Gwenn Ulliac

Enhanced electro-optical lithium niobate photonic crystal wire waveguide on a smart-cut thin film.

We report an electro-optically tunable photonic crystal linear cavity etched on a 200 nm lithium niobate waveguide ridge. The photonic crystal cavity and the ridge are both fabricated on a 1 μm thin film of lithium niobate obtained by smart-cut technology. The photonic crystal, of area 4x0.8 μm2, has been engineered to work in a slow light configuration so that the electro-optic effect is 20 times more important than in bulk material.

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.

Acousto-optically tunable lithium niobate photonic crystal

We report on an active two-dimensional lithium niobate photonic crystal (PhC) driven by stationary Rayleigh surface acoustic waves. The configuration relies on two interdigital transducers that modulate the refractive index through the acousto-optical effect. Highly efficient, compact acousto-optical PhCs with an active length of only 13 μm and a driving electrical power of 20 mW have been fabricated and characterized. Experiments show that an enhancement factor of the elasto-optical interaction of the order of 61 is obtained thanks to slow light effects in the PhC.

Observation of surface-guided waves in holey hypersonic phononic crystal

We observe experimentally the propagation of surface-guided waves in a hypersonic phononic crystal, both in the radiative and nonradiative regions of the spectrum. Combining electrical measurements in reflection and transmission as well as optical maps of the surface displacement, a band gap extending from 0.6 to 0.95 GHz is identified in a square lattice array of 1 μm radius air holes milled in lithium niobate. The optical measurements reveal the transmission of surface-guided waves above the band gap, well inside the sound cone.

Integrated temperature sensor based on an enhanced pyroelectric photonic crystal

In this paper, temperature variations are detected thanks to an enhanced nano-optical pyroelectric sensor. Sensing is obtained with the pyroelectric effect of lithium niobate (LN) in which, a suitable air-membrane photonic crystal cavity has been fabricated. The wavelength position of the cavity mode is tuned 11.5 nm for a temperature variation of only 32 °C. These results agree quite well with 3D-FDTD simulations that predict tunability of 12.5 nm for 32 °C. This photonic crystal temperature sensor shows a sensitivity of 0.359 nm/°C for an active length of only ~5.2 μm.

Guidance of surface waves in a micron-scale phononic crystal line-defect waveguide

We report on the direct observation of trapping and guiding of surface-guided elastic waves in a linear defect introduced into a micron-scale phononic crystal. Elastic field amplitude detection using laser scanning interferometry was used to characterize the different transmission regimes of the one-period wide line defect in a phononic crystal structure as a function of frequency and to discriminate phononic waveguiding from transmission outside the band gap. Surface density-of-states computations support the experimental observations.

6-micron interaction length electro-optic modulation based on lithium niobate photonic crystal cavity

We report on electro-optic modulation using a Lithium Niobate (LN) Photonic Crystal (PC) cavity structure. The compact device (6 μm in length) consists of a 2D photonic crystal cavity made on an Annealed Proton Exchange (APE) LN waveguide with vertical deposited electrodes. Experimental results show a tunability of 0.6 nm/V. This compact design opens a way towards micro and nano-scale tunable photonic devices with low driving electrical power.

Lithium niobate photonic crystal wire cavity: Realization of a compact electro-optically tunable filter

We report an electro-optically tunable filter using a lithium niobate photonic crystalcavity configuration with an efficient optical guiding geometry. The compact device (5.5 μm × 2.8 μm) was made on a hybrid waveguide combining an annealed proton exchange waveguide and a ridge waveguide realized by focused ion beam with vertically deposited electrodes. Due to the slow light and nonlinear effect in lithium niobate photonic crystal, experimental results show an enhanced tunability of ∼0.56 nm/V. This compact tunable photonic crystalcavity demonstration opens the path for the development of micro and nano-scale low-power driving active photonic devices.

Experimental evidence of enhanced electro-optic control on a lithium niobate photonic crystal superprism

We present experimental evidence of an electro-optic superprism photonic crystal fabricated on a lithium niobate substrate, in agreement with simulation results. In this work, rather than changing the incident wavelength or angle to achieve large light deflections, a direct modification of the band structure by the electro-optic effect causes changes in the propagation direction of the incident beam. Additionally, the chosen geometry allows significant ultrarefraction as the incident wavelength is varied giving rise to a double purpose active-passive photonic crystal light deflector that could present potential interest for optical communications.

Acoustic resonator based on periodically poled transducers: Concept and analysis

The demand for highly coupled high quality acoustic wave devices for radio-frequency (RF) signal processing based on passive devices has generated a strong innovative activity, yielding the investigation of new excitation principles and waveguide structures. Periodically poled transducers (PPTs) have been recently investigated [E. Courjon et al., J. Appl. Phys. 102, 114107 (2007)], as an alternative to classical interdigital transducers (IDTs) for the excitation and detection of guided acoustic waves. PPTs have two principal advantages compared to IDTs: the robustness of the excitation versus defects or surface contamination and the possibility to excite waves exhibiting a wavelength equal to the poling period. Here a new acoustic resonator concept is suggested, allowing high frequency operation with a simplified package. The idea consists of using a waveguide based on a PPT fabricated on a ferroelectric single-crystal substrate such as lithium niobate or tantalate inserted between two single-crystal subs...