Comb-rooted multi-channel synthesis of ultra-narrow optical frequencies of few Hz linewidth

• Main Authors: Jang, Heesuk, Kim, Byung Soo, Chun, Byung Jae, Kang, Hyun Jay, Jang, Yoon-Soo, Kim, Yong Woo, Kim, Young-Jin, Kim, Seung-Woo
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Article
• Language: English
• Published: 2019
• Subjects: Optical Frequency Synthesizer; Engineering::Mechanical engineering; Multi-channel
• Online Access: https://hdl.handle.net/10356/106762; http://hdl.handle.net/10220/48940
• Institution: Nanyang Technological University

We report a multi-channel optical frequency synthesizer developed to generate extremely stable continuous-wave lasers directly out of the optical comb of an Er-doped fiber oscillator. Being stabilized to a high-finesse cavity with a fractional frequency stability of 3.8 × 10−15 at 0.1 s, the comb-rooted synthesizer produces multiple optical frequencies of ultra-narrow linewidth of 1.0 Hz at 1 s concurrently with an output power of tens of mW per each channel. Diode-based stimulated emission by injection locking is a key mechanism that allows comb frequency modes to sprout up with sufficient power amplification but no loss of original comb frequency stability. Channel frequencies are individually selectable with a 0.1 GHz increment over the entire comb bandwidth spanning 4.25 THz around a 1550 nm center wavelength. A series of out-of-loop test results is discussed to demonstrate that the synthesizer is able to provide stable optical frequencies with the potential for advancing diverse ultra-precision applications such as optical clocks comparison, atomic line spectroscopy, photonic microwaves generation, and coherent optical telecommunications.