Low-loss optical-coupling structures are highly relevant for applications in fields as diverse as information and communication technologies, integrated circuits, or flexible and highly-functional polymer sensor networks. For this suitable and reliable production methods are crucial. Self-written waveguides are an interesting solution. In this work, we present a simple and efficient one-polymer approach for self-written optical connections between light-guiding structures such as single-mode and multi-mode optical fibers or waveguides that relies on self focusing of the light inside a photopolymerizing mixture. The optical connections are produced in a two-step process by writing into monomer resin using cw laser light in the blue wavelength range and subsequent UV curing. Since only one photopolymerizing resin is required, we reduced the fabrication complexity compared to previous approaches to obtain a waveguide embedded in a rigid cladding material. We discuss the production method, the results obtained as function of relevant process parameters such as writing speed or curing time, and evaluate optical properties and coupling efficiencies.
Abstract-Optical interconnects are the key components for integrated optics to link photonic integrated circuits or to connect external elements such as light sources and detectors. However, misalignment of the optical elements contained and its compensation is a remaining challenge for integrated optical devices. We present a novel method to establish rigid interconnects based on a 2-wavelength self-written waveguide process which automatically compensates for misalignment. We exemplarily demonstrate the capability of our process by writing interconnects between two multimode fibers as well as hot-embossed integrated polymer waveguides and a bare laser diode chip. The coupling efficiency of the interconnects obtained is analyzed with respect to misalignment. We found that coupling losses are as low as 1.3 dB if a lateral misalignment lies within a 10 µm interval, which is achieved by commercially available pick-and-place machines. Our approach is easily combined with high-throughput techniques such as hot embossing and enables low-cost production of interconnects even for mass fabrication in future applications.
Optical waveguides were fabricated on flexible foil substrates by ink-jet printing, to complement and enhance printed flexible electronics with optical networks. The 145 μm wide and 20 μm high transparent polymer tracks were created by printing subsequent tracks of an acrylate ink on polymer foil. A printable, optically transparent material was prepared by a combination of an acrylate resin with a low-viscosity, co-polymerising acrylate. This solved the problem of solvent evaporation for substrates with low heat tolerance. Thermally induced pinning, used to prevent the ink from spreading out on the substrate was achieved by heating the substrate to 60 °C, and found to be strongly affected by the time lapse between deposition of the individual layers. This tool allowed to increase the aspect ratio of the printed tracks from 0.07 to 0.17, and the contact angle of the printed tracks from 15°to 37°. After completion of the deposition step, the waveguides were polymerised under UV light, and covered by a printed upper cladding layer. In the optical evaluation, transmission could be demonstrated with an attenuation in the range of 1.4 dB cm −1 for a wavelength of 785 nm, with a significant portion of material attenuation.
We report on the fabrication and characterization of integrated Mach-Zehnder interferometers in polymer foil without an interaction window. The interferometers are based on inverted rib waveguides, which allow single mode behavior even for waveguide widths larger than a few micrometers. The phase change between the two interferometer arms upon a refractive index change of the analyte that serves as the upper cladding is generated by the asymmetricity of the two interferometer arms. A difference of the waveguide width in the straight part of the interferometer leads to different effective refractive indices and thus to a change in the interference signal. We show in small scale the process chain, which is compatible with a cost-effective roll-to-roll fabrication process. For a proof of principle we apply deionized water and a glucose solution as analytes to the sensor foils and detect the transmitted intensity as a measure of the induced phase change. A detection limit of 3·10⁻³ refractive index units is reached for homogeneous sensing at a total system length of 9.3 mm and a total waveguide core thickness of 3 μm.
Abstract. Polymer-based optical sensor networks on foils (planar optronic systems) are a promising research field, but it can be challenging to supply them with light. We present a solvent-free, ink-jet printable material system with optically active substances to create planar light sources for these networks. The ink is based on a UV-curable monomer, the fluorescent agents are EuðDBMÞ 3 Phen or 9,10-diphenylantracene, which fluoresce at 612 or 430 nm, respectively. We demonstrate the application as light source by printing a small area of fluorescent material on an optical waveguide fabricated by flexographic printing on PMMA foil, resulting in a simple polymer-optical device fabricated entirely by additive deposition techniques. When excited by a 405-nm laser of 10 mW, the emitted light couples into the waveguide and appears at the end of the waveguide. In comparison to conventional light sources, the intensity is weak but could be detected with a photodiode power sensor. In return, the concept has the advantage of being completely independent of any electrical elements or external cable connections.
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