All-optical format conversion plays an important role in future transparent optical networks in order to enhance reconfigurability. On the other hand, the polarizationdivision multiplexing (PDM) technique has been extensively studied for achieving high-speed and high-spectral-efficiency optical networks. Since the state of polarization of PDM signals are randomly changed along the transmission optical link, it is important to elaborately design a polarization-insensitive conversion scheme in such a network. In this paper, we proposed and experimentally demonstrated an all-optical nonreturn-to-zero-return-to-zero format conversion for PDM on-off keying (OOK), binary phase-shift keying (BPSK), and quadrature phase-shift keying (QPSK) signals. Polarization-insensitive operation is achieved by utilizing the merit of the dualorthogonal-pump four-wave mixing (FWM) process in a highly nonlinear fiber, and receiver-sensitivity-gain operation is observed in the conversion process. The bit error ratio (BER) results show that receiver-sensitivity gains of $1.5, $0.8, and 0.3 dB for the OOK, BPSK, and QPSK PDM signals at BER values of 10 À9 , 10 À9 , and 10 À3 are obtained, respectively.Index Terms: Format conversion, polarization division multiplexing (PDM), four-wave mixing (FWM), highly nonlinear fiber (HNLF).