Y. Pennec | Université de Lille (original) (raw)

Papers by Y. Pennec

Nature Communications, 2014

Recent years have witnessed the boom of cavity optomechanics, which exploits the confinement and ... more Recent years have witnessed the boom of cavity optomechanics, which exploits the confinement and coupling of optical waves and mechanical vibrations at the nanoscale 1,2 . Amongst the different physical implementations 3 , optomechanical (OM) crystals 4,5 built on semiconductor slabs are particularly interesting since they enable the integration and manipulation of multiple OM elements in a single chip and provide GHz phonons suitable for coherent phonon manipulation . Different demonstrations of coupling of infrared photons and GHz phonons in cavities created by inserting defects on OM crystals have been performed . However, the considered structures do not show a complete phononic bandgap at the frequencies of interest, which in principle should allow longer dephasing time, since acoustic leakage is minimized. In this work we demonstrate the excitation of acoustic modes in a 1D OM crystal properly designed to display a full phononic bandgap for acoustic modes at about 4 GHz. The confined phonons have an OM coupling ranging from the KHz to the MHz range with contributions from moving interfaces and the photoelastic effect that add constructively for many of them. The modes inside the complete bandgap are designed to have mechanical Q factors above 10 8 and invariant to fabrication imperfections, what would allow several coherent phonon manipulations at moderate cryogenic temperatures. At room temperature and atmospheric pressure, though, they present experimentally Q factors around 2000 limited by extrinsic damping and/or a combination of intrinsic phonon scattering mechanisms, like thermo-elastic decay or Akhieser. Interestingly, we also report the excitation of acoustic modes up to 8 GHz, the highest frequency reported so far.

2014 16th International Conference on Transparent Optical Networks (ICTON), 2014

ABSTRACT Recent years have witnessed the increase of interest in cavity optomechanics, which expl... more ABSTRACT Recent years have witnessed the increase of interest in cavity optomechanics, which exploits the confinement and coupling of optical waves and mechanical vibrations at the nanoscale. Amongst the different physical implementations, optomechanical (OM) crystals built on semiconductor slabs would enable the integration and manipulation of multiple OM elements in a single chip and provide GHz phonons suitable for coherent phonon manipulation. Different demonstrations of coupling of infrared photons and GHz phonons in cavities created by inserting defects on OM crystals have been performed. However, the considered structures do not show a complete phononic bandgap at the frequencies of interest, which in principle should allow longer dephasing time, since acoustic leakage is minimized. In this work we discuss the excitation of acoustic modes in a 1D OM crystal properly designed to display a full phononic bandgap for acoustic modes at about 4 GHz. The confined phonons have an OM coupling ranging from the kHz to the MHz range with contributions from moving interfaces and the photoelastic effect that add constructively for many of them. The modes inside the complete bandgap are designed to have high mechanical Q factors and invariant to fabrication imperfections, what would allow several coherent phonon manipulations at moderate cryogenic temperatures.

Optics express, Jan 9, 2011

We demonstrate theoretically that photons and acoustic phonons can be simultaneously guided and s... more We demonstrate theoretically that photons and acoustic phonons can be simultaneously guided and slowed down in specially designed nanostructures. Phoxonic crystal waveguides presenting simultaneous phononic and photonic band gaps were designed in perforated silicon membranes that can be conveniently obtained using silicon-on-insulator technology. Geometrical parameters for simultaneous photonic and phononic band gaps were first chosen for optical wavelengths around 1550 nm, based on the finite element analysis of a perfect phoxonic crystal of circular holes. A plain core waveguide was then defined, and simultaneous slow light and elastic guided modes were identified for some waveguide width. Joint guidance of light and elastic waves is predicted with group velocities as low as c/25 and 180 m/s, respectively.

Physical Review B, 2010

We study theoretically the simultaneous existence of phononic and photonic band gaps in a periodi... more We study theoretically the simultaneous existence of phononic and photonic band gaps in a periodic array of silicon pillars deposited on a homogeneous thin silica plate. Several lattices, namely, square, triangular, and honeycomb are investigated for a wide range of geometrical parameters. We discuss the most suitable cases for dual phononic-photonic band gaps, especially in comparison to the more conventional structures constituted by a periodic array of holes in a membrane.

Physical Review B, 2008

We introduce a supercell plane wave expansion ͑SC-PWE͒ method for the calculation of elastic band... more We introduce a supercell plane wave expansion ͑SC-PWE͒ method for the calculation of elastic band structures of two-dimensional phononic crystal plates. We compute the band structure of solid-solid and air-solid two-dimensional phononic crystal plates. The air is modeled as a low impedance medium ͑LIM͒ with very low density and very high velocities of sound. We investigate the influence of the constituent materials, of the plate thickness, and of the geometry of the array on the band structure. We establish the range of validity of the SC-PWE method in terms of the rate of convergence with respect to the number of plane waves and contrast in physical properties of the matrix and inclusion materials. We show that for high contrast solid-solid phononic crystal plates, our SC-PWE method, as other PWE-based methods introduced to date, suffers from convergence difficulties. In the case of air ͑modeled as the LIM͒ holes-solid plates, we demonstrate that the SC-PWE method leads to fast convergence for a wide range of values of solid physical properties. With these constituent materials, we find that the largest absolute forbidden bands occur in the band structure of the phononic crystal plate provided the thickness of the plate is of the order of magnitude of the periodicity of the array of inclusions. We demonstrate the existence of guided modes in an air-silicon phononic crystal plate containing a linear defect. M x = M y = 3, M z = 2 (245) M x = M y = 3, M z = 3 (343) M x = M y = 4, M z = 2 (405) M x = M y = 4, M z = 3 (567) M x = M y = 4, M z = 4 (729) M x = M y = 5, M z = 2 (605) M x = M y = 5, M z = 3 (847) M x =M y =5, M z =4 (1089) M x =M y =5, M z =5 (1331) M x =M y =6, M z =2 (845)

