Efficiently adding mode multiplexing for cost-effective,high-capacity fiber links

For decades,a powerful approach to adding data capacity in an optical communication link has been to multiplex independent data-carrying channels and transmit them simultaneously along a fiber.^(1)For example,wavelength-division-multiplexing(WDM)was a key technology in the 1990s and early 2000s to dramatically increase aggregate capacity in a fiber by multiplexing beams of different wavelengths.^(2)For the past roughly 15 years,there has been great promise that space-division-multiplexing(SDM)may bring similar capacity enhancements to optical fiber communications.^(1–3)

Integrated sensing and communication in an optical fibre

The integration of high-speed optical communication and distributed sensing could bring intelligent functionalities to ubiquitous optical fibre networks,such as urban structure imaging,ocean seismic detection,and safety monitoring of underground embedded pipelines.This work demonstrates a scheme of integrated sensing and communication in an optical fibre(ISAC-OF)using the same wavelength channel for simultaneous data transmission and distributed vibration sensing.The scheme not only extends the intelligent functionality for optical fibre communication system,but also improves its transmission performance.A periodic linear frequency modulation(LFM)light is generated to act as the optical carrier and sensing probe in PAM4 signal transmission and phase-sensitive optical time-domain reflectometry(Φ-OTDR),respectively.After a 24.5 km fibre transmission,the forward PAM4 signal and the carriercorrespondence Rayleigh backscattering signal are detected and demodulated.Experimental results show that the integrated solution achieves better transmission performance(~1.3 dB improvement)and a larger launching power(7 dB enhancement)at a 56 Gbit/s bit rate compared to a conventional PAM4 signal transmission.Meanwhile,a 4m spatial resolution,4.32-nε/√Hz strain resolution,and over 21 kHz frequency response for the vibration sensing are obtained.The proposed solution offers a new path to further explore the potential of existing or future fibre-optic networks by the convergence of data transmission and status sensing.In addition,such a scheme of using shared spectrum in communication and distributed optical fibre sensing may be used to measure non-linear parameters in coherent optical communications,offering possible benefits for data transmission.

Ultra-flat dispersion in an integrated waveguide with five and six zero-dispersion wavelengths for mid-infrared photonics

We propose a new type of dispersion flattening technology, which can generate an ultra-flat group velocity dispersion profile with five and six zero-dispersion wavelengths(ZDWs). The dispersion value varies from-0.15 to 0.35 ps/(nm·km) from 4 to 8 μm, which to the best of our knowledge is the flattest one reported so far, and the dispersion flatness is improved by more than an order of magnitude. We explain the principle of producing six ZDWs. Mode distribution in this waveguide is made stable over a wide bandwidth. General guidelines to systematically control the dispersion value, sign, and slope are provided, and one can achieve the desired dispersion by properly adjusting the structural parameters. Fabrication tolerance of this waveguide is also examined.

Single-End Adaptive Optics Compensation for Emulated Turbulence in a Bi-Directional 10-Mbit/s per Channel Free-Space Quantum Communication Link Using Orbital-Angular-Momentum Encoding

A single-end adaptive-optics(AO)module is experimentally demonstrated to mitigate the emulated atmospheric turbulence efects in a bi-directional quantum communication link,which employs orbital angular momentum(OAM)for data encoding.A classical Gaussian beam is used as a probe to detect the turbulence-induced wavefront distortion in the forward direction of the link.Based on the detected wavefront distortion,an AO system located on one end of the link is used to simultaneously compensate for the forward and backward channels.Specifcally,with emulated turbulence and when the probe is turned on,the mode purity of photons carrying OAMℓ=1 is improved by∼21%with AO mitigation.We also measured the performance when encoding data using OAM{ℓ=−1,+2}and{ℓ=−2,+1}in the forward and backward channels,respectively,at 10 Mbit/s per channel with one photon per pulse on average.For this case,we found that the AO system could reduce the turbulence efects increased quantum-symbolerror-rate(QSER)by∼76%and∼74%,for both channels in the uni-directional and bi-directional cases,respectively.Similar QSER improvement is observed for the opposite direction channels in the bi-directional case.

Orbital-angular-momentum-based reconfigurable optical switching and routing

Orbital angular momentum(OAM) has gained interest due to its potential to increase capacity in optical communication systems as well as an additional domain for reconfigurable networks. This is due to the following:(i) coaxially propagated OAM beams with different charges are mutually orthogonal,(ii) OAM beams can be efficiently multiplexed and demultiplexed, and(iii) OAM charges can be efficiently manipulated. Therefore, multiple data-carrying OAM beams could have the potential capability for reconfigurable optical switching and routing. In this paper, we discuss work involving reconfigurable OAM-based optical add/drop multiplexing, space switching,polarization switching, channel hopping, and multicasting.

Quantifying Information via Shannon Entropy in Spatially Structured Optical Beams

While information is ubiquitously generated,shared,and analyzed in a modern-day life,there is still some controversy around the ways to assess the amount and quality of information inside a noisy optical channel.A number of theoretical approaches based on,e.g.,conditional Shannon entropy and Fisher information have been developed,along with some experimental validations.Some of these approaches are limited to a certain alphabet,while others tend to fall short when considering optical beams with a nontrivial structure,such as Hermite-Gauss,Laguerre-Gauss,and other modes with a nontrivial structure.Here,we propose a new definition of the classical Shannon information via the Wigner distribution function,while respecting the Heisenberg inequality.Following this definition,we calculate the amount of information in Gaussian,Hermite-Gaussian,and LaguerreGaussian laser modes in juxtaposition and experimentally validate it by reconstruction of the Wigner distribution function from the intensity distribution of structured laser beams.We experimentally demonstrate the technique that allows to infer field structure of the laser beams in singular optics to assess the amount of contained information.Given the generality,this approach of defining information via analyzing the beam complexity is applicable to laser modes of any topology that can be described by well-behaved functions.Classical Shannon information,defined in this way,is detached from a particular alphabet,i.e.,communication scheme,and scales with the structural complexity of the system.Such a synergy between the Wigner distribution function encompassing the information in both real and reciprocal space and information being a measure of disorder can contribute into future coherent detection algorithms and remote sensing.

Quantifying Information via Shannon Entropy in Spatially Structured Optical Beams

While information is ubiquitously generated,shared,and analyzed in a modern-day life,there is still some controversy around the ways to assess the amount and quality of information inside a noisy optical channel.A number of theoretical approaches based on,e.g.,conditional Shannon entropy and Fisher information have been developed,along with some experimental validations.Some of these approaches are limited to a certain alphabet,while others tend to fall short when considering optical beams with a nontrivial structure,such as Hermite-Gauss,Laguerre-Gauss,and other modes with a nontrivial structure.Here,we propose a new definition of the classical Shannon information via the Wigner distribution function,while respecting the Heisenberg inequality.Following this definition,we calculate the amount of information in Gaussian,Hermite-Gaussian,and LaguerreGaussian laser modes in juxtaposition and experimentally validate it by reconstruction of the Wigner distribution function from the intensity distribution of structured laser beams.We experimentally demonstrate the technique that allows to infer field structure of the laser beams in singular optics to assess the amount of contained information.Given the generality,this approach of defining information via analyzing the beam complexity is applicable to laser modes of any topology that can be described by well-behaved functions.Classical Shannon information,defined in this way,is detached from a particular alphabet,i.e.,communication scheme,and scales with the structural complexity of the system.Such a synergy between the Wigner distribution function encompassing the information in both real and reciprocal space and information being a measure of disorder can contribute into future coherent detection algorithms and remote sensing.