Alexis Caspar

Simple production of membrane-based LiNbO 3 micro-modulators with integrated tapers.

We report on free-standing electro-optical LiNbO3 waveguides with integrated tapers made by optical grade dicing. Membranes with a calibrated thickness are produced simultaneously with tapers acting as spot-size converters. Thereby, thicknesses from 450 to 500 μm can simply be achieved together with integrated tapers guaranteeing low insertion losses. These developments open the way to the low-cost production of compact and low-power-consuming electro-optical components. As an example, a 200 μm-long free-standing electro-optical Fabry-Perot is demonstrated with a figure of merit of only 0.19 V·cm in a 4.5 μm-thick membrane.

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.

E-field fiber tip sensors by exploiting the electro-optic tunability of lithium niobate photonic crystals (Conference Presentation)

Biomedical engineering (BME), electrophysiology, Electromagnetic Compatibility (EMC) or aerospace and defense fields demand compact electric field sensors with very small spatial resolution, low sensitivity and large bandwidth. We show that the electro-optical property of lithium niobate coupled with the tunability of photonic crystals can answer this request through Lab-on-Fiber technology. First, band diagram calculations and Finite Difference Time Domain (FDTD) simulations analysis lead to the design of the most suitable two-dimensional photonic crystal geometry. We show that light normal incidence on rectangular array of air holes in free standing X-cut thin film lithium niobate produces a very sharp and E-field sensitive Fano resonance at a wavelength of 1550nm. Then, in order to concentrate the E-Field to be detected in the photonic crystal area (20μm*20μm*0.7μm) we design a thin metallic antenna, scaled down them in such a way that it does not produce any disturbances while increasing the sensitivity. The LN membrane with the antenna is fabricated by standard clean room processes and Focused Ion Beam (FIB) is used to mill the photonic crystal. Then, by means of a flexible/bendable transparent membrane, we were able to align and to attach the photonic crystal onto a ferrule ending polarization maintained optical fiber. Optical characterizations show that the Fano resonance is easily modulated (wavelength shifted) by the surrounding E-field. The novel non-intrusive E-field sensor shows linearity, low sensitivity, large bandwidth (up to 100GHz) and a very small spatial resolution (≈20μm). To the best of our knowledge, this spatial resolution has never been achieved in E-field optical sensing before.

LiNbO3 integrated microdisk resonator fabricated by optical grade dicing and precise robotic positioning

Lithium niobate (LiN bO3) microresonators have attracted much interest over the last decade, due to the electrooptical, acousto-optic and non-linear properties of the material, that can advantageously be employed in combination with thin resonances of optical microcavities for applications as varied as integrated gyrometers, spectrometers or dynamic filters. However the integration of micrometer scale cavities with an input/output waveguide is still a critical issue. Here we propose an innovative approach, allowing low insertion losses and easy pigtailing with SMF fibers. The approach consists in producing and optimizing separately a membrane-based LiNbO3 waveguide with Spot-Size Converters, and a thin microdisk. The two elements are dynamically assembled and fixed in a second step. Additionally to the proposed integrated microresonator, this approach opens the way to the production of 3D hybrid photonic systems.

Optical-coherence-tomography characterization of free standing electro-optical micro and nanostructures

Thin-film-based LiNbOs components have been experiencing an increasing success over the past decade due to their potentiality to enhance electro-optical (EO) or nonlinear (NL) effects [1, 2]. Therefore, their production at low cost is becoming a major challenge. In [3, 4], we proposed a precise-dicing-based technique for the low-cost production of confined LiNbO3 waveguides with integrated Spot-Size-Converters, and we achieved a four-time reduction of the driving power while keeping insertion losses lower than 3 dB. Here we go one step further by proposing free-standing electro-optical micro and nanostructures in sub-micrometer-thin layers of LiNbO3. We also employ an Optical-Coherence-Tomography (OCT)-based characterization method to evaluate the birefringence, group velocity, propagation losses, and electro-optical sensitivity of the membranes.

Electro-optical enhanced photonic crystal fiber-tip sensor based on LiNbO 3 for E-field detection

Non-intrusive electric field sensing devices have recently attracted attention due to their capability to face the problem derived from the conventional sensing probes which present a large sensing area and are based on conductive materials, distorting the field to be measured. This constraint is solved by employing all optical and compact probes which rely on electro-optical materials. However, all the electro-optical sensing devices are limited to sensibilities of the order of mV. For high sensing applications, nanophotonics is needed in order to enhance the electro-optical effect. Recently, the “Lab-on-fiber” technology has emerged, leading to optical nanoprobes which offer a broad range of sensing applications such as biological and chemical sensing, acoustic detection and temperature sensing [1]. In this work, we have designed and fabricated an E-field fiber tip sensor based on a LiNbO3 thin film with mV sensitivity. In [2], we demonstrate that combining the thin film with periodical structures, the pyroelectric effect presents a higher sensitivity than other configurations. Moreover, in [3] we perform an accurate theoretical sensitivity analysis for E-field sensing in similar structures which show up the Fano resonances, characteristic for its asymmetrical high aspect-ratio, estimating a theoretical sensitivity of 50uV/m.

Photo-Robotic Positioning for Integrated Optics

High positioning accuracy is a crucial need to perform successfully complex tasks such as micromanipulation and microassembly. This especially enables to provide high performances or to propose new functionalities/products, notably for integrated optical devices. The objective of the letter is to align two optical structures in multi-DOF way with very high accuracy. The originality of the approach relies on robotic positioning associated with the use of interfered reflected light irradiance as a feedback signal rather than transmitted power. Fabry–Perot interference principle is especially used to provide a fast and high accurate measurement. An opto-mechanical model that relates the optical component poses with the interfered reflected light is proposed. Experimental results are investigated based on a robotic multi-DOF platform, used to relatively align an optical component to an optical fiber. The obtained results establish that the model fits with experiments with a standard deviation below

Lithium Niobate Optical Waveguides and Microwaveguides

0.0281^{\circ }

Towards highly reliable, precise and reproducible fabrication of photonic crystal slabs on lithium niobate

. This model associated with an automated positioning strategy shows that it is possible to maximize reflectivity within less than 6 s, including multi-DOF angular misalignments identification and compensation.