F. Lozes-Dupuy

1.5μm room-temperature emission of square-lattice photonic-crystal waveguide lasers with a single line defect

Narrow waveguides consisting of a single defect-line (W1) in a square lattice photonic crystal are fabricated on InP using the substrate approach. A single-mode distributed-feedback laser emission is obtained under optical pumping at room temperature. Lasing occurs at the second folding point of the dispersion curve of the fundamental waveguide mode (wave vector k=0). The emitted wavelength ranges from 1420to1580nm for a lattice period varying from 460to520nm and a constant air filling factor of ∼26%. The highly monomode behavior is explained using two-dimensional plane-wave models. Similar experiments conducted on triangular lattice W1 waveguides do not yield a laser emission. Three-dimensional simulations confirm that triangular lattice W1 waveguides suffer higher losses than their square homologues.

Carrier‐induced change due to doping in refractive index of InP: Measurements at 1.3 and 1.5 μm

Accurate measurements of the InP refractive index as a function of free‐carrier doping are reported at 1.3 and 1.5 μm, the two strategic wavelengths for optical communications. A total of 21 samples with different N‐ and P‐doping levels have been measured using a novel and simplified grating‐coupling technique. In contrast to the conventional method, this only involves the use of a directly etched diffraction grating on the sample surface, thereby avoiding the necessity of a specific guiding layer. The measured index, in agreement with earlier predictions, decreases by more than 0.05 when the N doping is increased from below 1015 to about 1019 electrons per cubic centimeter. This effect, however, is much less pronounced with P doping than with N doping.

Controlled reflectivities in self-collimating mesoscopic photonic crystal

We propose a simple, fast, and accurate method to design complex layered photonic crystal structures that exhibit mesoscopic self-collimation. We apply this method to the control of the overall reflectivity of such structures, and we numerically demonstrate high-transmissivity (>99%) self-collimating waveguides and high-reflectivity (>99%) self-collimating Bragg mirrors.

Stable planar mesoscopic photonic crystal cavities.

Mesoscopic self-collimation (MSC) in mesoscopic photonic crystals with high reflectivity is exploited to realize a novel high Q-factor cavity by means of mesoscopic PhC planar mirrors. These mirrors efficiently confine a mode inside a planar Fabry-Perot-like cavity, that results from a beam focusing effect that stabilizes the cavity even for small beam sizes, resembling the focusing behavior of curved mirrors. Moreover, they show an improved reflectivity with respect to their standard distributed Bragg reflector counterparts that allows higher compactness. A Q-factor higher than 10⁴ has been achieved for an optimized 5-period-long mirror cavity. The optimization of the Q-factor and the performances in terms of energy storage, field enhancement, and confinement are detailed.

GaAs based mid infrared filter with resonant gratings

Many applications -like spectroscopy- require spectral filtering, commonly achieved using Fabry-Pérot stacks. These can be designed to fulfill varying requirements (central wavelength, bandwidth and rejection). However, practical fabrication of the stack imposes some limitations. Indeed, reducing the bandwidth requires an increasing number of layers and ultra-narrowband filters are hard to fabricate. Similarly, extending to long wavelengths necessitates thicker layers that are not easily grown or deposited. Ultra-narrow-band filters in the mid-infrared are thus particularly difficult to obtain using this approach. In that particular aspect, resonant grating filters are an extremely interesting alternative. Especially for narrow band free-space filtering in the MIR region, as required for gas sensing (CH4, CO,…). A resonant grating filter is a sub-wavelength periodically structured planar waveguide that reflects and transmits light specularly, with the same reflection and transmission coefficient than that of the unstructured waveguide, except at resonance, where the structure exhibit one pole (100% reflection) and one zero (0% reflection)[1]. These are due to the diffraction grating that couple the incident beam, for a given wavelength and incident angle, and thus excite a mode in the structure (Figure 1 left). By reciprocity, this grating will also uncouple the mode to emit light.

Photonic crystals for planar laser sources: New functionalities and outlook

By harnessing the potential of photonic crystal waveguide, we have developed inherently single-mode DFB lasers that can be integrated in arrays. We propose and demonstrate two methods (affine deformation and double deformation) for fine optimization and control of both the emission wavelength and the mode discrimination of such lasers. Integrated arrays of single-mode DFB lasers on membrane emitting around 990 nm with wavelength spacing under 0.2 nm are experimentally reported. Theoretical Q factor above 6.105 are obtained. Using double deformation, laser emission characteristics and performances remain unchanged under optical feedback above 10%.

2D hexagonal resonant grating filters performances: Measurement and modelling

Resonant grating filters (RGF) are basically a planar waveguide with a sub-wavelength periodic structuration that transmits and reflects light specularly. It is well known that the reflectivity of such a structure presents anomalies (or peaks) versus the wavelength, generated by the coupling and out-coupling of a mode of the waveguide [1]. These peaks can be tailored in order to create free-space narrow band reflection filters. The fabrication processing and the demonstration of high performance, narrow band filters using 2D lattices to exhibit nearly polarization independent behavior have already been reported [2, 3].

Ultra-high Q photonic crystal waveguides for DFB laser operation

In the recent years, 2D photonic crystals (PhCs) have paved the way towards integrated optics. One major challenge is the development of laser sources compatible with this approach. It has recently been shown that planar PhC waveguides could be used to design Distributed Feedback (DFB) lasers [1], and that closely spaced single mode lasers arrays can be designed using a so-called affine deformation of the PhC lattice [2]. However, using such waveguides, the quality factor of the DFB mode remains rather low (Q ∼ 104) and the discrimination between the 2 DFB modes is not always high enough to ensure single mode emission, especially for large deformations.