“Hiding” a low-intensity 50 Gbit/s QPSK free-space OAM beam using an orthogonal coaxial high-intensity 50 Gbit/s QPSK beam
Abstract
In this paper, we experimentally demonstrate an approach that “hides” a low-intensity 50 Gbit/s quadrature-phase-keying (QPSK) free-space optical beam when it coaxially propagates on the same wavelength with an orthogonal high-intensity 50 Gbit/s QPSK optical beam. Our approach is to coaxially transmit the strong and weak beams carrying different orthogonal spatial modes within a modal basis set, e.g., orbital angular momentum (OAM) modes. Although the weak beam has much lower power than that of the strong beam, and the beams are in the same frequency band and on the same polarization, the two beams can still be effectively demultiplexed with little inherent crosstalk at the intended receiver due to their spatial orthogonality. However, an eavesdropper may not readily identify the weak beam when simply analyzing the spatial intensity profile. The correlation coefficient between the intensity profiles of the strong beam and the combined strong and weak beams is measured to characterize the potential for “hiding” a weak beam when measuring intensity profiles. Such a correlation coefficient is demonstrated to be higher than 0.997 when the power difference between the strong fundamental Gaussian beam and the weak OAM beam is ∼ 8 , ∼ 10 , and ∼ 10 d B for the weak OAM − 1 , − 2 , and − 3 beams, respectively. Moreover, a 50 Gbit/s QPSK data link having its Q factor above the 7% forward error correction limit is realized when the power of the weak OAM − 3 beam is 30 dB lower than that of the strong fundamental Gaussian beam.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Aug 20, 2020
- Source ID
- 10.1364/ao.396386
Entities
People
- Ahmed Almaiman
- Alan E. Willner
- Cong Liu
- Hao Song
- Haoqian Song
- Kai Pang
- Karapet Manukyan
- Long Li
- Moshe Tur
- Nadav Cohen
- Runzhou Zhang
- Shlomo Zach
- Zhe Zhao
Organizations
- Defense Security Cooperation Agency
- National Science Foundation
- Office of Naval Research