This paper explains and demonstrates the unique properties of micron-size silicon-on-insulator (SOI) waveguides. It gives an overview of the silicon photonics research at VTT, as well as latest R&D highlights. The benefits of high mode confinement in rib and strip waveguides are described, reaching from low losses and small footprint to polarization independent operation and ultra-wide wavelength range from 1.2 to over 4 μm. Most of the results are from photonic integrated circuits (PICs) on 3 μm SOI, while a 25 Gbps link with a transceiver on 12 μm SOI is also reported. Wavelength multiplexing and filtering is demonstrated with some breakthrough performance in both echelle gratings and arrayed waveguide gratings. Lowest losses are below 1 dB and lowest cross-talk is below -35 dB. Progress towards monolithically integrated, broadband isolators is described, involving polarization splitters, reciprocal polarization rotators and nonreciprocal Faraday rotation in 3 μm SOI waveguide spirals. Quick update is presented about switches, modulators and Ge photodiodes up to 15 GHz bandwidth. Hybrid integration of lasers, modulators and photodiodes is also reported. The added value of trimmed SOI wafers and cavity-SOI wafers in Si photonics processing is addressed. Latest results also include up-reflecting mirrors with <0.5 dB loss, which support wafer-level testing and packaging.
Diffraction gratings were designed and fabricated on a SiN/SiO<sub>2</sub> planar waveguide to couple light from a low power 488 nm
laser beam into the planar waveguide. The light propagating in the waveguide was then used to detect fluoresceine from
volume on the planar waveguide surface. The results demonstrate the capability for very simple and fast analytical
throughput for quantification of fluorescent samples, essentially without cross-talk. The transmission measurements show
about 10% diffraction efficiency with 0.06° FWHM. The diffraction efficiency and the incidence angle for the maximum
diffraction efficiency were observed to be highly dependent on the process parameters used to fabricate the gratings. The
fluorescence signal was observed to be linear for fluoresceine concentrations between 10<sup>-9</sup> and 10<sup>-3</sup> M.
Several microfluidic platforms incorporating cavities and channels have been designed and fabricated in silicon and fused silica. C4F8 and SF6 plasmas are used to etch reproducibly 400 μm features in silicon and 150 μm in fused silica. Hydrophilic surface characteristics allow capillary action without external pumping or electro-osmosis. Filling of poled cavities can be triggered by increasing temperature i.e. by tuning hydrophobicity of a channel. The pole structure can also be used for sieving particles of different size or elasticity. In this work, agarose beads trapped by poles were used for solid phase extraction. By covering the microfluidic features, filling is also achieved by cooling the substrate. Filling velocities of aqueous solutions have been observed to depend strongly on liquid composition, but also final treatment and roughness of silicon or silica surface. Mixing of two aqueous solutions can also be triggered by increasing temperature. Cavities with pre-immobilised substance can be filled simultaneously or, if necessary, sequentially. Various non-leaking 3D channel networks can be constructed by gluing, fusion or anodic bonding of many silicon or glass wafers including via holes. Integrating of electrical circuits for both silicon and silica is possible by standard IC technology.
Heated liquid cavities have been studied. Microlitre scale liquid cavities were etched to the surface of a silicon wafer. Liquid cavities were sealed with a glass cover. Integration of active components to the silicon support is also possible. A heater and a thermistor element are integrated into the silicon support. A pole structure was used within the wells for thermal optimization and self-feeding. The pole structure increases the surface area between silicon and liquid, which enhances thermal transport between silicon and liquid. The temperature of the water is also more uniform. The pole structure also makes the liquid cavity semiporous, enabling the self-feeding of samples due to capillary force. Active silicon support could be used in diagnostics and in biotechnology. Silicon supports were tested in PCR (Polymerace Chain Reaction). The construction of the temperature controlling setup for the silicon support is described. Temperature controlling setup is an independent measuring setup. Interface to the silicon support is made with a printed board to a microscope glass slide format. It is possible to use the printed board interface in a microarray reader. The contruction of a fluorescence measurement setup based on a microarray reader is described.
Analytical systems based on immunochemistry are largely used in medical diagnostics and in biotechnology. There is a significant pressure to develop the present assay formats to become easier to use, faster, and less reagent consuming. Further developments towards high density array--like multianalyte measurement systems would be valuable. To this aim we have studied the applicability of fluorescence resonance energy transfer and time-resolved fluorescence resonance energy transfer in immunoassays on microspots and in microwells. We have used engineered recombinant antibodies detecting the pentameric protein CRP as a model analyte system, and tested different assay formats. We describe also the construction of a time-resolved scanning epifluorometer with which we could measure the FRET interaction between the slow fluorescence decay from europium chelates and its energy transfer to the rapidly decaying fluorophore Cy5.
A multilayer capillary fiber was designed for optical sensor applications and its optical properties were evaluated by using a fluorescent layer immobilized on its inner surface. This fiber structure combines a large interaction surface (the inner wall of the capillary fiber) for binding of fluorescent indicators with evanescent wave fluorescence measurement, which may facilitate the design of pseudohomogeneous assays without separation of the bound from nonbound fluorescent indicator. The inner surface of the capillary was derivatized by aminosilanization, followed by biotinylation and addition of streptavidin. This biotin- streptavidin coating facilities subsequent immobilization of any biotinylated species (e.g. antibodies, antigens, etc.) participating in specific molecular recognition. We have evaluated some properties of this capillary fiber design by using fluorescent proteins immobilized on the inner wall of capillary by biotin-avidin-interaction. Fluorescence was excited by a HeNe-laser (fluorescent indicator APC; (lambda) <SUB>em</SUB> equals 660 nm) and by a Ar-laser (fluorescent indicator RPE, (lambda) <SUB>em</SUB> equals 578 nm), and measured with a spectrum analyzer.