Wideband and high-resolution spectroscopy based on an ultra-fine electro-optic frequency comb with seed lightwave selection via injection locking
Bingxin Xu, Xinyu Fan, Shuai Wang, Zuyuan He
Abstract
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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>300</mml:mn> <mml:mspace width="thinmathspace"/> <mml:mspace width="thinmathspace"/> <mml:mtext>µ</mml:mtext> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:math> between adjacent lines, by which the figure of merit reaches <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>3.39</mml:mn> <mml:mo>×</mml:mo> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>7</mml:mn> </mml:msup> </mml:mrow> </mml:math> . The system promotes more prospects in practical spectroscopic and sensing applications.