This article introduces an optically controlled terahertz modulator on a substrateless silicon waveguide platform that fulfills requirements for system-level compactness and miniaturization. The modulator incorporates a dipole resonator and a 1-D photonic crystal cavity to enhance the sensitivity of the terahertz waveguide to optical stimulus that interferes with the resonance system. An enhanced modulation depth of 15.52 dB with a low insertion loss of 2.11 dB was achieved at 275.22 GHz with an optical excitation power of only 6.8 mW. The modulation frequency should reach gigahertz rates by employing ion implantation of the silicon or incorporating semiconductors with much faster recombination times than silicon.