Low-cost fabrication of optical waveguides, interconnects and sensing structures on all-polymer-based thin foils

Abstract

Micro-optical sensors based on optical waveguides are widely used to measure temperature, force and strain but also to detect biological and chemical substances such as explosives or toxins. While optical micro-sensors based on silicon technology require complex and expensive process technologies, a new generation of sensors based completely on polymers offer advantages especially in terms of low-cost and fast production techniques. We have developed a process to integrate micro-optical components such as embedded waveguides and optical interconnects into polymer foils with a thickness well below one millimeter. To enable high throughput production, we employ hot embossing technology, which is capable of reel-to-reel fabrication with a surface roughness in the optical range. For the waveguide fabrication, we used the thermoplastic polymethylmethacrylate (PMMA) as cladding and several optical adhesives as core materials. The waveguides are characterized with respect to refractive indices and propagation losses. We achieved propagation losses are as low as 0.3 dB/cm. Furthermore, we demonstrate coupling structures and their fabrication especially suited to integrate various light sources such as vertical-cavity surface-emitting lasers (VCSEL) and organic light emitting diodes (OLED) into thin polymer foils. Also, we present a concept of an all-polymer and waveguide based deformation sensor based on intensity modulation, which can be fabricated by utilizing our process. For future application, we aim at a low-cost and high-throughput reel-to-reel production process enabling the fabrication of large sensor arrays or disposable single-use sensing structures, which will open optical sensing to a large variety of application fields ranging from medical diagnosis to automotive sensing.

Towards fabrication and application of polymer based photonics networks and sensors

“…Left: Sketch of the self-written interconnect approach achieved by using two different light fields for the writing process. Right: Microscope image of a fabricated self-written interconnect (from [9]).…”

“…b) Photography of a hot embossed grating structure. Bottom panel: SEM image of a hot embossed transmission surface grating (from [9]). c) SEM image of hot embossed focusing grating.…”

“…Left panel: Overview of the developed optical waveguide fabrication process chain: (a) heating of stamp and cladding material, (b) hot embossing of cladding structure, (c) cooling and demolding step, (d) deposition of the core material through spin-coating, (e) doctor blading step, and (f) UV-curing of the core material (from[9]). Right panel: photograph of the central part of the hot embossing machine used in this work.…”

“…b) Result of a slotting fabrication process. Bottom panel: Photograph of manufactured waveguide equipped with a micro-mirror for outcoupling of the light (from[9]). c) image of light being coupled out from polymer waveguide using a mirror coupler.…”

Improving partial wetting resolution on flexible substrates for application of polymer optical waveguides

“…Fabrication technologies, such as hot embossing 6 which is also suitable for the fabrication of planar polymer waveguides with Bragg gratings, 7 injection molding, 8 and UVnanoimprinting, 9 have already been successfully used for this purpose at high throughput, but these methods require elaborate and cost-intensive tools. Especially, iteration cycles for complete shaping and damage-free demolding of the tool lead to a low variability when the layout of the optical waveguides is changed.…”