Jarkko Puustinen

Fabrication of optical waveguides by imprinting: Usage of positive tone resist as a mould for UV-curable polymer

Optical ridge type waveguides based on UV-curable polymer were fabricated by imprinting method. Positive tone resist patterned on a silicon wafer was used as a mould. The characterization of waveguides was carried out by coupling TE-polarized light from a tapered fiber into a waveguide with 30 mm length and mapping the intensity distribution with another tapered fiber at the output facet of a waveguide. Proper single- or multimode operation was observed depending on the waveguide width being either 2 microm or 6 microm. Experimental observations on the mode profiles were also supported by the simulation results. Average power transmissions of 32% at 1530 nm wavelength and 45% at 1310 nm wavelength were characterized. The results suggest that the simple mould fabrication process might be a useful technique for device prototyping and that the performance of replicated waveguides can meet the requirements for certain applications.

UV-Imprinted Single-Mode Waveguides With Low Loss at Visible Wavelength

We demonstrate polymeric single-mode waveguides with low loss at visible wavelength. Inverted ridge waveguides were fabricated by a low-cost UV-imprinting method. An average propagation loss of 0.19 dB/cm was obtained at 638 nm wavelength by investigating the transmission properties of spiral waveguides with the overall length of 23.3 cm. Payne–Lacey scattering model predicts that the scattering loss due to imprint replication is dominated by the sidewall roughness. It is envisaged that the used low-cost fabrication method and waveguide configuration can have potential in power budget sensitive applications.

Manipulation of optical field distribution in layered composite polymeric-inorganic waveguides

We discuss the manipulation of optical field distribution in a low-refractive index polymeric waveguide by depositing a thin high refractive index Ta2O5 film on top of the waveguide. According to microstructure studies, the sputtered Ta2O5 thin films deposited on the polymer layer were very smooth with root mean square surface roughness value of 0.58 nm, had amorphous phase, and were optimal for integrated optical devices. Both computational and experimental optical studies suggest that the inorganic-polymeric composite waveguide design greatly increases the intensity distribution of the propagating mode at the surface. Consequently, the interaction of the optical field with the ambient surrounding medium is enhanced by a factor of about 1.7 in order of magnitude.

Variations of Optical Properties with Phase Co-Existence in PZT Thin Films

Polycrystalline Pb(Zr x Ti1 − x )O 3 thin films with various thicknesses were deposited at room temperature on MgO (100) substrates by pulsed laser deposition. X-ray diffraction and atomic force microscopy were used to characterize the crystal structure and morphology and spectrophotometry measurements at wavelengths from 180 nm to 3000 nm, and prism-coupler method were used in the optical characterization of the thin films. A thickness-temperature phase-diagram is presented. Phase co-existence was found to increase curvature and roughness of the films, causing broadening of guiding TE 0 modes, whereas in single phase oriented films FWHM Δ β mode values were smaller.

Atmospheric oxidation and carbon contamination of silver and its effect on surface-enhanced Raman spectroscopy (SERS).

Surface-enhanced Raman spectroscopy (SERS) is considered a highly promising technology for different analytical purposes. The applications of SERS are still quite limited due its relatively poor quantitative repeatability and the fact that SERS is very sensitive to oxidation, which is a challenge especially with silver based SERS substrates. Here, the link between these phenomena is investigated by exposing silver SERS substrates to ambient laboratory air. We show that SERS intensity decreases exponentially after the exposure, which consequently leads to an increasing standard deviation (σ) in intensity. Within a five-hour measurement window, the SERS intensity already drops by 60%, while σ triples from 7% to 21%. The SERS results are supplemented by elemental analysis, which shows that oxidation and atmospheric carbon contamination coincide with the rapid SERS intensity decrease. The results emphasize how sensitive SERS is towards atmospheric contamination and how it can also reduce the measurement repeatability – even if the substrates are exposed to air just for a very short period of time.

