Fiber taper diameter characterization using forward Brillouin scattering

Abstract

We propose a fast and non-destructive method to characterize the absolute diameter and uniformity of micrometer-scale fiber tapers using a pump and probe forward Brillouin scattering setup. The fundamental torsional-radial acoustic mode supported by the wire is excited using a pulsed pump laser and oscillates at a frequency that is inversely proportional to the taper waist diameter. This standing time-varying torsional-radial wave induces polarization modulation on a probe signal, whose spectrum structure reveals the sample diameter and its non-uniformity. By comparing our results with measurements using scanning-electron microscopy, a relative deviation of 1% or less was demonstrated, and diameter non-uniformity of less than 0.5% could be detected.

Chalcogenide Taper and Its Nonlinear Effects and Sensing Applications

“…Based on the measurements of radial-and torsional-radial-guided acoustic modes, many sensing applications have been investigated such as impedance measurement (Antman et al, 2016) and absolute diameter characterization (Jarschel et al, 2018). A new approach for humidity sensing based on As 2 Se 3 -PMMA tapers can be achieved due to the impedance changed in the PMMA cladding induced by the water absorption property of the PMMA material.…”

High Resolution Brillouin Sensing of Micro-Scale Structures

“…where d is the fibre outer diameter, v t,m is the m th transverse mode acoustic velocity, and y m the m th zero of the Bessel function describing the boundary conditions for the free fibre surface [64]. This forward BFS as described in Equation (2) has been utilized to determine the strain coefficient in silica fibre [65] and the temperature coefficient in highly nonlinear fibre [66] and PCF [67], sound velocity in silica fibre [63], and the core diameter of the tapered fibre [37]. The intrinsic linewidth of the Brillouin gain spectrum is determined by the phonon lifetime and the structural irregularities of the waveguide.…”

“…Forward Brillouin scattering has been exploited to measure the core diameter of a micro-fibre by monitoring the forward BFS [37], which is inversely related to the diameter of the micro-fibre, as expressed in Equation (2). In addition, the effect of geometry on the transverse opto-acoustic responses in micro-scale waveguides has been studied in different platforms.…”

“…Energy conservation implies that: ω p − ω s = Ω, where ω p and ω s are the pump and signal frequencies, respectively, and Ω is the acoustic angular frequency. The acoustic field takes the form of either transverse, longitudinal, or a superposition of both waves, which can be utilized to measure the geometrical features of the waveguide such as the core diameter [37] and detect waveguide irregularities [38]. However, in order to make a distributed measurement along the waveguide, the SBS response needs to be localized.…”

Giant Brillouin amplification in gas using hollow-core waveguides

“…In that work, the peak gain coefficient reached 4 × 10 −14 m/W, which remains 1000 times smaller than the peak backward Brillouin gain coefficient in fibres with a solid silica core (SMF). This gain is clamped down as a consequence of the non-uniformity of the core diameter [32], since it causes a inhomogeneous gain linewidth broadening. Globally, no strong lightsound interaction in gaseous media has been reported so far.…”