Chromatic dispersion compensation in wavelength division multiplexed optical transmission systems

Abstract

A method and apparatus is provided for managing dispersion in a WDM optical transmission system so that transmission performance is improved. The usable optical bandwidth of the transmission system is divided into sub-bands that individually undergo dispersion compensation before being re-combined. Accordingly, in comparison to known dispersion mapping techniques, more WDM data channels reside near a wavelength corresponding to the average zero dispersion wavelength.

What is claimed is:  
     
       1. A WDM optical communication system, comprising: 
       a transmitter and a receiver;  
       an optical fiber transmission path coupling said transmitter to said receiver, said transmission path including at least one optical amplifier;  
       a dispersion compensator disposed at an intermediate point along said transmission path, said compensator including:  
       an optical splitter for dividing a signal introduced therein onto a plurality of optical paths, said signal having a prescribed bandwidth;  
       a bandpass filter disposed along each of said optical paths, said filters dividing the prescribed bandwidth of the signal into a plurality of distinct sub-bands;  
       a dispersion compensating element coupled to each of the bandpass filters, said dispersion compensating optical elements each substantially compensating for dispersion at a prescribed wavelength within the bandpass of its respective bandpass filter;  
       a coupler for recombining said distinct sub-bands and coupling said recombined distinct sub-bands onto said optical fiber transmission path.  
     
     
       2. The communication system of  claim 1  wherein said plurality of sub-bands are substantially non-overlapping in wavelength. 
     
     
       3. The system of  claim 1  wherein said dispersion compensating elements are single-mode optical fibers. 
     
     
       4. The system of  claim 1  wherein said dispersion compensating elements are fiber diffraction gratings. 
     
     
       5. The system of  claim 4  wherein said fiber diffraction gratings are chirped gratings. 
     
     
       6. The system of  claim 5  wherein said gratings are linearly chirped. 
     
     
       7. The system of  claim 5  wherein said gratings are quadratically chirped. 
     
     
       8. The system of  claim 1  wherein said signal is a soliton signal. 
     
     
       9. The system of  claim 1  further comprising an additional dispersion compensating element preceding said optical splitter for providing a common amount of dispersion to all of the sub-bands. 
     
     
       10. The system of  claim 9  wherein said additional dispersion compensating element is an extension of the fiber transmission path. 
     
     
       11. The system of  claim 1  further comprising a plurality of loss elements disposed in said optical paths to provide gain equalization to the sub-bands. 
     
     
       12. The system of  claim 1  wherein said prescribed wavelengths are substantially equal to center wavelengths of the respective bandpass filters. 
     
     
       13. The system of  claim 12  wherein said prescribed wavelengths are offset from the respective center wavelengths by a predetermined amount. 
     
     
       14. The system of  claim 4  wherein said plurality of optical paths are defined by reflections from different fiber gratings. 
     
     
       15. A dispersion compensator for use in a WDM optical communication system that includes a transmitter, receiver, and an optical fiber transmission path coupling said transmitter to said receiver, said transmission path including at least one optical amplifier, said dispersion compensator comprising: 
       an optical splitter for dividing a signal introduced therein onto a plurality of optical paths, said signal having a prescribed bandwidth, said optical splitter being adapted to receive said signal from an intermediate point along said optical fiber transmission path;  
       a bandpass filter disposed along each of said optical paths, said filters dividing the prescribed bandwidth of the signal into a plurality of distinct sub-bands;  
       a dispersion compensating optical element coupled to each of the bandpass filters, said dispersion compensating optical elements each substantially compensating for dispersion at a prescribed wavelength within the bandpass of its respective bandpass filter;  
       a coupler for recombining said distinct sub-bands, said coupler being adapted to couple said recombined distinct sub-bands onto said optical fiber transmission path.  
     
     
       16. The dispersion compensator of  claim 15  wherein said plurality of sub-bands are substantially non-overlapping in wavelength. 
     
     
       17. The dispersion compensator of  claim 15  wherein said dispersion compensating elements are single-mode optical fibers. 
     
     
       18. The dispersion compensator of  claim 15  wherein said dispersion compensating elements are fiber diffraction gratings. 
     
     
       19. The dispersion compensator of  claim 18  wherein said fiber diffraction gratings are chirped gratings. 
     
     
       20. The dispersion compensator of  claim 19  wherein said gratings are linearly chirped. 
     
     
       21. The dispersion compensator of  claim 19  wherein said gratings are quadratically chirped. 
     
     
       22. The dispersion compensator of  claim 15  wherein said signal is a soliton signal. 
     
     
       23. The dispersion compensator of  claim 15  further comprising an additional dispersion compensating element preceding said optical splitter for providing a common amount of dispersion to all of the sub-bands. 
     
