Mathias Perrin

Improvements of solid-core photonic bandgap fibers by means of interstitial air holes

We report the fabrication, characterization and modeling of a solid-core photonic bandgap fiber with interstitial air holes between the cladding rods. The presence of these interstitial air holes leads to a great improvement of optical properties for this kind of fiber. Particularly, we demonstrate that confinement losses and bend sensitivity are substantially reduced. Our experimental results for this new solution are well supported by numerical results.

Coexistence of total internal reflexion and bandgap modes in solid core photonic bandgap fibre with intersticial air holes.

In this article, we deal with new properties of a Solid Core Photonic Bandgap (SC-PBGF) fiber with intersticial air holes (IAHs) in its transverse structure. It has been shown recently, that IAH enlarges its bandgaps (BG), compared to what is observed in a regular SC-PBGF. We shall describe the mechanisms that account for this BG opening, which has not been explained in detail yet. It is then interesting to discuss the role of air holes in the modification of the Bloch modes, at the boundaries of the BG. In particular, we will use a simple method to compute the exact BG diagrams in a faster way, than what is done usually, drawing some parallels between structured fibers and physics of photonic crystals. The very peculiar influence of IAHs on the upper/lower boundaries of the bandgaps will be explained thanks to the difference between mode profiles excited on both boundaries, and linked to the symmetry / asymmetry of the modes. We will observe a modification of the highest index band (n(FSM)) due to IAHs, that will enable us to propose a fiber design to guide by Total Internal Reflection (TIR) effect, as well as by a more common BG confinement. The transmission zone is deeply enlarged, compared to regular photonic bandgap fibers, and consists in the juxtaposition of (almost non overlapping) BG guiding zones and TIR zone.

Left-handed electromagnetism obtained via nanostructured metamaterials: Comparison with that from microstructured photonic crystals

In this work, we review some of the key issues for designing dielectric and metallic arrays in the diffraction or refraction regimes with main emphasis on left-handed electromagnetism. We first discuss dispersion characteristics of periodic dielectric arrays which are structured on the wavelength scale (photonic crystals for optics and electromagnetic band gaps for microwaves) with special attention paid to propagation and refraction effects. Special attention was also paid to the isotropy properties in the Brillouin zone with the prospects of defining a negative refractive index. Then, we considered metallic structures which permit one to synthesize double-negative media with the goal of pushing their operation frequency into the infrared region. For both classes of microstructures and nanostructures, the technological challenges will be addressed by considering air hole arrays in a high refractive index semiconductor substrate and embedded C-shaped and wire metal arrays patterned on low index substrates.

Anomalous Light Absorption around Subwavelength Apertures in Metal Films

In this Letter, we study the heat dissipated at metal surfaces by the electromagnetic field scattered by isolated subwavelength apertures in metal screens. In contrast to the common belief that the intensity of waves created by local sources should decrease with the distance from the sources, we reveal that the dissipated heat at the surface remains constant over a broad spatial interval. This behavior that occurs for noble metals at near infrared wavelengths is observed with nonintrusive thermoreflectance measurements and is explained with an analytical model, which underlines the intricate role played by quasicylindrical waves in the phenomenon. Additionally, we show that, by monitoring the phase of the quasicylindrical waves, the total heat dissipated at the metal surface can be rendered substantially smaller than the heat dissipated by the launched plasmon. This interesting property offers an alternative to amplification for overcoming the loss issue in miniaturized plasmonic devices.

Eigen-energy effects and non-orthogonality in the quasi-normal mode expansion of Maxwell equations

We derive a quasi-normal mode theory for three-dimensional scatterers, taking care to remove an hypothesis of weakly dispersive materials implicitely used in previous works. In our approach, the normalized modes remain unchanged, but the analytic expansion coefficients onto the set of QNM are modified. In particular, we take into account in a simple way the non-orthogonality of the modes, and we set up a rigourous frame, to treat the case where several QNMs are excited. Eventally, the complex concept of PML integration, previously introduced, becomes unnecessary, even to compute the QNM mode volume. Besides, crossover integrals of QNM fields over the whole space can now be written rigourously, as integrals on the finite volume of the scatterer, without surface terms.

