We present power stable fiber Bragg gratings for linear fiber lasers in the 2 µm wavelength range. The FBG were inscribed through the coating material using infrared femtosecond laser pulses. By improved inscription parameters signal light scattering at the induced structure resulting in heating and shifting of the resonance laser was minimized. A stable linear polarized fiber laser at 2 µm with an output power of 50 W was implemented.
We report on the investigation of realization limits of ultrashort pulse written volume-Bragg-gratings with respect to the laser pulse repetition rate. The VBGs are directly inscribed in fused silica by applying ultrashort laser pulses and the phase mask scanning technique. In order to investigate the scaling potential of the realization process of such gratings by means of higher repetition rates we investigate the fundamentally given material constraints. These investigations will help to pave the way of this realization scheme for VBGs beyond the prototype regime.
We present an investigation of birefringence in ultrashort pulse and phase mask written fiber Bragg gratings (FBGs). Polarization dependent loss and shift of the resonance wavelength as well as the polarization extinction ratio of the FBGs was determined. As expected, we could find a significant dependency connecting the grating strengths and the birefringence . For high reflector gratings, birefringence of up to 10^-5, corresponding to a resonance wavelength shift of up to 10 pm was measured. The results show excellent suitability for usage of the FBGs in linear polarized fiber lasers.
We report on the selective modal control of tailored femtosecond-written long period fiber gratings (LPFG). It is shown that the excitation of higher order cladding modes is possible with strong selectivity and high precision. The coupling behavior of several gratings dependent on the modified core cross section is determined theoretically and confirmed by experiments. Additional mode field measurements proof our concept. The presented tool could pave the way for a completely new branch of fiber integrated devices such as highly efficient transmission gratings or mode converters.
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