Neil Troy

Direct femtosecond laser waveguide writing inside zinc phosphate glass

We report the relationship between the initial glass composition and the resulting microstructural changes after direct femtosecond laser waveguide writing with a 1 kHz repetition rate Ti:sapphire laser system. A zinc polyphosphate glass composition with an oxygen to phosphorus ratio of 3.25 has demonstrated positive refractive index changes induced inside the focal volume of a focusing microscope objective for laser pulse energies that can achieve intensities above the modification threshold. The permanent photo-induced changes can be used for direct fabrication of optical waveguides using single scan writing techniques. Changes to the localized glass network structure that produce positive changes in the refractive index of zinc phosphate glasses upon femtosecond laser irradiation have been studied using scanning confocal micro-Raman and fluorescence spectroscopy.

Femtosecond laser writing of waveguides in zinc phosphate glasses [Invited]

We have studied the relationship between the initial glass composition and the structural changes associated with laser-induced refractive index modification in a series of Er-Yb doped and undoped zinc phosphate glasses. White light microscopy and waveguide experiments are used together with Raman and fluorescence spectroscopy to characterize the structural changes. The correlation between Raman peak shifts and fluorescence from phosphorus–oxygen hole center (POHC) defects indicates that fs-laser writing results in a depolymerization of the phosphate glass network. The results also show that the exact glass composition should be taken into account when fabricating waveguide devices in phosphate glasses, in order to both expand the fs-laser processing conditions and maximize favorable morphological changes for 3-D photonic devices.

Single-pass waveguide amplifiers in Er-Yb doped zinc polyphosphate glass fabricated with femtosecond laser pulses

We have investigated the direct fabrication of subsurface waveguide amplifiers in Er-Yb zinc polyphosphate glass by utilizing the relationship between the initial glass composition and the resulting changes to the network structure after modification by fs laser pulses. Waveguides, exhibiting internal gain of 1 dB/cm at 1.53 μm when pumped with 500 mW at 976 nm, were directly fabricated using a regenerative amplified Ti:sapphire 1 kHz, 180 fs laser system. Optical properties as well as insertion losses and internal gain are reported.

Effects of rare-earth doping on femtosecond laser waveguide writing in zinc polyphosphate glass

We have investigated waveguide writing in Er-Yb doped zinc polyphosphate glass using a femtosecond laser with a repetition rate of 1 KHz. We find that fabrication of good waveguides requires a glass composition with an O/P ratio of 3.25. The dependence on laser writing parameters including laser fluence, focusing conditions, and scan speed is reported. Waveguide properties together with absorption and emission data indicate that these glasses can be used for the fabrication of compact, high gain amplifying devices.

Role of hydrogen loading and glass composition on the defects generated by the femtosecond laser writing process of fiber Bragg gratings

The creation of fiber Bragg gratings (FBGs) in optical fibers by laser irradiation causes the formation of defects in the modified glass. We have used confocal fluorescence spectroscopy to identify the location and types of defects formed after writing FBGs with the femtosecond laser phase mask technique. Our results show that non-bridging oxygen hole centers (NBOHCs) and self-trapped excitons (Eδ’) are formed throughout all-silica core Sumitomo Z-fiber. Similar defects are observed for Ge-doped silica fiber, Corning SMF-28, but in this case the relative concentrations of NBOHC and Eδ’ vary from the core to the cladding. In both fibers, hydrogen loading prior to irradiation appears to passivate the defects except in the Ge-doped core where the NBOHC defects persist.

Thermal annealing of femtosecond laser written structures in silica glass

We have investigated the thermal stability of femtosecond laser modification inside fused silica. Raman and FL spectroscopy show that fs-laser induced non-bridging oxygen hole center (NBOHC) defects completely disappear at 300 °C, whereas changes in Si-O ring structures only anneal out after heat treatment at 800-900 °C. After annealing at 900 °C optical waveguides written inside the glass had completely disappeared whereas more significant damage induced in the glass remained. The results are related to different types of bond rearrangements in the glass network.

Structural modification in Er-Yb doped zinc phosphate glasses with megahertz repetition rate femtosecond pulses

Focused femtosecond laser pulses from a 1 MHz fiber laser were used to create modifications in Er- Yb doped zinc phosphate glass. Two glasses with similar phosphate glass networks but different network modifiers were investigated. To understand the resulting changes caused by the femtosecond laser pulses various characterization techniques were employed: glass structural changes were investigated with confocal Raman spectroscopy, defect generation as well as local Er and Yb environment were investigated with confocal fluorescence spectroscopy, and elemental segregation resulting from heat accumulation effects was ascertained by scanning electron microscopy.

Femtosecond Laser Writing of Waveguides in Glass

Femtosecond laser writing was used to fabricate waveguides in undoped and rare-earth doped polyphosphate glasses. The influence of glass composition and laser parameters on waveguide properties and structural changes in the glass will be discussed.