Inter-Symbol Interference-Suppressed Colorless DPSK Demodulation

Abstract

An optical device includes an interferometer for a received optical differential phase shift keying DPSK signal, and an equalizer integrated with the interferometer in a manner for reducing from optical filtering effects an interference by signal bits of the DPSK signal with signal bits of a contiguous DPSK signal. The interferometer is a Michelson delay interferometer type, but can also be a Mach-Zehnder delay interferometer type on fiber, waveguide or other optical structure. The equalizer is a Fabry-Perot type equalizer, but can be a ring resonator type or a fiber based equalizer.

1 . An optical device comprising:
 an interferometer for a received optical differential phase shift keying DPSK signal, and   an equalizer integrated with said interferometer in a manner for reducing from optical filtering effects an interference by signal bits of the DPSK signal with signal bits of a contiguous DPSK signal.   
   
   
       2 . The optical device of  claim 1 , wherein said equalizer is integrated with said interferometer by one of: optically placing said equalizer  807  at an input of said interferometer; optically placing said equalizer  808  at a constructive path of said interferometer; and optically placing said equalizer  814  having half of a filter ripple depth at an input and a constructive path of said interferometer. 
   
   
       3 . The optical device of  claim 1 , wherein said equalizer is integrated with said interferometer by optically placing a first of said equalizer  811  at an input and constructive path of said interferometer and a second of said equalizer  813  at a destructive path of said interferometer, said first and second of said equalizer having half of a filter ripple depth. 
   
   
       4 . The optical device of  claim 1 , wherein said equalizer is integrated by one of: optically placing a first of said equalizer  907  inside said interferometer between a beam splitter/combiner  801  and a first reflecting mirror  803  and optically placing a second of said equalizer  909  inside said interferometer between said beam splitter/combiner  801  and a second reflecting mirror  805 ; and optically integrating a first of said equalizer  907  inside said interferometer with a first reflecting mirror  911  and optically integrating a second of said equalizer inside said interferometer with a second reflecting mirror  913 . 
   
   
       5 . The optical device of  claim 1 , wherein said Interferometer has a prism or 2 mirrors for its constructive and destructive reflectors  917 ,  919  and said equalizer is integrated by one of: optically placing said equalizer  915  at an input of said interferometer; and optically placing a first of said equalizer  921  at a constructive path of said interferometer and a second of said equalizer  923  at a destructive path of said interferometer. 
   
   
       6 . The optical device of  claim 1 , wherein said Interferometer includes a prism or 2 mirrors for its constructive and destructive path reflectors  917 ,  919  and said equalizer is integrated by one of: optically placing said equalizer  927  in both a constructive path and a destructive path of said interferometer with a reflective mirror or prism  925  in an optical path of said constructive path before said equalizer  927 ; and optically placing said equalizer  931  in both constructive and destructive paths of said interferometer with a lens  929  in an optical path of both said constructive and destructive paths before said equalizer  931  and a reflective mirror or prism  930  in an optical path of said constructive path before said lens  929 . 
   
   
       7 . The optical device of  claim 1 , wherein said interferometer is one of a Michelson type delay interferometer, a Mach-Zehnder type delay interferometer based on optical fiber or optical waveguide or planar lightwave circuit. 
   
   
       8 . The optical device of  claim 1 , wherein said equalizer is one of a Fabry-Perot PT type equalizer, a ring resonator type and a fiber based structure. 
   
   
       9 . The optical device of  claim 1 , further comprising a layer of glass in at least one optical path of said integrated interferometer or equalizer for varying temperature of said glass to change the index of refraction of said glass thereby varying an optical path through said glass. 
   
   
       10 . The optical device of  claim 1 , wherein said interferometer and equalizer are integrated for reducing inter-symbol interference in a 40 Gb/s DPSK signal in a 50 GHz spaced DWDM communication system. 
   
   
       11 . A method comprising the steps of:
 providing constructive and destructive optical paths for a received optical differential phase shift keying DPSK signal, and   integrating an equalizer with said providing for reducing from optical filtering effects an interference by signal bits of the DPSK signal with signal bits of a contiguous DPSK signal.   
   
   
       12 . The method of  claim 1 , wherein said integrating includes one of: optically placing said equalizer  807  at an input of said providing; optically placing said equalizer  808  at said constructive path; and optically placing said equalizer  814  having half of a filter ripple depth at an input of said providing and said constructive path. 
   
   
       13 . The method of  claim 11 , where said integrating includes optically placing a first of said equalizer  811  at an input and said constructive path of said providing and optically placing a second of said equalizer  813  at said destructive path, said first and second of said equalizer having half of a filter ripple depth. 
   
   
       14 . The method of  claim 11 , wherein said integrating includes one of: optically placing a first of said equalizer  907  inside an interferometer from said providing between a beam splitter/combiner  801  and a first reflecting mirror  803  and optically placing a second of said equalizer  909  inside said interferometer between said beam splitter/combiner  801  and a second reflecting mirror  805 ; and optically placing a first of said equalizer  907  inside an interferometer from said providing with a first reflecting mirror  911  and optically integrating a second of said equalizer inside said interferometer with a second reflecting mirror  913 . 
   
   
       15 . The method of  claim 11 , wherein said providing comprises providing an Interferometer with a prism or 2 mirrors for its constructive and destructive reflectors  917 ,  919  and said integrating includes one of: optically placing said equalizer  915  at an input of said interferometer; optically placing a first of said equalizer  921  at a constructive path of said interferometer and a second of said equalizer  923  at a destructive path of said interferometer. 
   
   
       16 . The method of  claim 11 , wherein said providing comprises providing an Interferometer with a prism or 2 mirrors for its constructive and destructive path reflectors  917 ,  919  and said integrating includes one of: optically placing said equalizer  927  in both said constructive and destructive paths of said interferometer with a reflective mirror or prism  925  in an optical path of said constructive path before said equalizer  927 ; and optically placing said equalizer  931  in both said constructive and destructive paths of said interferometer with a lens  929  in an optical path of both said constructive and destructive paths before said equalizer  931  and a reflective mirror or prism  930  in an optical path of said constructive path before said lens  929 . 
   
   
       17 . The method of  claim 11 , wherein said constructive and destructive paths are provided by one of a Michelson type delay interferometer and a Mach-Zehnder type delay interferometer based on optical fiber or optical waveguide or planar lightwave circuit, and the equalizer is one of a Fabry-Perot PT type equalizer, a ring resonator and a fiber based equalizing. 
   
   
       18 . The method of  claim 11 , wherein equalizer is one of a Fabry-Perot PT type equalizer, a ring resonator and a fiber based equalizing. 
   
   
       19 . The optical device of  claim 11 , further comprising varying temperature of a layer of glass in an optical path of said separating with integrated equalizing for changing the index of refraction of said glass thereby varying said optical path through said glass. 
   
   
       20 . The method of  claim 1 , wherein separating with integrated equalizing reduces inter-symbol interference in a 40 Gb/s DPSK signal in a 50 GHz spaced DWDM communication system.