Parameter control, characterization, and optimization in the fabrication of optical fiber near-field probes

Abstract

Tip diameter and transmission efficiency of a visible-wavelength near-field optic probe determine both the lateral spatial resolution and experimental utility of the near-field scanning optical microscope. The commonly used tip fabrication technique, laser-heated pulling of fused-silica optical fiber followed by aperture formation through aluminization, is a complex process governed by a large number of parameters. An extensive study of the pulling parameter space has revealed a time-dependent functionality between the various pulling parameters dominated by a photon-based heating mechanism. The photon-based heat source results in a temperature and viscosity dependence that is a complex function of time and fiber diameter. Changing the taper of the optical probe can affect transmission efficiency by an order of magnitude or more.

Transmission near-field scanning microscope for infrared chemical imaging

“…The CO 2 laser power density was 10 W/cm 2 , and the cross section of the beam in the fiber plane ϳ1 mm 2 . The result of this analysis shows that by using conventional pulling methods, 14 the pulling takes approximately 100 ms while the cutoff diameter for guided propagation occurs at ϳ5 ms before the final separation of the fiber. The pulling parameters ͑heating power, pulling speed, time͒ can be controlled dynamically up to 1 ms. Knowing that fast pulling velocities lead to long tapers while slow pulling velocities lead to blunt tips and short tapers, a two-step pulling technique was adopted in which we begin by a slow pull resulting in a taper larger than the wavelength of light, and just before the end, we elongate the remaining molten material in a second abrupt taper ending in a sharp tip.…”

Review of near-field optics and superlenses for sub-diffraction-limited nano-imaging

“…chemical etching [76][77][78][79][80] or "heating and pulling." 77,81,82 Fig. 3 shows the typical processing techniques for producing tapered fiber aperture probes.…”

Scanning near-field optical microscopy with aperture probes: Fundamentals and applications

“…The resulting tip shapes depend heavily on the temperature and the timing of the heating and pulling, as well as on the dimensions of the heated area. 44,57,58 The pulling method has the advantage that the glass surface on the taper is very smooth, which positively influences the quality of the evaporated metal layer. Furthermore, pulled tips often exhibit flat facets at the apex due to a final fracture during pulling which facilitates the formation of an aperture during evaporation.…”