Hybrid cavity–iodine-locked optical frequency reference with 3 × 10 −15 instability across six decades

Optical frequency references with excellent frequency stability have wide applications in precision measurement fields. In this paper, we demonstrate an ultra-stable laser source with excellent performance based on the hybrid locking of an FP cavity and molecular iodine. We develop a theoretical hybrid locking model and implement its derived control scheme, achieving an operation independent of external frequency references. Based on the electro-optic frequency comb (EOFC) composed of an electro-optic modulator, we lock the laser frequency to the two references simultaneously, enabling the laser frequency to have the stability advantages of both references and providing an absolute frequency reference. The measured fractional frequency instability of the laser reaches about 3 × 10^{-15} across six decades of averaging time, from 0.1 s to 10^{5} s. The frequency drift rate reaches 1.3 × 10^{-19} /s. This space-qualified optical frequency reference is a promising candidate for future space-based frequency standards.