A compact, transportable 1550 nm ultra-stable laser system with Hertz linewidth

We demonstrate a compact, transportable 1550 nm ultra-stable laser system with Hertz linewidth. The laser frequency is frequency stabilized to a vertically mounted, vibration-insensitive and high-fineness ultra-low-expansion (ULE) cavity with Pound-Drever-Hall (PDH) method. Optical boards designed by topology optimization and miniaturized optical component mounts without kinematic adjustment are designed to achieve a high level of integration and stability. The self-developed electronics and automatic locking module ensure fully automatic operation of the system. The entire ultra-stable laser system is highly integrated in a 19-inch 6 U chassis with a mass of about 35 kg. The prototype performs beat frequency comparison measurement with another ultra-stable laser system in the laboratory. The fractional frequency instability of a single system is achieved 4×10-15\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$4 \times 10^{-15}$$\end{document} at 1 s averaging time preliminarily, and the linewidth is 1.3 Hz. The portable ultra-stable laser system we developed is expected to have significant implications for precision measurement and other applications.