Abstract
Practical quantum cryptography over long fiber is of current research interest. Quantum cryptography based on four single-photon polarizations (vertical, horizontal, right-circular. left-circular)1 is difficult in fiber, although experimental efforts have been reported.2 Two orthogonal components of the single-photon Field can be transmitted through two arms of Mach-Zebnder interferometer.3 The four polarizations correspond to relative phase 0, π, π/2, or 3π/2, which is even more difficult to maintain between two fibers. Time-division3,4 and frequency-division5 multiplexing schemes have been proposed to circumvent the difficulty by putting two arms into a fiber. They both require precisely matched multiplexer and demultiplexer.
© 1997 Optical Society of America
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