Optical communication transmission system

Abstract

An optical communication transmission system including an optical amplifier lumped repeater system of the present invention includes, for the purpose of preventing degradation of the transmission characteristic arising from wavelength dispersion of optical fibers due to raised power of the optical signal, transmission optical fibers provided for all or most of the repeating sections and having wavelength dispersion values set to different values from zero, and optical fibers provided for the individual sections to compensate for the sum of wavelength dispersion of the sections so as to reduce the total wavelength dispersion to zero. The optical fiber for compensation for each section may be replaced by a substitutive compensation element. Alternatively, very small wavelength dispersion which remains due to failure in compensating to zero dispersion may be compensated for using a dispersion equalizer of an electric system in the reception section.

What is claimed is:  
     
       1. A long-haul optical amplifier lumped repeater communication system comprising: 
       an optical transmitter generating a light signal;  
       a first optical transmission link connected to said optical transmitter and having a zero dispersion wavelength of a value different from the transmission wavelength of the optical transmitter;  
       a plurality of optical amplifier-repeaters, one of the optical amplifier-repeaters being connected to the first optical link;  
       a plurality of intermediate optical transmission links interconnecting the plurality of amplifier-repeaters, each of said plurality of optical transmission links having a zero dispersion wavelength of a value different from the transmission wavelength of the optical transmitter;  
       an optical receiver; 
       a terminating optical transmission link connected between one of the optical amplifier-repeaters and the optical receiver and having a zero dispersion wavelength of a value different from the transmission wavelength of the optical transmitter;  
       a plurality of dispersion compensating means, each connected to respective one of said first, intermediate and terminating optical links so that the total dispersion of the system is approximately equal to zero.  
     
     
       2. The long-haul optical amplifier lumped repeater communication system of  claim 1 , wherein said plurality of dispersion compensating means introduce chromatic dispersion so that the total dispersion of each optical transmission link and a dispersion compensating means connected thereto adds up to zero. 
     
     
       3. The long-haul optical amplifier lumped repeater communication system of  claim 1 , wherein said optical transmitter includes an optical amplifier and wherein said optical receiver includes an optical amplifier. 
     
     
       4. The long-haul optical amplifier lumped repeater communication system of  claim 1 , wherein said plurality of dispersion compensating means are included in said plurality of optical amplifier-repeaters. 
     
     
       5. An optical amplifier repeater in an optical transmission line with an optical transmission link having a zero dispersion wavelength of a value different from the wavelength of a received optical signal for amplifying said received optical signal from said optical transmission link comprising: 
       
         a dispersion compensator connected to said optical transmission link for compensating chromatic dispersion resulted from said optical transmission link such that chromatic dispersion substantially equals zero and outputting a compensated signal;  
       
       
         an optical amplifier connected to said dispersion compensator for optically amplifying said compensated signal and outputting an amplified signal as an output optical signal of said optical amplifier repeater.  
       
     
     
       6. An optical amplifier repeater as claimed in  claim 5 , wherein said dispersion compensator comprises an optical fiber having chromatic dispersion characteristics of different polarity from that of said optical transmission link.  
     
     
       7. A long- haul optical amplifier lumped repeating method for transmitting an optical signal via first to N - th optical transmission links which are connected in a cascade arrangement, each of said first to N - th transmission links having a zero dispersion wavelength of a value different from the wavelength of said optical signal, where N is an integer greater than  1 , comprising the steps of:    
       ( a )  generating and supplying, at the transmitting side, an optical signal to said first optical link;    
       ( b )  repeating,  ( N− 1   )  times, the following step b -   1   )  from I= 2  to I=N,    
         b -   1   )  amplifying an optical signal supplied from said  ( I -   1   ) th optical transmission link to output the amplified optical signal to said Ith optical transmission link:    
       ( c )  compensating chromatic dispersion included in at least one of the output optical signals from said first to  ( N− 1   ) th optical transmission links; and    
       ( d )  supplying an optical signal from Nth optical transmission link to a destination side, wherein    
         at least one step of compensating for chromatic dispersion is inserted in said step  ( b ) , said compensating step compensating chromatic dispersion included in said optical signal supplied therein so that the total dispersion from the transmitting side to said destination side may be substantially equal to zero.    
     
     
       8. An optical communication transmission system, comprising: 
       
         a plurality of optical amplifiers located in a cascade arrangement on a transmission line having a zero dispersion wavelength at a wavelength different from the wavelength of a transmission light, for optically amplifying the transmission light to output an amplified transmission light; and  
       
       
         at least one dispersion compensator located between said optical amplifiers, for compensating chromatic dispersion included in said amplified transmission light such that the chromatic dispersion included in said amplified transmission light from said transmission line substantially equals zero.  
       
     
     
       9. An optical communication transmission system as claimed in  claim 8 , wherein said dispersion compensator makes the total dispersion of said system substantially equal to zero.  
     
     
       10. An optical communication transmission system as claimed in  claim 8 , wherein said optical amplifiers include an erbium doped optical fiber amplifier.  
     
     
       11. An optical communication transmission system as claimed in  claim 8 , further comprising: 
       
         a light generator for generating said transmission light; and  
       
       
         a dispersion shift optical fiber located between said optical amplifiers, having a zero dispersion wavelength of a value different from the wavelength of said transmission light.  
       
