Security enhancement for adaptive optics aided longitudinal orbital angular momentum multiplexed underwater wireless...

Area of Science:

• Optical Communications
• Quantum Information Science
• Signal Processing

Background:

• Turbulence-induced crosstalk degrades performance in underwater optical communication systems.
• Longitudinal orbital angular momentum multiplexing (LOAMM) offers potential for robust optical communication.
• Physical layer security is crucial for secure underwater data transmission.

Purpose of the Study:

• To propose and investigate a defocus measurement aided adaptive optics (DMA-AO) technique for turbulence compensation in LOAMM underwater wireless optical communication (UWOC) systems.
• To enhance the physical layer security of LOAMM-based UWOC systems.
• To analyze the statistical properties of optical signal irradiance and derive security metrics.

Main Methods:

• A DMA-AO technique utilizing a phase retrieval algorithm and probe beam for phase reconstruction of distorted orbital angular momentum (OAM) beams.
• Development of a mixture generalized gamma-Johnson SB (GJSB) distribution to model the probability density function (PDF) of reference-channel irradiance.
• Analytical derivation of the probability of strictly positive secrecy capacity (SPSC) for single-input single-output (SISO) systems and investigation for multiple-input multiple-output (MIMO) systems.

Main Results:

• The DMA-AO technique effectively compensates for turbulence in LOAMM UWOC systems.
• The GJSB distribution provides a tractable model for irradiance fluctuations.
• Closed-form expressions for SPSC were obtained, and average secrecy capacity (ASC) was investigated for MIMO systems.

Conclusions:

• The proposed DMA-AO technique significantly enhances the physical layer security of LOAMM UWOC systems.
• LOAMM systems with DMA-AO show superior security performance compared to traditional Laguerre-Gaussian (LG) beam-based systems.
• This approach offers a promising solution for secure underwater optical communication.