Fiber Bragg grating inscription combining DUV sub-picosecond laser pulses and two-beam interferometry

Abstract

The combination of fiber Bragg grating inscription with femtosecond laser sources and the usage of the Talbot interferometer setup not only gives access to the fabrication of Bragg gratings in new types of materials but also allows, at the same time, to keep the high flexibility of an interferometric setup in choosing the Bragg grating wavelength. Since the spatial and temporal coherence properties of the femtosecond laser source differ strongly from those of conventional laser sources, specific limits and tolerances in the interferometric setup have to be considered. Such limits are investigated on the basis of an analytical ray tracing model. The results are applied to tolerance measurements of fiber Bragg grating reflections recorded with a DUV sub-picosecond laser source at 262 nm. Additionally we demonstrate the wavelength versatility of the two-beam interferometer setup for femtosecond inscription over a 40 nm wavelength band. Inscription experiments in Al/Yb doped silica glasses are demonstrated as a prove for the access to non-photosensitive fibers.

Transverse propagation of ultraviolet and infrared femtosecond laser pulses in photonic crystal fibers

“…Owing to the high peak power in short laser pulses, the refractive index change can even be induced in non-photosensitive fibers via one or more multi-photon absorption processes [4]. Harmonics of a Ti:Sapphire laser at UV 267nm [5] and IR 800nm [6] are commonly used for that purpose. In the first case the refractive index change is induced by a two photon absorption process, while in the latter it involves a five photon absorption process [4].…”

Femtosecond pulse written fiber gratings: a new avenue to integrated fiber technology

“…In most cases, a chirped or regeneratively amplified Ti:Sapphire laser system is used that typically provides 50-150 fs pulses at a repetition rate of 1 kHz at 800 nm (e. g. [43][44][45][46][47][48]). Frequency doubling or quadrupling is employed, whereas inscription wavelengths in the VIS or UV are desired to realize shorter periods [40,[49][50][51][52][53]. Typically, the output beam is attenuated with a half-wave-plate beam-splitter combination, since pulse energies of the order of 1 μJ suffice for point-wise inscription with high-NA objectives.…”

“…The transition from UV lasers to the use of ultrashort laser systems is nontrivial because of the short spatial coherence length of femtosecond pulses (approximately 30 microns for a 100 fs pulse). Although not impossible, free beam interference setups with long optical paths require very careful alignment [49,50].…”

Trends in Bragg Grating Technology for Optical Fiber Sensor Applications

“…Usually, such fibers do not require doping of the fiber core for achieving guiding properties. Therefore the question arises how to make FBGs in such fibers [9,10,11].…”