Aiming for suppressing side-mode and spectrum broadening, a slit beam-shaping method and super-Gaussian apodization processing for femtosecond laser point-by-point (PbP) inscription technology of fiber Bragg gratings (FBGs) are reported here. High-quality FBGs, featuring narrow bandwidth of less than 0.3 nm, high reflectivity above 85%, low insertion loss (0.21 dB), and low cladding loss (0.82 dB), were obtained successfully. By a semi-automatic PbP inscription process, an array consisting of six FBGs, exhibiting almost no side-mode peaks with high suppression ability and narrow bandwidth, was fabricated along three independently developed single-mode fibers with an interval of 20 mm.

Ultrashort pulsed Bessel beams with intrinsic nondiffractive character and potential strong excitation confinement down to 100 nm can show a series of advantages over Gaussian beams in fabricating efficient Bragg grating waveguides (BGWs). In this work, we focus on parameter management for the inscription of efficient BGWs using the point-by-point method employing Bessel beams. Due to their high aspect ratio, the resulting one-dimensional void-like structures can section the waveguides and interact efficiently with the optical modes. Effective first-order BGWs with low birefringence can then be fabricated in bulk fused silica. By controlling the size and the relative location of grating voids via the Bessel pulse energy and scan velocities, the resonant behaviors of BGWs can be well regulated. A high value of 34 dB for 8 mm length is achieved. A simple predictive model for BGWs is proposed for analyzing the influences of processing parameters on the performance of BGWs. The technique permits multiplexing several gratings in the same waveguide. Up to eight grating traces were straightforwardly inscribed into the waveguide in a parallel-serial combined mode, forming the multiplex BGWs. As an application, the multiplex BGW sensor with two resonant peaks is proposed and fabricated for improving the reliability of temperature detection.