Broadband Circular Polarizer Based on Chirped Double-Helix Chiral Fiber Grating

• Published in: Materials Vol. 15; no. 9; p. 3366
• Main Authors: Xue, Linlin, Timoteo, Bras Samuel Malumba, Qiu, Weiwei, Wang, Zhongpeng
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 07.05.2022; MDPI
• Subjects: Bandwidths; Broadband; chiral fiber grating; circular polarizer; Coupled modes; Coupling; Extinction; Gratings (spectra); leaky mode coupling; Leaky modes; Phase matching; Polarizers; Refractivity; circular polarizer; chiral fiber grating; leaky mode coupling; broadband
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma15093366

We propose an all-fiber broadband circular polarizer based on leaky mode coupling and a phase-matched turning point (PMTP) in a chirped, double-helix, chiral, long-period, fiber grating (CLPG). The CLPG was coated with a material in which the refractive index was higher than that of the fiber cladding, enabling the coupling of the core mode to leaky modes to achieve a desired extinction ratio. The complex coupled-mode theory was employed to investigate the coupling mechanism and conditions under which the desired coupling efficiency could be achieved. Moreover, the PMTP in phase-matched curves, which resolved the conflict between the operating bandwidth and the grating pitch range of the CLPG and made a large bandwidth with a small grating pitch possible, was used in the design to achieve a compact structure. Finally, two broadband circular polarizers with an extinction ratio above 25 dB were simulated; one had a bandwidth of over 120 nm and a length of 3.5 cm, and the other had a bandwidth of over 300 nm and a length of 8 cm.