Using the Orbital Angular Momentum of Light Waves for Communications: Potentials and Challenges

Speaker: Prof. Si-Yuan Yu (University of Bristol)

Time and Date: 10:00- , Oct. 26, 2013

Place: Room B415, Building of Computing Centre, Handan Campus

 

 

Abstract

The principles and recent progress in communications using the orbital angular momentum (OAM) of electromagnetic waves is reviewed. Several main obstacles to high capacity OAM communications are discussed to give an outlook to the potentials and challenges of this technology.

The orbital angular momentum (OAM) of EM waves or photons was established only in 1992 by Allen et al who linked OAM to the azimuthal angular phase shift of an beam around its axis of propagation. An lth order OAM mode will have l× 2πazimuthal phase shift.

Communications systems using EM waves as carrier can use OAM-based transmission to greatly increase capacity and spectrum efficiency within existing spectral bandwidth. OAM division multiplexing (OAM-DM) exploiting the orthogonality between OAM modes is another means of multiplying the capacity of a single physical channel, in addition to other multiplexing schemes such as WDM or OFDM, and is superior over OAM encoding which encodes information onto the OAM values of light (similar to amplitude or phase modulation) in terms of both spectrum efficiency and compatibility with existing techniques.

In optical fibre communication, the capacity of OAM-DM will be limited firstly by the number of OAM modes supported by the transmitter, receiver and fibre. Integrated OAM DEMUX devices will be key to the transceiver capacity and several approaches are being developed. Fibres structures supporting high order OAM modes can be developed, and need to be optimized for the various transmission characteristics including dispersion. The ultimate limit to OAM communications will likely to be the linear and nonlinear crosstalks between OAM channels. In fibres, linear OAM mode coupling arises when the fibre is perturbed from the ideal straight cylindrical shape, and needs to be studies and mitigated. Nonlinear coupling between OAM modes is likely to be small due to large mode area and lack of synchronism between their propagation constants.

Just as wavelength in WDM systems, OAM as a channel label may also be used as a networking resource for routing. All-optical routing schemes based on the conversion of OAM modes could be developed as corresponding OAM mode converter could be devised.

 

 

Biography

Prof. Siyuan Yu received his Bachelor’s Degree from Tsinghua University in 1984, Master degree from Wuhan Institute of Post and Telecommunications in 1987 (both in China), and PhD degree from the Dept. of Electronics and Electrical Engineering, University of Glasgow, UK, in 1997. Since 1996 he has been with the Department of Electrical and Electronic Engineering, University of Bristol, UK. He is currently also a Special Guest Professor at the State Key Laboratory of Optoelectronc Materials and Technologies, Sun Yat-sen University, Guangzhou, China. His main research interests are in photonic integrated circuits for advanced optical communications networks.