Internet data traffic capadty is rapidly reaching limits imposed by optical fiber nonlinear effects. Having almost exhausted available degrees of freedom to orthogonally multiplex data, the ...possibility is now being explored of using spatial modes of fibers to enhance data capadty. We demonstrate the viability of using the orbital angular momentum (OAM) of light to create orthogonal, spatially distinct streams of data-transmitting channels that are multiplexed in a single fiber. Over 1.1 kilometers of a specially designed optical fiber that minimizes mode coupling, we achieved 400-gigabits-per-second data transmission using four angular momentum modes at a single wavelength, and 1.6 terabits per second using two OAM modes over 10 wavelengths. These demonstrations suggest that OAM could provide an additional degree of freedom for data multiplexing in future fiber networks.
Space-time duality in paraxial optical wave propagation implies the existence of intriguing effects when light interacts with a material exhibiting two refractive indexes separated by a boundary in ...time. The direct consequence of such time-refraction effect is a change in the frequency of light while leaving the wavevector unchanged. Here, we experimentally show that the effect of time refraction is significantly enhanced in an epsilon-near-zero (ENZ) medium as a consequence of the optically induced unity-order refractive index change in a sub-picosecond time scale. Specifically, we demonstrate broadband and controllable shift (up to 14.9 THz) in the frequency of a light beam using a time-varying subwavelength-thick indium tin oxide (ITO) film in its ENZ spectral range. Our findings hint at the possibility of designing (3 + 1)D metamaterials by incorporating time-varying bulk ENZ materials, and they present a unique playground to investigate various novel effects in the time domain.
The recognition in the 1990s that light beams with a helical phase front have orbital angular momentum has benefited applications ranging from optical manipulation to quantum information processing. ...Recently, attention has been directed towards the opportunities for harnessing such beams in communications. Here, we demonstrate that four light beams with different values of orbital angular momentum and encoded with 42.8 × 4 Gbit s-1 quadrature amplitude modulation (16-QAM) signals can be multiplexed and demultiplexed, allowing a 1.37 Tbit s-1 aggregated rate and 25.6 bit s-1 Hz-1 spectral efficiency when combined with polarization multiplexing. Moreover, we show scalability in the spatial domain using two groups of concentric rings of eight polarization-multiplexed 20 × 4 Gbit s-1 16-QAM-carrying orbital angular momentum beams, achieving a capacity of 2.56 Tbit s-1 and spectral efficiency of 95.7 bit s-1 Hz-1 . We also report data exchange between orbital angular momentum beams encoded with 100 Gbit s-1 differential quadrature phase-shift keying signals. These demonstrations suggest that orbital angular momentum could be a useful degree of freedom for increasing the capacity of free-space communications.
A Different Angle on Light Communications Willner, Alan E.; Wang, Jian; Huang, Hao
Science (American Association for the Advancement of Science),
08/2012, Letnik:
337, Številka:
6095
Journal Article
Recenzirano
Can “twisted” light beams enhance optical communication systems?
A conventional propagating free-space laser beam typically has an approximately flat phase front and exhibits an intensity profile ...that decreases as a function of the radial distance from the beam center. However, in the 1990s, it was shown that propagating light waves can contain an interesting property known as orbital angular momentum (OAM) (
1
). OAM implies that the light wave's phase front is twisting along the direction of propagation. This twisting of the phase front into a corkscrew shape results in a doughnut-like ring intensity profile (
2
). It was then demonstrated that a given optical beam with OAM can be encoded with data (
3
–
5
). Moreover, a radiowave field trial showed that a free-space radio data link can use OAM for transmission (
6
). Recent work has demonstrated a 2.56 terabits per second (Tbit/s) free-space optical data transfer using OAM (
7
).
All-Optical Signal Processing Willner, Alan E.; Khaleghi, Salman; Chitgarha, Mohammad Reza ...
Journal of lightwave technology,
02/2014, Letnik:
32, Številka:
4
Journal Article, Conference Proceeding
Recenzirano
Optical signal processing brings together various fields of optics and signal processing - namely, nonlinear devices and processes, analog and digital signals, and advanced data modulation formats - ...to achieve high-speed signal processing functions that can potentially operate at the line rate of fiber optic communications. Information can be encoded in amplitude, phase, wavelength, polarization and spatial features of an optical wave to achieve high-capacity transmission. We revisit advances in the key enabling technologies that led to recent research in optical signal processing for digital signals that are encoded in one or more of these dimensions. Various optical nonlinearities and chromatic dispersion have been shown to enable key sub-system applications such as wavelength conversion, multicasting, multiplexing, demultiplexing, and tunable optical delays. We review recent advances in high-speed optical signal processing applications in the areas of equalization, regeneration, flexible signal generation, and optical control information (optical logic and correlation).
This tutorial highlights challenges and opportunities in achieving efficient flexible optical networks. Optical signal processing may potentially increase network flexibility because of its ...functions' transparency, tunability, and reconfigurability. We review recent advances in high-speed optical signal processing techniques that might enable flexible networks. Various optical approaches that enable key functions are discussed, including format conversion, increases in spectral efficiency, and phase-sensitive operations. We also discuss the potential utilization of basic enabling technologies, such as optical frequency combs and optical nonlinear devices.
There is a continuing growth in the demand for data bandwidth, and the multiplexing of multiple independent data streams has the potential to provide the needed data capacity. One technique uses the ...spatial domain of an electromagnetic (EM) wave, and space division multiplexing (SDM) has become increasingly important for increased transmission capacity and spectral efficiency of a communication system. A subset of SDM is mode division multiplexing (MDM), in which multiple orthogonal beams each on a different mode can be multiplexed. A potential modal basis set to achieve MDM is to use orbital angular momentum (OAM) of EM waves. In such a system, multiple OAM beams each carrying an independent data stream are multiplexed at the transmitter, propagate through a common medium and are demultiplexed at the receiver. As a result, the total capacity and spectral efficiency of the communication system can be multiplied by a factor equal to the number of transmitted OAM modes. Over the past few years, progress has been made in understanding the advantages and limitations of using multiplexed OAM beams for communication systems. In this review paper, we highlight recent advances in the use of OAM multiplexing for high-capacity free-space optical and millimetre-wave communications. We discuss different technical challenges (e.g. atmospheric turbulence and crosstalk) as well as potential techniques to mitigate such degrading effects.
This article is part of the themed issue ‘Optical orbital angular momentum’.
There is a growing interest in structured light, especially orbital angular momentum (OAM) beams, due to its unique amplitude and phase structure. Multiple orthogonal OAM beams can be utilized to ...enable high-capacity communication systems in various scenarios. This review will discuss the properties, challenges, advances, and perspectives of OAM-based optical communications, including the following (a) basic multiplexing and encoding links; (b) OAM-based communication in free space and fiber; (c) technical hurdles; (d) mitigation approaches; (e) encoded quantum communications; (f) advanced topics including different frequency ranges and novel beams; and (g) ecosystem and commercialization.
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 show up to a 40-Gbit/s link by multiplexing and transmitting 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 40-Gbit/s link, data is modulated in the IR, and OAM imprinting is performed in the green using a specially-designed metasurface phase mask. For the 4-Gbit/s link, 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.
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