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.
A fully polymer slot Young interferometer operating at 633 nm wavelength was fabricated by using nanoimprint molding method. The phase response of the interference pattern was measured with several concentrations of glucose-water solutions, utilizing both TE and TM polarization states. The sensor was experimentally found to detect a bulk refractive index change of 6.4×10<sup>-6</sup> RIU. Temperature dependency of silicon slot waveguide has been demonstrated to be reduced with composite slot waveguide structure. The slot filled with thermally stable polymer having negative thermo-optic coefficient showed nearly an athermal operation of silicon slot waveguide. Experimental results show that the slot waveguide geometry covered with Ormocomp has thermo-optical coefficient of 6 pm/K.
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 demonstrate low-loss silicon slot waveguides filled with single and dual atomic layer deposited oxide layers.
Propagation losses less than 5 dB/cm and 8 dB/cm are achieved for the waveguides with single (Al<sub>2</sub>O<sub>3</sub>) and double
(Al<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub>) layers, respectively. The devices are fabricated using low-temperature CMOS compatible processes. The
geometries allow nonlinearities nearly two orders of magnitude smaller than plain silicon waveguides.
Polymers are important materials in fabrication of photonics devices due to their good optical properties, such as, high
transmittivity, versatile processability also at low temperatures allowing potential for low-cost fabrication. A critical
requirement in the fabrication of integrated optical devices has been selecting a most suitable method for patterning the
ridge bounding the optical mode in the waveguide. In this paper, we discuss a UV-imprint fabrication of polymeric
single-mode waveguides with different configurations: ridge type, inverted rib type and layered composite waveguides.
A ridge waveguide type consists of a strip waveguide superimposed onto a slab waveguide made of the same material.
When patterning a ridge by imprinting technique, a residual layer is formed underneath the imprinted ridges. A too thick
residual layer might cause a loss of propagation mode due to power leakage to the slab guide, which might require a
subsequent etching step. In inverted rib waveguide structure, a groove of cladding material is patterned by imprinting.
This is followed by the filling of the groove with a core material. From the imprint fabrication point of view, the
fabrication tolerances can be relaxed because the residual slab layer underneath the waveguide can have arbitrary
thickness. Besides fabrication of above mentioned waveguide structures, we also investigate the possibility to produce
composite waveguide devices by depositing inorganic thin films with high-refractive index on UV-imprinted polymeric
structures with low-refractive. The purpose to use composite structures is to manipulate the optical field distribution in
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.
We present the design of a novel, CMOS compatible, waveguide structure capable of multifrequency transmission bands
with strongly enhanced band-edge states. The concept of the structure is based on the aperiodic Thue-Morse fractal
ordering of dielectric scattering subunits combined with a traditional channel-waveguide scheme. The design of the
waveguide has been carefully optimized in order to ensure its manufacturability within standard CMOS processing. Due
to the lack of translational symmetry, the proposed Thue-Morse waveguide is characterized by multiple photonic
pseudoband-gaps and quasi-localized field states exhibiting large field enhancement effects.
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 <sup>29</sup>Si 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.
We report on the fabrication of transparent, conductive and directly photopatternable, pure and Sb-doped tin dioxide thin films. Precursors used were antimony(III)isopropoxide and a photo-reactive tin alkoxide synthesized from tin(IV)isopropoxide and methacrylic acid. The synthesis of methacrylic acid modified tin alkoxide was monitored in-situ using IR- and ESI-TOF mass spectroscopic techniques. Sb-doped organo-tin films were deposited via single layer spin coating. After deposition the films were patterned via photopolymerization, using a mercury I-line UV-lamp. All investigated materials could be patterned with 3 μm features. After development in isopropanol, the films were annealed in air, in order to obtain crystalline and conductive films. The electrical conductivities of the annealed thin films with, and without, UV-irradiation were determined using a linear four-point method. The direct photopatterning process was found to increase the film conductivity for all the Sb-doping levels tested. The mechanisms for the increased conductivity were characterized using AFM, XPS and XRD techniques.
The scalability to mass production and low cost are two driving forces towards multimode waveguide technologies. Organic-inorganic hybrid materials realized by sol-gel technology are promising choices for the fabrication of integrated optical circuits. This paper describes fabrication and characterization of the photo-patternable materials that are based on the sol-gel technology. The materials can be processed directly, using UV lithographic processing. Tailored polymeric materials are achieved, avoiding the use of the previously developed pre-hydrolyzed zirconium sol-gel precursors, which exhibit a lack of environmental stability. Films, which behave as a negative tone photoresist under UV-exposure, are fabricated by the spin-coating method on various substrates. The procedure shows the possibility for tailoring the refractive index and birefringence of the materials by varying the composition concentrations of the hybrid polymer system. Refractive indices vary from 1.4770 to 1.4950. The synthesized material also exhibits the possibility for birefringence optimization depending on the composition concentrations. The direct lithography process was demonstrated on various substrate materials (i.e., silicon wafer, glass, quartz, as well as flexible plastics, LTCC and semiconductor materials). The film waveguides are characterized by using of prism coupling technique at various wavelengths. The morphology of the optical structures is measured with a white-light interferometer.
Lithographic patterning of organic-inorganic hybrid materials processed by the use of sol-gel technology allows for the generation of waveguide structures at low temperatures onto polymer or ceramic substrates. In addition, sol-gel technology provides the possibility to process precision structures, such as, grooves and cavities, which are applicable for the passive alignment of photonic devices. This provides the possibility for the realization of mass-producible photonic circuits onto large-area substrates. At the moment, the most potential applications are systems based on then use of multimode waveguide structures. Actually, when utilizing sol-gel technology, the challenge is how to process homogenous, low-loss and high-aspect-ratio structures. In addition, when aiming to highly mass-producible multimode modules, the key issue is the alignment of photonic devices preferably by the use of passive precision structures. In the future, when the systems need to be more complicated, the modeling of systems requires sophisticated 3D modeling tools. In this paper, the processing of multimode structures with sol-gel technologies is described, and the characterization results of prototype devices are reported. In addition, molding and cofiring technologies potentially applicable for the hybrid integration of photonic modules are reviewed. Finally, the future research aims for the commercialization of photonic modules based on the use of sol-gel technologies are envisioned.