Advances on Mode-Coupling Theories, Fabrication Techniques, and Applications of the Helical Long-Period Fiber Gratings: A Review

Abstract

In this paper, we have briefly review the developing history and recent advances made with regard to helical long-period fiber gratings (HLPGs) in three aspects, i.e., the mode-coupling theories, the fabrication techniques, and the applications. It is shown that, due to the intrinsic helicity characteristics, which are especially suitable to control the loss, polarization, and orbit-angular-momentum (OAM) states of the light in optical fiber, HLPGs have recently attracted great research interest and have found various applications, such as the mode-converters, the torsion sensors, the band-rejection filters, wave plates, linear- and circular-light polarizers, and OAM mode generators, etc. It is believed that HLPGs and the HLPGs-based devices would find further applications to not only the fields of optical sensors and optical communication, but also other fields such as ultrahigh precision measurement, quantum optics, and biochemistry, etc.

Properties of off-axis helical long-period fiber gratings

“…CO 2 激光 >1 dB [18] <1 dB [19] 优点: 灵活、高品质; 缺点: 光路调试麻烦、昂贵 氢氧火焰 <1 dB [33] ≈ 1 dB [34] 优点: 加热面积较宽, 加热温度均匀; 缺点: 氢气有一定危险性 二电极电弧放电 >1 dB [25] >1 dB [27] 优点…”

Transmission and Generation of Orbital ANGULAR Momentum Modes in Optical Fibers

“…In addition to OAM modes generators, chiral fiber gratings can also be applied as torsion sensors, band-rejection filters, wave plates and linear-and circular-light polarizers. The mode-coupling theories, fabrication techniques and applications of helical fiber gratings can be found in a detailed and comprehensive review contributed by Zhao Hua and Li Hongpu [80].…”

Mechanically Induced Long-Period Fiber Gratings and Applications

“…Additional advantages are their ease of implementation for both point and quasi-distributed measurements, their adaptability to a wide variety of applications such as those in the oil and gas sectors or electromagnetic environments, and their cost-effectiveness. The intrigue in fiber gratings, which are characterized by a periodic modulation of the refractive index within the core or cladding of a fiber along its direction of propagation, has been widespread among scholars globally [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. These fiber gratings are categorically divided based on their operational principles into two main types: fiber Bragg gratings (FBGs) and long-period fiber gratings (LPFGs).…”