Analysis of Phase Shift Tolerance in a Coherent OCDM System Using FBG Phase En/Decoders

Renichi MORITOMO  Tomoaki NAKAMURA  Yasuhiro KOTANI  Saeko OSHIBA  

IEICE TRANSACTIONS on Communications   Vol.E91-B   No.8   pp.2509-2515
Publication Date: 2008/08/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e91-b.8.2509
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Next Generation Broadband Access Technologies)
optical code division multiplexing,  coherent OCDM,  FBG phase encoder,  wavelength dependence,  

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We previously reported, for a coherent optical code division multiplexing (OCDM) system using fiber Bragg grating (FBG) phase en/decoders, that the signals exhibited phase shift tolerance for a difference between the light source wavelength and the Bragg wavelength of an FBG phase en/decoder when the two signals were multiplexed. However, the phase conditions of only the central wavelength among the ones forming a pulse were analyzed. For a more specific consideration, we calculated the phase of each wavelength forming the decoded pulse. In this report, the measured and calculated reflecting properties were compared and the reliability of the method was confirmed. We calculated the phase conditions of the decoded pulses and clarified the phase characteristics with regard to the phase modulation and the interference between pulses overlapped during decoding. For the realization of an asynchronous access, the FBG phase en/decoders should be designed so that the spreading time is the inverse of 2(texttransmission rate).