This paper investigates an optical transmission architecture of a passive optical network (PON), which is compatible with the millimeter-wave radio-over-fiber and free-space optics systems (RoF-FSO) under weak-to-strong atmospheric turbulence (AT) regimes to enable seamless connectivity as part of next-generation broadband wireless access networks. We first analyze and evaluate in simulation the transmission performance of the integrated system at 40 GHz for 10 Gb/s N-pulse amplitude modulation (N-PAM) with N = 2, 4. Link performance shows that, 4-PAM outperforms 2-PAM in terms of tolerance to the combined impairment of fiber chromatic dispersion and AT. We then experimentally demonstrate the proof-of-concept integrated RoF-FSO-PON at 25 GHz using 20 MHz M-quadrature amplitude modulation (M-QAM) signals with M = 4, 16, 64. We show that, for QAM with a higher-order M, the link performance is being more affected by the combined impairments.