     
       24. The system of  claim 23  wherein said additional dispersion compensating element is an extension of the fiber transmission path. 
     
     
       25. The dispersion compensator of  claim 15  further comprising a plurality of loss elements disposed in said optical paths to provide gain equalization to the sub-bands. 
     
     
       26. The dispersion compensator of  claim 15  wherein said prescribed wavelengths are substantially equal to center wavelengths of the respective bandpass filters. 
     
     
       27. The dispersion compensator of  claim 26  wherein said prescribed wavelengths are offset from the respective center wavelengths by a predetermined amount. 
     
     
       28. The dispersion compensator of  claim 18  wherein said plurality of optical paths are defined by reflections from different fiber gratings. 
     
     
       29. A method for compensating for dispersion in a WDM optical communication system that includes a transmitter, receiver, and an optical fiber transmission path coupling said transmitter to said receiver, said method comprising the steps of: 
       splitting a signal at an intermediate point along the transmission path to be directed onto a plurality of optical paths, said signal having a prescribed bandwidth;  
       filtering the signals along each of said optical paths to divide the prescribed bandwidth of the signal into a plurality of distinct sub-bands;  
       compensating for dispersion at a prescribed wavelength within the distinct sub-bands;  
       recombining said distinct sub-bands and directing said recombined distinct sub-bands onto said optical fiber transmission path.  
     
     
       30. The method of  claim 29  wherein said plurality of sub-bands are substantially non-overlapping in wavelength. 
     
     
       31. The method of  claim 29  wherein the step dispersion compensation is accomplished with single-mode optical fibers. 
     
     
       32. The method of  claim 29  wherein the step of dispersion compensation is accomplished with fiber diffraction gratings. 
     
     
       33. The method of  claim 32  wherein said fiber diffraction gratings are chirped gratings. 
     
     
       34. The method of  claim 33  wherein said gratings are linearly chirped. 
     
     
       35. The method of  claim 33  wherein said gratings are quadratically chirped. 
     
     
       36. The method of  claim 29  wherein said signal is a soliton signal. 
     
     
       37. The method of  claim 29  further comprising the step of compensating for a select amount of dispersion prior to the step of filtering the signals. 
     
     
       38. The method of  claim 37  wherein said select amount of dispersion compensation is provided along a portion of said fiber transmission path. 
     
     
       39. The method of  claim 29  further comprising the step of introducing loss along the optical paths to provide gain equalization to the sub-bands. 
     
     
       40. The method of  claim 29  wherein said prescribed wavelengths are substantially equal to center wavelengths of respective bandpass filters employed to perform the step of filtering the signals. 
     
     
       41. The method of  claim 29  wherein said prescribed wavelengths are offset from the respective center wavelengths by a predetermined amount. 
     
     
       42. The method of  claim 32  wherein said plurality of optical paths are defined by reflections from different fiber gratings. 
     
     
       43. A WDM optical communications system, comprising: 
       a transmitter and a receiver;  
       an optical fiber transmission path coupling said transmitter to said receiver, said transmission path including at least one optical amplifier;  
       a dispersion compensator disposed at an intermediate point along said transmission path, said compensator including:  
       a wavelength routing device for dividing a signal having a prescribed bandwidth into a plurality of distinct sub-bands;  
       a plurality of output paths for respectively receiving said plurality of distinct sub-bands;  
       a dispersion compensating optical element coupled to each of the output paths, said dispersion compensating optical elements each substantially compensating for dispersion at a prescribed wavelength within the bandpass of its respective sub-band;  
       a coupler for recombining said distinct sub-bands and coupling said recombined distinct sub-bands onto said optical fiber transmission path.  
     
     
       44. The communication system of  claim 43  wherein said plurality of sub-bands are substantially non-overlapping in wavelength. 
     
     
       45. The system of  claim 43  wherein said dispersion compensating elements are single-mode optical fibers. 
     
     
       46. The system of  claim 43  wherein said dispersion compensating elements are fiber diffraction gratings. 
     
     
       47. The system of  claim 46  wherein said fiber diffraction gratings are chirped gratings. 
     
     
       48. The system of  claim 47  wherein said gratings are linearly chirped. 
     
     
       49. The system of  claim 47  wherein said gratings are quadratically chirped. 
     
     
       50. The system of  claim 43  wherein said signal is a soliton signal. 
     
     
       51. The system of  claim 43  further comprising an additional dispersion compensating element preceding said wavelength routing device for providing a common amount of dispersion to all of the sub-bands. 
     
