Blandine Guichardaz

High aspect ratio lithium niobate ridge waveguides fabricated by optical grade dicing

We report the development of a quick process for fabricating lithium niobate ridge waveguides with smooth walls, aspect ratios larger than 500 and side-wall verticality of 88?. The method is based on optical grade dicing, and allows the fabrication of ridges with a top width of 1??m and a depth of more than 500??m. Smart-cut ridge waveguides and strongly confined proton exchanged ridge waveguides are demonstrated. We show that the method enables the fabrication of ridge waveguides with propagation losses as low as 0.5?dB?cm?1. A new fabrication process is thus proposed for the fabrication of optical components with enhanced acousto-optic, electro-optic or nonlinear interactions. The high aspect ratios open opportunities towards the development of 3D photonic components in thin films of LiNbO3, and towards hybrid integration of LiNbO3 components.

Optimization of LiNbO 3 photonic crystals: toward 3D LiNbO 3 micro-components

We report easy-to-implement techniques to improve the reflectivity of LiNbO₃ photonic crystals within the photonic bandgap. Firstly, we show that widening the channel waveguides confines the optical modes in the vertical direction, which leads to the development of the first 2D-PhCs on Ti-indiffused LiNbO₃ waveguides. We also report the first optical characterization of PhCs implemented on ridge LiNbO₃ waveguides. The reflectivity is measured using a swept-source optical coherence tomography (OCT) system, together with the transmission spectrum. Finally we report 3D-PhCs LiNbO₃ fabricated by Focused Ion Beam milling on the side of ridge waveguides.

Acoustic resonator based on periodically poled lithium niobate ridge

The constant improvement of industrial needs to face modern telecommunication challenges leads to the development of novel transducer principles as alternatives to SAW and BAW solutions. The main technological limits of SAW (short-circuit between electrodes) and BAW (precise thickness control) solutions can be overcome by a new kind of transducer based on periodically poled ferroelectric substrate. The approach proposed in this paper exploits a ridge structure combined with a periodically poled transducer (PPT), allowing for the excitation of highly coupled modes unlike previously published results on planar PPTs. High-aspect-ratio ridges showing micrometer dimensions are achieved by dicing PPT plates with a diamond-tipped saw. An adapted metallization is achieved to excite acoustic modes exhibiting electromechanical coupling in excess of 15% with phase velocities up to 10 000 m·s-1. Theoretical predictions show that these figures may reach values up to 20% and 18 000 m·s-1, respectively, using an appropriate design.

High Overtone Bulk Acoustic Resonators Based on Thinning Single-crystal Piezoelectric Layers

Bulk acoustic waves excited in thin piezoelectric films have revealed their capabilities for addressing the problem of high frequency RF filters (above 1 GHz). In this paper, we propose an alternative to thin film deposition consisting in single crystal wafers bonded on a substrate (for instance silicon) and thinned, allowing for plate thickness close to 10 mum. This has been achieved on 3 inches wafers and allows for an accurate selection of the wave characteristics. More, the properties of the piezoelectric material are found conform with tabulated values, enabling one to reliably design any passive signal processing device.

Watt-level Tm:LiYF 4 channel waveguide laser produced by diamond saw dicing

Low-loss surface channel waveguides with a cross-section of 30 × 30 μm2 are produced by diamond saw dicing of 6.2 at.% Tm3+, 3.5 at.% Gd3+:LiYF4 films grown by liquid phase epitaxy (LPE) on (001)-oriented bulk undoped LiYF4 substrates. Pumped by a Ti:Sapphire laser at 783 nm, a continuous-wave Tm:LiYF4 waveguide laser generated 1.30 W at 1880 nm (for π-polarization) with a slope efficiency of 80% with respect to the absorbed pump power. The laser threshold was at 80 mW. The waveguide morphology was studied revealing low roughness (3 ± 2 μm) as expressed by the propagation losses of <0.3 dB/cm. A combination of LPE and diamond saw dicing is a promising technology for multi-watt single-mode channel waveguide lasers and amplifiers.

New radio-frequency resonators based on periodically poled lithium niobate thin film and ridge structures

In this paper, we present new results on the development of an original acoustic waveguides concept based on a Periodically Poled Lithium Niobate transducer. Periodically poled transducers have been investigated recently as an alternative to classical inter-digital transducers for the excitation and detection of guided acoustic waves. We expose here two different structures of RF resonators based on this concept: a “Silicon/Gold layer/PPLN thin film/Gold layer/Silicon” stack and a PPLN-ridge structure. Simulations, fabrication and experimental results of both resonators are presented. “Si/10 μm-thick PPLN/Si” and “PPLN-ridge (11 μm-wide and 250 μm-deep)” resonators with a poling period of 50 μm have been achieved. The experimental admittances of these devices have pointed out the existence of an isolated mode operating at frequencies near 110 MHz for the stack structure and near 160 MHz with an electromechanical coupling of about 19 % for the ridge structure. These results are in agreement with the finite and boundary elements simulations.

Highly coupled resonator based on ridge-shaped periodically poled materials for radio-Frequency applications

Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) devices are largely used in telecommunication for radio Frequency (RF) signal processing. Nevertheless, these devices are limited by various factors such as short-circuit between electrodes for SAW and precise thickness control for BAW. This paper shows the interest of a new kind of transducer using Periodically Poled Lithium Niobate (PPLN) developed to overcome SAW and BAW technological limits. A former PPLN-based wave-guide was presented some years ago exploiting planar technologies. The novelty of the present work lies in the 3D structuring of the transducer allowing for very high aspect ratio structures exhibiting a theoretical electromechanical coupling about 20% and a phase velocity up to 20 km.s-1.

Characterization of extremely short LiNbO3 Bragg gratings

A five micrometer long Bragg grating in titanium indiffused lithium niobate ridge waveguide was fabricated by combining optical grade dicing and Focused Ion Beam. The 53% reflectivity is measured using a swept-source optical coherence tomography.