Mode Coupling in Few-Mode Fibers Induced by Mechanical Stress

Abstract

We investigate mode coupling in few-mode fibers induced by homogeneously and periodically applied mechanical stress. To view the power transfer between individual modes, a modal decomposition is performed at the end of the fiber using computer-generated holograms. Coupling between polarization and angular degenerated modes as well as between nondegenerated modes is confirmed experimentally and coupling parameters are inferred. The presented studies pave the way to detailed investigations of mode coupling in mode-multiplexed telecommunication systems and high-power high beam quality fiber lasers.

Distributed Transverse Stress Sensor Based on Mode Coupling in Weakly-Coupled FMF

“…In this paper, we propose a novel DTSS mechanism based on linearly-polarized (LP) mode coupling effect under transverse stress in weakly-coupled few-mode fibers (FMFs), which is quite different with previous studies for DOFSs over FMFs such as monitoring multiple parameters simultaneously with multiple LP modes or improving system performance utilizing transmission characteristics of FMFs [15]. There also have been some studies for stress measurement utilizing mode coupling effect [16][17][18][19], but all of them are based on fiber gratings, which is only suitable for single or multiple-point measurements instead of distributed sensing. In the proposed scheme, multiple LP modes in the FMF could be considered as independent spatial channels because of ultralow inherent modal crosstalk, while a transverse stress may induce quantifiable and spatiallyyangyupku@pku.edu.cn; zuomq@pku.edu.cn; cjyx@pku.edu.cn; yuyanggao@pku.edu.cn; yujinyi@pku.edu.cn; chenzy@pku.edu.cn; heyongqi@pku.edu.cn; juhao_li@pku.edu.cn).…”

“…We adopt a simplified fiber deformation model for a twomode case to investigate the relation between coupled mode power and applied transverse stress [17]. Assuming that the step-index circular-core (SI-CC) TMF removed of the coating is subjected to a small transverse stress in the y-axis, the fiber core will suffer from the slight effects including birefringence, elliptical deformation, and displacement perturbation [17], among which only displacement perturbation is important because coupling can only occur between two LP modes when their azimuthal orders differ by ±2 for elliptical deformation and that is dissatisfied in TMFs [22], and birefringence can only cause coupling between the polarization components of one mode and we only consider the superposition of them [22]. The core cross-section under displacement in the stress direction is shown in Fig.…”

Spectral Characteristics of Square-Wave-Modulated Type II Long-Period Fiber Gratings Inscribed by a Femtosecond Laser

“…Up to now, many methods have been utilized to fabricate LPFGs, including mechanical stress [ 13 , 14 ], electrical arc [ 15 , 16 ], CO 2 laser [ 2 , 17 ], femtosecond laser [ 18 , 19 ], and so on. Exerting periodical mechanical stress on a few-mode fiber could induce coupling between two copropagating core-guided modes, but such LPFGs could persist when mechanical stress was released [ 20 ]. A periodic taped structure induced by an electrical arc or structuring a fiber with a CO 2 laser could also realize the fabrication of LPFGs [ 21 , 22 , 23 , 24 ], but these LPFGs were relatively fragile because a few sections of the fiber became thinner just like microfibers [ 25 , 26 , 27 ].…”

Dual-Core Transversally Chirped Microstructured Optical Fiber for Mode-Converter Device and Sensing Application

“…This technique is known as spatial division multiplexing (SDM) and can be implemented in two different schemes. Intuitively, in the multi-core fiber (MCF) scheme, each core acts as an independent channel for sending the information [1], while in the modal division multiplexing (MDM) scheme, each mode is considered an independent transmission channel as in singlemode fiber [3,4]; hence, the key is to convert the fundamental fiber modes to higher order modes. As the processing systems are not prepared to work with hundreds of modes, in the MDM scheme it is preferred to work with few modes fibers (FMFs) [3,4].…”

“…Intuitively, in the multi-core fiber (MCF) scheme, each core acts as an independent channel for sending the information [1], while in the modal division multiplexing (MDM) scheme, each mode is considered an independent transmission channel as in singlemode fiber [3,4]; hence, the key is to convert the fundamental fiber modes to higher order modes. As the processing systems are not prepared to work with hundreds of modes, in the MDM scheme it is preferred to work with few modes fibers (FMFs) [3,4]. As with any new technology, emerging SDM systems require the development of new components such as optical fibers that support multiple spatial modes and integrated mode converters to control propagating modes, spatial mode multiplexers (SMUXs) and demultiplexers (SDEMUXs).…”