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We present a femtosecond laser written, apodized chirped fiber Bragg grating (acFBG) used for dispersion control inside picosecond all-fiber lasers. A fiber fixation setup enables a plane-by-plane (pbp) written acFBG in a standard, polarization-maintaining fiber by applying a beam-slit configuration. The spectral specifications of the acFBG are examined in detail, and the grating is validated inside a mode-locked fiber laser oscillator. This letter provides a route to the fast prototyping of acFBGs with customized parameters for use as dispersion compensating elements inside ultrafast all-fiber lasers.

Hydrogen has attracted much attention as a source of clean and sustainable energy. However, one of the drawbacks of handling hydrogen as a power source is its volatility and flammability. Moreover, hydrogen leakages in gas pipelines or tanks can generate highly explosive gas mixtures in air, if the hydrogen concentrations exceed 4 %. Therefore, in order to increase the security, monitoring of hydrogen concentrations in hydrogen infrastructures is mandatory. Remote sensing systems using passive fiber optical sensors are predestined for these kinds of applications. In this paper, a sensor based on evanescent field fiber Bragg grating (FBG), coated with palladium (Pd) nanoparticles is proposed. Thereby, the intensity change of the sensor signal correlates with the hydrogen concentration. The detection range of the sensor is between 0.5% to 5% H2 in nitrogen or synthetic air atmosphere and therefore shows great potential for the detection of hydrogen leakages below the explosive limit of 4%.

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