Abstract:Spatial division multiplexed optical transmission over a multi-ring-core orbital angular momentum (OAM) fibre is reported for the first time. The seven cores in the fibre each supports OAM modes belonging to mode groups (MGs) of topological charge |l| = 0–4. The MGs of |l| = 1–4 each contains four near-degenerate OAM modes that carry the combinations of opposite orbital and spin angular momenta. The weak coupling between these higher-order MGs as well as between the cores enables the simultaneous transmission … Show more
“…7 , to precisely generate one specific OAM mode in each core of the 7-core RCF. The principle of the coupling scheme can be found in the paper 41 and the detailed parametres are listed in Supplement S 12 . Fig.…”
Space-division multiplexing (SDM), as a main candidate for future ultra-high capacity fibre-optic communications, needs to address limitations to its scalability imposed by computation-intensive multi-input multi-output (MIMO) digital signal processing (DSP) required to eliminate the crosstalk caused by optical coupling between multiplexed spatial channels. By exploiting the unique propagation characteristics of orbital angular momentum (OAM) modes in ring core fibres (RCFs), a system that combines SDM and C + L band dense wavelength-division multiplexing (DWDM) in a 34 km 7-core RCF is demonstrated to transport a total of 24960 channels with a raw (net) capacity of 1.223 (1.02) Peta-bit s−1 (Pbps) and a spectral efficiency of 156.8 (130.7) bit s−1 Hz−1. Remarkably for such a high channel count, the system only uses fixed-size 4 × 4 MIMO DSP modules with no more than 25 time-domain taps. Such ultra-low MIMO complexity is enabled by the simultaneous weak coupling among fibre cores and amongst non-degenerate OAM mode groups within each core that have a fixed number of 4 modes. These results take the capacity of OAM-based fibre-optic communications links over the 1 Pbps milestone for the first time. They also simultaneously represent the lowest MIMO complexity and the 2nd smallest fibre cladding diameter amongst reported few-mode multicore-fibre (FM-MCF) SDM systems of >1 Pbps capacity. We believe these results represent a major step forward in SDM transmission, as they manifest the significant potentials for further up-scaling the capacity per optical fibre whilst keeping MIMO processing to an ultra-low complexity level and in a modularly expandable fashion.
“…7 , to precisely generate one specific OAM mode in each core of the 7-core RCF. The principle of the coupling scheme can be found in the paper 41 and the detailed parametres are listed in Supplement S 12 . Fig.…”
Space-division multiplexing (SDM), as a main candidate for future ultra-high capacity fibre-optic communications, needs to address limitations to its scalability imposed by computation-intensive multi-input multi-output (MIMO) digital signal processing (DSP) required to eliminate the crosstalk caused by optical coupling between multiplexed spatial channels. By exploiting the unique propagation characteristics of orbital angular momentum (OAM) modes in ring core fibres (RCFs), a system that combines SDM and C + L band dense wavelength-division multiplexing (DWDM) in a 34 km 7-core RCF is demonstrated to transport a total of 24960 channels with a raw (net) capacity of 1.223 (1.02) Peta-bit s−1 (Pbps) and a spectral efficiency of 156.8 (130.7) bit s−1 Hz−1. Remarkably for such a high channel count, the system only uses fixed-size 4 × 4 MIMO DSP modules with no more than 25 time-domain taps. Such ultra-low MIMO complexity is enabled by the simultaneous weak coupling among fibre cores and amongst non-degenerate OAM mode groups within each core that have a fixed number of 4 modes. These results take the capacity of OAM-based fibre-optic communications links over the 1 Pbps milestone for the first time. They also simultaneously represent the lowest MIMO complexity and the 2nd smallest fibre cladding diameter amongst reported few-mode multicore-fibre (FM-MCF) SDM systems of >1 Pbps capacity. We believe these results represent a major step forward in SDM transmission, as they manifest the significant potentials for further up-scaling the capacity per optical fibre whilst keeping MIMO processing to an ultra-low complexity level and in a modularly expandable fashion.
“…However, the designed fiber has high manufacturing precision requirement and doping concentrations is higher than those of currently commercialized fibers. Potential preparation methods including plasma chemical vapor deposition (PCVD) 59 and the extrusion of glass discs 60 could be feasible. Furthermore, the mode coupling and stability of the fiber are subject to environmental and mechanical strains, necessitating consideration of compensation mechanisms during fiber drawing and practical application.…”
Beams carrying orbital angular momentum (OAM) have exhibited significant potential across various fields, such as metrology, image coding, and optical communications. High-performance broadband coherent OAM sources are critical to the operation of optical systems. The emission of dispersive waves facilitates the efficient transfer of energy to distant spectral domains while preserving the coherence among the generated frequency components. Light sources that maintain consistency over a wide range can increase the efficiency of optical communication systems and improve the measurement accuracy in imaging and metrology. In this work, we propose a germanium-doped double ring-core fiber for five OAM dispersive waves (DWs) generation. The OAM1,1 mode supported in the fiber exhibits three zero-dispersion wavelengths (ZDWs) located at 1275, 1720 and 2325 nm. When pumped under normal dispersion, the output spectrum undergoes broadening and exhibits five DWs, situated around 955, 1120, 1450, 2795 and 2965 nm, respectively. Concomitant with blue-shifted and red-shifted dispersive waves, the spectrum spans from 895 to 3050 nm with high coherence. The effect of the fiber and input pulse parameters on DWs generation, as well as the underlying dynamics of the dispersive wave generation process, are discussed. As expected, the number and location of DWs generated in the output spectrum have agreement with the prediction of the phase-matching condition. Overall, this multiple DWs generation method in the proposed fiber paves the way for developing efficient and coherent OAM light sources in fiber-based optical systems.
“…A potential method to produce the proposed fiber is using plasma chemical vapor deposition (PCVD) and fiber drawing instruments. [ 47 ] Another alternative method to fabricate ring‐core fiber is extruding alternately stacked high‐ and low‐index glass discs through a circular aperture, where the thickness of the high‐index rings can be down to 0.3 μm. [ 48 ] The background cladding material of the designed fiber is pure silica, which has been extensively applied in optical fiber manufacturing for its excellent physical properties and mature manufacturing process.…”
With the exponential growth of the carrying information in optical communication systems, tremendous efforts have been made to further boost the channel capacity and spectral efficiency. Multiplexing is one of the most efficient methods, which contains optical time-division multiplexing (OTDM), [1][2][3] wavelength division multiplexing (WDM), [4][5][6] and space-division multiplexing (SDM) techniques. [7][8][9] SDM simultaneously transmits multiple independent data channels in multicore or multimode fiber. Particularly, if the channels are orthogonal to each other, the different beams can be efficiently (de-)multiplexed and propagate with little inherent crosstalk, which could tremendously improve the information transmission capacity. [10] L. Allen et al. reported that helically phased beams featured by an azimuthal phase term exp(ilφ) carry an orbital angular momentum (OAM) of lℏ per photon, where l is the topological charge, φ represents the azimuthal angle, and ℏ denotes the Plank's constant h divided by 2п. [11] OAM theoretically has an infinite quantity of intrinsic orthogonality modes with varied topological charges, thus having the potential to provide a great amount of independent channels for the SDM system. [12][13][14][15][16] The phase front of beams carrying OAM modes twists along the transmission path, which leads to an annular intensity distribution. It has attracted extensive attention for various applications in optical tweezers, [17,18] sensing, [19,20] and communications in the classical [21,22] and quantum regimes. [23] Research into OAM multiplexing for communication originated from free-space communication systems. [24,25] However, the interferences from ambient microparticles
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