Femtosecond laser plane-by-plane inscription of ultra-short DBR fiber lasers for sensing applications

We propose and demonstrate the inscription of ultra-short distributed Bragg reflector fiber lasers (DBR-FLs) in Er/Yb co-doped fiber (EYDF) using a femtosecond laser plane-by-plane (Pl-b-Pl) method. By integrating the spherical aberration (SA) with a laser 2D scanning process, a planar refractive index modification (RIM) region can be induced in the fiber core. Thanks to the Pl-b-Pl inscription, a high-quality fiber Bragg grating (FBG) in an EYDF is produced, exhibiting a grating strength exceeding 40 dB and an insertion loss of 0.1 dB. Subsequently, an ultra-short DBR-FL with an entire length of 7.3 mm is fabricated by the Pl-b-Pl inscription. The Pl-b-Pl ultra-short DBR-FL exhibits an improved slope efficiency of 0.7% compared with the DBR-FLs fabricated using another two direct-writing techniques, namely line-by-line (LbL) and and single-polarization radiation with a narrow linewidth (9.4 kHz) and a low relative intensity noise (-105.8 dB/Hz). Moreover, a wavelength-division-multiplexed array consisting of eight ultra-short DBR-FLs with distinct lasing wavelengths is successfully created. The Pl-b-Pl ultrashort DBR-FLs with excellent output performances offer significant potential for high-sensitivity sensing applications requiring high spatial resolution.