     
     
       12. An optical communication transmission system as claimed in  claim 11 , wherein said light generator comprises: 
       
         a semiconductor laser source for outputting optical power;  
       
       
         a modulator for modulating said optical power with a modulation signal having a predetermined bit rate to generate said transmission light.  
       
     
     
       13. An optical communication transmission system as claimed in  claim 12 , wherein said bit rate of said modulation signal is equal to or more than  10  GB/s.  
     
     
       14. An optical communication transmission system as claimed in  claim 12 , wherein said bit rate of said modulation signal is equal to or more than  5  GB/s.  
     
     
       15. An optical communication transmission system as claimed in  claim 11 , wherein said dispersion compensator comprises a dispersion compensation optical fiber having a zero dispersion wavelength of a value different from the wavelength of said transmission light.  
     
     
       16. An optical communication transmission system as claimed in  claim 15 , wherein said dispersion compensation optical fiber is inserted after said dispersion shift optical fiber between said optical amplifiers adjacently located.  
     
     
       17. An optical communication transmission system as claimed in  claim 8 , wherein the wavelength of said transmission light is selected to be either of a  1 . 3  μm band or a  1 . 5  μm band.  
     
     
       18. An optical communication transmission system as claimed in  claim 15 , wherein said dispersion compensator comprises a dispersion compensation optical fiber having dispersion characteristics of different polarity from that of said dispersion shift optical fiber.  
     
     
       19. An optical communication transmission system as claimed in  claim 18 , wherein said dispersion of said dispersion compensation optical fiber has a positive value and said dispersion of said dispersion shift optical fiber has a negative value.  
     
     
       20. An optical communication transmission system as claimed in  claim 19 , wherein an absolute value of said dispersion of said dispersion compensation optical fiber is larger than that of said dispersion of said dispersion shift optical fiber.  
     
     
       21. An optical communication transmission system as claimed in  claim 15 , wherein the length of said dispersion compensation optical fiber is shorter than that of said dispersion shift optical fiber.  
     
     
       22. An optical communication transmission system having a plurality of optical amplifiers located in a cascade arrangement, each of said optical amplifiers amplifying transmission light to output an amplified transmission light, comprising: 
       
         at least two pieces of dispersion compensation optical fiber having substantially a zero dispersion wavelength of a value different from the wavelength of said transmission light, for compensating dispersion included in said amplified transmission light;  
       
       
         at least two pieces of dispersion shift optical fiber having substantially a zero dispersion wavelength of a value different from the wavelength of said transmission light; and  
       
       
         wherein said dispersion compensation optical fiber and said dispersion shift optical fiber are alternately located with respect to one another and said plurality of optical amplifiers are connected to said interconnected dispersion shift optical fiber and dispersion compensation optical fiber;  
       
       
         whereby the dispersion in the amplified transmission light substantially equals zero.  
       
     
     
       23. An optical transmission signal transmitted on a transmission line having substantially a zero dispersion wavelength of a value different from the wavelength of said optical transmission signal, wherein said optical transmission signal is optically amplified into a first amplified optical transmission signal, dispersion included in said first amplified optical transmission signal is compensated such that the dispersion substantially equals zero, and said dispersion compensated first amplified optical transmission signal is optically amplified into a second amplified optical transmission signal.  
     
     
       24. An optical transmission signal as claimed in  claim 23 , wherein said optical transmission signal is output from a semiconductor laser source.  
     
     
       25. An optical communication transmission system, comprising: 
       
         a plurality of optical amplifiers located on a transmission line constructed of a dispersion shift optical fiber having a zero dispersion wavelength of a value different from the wavelength of transmission light, for amplifying said transmission light; and  
       
       
         a plurality of dispersion compensators located on said transmission line at a predetermined interval, for compensating dispersion included in said transmission light such that dispersion substantially equals zero.  
       
     
     
       26. An optical communication transmission system as claimed in  claim 25 , wherein said dispersion compensator comprises a dispersion compensation optical fiber having substantially a zero dispersion wavelength of a value different from the wavelength of said transmission light.  
     
     
       27. An optical communication transmission system as claimed in  claim 25 , wherein a wavelength of said transmission light is within a  1 . 5  μm band.  
     
     
       28. An optical communication transmission method, comprising the steps of: 
       
         generating transmission light;  
       
       
         amplifying said transmission light by a plurality of amplifiers located in a cascade arrangement on a transmission line of dispersion shifted optical fibers having a zero dispersion wavelength of a value different from the wavelength of said transmission light to output amplified transmission light; and  
       
       
         compensating dispersion included in said amplified transmission light between said optical amplifiers such that the dispersion of said amplified transmission light output from the transmission line is substantially zero.  
       
     
     
       29. An optical amplifier repeater in an optical transmission line with an optical transmission link having a zero dispersion wavelength of a value different from the wavelength of a received optical signal for amplifying said received optical signal from the optical transmission link; comprising; 
       
         a dispersion compensator for compensating chromatic dispersion resulted from said optical transmission link such that chromatic dispersion substantially equals zero and outputting a compensated signal; and  
       
       
         an optical amplifier for optically amplifying said compensated signal and outputting an amplified signal as an output optical signal of said optical amplifier repeater.