Picosecond to femtosecond pulses from high power self mode-locked ytterbium rod-type fiber laser

We have designed an ytterbium rod-type fiber laser oscillator with tunable pulse duration. This system that delivers more than 10 W of average power is self mode-locked. It yields femtosecond to picosecond laser pulses at a repetition rate of 74 MHz. The pulse duration is adjusted by changing the spectral width of a band pass filter that is inserted in the laser cavity. Using volume Bragg gratings of 0.9 nm and 0.07 nm spectrum bandwidth, this oscillator delivers nearly Fourier limited 2.8 ps and 18.5 ps pulses, respectively. With a 4 nm interference filter, one obtains picosecond pulses that have been externally dechirped down to 130 fs.

Multilayer Langmuir-Blodgett films as diffractive external 3D photonic crystal in blue OLEDs

Three-dimensional Langmuir-Blodgett films made of silica beads are theoretically and experimentally investigated in order to improve the relatively small efficiency of blue OLEDs. Using films made of 5 layers of beads, we fabricated OLEDs emitting at 476 nm, and measured a gain of around 40% on their external quantum efficiency. An optical model has been developed to accurately handle the fact that the organic emitting layer and the photonic extraction layer are separated by a distance greater than 1000 wavelength. The latter also permits to describe rapidly this three-dimensional optical OLED cavity, without redoing all the numerical simulations when the optical properties of the organic layers are changed (material index, thicknesses).

8 watts actively mode-locked Ytterbium doped fiber laser delivering 15 ps pulses at 40 MHz

Several industrial applications require highly reliable and efficient laser systems delivering high average power in the modelocking regime. For this purpose, the frequency feedback laser architecture which is based on doped fibers and acousto-optic modulator has numerous advantageous compared to passive ML with SESAM.

Direct Wavefront Measurement of Terahertz Pulses Using Two-Dimensional Electro-Optic Imaging

We report on the development of a wavefront sensor for terahertz pulses using a direct two-dimensional electro-optic imaging system composed of a ZnTe crystal and a CMOS camera. By measuring the phase variation of the terahertz electric field in the crystal plane, we are able to reconstruct the terahertz (THz) wavefront in order to determine the optical aberrations of the optical system. Associated with deformable mirrors or specifically designed optics, the sensor will open the route to terahertz adaptive optics.

Modal description of optical nanoresonators

Photonic and plasmonic resonators are dielectric or metallic optical devices that confine light at a scale smaller than the wavelength. They have many applications, especially in sensing,1 nonlinear nano-optics,2 or quantum optics.3 More generally, microand nanoresonators play an important role in the conversion of energy from localized fields to radiating waves. They are therefore studied by different communities interested in wave physics, including optics, microwave, and acoustics researchers. With today’s numerical tools, it is possible to design and analyze microand nanoresonators directly by solving Maxwell’s equations. However, such numerical studies need to repeat many independent computations, as the polarization, incidence, and frequency of the excitation fields are varied. The numerical load may be heavy, and, above all, the computed data obtained with these brute-force calculations may still hide much knowledge about the physical mechanisms at play. To bypass such difficulties, it is tempting to rely on mode theory, which allows us to represent the resonator response as a weighted sum of mode contributions. Each mode is computed only once, because it is independent of the excitation. Eigenstates of a system are often a particularly useful type of mode to consider. Introducing such eigenstates to study a system’s response is a very common framework in many areas of fundamental and applied physics, as one can lean on some important mathematical properties of these modes, such as completeness and orthogonality. The latter has a physical meaning of fundamental importance: once a mode is excited, it cannot transfer its energy to another mode. Such modes are usually referred to as normal modes in the literature. However, normal-mode theories rely on the energy dissipation in the system being small enough for the theory to be accurate. This key assumption may remain approximately valid Figure 1. (a) Plot of the intensity distribution, jEz j, for a normalized quasinormal mode of a 30nm-diameter and 100nm-long cylindrical gold nanorod (dashed line). (b) Purcell factor (enhancement of spontaneous emission rate) of a dipole located on the rod axis 10nm from the rod and polarized along its axis. (c) Extinction cross-section of the rod under illumination by a plane wave polarized along the rod axis. In (b) and (c), black circles are fully vectorial numerical results obtained with the COMSOL Multiphysics software. The red solid curves represent the predictions of our analytical modal method.4