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We propose and fabricate a novel ring-core photonic crystal fiber that supports 4 groups of OAM modes with 2.13 × 10^−3 minimum difference of effective indices at 1550 nm. The realized fiber is expected to be a good platform for OAM mode transmission.
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... low intermodal coupling (including the fundamental mode HE 1 1 ). Note that the smallest effective index difference between OAM modes belonging to the same group (Δn eff OAM ) is 2.13 × 10 −3 , which is significantly larger than the value of 4.345 × 10 −4 reported previously 5 . Simulations have been performed over a 750 nm wavelength range. Fig. 3 shows the effective indices of the vector modes of the fiber as a function of the wavelength. It can be seen that all the modes are well separated over the entire bandwidth, the separation increasing with the wavelength. Besides the fact that the potential interest is for applications in the C-band, the fiber could then be used in ...
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Citations
... Traditional multimode fibers, however, cannot be used for high-capacity OAM transmissions because of the unpredictable chromatic dispersion and minor refractive index variations [1]. In order to increase the OAM mode transmission capacity, it has been claimed that specifically developed PCF, twisted air-core fiber, magnetic fluidcontaining fiber, inverse parabolic graded-index fiber and others [2][3][4][5][6][7] have been used. Among these, the ring core PCF has shown the most promising outcome by incorporating a higher refractive guided region and can offer additional freedom to adjust the key matrices of the fiber such as mode purity, loss due to leakage in the cladding, non-linear characteristics, chromatic dispersion and so on. ...
A Deep Learning model will be a promising method for evaluating the parameters of the photonic crystal fiber for transmitting orbital angular modes, which is a challenge for the finite element method (FEM) owing to the FEM's high processing power and time requirements. This paper evaluates multiple Artificial Neural Network (ANN) models built from scratch to map design parameters and optical characteristics: Effective Refractive Index (Neff), Mode Purity (η), Dispersion(D), Effective Area (Aeff) & Nonlinearity (γ) of Ring Core Photonic Crystal Fiber (RC-PCF) employed for OAM transmission with notable precision having mean squared error of 0.02815 requiring significantly less time (approximately 4% of the time required in COMSOL Multiphysics), which can be regarded as a considerable substitute to simulative processes in terms of computational resources and complexity associated with the rigorous modeling through trial and error approach conventional numerical simulation techniques.
... Regarding large capacity OAM transmission, conventional multimode fibers cannot be utilized due to the uncontrolled chromatic dispersion and narrow refractive index differences [6]. Consequently, specially designed photonic crystal fiber (PCF), ring core fiber, twisted air-core fiber have been reported over the years to enhance the OAM mode transmission capacity [7,8,9]. Among these, the PCF can provide more flexibility to optimize the performance parameters for instance confinement loss, non-linearity, dispersion of the fiber, which is characterized as having a micro-structured arrangement of materials in the background material with a different refractive index [10]. ...
... Microstructured fibers and photonic crystal fibers (PCF) in particular have recently attracted significant research interest towards alleviating the above limitations of solid-core fibers by exploiting the significantly increased design freedom afforded by the holey structure and the unique modal properties that emerge [21][22][23][24][25][26]. A particular design of annular-core photonic crystal fiber (AC-PCF) recently proposed the theoretical ability to enforce mono-radial vector-vortex mode guiding while preventing higher-radial order modes over a very large bandwidth [27]. ...
The stable propagation of orbital angular momentum and cylindrical vector beams in a newly designed annular core photonic crystal fiber (AC-PCF) tailored for the broadband single-radial order beam transmission (within the so-called "endlessly mono-radial" guiding regime) is demonstrated for the first time. It is shown that the vector-vortex beams can maintain high mode purities above 18 dB after propagation in the fiber under test over all of the wavelength range from 805 to 845 nm (over 17 THz bandwidth) investigated with the help of a tunable laser and an S-plate for the generation of singular beams in free space. Our results confirm that the AC-PCF is a promising design for the broadband transmission of vector-vortex beams that have potential applications in space-division multiplexing, quantum communications, optical sensing and trapping.
... At present, the fabrication of PCF and the doping process of the ion have been matured. A fiber similar to the C-PCF structure has been drawn and experimented on [36][37][38]. Therefore, it is feasible to manufacture the OAM-EDFA based on C-PCF. ...
Orbital angular momentum (OAM) mode-division multiplexing (MDM) has recently been under intense investigations as a new way to increase the capacity of fiber communication. In this paper, a two-layer Erbium-doped fiber amplifier (EDFA) for an OAM multiplexing system is proposed. The amplifier is based on the circular photonic crystal fiber (C-PCF), which can maintain a stable transmission for 14 OAM modes by a large index difference between the fiber core and the cladding. Further, the two-layer doped region can balance the amplification performance of different modes. The relationship between the performance and the parameters of the amplifier is analyzed numerically to optimize the amplifier design. The optimized amplifier can amplify 18 modes (14 OAM modes) simultaneously over the C-band with a differential mode gain (DMG) lower than 0.1 dB while keeping the modal gain over 23 dB and noise figure below 4 dB. Finally, the fabrication tolerance and feasibility are discussed. The result shows a relatively large fabrication tolerance in the OAM EDFA parameters.
... Therefore, it is necessary to generate fiber structure with a large effective mode field area as far as possible, so as to improve the quality of mode transmission. The area of the effective mode field can be obtained by the following formula [33]: ...
Orbital angular momentum modes in optical fibers have polarization mode dispersion. The relationship between polarization mode dispersion and the birefringence vector can be deduced using an optical fiber dynamic equation. First, a mathematical model was established to formulate mode dispersion caused by stress-induced birefringence. Second, in the stress-induced birefringence simulation model, the finite element method was used to analyze the transmission characteristics of the hollow-core circular photonic crystal fiber. Finally, mode dispersion caused by stress-induced birefringence was obtained using theoretical derivation and simulation analyses. The results showed that the new fiber type has good transmission characteristics and strong stress sensitivity, which provide key theoretical support for optimizing the structural parameters of optical fiber and designing stress sensors.
We propose a photonic crystal fiber with a high refractive index ring, which supports up to 180 orbital angular momentum (OAM) modes without any high order radial modes from 1.5 um to 1.7 um. The finite element method is employed to numerically study the properties of the designed fiber. Further research shows that the refractive index differences of all the eigenmodes are above 210^(-3), which indicates that the corresponding eigenmodes can be well-separated and ensures the stable transmission of OAM modes. In addition, it is quite interesting that the high order radial modes are significantly suppressed via increasing the radius of the cladding in the design, while most of the OAM modes are without phase distortion, which is beneficial for the (de)multiplexing of the OAM modes. Particularly, the mode quality of all the eigenmodes is higher than 94.9% and the chromatic dispersion is flat with minimum value of the dispersion variation is 0.36 ps/(kmnm). Moreover, the designed fiber possesses various advantages such as low nonlinear coefficient (<0.7 /W/km) and confinement loss (on the order between 10^(-12) and 10^(-7) dB/m). The proposed fiber has shown great potential for high capacity OAM mode division multiplexing communications.
