A quad-mode optical carrier generated by mode-deviated injection-locking a vertical-cavity surface-emitting laser (VCSEL) at a beating frequency of 40 GHz is demonstrated for establishing a long-reach millimeter-wave over fiber (MMWoF) link, in which only one mode of the quad-mode optical carriers is modulated by the 16-quadrature amplitude modulation (16-QAM) orthogonal frequency division multiplexing (OFDM) data stream to achieve an optical single-carrier modulation (OSCM). Such an OSCM operation reduces the long-reach single-mode-fiber (SMF) transmission induced RF power fading effect to significantly suppress the frequency notch in the modulated spectrum of the delivered QAM-OFDM data after remotely heterodyne detection. With destructively interfered beating the quad-mode optical carrier at the remote node, the peak power of the optically heterodyned MMW central carrier can be attenuated by 38.3 dB, which saves the gain of the photodetector and electrical amplifier to efficiently boost the carried QAM-OFDM data. This architecture ensures sufficient power of the 16-QAM OFDM data after optoelectrical conversion and facilitates the quad-mode optical carrier based MMWoF link to achieve 50-km wired SMF and 10-m wireless MMW transmissions with the error vector magnitude of 17.2%, signal-to-noise ratio of 15.28 dB, and bit error rate of 3.5×10-3at a data rate of 12 Gbps.