Damien Bernier

Compact, low cross-talk CWDM demultiplexer using photonic crystal superprism

This paper addresses the problem of a photonic crystal (PhC) superprism design for coarse wavelength division multiplexing (CWDM) application. The proposed solution consists in using a PhC structure that presents an efficient balance between the wavelength dispersion and the beam divergence. It is shown that a bidimensional rhombohedral lattice PhC displays both a high beam collimation and an important wavelength dependant angular dispersion. We report the design, fabrication and experimental demonstration of a 4-channel optical demultiplexer with a spectral spacing of 25 nm and a cross-talk level of better than -16 dB using a 2800 microm(2) PhC region. The minimum of insertion losses of the demultiplexer is less than 2 dB. The obtained results present an important milestone toward PhC devices for practical applications.

Design and process development of a photonic crystal polymer biosensor for point-of-care diagnostics

In this work, we report advances in the fabrication and anticipated performance of a polymer biosensor photonic chip developed in the European Union project P3SENS (FP7-ICT4-248304). Due to the low cost requirements of point-ofcare applications, the photonic chip is fabricated from nanocomposite polymeric materials, using highly scalable nanoimprint- lithography (NIL). A suitable microfluidic structure transporting the analyte solutions to the sensor area is also fabricated in polymer and adequately bonded to the photonic chip. We first discuss the design and the simulated performance of a high-Q resonant cavity photonic crystal sensor made of a high refractive index polyimide core waveguide on a low index polymer cladding. We then report the advances in doped and undoped polymer thin film processing and characterization for fabricating the photonic sensor chip. Finally the development of the microfluidic chip is presented in details, including the characterisation of the fluidic behaviour, the technological and material aspects of the 3D polymer structuring and the stable adhesion strategies for bonding the fluidic and the photonic chips, with regards to the constraints imposed by the bioreceptors supposedly already present on the sensors.

Computation of light refraction at the surface of a photonic crystal using DtN approach

What we believe to be a new rigorous theoretical approach to the refraction of light at the interface of twodimensional photonic crystals is developed. The proposed method is based on the Dirichlet-to-Neumann (DtN) approach which consists of computing exactly the DtN operators associated with each half-space on both sides of the interface. It fully uses the properties of periodic optical media and takes naturally into account both the evanescent and propagative Bloch modes. Contrary to other proposed approaches, the new method is not based on modal expansions and their complicated electromagnetic field matching at the interfaces, but uses an operator vision. Intrinsically, each operator represents the effect along the interface of a particular medium independently of any medium and/or material that is placed in the other half-space. At the end, the whole computational effort to estimate DtN operators is restricted to the computation of a finite element problem in the periodicity cell of the photonic crystal. Field computations in arbitrary large part of the optical media can be then performed with a negligible computational effort. The method has been applied to the case of incoming plane waves as well as Gaussian beam profiles. It has successfully been compared with the standard plane wave expansion method and finite difference time domain (FDTD) simulations in the case of negative refraction, strongly dispersive, and lensing configurations. The proposed approach is amenable to the generalized study of dispersive phenomena in planar photonic crystals by a rigorous modeling approach avoiding the main drawbacks of FDTD. It is amenable to the study of arbitrary cascaded periodic optical media and photonic crystal heterostructures.

NIL fabrication of a polymer-based photonic sensor device in P3SENS project

We present the most recent results of EU funded project P3SENS (FP7-ICT-2009.3.8) aimed at the development of a low-cost and medium sensitivity polymer based photonic biosensor for point of care applications in proteomics. The fabrication of the polymer photonic chip (biosensor) using thermal nanoimprint lithography (NIL) is described. This technique offers the potential for very large production at reduced cost. However several technical challenges arise due to the properties of the used materials. We believe that, once the NIL technique has been optimised to the specific materials, it could be even transferred to a kind of roll-to-roll production for manufacturing a very large number of photonic devices at reduced cost.

Composite polymeric-inorganic waveguide fabricated by injection molding for biosensing applications

Inorganic based optical transducers have demonstrated their suitability for labelled and label-free sensing of biomolecules but suffer from their relatively high cost. Photonic structures fabricated in polymer by molding techniques could drastically reduce the cost per test and pave the way for label-free screening in point-of care environment where the cost per test is an essential concern. In this paper we present the advances in the fabrication of waveguides with cyclo olefin copolymer (COC) cladding and TiO2 core with mass-production compatible injection molding and evaporation. We demonstrate the optical propagation in a slab waveguide supporting both transverse electric and magnetic modes and monitor the response of the phase difference between the two modes when a droplet of water is deposited on the chip.

A superprism-based photonic crystal demultiplexer in nearly-perfect collimation conditions

Superprism phenomena in planar photonic crystals (PhCs) can be used for the realization of compact demultiplexers. Yet, strong dispersion is most often accompagnied by strong diffraction. The design, fabrication, and experimental characterization of a PhC demultiplexer is presented. A special care is taken to excite the equi-frequency surfaces in dispersive and simultaneously nearly-collimated regions. The structure is fabricated on a SOI substrate using e-beam lithography and RIE etching. With four output channels, its footprint is 2800μm2. It is characterized by a -16 dB level of crosstalk around λ = 1550 nm, with 2dB loss.