Version 2 2024-01-05, 19:07Version 2 2024-01-05, 19:07
Version 1 2024-01-05, 07:44Version 1 2024-01-05, 07:44
journal contribution
posted on 2024-01-05, 19:07authored byYiran Zhao, Ziping Li, Xuhong Ma, Kang Zhou, Wen Guan, Chenjie Wang, Shumin Wu, Han Liu, Wenjian Wan, J. C. Cao, Ya Zhang, Heping Zeng, Hua Li
Frequency
combs show various application potentials in high precision
spectroscopy, imaging, communications, and so on. In the terahertz
(THz) region, semiconductor-based quantum cascade lasers (QCLs) are
good candidates for frequency comb and dual-comb operations. THz dual-comb
sources can be obtained by beating two THz QCL combs with a slight
difference in the repetition frequencies. A free-running THz dual-comb
source normally shows relatively large phase noise, which strongly
hinders its high precision applications. Different approaches, e.g.,
digital algorithms, active phase locking of one dual-comb line, self-reference
techniques, etc., have already been employed to stabilize THz dual-comb
sources. Up to now, a complete locking of a THz dual-comb source using
hardware locking elements has never been demonstrated. Here, we propose
a hybrid locking method to simultaneously stabilize both dual-comb
offset and repetition frequencies of a THz QCL dual-comb source. Experimental
results demonstrate that the stability of all dual-comb lines is improved
significantly when the proposed hybrid locking is applied to the dual-comb
source. Under the hybrid locking condition, the measured “maxhold”
dual-comb line width can reach a record of 5.7 kHz. Furthermore, the
recorded time trace of the dual-comb signal shows pulse-like behavior
during a large time scale of 100 μs, which verifies that the
proposed method functions well for an active locking of a THz QCL
dual-comb source.