A. Monmayrant

A newcomer's guide to ultrashort pulse shaping and characterization

This tutorial gives an overview of the most widespread techniques of both ultrashort pulse shaping and pulse characterization.

Tunable, polarization independent, narrow-band filtering with one-dimensional crossed resonant gratings

We propose an optical component for widely tunable, narrow-band filtering. It takes advantage of the tunability properties, with respect to the angle of incidence, of guided-mode resonance filters. The intrinsic polarization sensitivity of the resonances is suppressed by exciting the modes through two identical, differently oriented one-dimensional gratings flanking a thick substrate. An example is provided that theoretically shows a polarization independent peak at 1.6 μm with a Q factor of 13,000 and a reflectivity greater than 99% at resonance, which is tunable over 100 nm. Finally, we discuss the fabrication limitations and conclude that the proposed configuration is realistic.

Experimental demonstration of 1D crossed gratings for polarization-independent high-Q filtering

We demonstrate experimentally a spectral filter with high Q-factor (≃3238), wide accordability range (1500-1600 nm) with respect to the angle of incidence, and record polarization independence. This work is an experimental validation of the theoretical work reported in [Opt. Lett. 36, 1662 (2011)]: the filter is composed of two 1D crossed gratings engraved on each side of a planar waveguide. We provide a good comparison with theory and physical interpretations of the features observed experimentally.

High-order modes in cavity-resonator-integrated guided-mode resonance filters (CRIGFs).

Cavity-resonator-integrated guided-mode resonance filters (CRIGFs) are optical filters based on weak coupling by a grating between a free-space propagating optical mode and a guided mode, like guided-mode resonance filters (GMRFs). As compared to GMRFs they offer narrowband reflection with small aperture and high angular acceptance. We report experimental characterization and theoretical modeling of unexpected high-order reflected modes in such devices. Using coupled-mode modeling and moiré analysis we provide physical insight on key mechanisms ruling CRIGF properties. This model could serve as a simple and efficient framework to design new reflectors with tailored spatial and spectral modal reflectivities.

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.

2 × 1D crossed strongly modulated gratings for polarization independent tunable narrowband transmission filters

We design a narrowband polarization independent transmission guided mode resonance filter whose center wavelength is tunable with respect to the angle of incidence. The device is composed of two identical structures assembled back to back. Each half structure is a dielectric multilayer stack in which a grating is engraved. This so-called 2×1D crossed gratings component has already been demonstrated for reflection filtering [Opt. Lett.36, 1662 (2011)OPLEDP0146-959210.1364/OL.36.001662; Opt. Lett.39, 6038 (2014)OPLEDP0146-959210.1364/OL.39.006038]. The functioning in transmission requires the use of a high index material for the grating bumps. For the design, we resort to a clustering global optimization algorithm, used for the first time to our knowledge for grating structures. We demonstrated two filters with a quality factor of about 4000, tunable over more than 15 nm when the angle of incidence varies over a range of 4°, and with a transmittivity at resonance greater than 95% whatever the incident polarization.

Adaptive, Hyperspectral Imager: Design, Modeling, and Control

An adaptive, hyperspectral imager is presented. We propose a system with easily adaptable spectral resolution, adjustable acquisition time, and high spatial resolution which is independent of spectral resolution. The system yields the possibility to define a variety of acquisition schemes, and in particular near snapshot acquisitions that may be used to measure the spectral content of given or automatically detected regions of interest. The proposed system is modelled and simulated, and tests on a first prototype validate the approach to achieve near snapshot spectral acquisitions without resorting to any computationally heavy post-processing, nor cumbersome calibration

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.

High reflectivity small aperture resonant grating filters for laser diode spectral stabilisation

Resonant grating filters are new optical components of high interest for optical reinjection in a laser diode as they provide simultaneously high reflectivity and high spectral selectivity. However, their usefulness is limited by a low angular tolerance that requires the use of collimated beams. Following the proposal from Ura et al. [1], we demonstrated small aperture resonant grating filters with a high modal reflectivity (larger than 60%), a narrow linewidth (1.5 nm at 850 nm) and a large angular tolerance (larger than 9, FWHM) [2]. In this paper, we discuss the design and performance properties of such filters, and demonstrate spectral stabilization of a laser diode with resonant grating filters.

Achromatic critically coupled racetrack resonators

In this paper, we investigate the spectral response of whispering-gallery-mode (WGM) resonators coupled to their access waveguide with a view to design their constitutive waveguides to promote critical-coupling over a wide spectral range and thereby facilitate their use for high-sensitivity sensing or nonlinear frequency conversion applications. The carried-out theoretical analysis is based on the universal response functions of singlemode and unidirectional devices. A coupled-mode treatment of the coupling region enables to derive two sets of favorable designs. The identified resonator/access waveguide systems exploit waveguides with mismatched propagation constants forming a coupling section exhibiting either an achromatic beat-length or an achromatic power-transfer coefficient. This generic model is followed by a numerical case study of vertically-coupled Si3N4 racetrack resonators. The conventional (quasi-)phase-matched configuration, treated as a reference case, is shown to display a critical-coupling bandwidth of 23 nm at a wavelength of 1550nm, whereas the proposed new designs demonstrate critical bandwidths larger than 330nm, i.e. exhibit bandwidths enhanced by more than one order of magnitude.