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Orthogonal cross-phase-modulation (XPM) scheme in a nonlinear optical loop mirror (NOLM) is proposed to simultaneously convert four synchronized 10-Gb/s nonreturn-to-zero signals into return-to-zero (RZ) format. Modulation format conversion is achieved by using a synchronized optical control pulse train as the pulse carver in a NOLM. The control pulse train and the targeted signals are orthogonal in their states of polarization. This orthogonal nonlinear interaction substantially suppresses the undesirable four-wave mixing (FWM) induced crosstalk in the multichannel operation. Experimental demonstration of the proposed scheme shows that the suppression of the generated FWM idler is >26 dB. Error-free operation is achieved for the four converted 10-Gb/s RZ signals in a single NOLM by sharing the nonlinear XPM effect induced by the control pulse train.