Self-Referenced Terahertz Semiconductor Dual-Comb Sources

TL;DR

This paper introduces a self-reference stabilization method for terahertz quantum cascade laser dual-comb sources, significantly enhancing their long-term stability without external locking components, enabling high-precision applications.

Contribution

A novel self-reference technique for fully stabilizing THz QCL dual-comb sources without external components, improving stability and linewidth performance.

Findings

Achieved a record linewidth of 14.8 kHz over 60 seconds.

Demonstrated a reduction from 2 MHz to 14.8 kHz linewidth with self-reference.

Enhanced long-term stability of THz dual-comb signals.

Abstract

Employing two frequency combs with a slight difference in repetition frequencies, the dual-comb source shows unique advantages in high precision spectroscopy, imaging, ranging, communications, etc. In the terahertz (THz) frequency range, the electrically pumped quantum cascade laser (QCL) offers the possibility of realizing the compact dual-comb source due to its semiconductor-based chip-scale configuration. Although the active stabilization of a THz QCL dual-comb source was demonstrated by phase locking one of the dual-comb lines, the full stabilization of all dual-comb lines is still challenging. Here, we propose a self-reference method to obtain a fully stabilized dual-comb signal on a pure THz QCL platform. Without using any external locking components, we filter out one dual-comb line and beat it with the whole dual-comb signal, which eliminates the common carrier offset frequency noise and reduces the dual-comb repetition frequency noise. It is experimentally demonstrated that the self-reference technique can significantly improve the long-term stability of the dual-comb signal. A record of the ``maxhold" linewidth of 14.8 kHz (60 s time duration) is obtained by implementing the self-reference technique, while without the self-reference the dual-comb lines show a ``maxhold" linewidth of 2 MHz (15 s time duration). The method provides the simplest way to improve the long-term stability of THz QCL dual-comb sources, which can be further adopted for high precision measurements.