The Free Space Optical Communication (FSOC) technology has gained widespread popularity due to its multitude of advantages. FSOC offers enhanced security due to its narrow beam, Line-of-Sight (LoS) nature, and resistance to Electromagnetic Interference (EMI). However, ensuring data confidentiality in case of interception is critical. This work demonstrates data encryption using the Advanced Encryption Standard-128 (AES-128) to secure FSOC links. An encrypted optical signal was transmitted over a 2 km link and successfully decrypted at the receiver, ensuring that intercepted data remains unintelligible without the decryption key. This approach enhances FSOC’s reliability for secure transmission of sensitive or confidential information.
The Free Space Optical Communication (FSOC) technology has gained widespread popularity due to its multitude of advantages. FSOC offers enhanced security due to its narrow beam, Line-of-Sight (LoS) nature, and resistance to Electromagnetic Interference (EMI). However, ensuring data confidentiality in case of interception is critical. This work demonstrates data encryption using the Advanced Encryption Standard-128 (AES-128) to secure FSOC links. An encrypted optical signal was transmitted over a 2 km link and successfully decrypted at the receiver, ensuring that intercepted data remains unintelligible without the decryption key. This approach enhances FSOC’s reliability for secure transmission of sensitive or confidential information.
The growing awareness of the vulnerability of information transmitted on communication systems within the government, military and commercial sectors, has stimulated a number of areas of research within the optical community to design optical hardware encryption systems providing inherent immunity to espionage techniques. This paper describes a hardware optical encryption technique that utilises off the shelf telecommunication equipment and negates the necessity for an independent key distribution system with respect to the data transmission system, as is common with alternative encryption system implementations. This method also lends itself easily to fiber optic or free space communication and is applicable within any optical waveband. The encryption-decryption of the optical signal is achieved through low coherence optical interferometry. This requires the instantaneous processing and analysis of the signal, optically, to retrieve the relevant optical phase information hidden in the transmitted optical noise. This technology allows an authorised user to transmit encrypted information at a high data rate securely, while maintaining opaqueness to an unauthorised observer that data transmission is occurring. As the instantaneous optical field properties of the signals present in the system are essential to the optical encryption - decryption process, the system is inherently protected against electronic recording and advances in computational decryption algorithms. For organisations wishing to protect sensitive data and levels of communication activity these are highly desirable features.
Abstract To the best of our knowledge, this study is the first to build a secure free space optical communication system with a high bit rate of 80 Gb/s wavelength division multiplexing using a Hill coding cipher. The signal message was encrypted by applying an algorithm secure coding. According to the obtained results, in the event of favorable weather (fog), the link distance was about 4.4 km. The link distance was degraded in the bad weather (dust) to become 1.4. Furthermore, the suggested system has a communication merit (bitrate product repeater distance) of roughly 352 Gb/s km in fog conditions and 112 Gb/s km in dust conditions. This is regarded as the highest communication merit when compared to prior attempts and investigations. The effectiveness of the proposed encryption cipher has also been evaluated by a revision of various security studies, key space, correlations, histogram analyses, and results comparison with other alternative approaches. When compared to earlier studies and researches, this is thought to have the best communication merit. In addition, According to the outcomes, integrating cryptographic encryption and decryption methods into FSO systems maintained data security and offered resistance to eavesdropping assaults.
Free Space Optical (FSO) communication has potential terrestrial and non-terrestrial applications. It allows large bandwidth for higher data transfer capacity. Due to its high directivity, it has a potential security advantage over traditional radio frequency (RF) communications. However, eavesdropping attacks are still possible in long non-terrestrial transmission FSO links, where the geometry of the link allows foreign flying objects such as Unmanned Aerial vehicles (UAVs) and drones to interrupt the links. This exposes non-terrestrial FSO links to adversary security attacks. Hence, data security techniques implementation is required to achieve immune FSO communication links. Unlike the commonly proposed physical layer security techniques, this paper presents a lab-based demonstration of a secured FSO communication link based on data cryptography using the GNU Radio platform and software-defined radio (SDR) hardware. The utilized encryption algorithm (Xsalsa20) in this paper requires high-time complexity to be broken by power-limited flying objects that interrupt the FSO beam. The results show that implementing cryptographic encryption techniques into FSO systems provided resilience against eavesdropping attacks and preserved data security. The experiment results show that, at a distance of 250 mm and laser output power of 10 mW, the system achieves a packet delivery rate of 92% and transmission rate of 10 Mbit/s. This is because the SDR used in this experiment requires a minimum received electrical amplitude of 27.5 mV to process the received signal. Long distance and higher data rates can be achieved using less sensitive SDR hardware.
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.
The secure distribution of the secret random bit sequences known as 'key' material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is a new technique for secure key distribution with single-photon transmissions: Heisenberg's uncertainty principle ensures that an adversary can neither successfully tap the key transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non- orthogonal photon polarization states to generate shared key material over line-of-sight optical links. Key material is built up using the transmission of a single-photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. We have developed and tested a free-space quantum key distribution (QKD) system over an outdoor optical path of approximately 1 km at Los Alamos National Laboratory under nighttime conditions. Results show that free-space QKD can provide secure real-time key distribution between parties who have a need to communicate secretly. Finally, we examine the feasibility of surface to satellite QKD.
Free-space optical (FSO) communication offers high capacity, license-free spectrum, and immunity to electromagnetic interference, making it a promising solution for future wireless links. However, practical deployment of FSO systems remains challenged by issues of link security and reliable transmission under atmospheric turbulence. In this work, we investigate the use of nonseparability encoding based on vectorial structured light as a turbulence-resilient and secure transmission approach. Through simulations and experiments, we compare multi-level nonseparability encoding with conventional amplitude modulation under various turbulence strengths and eavesdropping scenarios. The results demonstrate that vectorial structured light exhibits inherent security advantages, imposing higher optical signal-to-noise ratio penalties on eavesdroppers and making information recovery from partial interception significantly more difficult. These findings confirm the potential of nonseparability-based encoding for enhancing both security and robustness in FSO communication systems.