     
       52. The system of  claim 51  wherein said additional dispersion compensating element is an extension of the fiber transmission path. 
     
     
       53. The system of  claim 43  further comprising a plurality of loss elements disposed in said optical paths to provide gain equalization to the sub-bands. 
     
     
       54. The system of  claim 43  wherein said prescribed wavelengths are substantially equal to center wavelengths of the respective bandpass filters. 
     
     
       55. The system of  claim 54  wherein said prescribed wavelengths are offset from the respective center wavelengths by a predetermined amount. 
     
     
       56. The system of  claim 46  wherein said plurality of optical paths are defined by reflections from different fiber gratings. 
     
     
       57. The system of  claim 43  wherein said coupler comprises a second wavelength routing device. 
     
     
       58. A WDM optical communication system, comprising: 
       a transmitter and a receiver;  
       an optical fiber transmission path coupling said transmitter to said receiver, said transmission path including at least one optical amplifier;  
       a dispersion compensator disposed at an intermediate point along said transmission path, said compensator including:  
       a circulator having at least an input port for receiving optical signals from the transmission path, an output port for transmitting optical signals onto the transmission path, and a third port;  
       a wavelength routing device coupled to said third port of the circulator for dividing a signal having a prescribed bandwidth into a plurality of distinct sub-bands;  
       a plurality of output paths for respectively receiving said plurality of distinct sub-bands;  
       a dispersion compensating optical element coupled to each of the output paths, said dispersion compensating optical elements each substantially compensating for dispersion at a prescribed wavelength within the bandpass of its respective sub-band;  
       a Faraday rotator mirror coupled to each of the dispersion compensating optical elements.  
     
     
       59. The communication system of  claim 58  wherein said plurality of sub-bands are substantially non-overlapping in wavelength. 
     
     
       60. The system of  claim 58  wherein said dispersion compensating elements are single-mode optical fibers. 
     
     
       61. The system of  claim 58  wherein said signal is a soliton signal. 
     
     
       62. The system of  claim 58  further comprising an additional dispersion compensating element preceding said wavelength routing device for providing a common amount of dispersion to all of the sub-bands. 
     
     
       63. The system of  claim 62  wherein said additional dispersion compensating element is an extension of the fiber transmission path. 
     
     
       64. The system of  claim 58  further comprising a plurality of loss elements disposed in said optical paths to provide gain equalization to the sub-bands. 
     
     
       65. The system of  claim 58  wherein said prescribed wavelengths are substantially equal to center wavelengths of the respective bandpass filters. 
     
     
       66. The system of  claim 65  wherein said prescribed wavelengths are offset from the respective center wavelengths by a predetermined amount. 
     
     
       67. A dispersion compensator comprising: 
       
         a plurality of optical paths configured to carry a wavelength division multiplexed optical signals having a prescribed bandwidth;  
       
         a bandpass filter disposed along each of said optical paths, said filters dividing the prescribed bandwidth of the signal into a plurality of distinct sub - bands; and    
       
         a dispersion compensating element coupled to each of said bandpass filters, said dispersion compensating optical elements each substantially compensating for dispersion at a prescribed wavelength within the bandpass of its respective bandpass filter. 
       
     
     
       68. The dispersion compensator in accordance with  claim 67  wherein said prescribed wavelengths are substantially equal to center wavelengths of the respective bandpass filters. 
     
     
       69. The dispersion compensator in accordance with  claim 67  wherein said dispersion compensating elements are single- mode optical fibers.   
     
     
       70. The dispersion compensator in accordance with  claim 67  wherein said plurality of sub- bands are substantially non - overlapping in wavelength.   
     
     
       71. A method for compensating for dispersion in a wavelength division multiplexed optical communication system that includes optical signal having a prescribed bandwidth and a plurality of optical paths configured to carry said optical signal, said method comprising the steps of: 
         filtering the signals along each of said optical paths to divide the prescribed bandwidth of the signal into a plurality of distinct sub - bands; and    
         compensating for dispersion at a prescribed wavelength within the distinct sub - bands.   
     
     
       72. The method for compensating for dispersion in accordance with  claim 71  wherein said prescribed wavelengths are substantially equal to center wavelengths of respective bandpass filters employed to perform the step of filtering the signals. 
     
     
       73. The method for compensating for dispersion in accordance with  claim 71  wherein said prescribed wavelengths are offset from respective center wavelengths with the distinct sub- bands by a predetermined amount.   
     
     
       74. The method for compensating for dispersion in accordance with  claim 71  wherein said plurality of sub- bands are substantially non - overlapping in wavelength.