We propose a novel high-capacity and low-latency front-haul system for small cells-based heterogeneous wireless networks. We experimentally demonstrate a proof-of-concept seamless convergence of radio-over-fiber (RoF) and millimeter-wave (MMW) system at 90 GHz for high-speed wireless signal transmission. Simultaneous transmission and demodulation of standard-compliant very-high-throughput WLAN IEEE 802.11ac and high-speed LTE-A signals over the system are successfully confirmed for the downlink direction. Satisfactory transmission performance over the converged 10-km RoF and a 5-m 90-GHz wireless link is achieved. The measured root-mean-square error vector magnitude is much better than the requirement defined by the standards.