RESEARCH ARTICLE

Multi-octave two-color soliton frequency comb in integrated chalcogenide microresonators

Huanjie Cheng, Guosheng Lin, Di Xia, Liyang Luo, Siqi Lu, Changyuan Yu, Bin Zhang

2024, 17(4): 36.https://doi.org/10.1007/s12200-024-00139-x

Abstract：Mid-infrared (MIR) Kerr microcombs are of significant interest for portable dual-comb spectroscopy and precision molecular sensing due to strong molecular vibrational absorption in the MIR band. However, achieving a compact, octave-spanning MIR Kerr microcomb remains a challenge due to the lack of suitable MIR photonic materials for the core and cladding of integrated devices and appropriate MIR continuous-wave (CW) pump lasers. Here, we propose a novel slot concentric dual-ring (SCDR) microresonator based on an integrated chalcogenide glass chip, which offers excellent transmission performance and flexible dispersion engineering in the MIR band. This device achieves both phase-matching and group velocity matching in two separated anomalous dispersion regions, enabling phase-locked, two-color solitons in the MIR region with a commercial 2-μm CW laser as the pump source. Moreover, the spectral locking of the two-color soliton enhances pump wavelength selectivity, providing precise control over soliton dynamics. By leveraging the dispersion characteristics of the SCDR microresonator, we have demonstrated a multi-octave-spanning, two-color soliton microcomb, covering a spectral range from 1156.07 to 5054.95 nm (200 THz) at a -40 dB level, highlighting the versatility and broad applicability of our approach. And the proposed multi-octave MIR frequency comb is relevant for applications such as dual-comb spectroscopy and trace-gas sensing.

研究背景

在中红外（MIR）波段，由于分子振动吸收强烈，Kerr微梳在便携式双梳光谱测量和精密分子传感领域具有重要应用。然而，由于缺乏合适的集成光子材料和连续波泵浦激光器，实现紧凑型、跨倍频程的Kerr微梳仍然是一个挑战。

主要内容

本文提出了一种基于集成硫系玻璃（ChG）芯片的新型狭缝同心双环（SCDR）微腔。它在MIR波段具有出色的传输性能和灵活的色散调控能力，可在两个反常色散区实现相位匹配和群速度匹配，使得在MIR波段实现锁相双色孤子成为可能。通过设计SCDR微谐振器的色散特性，采用数值仿真验证了基于该双色孤子微腔的跨多倍频程频率梳产生，在-40 dB的水平上覆盖了1156.07-5054.95 nm（200 THz）的光谱范围。

创新点

提出了一种基于ChG的SCDR微腔，实现了跨多倍频程的双色孤子微梳。SCDR微腔的结构促进了模式耦合，使得群速度匹配和两个反常色散区的形成成为可能，对孤子间的切伦科夫辐射及双色孤子的产生至关重要。在微腔中引入狭缝结构可以精确设计积分色散曲线，从而实现相位匹配位置的可调，并拓宽频率梳带宽以跨越多个倍频程。

方法

通过精确设计SCDR微腔的色散曲线，在两个反常色散区实现了相位匹配和群速度匹配，实现了相位匹配位置的可调，拓宽了梳状谱的带宽。使用Lugiato-Lefever方程模拟了在集成硫系SCDR微腔中双色孤子的产生。

结果

通过深入的模拟，该研究验证了跨越多倍频程的双色孤子微梳产生，在-40 dB的水平上覆盖了1156.07-5054.95 nm（200 THz）的光谱范围，所需2 μm泵浦光的功率只有60mW。光谱和时域波形的分析揭示了双色孤子的光谱锁定特性，这增强了泵浦波长选择性，提供了对孤子动力学的精确控制。

总结

SCDR微腔能够采用普通的泵浦源生成具有可定制光谱轮廓的宽带MIR频率梳。这项研究不仅有助于开发高效的MIR频率梳源，而且为医学诊断、环境监测和材料科学中的一系列应用铺平了道路。研究结果强调了创新的微腔设计在突破频率梳产生的局限性方面的重要性，也突显了这一有前景的光子技术领域未来发展的潜力。