Polymers have become an important material group in fabricating discrete photonic components and integrated optical devices. This is due to their good properties: high optical transmittance, versatile processability at relative low temperatures and potential for low-cost production. Recently, nanoimprinting or nanoimprint lithography (NIL) has obtained a plenty of research interest. In NIL, a mould is pressed against a substrate coated with a moldable material. After deformation of the material, the mold is separated and a replica of the mold is formed. Compared with conventional lithographic methods, imprinting is simple to carry out, requires less-complicated equipment and can provide high-resolution with high throughput. Nanoimprint lithography has shown potential to become a method for low-cost and high-throughput fabrication of nanostructures. We show the development process of nano-structured, large-area multi-parameter sensors using Photonic Crystal (PC) and Surface Enhanced Raman Scattering (SERS) methodologies for environmental and pharmaceutical applications. We address these challenges by developing roll-to-roll (R2R) UV-nanoimprint fabrication methods. Our development steps are the following: Firstly, the proof of concept structures are fabricated by the use of wafer-level processes in Si-based materials. Secondly, the master molds of successful designs are fabricated, and they are used to transfer the nanophotonic structures into polymer materials using sheet-level UV-nanoimprinting. Thirdly, the sheet-level nanoimprinting processes are transferred to roll-to-roll fabrication. In order to enhance roll-to-roll manufacturing capabilities, silicone-based polymer material development was carried out. In the different development phases, Photonic Crystal and SERS sensor structures with increasing complexities were fabricated using polymer materials in order to enhance sheet-level and roll-to-roll manufacturing processes. In addition, chemical and molecular imprint (MIP) functionalization methods were applied in the sensor demonstrators. In this paper, the process flow in fabricating large-area nanophotonic structures by the use of sheet-level and roll-to-roll UV- nanoimprinting is reported.
Low-loss polymeric optical waveguides were fabricated by UV-nanoimprinting. With this technique the waveguides are
directly patterned by imprinting of the UV-curable optical polymer materials, i.e. no etching processes are needed. By
properly manufactured imprinting molds, very smooth waveguide surfaces are achieved and the optical loss is dominated
by the material attenuation. The advantages of the manufacturing technology include the potential scalability onto large
substrate areas and applicability for fabrication on various substrate materials. For instance, printed circuit boards are
interesting substrates for high-bit-rate optical interconnection applications requiring long waveguides, and glass and
plastic sheets are interesting for sensor applications. The technology also promises for low overall costs, as it is a
relatively simple high-throughput replication process. Both ridge-type and inverted-rib-type single-mode waveguides
were fabricated using Ormocer hybrid polymer materials having low optical attenuation. Very low loss waveguides were
demonstrated by fabrication long waveguides in a spiral shape. The optical attenuation was characterized of 27 cm-long
inverted-rib waveguide spirals having 2 μm-wide cores. The measured average attenuation was 0.25 and 0.56 dB/cm at
the wavelengths of 638 and 1310 nm, respectively.
We discuss the applicability of using polymers for producing slot waveguide modes in single and triple-slot waveguide
structures. We use finite element method to computationally study the field confinement and enhancement in the slot
region with and without high refractive index coating on the top of the low index polymeric waveguide. The sensitivity
to refractive index shift in ambient surrounding is improved almost five times in proposed high index coated polymer
triple-slot waveguide structure compared to the ridge polymer waveguide.
The driving force behind combining the nanoimprinting and photolithography is to effectively utilize the advantages of
both patterning techniques simultaneously. Conventional shadow-mask UV-lithography can be used to pattern micron-scale
structures uniformly over large areas, whereas nanoimprinting enables patterning of nanoscale features, which can
also be tilted or round-shaped. We present the work on direct patterning of micro-optical structures by combined
nanoimprinting and lithography using modified mask aligner, hybrid mask mold and directly patternable, UV-curable
materials. Patterning of structures is carried out in wafer-level fashion. Hybrid mask mold fabrication can be realized for
example by modifying conventional shadow-mask using focused ion beam (FIB) milling, or by patterning a mold area on
shadow-mask surface by nanoimprinting. One of the advantages of proposed fabrication method is that there is no need
for reactive ion etching (RIE) process steps. We present also near-field holography (NFH) as a method of grating mold
fabrication. Fabricated micro-optical structures include directly patterned waveguides with light coupling gratings, and
also pyramid-shaped gratings which show antireflection properties in the mid-infrared spectral region.
In the last decade, the processing of the waveguide structures on various substrates under mild conditions has been an appealing aim. The lithographic patterning of organic-inorganic hybrid materials processed by means of sol-gel technology allows the production of waveguides and other optical components.
We describe the synthesis of a new, photo-patternable, organically modified material with an improved ageing stability. Synthesis step does not involve widely used zirconia precursors, but it retains the same possibility of altering the refractive index by tailoring of the material composition. Refractive index values varied from 1.4700 to 1.5100. Measured birefringence values meet the requirements of most integrated planar optic applications. The synthesized material is compatible with silicon, glass and plastic substrates.
Material was analyzed using 29Si NMR techniques. The processed slab waveguides were characterized by using the prism coupling technique at various wavelengths. The attenuation in the waveguide was determined by the cut-back method, and it was found to be less than 0.5dB/cm at the wavelength of 830 nm. The morphology of the microstructures was measured by using the interferometer equipment. Slab waveguides rms values were in order of only 2 nm.