Low Spontaneous Brillouin Scattering in Anti-Resonant Hollow-Core

Brillouin light scattering (BLS) is a spectroscopic technique that uses inelastic light scattering to derive the elastic and magnetic properties of a broad range of materials. Although BLS usually employs free-space optics, in certain applications, the usage of optical fibers is beneficial. However, spontaneous BLS, which occurs in solid core fibers at the GHz frequency range [1], makes them barely suitable for BLS experiments. Newly designed Antiresonance Hollow Core Fibers (AR-HCFs) [2] are promising candidates for the mitigation of both fiber loss and BLS noise.

We compare the BLS spectrum in the GHz range of two fibers (Polarization-Maintaining (PM) and AR-HCF). In addition to strong longitudinal and transverse phonon spectral peaks, the PM fiber spectrum features broadband noise. The AR-HCF’s spectrum consists of multiple modes of at least two orders of magnitude lower intensity. Finite-element simulations revealed that the observed modes appear due to confinement in the AR-HCF guiding capillary walls (~200 nm). Our findings demonstrate that AR-HCFs are a superior solution for low-noise light guidance and can inform the design of future fibers [3].