Miniature 3-ml Fabry-Perot cavity delivers thermal-noise-limited 5e-15 instability in self-injection-locked diode laser

The system combines a microring resonator for self-injection locking with a miniature cavity, suppressing technical noise sources including residual amplitude modulation to reach the thermal noise floor. This performance matches or exceeds prior compact systems while using conventional multilayer mirrors rather than exotic coatings. The 3-ml volume and potential for Kerr comb generation in the same microring point toward chip-scale integration for transportable optical clocks and low-noise microwave synthesis.

Prior compact cavity-stabilized lasers often required higher finesse or cryogenic operation to approach thermal limits; this work demonstrates that careful residual amplitude modulation control suffices at room temperature with moderate finesse. Related efforts at NIST and PTB have pursued similar miniaturization but typically report higher instability floors when scaling volume below 10 ml. The arXiv preprint explicitly quantifies the noise budget, isolating cavity thermal noise as the dominant term.

Integration with existing silicon-nitride microring platforms could accelerate deployment in fielded optical frequency standards. Remaining challenges include vibration sensitivity and long-term drift from mirror coating aging, both addressable through established engineering paths.

Next milestones include integration with a strontium lattice clock and demonstration of 10^{-17} instability at 100 s averaging in a transportable package within two years.