400-Gbit/s QPSK free-space optical communication link based on four-fold multiplexing of Hermite–Gaussian or Laguerre–Gaussian modes by varying both modal indices

Abstract

We experimentally demonstrate the four-fold multiplexing of Hermite-Gaussian (HG) or Laguerre-Gaussian (LG) modes to achieve a 400 Gbit/s quadrature-phase-shift-keyed (QPSK) free-space optical communication link. In this experiment, both modal indices for the HG and LG modes are simultaneously utilized to achieve a larger potential orthogonal modal space. Moreover, we also investigate and compare the effects of aperture size, lateral displacement, and rotation on the system. We measure the degree of performance degradation due to the following: (1) a receiver aperture with a limited size causes power loss and crosstalk for both HG and LG modes; (2) a lateral misalignment between the transmitter and receiver which leads to crosstalk for LG modes, but might not affect HG or HG modes due to axial symmetry; and (3) a rotational misalignment between the transmitter and receiver which causes crosstalk for the HG modes, but does not tend to affect the LG modes due to azimuthal symmetry.

Structured Light in Turbulence

“…IV-B. Subsequently there have been several experimental demonstrations using multiple mode bases and/or indices to increase the resilience to turbulence [133][134][135].…”

Perspective on using multiple orbital-angular-momentum beams for enhanced capacity in free-space optical communication links

“…This onedimensional system can accommodate many orthogonal beams, but a system designer could also use the other beam modal index in order to possibly achieve a larger two-dimensional set of data channels. This two-dimensional approach was shown experimentally for LG and HG beams [6,34]. It is important to note that a significant challenge is the sufficient capture of the beam at the receiver aperture to ensure accurate phase recovery and orthogonality along both indices [34].…”

“…Moreover, since all the beams are in the same frequency band, the system spectral efficiency (i.e., bits/s/Hz) is also increased. These multiplexed orthogonal OAM beams are a form of mode-division multiplexing (MDM), a subset of space-division multiplexing [4][5][6][7].…”

Adaptive Demodulation Technique for Efficiently Detecting Orbital Angular Momentum (OAM) Modes Based on the Improved Convolutional Neural Network

“…For 4-ary OAM system, databases are divided into 4 classes with OAM modes l = 1, 4, 7, 10. Correspondingly, 8, 10 and 16 classes are respectively divided for 8-ary with l = 1, 3, 5, 7, 9, 11, 13, 15, 10-ary with l = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 16-ary OAM system with l = 1, 2, 3, 4, 5,6,7,8,9,10,11,12,13,14,15,16. Meanwhile, to compare performance under the same conditions, each of classes contains 200 images for training and 50 images for testing.…”

“…comprising an azimuthal phase term of exp(ilϕ) have an OAM ofh per photon, where l represents OAM mode, ϕ is azimuthal angle, andh is Plank's constant h divided by 2π [5]- [7]. Benefited from the orthogonality between different OAM modes, the ever-increasing capacity demands in FSO communication system is possible to be significantly improved by OAM division multiplexing (OAM-DM) where the OAM beams are treated as signal carriers [11]- [14], and OAM shift keying (OAM-SK) where each OAM state represents a data symbol, thus the information can be effectively modulated into diverse OAM modes [15]- [18].…”