Christopher Miese

Laser induced nanogratings beyond fused silica - periodic nanostructures in borosilicate glasses and ULE™

We report on the ultrashort pulse laser induced formation of birefringent structures in the volume of different glasses: Borofloat 33, BK7 and ULE™. Using polarization contrast and scanning electron microscopy we could prove that this birefringence is induced by nanogratings. We were able to identify the pulse duration as a crucial process parameter for the generation of nanogratings in these glasses. The achieved birefringence in ULE is comparable to fused silica, while borosilicate glasses show much less birefringence (only about 12%). Remarkably, the period of the nanogratings is also dependent on the type of the glass, being 250 nm for ULE and only 60 nm in case of Borofloat 33.

Integrated photonic building blocks for next-generation astronomical instrumentation I: the multimode waveguide

We report on the fabrication and characterization of composite multimode waveguide structures that consist of a stack of single-mode waveguides fabricated by ultrafast laser inscription. We explore 2 types of composite structures; those that consist of overlapping single-mode waveguides which offer the maximum effective index contrast and non-overlapped structures which support multiple modes via strong evanescent coupling. We demonstrate that both types of waveguides have negligible propagation losses (to within experimental uncertainty) for light injected with focal ratios >8, which corresponds to the cutoff of the waveguides. We also show that right below cutoff, there is a narrow region where the injected focal ratio is preserved (to within experimental uncertainty) at the output. Finally, we outline the major application of these highly efficient waveguides; in a device that is used to reformat the light in the focal plane of a telescope to a slit, in order to feed a diffraction-limited spectrograph.

Femtosecond Chirped Pulse Oscillators for high-speed Photonic device fabrication

The invention of the Chirped Pulse Oscillator (CPO) concept enabled the generation of sub-50 fs laser pulses at MHz repetition rates with an energy approaching the μJ-level directly out of an oscillator. Such laser sources close the gap between low-energy oscillators on the one hand and complex amplifier systems on the other hand and are perfectly suited for high-speed fabrication of Photonic devices with feature sizes down to the sub-micron regime. In this paper we review the latest advances in CPO development and report on our capabilities to utilize those sources to fabricate integrated devices in a variety of passive as well as active materials.

Ultrafast laser direct-write inscription of monolithic fibre and waveguide lasers

The use of a scanned femtosecond laser focus to create optical waveguide devices is an established and powerful technique [1] with applications in sensing and quantum information [2]. Using a sub-surface focussed femtosecond laser, a dielectric material can be modified at a highly localised point without surrounding material modification. By controlling the laser-photonic material interactions and fabrication parameters [3–5], a permanent change in the refractive index of the material can be achieved. Not only can this direct-write technique be carried out rapidly, it is readily compatible with existing fibre systems, it does not require a lithographic mask and it can be conducted in a regular laboratory environment with the minimum of sample preparation.

Femtosecond laser direct-written waveguides in bismuth germanate for spatial resolved radiation detection

We demonstrate direct laser written low loss waveguides in bismuth germanate for sensing applications in high energy physics. We discuss the suitability of waveguide arrays in this material for spatial resolved radiation detection.

Femtosecond Laser Written Bragg Gratings

We report a new technique for adaptive optical laser writing in a wide range of media, a new model for waveguide-Bragg grating erasure and a 3D imaging technique that reveals exquisite details of photonic devices.

Fast Direct Fabrication of Waveguide Bragg Gratings

We identified a narrow processing window to direct write waveguides incorporating Bragg gratings in a single process step. We utilised a 5.1 MHz femtosecond laser combined with a Pockels cell to modulate the pulse energy.

Single-stage Pulse Compression and High-Energy Supercontinuum generation from a Chirped-pulse oscillator

We demonstrate the generation of high-energy supercontinuum pulses by coupling the uncompressed pulses of a Ti:sapphire Chirped-pulse oscillator into a microstructure fibre which features a highly anomalous dispersion at the centre wavelength of the laser.