Stable orbital angular momentum mode generator based on helical long-period fiber grating

• Published in: Optical fiber technology 2022-10, Vol.73, p.103019, Article 103019
• Main Authors: Ma, Chao, Wang, Donghui, Deng, Hongchang, Yuan, Libo
• Format: Article
• Language: English
• Subjects: Double-clad fiber; Helical long-period fiber grating; Orbital angular momentum mode generator
• ISSN: 1068-5200; 1095-9912
• DOI: 10.1016/j.yofte.2022.103019

•A stable orbital angular momentum mode generator was fabricated by twisting a double-clad fiber with laser heating technology.•The proposed grating can directly generate the orbital angular momentum mode by coupling the light wave into the inner cladding mode.•The generated mode is more resistant to external interference, especially in terms of strain and surrounding refractive index. We developed a helical long-period fiber grating (HLPG), which was formed by twisting step-index double-clad fiber (SDF) under the irradiation of a CO2 laser, and can generate stable orbital angular momentum (OAM) mode. The mode coupling and transmission characteristics of the SDF-HLPG were investigated both theoretically and experimentally. The results prove that this grating can couple the light wave into the inner cladding mode of the SDF, and directly generate OAM mode. Subsequently, the tolerance of the SDF-HLPG to environmental disturbance was also evaluated. The OAM mode has low sensitivities to mechanical torsion and bending, and has almost no responses to strain and surrounding refractive index. This indicates that the SDF provides a channel for the OAM mode to avoid high external interference. Therefore, this kind of SDF-HLPG has the potential for communication applications.