Amélie Têtu

Photonic-crystal waveguide biosensor.

A photonic-crystal waveguide sensor is presented for biosensing. The sensor is applied for refractive index measurements and detection of protein-concentrations. Concentrations around 10 mug/ml (0.15muMolar) are measured with excellent signal to noise ratio, and a broad, dynamic refractive index sensing range extending from air to high viscous fluids is presented.

Broadband topology-optimized photonic crystal components for both TE and TM polarizations

Several planar photonic crystal components topology-optimized for TE-polarized light, including 60 masculine bends, Y-splitters, and 90 masculine bends, have been characterized for the TM polarization. The experimental results are confirmed by finite-difference time-domain calculations. The surprising efficiency for TM-polarized light is found and paves the way for photonic crystal components suitable for both polarizations.

Mapping the broadband polarization properties of linear 2D SOI photonic crystal waveguides

Both quasi-TE and TM polarisation spectra for a silicon-on-insulator (SOI) waveguide are recorded over (1100-1700)nm using a broadband supercontinuum source. By studying both the input and output polarisation eigenstates we observe narrowband resonant cross coupling near the lowest quasi-TE mode cut-off. We also observe relatively broadband mixing between the two eigenstates to generate a complete photonic bandgap. By careful analysis of the output polarisation state we report on an inherent non-reciprocity between quasi TE and TM fundamental mode cross coupling. The nature of polarisation distinction in such bandgap structures is discussed in the context of polarisation scattering at an interface.

Photonic Crystal Waveguide-based Biosensor

Protein detection using a photonic crystal waveguide-based biosensor is presented using two different sensing features for the device - the bandgap-edge, a common-known feature, and a novel feature arising due to polarization mixing.

Topology-optimized and dispersion-tailored photonic crystal slow-light devices

We review our work done for topology optimization of passive photonic crystal component parts for broadband and wavelength dependent operations. We show examples of low-loss topology-optimized bends and splitters optimized for broadband transmission and demonstrate the applicability of topology optimization for designing slow-light and/or wavelength selective component parts. We also present how the dispersion of light in the slow-light regime of photonic crystal waveguides can be tailored to obtain filter functionalities in passive devices and/or to obtain semi-slow light having a group velocity in the range ~(c0/15 - c0/100); vanishing, positive, or negative group velocity dispersion (GVD); and low-loss propagation in a practical ~5-15 nm bandwidth.

Generation of ultra-narrow sensing filters using cross polarisation in a linear SOI photonic crystal waveguide

A narrow band (3dB bandwidth <2nm) transmission notch filter based on polarisation conversion within a photonic crystal waveguide is demonstrated. Signal contrast between quasi- TE and TM eigenstates reaching 40dB is achieved. Further, multiple resonant wavelength coupling between the two eigenstates is also observed. These offer a novel alternative approach to sensing and biodiagnostics compared to previous use of the band edge of a photonic crystal waveguide.

Band Edge effects in Photonic Crystal Waveguides: Polarisation Conversion

Narrowband polarisation conversion from TE to TM and back is observed at the quasi- TE transmission band edge of a linear photonic SOI photonic crystal waveguide.

Protein detection with a planar photonic-crystal sensor

The paper presents specific protein detection with a planar photonic crystal waveguide (PC-WG) sensor. The advantages of the device we suggest are that it is realized in silicon and can be integrated on a SOI-wafer (silicon-on-insulator) along with other electronic and optical devices. Thus, the fabrication technology used for the sensor is the same as for CMOS electronic devices. The PC-WG can be made very compact and the sample volume to be analyzed can also be reduced considerably compared to many other biosensors presented in the literature.

Optimization of photonic crystal 60° waveguide bends in the slow light regime for broadband transmission

We present results for broadband transmission through photonic crystal waveguide bends optimized for slow-light modes. Theoretical analysis is complemented by experimental verification of designs including topology optimized ones fabricated in SOI material.

Passive integrated circuits utilizing slow light in photonic crystal waveguides

We report thorough investigations of photonic crystal waveguide properties in the slow light regime. The transmission and the group index near the cutoff wavelengths oscillate in phase in close analogy with the 1D photonic crystal behavior. The influence of having a finite number of periods in the photonic crystal waveguide is addressed to explain the spiky character of both the transmission and group index spectra. The profile of the slow-light modes is stretched out into the first and second rows of the holes closest to the waveguide channel. One of our strategies to ameliorate the design of photonic crystal devices is to engineer the radii of holes in these rows. A topology optimization approach is also utilized to make further improvements. The results of the numerical simulations and the optical characterization of fabricated devices such as straight waveguides with bends and couplers are presented. A nice match is found between theory and experiment.