Arnaud Zoubir

Direct femtosecond laser writing of waveguides in As2S3 thin films

Single-channel waveguides and Y couplers were fabricated in chalcogenide thin films by use of femtosecond laser pulses from a 25-MHz repetition rate Ti:sapphire laser. Refractive-index differentials (delta n > 10(-2)) were measured through interferometric microscopy and are higher than the typical values reported for oxide glasses. The dependence of the index differential on the peak intensity reveals the nonlinear nature of the photosensitivity in arsenic trisulfide below its bandgap energy, and the refractive-index change is correlated to the photoinduced structural changes inferred by Raman spectroscopy data. A free-electron model to predict the parametric dependence of delta n is proposed.

Femtosecond laser fabrication of tubular waveguides in poly(methyl methacrylate)

Femtosecond laser direct writing is employed for the fabrication of buried tubular waveguides in bulk poly(methyl methacrylate). A novel technique using selective chemical etching is presented to resolve the two-dimensional refractive-index profile of the fabrication structures. End-to-end coupling in the waveguides reveals a near-field intensity distribution that results from the superimposition of several propagating modes with different azimuthal symmetries. Mode analysis of the tubular waveguides is performed using the finite-difference method, and the possible propagating mode profiles are compared with the experimental data.

Optical properties of infrared femtosecond laser-modified fused silica and application to waveguide fabrication

We investigate the changes in the optical properties of fused silica exposed to intense infrared femtosecond pulses. The laser-induced absorption spectrum reveals the creation of color centers inside the glass matrix, comparable with those observed in ultraviolet-exposed fused silica. The laser-induced absorption is associated with a laser-induced refractive-index change, which can be used for waveguide fabrication. The change in third-order susceptibility in such waveguides is measured by third-harmonic-generation microscopy as a function of the irradiation parameters.

Femtosecond laser microstructuring and refractive index modification applied to laser and photonic devices

Rapid progress has been made in the last few years in the development direct-write, femtosecond laser micro-structuring and waveguide writing techniques in various materials, particularly semiconductor and other photo-sensitive glasses. There is considerable potential for this becoming a disruptive technology in photonic device fabrication, perhaps even leading to the development of devices that are difficult to fabricate by any other technique. We will review these developments, and with an optimistic eye, offer some perspectives on the future of this technology for opto-electronic systems.

Ablation and optical property modification of transparent materials with femtosecond lasers

Because of the unique laser-matter interaction processes involved, femtosecond laser micro-machining and femtosecond laser materials processing techniques are developing rapidly to stages where they may be introduced into manufacturing. Yet in both these areas, some complex interaction phenomena are not fully understood. In this talk we describe two studies of fundamental processes that impact both of these areas. These studies were made in transparent media, but their findings will be applicable to many non-transparent materials. Micro-machining in confined regions can give rise to new physical mechanisms emerging to dominate the machining process. We show this occurs in deep hole drilling of glasses by femtosecond laser pulse, where self-focusing effects takes over in the ablating process. The conditions under which this occurs will be described, and other configurations discussed where these phenomena may be important. At intensities below that required for ablation, structural modification of materials may be effected by femtosecond laser pulses. This has opened pathways towards direct femtosecond laser writing of optical waveguides, micro-fluidic systems and other structures. We will describe the controlled variation of refractive index that can be created in certain types of glasses and there potential for optical waveguides, and active optical elements. The evolution of these techniques will lead to their eventual integration for the fabrication of multi-component systems on a single chip.

Technology developments toward the practical use of femtosecond laser micromaterials processing

We describe several scenarios of basic femtosecond machining and materials processing that should lead to practical applications. Included are results on high through-put deep hole drilling in polymers and glasses in ambient air, and precision high speed micron-scale surface modification of materials.

Evolution of the linear and nonlinear optical properties of femtosecond laser exposed fused silica

Three fused silica samples possessing different impurity levels and exposed to a near infrared femtosecond laser are investigated. The laser-induced defects are identified from absorption, luminescence, and Raman spectroscopy. Their linear and nonlinear optical properties are measured from Kramers-Kronig calculations and third-harmonic generation microscopy experiments. No conclusive correlation between the change in the optical properties, the initial impurity levels, and the photoinduced structures could be established based on the results obtained in this study. In addition, several hypotheses (densification and color center formation) have been rejected to explain why the linear and nonlinear optical properties of the photoinduced structures follow a contradicting evolution. This phenomenon is attributed to an experimental artifact on the measurement of the third-order susceptibility due to scattering of the photoinduced structures.

Femtosecond fabrication of waveguides and gratings in chalcogenide thin films

Summary from only given. Amorphous chalcogenide glass (ChG) films are candidates for all-optical integrated circuits for the telecommunication industry due to their excellent infrared transparency, large nonlinear refractive index, and low phonon energies. This paper describes for the first time to our knowledge, material ablation and corresponding structural changes in single and multilayer ChG thin films, using an unamplified Ti:sapphire laser.

Photo-induced optical and physical property modifications in chalcogenide thin films by femtosecond irradiation

Multiphoton processes were shown to influence photo-induced exposure response in As-S-Se thin films written with sub-bandgap femtosecond radiation. Structural and/or electronic defects are established to be responsible for composition-dependent effects on the resulting material modifications.

Nonlinear optics of femtosecond laser-modified fused silica - applications to waveguide fabrication

Absorption and photoluminescence spectroscopy, and third-harmonic confocal microscopy are used for the first time to characterize the linear and non-linear properties, crucial for the fabrication of active elements, of femtosecond laser-written waveguides in fused silica.