Design and performance analysis of a six-state QKD over FSO and optical fiber utilizing switch-controlled polarization generation for secure optical communications
Shelan Khasro Tawfeeq, Yousif I. Hammadi, Ahmed Ismael Khaleel
Abstract Quantum key distribution (QKD) is a process that utilizes the principles of quantum mechanics to securely share a secret key between two parties, ensuring unconditional security. Diverse QKD protocols are established to guarantee the security and integrity of information against any attempts by an eavesdropper monitoring the transferred photons. One of these protocols is the six-state protocol. This work employs OptiSystem 21.1 simulation software to design and emulate the six-state protocol, wherein polarization states are produced through random switching control rather than optical modulators. The protocol’s performance, indicated by quantum bit error rate and secure key rate, is analytically examined for both free space optical (FSO) channel and optical fiber channel, incorporating parameters from two types of commercial single-photon detectors to enhance realism. The maximum secure key rate attains 5.439 Mbps at 10 km of optical fiber, in contrast to 1.674 Mbps at 0.2 km under clear weather conditions in the FSO quantum channel utilizing ID 281 single-photon detector modules across both channels. The maximum distance that guarantees secure key rate with ID 281 for FSO channel is 2 km with 1760 bps with heavy haze compared to 100 km optical fiber with secure key rate of 15,000 bps.
Abstract Quantum key distribution (QKD) is a process that utilizes the principles of quantum mechanics to securely share a secret key between two parties, ensuring unconditional security. Diverse QKD protocols are established to guarantee the security and integrity of information against any attempts by an eavesdropper monitoring the transferred photons. One of these protocols is the six-state protocol. This work employs OptiSystem 21.1 simulation software to design and emulate the six-state protocol, wherein polarization states are produced through random switching control rather than optical modulators. The protocol’s performance, indicated by quantum bit error rate and secure key rate, is analytically examined for both free space optical (FSO) channel and optical fiber channel, incorporating parameters from two types of commercial single-photon detectors to enhance realism. The maximum secure key rate attains 5.439 Mbps at 10 km of optical fiber, in contrast to 1.674 Mbps at 0.2 km under clear weather conditions in the FSO quantum channel utilizing ID 281 single-photon detector modules across both channels. The maximum distance that guarantees secure key rate with ID 281 for FSO channel is 2 km with 1760 bps with heavy haze compared to 100 km optical fiber with secure key rate of 15,000 bps.
Abstract With increasing demands for secure high-speed wireless communications, integration of quantum key distribution (QKD) into light fidelity (LiFi) systems is a promising method for boosting data confidentiality in optical wireless networks. The BB84 protocol and Mach–Zehnder modulator (MZM) are utilized with a pump-assisted continuous wave laser at 1,550 nm and polarization control components to encode quantum states onto photons. They are transmitted on free space optical (FSO) links with a length ranging from 2 km to 8 km and received using Avalanche photodiodes (APDs) and optical filters. Performance analysis conducted using bit error rate (BER) and Q-factor analysis. BER maintained at zero across all tested configuration and transmission distance up to 8 km indicating excellent signal integrity and security. A highest Q-factor achieved a maximum of 3,055.9, which ensures signal integrity and low interference noise. The system operates at a simulated data rate of 10 Gbps, suitable for high speed optical wireless communication. Consistently high eye height (∼172,210 units) and stable decision thresholds confirm minimal inter-symbol interference and accurate symbol recognition. And the Poincaré sphere showed even polarization stability for different optical power levels. This work presents a simulation-based implementation of a polarization encoded QKD system over a LiFi-enabled FSO communication channel, aiming to enhance secure optical wireless communication. Calculated based on quantum bit error rate (QBER) and included in the theoretical analysis to demonstrate practical secure throughput.
