The use of ultrashort laser pulses for fiber grating inscription has many advantages in comparison to continuous wave and long pulse lasers. The most important one is that it allows inscription in nonphotosensitive fiber materials. In this paper the principal inscription techniques and the physical properties of femtosecond (fs) pulse written in-fiber gratings are reviewed. The role of focusing and order walk-off on the inscribed structures is emphasized. A fs pulse written fiber Bragg grating (FBG) also has a unique coupling behavior, due to a refractive index change that is independent from the fiber geometry. Selected applications of such gratings for sensing and fiber lasers are discussed.

We demonstrate apodized fiber Bragg gratings inscribed with a point-by-point technique. We tailor the grating phase and coupling amplitude through precise control over the longitudinal and transverse position of each laser-inscribed modification. This method of apodization is facilitated by the highlylocalized, high-contrast modifications generated by focussed IR femtosecond laser inscription. Our technique provides a simple method for the design and implementation of point-by-point fiber Bragg gratings with complex apodization profiles. The femtosecond laser-material interaction, which relies upon nonlinear processes, enables grating inscription into almost any fiber material without requiring photosensitivity [10]. A further advantage of this technique is the hightemperature stability of the gratings due to the structural modification of the glass [11].The side-band reflection peaks typical of uniform FBG spectra can be problematic for many applications, causing crosstalk in WDM systems, instabilities in Q-switched fiber lasers and linewidth broadening in high power fiber lasers [2,12].To eliminate these unwanted side-bands it is necessary to fabricate gratings with an apodized profile, where the grating strength varies as a function of length and is typically weaker at both ends of the grating. Various techniques have been developed for fabricating apodized FBGs using holographic inscription, such as phase-mask dithering and the use of phase-masks with varying diffraction efficiency [13,14]; however, these methods are specific to holographic inscription techniques and do not translate directly to PbP inscription. To fabricate apodized PbP gratings one might consider modulating the laser pulse energy during inscription; however, this is likely to be very challenging due to the highlynonlinear laser-material interaction processes.In this letter we report apodized fibre Bragg gratings inscribed using a point-by-point technique. Our apodization approach is to tailor the local coupling amplitude of the gratings through precise control over the transverse position of 1

We present volume Bragg gratings (VBGs) with a period of 1.075 µm inscribed in fused silica using a femtosecond laser and a phasemask. The femtosecond-inscribed VBGs can be used as reflecting elements with reflectivities of about 80% for a 1-mm-long grating. Due to the nonsinusoidal refractive-index shape, higher order Bragg resonances up to the 7th reflection order could be measured. Therefore, the Bragg gratings also reflect light in the visiblewavelength range

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We demonstrate a new fiber based concept to filter azimuthally or radially polarized light. This concept is based on the lifting of the modal degeneracy that takes place in high numerical aperture fibers. In such fibers, the radially and azimuthally polarized modes can be spectrally separated using a fiber Bragg grating. As a proof of principle, we filter azimuthally polarized light in a commercially available fiber in which a fiber Bragg grating has been written by a femtosecond pulsed laser.