physica status solidi (c), 2004

ABSTRACT

Photonics and Nanostructures - Fundamentals and Applications, 2008

Using the finite element method (FEM), we investigate the existence of absolute band gaps and loc... more Using the finite element method (FEM), we investigate the existence of absolute band gaps and localized modes associated with a guide in thin films of phononic crystals. Two different structures based on two-dimensional (2D) phononic crystals are considered, namely a free standing plate and a plate deposited on a silicon substrate. The 2D phononic crystal is constituted by a square array of cylindrical holes drilled in an active piezoelectric PZT5A matrix. We demonstrate the existence of absolute band gap in the band structure of the phononic crystal plate and, then, the possibility of guided modes inside a linear defect created by removing one row of air holes. In the case of the supported plate, we show the existence of an absolute forbidden band in the plate modes when the thickness of the substrate significantly exceeds the plate thickness. #

Optics Express, 2010

We discuss the simultaneous existence of phononic and photonic band gaps in a periodic array of h... more We discuss the simultaneous existence of phononic and photonic band gaps in a periodic array of holes drilled in a Si membrane. We investigate in detail both the centered square lattice and the boron nitride (BN) lattice with two atoms per unit cell which include the simple square, triangular and honeycomb lattices as particular cases. We show that complete phononic and photonic band gaps can be obtained from the honeycomb lattice as well as BN lattices close to honeycomb. Otherwise, all investigated structures present the possibility of a complete phononic gap together with a photonic band gap of a given symmetry, odd or even, depending on the geometrical parameters.

Journal of Applied Physics, 2007

We investigate the possibility of designing phononic crystal-based devices for telecommunication ... more We investigate the possibility of designing phononic crystal-based devices for telecommunication applications using materials commonly employed in microfabrication. We focus our attention on a phononic crystal made of a square array of cylindrical holes drilled in an active piezoelectric PZT5A matrix. Two different structures are considered, namely, a freestanding phononic crystal plate and a plate deposited on a silicon substrate. The geometrical characteristics of the phononic crystal plates ͑lattice parameter and thickness͒ were chosen to ensure the existence of an absolute band gap around 1.5 GHz; a common frequency in radio frequency telecommunications. Computations of the dispersion curves of these active structures were conducted with the help of the finite element method. We demonstrate the existence of absolute band gaps in the band structure of the phononic crystal plates and, then, the possibility of guided modes inside a linear defect created by removing one row of air holes in the phononic crystal. In the case of the supported phononic crystal plates, we show the existence of an absolute forbidden band in the plate modes when the thickness of the substrate significantly exceeds the plate thickness. We discuss the conditions to realize waveguiding through a linear defect inside the supported plate. The present work provides evidences that phononic crystal properties can be integrated with existing silicon based microdevice technology.

Journal of Applied Physics, 2011

We discuss two points related to the simultaneous existence of phononic and photonic band gaps in... more We discuss two points related to the simultaneous existence of phononic and photonic band gaps in a two-dimensional crystal constituted by a square array of holes drilled in a matrix. In a first part, using the case of a sapphire sample in the microwave range, we show that in addition to the phononic gap, an absolute photonic gap may be obtained making use of the high values as well as the anisotropy of the dielectric matrix elements in the microwave regime. In a second part, using the case of silicon in the telecom frequency range, we demonstrate that absolute photonic and phononic gaps may be obtained by making a combination of two crystals having slightly different filling factors. The calculations of the band structures and transmission coefficients were mainly computed using the finite difference time domain method.

IEEE Photonics Technology Letters, 2000

We report experimental evidence of light guiding at telecommunication wavelengths along line-defe... more We report experimental evidence of light guiding at telecommunication wavelengths along line-defect honeycomblattice photonic crystal waveguides created in suspended silicon slabs. Numerical results show that the guided bands correspond to modes below the cladding light line so they are inherently lossless, although the measurements show quite high losses owing to fabrication imperfections. Honeycomb photonic crystals are a suitable platform for confining light and sound in nanoscale waveguides.

AIP Advances

We discuss theoretically the simultaneous existence of phoxonic, i.e., dual phononic and photonic... more We discuss theoretically the simultaneous existence of phoxonic, i.e., dual phononic and photonic, band gaps in a periodic silicon strip waveguide. The unit-cell of this one-dimensional waveguide contains a hole in the middle and two symmetric stubs on the sides. Indeed, stubs and holes are respectively favorable for creating a phononic and a photonic band gap. Appropriate geometrical parameters allow us to obtain a complete phononic gap together with a photonic gap of a given polarization and symmetry. The insertion of a cavity inside the perfect structure provides simultaneous confinement of acoustic and optical waves suitable to enhance the phonon-photon interaction.