Dual-Wavelength External Cavity Lasers Using Polymer Photonic Integrated Circuits for Optical Heterodyne RF Signal Generation

RF photonics has emerged as a key technology for the generation and processing of high-frequency RF signals required in 6G wireless communications, photonic radar, and high-resolution sensing systems. In particular, optical heterodyning-based RF signal generation offers the advantage of controlling the RF frequency through optical wavelength tuning. In this study, a dual-wavelength external cavity laser based on a fluorinated polyimide photonic integrated circuit is designed and fabricated. The photonic integrated circuit incorporates waveguide Bragg gratings, thermo-optic phase modulators, and a 2 × 2 multimode interference coupler to realize two external cavity lasers and combine their outputs on a single chip. The high thermo-optic efficiency of the polymer waveguides enables wide and continuous laser wavelength tuning. Based on this tuning capability, optical heterodyne RF signal generation is experimentally demonstrated using the dual-wavelength external cavity laser. The measured RF frequencies closely match the calculated values obtained from the optical wavelength differences. Continuous RF frequency tuning through Bragg wavelength and cavity mode tuning was experimentally demonstrated up to the measurement-limited frequency of 40 GHz, confirming the feasibility of polymer photonic integrated circuits for compact and widely tunable RF photonic sources.