A Planar low-cost full-polymer Optical Humidity Sensor

AbstractWe present an all-polymer optical humidity sensor, based on a 1mm plastic optical fiber (POF) with a U-bend, cladded with poly(N,N-dimethylacrylamide) (PDMAA) in the sensing region. The cladding changes its scattering properties on absorption of environmental humidity, thus modulating the transmitted optical power through the sensor. We explain the working principle of the sensor and show experimental results regarding scattering behavior of the cladding material and sensitivity to sudden humidity changes. We also propose a planar layout suitable for application to a hot embossing or lamination process for large-scale fabrication

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

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. © 2016 SPIE.DFG/CRC/PlanO

Manufacturing and characterization of femtosecond laser-inscribed Bragg grating in polymer waveguide operation in an IR-A wavelength range

Optical sensors, such as fiber Bragg gratings, offer advantages compared to other sensors in many technological fields due to their outstanding characteristics. This sensor technology is currently transferred to polymer waveguides that provide the potential for cost-effective, easy, and flexible manufacturing of planar structures. While sensor production itself, in the majority of cases, is performed by means of phase mask technique, which is limited in terms of its degrees of freedom, other inscription techniques enable the manufacture of more adaptable sensor elements for a wider range of applications. In this article, we demonstrate the point-by-point femtosecond laser direct inscription method for the processing of polymer Bragg gratings into waveguides of the epoxy-based negative photoresist material EpoCore for a wavelength range around 850 nm. By characterizing the obtained grating back-reflection of the produced sensing element, we determined the sensitivity for the state variables temperature, humidity, and strain to be 45 pm/K, 19 pm/%, and 0.26 pm/με, respectively. Individual and more complex grating structures can be developed from this information, thus opening new fields of utilization

Digital mirror devices and liquid crystal displays in maskless lithography for fabrication of polymer-based holographic structures

Polymer-based holographic and diffractive optical elements have gained increasing interest due to their potential to be used in a broad range of applications, such as illumination technology, micro-optics, and holography. We present a production process to fabricate polymer-based diffractive optical elements and holograms. The process is based on maskless lithography, which is used to fabricate optical elements in photoresist. We discuss several lab-level lithography setups based on digital mirror devices and liquid crystal devices with respect to illumination efficiency, resolution, and contrast. The entire optical setup is designed with emphasis on low-cost components, which can be easily implemented in an optical research lab. In a first step, a copy of the microstructures is replicated into optical polymeric materials by means of a soft stamp hot embossing process. The soft stamp is made from polydimethylsiloxan, which is coated onto the microstructure in the photoresist. The hot embossing process is carried out by a self-made and low-cost hot embossing machine. We present confocal topography measurements to quantify the replication accuracy of the process and demonstrate diffractive optical elements and holographic structures, which were fabricated using the process presented. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE).DFG/CRC/PlanOSGerman Federation of Industrial Research Associations (AiF)/EFB ZN 50

Lab-level and low-cost fabrication technique for polymer based micro-optical elements and holographic structures

Polymer based diffractive optical elements have gained increasing interest due to their potential to be used in various applications such as illumination technology, micro optics and holography. We present a novel production process to fabricate polymer based diffractive optical elements and holograms. The process is based on maskless lithography, which is used to fabricate optical elements in photoresist. We discuss several lab-made lithography setups based on digital mirror devices and liquid crystal devices with respect to light efficiency, resolution and contrast. The whole optical setup is designed with an emphasis on low-cost setups, which can be easily implemented in an optical research lab. In a subsequent step, a copy of the microstructures is easily replicated into optical polymeric materials by means of a soft stamp hot embossing process step. The soft stamp is made from Polydimethylsiloxan, which is coated onto the microstructure in resist. The hot embossing process is carried out by a self-made and low-cost hot embossing machine. We present confocal topography measurements to quantify the replication accuracy of the process and demonstrate diffractive optical elements and holographic structures, which were fabricated using the process presented. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.DFG/CRC/PlanOSGerman Federation of Industrial Research Associations (AiF)/EFB ZN 50

Manufacturing of embedded multimode waveguides by reactive lamination of cyclic olefin polymer and polymethylmethacrylate

We demonstrate the manufacturing of embedded multimode optical waveguides through linking of polymethylmethacrylate (PMMA) foils and cyclic olefin polymer (COP) filaments based on a lamination process. Since the two polymeric materials cannot be fused together through interdiffusion of polymer chains, we utilize a reactive lamination agent based on PMMA copolymers containing photoreactive 2-acryloyloxyanthraquinone units, which allows the creation of monolithic PMMA-COP substrates through C-H insertion reactions across the interface between the two materials. We elucidate the lamination process and evaluate the chemical link between filament and foils by carrying out extraction tests with a custom-built tensile testing machine. We also show attenuation measurements of the manufactured waveguides for different manufacturing parameters. The lamination process is in particular suited for large-scale and low-cost fabrication of board-level devices with optical waveguides or other micro-optical structures, e.g., optofluidic devices. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).DFG/SFB/TRR 12

Simulation, production and evaluation of optical strain sensors for integration in thin polymer foil

Diese Arbeit ist entstanden im Rahmen des Sonderforschungsprogramms SFB 123 ” PlanOS“ und beschreibt die Auslegung, Herstellung und Charakterisierung zweier polymerbasierter Dehnungssensoren, die ausschließlich auf Multimode-Wellenleitern beruhen

Foil-integrated 2D optical strain sensors

We present two novel approaches to 2D optical strain sensing in thin polymer foils that allow for mass-production by MEMS production techniques. The sensor principles are based on purely optical methods: the sensitive detection of either wavelength or intensity transfer functions in specifically designed planar waveguide structures. The goal is to develop 2D strain sensor arrays that are easy to integrate in flexible polymer foils and which can be applied to a wide range of measurement applications in research and technology. We discuss the sensor concepts and analyze their performance under optimal conditions

Development of a Polymeric Arrayed Waveguide Grating Interrogator for Fast and Precise Lithium-Ion Battery Status Monitoring

We present the manufacturing and utilization of an all-polymer arrayed waveguide grating (AWG) interacting with a fiber Bragg grating (FBG) for battery status monitoring on the example of a 40 Ah lithium-ion battery. The AWG is the main component of a novel low-cost approach for an optical interrogation unit to track the FBG peak wavelength by means of intensity changes monitored by a CMOS linear image sensor, read out by a Teensy 3.2 microcontroller. The AWG was manufactured using laser direct lithography as an all-polymer-system, whereas the FBG was produced by point-by-point femtosecond laser writing. Using this system, we continuously monitored the strain variation of a battery cell during low rate charge and discharge cycles over one month under constant climate conditions and compared the results to parallel readings of an optical spectrum analyzer with special attention to the influence of the relative air humidity. We found our low-cost interrogation unit is capable of precisely and reliably capturing the typical strain variation of a high energy pouch cell during cycling with a resolution of 1 pm and shows a humidity sensitivity of −12.8 pm per %RH