Optical Code Division Multiplexing (OCDM) and Its Applications to Photonic Networks

Optical code division multiplexing (OCDM) is the other class of multiplexing techniques than time division multiplexing (TDM), wavelength division multiplexing (WDM) and space division multiplexing (SDM). OCDM has been proposed in mid ’70s. It has been long since OCDM remains outside the mainstream of research community of optical communications, however, possible scarcity of the wavelength resource in future photonic networks, the simple access protocol as well as versatility of optical codes motivate recent growth of OCDM research activities. In this paper, first, fundamentals of OCDM concept are presented, highlighting optical encoding and optical time gate detection which realize time spreading/despreading. Next, current research activities of OCDM are reviewed by focusing particularly on the optical implementations and the proof-of-concept experiments. It is devoted to three categories; high bit rate pointto-point transmissions, gigabit multiple access, followed by optical path networks using optical code. Finally, future issues are briefly summarized. key words: optical communications, code division multiplexing, wireless CDMA, multiple access, optical network