Optical nanofiber coupler sensors operating in the cut-off wavelength region

Abstract

An ultrasensitive optical nanofiber coupler (NFC) for thermal and refractive index sensing with nanoscale dimension is proposed and experimentally demonstrated. The NFC operating near the cut-off region of the higher order modes is fabricated by fusing and pulling two standard telecom fibers using the modified flame brushing technique. Due to the sub-micron diameter, the NFC exhibits an anomalous behavior in close proximity to the odd supermode cut-off wavelength, where the high extinction ratio spectral oscillations exhibit very slow oscillations. The sensitivity of this region is exploited for thermal sensing over a broad range of temperatures (84 °C–661 °C). An average temperature sensitivity of 55 pm/°C and a maximum sensitivity of 60 pm/°C at the highest temperature were demonstrated. Owing to its small size, the thermal sensor exhibits a fast response time of ~7.2 ms. The sensor capability for detecting refractive index changes is also examined with different ethanol concentrations. A record sensitivity of 4.80×10⁵ nm/RIU was achieved, which is the highest reported value in all optical fiber refractometers.

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Identifiers

ORCID for Timothy Lee: orcid.org/0000-0001-9665-5578

ORCID for Gilberto Brambilla: orcid.org/0000-0002-5730-0499

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