Simple 60-GHz Radio-over-Fiber System with Transmission Distance Improvement Employing Signal-to-Signal Beat Noise Compensation

We propose a simple 60-GHz RoF system using one single-electrode Mach-Zehnder modulator (MZM). By choosing proper carrier frequencies of two MZM driving signals, fiber transmission distance can be extended up to 12 km. Compared with conventional intensity modulation with direct detection using 60-GHz MZM or electro-absorption modulator (EAM), the proposed RoF system can support longer fiber transmission distance (up to 12 km) and has less bandwidth requirement of optical orthogonal frequency-division multiplexing (OFDM) transmitter (34 GHz vs. 64 GHz). However, the generated 60-GHz OFDM signal will have beat noise after square-law photo-detection. In this paper, the beat noise is analytically analyzed. Hence, the beat noise mitigation algorithm with the beat noise re-construction technique is proposed and utilized to reduce beat-noise-induced interference and improve signal-to-noise ratio (SNR). 60-GHz 13.75-Gbps quadrature phase shift keying (QPSK) and 20.625-Gbps 8-quadrature-amplitude-modulation (QAM) OFDM signals with 3-m wireless transmission are experimentally demonstrated and transmitted over 12-km and 6-km single-mode fiber, respectively.