Idealphotonics' has launched an optical reference cavity with a crystal film mirror. This Fabry-Perot resonator, constructed using highly reflective crystal film mirrors (such as SiO₂/Ta₂O₅ multilayer films), utilizes ultra-low-loss optical feedback to generate an extremely narrow linewidth reference frequency, providing a highly stable wavelength reference for laser frequency stabilization.The ultra-narrow linewidth and thermal noise-limited stability are achieved through a high-Q design of the single-crystal dielectric film and a zero-expansion structure, minimizing the impact of environmental disturbances on the resonant frequency.