Phase screen prediction using deep phase network for FSO links.

Due to the presence of air turbulence in free-space optical (FSO) links, random fluctuations in wavefront phase and amplitude of the optical signal are reduced after it propagates through the air channel, which degrades the performance of free-space optical communication (FSOC) systems. Phase screen reflects the phase distortions resulting from air turbulence. Accordingly, accurate prediction with respect to phase screen is of significance for the FSOC.

Slant-path coherent free space optical communications over the maritime and terrestrial atmospheres with the use of adaptive optics for beam wavefront correction.

As a continuation of our previous work [Appl. Opt.54, 1453 (2015)APOPAI0003-693510.

Unified direct and coherent orthogonal frequency division multiplexing optical transmission scheme.

We experimentally demonstrate a novel unified direct and coherent orthogonal frequency division multiplexing (OFDM) scheme. This self-coherent OFDM scheme simplifies receiver architecture and provides interchangeability between direct and coherent receivers using the same unified transmitter. We have experimentally verified the resilience of this scheme to fiber nonlinearities and achieved receiver sensitivity improvement of up to 1.

Coherent free space optics communications over the maritime atmosphere with use of adaptive optics for beam wavefront correction.

We evaluate the performance of the coherent free space optics (FSO) employing quadrature array phase-shift keying (QPSK) modulation over the maritime atmosphere with atmospheric turbulence compensated by use of adaptive optics (AO). We have established a comprehensive FSO channel model for maritime conditions and also made a comprehensive comparison of performance between the maritime and terrestrial atmospheric links. The FSO links are modeled based on the intensity attenuation resulting from scattering and absorption effects, the log-amplitude fluctuations, and the phase distortions induced by turbulence.

All-optical cryptography of M-QAM formats by using two-dimensional spectrally sliced keys.

There has been an increased interest in enhancing the security of optical communications systems and networks. All-optical cryptography methods have been considered as an alternative to electronic data encryption. In this paper we propose and verify the use of a novel all-optical scheme based on cryptographic keys applied on the spectral signal for encryption of the M-QAM modulated data with bit rates of up to 200 gigabits per second.

Evaluation of channel capacities of OAM-based FSO link with real-time wavefront correction by adaptive optics.

We have evaluated the channel capacity of OAM-based FSO link under a strong atmospheric turbulence regime when adaptive optics (AO) are employed to correct the wavefront phase distortions of OAM modes. The turbulence is emulated by the Monte-Carlo phase screen method, which is validated by comparison with the theoretical phase structure function. Based on that, a closed-loop AO system with the capability of real-time correction is designed and validated.