Twisted single-ring hollow-core fiber for broadband chiral detection in nanoliter volumes

Abstract The ongoing evolution of hollow-core fibers (HCFs) continues to inspire the development of optofluidic platforms with enhanced sensitivity and minimal sample requirements. Here, we utilize the intrinsic advantages of anti-resonant reflection HCFs—such as low optical loss and broadband transmission—to realize a twisted single-ring HCF (SR-HCF) tailored for polarization-sensitive chiral detection. We optimize the fiber geometry to ensure single-mode operation by strongly attenuating higher-order modes ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>&gt;</mml:mo> </mml:mrow> </mml:math> 50 dB m −1 ) while maintaining low loss for the fundamental mode ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>&lt;</mml:mo> </mml:mrow> </mml:math> 0.1 dB m −1 ) and reducing the sample volume to only ∼ 660 nl per 34 cm fiber length. By applying a constant twist along the fiber length, we minimize birefringence and ensure stable transmission of linear polarization states with polarization extinction ratios surpassing 38 dB. After injecting an aqueous solution of an optically active molecule, we measure its optical rotation at different wavelengths with millidegree-level sensitivity and remarkable robustness against misalignment. Measurements with different enantiomeric excess concentrations are in good agreement with independent liquid chromatography characterization.