We successfully demonstrate 1Gb/s degenerate entanglement assisted communication systems operating in C-band, which do not require the phase-conjugation, based on 780nm pump laser and employing either type-0 or type-II PPLN waveguide to generate signal and idler photons at 1560 nm.
We propose a degenerate entanglement-assisted (EA) free-space optical (FSO) communication system employing spatial light modulator (SLM)-based beam steering and a novel dual-pump configuration. The system utilizes a type-0 periodically poled lithium niobate (PPLN) waveguide to generate signal and idler photon pairs at 1570 nm, using two independent low-cost C- and L-band pump lasers. To enable homodyne detection, unmodulated idler photons are transmitted alongside modulated signal photons thus avoiding the need for phase conjugation and quantum memories. We demonstrate 1 Gb/s degenerate entanglement assisted transmission over a 1.5 km terrestrial FSO link at the University of Arizona campus, operating in the L-band. Experimental results show that the proposed degenerate EA system significantly outperforms its classical counterpart, particularly under strong atmospheric turbulence conditions.
A high-speed entanglement assisted communication that operates at 10 Gb/s is proposed, which performs a highly efficient, PPLN-waveguide-based, entanglement generation by making the simultaneous use of S- and L-band pumps. The two-pump-based entanglement generation source satisfies the quasi-phase-matching-condition over the entire C-band. To improve the system reliability, our system performs the phase-conjugation on idler photons in contrast to conventional ways of performing the phase-conjugation on signal photons. To study the performance of the proposed entanglement-assisted system we have developed the 1.5 km long outdoor free-space optical (FSO) link at the University of Arizona campus. Experimental results indicate that the proposed entanglement-assisted system significantly outperforms the classical counterpart at 10 Gb/s, operated in strong turbulence regime. We also demonstrate that the traditional entanglement-assisted system performing the optical phase conjugation on signal photons at the receiver side is not operational at all in strong turbulence regime given that it is extremely difficult to perform the phase-conjugation on weak signal photons when the number of received photons is low. To improve the system performance the adaptive optics is performed on signal photons.
Optical communications over terrestrial free-space optical (FSO) channels are affected by various effects including diffraction, absorption, scattering, and turbulence effects. In several recent papers we have shown that entanglement assisted (EA) communication systems significantly outperform corresponding classical counterparts in strong turbulence regime. In traditional EA communications the phase-conjugation, required before the homodyne detection takes place, is performed on signal photons. However, given that many photons get lost due to diffraction, scattering, absorption, and turbulence effects, it is extremely difficult to perform the phase-conjugation on received signal photons when average number of received photons is smaller than 1. To solve this problem, we recently have proposed to perform phase-conjugation on bright idler photons instead. To operate the EA communication system over turbulent FSO links it is required to generate many bright entangled photons so that signal photons can survive beyond strong turbulence regime. To solve this problem, we have proposed to properly design periodically poled lithium niobate waveguides so that we can use telecom available lasers operated in S-, C-, and L-bands as the pump lasers instead of high-cost 780 nm pump lasers. In this invited paper, we will review our recent activities in EA communion studies over terrestrial FSO links and present recent experimental results demonstrating that EA communication systems performing the phase-conjugation on idler photons significantly outperforms both classical counterpart and the EA communications with phase-conjugated receiver in strong turbulence regime.
We propose a low-complexity degenerate entanglement-assisted (DEA) system suitable for radar, communication, and LiDAR applications. The proposed DEA system employs on transmitter side a continuous wave (CW) dual-pump-based approach, a type-0 periodically poled lithium niobate (PPLN) waveguide, an optical bandpass filter, and a proposed single-drive Mach-Zehnder modulator. On receiver side, for communication and radar applications, the proposed balanced receiver is used as the entanglement-assisted detector. For LiDAR applications, on the other hand, the DEA detector array is used on receiver side. Two independent CW pump lasers operated at telecom wavelengths are employed in the dual-pump-based approach. For radar and LiDAR applications, the portion of degenerate entangled photons is employed as the reference signal and the rest to transmit the probe signal. We also propose a DEA triple-function radar-communication-LiDAR system. To demonstrate the quantum advantage, we conducted 1 Gb/s DEA radar and communication experiments over terrestrial free-space optical (FSO) link at the University of Arizona campus, between ECE Dept. and Optical Sciences Meinel buildings. We demonstrate that in the presence of the atmospheric turbulence in the saturation regime the proposed low-complexity DEA quantum radar and communication system outperform significantly corresponding classical counterparts.