High-capacity millimetre-wave communications with orbital angular momentum multiplexing

Abstract

One property of electromagnetic waves that has been recently explored is the ability to multiplex multiple beams, such that each beam has a unique helical phase front. The amount of phase front ‘twisting’ indicates the orbital angular momentum state number, and beams with different orbital angular momentum are orthogonal. Such orbital angular momentum based multiplexing can potentially increase the system capacity and spectral efficiency of millimetre-wave wireless communication links with a single aperture pair by transmitting multiple coaxial data streams. Here we demonstrate a 32-Gbit s−1 millimetre-wave link over 2.5 metres with a spectral efficiency of ~16 bit s−1 Hz−1 using four independent orbital–angular momentum beams on each of two polarizations. All eight orbital angular momentum channels are recovered with bit-error rates below 3.8 × 10−3. In addition, we demonstrate a millimetre-wave orbital angular momentum mode demultiplexer to demultiplex four orbital angular momentum channels with crosstalk less than −12.5 dB and show an 8-Gbit s−1 link containing two orbital angular momentum beams on each of two polarizations.

Planar millimetre‐wave antenna simultaneously producing four orbital angular momentum modes and associated multi‐element receiver array

“…In this way, the whole spatial extent of the mode is used in the de-multiplexing process, allowing all OAM modes to retain their mutual orthogonality [14][15][16]. A similar approach has been applied to millimetre wave communications links over a 2.5 m distance using four antennas and spiral phase plates operating with modes l  {±1,±3} and cross-talk between of -12 to -14 dB [4]. However, whole-aperture receivers are unattractive for longer free-space link distances because the receiving aperture must increase with the link distance in order to receive sufficient power.…”

“…The divergence angle has scaled according to 4 Despite the different peak gain positions for the two mode numbers, there is enough overlap in the two modes to allow both to be detected over an angular range in excess of 30 (15°  θ  45° ). However, a two-element receive array implementing the phase gradient method is unable to be used in this case, because it cannot discriminate between modes of different numbers when both are present (except at the extreme edges of the angular range where one mode is substantially stronger than the other).…”

“…These are connected by a phase-preserving system such as waveguides of equal length, or radio-over-fibre [22] Our work is expected to find application wireless communications systems that require enhanced spectral efficiency over line of sight links, including wireless back haul, and short range communications within data centres [4]. These line of sight links offer no diversity gain, eliminating the advantages of MIMO, and the line of sight requirement precludes the use of multiple links via beamforming techniques.…”

Controllable all-fiber generation/conversion of circularly polarized orbital angular momentum beams using long period fiber gratings

“…A beam of light carrying OAM possesses a phase φ(l,ϕ) = exp(ilϕ) in the transverse plane, where ϕ is the azimuth angle and l is the topological charge number. As the unique characteristics of the OAM light beam were found, a number of attempts to generate and manipulate the OAM beams were proposed based on discrete free space optical systems [6][7][8][9][10][11] and optical fiber components [12][13][14][15][16][17][18].…”

“…As one of the most fundamental physical quantities in classical and quantum electrodynamics, orbital angular momentum (OAM) of light has initiated widespread interest in many areas, including optical tweezers [1], atom manipulation [2][3][4], nanoscale microscopy [5], quantum information processing, and large-capacity optical communication [6][7][8]. A beam of light carrying OAM possesses a phase φ(l,ϕ) = exp(ilϕ) in the transverse plane, where ϕ is the azimuth angle and l is the topological charge number.…”