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This paper proposes and numerically demonstrates an all-optical on-off keying (OOK) to 16 quadrature amplitude modulation (QAM) format conversion using nonlinear optical loop mirror (NOLM) based on cross-phase modulation (XPM) and parametric amplification in optical fibers. The 16-QAM signal is generated by the superposition of two quadrature phase shift keying (QPSK) signals with different amplitudes. OOK to QPSK modulation format conversion is achieved by XPM in one highly nonlinear fiber (HNLF). The amplitude ratio 2:1 of two QPSK signals can be realized by parametric amplification. The feasibility of OOK to 16-QAM modulation format conversion is confirmed at the symbol rate of 10 Gs/s by numerical simulation with the length of 27 - 1 pseudo random binary sequence (PRBS) input OOK signals. The tolerance of power deviation of the converter is also analytically evaluated.