Disposable photonic integrated circuits for evanescent wave sensors by ultra-high volume roll-to-roll method

Flexible photonic integrated circuit technology is an emerging field expanding the usage possibilities of photonics, particularly in sensor applications, by enabling the realization of conformable devices and introduction of new alternative production methods. Here, we demonstrate that disposable polymeric photonic integrated circuit devices can be produced in lengths of hundreds of meters by ultra-high volume roll-to-roll methods on a flexible carrier. Attenuation properties of hundreds of individual devices were measured confirming that waveguides with good and repeatable performance were fabricated. We also demonstrate the applicability of the devices for the evanescent wave sensing of ambient refractive index. The production of integrated photonic devices using ultra-high volume fabrication, in a similar manner as paper is produced, may inherently expand methods of manufacturing low-cost disposable photonic integrated circuits for a wide range of sensor applications.

Room temperature curable zirconium silicate dielectric ink for electronic applications

A facile formulation of room temperature curable and screen printable zirconium silicate (ZrSiO4) ink has been developed. The ZrSiO4 ink printed on the flexible BoPET (biaxially-oriented polyethylene terephthalate) substrate showed a surface roughness of ∼160 nm for a printed layer thickness of 25 μm. The screen printed ZrSiO4 layer on the BoPET substrate has a relative permittivity of 3.01 and a dielectric loss of 0.0058 at 10 GHz. It showed a temperature coefficient of relative permittivity of 55 ppm per °C in the temperature range of 25–60 °C at 15 GHz. The room temperature curability, low dielectric loss, low relative permittivity, mechanical and temperature stability of microwave dielectric properties of the printed ZrSiO4 layer make it suitable for printed microwave applications.

Nanoimprint Fabrication of Slot Waveguides

A nanoimprint mold for optical waveguide applications was fabricated by combining photolithography and focused ion beam (FIB) milling. The feasibility of the proposed method was demonstrated by imprinting 15-mm-long Y-branch waveguides, which had nanoscale slots embedded in one arm. Structural analysis of the FIB milled region showed surface roughness values below 2.5 nm. Characterization of the fabricated waveguides proved that 44% of the optical power was transmitted through the slot-embedded waveguide arm. Operation of slot waveguide was demonstrated at a wavelength of 1305 nm using Young interferometer devices.

Self-modulation of ultra-fast laser pulses with 1550 nm central wavelength in VO2 thin films

The possibility to use an ultra-fast laser operating at 1550 nm wavelength to induce intensity self-modulation in metal-insulator phase transition VO2 thin films was investigated. The results show that a self-modulation value upto 0.55 can be obtained by using z-scan method. In comparison, an externally triggered phase transition induced by heating the sample produced a modulation depth of 0.995 corresponding to almost complete light absorption. The results suggest that significant self-modulation can be produced by fs laser pulses, but the modulation strength is partially suppressed by incomplete transition from a transparent to an absorbing state and potentially time delay in the rise of absorbance.

Disposable (bio)chemical integrated optical waveguide sensors implemented on roll-to-roll produced platforms

To enable wide spread dissemination of sensors in cost-critical applications and resource poor settings, methods to implement sensor chips using low-cost materials and mass-manufacturing methods are developed. In this paper we demonstrate that disposable polymeric integrated Young interferometer (YI) sensor chips, implemented on roll-to-roll mass-manufactured waveguides, are applicable for analyte specific sensing of small molecules and for multi-analyte detection of biomolecules. For the chemical sensing of small molecules, a sensor chip was functionalized with a molecularly imprinted polymer (MIP). We demonstrate that the MIP receptor layer is compatible with a polymer-based evanescent wave sensor for direct refractive index sensing. For multi-analyte detection of biomolecules, antibody-based receptor layers were patterned by inkjet printing onto the sensor surface demonstrating the applicability of the method with integrated YI chips. Demonstration of the analyte specific chemical- and biosensing with disposable polymeric YI sensor chips opens new possibilities to implement low-cost (bio)chemical sensors.