Ring-core fiber with negative curvature structure supporting orbital angular momentum modes

Abstract

Compared to glass walls with a positive curvature, those with a negative curvature have been proven to have stronger confinement of light. Therefore, we change the multi-layered air holes in a photonic crystal fiber into several negative curvature tubes. As a result, the confinement medium is shifted from a low-index cladding material into a special structure. The theoretical analysis shows that each vector eigenmode has a corresponding threshold value for the outer tube thickness. It means that we can confine the target modes and filter the unnecessary modes by shifting the outer tube thickness. After substantial investigation on this fiber, we obtain the appropriate values for each structural parameter and then fabricate this negative curvature ring-core fiber under the guidance of the simulation results. Firstly, we draw the central cane under vacuum condition, then stack the cane and six capillaries to form the preform, and finally draw the ring-core fiber by using vacuumization method. The fiber test experiment indicates that the fiber length should be at least 15 m∼20 m to form the donut facula, and the tested losses of OAM +1,1 , OAM +2,1 , OAM +3,1 , and OAM +4,1 are 0.30 dB/m, 0.36 dB/m, 0.37 dB/m, and 0.42 dB/m, respectively.

Transmission and Generation of Orbital ANGULAR Momentum Modes in Optical Fibers

“…Enlightened by the negative-curvature fibers, our group studied a new kind of negativecurvature ring-core fiber (NC-RCF). The loss comparison between the multi-layered hollowcore fiber and negative-curvature hollow-core fiber is shown in Figure 10a [39]. When the number of air-silica interfaces is the same (four layers), the confinement loss of negativecurvature hollow-core fiber is much lower.…”

“…Our group also attaches great importance to the study of OAM-related optical fibers and fiber devices. A kind of microstructure RCF employing negative curvature cladding structures was proposed and fabricated [39,40]. Under experimental test, it showed low transmission loss of the first-order OAM modes with the value of 0.095 dB/m.…”

Ring fiber made of silica glass for transmitting OAM modes

“…1 (left). Its creation was based on the already known designs of the ring fiber with an air cavity inside the core and a solid-state cladding [2] and the ring fiber created on the basis of a hollow core fiber with a negative curvature of the core-cladding boundary [4]. When creating it, the fact was taken into account that the greatest stability of the OAM modes during propagation and the greatest difference in the values of effective refractive index Neff for the fiber vector modes is achieved with an increase in the radius of the core of the ring fiber and with the greatest value of the refractive index contrast between the core and the cladding [2].…”

“…When creating it, the fact was taken into account that the greatest stability of the OAM modes during propagation and the greatest difference in the values of effective refractive index Neff for the fiber vector modes is achieved with an increase in the radius of the core of the ring fiber and with the greatest value of the refractive index contrast between the core and the cladding [2]. Based on the known literature data [2,4], the ring core fiber was designed with the air cavity diameter inside the ring of 30 μm, the thickness of the core wall ring of 1.55 μm and with a smaller thickness of the jumpers attaching it to the support pipe. In this case, we obtained 12 eigenmodes of the ring fiber with one maximum of the electric field in the radial direction in the core wall at a wavelength of 1.55 μm and with losses of the order of 1-2 dB/km (Fig.…”

Кольцевой Световод Из Кварцевого Стекла Для Передачи ОАМ Мод

“…1(левый). За основу при его создании были взяты уже известные конструкции кольцевого световода с воздушной полостью внутри сердцевины и твердотельной оболочкой [2] и кольцевого световода, созданного на основе полого световода с отрицательной кривизной границы сердцевина -оболочка [4]. При его создании был принят во внимание тот факт, что наибольшая стабильность ОАМ мод при распространении и наибольшая разность по значениям neff для векторных мод световода достигается при увеличении радиуса сердцевины кольцевого световода и при наиболее большом значении контраста между показателем преломления сердцевины и показателем преломления оболочки [2].…”