Mode-Division-Multiplexing of Multiple Bessel-Gaussian Beams Carrying Orbital-Angular-Momentum for Obstruction-Tolerant Free-Space Optical and Millimetre-Wave Communication Links

Abstract

We experimentally investigate the potential of using ‘self-healing’ Bessel-Gaussian beams carrying orbital-angular-momentum to overcome limitations in obstructed free-space optical and 28-GHz millimetre-wave communication links. We multiplex and transmit two beams (l = +1 and +3) over 1.4 metres in both the optical and millimetre-wave domains. Each optical beam carried 50-Gbaud quadrature-phase-shift-keyed data, and each millimetre-wave beam carried 1-Gbaud 16-quadrature-amplitude-modulated data. In both types of links, opaque disks of different sizes are used to obstruct the beams at different transverse positions. We observe self-healing after the obstructions, and assess crosstalk and power penalty when data is transmitted. Moreover, we show that Bessel-Gaussian orbital-angular-momentum beams are more tolerant to obstructions than non-Bessel orbital-angular-momentum beams. For example, when obstructions that are 1 and 0.44 the size of the l = +1 beam, are placed at beam centre, optical and millimetre-wave Bessel-Gaussian beams show ~6 dB and ~8 dB reduction in crosstalk, respectively.

Orbital Angular Momentum Waves: Generation, Detection, and Emerging Applications

“…With OAM-DM, the on and off states of each OAM mode can represent either a "1" or a "0", so that the two-bit set of {00, 01, 10, 11} can be mapped on the multiplexed modes {00, 0 1 , 0 0, 0 1 }. Using this idea, [99] OAM-SK [69], [96], [97], [107] OAM-DM [73], [98]- [106], [108], [109] PDM [98], [101], [102] WDM [98], [102], [104] Free-space optical OAM communications Optical OAM fiber communications Radio OAM communications…”

“…By multiplexing LG beams with different p, the system capacity and transmission rate can be improved. In addition to LG beams, Bessel beams with non-diffractive properties, because of their self-healing properties after encountering an obstruction, also have a great application potential in free-space optical communications [106]- [108]. Perfect vortex beams, obtained by the Fourier Fig.…”

Roadmap on structured light

“…It might be important to explore beams whose phase and amplitude could survive a partial beam obstruction. At present, 'propagation-invariant' structured Bessel beams have shown promise, but only over limited distances [194]. Owing to their propagation-invariance property, Bessel beams are able to 'self-heal', i.e.reconstruct their complex field when subjected to an obstruction or distortion.…”

Recent advances in high-capacity free-space optical and radio-frequency communications using orbital angular momentum multiplexing

“…rain, fog and obstructions) remains challenging. It would be important to investigate the system performance under these conditions and develop potential techniques to combat the degradation effects [70]. 3.…”

“…The effects of other channel conditions beyond pure LOS free-space propagation were also investigated recently. Initial studies on the effects of multi-path and object obstructions have been performed [70,71]. As shown in [71], a specular reflectioninduced multi-path distorts received OAM beams and causes intra-channel and inter-channel crosstalk, resulting in significant system performance degradations.…”