Free-Space Optical (FSO) communication technology can cater to various types of connectivity requirements within optical networks, including core, edge, and access networks. However, the performance of FSO communication links can be adversely affected by severe atmospheric conditions, such as turbulence and weather-related factors. In this study, we have investigated the benefits of photon entangled 16-QAM- FSO link in improving the performance of FSO communication under diverse weather and atmospheric turbulence conditions. The efficient implementation of a practical secure quantum communication network may revolutionize the terrestrial and non-terrestrial communication both form speed and security point of view.
Free-Space Optical (FSO) communication technology can cater to various types of connectivity requirements within optical networks, including core, edge, and access networks. However, the performance of FSO communication links can be adversely affected by severe atmospheric conditions, such as turbulence and weather-related factors. In this study, we have investigated the benefits of photon entangled 16-QAM- FSO link in improving the performance of FSO communication under diverse weather and atmospheric turbulence conditions. The efficient implementation of a practical secure quantum communication network may revolutionize the terrestrial and non-terrestrial communication both form speed and security point of view.
Free-space optical communication links are promising channels for establishing secure quantum communication. Here we study the transmission of nonclassical light through a turbulent atmospheric link under diverse weather conditions, including rain or haze. To include these effects, the theory of light transmission through atmospheric links in the elliptic-beam approximation presented by Vasylyev et al. [D. Vasylyev et al., Phys. Rev. Lett. 117, 090501 (2016)] is further generalized. It is demonstrated, with good agreement between theory and experiment, that low-intensity rain merely contributes additional deterministic losses, whereas haze also introduces additional beam deformations of the transmitted light. Based on these results, we study theoretically the transmission of quadrature squeezing and Gaussian entanglement under these weather conditions.
One of the most rapidly developing communication technologies is quantum communication. Quantum Free-Space Optical Communication (FSO) provides unlimited bandwidth for data transmission. A key barrier to FSO links is associated with the losses caused by atmospheric absorption and scattering of molecules and aerosols. In the present study, we analyze the performance of a free-space classical link for 650 nm, 785 nm, 850 nm and 1550 nm wavelengths for a link range of 0.5 Km and 50 Km. The losses due to atmospheric components such as rain, fog, snow and turbulence are predicted for different wavelengths. Also, we presented similar analysis for free space quantum link using difference frequency generation(DFG) method for both short range (0.5 Km) and long-range link (50 Km) under diverse weather conditions. It is done by combining weak wavelengths of 650 nm, 785 nm, 850 nm and 1550 nm, along with a tunable pump LASER (Krypton) to generate IR B waves (1400 nm - 3000 nm). The total atmospheric losses with DFG is compared with the losses generated without using DFG.
Abstract This investigation examines the use of a Quadrature Phase Shift Keying (QPSK)-based Free-space Optical (FSO) Communication system combined with Quantum Key Distribution (QKD) for improved security and dependability in disaster management situations. We tackle the problems caused by atmospheric turbulence by utilizing a hybrid gamma–gamma and log–normal channel model to precisely characterize the FSO link. The proposed system’s purpose is to offer secure, high-bandwidth communication for emergency response coordination, telemedicine, and data transmission in environments affected by disasters. We present a system design and performance evaluation based on the hybrid atmospheric model, discuss the potential advantages, drawbacks, and countermeasures of the approach, and propose future research avenues, encompassing real-time adjustment, modulation variability, and field testing. Our implementation of real-time adaptation mechanisms lowers the BER by about 30 % under conditions affected by turbulence, while hybrid FSO/RF switching maintains uninterrupted connectivity during severe atmospheric attenuation.
Free-space optical (FSO) communication provides a promising alternative solution to the traditional radio frequency (RF) communications. Compared to the RF technology, there are many advantages of FSO communications, such as ultra-high bandwidth, license-free spectrum, low inter-channel interference, and energy-efficient transmission. The potential applications for FSO communication include the last-one-mile access link from the fiber-based backbone network, low earth orbit (LEO) satellite communications, high-altitude base station platforms or vehicles, deep-space communications, and in-building automation connections. As the FSO technology becomes mature and increasingly involved, the security and reliability requirements of such applications also become crucial. Regarding the security issues, although the FSO communication is inherently more secure than the RF counterpart due to high directivity of its line-of-sight (LOS) link, it can still suffer from optical wire-tapping attack. There are many different application schemes that an eavesdropper can still probe the FSO link. Traditionally, to protect the communication, many works have been done on encryption layer and upper network layer, such as computationally intensive cryptographic algorithms and message exchanging protocols. In recent years, physical-layer security (PLS) has been getting more attentions as it provides an extra layer of security against eavesdropping. The PLS schemes, in general can be categorized into two main categories: classical PLS and quantum key distribution (QKD) protocols. The classical PLS is based on the information theoretic security analysis, while the QKD security is guaranteed by the quantum mechanics laws. Both techniques have been studied for FSO channels. In the first half of this dissertation, we study the PLS in a LOS FSO channel using orbital angular momentum (OAM) multiplexing and show that higher secrecy capacity can be achieved using OAM multiplexing technology in the presence of atmospheric turbulence effects. Then, we proposed an adaptation scheme for QKD system over FSO channel with different QKD protocols, i.e. BB84 and decoy state protocols. By adapting the source brightness based on the channel condition, we optimized the secret key rate (SKR) of the QKD system. Furthermore, we proposed a multiple spatial modes-based QKD system with backpropagation method to increase the total SKR through parallel channels. Regarding the reliability of an optical communication system as well as information reconciliation for both PLS and QKD schemes, the forward error correction (FEC) becomes an essential technique to enable high-speed transmission. The FEC with low-density parity-check (LDPC) codes has been studied for decades from LDPC block codes to the most recent spatially-coupled (SC) LDPC codes. For FSO communications, due to the time-varying nature of FSO channels, the capability of rate adaptation is important to achieve a consistent reliable transmission. In the second half of this dissertation, we proposed unified FPGA-based architecture to implement both quasi-cyclic (QC) LDPC codes and SC-LDPC codes with rate adaptation capability. The performance is verified through FPGA emulation to show good error floor properties. To further validate the rate adaptation capability, we have built a spatial light modulator (SLM)-based FSO channel emulator to test the adaptive coding scheme. Furthermore, we have conducted a fiber-based experiment with our rate adaptative coding scheme to show that the proposed adaptive coding scheme can be also used in dynamic fiber-based networks.
With the continued development of optical wireless communications, the security performance of free space optical (FSO) communications is the most crucial aspect that should receive significant attention. Despite the fact that FSO communications are considered more secure than radio frequency systems, their link performance degrades due to some environmental factors such as atmospheric turbulence, fog, and non-zero boresight pointing errors. The combined effect of these factors on the secrecy performance of FSO communication systems over the generalized Malaga- M fading channel is investigated in this paper. This work assumes a more realistic eavesdropping scenario in which both legitimate and unauthorized receivers are located on the same receiving plane. Secrecy outage probability and strictly positive secrecy capacity are expressed in exact closed-form expressions in this work. The results show that the FSO system has acceptable secrecy performance in moderate and light fog, with potential reach distances ranging from hundreds of meters to a few kilometers. Monte-Carlo simulations are used to verify the numerical results.