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Point-by-point inscription of phase-shifted fiber Bragg gratings with electro-optic amplitude modulated femtosecond laser pulses

: Burgmeier, J.; Waltermann, C.; Flachenecker, G.; Schade, W.


Optics Letters 39 (2014), Nr.3, S.540-543
ISSN: 0146-9592
Fraunhofer HHI ()

Femtosecond laser pulses were used for the direct point-by-point inscription of phase-shifted fiber Bragg gratings (FBGs) in a single fabrication step without postprocessing. An electro-optic amplitude modulator is used in the setup to generate a defined delay between two identical laser pulse trains for the grating inscription. The grating structure with a central phase shift is formed by focusing the modulated laser pulses into the core of a fiber, while the fiber is translated with a constant velocity. The induced phase shift leads to a narrow transmission band with a bandwidth considerably below 10 pm within the stop band of the FBG. The inscribed FBGs show a birefringence of 3.9 x 10(-5) whereas their temperature and strain sensitivities are 10.4 pm/K and 1.4 pm/mu strain, respectively. The fabrication process is fast and offers a high grade of flexibility for the control of all grating parameters.