Clara Rivero

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.

Tellurite glasses with peak absolute Raman gain coefficients up to 30 times that of fused silica.

An experimental system has been assembled to measure the absolute values of the Raman gain spectrum for millimeter-thick glass samples. Results are reported for two new oxide glasses with Raman gain coefficients as much as 30 times larger than that of fused silica and more than twice its spectral coverage.

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 ...

Bulk-film structural differences of chalcogenide glasses probed in situ by near-infrared waveguide Raman spectroscopy

Abstract Thin film devices based on chalcogenide glasses (ChGs) are attractive for integrated optics applications due to their good infrared transmission and high nonlinear Kerr effects. To reveal structural variations which impact physical properties depending on material processing and in-use laser conditions we employ waveguide Raman spectroscopy (WRS) in ChG thin films and fibers using excitation in the near-infrared (NIR). The Raman spectra reveal significant microstructural differences between fibers drawn from bulk As 2 S 3 glasses and unannealed films in that the latter contain As 4 S 4 molecular subunits. The high signal-to-noise ratio and the absence of undesired photoreactions make NIR WRS a versatile new approach to in situ characterization of infrared waveguide devices.

Resolved discrepancies between visible spontaneous Raman cross-section and direct near-infrared Raman gain measurements in TeO2-based glasses.

Disagreements on the Raman gain response of different tellurite-based glasses, measured at different wavelengths, have been recently reported in the literature. In order to resolve this controversy, a multi-wavelength Raman cross-section experiment was conducted on two different TeO2-based glass samples. The estimated Raman gain response of the material shows good agreement with the directly-measured Raman gain data at 1064 nm, after correction for the dispersion and wavelength-dependence of the Raman gain process.

Thermally activated silver diffusion in chalcogenide thin films

Abstract Thin arsenic trisulfide films were deposited by thermal evaporation and thermally activated silver diffusion into these films was studied. UV–vis transmission and Rutherford backscattering spectrometry (RBS) was used for characterization of film property changes with Ag incorporation. The straightforward analysis proposed by Swanepoel, which allows determination of the dispersion relation and the film thickness from the optical transmission spectrum, was extended and applied to the chalcogenide thin films. RBS shows that silver diffusion mechanism depends strongly on an eventual annealing between the chalcogenide and silver deposition step. Without annealing the silver diffusion takes place by exchange between silver and arsenic atoms whereby sulfur atoms remain stationary, and arsenic accumulation occurs at the surface. For annealed samples silver diffuses without changing the film stoichiometry. In this case, the diffusion is much slower and the profile is more step-like. The possibility of using this technique for channel waveguide fabrication is demonstrated.

Raman gain measurements in bulk glass samples

Increased interest in highly nonlinear glasses for use as Raman amplifiers has encouraged the development of an experimental apparatus to measure the material Raman gain coefficient on millimeter-thick bulk glass samples. Apparatus design considerations, details of the apparatus, and justification for the data analysis employed are provided. The apparatus is a powerful tool offering the ability to quickly screen glass samples over a wide range of compositions without the time and cost of fiberizing candidate materials into a guiding geometry to directly measure Raman gain.

Influence of modifier oxides on the structural and optical properties of binary TeO2 glasses

Five different glass compositions with equal TeO2 molar concentration and various intermediate constituents were prepared to examine the influence of such intermediate species on the tellurite network. A correlation between the glasses’ structural network and optical properties is presented. Peak Raman gain coefficients, on the order of 40 times the gain of SiO2, are reported in this paper.

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.