Localized tilted fiber Bragg gratings induced by femtosecond laser line-by-line inscription

Localized tilted fiber Bragg gratings (TFBGs) with low insertion loss are reported. A series of second-order TFBGs with tilt angles of 0 degrees, 7 degrees, 14 degrees, and 21 degrees was inscribed line by line directly in a single-mode fiber. For the 7 degrees TFBG, the Bragg resonance was 2.4 dB at 1550 nm, and the maximum cladding-mode resonance reached 24.6 dB with an insertion loss of 0.8 dB, the same level as that for TFBGs fabricated by the phase-mask method. The range in cladding-mode resonance for the TFBGs obtained was wider than 170 nm with an intensity exceeding 20 dB. Combined with microscope images, the formation of these localized TFBGs and their spectral performance are discussed. The effect of an inscription offset along the y-axis direction was further investigated. With increasing offset, the intensity of the cladding-mode resonance dropped rapidly. The refractive index response sensitivity of the 7 degrees TFBG was measured at 507.54 nm/RIU. (C) 2021 Optical Society of America

Automated summary

This study reports the fabrication of localized tilted fiber Bragg gratings (TFBGs) with low insertion loss and investigates their spectral performance. TFBGs with different tilt angles were inscribed directly in a single-mode fiber, showing wide cladding-mode resonance range and high refractive index response sensitivity. The impact of inscription offset on the TFBG intensity was also studied.