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ELOS 2021

Ligang Huang

Ligang Huang, Speaker at Ligang Huang: Speaker for Optics Conference
Chongqing University, China
Title : External cavity self-adaptive lasers assisted by distributed feedbacks


With excellent properties of the high purity spectrum and long coherent length, narrow-linewidth lasers can be applied in many fields, such as optical quantum information, low-noise microwave generation, high-resolution spectroscopy, precise sensing, high-speed optical coherent communication and so on. Herein, commencing from the in-depth analysis for the effective suppression of spontaneous emission under the excitation of a cavity signal, we propose a compression scheme to extremely compress laser linewidth assisted by a distributed feedback. Subsequently, we develop a novel laser configuration that comprises the main laser cavity and an external cavity with a distributed feedback characteristic. To provide an excitation signal required for linewidth compression, we inject into the main cavity through the distributed feedback structure a cavity mode signal matched with the output wavelength. Moreover, we conduct an experimental investigation based on an on-chip laser system with a distributed feedback. Eventually, an ultra-narrow linewidth laser with a side mode suppression ratio (SMSR) greater than 80 dB, an output linewidth of 10 Hz, and a relative intensity noise (RIN) less than -150 dB/Hz is successfully obtained under normal conditions. The proposed concept is valid in any other gain-types lasers with various wavelengths, providing a new perspective for extreme modulation of other laser parameters. We further explore the linewidth compression in tunable lasers. With all-optical tunable narrow-band fiber Bragg gratings and RBS linewidth compression, we obtain tunable fiber lasers with a precise tuning step of less than 0.02 nm and linewidth of about 200 Hz. With all-fiber acousto-optical tunable filters, we obtain fast tunable narrow-linewidth fiber lasers with a tuning band of 20 nm and switching time of less than 1 ms.  Finally, we propose parameter measurement methods of ultra-narrow-linewidth lasers. For frequency-stabilized lasers, we propose an ultra-narrow linewidth measurement method based on the short delayed fiber self-heterodyne interferometer (SDSHI). For wavelength-swept lasers, we propose the measurement method of transient frequency noise and linewidth.


Ligang Huang is a Chinese Physicist. He received Ph.D. in Physics from Nankai University (China) in 2016. Since September 2020, he works as an associate professor at the College of Optoelectronic Engineering in Chongqing University, China. His research interests include narrow-linewidth lasers, laser parameter measurement, all-fiber acousto-optic tunable filters and whispering-gallery-mode tunable filters. He is author or co-author of more than 50 peer-reviewed journal papers in the field of narrow-linewidth lasers and tunable filters, which have been cited by more than 500 times.