Optical Phase Add–Drop for Format Conversion Between DQPSK and DPSK and its Application in Optical Label Switching Systems

We propose and experimentally demonstrate an optical phase “add–drop” scheme to enable the format conversion between a 20-Gb/s differential quadrature phase-shift keying (DQPSK) and 10-Gb/s differential phase-shift keying. Meanwhile, the incoming DQPSK could be directly forwarded to another wavelength through the proposed optical phase “drop” scheme, which is implemented by four-wave-mixing effect in highly nonlinear fiber. By orthogonally encoding the label and payload of the optical packet on the in-phase ( $I$) and quadrature ( $ Q $) components of DQPSK, the proposed scheme could be applied in the optical label switching networks. The label erasing and rewriting of optical packets can be achieved through the proposed optical phase “drop” and “add” schemes, respectively.