Hybrid-Integrated Dual III-V/Si3N4 Laser Module for Widely Tunable Terahertz Generation

Continuous wave (CW) photomixing is a widely utilized method for terahertz (THz) radiation generation, with diverse applications in sensing, spectroscopy, and wireless communication. However, most existing systems are dependent on discrete, bulky components, highlighting the demand for integrated solutions that can enhance energy efficiency, flexibility, and stability. Here, we exploit the advantages of silicon photonics within the THz domain utilizing a hybrid-integrated dual III-V/Si3N4 narrow-linewidth laser module to generate widely tunable THz waves, whose frequency is determined by the frequency difference of the lasers. To enhance the frequency stability of the produced THz signal, we synchronize thermal noise by integrating two external laser cavities on the same chip. Further, synchronization of electrical noise is accomplished by electrically connecting the two gain sections in series using a low-noise current source. The external cavity lasers incorporating low-loss Si3N4 microring resonator (MRR) filters, deliver optical power up to 13 dBm, exhibit a broad wavelength tuning range of approximately 55 nm, and maintain a narrow optical intrinsic linewidth below 0.77 kHz. By adjusting the laser frequency interval in the heterodyne synthesis setup, we achieved CW THz generation over a wide tuning range from 95.2 GHz to 1.012 THz. The 3-dB THz electrical linewidth is estimated to be less than 31 kHz. As far as we know, this represents the narrowest linewidth for THz signals generated by heterodyne synthesis with free-running integrated sources over such a wide tuning range. The hybrid-integrated narrow-linewidth compact dual laser module possesses a long-term THz frequency drift of 65 MHz, measured for 10 hours. Our study therefore highlights the huge potential of silicon photonics technology in the THz domain.