Complementary hybrid dual-comb spectroscopy

Optical frequency combs generate precise optical frequencies tightly linked to stable microwave references. Dual-comb spectroscopy (DCS) utilizes the coherent interference of two combs with appropriately controlled different repetition frequencies. To improve its performance far beyond the trade-off relationship between its frequency resolution and measurement speed, we present a complementary hybridization approach consisting of a fiber-laser-based comb and an electro-optic-modulator-based comb with a near-integer multiple repetition frequency relationship. We suppressed relative phase noise by locking two distant EOM comb modes to one of the fiber comb modes and a cavity-locked laser, which was an optical reference of the fiber comb, and achieved a figure of merit of 4.3 × 10⁷ Hz½ . Finally, we revisit signal to noise ratio theory to derive a relationship applicable to this configuration and discuss future perspective as regards performance improvement.