Abstract
To address the severe competition from amplified spontaneous emission (ASE) around 1030 nm in 980 nm ytterbium-doped fiber lasers (YDFL), this paper proposes and experimentally demonstrates a broadband, high-rejection ASE filtering scheme based on a multi-angle complementary cascaded chirped tilted fiber Bragg grating (CTFBG). CTFBGs with tilt angles of 5°, 8.5°, and 8.5° were fabricated on HI1060 fiber using a 248 nm excimer laser phase-mask method. The 3-dB bandwidths of the individual gratings are 19 nm, 38 nm, and 39 nm, with corresponding rejection depths of 5 dB, 7.8 dB, and 11 dB, respectively. After cascading, the rejection depth reaches 18.82 dB and the 3-dB bandwidth expands to 54 nm. When integrated into a 980 nm fiber laser, the cascaded CTFBG achieves an ASE suppression of approximately 18 dB in the 1000–1050 nm range, significantly improving the output spectral purity. This scheme effectively overcomes the inherent trade-off between bandwidth and rejection depth of a single CTFBG, providing a compact, efficient, and easy-to-integrate solution for ASE suppression in short-wavelength YDFLs.