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We propose an optical signal-to-noise ratio (OSNR) monitoring technique for polarization-multiplexed (PM) quadrature phase shift keying (QPSK) systems with large inline chromatic dispersion (CD) based on artificial neural network (ANN) techniques. The transmitted signal is directly detected, and part of the corresponding radio frequency spectrum is used as the input to ANN. Simulation results for 112-Gb/s PM return-to-zero QPSK systems demonstrate an OSNR monitoring range of 12–24 dB in presence of CD up to 27000 ps/nm with a maximum monitoring error of 0.84 dB. Tolerance of the proposed technique on polarization-mode dispersion effects is also investigated.