Sub-megahertz spectral dip in a resonator-free twisted gain medium

• Published in: Nature photonics Vol. 16; no. 7; pp. 498 - 504
• Main Authors: Choksi, Neel, Liu, Yi, Ghasemi, Rojina, Qian, Li
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-07-2022; Nature Publishing Group
• Subjects: 639/624/1075/187; 639/624/400/385; 639/766/400/385; Applied and Technical Physics; Filters; Frequency dependence; Light; Microwave photonics; Optimization; Photonics; Physics; Physics and Astronomy; Polarization; Quantum Physics; Resonators; Room temperature; Spectroscopy
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-022-01015-w

Ultra-narrow optical spectral features resulting from highly dispersive light–matter interactions are essential for a broad range of applications such as spectroscopy, slow-light and high-precision sensing. Features approaching sub-megahertz or, equivalently,
Q
-factors up to one billion and beyond, are challenging to obtain in solid-state systems, ultimately limited by loss. We present a novel approach to achieve tunable sub-megahertz spectral features at room temperature without resonators. We exploit gain-enhanced polarization pulling in a twisted birefringent medium where polarization eigenmodes are frequency-dependent. Using Brillouin gain in a commercial spun fibre, we experimentally achieve a 0.72 MHz spectral dip, the narrowest backward Brillouin scattering feature ever reported. Further optimization can potentially reduce the linewidth to <0.1 MHz. Our approach is simple and broadly applicable, offering on-demand tunability and high sensitivity, with a wide range of applications such as microwave photonic filters, slow and fast light, and optical sensing.
Tunable sub-megahertz spectral features are demonstrated without resonators. The approach, which exploits gain-enhanced polarization pulling in a twisted birefringent medium, may be useful in applications such as microwave photonic filters, slow and fast light, and optical sensing.