Point-by-point inscription of apodized fiber Bragg gratings

Abstract

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

Low Raman-noise correlated photon-pair generation in a dispersion-engineered chalcogenide As_2S_3 planar waveguide

“…In the far detuned case, a coarse WDM separated the signal and idler, providing 50 dB of pump suppression. A four-port circulator with two narrow-band apodized point-by-point fiber Bragg gratings (FBG) with a 0.3 nm bandwidth [15] filtered the signal photons at 1489.4 nm, while a tunable BPF with 0.5 nm bandwidth was used for the idler photons at 1605.7 nm, together providing an additional 50 dB of out-of-band noise suppression. Photons were detected by InGaAs single-photon detectors (ID210) triggered at 50 MHz with a 1 ns detection window synchronous with the pump laser.…”

Fabricating waveguide Bragg gratings (WBGs) in bulk materials using ultrashort laser pulses

“…Gross et al used a two-step method to achieve Gaussian apodisation by inscribing a PbP WBG diagonally across a prefabricated waveguide [41], a process similar to one previously demonstrated in optical fibre [71]. Increasing the distance between the waveguide centre and the WBG modification decreases κ due to a decrease in overlap between the guided mode and the WBG.…”

Modeling of apodized point-by-point fiber Bragg gratings

“…This can also provide polarization discrimination which has been exploited for fiber laser applications [8]. Recently, a variety of complex grating structures (such as apodized, chirped, phase-shifted and superstructured gratings) have been demonstrated with the PbP technique by exploiting the unique morphology of these RIMs [9,10].…”