Lag‐Compensated Hyperfine Terahertz Dual‐Comb Interferometer beyond Intrinsic Resolution and Sensitivity

Abstract Optical coherence with high precision and sensitivity holds achievements in communication, metrology, and sensing. The optical vernier effect generated by the dual‐comb interference highlights coherence technology to heighten accuracy and sensitivity, particularly in the visible and infrared bands. However, the maturity in the frequency domain of the optical coherence may overshadow its attributes in the time domain, which are limited to enhancing comprehensive performance. This work provides a lag compensation technology in the time domain that enables hyperfine interference spectrum and vernier ultra‐resolution, verified by a cascading terahertz dual‐comb interferometer. This strategy proves a 71.4 times improvement in the vernier resolution beyond the intrinsic resolution, reaching the Nyquist sampling limit without necessitating unique optical materials or compromising device geometry. Furthermore, a universal Lag‐Interference‐Sensitivity correlation is established to guide an ultra‐sensitivity of 1.4 × 10 4 GHz·RIU −1 within the 0.2–1 THz range, defying two orders of magnitude compared to the existing reports. Finally, the application in biochemical sensing, reaching a sensitivity of 2.63 GHz·mm 2 ·ng −1 and an accuracy of 0.59 ng·mm −2 , outperforming current reports and stimulating further exploration of ultra‐sensitive terahertz biochemical on‐chip sensors, is demonstrated. This validation proves an appealing scheme for precision metrology and high‐resolution vernier sensing.