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Widely Tunable Polarization-Insensitive Nondegenerate Four-Wave Mixing Wavelength Conversion for DPSK Signal

We demonstrate all-optical wavelength conversion for return-to-zero differential phase-shift keying (RZ-DPSK) signal by dual-pump four-wave mixing in a highly nonlinear photonic crystal fiber. By exploiting the residual birefringence in the fiber, the polarization of the first pump can be adjusted to achieve polarization-insensitive operation. The wavelength of the second pump is free to tune to broaden the conversion bandwidth. Open eyes of the converted signals are obtained for polarization-scrambled 10-Gb/s RZ-DPSK signal over a down-conversion bandwidth of 27 nm. Bit-error measurement shows a maximum power penalty of 4.5 dB at the error-free detection level.