16 research outputs found
Experimental characterization of a 400 Gbit/s orbital angular momentum multiplexed free-space optical link over 120 m
We experimentally demonstrate and characterize the
performance of a 400-Gbit/s orbital angular momentum
(OAM) multiplexed free-space optical link over 120-
meters on the roof of a building. Four OAM beams, each
carrying a 100-Gbit/s QPSK channel are multiplexed and
transmitted. We investigate the influence of channel
impairments on the received power, inter-modal
crosstalk among channels, and system power penalties.
Without laser tracking and compensation systems, the
measured received power and crosstalk among OAM
channels fluctuate by 4.5 dB and 5 dB, respectively, over
180 seconds. For a beam displacement of 2 mm that
corresponds to a pointing error less than 16.7 μrad, the
link bit-error-rates are below the forward error
correction threshold of 3.8×10-3 for all channels. Both
experimental and simulation results show that power
penalties increase rapidly when the displacement
increases
Orbital Angular Momentum-based Space Division Multiplexing for High-capacity Underwater Optical Communications
To increase system capacity of underwater optical communications, we employ
the spatial domain to simultaneously transmit multiple orthogonal spatial
beams, each carrying an independent data channel. In this paper, we multiplex
and transmit four green orbital angular momentum (OAM) beams through a single
aperture. Moreover, we investigate the degrading effects of
scattering/turbidity, water current, and thermal gradient-induced turbulence,
and we find that thermal gradients cause the most distortions and turbidity
causes the most loss. We show systems results using two different data
generation techniques, one at 1064 nm for 10-Gbit/s/beam and one at 520 nm for
1-Gbit/s/beam, we use both techniques since present data-modulation
technologies are faster for infrared (IR) than for green. For the higher-rate
link, data is modulated in the IR, and OAM imprinting is performed in the green
using a specially-designed metasurface phase mask. For the lower rates, a green
laser diode is directly modulated. Finally, we show that inter-channel
crosstalk induced by thermal gradients can be mitigated using multi-channel
equalisation processing.Comment: 26 pages, 5 figure
Mode-division-multiplexing of multiple Bessel-Gaussian beams carrying orbital-angular-momentum for obstruction-tolerant free-space optical and millimetre-wave communication links
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-multiplexed free-space optical communication link using transmitter lenses
In this paper, we explore the potential benefits and limitations of using transmitter lenses in an orbital-angular-momentum (OAM)-multiplexed free-space optical (FSO) communication link. Both simulation and experimental results indicate that within certain transmission distances, using lenses at the transmitter to focus OAM beams could reduce power loss in OAM-based FSO links and that this improvement might be more significant for higher-order OAM beams. Moreover, the use of transmitter lenses could enhance system tolerance to angular error between transmitter and receiver, but they might degrade tolerance to lateral displacement
Orbital angular momentum beams generated by passive dielectric phase masks and their performance in a communication link
We demonstrate the generation of orbital angular momentum (OAM) beams using high-efficient polarization-insensitive phase masks. The OAM beams generated by the phase masks are characterized in terms of their tolerance to misalignment (lateral displacement or tilt) between the incident beam and phase mask. For certain scenarios, our results show that (a) when the tilt angle is within the range of −20 to +20 deg, the crosstalk among modes is less than −15 dB; and (b) lateral displacement of 0.3 mm could cause a large amount of power leaked to adjacent modes. Finally, OAM beams generated by the phase masks are demonstrated over a two-channel OAM-multiplexing link, each channel carrying a 40 Gbit/s data stream. An optical signal-to-noise-ratio (OSNR) penalty of ∼1 dB is measured without crosstalk at the bit error rate (BER) of 3.8 × 10^(−3). With crosstalk, an OSNR penalty of <1.5 dB<1.5 dB is observed at the same BER
Optical communications using orbital angular momentum beams
Orbital angular momentum (OAM), which describes the “phase twist” (helical phase pattern) of light beams, has recently gained interest due to its potential applications in many diverse areas. Particularly promising is the use of OAM for optical communications since: (i) coaxially propagating OAM beams with different azimuthal OAM states are mutually orthogonal, (ii) inter-beam crosstalk can be minimized, and (iii) the beams can be efficiently multiplexed and demultiplexed. As a result, multiple OAM states could be used as different carriers for multiplexing and transmitting multiple data streams, thereby potentially increasing the system capacity. In this paper, we review recent progress in OAM beam generation/detection, multiplexing/demultiplexing, and its potential applications in different scenarios including free-space optical communications, fiber-optic communications, and RF communications. Technical challenges and perspectives of OAM beams are also discussed