Jarno Petäjä

MEMS-Controlled Paper-Like Transmissive Flexible Display

A novel microelectromechanical-systems (MEMS)-controlled paper-like transmissive flexible display device was modeled by a combination of a cantilever with a flat plate and was realized by roll-to-roll printing process for the first time. This model provides predictions as well as improvement suggestions to both mechanical and electrical designs. A newly developed roll-to-roll printing process which was composed of flexography, gravure, lift-off, and lamination techniques used to manufacture this device was proved applicable on flexible electronics with high-volume, low-cost, and large-area solutions. This 20 V-driven device provided distinguishable three primary colors with averaged transmittance of 50% in visible region for full color flexible display applications and showed commercialization compatibility. Its electrical, mechanical, and optical characteristics excelled previous similar works. The proved major advantages of mechanical reliability, low operation voltage, and process simplicity done by this work made the MEMS flexible display an important alternative to electrophoretic, electrowetting, and electrochromic systems.

Polymeric slot waveguide at visible wavelength

Polymeric slot waveguide structure, which pushes the mode field toward the surrounding media, was designed and characterized. The slot waveguide was fabricated by using nanoimprint lithography, and the operation of the slot was demonstrated at 633 nm wavelength with an integrated Young interferometer. The experimental result shows that the nanolithography method provides possibilities to fabricate disposable slot waveguide sensors.

Micro Roll-to-Roll Patterning Process and Its Application on Flexible Display

Novel electrode patterning techniques on thin polymer substrates were developed on a roll-to-roll (reel-to-reel, R2R) printing system. Hot embossing, laser ablation, and lift-off processes were evaluated for mass production for active-matrix display arrays with 1000 µm display pixels by using the concept of micro electro mechanical system (MEMS) Fabry–Perot etalon. Among which, the newly developed lift-off flexography process provided the best pattern integrity with 100 µm resolution. The demonstrator of display array proved R2R printing systems possibility and capability under 1 m/s speed. A complete multilayer stack demonstration with alignment process also indicated its variable application. Further actuation for the MEMS display proved the robustness of device made by printing techniques.

Detection of Listeria innocua on roll-to-roll produced SERS substrates with gold nanoparticles

The rapid and accurate detection of food pathogens plays a critical role in the early prevention of foodborne epidemics. Current bacteria identification practices, including colony counting, polymerase chain reaction (PCR) and immunological methods, are time consuming and labour intensive; they are not ideal for achieving the required immediate diagnosis. Different SERS substrates have been studied for the detection of foodborne microbes. The majority of the approaches are either based on costly patterning techniques on silicon or glass wafers or on methods which have not been tested in large scale fabrication. We demonstrate the feasibility of analyte specific sensing using mass-produced, polymer-based low-cost SERS substrate in analysing the chosen model microbe with biological recognition. The use of this novel roll-to-roll fabricated SERS substrate was combined with optimised gold nanoparticles to increase the detection sensitivity. Distinctive SERS spectral bands were recorded for Listeria innocua ATCC 33090 using an in-house build (785 nm) near infra red (NIR) Raman system. Results were compared to both those found in the literature and the results obtained from a commercial time-gated Raman system with a 532 nm wavelength laser excitation. The effect of the SERS enhancer metal and the excitation wavelength on the detected spectra was found to be negligible. The hypothesis that disagreements within the literature regarding bacterial spectra results from conditions present during the detection process has not been supported. The sensitivity of our SERS detection was improved through optimization of the concentration of the sample inside the hydrophobic polydimethylsiloxane (PDMS) wells. Immunomagnetic separation (IMS) beads were used to assist the accumulation of bacteria into the path of the beam of the excitation laser. With this combination we have detected Listeria with gold enhanced SERS in a label free manner from such low sample concentrations as 104 CFU ml−1.

