Orbital angular momentum modes do not increase the channel capacity in communication links

Abstract

The orbital momentum of optical or radio waves can be used as a degree of freedom to transmit information. However, mainly for technical reasons, this degree of freedom has not been widely used in communication channels. The question is if this degree of freedom opens up a new, hitherto unused 'communication windowʼsupporting 'an infinite number of channels in a given, fixed bandwidth' in free space communication as has been claimed? We answer this question in the negative by showing that on the fundamental level, the mode density, and thus room for mode multiplexing, is the same for this degree of freedom as for sets of modes lacking angular momentum. In addition we show that modes with angular momentum are unsuitable for broadcasting applications due to excessive crosstalk or a poor signal-to-noise ratio.

Orbital Angular Momentum Generation and Detection by Geometric-Phase Based Metasurfaces

“…Different OAM states have been used to encode information in communications to enhance the channel capacity, both in free space [2][3][4][5][6][7][8][9] and optical fibers [10]. The main problem of practical application of OAM in communications is the significant crosstalk between OAM modes [11,12]. The spatial-dependence and divergency nature of OAM-carrying waves result in the their vulnerability to the atmosphere [13,14] and limited power received at the receiver side [15].…”

Roadmap on structured light

“…Of course, experimental studies can prove inconclusive, whilst others may lead to unexpected disputes over interpretation,most notably the question of whether genuinely useful enhancements of data transmission rates can be achieved using OAM-endowed radio waves [18].…”

Light, the universe and everything – 12 Herculean tasks for quantum cowboys and black diamond skiers

“…This degree of freedom is independent of polarization or wavelength and hence offers a method to increase further the information content of the link. There has recently been considerable interest in exploiting this spatial capability, and there has been considerable debate regarding the best strategy to adopt (124), (125), (126), (127). Various proposals have been made regarding encoding in plane waves, in Laguerre-Gaussian modes (as illustrated in Figure 23), in Hermite-Gaussian (HG) modes, more complex patterns (known as photonic lanterns) or in an entirely different strategy in which the available telescope aperture is simply divided into multiple sub-apertures.…”