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In this invited paper we review our recent research activities on experimental demonstration of entanglement based (EB) radars, operated over strong atmospheric turbulence channels. In conventional EB communications, sensing, and radars the phase-conjugation, required before homodyne detection takes place, is performed on received signal photons. In atmospheric turbulent channels, the signal photons are affected by diffraction, absorption, scattering, and atmospheric turbulence effects so that only limited number of weak target probe returned signal photons reach the receiver side in EB radars. Moreover, it is extremely difficult to perform any phase-conjugation on weak signal photons when the average number of received photons is <<1. To solve this problem, we have recently proposed to perform phase-conjugation on bright idler photons instead. Namely, we perform the wavelength conversion by the PPLN waveguide on bright idler photons, so that the idler photons will have the same wavelength as the signal photons, and after that we use a classical homodyne balanced detector as an entanglement assisted detector. To generate entangled photon pairs, we use C-/L-band tunable laser, EDFA, the PPLN waveguide, and WDM demultiplexers. To demonstrate the high-potential of the proposed EB radar concept, we developed an experimental outdoor free-space optical (FSO) testbed at the University of Arizona campus. Using this FSO testbed we experimentally demonstrate that the proposed EB radar significantly outperforms the corresponding classical counterpart and can operate in strong turbulence regime. To improve the detection probabilities further, we use deformable mirror-based adaptive optics. 

Two S-/L-band pumps, satisfying PPLN-waveguide quasi-phase-matching-condition, are used to generate bright entangled-photons providing needed flexibility in wavelength-selection over entire C-band. By performing phase-conjugation on idler photons, we demonstrate entanglement-assisted communication at 1Gb/s over 1.5km FSO link operated in beyond strong turbulence regime. 

Two S-/L-band pumps, satisfying PPLN-waveguide quasi-phase-matching-condition, are used to generate bright entangled-photons providing needed flexibility in wavelength-selection over entire C-band. By performing phase-conjugation on idler photons, we demonstrate entanglement-assisted communication at 1Gb/s over 1.5km FSO link operated in beyond strong turbulence regime. 

We demonstrate record 10 Gb/s entanglement assisted communication over 1.5 km long turbulent free-space optical link in which optical phase-conjugation is performed on bright idler photons. To further improve the system performance adaptive optics is used. 

We demonstrate record 10 Gb/s entanglement assisted communication over 1.5 km long turbulent free-space optical link in which optical phase-conjugation is performed on bright idler photons. To further improve the system performance adaptive optics is used. 

An entanglement-based continuous variable (CV) QKD scheme is proposed, performing information reconciliation over an entanglement-assisted link. The same entanglement generation source is used in both raw key transmission and information reconciliation. The entanglement generation source employs only low-cost devices operated in the C-band. The proposed CV-QKD scheme with information reconciliation over an entanglement-assisted link significantly outperforms the corresponding CV-QKD scheme with information reconciliation over an authenticated public channel. It also outperforms the CV-QKD scheme in which a classical free-space optical communication link is used to perform information reconciliation. An experimental demonstration over the free-space optical testbed established at the University of Arizona campus indicates that the proposed CV-QKD can operate in strong turbulence regimes. To improve the secret key rate performance further, adaptive optics is used.

 

The use of pre-shared entanglement in entanglement-assisted communication offers a superior alternative to classical communication, especially in the photon-starved regime and highly noisy environments. In this paper, we analyze the performance of several low-complexity receivers that use optical parametric amplifiers. The simulations demonstrate that receivers employing an entanglement-assisted scheme with phase-shift-keying modulation can outperform classical capacities. We present a 2x2 optical hybrid receiver for entanglement-assisted communication and show that it has a roughly 10% lower error probability compared to previously proposed optical parametric amplifier-based receivers for more than 10 modes. However, the capacity of the optical parametric amplifier-based receiver exceeds the Holevo capacity and the capacities of the optical phase conjugate receiver and 2x2 optical hybrid receiver in the case of a single mode. The numerical findings indicate that surpassing the Holevo and Homodyne capacities does not require a large number of signal-idler modes. Furthermore, we find that using unequal priors for BPSK provides roughly three times the information rate advantage over equal priors.

 

In this paper we are concerned with the low probability of detection (LPD) and covert radars employing optical incoherent sources. Key idea of our proposed LPD/covert radar concept is to hide the radar signal in solar radiation by employing the broadband (>30 nm) Erbium-doped fiber amplifier source, modulating such source output beam with a constant amplitude modulation format at high-speed, and detect the presence of the target by the cross-correlation method. To demonstrate the proposed concept we developed an outdoor free-space optical (FSO) testbed at the University of Arizona campus. To improve the tolerance to atmospheric turbulence effects the adaptive optics is used. We demonstrate that the LPD/covert radar concept over strong turbulent FSO channel is feasible in a desert environment. 

In this paper we present the experimental results demonstrating improvements in BERs from wavelength diversity in the LDPC coded LPI communication over a 1.5 km long free-space optical communication in the presence of strong atmospheric turbulence.