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

Abstract

<jats:p>A single-end adaptive-optics (AO) module is experimentally demonstrated to mitigate the emulated atmospheric turbulence effects 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. Specifically, with emulated turbulence and when the probe is turned on, the mode purity of photons carrying OAM <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi mathvariant="script">l</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn></mml:math> is improved by ~ 21 % with AO mitigation. We also measured the performance when encoding data using OAM <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mo stretchy="false">{</mml:mo><mml:mi mathvariant="script">l</mml:mi><mml:mo>=</mml:mo><mml:mo>-</mml:mo><mml:mn mathvariant="normal">1</mml:mn><mml:mo>,</mml:mo><mml:mo>+</mml:mo><mml:mn mathvariant="normal">2</mml:mn><mml:mo stretchy="false">}</mml:mo></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mo stretchy="false">{</mml:mo><mml:mi mathvariant="script">l</mml:mi><mml:mo>=</mml:mo><mml:mo>-</mml:mo><mml:mn mathvariant="normal">2</mml:mn><mml:mo>,</mml:mo><mml:mo>+</mml:mo><mml:mn mathvariant="normal">1</mml:mn><mml:mo stretchy="false">}</mml:mo></mml:math> 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 effects increased quantum-symbol-error-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.</jats:p>

Perspective on using multiple orbital-angular-momentum beams for enhanced capacity in free-space optical communication links

“…Another important advantage of OAM orthogonality is that one can use OAM mode order as a data encoding scheme [43][44][45][46]. For example in the case of a quantum communication system, an individual photon can carry one of the many different OAM values; this is similar to digital data taking on one of many different amplitude values.…”

Amplifying Orbital Angular Momentum Modes in Ring-Core Erbium-Doped Fiber

“…Similar to other mode bases in free space or in fiber [22][23][24], OAM beams with helical phase structure are another mode base related to the spatial domain. Thus, OAM-division multiplexing (OAM-DM), as a new multiplexing technique of space-division multiplexing (SDM), provides an alternative potential to enable the continuous increase of transmission capacity and spectral efficiency [15,16,[25][26][27][28][29][30][31]. Ring-core fiber (RCF) with an annual refractive index profile has been proven to be a preferable design for stable propagation of OAM modes in fibers since being first demonstrated in 2009 [32].…”

A Small-Divergence-Angle Orbital Angular Momentum Metasurface Antenna

“…Moreover, the OAM beams generated by metasurfaces show great performance in terms of pure, transmissivity, reflectivity, and shape of the phase front [31,32]. Multimode OAM beams can be generated by one single metasurface [33][34][35][36]. However, metasurfaces usually require at least hundreds of unit cells to obtain an accurate modification, which causes great challenges in terms of design and manufacture.…”