In a recent development, a research team led by Dr. Hua Li from the Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences (referred to as the Microsystems Institute), in collaboration with Professor Heping Zeng from East China Normal University and Associate Professor Yaxun Zhang from Tokyo University of Agriculture and Technology, has made significant progress in the field of Terahertz (THz) dual comb hybrid locking. The outcomes of this research have been published in "ACS Photonics" and selected as the cover paper.
Research Paper Cover
Highly Stable THz Semiconductor Dual Combs: Their Significant Applications in Precision Measurement, Sensing, and Communication. The Terahertz Photonics Research Team at the Microsystems Institute has, in their preliminary work based on semiconductor quantum cascade lasers (QCLs), achieved self-detected THz QCL dual combs and on-chip dual combs. They have continuously enhanced the long-term stability of the THz QCL dual comb sources by employing techniques such as microwave dual injection, phase-locked loops, and self-referencing.
Addressing the inherent characteristics of THz QCL dual comb stability, which primarily depends on the dual comb's carrier offset and repetition rate, the research team introduced a novel hybrid locking technique. This method utilizes microwave dual injection and phase-locked loops to lock the carrier offset and repetition rate of the dual combs, respectively. By comparing the dual comb spectra's "maximum hold" over 30 seconds under free-running, phase-locked only, and hybrid locking conditions, it was observed that hybrid locking could achieve locking of all comb lines, offering the most stable dual comb spectrum. Moreover, the 2-minute "maximum hold" dual comb spectrum under hybrid locking conditions was almost identical to that of the 30-second "maximum hold," indicating that hybrid locking can achieve long-term locking of the THz dual comb.
Researchers compared the results of the dual comb frequency Allan variance, amplitude Allan variance, and phase noise measured under different conditions to further prove that hybrid locking provides optimized frequency and amplitude stability, as well as phase noise reduction. This new hybrid locking method effectively enhances the long-term stability of THz semiconductor dual combs, laying a crucial foundation for their broad applications in THz spectral detection, sensing, and communication.
Schematic illustration of the principle behind hybrid locking of THz semiconductor dual combs. All images are from "ACS Photonics".
Relevant paper information: https://doi.org/10.1021/acsphotonics.3c01379
