Matthieu Roussey

Experimental and theoretical characterization of a lithium niobate photonic crystal

In this letter, we investigate the feasibility of tunable lithium niobate (LiNbO3) photonic crystals. The optical response through a LiNbO3 photonic structure is theoretically determined in order to obtain a photonic band gap with optimal tunability. We show by means of a finite difference time domain simulation that the optimal lattice parameters can provide a Δλ=7nm shift in the photonic band gap for a Δn=0.01 variation of the refractive index with an extinction ratio of −22.5dB. The fabrication process and the optical characterization of these novel photonic crystal structures are also reported. The extinction ratio of the measured photonic band gap is lower than −12dB.

Experimental and theoretical observations of the slow-light effect on a tunable photonic crystal

We describe how the susceptibility of a nonlinear material, such as lithium niobate, can change when the material is nanostructured. Indeed, we show, by the calculation of the local-field factor inside a photonic crystal, a significant augmentation of the susceptibility, especially at the edges of the photonic bandgap. In addition, and for the case of lithium niobate, we observe an increase of the second-order nonlinear coefficient. The experimental realization of an electro-optic tunable photonic crystal, based on a square lattice of holes, shows that the measured phenomenon completely agrees with the theoretical predictions.

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.

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.

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.

Slot waveguide ring resonators coated by an atomic layer deposited organic/inorganic nanolaminate.

In this study, slot waveguide ring resonators patterned on a silicon-on-insulator (SOI) wafer and coated with an atomic layer deposited nanolaminate consisting of alternating layers of tantalum pentoxide and polyimide were fabricated and characterized. To the best of our knowledge, this is the first demonstration of atomic layer deposition (ALD) of organic materials in waveguiding applications. In our nanolaminate ring resonators, the optical power is not only confined in the narrow central air slot but also in several parallel sub-10 nm wide vertical polyimide slots. This indicates that the mode profiles in the silicon slot waveguide can be accurately tuned by the ALD method. Our results show that ALD of organic and inorganic materials can be combined with conventional silicon waveguide fabrication techniques to create slot waveguide ring resonators with varying mode profiles. This can potentially open new possibilities for various photonic applications, such as optical sensing and all-optical signal processing.

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.