Troy Anderson

PROGRESS ON THE FABRICATION OF ON-CHIP, INTEGRATED CHALCOGENIDE GLASS (CHG)-BASED SENSORS

In this paper, we review ongoing progress in the development of novel on-chip, low loss planar molecular sensors that address the emerging need in the field of biochemical sensing. Chalcogenide glasses were identified as the material of choice for sensing due to their wide infrared transparency window. We report the details of manufacturing processes used to realize novel high-index-contrast, compact micro-disk resonators. Our findings demonstrate that our device can operate in dual modalities, for detection of the infrared optical absorption of a binding event using cavity enhanced spectroscopy, or sensing refractive index change due to surface molecular binding and extracting micro-structural evolution information via cavity enhanced refractometry.

Femtosecond laser photo-response of Ge 23 Sb 7 S 70 films

Ternary chalcogenide glass films from identical parent bulk glasses were prepared by thermal evaporation (TE) and pulsed laser deposition (PLD) and subjected to 810-nm femtosecond laser exposure at both kHz and MHz repetition rates. The exposure-induced modification on the glass films surface profile, refractive index, and structural properties were shown to be a function of laser irradiance, the number of laser pulses per focal spot, and repetition rate. Film response was shown to be related to deposition technique-related density and the number of glass bonds within the irradiated focal volume. The induced changes resulted from a reduction in glass network connectivity among GeS(4/2), GeS(4), S-S and S(3)Ge-S-GeS(3) units.

Studies on structural, electrical, and optical properties of Cu doped As–Se–Te chalcogenide glasses

Cu doped chalcogenide (ChG) glassy films in the As–Se–Te glass system have been prepared using thermal evaporation techniques. Single-source evaporation from bulk (1−x) As0.40Se0.35Te0.25+x Cu glasses with x=0.05, 0.075, 0.10, 0.125, and 0.15, as well as dual-source coevaporation from As-chalcogenide and Cu-chalcogenide binary glasses as source materials, has been explored. We have shown that it is not possible to deposit high concentration Cu doped ChG glassy films, from the Cu doped bulk samples using single-source evaporation. However, using the dual-source coevaporation technique, we have demonstrated that the films can be doped with high concentrations of Cu. Micro-Raman spectroscopy has been utilized to verify that Cu is introduced into the glass network without disrupting the basic As-chalcogen units. Optical measurements have shown that introduction of Cu decreases the band gap of As–Se–Te glasses. The electrical properties of the investigated films have been measured at different temperatures and...

Development of novel integrated bio/chemical sensor systems using chalcogenide glass materials

This paper reviews ongoing progress in the design and fabrication of new, on-chip, low loss planar molecular sensors. We report the details of device design, material selection and manufacturing processes used to realise high-index-contrast (HIC), compact micro-disk resonators. These structures have been fabricated in thermally evaporated As- and Ge-based chalcogenide glass films with PDMS (polydimethylsiloxane) micro-fluidic channels using standard UV lithography. Discussed are findings that demonstrate that our novel chalcogenide-based micro-fluidic device can be used as highly sensitive refractive index sensors.

Femtosecond laser written embedded diffractive optical elements and their applications

Femtosecond laser direct writing (FLDW) has been widely employed to create volumetric structures in transparent materials that are applicable as various photonic devices such as active and passive waveguides, couplers, gratings, and diffractive optical elements (DOEs). The advantages of fabrication of volumetric DOEs using FLDW include not only the ability to produce embedded 3D structures but also a simple fabrication scheme, ease of customization, and a clean process. DOE fabrication techniques using FLDW are presented as well as the characterization of laserwritten DOEs by various methods such as diffraction efficiency measurement. Fresnel zone plates were fabricated in oxide glasses using various femtosecond laser systems in high and low repetition rate regimes. The diffraction efficiency as functions of fabrication parameters was measured to investigate the dependence on the different fabrication parameters such as repetition rate and laser dose. Furthermore, several integration schemes of DOE with other photonic structures are demonstrated for compact photonic device fabrication.

Waveguide writing and characterization in Tellurite glass

Ultra-fast laser-induced positive refractive index changes in bulk Tellurite glass were investigated. The refractive indexes of waveguiding structures were measured using the far-field approach. Filamentation was observed for certain irradiation conditions.

Sub-micron machining of semiconductors: femtosecond surface ripples on GaAs by 2 μm laser light

In recent years, a major interest in surface as well as bulk property modification of semiconductors using laser irradiation has developed. A.Kar et al. [1][2] and E.Mazur et al. [3] have shown introduction and control of dopants by long-pulse laser irradiation and increased absorption due to femtosecond irradiation respectively. With the development of mid-IR sources, a new avenue of irradiation can be established in a spectral region where the semiconductor material is highly transparent to the laser radiation. The characterization of the light-matter-interaction in this regime is of major interest. We will present a study on GaAs and its property changes due to pulsed laser irradiation ranging from the visible to the mid-IR region of the spectrum. Long-pulse as well as ultra-short pulse radiation is used to modify the material. Parameters such as ablation threshold, radiation penetration depth and thermal diffusion will be discussed.

Refractive index modifications in Chalcogenide films induced by sub-bandgap near-IR femtosecond pulses

Refractive index modifications of film Ge_0.23Sb_0.07S_0.7 induced by 800 nm femtosecond laser irradiation are studied for laser repetition rates of 1 kHz and 80 MHz. Measurements are taken using an interferometric method and analysis of the transmission spectra.

Chalcogenide Glasses and Their Photosensitivity: Engineered Materials for Device Applications

Chalcogenide glasses are widely used in device applications which capitalize on their unique linear and nonlinear optical properties, and infrared transparency. The role of the glass’ photosensitivity in device fabrication and eventual use, is discussed.

Optical Coherence Microscopy for Nondestructive 3D Imaging of Femtosecond Laser Written Structures

Optical coherence microscopy (OCM) is used to image femtosecond laser direct written buried structures created within transparent media. Volumetric structures of optical damage and laser-induced refractive index change were produced in fused silica and borosilicate glass, respectively. Noninvasive 3D imaging of the structures was successfully demonstrated by a custom built OCM. High signal to noise ratio was obtained since the optical glasses have high transparency at the probe wavelength centered at 800 nm.