Photonic Generation of Equivalent Single Sideband Vector Signals for RoF Systems

A novel approach for generating RF vector signals with equivalent single sideband (SSB) modulation based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is proposed and experimentally demonstrated. One QPSK modulator in the DP-QPSK modulator is driven by a single-frequency RF signal. By properly setting its biases, a SSB carrier suppressed (SSB-CS) signal is generated. The other QPSK modulator in the DP-QPSK modulator is modulated by I/Q data streams, resulting in a baseband vector signal carried by the optical carrier. A polarizer is placed after the DP-QPSK modulator to combine the two signals with orthogonal polarization, leading to the generation of an equivalent SSB signal, which is free from the dispersion-induced power fading effect. By adjusting the angle of the polarizer, the carrier-to-sideband ratio can also be flexible tuned to maximize the transmission performance. The proposed system is verified by an experiment. The generation of a 1.25-GBd vector signal with QPSK modulation format at 10.5 GHz and the transmission of the signal over 25-km single-mode fiber are evaluated. An error-free transmission is achieved at a received optical power of -12 dBm and the power penalty is <;1 dB. The proposed approach features all-optical and compact configuration.