Dual-Tone QPSK Optical Millimeter-Wave Signal Generation by Frequency Nonupling the RF Signal Without Phase Precoding

A novel dual-tone quadrature phase-shift keying (QPSK) optical millimeter (mm)-wave signal generation by frequency nonupling the radio-frequency QPSK signal via an optical phase modulator (PM) without phase precoding is proposed. To enable the generated optical mm-wave signal to resist the fiber chromatic dispersion degradation, the unmodulated -fourth-order and the QPSK-modulated +fifth-order sidebands are abstracted from the generated sidebands, considering the phase periodicity of a QPSK signal. The opto-electrical conversion efficiency is maximized by optimizing the modulation index of PM. An optical mm-wave generator along with a radio-over-fiber link is built, and the eye diagrams, constellations, and BER curves demonstrate that the frequency nonupling dual-tone QPSK optical mm-wave signal performs well. The simulated results agree well with the theoretical prediction.