Clément Guyot

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.

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.

Low-loss LiNbO 3 tapered-ridge waveguides made by optical-grade dicing

We report on low-loss vertical tapers for efficient coupling between confined LiNbO3 optical ridge waveguides and Single Mode Fibers. 3D-Pseudo-Spectral-Time-Domain calculations and Optical-Coherence-Tomography-based methods are advantageously used for the numerical and experimental study of the tapers. The tapered-section is done simultaneously with the ridge waveguide by means of a circular precision dicing saw, so that the fabrication procedure is achieved in only two steps. The total insertion losses through a 1.6 cm long ridge waveguide are measured to be improved by 3 dB in presence of the taper. These tapered-ridge waveguides open the way to the low-cost production of low-loss phase modulators or resonators.

Optical and RF Characterization of a Lithium Niobate Photonic Crystal Modulator

We optically characterize a micrometric radio frequency electro-optic modulator based on a lithium niobate photonic crystal. With the vertically deposited sidewalls electrodes, the experimental results show a half-wave voltage length product Vπ*L figure of merit of 0.0063 V-cm, a bandwidth of ~1 GHz for an active interaction area of ~37 μm2. This is the smallest figure of merit measured on an electro-optic modulator to date by several orders of magnitude with respect to bulk lithium niobate.

Unbiased Electro-Optic Waveguide as a Sensitive Nuclear Magnetic Resonance Sensor

A pigtailed Ti:LiNbO3 waveguide is here associated to a specific nuclear magnetic resonant coil to perform a low invasive magnetic field measurement. The developed device exploits a passive electro-optic transduction between the measured magnetic field and polarization state modulation of a laser probe beam. Because of the use of integrated optics, the coil electromotive force induces a dramatically enhanced electric field, thus leading to sensitivity improvement. A minimum detectable magnetic field lower than 60 fT. Hz-1/2 is achieved at the resonant frequency of 128 MHz. A dynamic range exceeding 100 dB is experimentally demonstrated.

Novel multi-telescopes beam combiners for next generation instruments (FIRST/SUBARU)

Integrated optic devices are nowadays achieving extremely good performances in the field of astronomical interferometry, as shown by PIONIER or GRAVITY silica/silicon-based instruments, already installed at VLTI. In order to address other wavelengths, increase the number of apertures to be combined and eventually ensure on-chip phase modulation, we are working on a novel generation of beam combiners, based on the hybridization of glass waveguides, that can ensure very sharp bend radius, high confinement and low propagation losses, together with lithium niobate phase modulators and channel waveguides that can achieve on-chip, fast (<100kHz) phase modulation. The work presented here has been realized in collaboration with our technological partners TeemPhotonics for glass waveguides and iXBlue-PSD for lithium niobate phase modulators. We will present our results on a hybrid glass/niobate (passive/active) beam combiner that has been developed in the context of FIRST/SUBARU 9T beam combiner. The combiner is structured in three parts: a) the first stage (passive glass) achieves beam splitting from one input to eight outputs, and that for nine input fibers coming from the sub-apertures of the Subaru telescope; b) the second stage consists on a 72 channel waveguides lithium niobate phase modulator in a push-pull configuration that allows to modify on-chip the relative phase between the 36 pairs of waveguides; c) a final recombination system of Y-junctions (passive glass) that allows to obtain combination of each input to every other one. The aim of this presentation is to discuss different issues of the combiners, such as transmission, birefringence, half-wave voltage modulation and spectral range.

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.

Optical characterization of ultra-short Bragg grating on lithium niobate ridge waveguide

In this Letter, we report a technique to etch giant aspect ratio nanostructures in lithium niobate. An 8 μm long Bragg grating on a Ti:LiNbO3 ridge waveguide was fabricated by combining optical-grade dicing and focused ion beam milling. The reflectivity was evaluated using an optical coherence tomography system: it is measured to be 53% for the TM wave and 47% for the TE wave. We study by 2D-FDTD the modeled behavior of the electromagnetic field when an angle exists between two consecutive sidewalls of the grating in order to understand the difference between ideal Bragg grating and experimental samples. These simulations allow us to optimize the parameters in order to increase the reflection of the grating up to 80%.

Double polarization active Y-junctions in the mid-IR, based on Ti:diffused lithium niobate waveguides: first results on photonic crystal structures

We present our work on integrated optic beam combiners devoted to mid-infrared applications in the field of stellar interferometry, in particular for nulling interferometry, where high rejection ratios are needed. The main results obtained are the single-mode behavior of the waveguides at a central wavelength λ=3.39μm, in both TE and TM polarization, a high rejection ratio on the modulated signal (best value of 30dB) and low dispersion in wide-band configuration. In a second time, in order to improve the electro-optic response of the modulators, we have realized a photonic crystal inside one of the arms of the Y-junction. Theoretical results predict simultaneous TE and TM group index enhancement, which should give better electro-optic response, however, our preliminary experimental results do not show significant difference with the initial combiners. Perspectives on the future work will be presented.

First results on an electro-optic visible multi-telescope beam combiner for next generation FIRST/SUBARU instruments

Integrated optic devices are nowadays achieving extremely high performances in the field of astronomical interferometry, as shown by the PIONIER and GRAVITY instruments. Progress remains to be made in order to increase the number of apertures/beams/channels to be combined (up to 9) and eventually ensure on-chip phase modulation (for fringe temporal scanning). We present a novel generation of beam combiners, based on the hybridization of two integrated optic devices: (i) one producing glass waveguides, that can ensure very sharp bend radius, high confinement and low propagation losses, with (ii) a lithium niobate device providing phase modulators and channel waveguides that can achieve on-chip, fast (<100kHz) phase modulation. The aim of this work is to compare three different concepts for the new generation FIRST/SUBARU 9T instrument, in terms of transmission, birefringence, half-wave voltage modulation and spectral range.