Petri Stenberg

Atomic layer deposited titanium dioxide and its application in resonant waveguide grating

We demonstrate good optical quality TiO(2) thin films grown by atomic layer deposition at 120 degrees C. The optical properties were studied using spectroscopic ellipsometry and prism coupling methods. The refractive index was 2.27, and the slab waveguide propagation loss was less than 1dB/cm at 1.53microm. A high quality resonant waveguide grating was fabricated using a thin TiO(2) layer on top of a SiO(2) grating.

Low-Loss Titanium Dioxide Strip Waveguides Fabricated by Atomic Layer Deposition

We introduce low-loss amorphous titanium dioxide (TiO2) strip waveguides with sub-wavelength dimensions. The waveguides were fabricated by the combination of atomic layer deposition (ALD), electron beam lithography (EBL), and reactive ion etching (RIE). Propagation losses of the strip waveguides were found to be as low as 5.0 dB/cm at 1.55 μm wavelength. Those propagation losses are mostly due to the sidewall roughness of the waveguides that is caused by the lithography process. The propagation losses were further reduced by deposition, on the fabricated strip waveguides, of an additional layer of TiO2 made by using ALD. A supplementary layer of TiO2 with a thickness of 30 nm reduced the measured propagation losses from 5.0 ± 0.5 dB/cm to 2.4 ± 0.2 dB/cm at 1.55 μm wavelength. It is due to the fact that, after the redeposition process, the initial waveguide sidewall, i.e., the TiO 2/air interface, is virtually removed and the new sidewall has a reduced roughness.

Angled sidewalls in silicon slot waveguides: conformal filling and mode properties

Effect of angled sidewalls on the filling and properties of silicon slot waveguides is discussed. We demonstrate complete filling of slot waveguide structures with oxide material systems using the atomic layer deposition technique and discuss use of various slot filling materials. Properties of the optical modes in angled-sidewall slot waveguides are studied. Enhanced vertical confinement is obtained with certain waveguide parameters. The reduced effective mode area enhances e.g. nonlinear effects in the waveguide. We discuss the use of atomic layer deposition in realization of filled slot waveguides optimized for all-optical functionalities.

Towards athermal organic-inorganic guided mode resonance filters

We demonstrate guided-mode resonance filters featuring an amorphous TiO(2) layer fabricated by atomic layer deposition on a polymeric substrate. The thermal properties of such filters are studied in detail by taking into account both thermal expansion of the structure and thermo-optic coefficients of the materials. We show both theoretically and experimentally that these two effects partially compensate for each other, leading to nearly athermal devices. The wavelength shift of the resonance reflectance peak (< 1 nm) is a small fraction of the peak width (~11 nm) up to temperatures exceeding the room temperature by tens of degrees centigrade.

Replicable one-dimensional non-polarizing guided mode resonance gratings under normal incidence

Polarization-insensitive guided-mode resonance (GMR) filters have significant role in applications such as optical communication systems. Here, we report the design and fabrication of two types of simple-structured one-dimensional (1D) GMR gratings with non-polarizing resonance properties under normal incidence. A single-layer rectangular-profile TiO2 grating is fabricated by electron beam lithography and reactive ion etching, which demonstrates, for the first time in experiment, almost perfect non-polarizing filtering effect with 1D grating under normal incidence. Then, a TiO2-coated polycarbonate 1D GMR grating is fabricated by nanoimprinting and atomic layer deposition, which also exhibits good non-polarizing property and the potential of low-cost mass replication of such functional devices.

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.

Hydrogen silsesquioxane resist stamp for replication of nanophotonic components in polymers

We investigate an affordable, accurate and large-scale production method to fabricate subwavelength grating structures by hot embossing replication in polycarbonate substrates. We use inorganic hydrogen silsesquioxane (HSQ), a high resolution, binary, negative electron beam resist, on silicon substrate to make a stamp for replication. The stamp is fabricated without any etching processes and with simple process steps. The process starts by spin coating an HSQ-resist layer on a silicon substrate. The desired film thickness is achieved by adjusting the spinning speed and time. The resist material is then subjected to e-beam writing and development followed by a heat treatment to enhance the hardness and to obtain hot embossing stamp material properties comparable with solid SiO2. A comparison with and without the silicon etching is also performed. We demonstrate that a high quality stamp for thermal nano-imprint lithography for optical gratings can be fabricated using an inexpensive process without an etching step. The process results in a uniform imprinting density over the entire grating surface and high imprint fidelity. The reflectance spectra of replicated grating structures are also shown to be in agreement with theoretical calculations.

Polymeric slot waveguide interferometer for sensor applications

A refractive index sensor based on slot waveguide Young interferometer was developed in this work. The interferometer was fabricated on a polymer platform and operates at a visible wavelength of 633 nm. The phase shift of the interference pattern was measured with various concentrations of glucose-water solutions, utilizing both TE and TM polarization states. The sensor was experimentally observed to detect a refractive index difference of 6.4 × 10(-6) RIU. Furthermore, the slot Young interferometer was found to compensate for temperature variations. The results of this work demonstrate that high performance sensing capability can be obtained with a polymeric slot Young interferometer, which can be fabricated by a simple molding process.

A merged photonic crystal slot waveguide embedded in ALD-TiO 2

We demonstrate the concept of a merged nanoscale photonic crystal slot waveguide that acts as a bandpass filter in the near infrared region of the spectrum. The device is based on the integration of a photonic crystal cavity in a slot waveguide on a silicon on insulator substrate. The device is further embedded in amorphous titanium dioxide using atomic layer deposition, which allows to reduce two-photon absorption losses and creates the possibility to combine nonlinear guided-wave optics resulting from the strong field confinement in the slot region with slow light effects in the photonic crystal cavity. Our approach is fully compatible with complementary metal oxide semiconductor technology and opens up new perspectives for the integration of all-optical signal processing functionalities in hybrid silicon nanophotonics platforms.

High Aspect-Ratio Iridium-Coated Nanopillars for Highly Reproducible Surface-Enhanced Raman Scattering (SERS).

A variety of different gold and silver nanostructures have been proposed over the years as high sensitivity surface-enhanced Raman scattering (SERS) sensors. However, efficient use of SERS has been hindered by the difficulty of realizing SERS substrates that provide reproducible SERS response over the whole active area. Here, we show that atomic layer deposition (ALD) grown iridium can be used to produce highly reliable SERS substrates. The substrates are based on a periodic array of high aspect-ratio iridium coated nanopillars that feature efficient and symmetrically distributed hot spots within the interpillar gaps (gap width<10 nm). We show that the enhancement with the iridium based nanostructures is of significant magnitude and it equals the enhancement of silver based reference substrates. Most notably, we demonstrate that the ordered and well-defined plasmonic nanopillars offer a measurement-to-measurement variability of 5%, which paves the way for truly quantitative SERS measurements.