Spectra of spontaneous Raman scattering in taper-drawn micro/nano-fibers

We study the spontaneous Raman scattering (RS) in taper-drawn micro/nano-fibers (MNFs) by employing the photon counting technique. The spectra of RS in five MNFs, which are fabricated by using different heating flames (hydrogen flame or butane flame) and with different diameters, are measured within a frequency shift range of 1435 cm⁻¹–3200 cm⁻¹. From the measured spectra, we observe the RS peaks originated from silica and a unique RS peak with a frequency shift of ∼2905 cm⁻¹ (∼87.2 THz). Unlike the former ones, the latter one is not observable in conventional optical fibers. Furthermore, the unique peak becomes obvious and starts to rapidly increase with the decrease of the diameter of MNFs when the diameter is smaller than 2 μm, and the intensity of the unique peak significantly depends on the heating flame used in the fabricating process. Our investigation is useful for the entanglement generation or optical sensing using taper-drawn MNFs. (paper)