A fractal-based fibre for ultra-high throughput optical probes

Abstract

A core component of all scanning near-field optical microscopy (SNOM) systems is the optical probe, which has evolved greatly but still represents the limiting component for the system. Here, we introduce a new type of optical probe, based on a Fractal Fibre which is a special class of photonic crystal fibre (PCF), to directly address the issue of increasing the optical throughput in SNOM probes. Optical measurements through the Fractal Fibre probes have shown superior power levels to that of conventional SNOM probes. The results presented in this paper suggest that a novel fibre design is critical in order to maximize the potential of the SNOM.

Ultrafine Fiber Tip Etched in Hydrophobic Polymer Coated Tube for Near-Field Scanning Plasmonic Probe

“…Though the tip end ( ) should have a curvature determined by the SM, we assume it as Gaussian. The complex dielectric constant of the silver coating on the tip is expressed by the Drude dispersion relation (4) with plasmon angular frequency rad s, damping factor rad s and permittivity .…”

“…Chemical etching is widely used as it achieves fiber tips with much shorter cone and much larger angle, allowing higher transmission. Turner proposed an etching method [6] which leads to fabrication of a fiber probe [2], [4] tension meniscus (SM) of the HF acid solution along the fiber. In fact, there is a considerable amount of current interest in studying and making [7], [8] sharp fiber tips.…”

Endlessly adiabatic fibre

“…The MFD varies substantially with fibre diameter, restricting the maximum taper gradient. Shrinking the cladding [3], grading the index profile in the core (while retaining a uniform outer cladding) [4] or microstructuring [6] can reduce the MFD variation somewhat, but do not eliminate it. Now imagine a fibre where the mode does not change at all with fibre size, so 1/ = 0.…”

Self-Imaged Omnidirectional Fresnel Fibres

“…However, from our arguments above the very property of fractals, that of self-imaging, leads to structures which for all intensive purposes resemble omnidirectional filters and hence the same mechanism is invoked, despite their complexity. Solid core fractal fibres for assisting tapering have been recently proposed and demonstrated by scaling down a series of air hole rings towards the central core of the structured fibre [7]. [8] employed to generate the fractal zone cross-section (FZC).…”