval within C-band having a wavelength range from 1530 nm to 1560 nm, each optical channel being less than −3.5 dBm, optical modulation speed being 2.48 Gbits/second, inter-node span loss being less than 12 dB at 40 km.  
     
     
         18 . A method of wavelength division multiplexing for an optical network, comprising: 
 providing a plurality of redundant optical paths including a working path and a protection path as well as a plurality of network nodes redundantly connected through the optical paths in a predetermined configuration, at least one of the network nodes being connected to a client;    transmitting and receiving optical signals to and from the network nodes at a set of wavelengths, said transmitting and receiving further comprising:    converting a client optical signal at a first channel frequency from the client to a second channel frequency at one of the wavelengths to generate a converted client optical signal;    splitting the converted client optical signal into splitted and converted redundant client optical signals for the optical paths;    selectively multiplexing the splitted and converted redundant client optical signals to generate a wavelength division multiplexed optical signal;    selectively demultiplexing the wavelength division multiplexed optical signal to generate a wavelength division demultiplexed optical signal;    detecting a failure in the wavelength division demultiplexed optical signal to generate an optical path failure signal; and    switching from one of said optical paths to another of said optical paths in response to the optical path failure signal.    
     
     
         19 . The method of wavelength division multiplexing for an optical network according to    claim 18    wherein the predetermined configuration is a ring structure.  
     
     
         20 . The method of wavelength division multiplexing for an optical network according to    claim 19    wherein the predetermined configuration is a liner structure.  
     
     
         21 . The method of wavelength division multiplexing for an optical network according to    claim 18    wherein the network nodes include at least one main node and at least two local nodes.  
     
     
         22 . The method of wavelength division multiplexing for an optical network according to    claim 21    wherein the local nodes directly transmit the optical signals with each other without said main node.  
     
     
         23 . The method of wavelength division multiplexing for an optical network according to    claim 21    wherein the main node receives every one of the optical signals at one of the wavelengths from one of the local nodes and transmits the optical signals at a different one of the wavelengths to another of the local nodes.  
     
     
         24 . The method of wavelength division multiplexing for an optical network according to    claim 21    wherein said main node receives every one of the optical signals at one of the wavelengths from one of the local nodes and transmits optical signals at the same one of the wavelengths to the same one of the local nodes.  
     
     
         25 . The method of wavelength division multiplexing for an optical network according to    claim 18    further comprising flexibly modifying a number of the set of the wavelengths at each of the network node.  
     
     
         26 . The method of wavelength division multiplexing for an optical network according to    claim 18    wherein said multiplexing and said demultiplexing add and drop a single channel frequency.  
     
     
         27 . The method of wavelength division multiplexing for an optical network according to    claim 18    further comprising selectively connecting to establish a drop route and to establish a through route.  
     
     
         28 . The method of wavelength division multiplexing for an optical network according to    claim 18    further comprising amplifying the wavelength division multiplexed optical signal.  
     
     
         29 . A method of wavelength division multiplexing for an optical network, comprising: 
 providing a plurality of optical paths and a plurality of network nodes connected through the optical paths in a predetermined configuration, at least one of said network nodes being connected to a client;    transmitting and receiving a plurality of optical signals among the network nodes at a set of wavelengths;    selecting one of the optical paths for transmitting one of the optical signals for optimal through traffic;    detecting a failure in the optical signal to generate an optical path failure signal for a particular one of the optical paths; and    switching from the particular one of the optical paths to another of the optical paths for transmitting the one of the optical signals in response to the optical path failure signal.    
     
     
         30 . The method of wavelength division multiplexing for an optical network according to    claim 29    wherein the predetermined configuration is a ring structure.  
     
     
         31 . The method of wavelength division multiplexing for an optical network according to    claim 29    further comprising: providing dispersion shifted fibers with their chromatic dispersion at a wavelength near 1552 nm in the optical paths.  
     
     
         32 . The method of wavelength division multiplexing for an optical network according to    claim 31    wherein the optical input signals are multiplexed at 200 GHz interval within C-band having a wavelength range from 1530 nm to 1560 nm in the dispersion shifted fibers, each optical channel being less than −3.5 dBm, optical modulation speed being 2.48 Gbits/second, inter-node span loss being less than 12 dB at 40 km.  
     
     
         33 . A ring making optical network including a dispersion shifted optical fiber with a wave length in the vicinity of 1552 nm which shows substantially zero chromatic dispersion on at least a part of an optical fiber transmitting path, said optical network comprising: 
 a system which transmits a multiplexed optical signal having more than two wave lengths within a wave length range of 1530-1560 nm or the C-band at an interval of 200 GHz wherein    an optical input to the dispersion shifted fiber is less than −3.5 dBm per optical channel, a baud rate of light is less than 2.48 Gbit/s, and a span loss between nodes is less than 12 dB, in other words, an equivalent node interval is less than 40 Km.