Optical device, terminal apparatus, and system for wavelength division multiplexing

Abstract

Disclosed herein is an optical device, terminal apparatus, and system for wavelength division multiplexing (WDM). The optical device includes a WDM port adapted to WDM, a specific port to which a specific wavelength substantially central of WDM channels is allocated, a plurality of first ports to which longer wavelengths are allocated, a plurality of second ports to which shorter wavelengths are allocated, and first to fourth optical filters. The first optical filter couples the WDM port to the second optical filter by the specific wavelength, and also couples the WDM port to the second optical filter by the other plural wavelengths. The second optical filter couples the first optical filter to the third optical filter by the longer wavelengths, and also couples the first optical filter to the fourth optical filter by the shorter wavelengths. The third optical filter couples the second optical filter to the first ports, and the fourth optical filter couples the second optical filter to the second ports. The specific wavelength can be set equal to the cutoff wavelength of the second optical filter, so that the second optical filter can be easily manufactured. Further, a maximum

What is claimed is:  
     
         1 . An optical device comprising: 
 a WDM port adapted to wavelength division multiplexing (WDM);    first to N-th ports to which first to N-th wavelengths are respectively allocated, where N is an integer greater than 4; and    first to fourth optical filters;    said first optical filter coupling said WDM port to said i-th port by said i-th wavelength, where i is an integer satisfying 3≦i≦(N−2), and also coupling said WDM port to said second optical filter by the plural wavelengths except said i-th wavelength;    said second optical filter coupling said first optical filter to said third optical filter by said first to (i−1)-th wavelengths, and also coupling said first optical filter to said fourth optical filter by said (i+1)-th to N-th wavelengths;    said third optical filter coupling said second optical filter to said first to (i−1)-th ports respectively by said first to (i−1)-th wavelengths;    said fourth optical filter coupling said second optical filter to said (i+1)-th to N-th ports respectively by said (i+1)-th to N-th wavelengths.    
     
     
         2 . An optical device according to  claim 1 , wherein said first optical filter comprises a bandpass filter having a passband including said i-th wavelength.  
     
     
         3 . An optical device according to  claim 1 , wherein said second optical filter comprises any one of a long-wave pass filter and a short-wave pass filter.  
     
     
         4 . An optical device according to  claim 3 , wherein said second optical filter has a cutoff wavelength substantially equal to said i-th wavelength.  
     
     
         5 . An optical device according to  claim 1 , wherein: 
 said third optical filter comprises a plurality of bandpass filters respectively connected to said first to (i−1)-th ports; and    said fourth optical filter comprises a plurality of bandpass filters respectively connected to said (i+1)th to N-th ports.    
     
     
         6 . An optical device according to  claim 1 , wherein at least one of said first to fourth optical filters comprises a dielectric multilayer film.  
     
     
         7 . An optical device according to  claim 1 , wherein at least one of said first to fourth optical filters comprises an optical circulator having at least three ports, and a fiber grating connected to one of said at least three ports.  
     
     
         8 . An optical device according to  claim 1 , further comprising: 
 (N+1)-th to (N+j)-th ports to which (N+1)-th to (N+j)-th wavelengths are respectively allocated, where j is an integer greater than 2; and    fifth to seventh optical filters;    said fifth optical filter coupling said first optical filter to said (N+1)-th port by said (N+1)-th wavelength, and also coupling said first optical filter to said second optical filter by the plural wavelengths except said (N+1)-th wavelength;    said sixth optical filter coupling said second optical filter to said fourth optical filter by said (i+1)-th to N-th wavelengths, and also coupling said second optical filter to said seventh optical filter by said (N+2)-th to (N+j)-th wavelengths;    said seventh optical filter coupling said sixth optical filter to said (N+2)-th to (N+j)-th ports respectively by said (N+2)-th to (N+j)-th wavelengths.    
     
     
         9 . A system comprising: 
 first and second terminal apparatuses; and    an optical fiber transmission line connecting said first and second terminal apparatuses;    said first terminal apparatus comprising a plurality of optical transmitters for outputting a plurality of optical signals having different wavelengths, and an optical multiplexer for wavelength division multiplexing said plurality of optical signals and outputting resultant WDM signal light to said optical fiber transmission line;    said second terminal apparatus comprising an optical demultiplexer for separating WDM signal light transmitted by said optical fiber transmission line into a plurality of optical signals having different wavelengths, and a plurality of optical receivers for receiving said plurality of optical signals output from said optical demultiplexer;    at least one of said optical multiplexer and said optical demultiplexer comprising an optical device according to any one of  claims 1  to  8 .    
     
     
         10 . A system according to  claim 9 , further comprising at least one optical amplifier arranged along said optical fiber transmission line.  
     
     
         11 . A terminal apparatus comprising a plurality of optical transmitters for outputting a plurality of optical signals having different wavelengths, and an optical multiplexer for wavelength division multiplexing said plurality of optical signals; 
 said optical multiplexer comprising an optical device according to any one of  claims 1  to  8 .    
     
     
         12 . A terminal apparatus according to  claim 11 , further comprising a plurality of variable optical attenuators connected between said plurality of optical transmitters and said optical multiplexer.  
     
     
         13 . A terminal apparatus comprising an optical demultiplexer for separating wavelength division multiplexed signal light into a plurality of optical signals having different wavelengths, and a plurality of optical receivers for receiving said plurality of optical signals; 
 said optical demultiplexer comprising an optical device according to any one of  claims 1  to  8 .