IEEE Access

On the Degenerate Entanglement-Assisted Free-Space Optical Communication With SLM-Based Beam Steering Using Dual-Pump Lasers

Ivan B. Djordjević, Ignacio A. Rojas

Published Jan 1, 2025• 5 citations

Abstract

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.

DOI: 10.1109/access.2025.3607303

Related papers

Low-Complexity Degenerate Entanglement- Assisted Communication Systems for Strong Atmospheric Turbulence Channels

Ivan B. Djordjević

We propose a low-complexity degenerate entanglement-assisted free-space optical (FSO) communication system employing a two-pumps approach, a type-0 periodically poled lithium niobate (PPLN) waveguide, a multistage WDM demultiplexer, and a properly biased Mach-Zehnder modulator on transmitter side and, for binary phase-shift keying (BPSK) signaling, a single PIN photodetector or avalanche photodetector (APD) on a receiver side. Two-pumps-based approach utilizes two independent pump lasers operating at telecom wavelengths. The portion of degenerate entangled photons is used as the unmodulated carrier and the rest to transmit the modulated PSK/quadrature amplitude modulation (QAM) signal. The unmodulated portion of entangled photons is selected by properly choosing the bias voltage and phase representing the transmitted bits. In BPSK signaling, the unmodulated carrier photons are used on receiver side to reconstruct the transmitted symbol by beating them with modulated signal photons on either PIN photodetector or APD. We also describe how to implement the M-ary PSK and QAM transmitters for the degenerate entanglement assisted communications. Further, we propose a low-complexity PSK/QAM demodulator compatible with the proposed degenerate entanglement assisted communication concept. To demonstrate the quantum advantage, we conducted 1 Gb/s degenerate entanglement assisted BPSK experiments over a 1.5 km terrestrial FSO link we have developed previously at the University of Arizona, between ECE Dept. and Optical Sciences Meinel buildings. We demonstrate that in the strong atmospheric turbulence regime the proposed low-complexity degenerate entanglement assisted communication system performs significantly better compared to corresponding classical laser and thermal source-based communications counterparts.

IEEE AccessJan 1, 20262 citations

Entanglement Assisted LPI and Covert Communications With SLM-Based Beam Steering Over Turbulent Optical Channels

Ivan B. Djordjević, Ignacio A. Rojas

In secure communications, the primary focus is on safeguarding the content of the message. In contrast, low probability of intercept (LPI) communications prioritize the privacy of the communication process itself. The most restrictive form of LPI communication, where an adversary attempts to disrupt the communication once its presence is detected, is known as covert communication. To hide the transmitted signal in solar radiation, we propose using the Gaussian quantum states generated by the degenerate parametric down-conversion process with signal photons being modulated with the phase-shift keying (PSK). To detect the transmitted signal, we propose transmitting the unmodulated idler photons (serving as the reference) together with modulated signal photons. To establish the link, we use the spatial light modulator (SLM)-based beam steering. We successfully demonstrate dual-pump-lasers-based degenerate entanglement-assisted (EA) LPI communication at 1 Gb/s over a 1.5 km terrestrial free-space optical (FSO) link. For the same link, the number of achievable EA covert bits for EA covert FSO communication is significantly higher compared to the corresponding classical covert communication scheme.

IEEE AccessJan 1, 20252 citations

Two-Pumps-Based Degenerate Entanglement Assisted Communication with SLM-Based Beam Pointing

Ivan B. Djordjević, Ignacio A. Rojas

We successfully demonstrate two-pumps-based degenerate entanglement assisted free-space optical communication system at 1 Gb/s operating in L-band with SLM-based beam pointing by employing type-0 PPLN waveguide to generate signal and idler photons at 1570 nm.

Frontiers in OpticsJan 1, 20250 citations

Entanglement assisted free-space optical communication with two-pump-based entanglement generation outperforming classical laser communication in strong turbulence regime at 10 Gb/s

Vijay Nafria, Ivan B. Djordjević

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.

Optics ExpressDec 4, 20247 citations

Entanglement Assisted Communications with Phase-Conjugation on Idler Photons Outperforming Entanglement Assisted Systems with Phase-Conjugated Receivers

Ivan B. Djordjević

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.

International Conference on Transparent Optical NetworksJul 6, 20250 citations

Low-Complexity Degenerate Entanglement-Assisted Detection, Radars, LiDARs, and Triple-Function Radar-Communication-LiDAR System

Ivan B. Djordjević

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.

IEEE AccessJan 1, 20260 citations