Wideband and high-resolution spectroscopy based on an ultra-fine electro-optic frequency comb with seed lightwave selection via injection locking

The digital ultra-fine electro-optic frequency comb (UFEOFC) enables high-resolution spectroscopy in various applications with a limited bandwidth. In this Letter, we propose a novel, to the best of our knowledge, UFEOFC-based dual-comb spectroscopy to realize megahertz resolution and broadened bandwidth. An UFEOFC with 1 MHz line-spacing and 18 GHz bandwidth is generated and resolved in a dual-comb interferometer working in quasi-integer-ratio mode. One line selected from a master EOFC with 18 GHz line-spacing via optical injection locking serves as the seed lightwave. Successive selection of 20 lines realizes wideband measurement covering 360 GHz, and a reflectance spectrum of a phase-shift fiber Bragg grating is obtained in the demonstration. A spectrum with 360,000 lines is demodulated in 26 ms due to the low injection lock dead time set to be 300µs between adjacent lines, by which the figure of merit reaches 3.39×107. The system promotes more prospects in practical spectroscopic and sensing applications.