Markus Häyrinen

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.

Near-field characterization of a Bloch-surface-wave-based 2D disk resonator.

We present, to the best of our knowledge, the first experimental investigation of a two-dimensional disk resonator on a dielectric multilayer platform sustaining Bloch surface waves. The disk resonator has been patterned into a few tens of nanometer thin (∼λ/25) titanium dioxide layer deposited on the top of the platform. We characterize the disk resonator by multi-heterodyne scanning near-field optical microscopy. The low loss characteristics of Bloch surface waves allowed us to reach a measured quality factor of 2×103 for a disk radius of 100 μm.

Titanium dioxide slot waveguides for visible wavelengths

We present the first, to our knowledge, experimental demonstration of a titanium dioxide slot waveguide operating in the visible range of light. Ring resonators based on slot waveguides were designed, fabricated, and characterized for λ≃650  nm. The fabrication method includes atomic layer deposition, electron beam lithography, and reactive ion etching. The required narrow slot widths of a few tens of nanometers were achieved by using a conformal atomic layer re-coating technique. This unique feature-size-reduction technique was applied after the final etching step.

Impact of ALD grown passivation layers on silicon nitride based integrated optic devices for very-near-infrared wavelengths

A CMOS compatible post-processing method to reduce optical losses in silicon nitride (Si(3)N(4)) integrated optical waveguides is demonstrated. Using thin layer atomic layer deposition (ALD) of aluminum oxide (Al(2)O(3)) we demonstrate that surface roughness can be reduced. A 40 nm thick Al(2)O(3) layer is deposited by ALD over Si(3)N(4) based strip waveguides and its influence on the surface roughness and the waveguide loss is studied. As a result, an improvement in the waveguide loss, from very high loss (60 dB/cm) to low-loss regime (~5 dB/cm) is reported for a 220 nm x 500 nm Si(3)N(4) wire at 900 nm wavelength. This opens prospects to implement very low loss waveguides.

Tunable Bloch surface waves in anisotropic photonic crystals based on lithium niobate thin films

We present an original type of one-dimensional photonic crystal that includes one anisotropic layer made of a lithium niobate thin film. We demonstrate the versatility of such a device sustaining different Bloch surface waves (BSWs), depending on the orientation of the incident wave. By varying the orientation of the illumination of the multilayer, we measured an angle variation of 7° between the BSWs corresponding to the extraordinary and the ordinary index of the lithium niobate thin film. The potential of such a platform opens the way to novel tunable and active planar optics based on the electro- and thermo-optical properties of lithium niobate.

One-dimensional photonic crystals with cylindrical geometry

A one-dimensional photonic crystal (1DPC) consisting of a stack of alternate TiO(2) and Al(2)O(3) layers is deposited on the side wall of a glass rod by Atomic Layer Deposition. The stack is designed to sustain TE-polarized Bloch Surface Waves (BSW) in the visible spectrum at wavelengths shorter than 650 nm. Experimental evidence of light coupling and guiding capabilities of the 1DPC is provided together with a possible application for fluorescence-based remote sensors.

Ultra-thin Bloch-surface-wave-based reflector at telecommunication wavelength

We experimentally demonstrate the optical properties of gratings engraved in a single-mode waveguide fabricated on top of a dielectric multilayer platform. The structure can be approached as a reflector for Bloch-surface-wave-based two-dimensional optical systems. The gratings have been fabricated on a thin (∼λ/25) titanium dioxide layer with a thickness of a few tens of nanometers deposited on the top of a multilayer platform. The optical properties of the gratings have been characterized in the near field with the aid of multi-heterodyne scanning near-field optical microscopy. We investigate the surface wave’s interference pattern, produced by incident and reflected light in front of the gratings. The presented gratings behave as an efficient Bloch-surface–wave-based reflector at telecommunication wavelength.

Near-field investigation of Bloch surface wave based 2D optical components

We study the Bloch surface wave based nano-thin 2D optical components. The 2D elements are fabricated on the dielectric multilayer platform which sustains the Bloch surface waves. Such a platform is considered as a novel foundation for planar integrated optics. We exploit the total internal reflection configuration to achieve the phase matching condition for BSW excitation. Because of the evanescent behavior of the BSW, we use a scanning near field optical microscope to characterize the near-field properties of in-plane components. The 2D optical components include Disk resonators and Bessel-like beams.

Parabolic opening in atomic layer deposited TiO(2) nanobeam operating in visible wavelengths.

We investigate the feasibility of developing a one dimensional photonic crystal cavity on a TiO2 platform operating in the visible. The atomic layer deposition technique is used to finely adjust the parameters of the structure. We present the experimental demonstration of a nanobeam cavity with a quadratically tapered row of holes, in which a parabolic window is opened in order to facilitate the infiltration of gas, liquid, nonlinear material, or quantum emitters. The structure exhibits a photonic band gap between λ = 635 nm and λ = 690 nm and several resonances within the photonic band gap.

High-aspect-ratio electro-optical ridge waveguide made by precise dicing and atomic layer deposition

The development of all-optical, acousto-optical or electro-optical (EO) waveguides represents a stimulating challenge for the production of advanced functionalities in compact optical devices. In particular, high aspect ratio LiNbO3 ridge waveguides have attracted much interest over the past decade, due to their ability to enhance electro-optic effects while ensuring insertion losses lower than 3 dB [1, 2]. However, the large depth and high verticality of the ridge-based waveguides make the electrode deposition difficult to achieve. In particular, a thin and uniform dielectric buffer layer is needed between the ridge waveguide and the metallic electrode to avoid optical losses, but its deposition along deep ridges is highly challenging. Here we show how conformal dielectric buffer layers can be deposited along the ridge edges by Atomic Layer Deposition [3]. An innovative lift-off technique is also proposed, to provide well-defined electrodes.