Cost-effective packaging of laser modules using LTCC substrates

The modeling, realization and characterization of photonic module based on the use of Low Temperature Co-fired Ceramics (LTCC) technology is reported. The 3D modeling of the system provides possibility to optimize structures, materials and components in order to achieve optimal performance for the final product and still maintain reasonably low fabrication costs. The cost-effectiveness in the product can be further optimized using an iterative optimization process, in which the effect of module manufacturing tolerances and assembly process tolerances is simulated by a VisVSA Monte-Carlo simulation. The tolerance distributions produced by a VisVSA simulation are used as input parameters together with optical component tolerances in an ASAP Monte-Carlo simulation, in which the final module optical performance distribution in simulated production is obtained. The module cost, performance and optical performance limited yield is possible to define with this iterative process. As an example of this kind of packaging modeling, we present a demonstrator module having a high-power multimode laser diode with a 1μm x 100μm emitting area coupled to a 62.5/125μm graded-index (NA=0.275) multimode fiber. The tolerance modeling results are verified by experimental characterization of the packaged prototypes. Measured coupling efficiencies were in good agreement with simulated ones, when the fiber NA was 0.2 or larger. The measured coupling efficiency, however, was 38% lower than simulated, when the fiber NA was 0.12. This was probably due to the laser mode structure difference between simulation model and reality. Coupling efficiency of 0.46 was obtained in a passively aligned demonstrator module, when the nominal value was 0.48.

Stability optimization of microbial surface-enhanced Raman spectroscopy detection with immunomagnetic separation beads

Abstract. Immunomagnetic separation (IMS) beads with antibody coating are an interesting option for biosensing applications for the identification of biomolecules and biological cells, such as bacteria. The paramagnetic properties of the beads can be utilized with optical sensing by migrating and accumulating the beads and the bound analytes toward the focus depth of the detection system by an external magnetic field. The stability of microbial detection with IMS beads was studied by combining a flexible, inexpensive, and mass producible surface-enhanced Raman spectroscopy (SERS) platform with gold nanoparticle detection and antibody recognition by the IMS beads. Listeria innocua ATCC 33090 was used as a model sample and the effect of the IMS beads on the detected Raman signal was studied. The IMS beads were deposited into a hydrophobic sample well and accumulated toward the detection plane by a neodymium magnet. For the first time, it was shown that the spatial stability of the detection could be improved up to 35% by using IMS bead capture and sample well placing. The effect of a neodymium magnet under the SERS chip improved the temporal detection and significantly reduced the necessary time for sample stabilization for advanced laboratory testing.

Fiber pigtailed multimode laser module based on passive device alignment on an LTCC substrate

A concept that utilizes structured planar substrates based on low-temperature cofired ceramics (LTCC) as a precision platform for a miniature passive alignment multimode laser module is demonstrated. The three-dimensional shape of the laminated and fired ceramic substrate provides the necessary alignment structures including holes, grooves, and cavities for the laser-to-fiber coupling. The achieved passive alignment accuracy allows high coupling efficiency realizations of multimode fiber pigtailed laser modules. Thick-film printing and via punching can be incorporated in order to integrate electronic assemblies directly on the optomechanical platform. The platform is scalable, and it allows embedding of subsystems, such as silicon optical bench (SiOB), but it also provides the interface for larger optical systems. Temperature management of high-power laser diodes is achieved by realizing heat dissipation structures and a cooling channel into the LTCC substrate. The measured maximum laser metallization temperature was 70degC when a thermal power of 0.5 W was applied at the laser active area using a liquid cooling of 50 mL/min. The measured maximum temperature of the laser surface was about three times higher without liquid cooling. Optical coupling efficiency of the multimode laser systems was simulated using optical systems simulation software. The nominal coupling efficiency between 100times1 mum stripe laser and 62.5/125-mum graded index fiber (NA=0.275) was 0.37. The simulated coupling efficiency and alignment tolerances were verified by prototype realization and characterization. The measured alignment tolerance values between laser and fiber in AT prototype series were Deltax=7.7 mum, Deltay=7.6 mum, and Deltaz=10.8 mum (SD values). The corresponding values in A2 prototype series were Deltax=3.1 mum, Deltay=9.1 mum, and Deltaz=10.2 mum. The measured average coupling efficiency was 0.28 in AT series and 0.31 in A2 series. The coupling efficiencies of all operational prototypes varied from 0.05 to 0.43

Optical coupling structure made by imprinting between single-mode polymer waveguide and embedded VCSEL

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.

Long single-mode waveguides made by imprint patterning for optical interconnects and sensors

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.