Simultaneous turbulence mitigation and channel demultiplexing for two 100  Gbit/s orbital-angular-momentum...

Area of Science:

• Optical Communications
• Free-Space Optics
• Photonics

Background:

• Orbital-angular-momentum (OAM) multiplexing offers high-capacity data transmission.
• Turbulence in free-space optical links degrades signal quality and increases crosstalk.
• Adaptive optics techniques are crucial for mitigating turbulence effects.

Purpose of the Study:

• To experimentally demonstrate simultaneous turbulence mitigation and channel demultiplexing in a 200 Gbit/s OAM multiplexed link.
• To evaluate the effectiveness of adaptive wavefront shaping and diffusing (WSD) in reducing crosstalk and improving signal-to-noise ratio (SNR) under varying turbulence strengths.
• To quantify the performance improvements in terms of crosstalk reduction and SNR penalty.

Main Methods:

• Utilized adaptive wavefront shaping and diffusing (WSD) to mitigate turbulence.
• Emulated two strengths of atmospheric turbulence using different Fried parameter values (r0 = 0.4 mm and r0 = 1.0 mm).
• Experimentally measured crosstalk reduction between OAM modes (+1 and -1) and optical signal-to-noise ratio (OSNR) penalties for bit error rate (BER) performance.

Main Results:

• Crosstalk between OAM modes +1 and -1 was reduced by >10.0 dB and >5.8 dB, respectively, under weaker turbulence (r0 = 1.0 mm).
• Under stronger turbulence (r0 = 0.4 mm), crosstalk was further improved by >17.7 dB and >19.4 dB.
• Optical signal-to-noise ratio penalties were approximately 0.7 dB and 1.6 dB for OAM +1 and -1 modes under weaker turbulence, and 3.2 dB and 1.8 dB under stronger turbulence.

Conclusions:

• Adaptive wavefront shaping and diffusing effectively mitigates turbulence in OAM multiplexed links.
• The technique simultaneously reduces inter-modal crosstalk and improves SNR penalties, enhancing data transmission reliability.
• Demonstrated significant crosstalk reduction and acceptable SNR penalties, paving the way for robust high-capacity free-space optical communication systems.