Cedric Lopez

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.

Role of S/Se ratio in chemical bonding of As-S-Se glasses investigated by raman, x-ray photoelectron, and extended x-ray absorption fine structure spectroscopies

Chalcogenide glasses have attracted considerable attention and found various applications due to their infrared transparency and other optical properties. The As–S–Se chalcogenide glass, with its large glass-formation domain and favorable nonlinear property, is a promising candidate system for tailoring important optical properties through modification of glass composition. In this context, a systematic study on ternary As–S–Se glass, chalcogen-rich versus well-studied stochiometric compositions, has been carried out using three different techniques: Raman spectroscopy, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure spectroscopy. These complementary techniques lead to a consistent understanding of the role of S∕Se ratio in chalcogen-rich As–S–Se glasses, as compared to stochiometric composition, and to provide insight into the structural units (such as the mixed pyramidal units) and evidence for the existence of homopolar bonds (such as Se–Se, S–S, and Se–S), which are the ...

Refractive index measurements of planar chalcogenide thin film

Abstract We report on the measurements of the refractive index of As–S–Se chalcogenide glasses near 1.55 μm. The measurements were made on annealed and non-annealed samples of thermally evaporated thin films. The data for two different series of glasses are presented: the compositions As40S60−xSex and the compositions AsxS(100−x)/2Se(100−x)/2 where the ratio of sulfur to selenium is kept constant (1:1). It has been found that replacing sulfur by selenium in the first series increases the refractive index from 2.4 to 2.8 and increasing the arsenic content in the second series increases the refractive index. In all cases, it has been found that annealing the samples increase the refractive index. The accuracy in the refractive index measurement is ±0.2%.

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.

X-ray photoelectron spectroscopic investigation of surface chemistry of ternary As-S-Se chalcogenide glasses

Chalcogenide glasses belong to an important class of materials, due to their good infrared transmission, and low-phonon energy as compared to other oxide glasses. Structural and chemical variations imposed by glass processing conditions, e.g., film deposition, can lead to changes in the linear and nonlinear optical properties. X-ray photoelectron spectroscopy (XPS) has been employed to study As–S–Se glasses of differing chemical compositions, in the film and the bulk form, to understand any variations in chemical bond configuration and their electronic structure. The molecular environments of As and Se for As–S–Se samples with varying S/Se ratio (fixed As content) and As content (fixed S/Se ratio) are studied by monitoring the XPS chemical shifts. The surface chemistry of the bulk and thin-film chalcogenide glasses are also compared to determine the effect of glass processing conditions for better chalcogenides for potential waveguide applications.

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.

Refractive index measurements of planar chalcogenide waveguide

We report results from a systematic study of the linear refractive index of thin films made of As-S-Se glasses which are part of the chalcogenide family. We have studied eight different compositions. The refractive index are measured by the mean of a grating coupling experiment. The measurements are performed around 1.5μm for both annealed and non-annealed glasses. We observe that annealing the samples increases their refractive index. We also note that the increase of Selenium concentration increases the refractive index and the decrease of Arsenic concentration decreases the refractive index.

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.