A novel method for fabricating a single mode optical interconnection platform is presented. The method comprises the miniaturized assembly of optoelectronic single dies, the scalable fabrication of polymer single mode waveguides and the coupling to glass fiber arrays providing the I/O’s. The low cost approach for the polymer waveguide fabrication is based on the nano-imprinting of a spin-coated waveguide core layer. The assembly of VCSELs and photodiodes is performed before waveguide layers are applied. By embedding these components in deep reactive ion etched pockets in the silicon substrate, the planarity of the substrate for subsequent layer processing is guaranteed and the thermal path of chip-to-substrate is minimized. Optical coupling of the embedded devices to the nano-imprinted waveguides is performed by laser ablating 45 degree trenches which act as optical mirror for 90 degree deviation of the light from VCSEL to waveguide. Laser ablation is also implemented for removing parts of the polymer stack in order to mount a custom fabricated connector containing glass fiber arrays. A demonstration device was built to show the proof of principle of the novel fabrication, packaging and optical coupling principles as described above, combined with a set of sub-demonstrators showing the functionality of the different techniques separately. The paper represents a significant part of the electro-photonic integration accomplishments in the European 7th Framework project “Firefly” and not only discusses the development of the different assembly processes described above, but the efforts on the complete integration of all process approaches into the single device demonstrator.
In the Information and Communications Technology (ICT) sector, the demands on bandwidth continually grow due to
increased microprocessor performance and the need to access ever increasing amounts of stored data. The introduction of
optical data transmission (e.g. glass fiber) to replace electronic transmission (e.g. copper wire) has alleviated the
bandwidth issue for communications over distances greater than 10 meters, however, the need has arisen for optical data
transfer over shorter distances such as those found inside computers. A possible solution for this is the use of low–cost
single mode polymer based optical waveguides fabricated by direct patterning Nanoimprint Lithography (NIL). NIL has
emerged as a scalable manufacturing technology capable of producing features down to the hundred nanometer scale
with the potential for large scale (roll-to-roll) manufacturing.
In this paper, we present results on the modeling, fabrication and characterization of single mode waveguides and optical
components in low-loss ORMOCER™ materials. Single mode waveguides with a mode field diameter of 7 μm and
passive structures such as bends, directional couplers and multi-mode interferometers (MMIs) suitable for use in 1550
nm optical interconnects were fabricated using wafer scale NIL processes. Process issues arising from the nano-imprint
technique such as residual layers and angled sidewalls are modeled and investigated for excess loss and higher order
mode excitation. Conclusions are drawn on the applicability of nano-imprinting to the fabrication of circuits for intrachip/
board-level optical interconnect.
Polymer-based integrated optics is attractive for inter-chip optical interconnection applications, for instance, for coupling photonic devices to fibers in high density packaging. In such a hybrid integration scheme, a key challenge is to achieve efficient optical coupling between the photonic chips and waveguides. With the single-mode polymer waveguides, the alignment tolerances become especially critical as compared to the typical accuracies of the patterning processes. We study novel techniques for such coupling requirements. In this paper, we present a waveguide-embedded micro-mirror structure, which can be aligned with high precision, even active alignment method is possible. The structure enables 90 degree bend coupling between a single-mode waveguide and a vertical-emitting/detecting chip, such as, a VCSEL or photodiode, which is embedded under the waveguide layer. Both the mirror structure and low-loss polymer waveguides are fabricated in a process based mainly on the direct-pattern UV nanoimprinting technology and on the use of UVcurable polymeric materials. Fabrication results of the coupling structure with waveguides are presented, and the critical alignment tolerances and manufacturability issues are discussed.
This paper describes experimental measurement results for photonic crystal sensor devices which have been functionalized for gas sensing applications. The sensor consists of a two dimensional photonic crystal etched into a slab waveguide having a refractive index of 1.7-1.9. Test devices were fabricated from SiON material on silicon / silicon dioxide platform, and also in polymer materials on silicon platform. The inorganic photonic crystals were made using direct write electron-beam lithography and reactive ion etching. The polymeric devices were made by nano-imprint lithography using the SiON structure as the imprint master. The high refractive index polymer was composed of a TiO2 - UV resin nanocomposite having a nanoparticle fraction between 50 and 60 wt%. This resulted in a tunable refractive index between 1.7 and 1.85. Devices were functionalized for gas sensing applications by coating the surface with a chemical receptor. This responsive layer reacts with the target gas and changes its refractive index. This change causes the angle of out-coupling to change slightly. In this paper we report successful detection of formaldehyde in air at sub ppm levels, and discuss details of chemical functionalization of the PC sensor.
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.
We present designs for sharp bends in polymer waveguides using colloidal photonic crystal (PhC) structures. Both silica
(SiO2) sphere based colloidal PhC and core-shell colloidal PhC structures having a titania (TiO2) core inside silica (SiO2)
shells are simulated. The simulation results show that core-shell Face Centered Cubic (FCC) colloidal crystals have a
sufficient refractive index contrast to open up a bandgap in the desired direction when integrated into polymer
waveguides and can achieve reflection <70% for the appropriate plane. Different crystal planes of the FCC structure are
investigated for their reflection and compared with the calculated bandstructure. Different techniques for fabrication of
PhC on rectangular seed layers namely slow sedimentation; spin coating and modified doctor blading are discussed and
investigated. FCC and Random FCC silica structures are characterized optically to show realisation of (001) FCC.
The increasing request for higher data speeds in the information and communication technology leads to continuously
increasing performance of microprocessors. This has led to the introduction of optical data transmission as a replacement
of electronic data transmission in most transmission applications longer than 10 meters. However, a need remains for
optical data transmission for shorter distances inside the computer. This paper gives an overview of the Joint European
project FIREFLY, in which new polymer based single mode waveguides are developed for integration with VCSELs,
splitters and fibers that will be manufactured using multi-layer nanoimprint lithography (NIL). Innovative polymers, new
applications of nano-technology, new methods for optical coupling between components, and the integration of all these
new components are the technical ingredients of this ambitious project.
A coating based FBG humidity sensor is developed for distributed humidity sensing. The sensitivity of the coated FBG is
optimized by varying the chemical composition and the thickness of the coating. A sensitivity of ~2 pm/%RH and a
rapid response are demonstrated. The composition of the coating can be adapted for sensing other chemical elements.
For the design and modeling of the responsive polymer coatings, a toolbox is developed. Using this toolbox, sensors for
sour gas like CO2 and H2S for the Oil&Gas industry are developed. The results match well with the prediction.
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