Guided-mode based Faraday rotation spectroscopy within a photonic bandgap fiber

Microstructured optical fibers provide a unique environment for new compact sensing of gases as they offer advantages
including long optical pathlengths, strong confinement of high power light and extremely small sample volumes
compared to free-space gas sensing architectures. Here we investigate the interaction of a modulated magnetic field with
guided light to detect a paramagnetic active gaseous medium within a hollow-core photonic bandgap fiber (HC-PCF).
This novel fiber-optic approach to Faraday Rotation Spectroscopy (FRS) demonstrates the detection of molecular oxygen
at 762.309 nm with nano-liter detection volume. By using a differential detection scheme for improved sensitivity,
guided-mode FRS spectra were recorded for different coupling conditions of the light (i.e., different light polarization
angles) and various gas sample pressures. The observed FRS signal amplitudes and shapes are influenced by the
structural properties of the fiber, and magneto-optical properties of the gas sample including the magnetic circular
birefringence (MCB) and the magnetic circular dichroism (MCD). A theoretical model has been developed to simulate
such FRS signals, which are in good agreement with the observed experimental results and provide a first understanding
of guided-mode FRS signals and dynamics of the magneto-optical effects inside the optical fiber. The results show that
microstructured optical fibers can offer a unique platform for studies concerning the propagation of light in linearly and
circularly birefringent media.
Autorzy / Authors: 
F. V. Englich, M. Grabka, D. G. Lancaster, T. M. Monro
Proc. of SPIE 8632, 86320L
Tematyka badań: 
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