Jyrki Saarinen

Hybrid layered polymer slot waveguide Young interferometer.

We demonstrate a polymer slot waveguide Young interferometer coated with a bilayer of Al2O3/TiO2. The approach enables relaxed dimensions of the polymer waveguide which simplifies the fabrication of the structure with a resolution of 50 nm. The layers were coated by an atomic layer deposition technique. The feasibility of the device was investigated by exploiting the interferometric structure as a bulk refractive index sensor operating at 975 nm wavelength for detection of an ethanol-water solution. A refractive index change of 1 × 10-6 RIU with a sensing length of only 800 µm was detected. The approach confirms the possibility of realizing a low cost device with a small footprint and enhanced sensitivity by employing the TiO2 rails in the sides of the slot waveguide.

Enhanced sensitivity in polymer slot waveguides by atomic layer deposited bilayer coatings

The refractive index sensitivity of a polymer slot waveguide coated with a bilayer of Al₂O₃/TiO₂ was investigated theoretically and optimized for biosensor applications. The influence of atomic-layer-deposition-coated thin high-refractive-index layers on the slot confinement factor and the homogeneous sensitivity of polymer slot waveguides with different geometries were simulated. The results were compared with those of an optimized noncoated polymer slot waveguide, both operating at visible wavelengths. The simulations reveal that the proposed structure offers a significant improvement in the confinement factor and the sensitivity. These calculations present guidelines for the design and fabrication of relatively sensitive polymer slot waveguide devices for low-cost biochemical sensor applications.

Influence of an Al2O3 surface coating on the response of polymeric waveguide sensors

The responses of a polymer ridge waveguide Young interferometer with and without a bilayer of Al2O3/TiO2, fabricated by atomic layer deposition, are studied and compared when applied as an aqueous chemical sensor. The phase shift of the guided mode, as a result of the change in refractive index of the cover medium, is monitored. The results indicate that the over-coating affects the linearity of the sensor response. The effect of concentration on the linearity of the sensor response is investigated by applying different concentrations of water-ethanol solution. Although the performance of the sensor is improved by the additional layers, the study reveals a non-monotonic behavior of the device. We show that it comes mainly from the adsorption of ethanol molecules on the surface of the films. Such an understanding of the platform is crucial for sensing of analytes involving polar molecules.

Design and characterization of 3D-printed freeform lenses for random illuminations

A combination of light-emitting diodes (LEDs) with freeform optics has been recently investigated widely for energy efficient illumination due to its high optical performance and compact size. The freeform optics design methods are application specific. The transformation of the light source into the target irradiance distribution using freeform optics usually leads to solving an inverse problem, which can be formulated by using a point light source, geometrical optics, monotonic ray bending and lossless system. Here, a customized algorithm is proposed to design freeform lenses for both LED source based simple uniform rectangular illumination and collimated light source based complex image target irradiance distributions by numerically solving the elliptic Monge-Ampère equation. The optical performance of the lenses is examined theoretically by using commercial ray tracing software. Additive manufacturing (also called as 3D printing), a layer-by-layer printing of patterned material, is considered as novel option for low-cost and rapid manufacturing of optics. Recently, 3D printed ISO-standard ophthalmic lenses have been produced using Printoptical® technology (US Patent No. 13/924,974): a modified ink-jet printing technology that deposits micro-droplets Opticlear, which is a PMMA-like UV-curable polymer. In our work, the Printoptical® technology is further extended to freeform lenses using Opticlear, which is a PMMA like UV-curable polymer. The metrology of the freeform lenses is studied using white-light interferometry and VR-3000 series 3D surface profile macroscope.

Polymer strip-loaded waveguides on ALD-TiO2 films

We propose and demonstrate a low cost, large area, and mass production compatible method to fabricate strip-loaded waveguide structures. The structure is fabricated by combination of Atomic Layer Deposition and replication technique without applying any etching process to form the strip. The waveguide was realized in ring resonator configuration which eases the characterization process. The guiding layer is a 200 nm-thick TiO2 layer integrated with polymer strips to load light in the high index thin film. Due to the characteristic of the applied fabrication technique, achieving a very low propagation losses is expected.

Billion Droplets Harnessed to Form 3d Printed Optics

3D printing for optics utilizes inkjet printing of UV curable materials. Even billion tiny droplets build up macroscopic optical components with nanoscale surface roughness without any need for postprocessing.