Gorgi Kostovski

Nanoimprinted optical fibres: Biotemplated nanostructures for SERS sensing

Nanoimprint lithography is used to pattern the endface of an optical fiber. A biological nanotemplate is replicated into polymer and coated with metal. Observed enhancement of through-fibre Raman scattering validates the approach.

The optical fiber tip: an inherently light-coupled microscopic platform for micro- and nanotechnologies.

The flat tip of an optical fiber is a unique and unconventional platform for micro and nanotechnologies. The small cross-section and large aspect ratio of the fiber provide an inherently light-coupled substrate that is uniquely suited to remote, in vivo and in situ applications. However, these same characteristics challenge established fabrication technologies, which are best suited to large planar substrates. This review presents a broad overview of strategies for patterning the flat tip of an optical fiber. Techniques discussed include self-assembly, numerous lithographies, through-fiber patterning, hybrid techniques, and strategies for mass manufacture, while the diverse applications are discussed in context throughout.

Sub‐15nm Optical Fiber Nanoimprint Lithography: A Parallel, Self‐aligned and Portable Approach

We demonstrate the parallel patterning of multiple optical-fiber facets using nanoimprint lithography on a novel platform. A resolution of better than 15 nm is demonstrated and up to 40 optical-fiber facets have been imprinted in parallel. The lithography platform features a self-alignment mechanism (see figure) that greatly relaxes the mechanical requirements, allowing for the demonstration of a compact, portable imprinting-module and the accommodation of non-planar, biological molds. The imprinted fibers are metalized and employed as bi-directional probes for surface-enhanced Raman scattering.

Polymer long-period raised rib waveguide gratings using nano-imprint lithography

This letter presents the fabrication and demonstration of a long-period raised rib waveguide grating using nano-imprint lithography. The device consists of a lower UV15 cladding, where relief-gratings are implemented, and an NOA73 raised rib core waveguide. Spectral transmission reveals a resonance at 1585 nm with about 10-dB rejection and 12-nm linewidth.

Optical fiber sensor based on oblique angle deposition

The technique of oblique angle deposition has been extended to the fabrication of nanostructured metal coatings on the tips of standard silica optical fibers by thermal evaporation. The coatings are initiated as metal island films, which grow into extended rodlike structures as the deposition continues. The nanorod coatings demonstrate excellent surface-enhanced Raman scattering performance with variability of less than 10% as shown by direct measurements off the fiber tip with thiophenol as a test analyte. However, in the remote sensing configuration, the nanorod structures perform no better than thin metal island films. This appears to be mainly due to reduced transmission when nanorod lengths exceed ~100 nm. Moreover, the variability of remote measurements is increased to 18%. This is believed to be due to variations in coupling efficiency.

Dynamic manipulation of modes in an optical waveguide using dielectrophoresis

The emergence of optofluidics has brought a high degree of tuneability and reconfigurability to optical devices. These possibilities are provided by characteristics of fluids including mobility, wide range of index modulation, and abrupt interfaces that can be easily reshaped. In this work, we created a new class of optofluidic waveguides, in which suspended mesoparticles were employed to greatly enhance the flexibility of the system. We demonstrated tuneable quasi single mode waveguides using spatially controllable mesoparticles in optofluidics. The coupling of waveguiding modes into the assembly of mesoparticles produces strong interactions and resonant conditions, which promote the transitions of the waveguiding modes. The modal response of the system depends on the distribution of packed particles above the polymeric rib waveguide which can be readily controlled under the appropriate combination of dielectrophoresis and hydrodynamic forces.

Sidewall corrugation lithography: Bulk fabrication of ordered nanowires, nanoribbons, and nanorings

A general technique for three-dimensional nanofabrication is demonstrated by employing photolithographic standing wave corrugations as nanoscale templates. The line-of-sight deposition of a variety of materials demonstrates vertical stacks of nanowires and nanoribbons that take the forms of straight lengths, circular rings, and multilayer structures. Contact photolithography is used to fabricate the micron-scale corrugated templates from which nanofeatures with widths ranging from 65to∼20nm are derived.

Nanoimprinting on optical fiber end faces for chemical sensing

Optical fiber surface-enhanced Raman scattering (SERS) sensors offer a potential solution to monitoring low chemical concentrations in-situ or in remote sensing scenarios. We demonstrate the use of nanoimprint lithography to fabricate SERS-compatible nanoarrays on the end faces of standard silica optical fibers. The antireflective nanostructure found on cicada wings was used as a convenient template for the nanoarray, as high sensitivity SERS substrates have previously been demonstrated on these surfaces. Coating the high fidelity replicas with silver creates a dense array of regular nanoscale plasmonic resonators. A monolayer of thiophenol was used as a low concentration analyte, from which strong Raman spectra were collected using both direct endface illumination and through-fiber interrogation. This unique combination of nanoscale replication with optical fibers demonstrates a high-resolution, low-cost approach to fabricating high-performance optical fiber chemical sensors.

Nanolithography by elastomeric scattering mask: An application of photolithographic standing waves

An application is demonstrated for the much maligned standing wave in photolithography that is responsible for the sidewall corrugations in photoresist patterns. We demonstrate the realization of a polydimethylsiloxane (PDMS) scattering mask through the casting of these sidewall corrugations and their application as the masking components in an otherwise transparent bulk of PDMS. Photoresist structures with widths in the order of 80nm are realized by the application of this mask, demonstrating excellent correlation with the lateral depths of the sidewall corrugations. The continuity of the sidewall corrugations around corners makes both straight and curved lines realizable with equal simplicity.

A novel Surface Tension Assisted Lithography (STAL) technique for microfabrication of 3D structures

A novel Surface Tension Assisted Lithography (STAL) technique is proposed to fabricate 3D structures in the photo-patternable polymer, SU-8, using a sequence of soft-imprint lithography, photo-lithography, and polymer reflow. The dimensions of the reflowed 3D structures are controlled by the volume of material initially displaced by soft-imprinting, and the lateral dimensions of the reflow container, defined by photo-lithography.