RESUMO
Orbital angular momentum (OAM) beams with different angular indices l have the potential to greatly increase communication capacity. However, the finite aperture of optical systems limits the value of the angular index. In order to fully use the orthogonal mode channels supported in the fiber for high-capacity communications, we propose extending the radial indices p of OAM modes as an additional multiplexing dimension. In this paper, we introduce spatially discrete multiple phase planes to multiplex the angular and radial OAM modes simultaneously. Due to the orthogonal property of the central symmetric OAM modes, a two-dimensional (2D) input Gaussian beams array can be converted to coaxial OAM modes through Cartesian to log-polar coordinate transformation by inverse design. For a proof-of-concept demonstration, a 10-mode multiplexer for high-order radial OAM modes was designed using five phase planes. The fabricated multiplexer generated high-quality multiplexed OAM modes with a loss of less than 5.4â dB. The multiplexed OAM modes were coupled into a specially designed ring-core fiber by mode-field matching, achieving stable mode transmission in 2â km fiber. The approach provides a scalable technology to increase the number of transmission channels and could lead to the practical applications of OAM multiplexing in communication.
Assuntos
Dispositivos Ópticos , Movimento (Física) , Distribuição NormalRESUMO
The linear polarized (LP) mode multiplexer based on the inverse designed multi-plane light conversion (MPLC) has the advantages of low insertion loss and low mode crosstalk. However, the multiplexer also requires the fabrication and alignment accuracy in experiments, which have not been systematically analyzed. Here, we perform the error tolerance analysis of the MPLC and summarize the design rules for the LP mode multiplexer/demultiplexer. The error tolerances in the fabrication process and experimental demonstration are greatly released with proper parameters of the input/output optical beam waist, the pitch of optical beam array, and the propagation distances between the phase plane. To proof this design rule, we experimentally demonstrate the LP mode multiplexer generating LP01, LP11a, LP11b, LP21 modes and coupling to the few mode fiber, with the insertion loss lower than -5 dB. The LP modes are demultiplexed by MPLC, with the crosstalk of different mode groups lower than -10 dB. LP modes carrying 10 Gbit/s on-off keying signals transmit in a 5 km few mode fiber. The measured bit error rates (BER) curves of the LP01, LP11a, LP21 modes have the power penalties lower than 12 dB.
RESUMO
A parallel bit-interleaved filter-bank multicarrier/offset quadrature amplitude modulation (FBMC/OQAM) security strategy based on four-dimensional chaos is proposed in this paper. After the QAM constellation point distribution is disturbed, the modulated FBMC bits and symbols are interleaved and encrypted to realize the improvement of the FBMC/OQAM system physical layer security performance. The chaotic sequence generated by the four-dimensional hyperchaotic system is optimized and calculated to control the disturbance process, which enhances the performance of the system against illegal malicious attacks. The parallel encryption scheme proposed in this scheme increases the encryption efficiency by 1.43 times; can provide a keyspace of 1090 size, which effectively resists brute force attacks; and improves the physical layer security of the system. The proposed FBMC/OQAM parallel bit interleaved encryption scheme using a 5 km weakly coupled four-mode fiber achieves a 3×10 Gb/s multiple-input multiple-output-free transmission. The experimental results show that this scheme can effectively improve the security performance of the system, and combines the few-mode multiplexing technology with advanced modulation. It is a candidate for the future large-capacity and high-security optical transmission system.
RESUMO
The amount of information is increasing rapidly to reach the capacity limit of single mode fiber. Cylindrical vector beams (CVBs) as the eigenmodes of fiber have been demonstrated to increase the capacity in multiplexing optical communication. As a key component of CVB multiplexing, a sorter based on spin-dependent vortex Dammann grating has advantages of uniform power distribution and compact size. Here, we propose and demonstrate a spin-dependent vortex Dammann grating device that can realize the sorting of multiple CVBs. By a spin-dependent focusing lens, the spin components of the CVBs are selectively focused or derived; therefore, the coaxially incident CVBs are separated effectively. We also experimentally demonstrate the CVB demultiplexing communication enabled by the grating with low channel cross talk satisfying the communication requirement.
RESUMO
With growing data demands, the capacity of the single-mode fiber will reach its limit. Cylindrical vector beams (CVBs) as the eigenmodes of fiber have been demonstrated to increase the capacity in multiplexing optical communication. As a key component of CVB multiplexing, the sorter based on spin-dependent optical geometric transformation has the advantages of high efficiency and a large channel number. However, the demonstrated spatial resolution of the CVB sorter was not sufficient to separate the adjacent CVB orders. Therefore, there were still serious crosstalk issues for the CVB multiplexing channels. Here, we propose and demonstrate the high-resolution CVBs sorting by introducing fan-out structures in the spin-dependent optical geometric transformation. The crosstalk among the CVBs are suppressed compared with the original design. In addition, a cylindrical lens is used to modify the output beams to Gaussian shape. We experimentally demonstrate the sorting of 4 coaxial CVB channels to standard multimode fiber array. In the numerical modeling, we also design the CVB sorter for free space to integrated waveguide array demultiplexing.
