Polarization-Modulation, I/Q-Demodulation Photonic Bandpass Sampling for Wideband, Multicarrier RF Application

Abstract

Radio frequency (RF) photonic link under phase or polarization modulation and coherent in-phase/quadrature (I/Q) demodulation (ΦM/IQ or PolM/IQ) has been reported with unprecedented dynamic range performance, benefiting from the ultrahigh linear transfer function of electro-optic phase modulator. But the ideal linear demodulation cannot be preserved during traditional down-conversion, which is a must from high-carrier application. In this paper, we propose and demonstrate that PolM/IQ link employing ultrashort optical bandpass sampling delivers both multicarrier down-conversion and full linearization. The pulse train, equivalently a frequency comb with uniform amplitude and phase in frequency domain, is able to down-convert signal and all nonlinear spurs that are collected by the following analog-to-digital convertor (ADC), so that the original linearization algorithm stands. Our method releases the requirement of ADC and digital processing greatly. The bandwidth after bandpass sampling is confined within the first Nyquist zone, and the minimum value can be as small as signal bandwidth, much less than original which should be several times of the maximum carrier frequency. We demonstrate such linearization experimentally with two dual-carrier RF signals as input, covering multiple octave spans.