To improve the issues of power fluctuation, frequency drift, and low signal-to-noise ratio inherent in traditional terahertz signal generation using optical heterodyne methods, a dual-wavelength coherent light source structure based on double-ring cavities is designed. The structure combines an optical frequency comb (OFC) generated by cascaded external modulators with independent double-ring cavities, achieving stable single-longitudinal-mode coherent dual light source output. Simulation results indicate that the average optical powers of the light sources at wavelengths of 1550.07?nm and 1552.46?nm are 14.75?dBm and 14.77?dBm, respectively, with power fluctuations below 0.03?dB. To further validate the communication performance of the output dual light sources, a simulation analysis is conducted on the transmission of 16-ary quadrature amplitude modulation (16QAM) signals and probability shaped (PS) 64-ary quadrature amplitude modulation (64QAM) signals over 30?km of single-mode fiber (SMF). The results show that the bit error rates for both modulation formats remain below the threshold of forward error correction codes.