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- Title
Spectral Characteristics of Square-Wave-Modulated Type II Long-Period Fiber Gratings Inscribed by a Femtosecond Laser.
- Authors
Zhao, Xiaofan; Li, Hongye; Rao, Binyu; Wang, Meng; Wu, Baiyi; Wang, Zefeng; Kalli, Kyriacos
- Abstract
We study here the spectral characteristics of square-wave-modulated type II long-period fiber gratings (LPFGs) inscribed by a femtosecond laser. Both theoretical and experimental results indicate that higher-order harmonics refractive index (RI) modulation commonly exists together with the fundamental harmonic RI modulation in such LPFGs, and the duty cycle of a square wave has a great influence on the number and amplitudes of higher-order harmonics. A linear increase in the duty cycle in a series of square wave pulses will induce another LPFG with a minor difference in periods, which is useful for expanding the bandwidth of LPFGs. We also propose a method to reduce insertion loss by fabricating type II LPFGs without higher-order harmonic resonances. This work intensifies our comprehension of type II fiber gratings with which novel optical fiber sensors can be fabricated.
- Subjects
OPTICAL fiber detectors; FIBER lasers; SQUARE waves; INSERTION loss (Telecommunication); REFRACTIVE index; FIBERS; PLASTIC optical fibers; FEMTOSECOND lasers
- Publication
Sensors (14248220), 2021, Vol 21, Issue 9, p3278
- ISSN
1424-8220
- Publication type
Article
- DOI
10.3390/s21093278