Quantum Key Distribution (QKD) is a secure communication that uses a quantum encryption protocol in quantum physics using the principle of quantum mechanics. It solves the problems of key distribution between the sender and receiver and uses a special quantum channel to transfer keys in classical computers and also in the field of quantum computing (QC) in the future. Various protocols are designed in quantum key distribution to ensure the security and integrity of data from any surveillance or attack from some eavesdroppers when sending quantum states (photons) through a special quantum communication channel. The analysis of the device is used in the effective simulation process using quantum entanglement technology. The use of OptiSystem software is a simulation application Optical is used in telecommunications. When using for 6DP in distributing quantum keys across the optical fiber channel, quantitative results appear in 6 using networking technology. We improved in the sifted key rate and the QBER rate. Through these results, we believe 6DP is more secure and reliable. For the rest of the protocols in the distribution of quantum keys using quantum entanglement.
Quantum Key Distribution (QKD) is a potential defense against future quantum attacks that can break traditional encryption algorithms, such as RSA and ECC. The current work is based on the development of the BB84 protocol with the features of utilizing quantum mechanics and eavesdropping detection through signal disturbance. A simulation of the BB84 protocol was built using polarization encoding over a 10 km single-mode optical fiber using OptiSystem software. The system consists of standard telecom equipment, such as a continuous wave laser at a frequency of 193.1 THz, polarization controllers, and single-photon detectors. Both secure and insecure cases were simulated, where an attacker (Eve) had used an intercept-resend attack. The outcome showed significant Bit Error Rate (BER) and Quantum Bit Error Rate (QBER) increases during attacks, thus proving the protocol's vulnerability to interference. In addition, a special intrusion detection system based on BER was used to identify such anomalies in real-time. The simulation illustrates the feasibility of using QKD in today's optical networks to secure communications.
Due to the fast-paced advancements of the quantum computing field, current public key cryptographic protocols need to be rethought. One promising solution is Quantum Key Distribution (QKD), whose security is robust to any computational advancement. The security of QKD relies on the laws of quantum mechanics, ensuring that any eavesdropper attempting to access the data will be detected. In particular, polarization-encoding QKD systems allow to generate secret keys in two remote locations to encode/decode information, using the State of Polarization (SOP) of single photons. Although its security has been theoretically proven, its practical implementation poses some challenges, part of which are the main focus of this PhD thesis. One relevant process in QKD systems is the synchronization between the transmitter and receiver, namely, the frame synchronization. This way, in this thesis, a frame synchronization method is developed and implemented, showing its potential for the use in prepare-and-measure QKD systems. The developed method has been shown to be effective, even with a low number of photons reaching the receiver. Furthermore, its architecture allows it to be adjusted for different attenuation regimes of the QKD system. The ability to encode data on the physical properties of single photons, in this case, polarization, highly depends on the capacity to accurately generate the required polarization states on demand. This way, an automatic SOP generation method, comprising an optical polarization monitoring system and a dedicated algorithm was developed and implemented, capable of generating four SOPs. This method reached an average Quantum Bit Error Rate (QBER) of 0.75%, which is well below the security threshold. After the SOP generation, and their transmission through the quantum channel, polarization alignment algorithms are required to compensate for the random rotations induced by birefringence in the optical fiber. In this thesis, a non-iterative polarization compensation method was implemented. This method requires only three QBER estimations to re-align the polarization, reaching average QBERs of 1.8%. Additionally, multiple iterative methods were implemented for comparison purposes, with the results clearly showing a better efficiency of the deterministic method. Beyond fiber-based transmissions, free-space transmissions were analysed due to their ability to reach sites without installed fiber and due to its potential for satellite-based quantum communications. This thesis demonstrates the feasibility of polarization-encoding QKD over free-space channels, by subjecting quantum signals to atmospheric turbulence to study its impact. In that sense, polarization variations over a 1.8 km outdoor free-space channel were monitored, to understand the effect of atmospheric turbulence on polarization. These results have shown that SOP variations in free-space links are slow, allowing their compensation. Furthermore, it was identified that, under conditions tested, the Secret Key Rate (SKR) could reach values up to 8.7×10ˉ⁴ bits per second, allowing QKD over free space for distances up to 2.31 km.
It has been widely recognized that the underlying principles of quantum mechanics could be used to enable secure communications, without any additional conventional cryptographic systems, while utilizing the properties of the photons. Considerable research efforts have been invested to develop an efficient quantum key distribution (QKD) scheme over either free-space optical or fiber-optics channels. Most of these research efforts have been focused on a two-dimensional QKD, commonly realized by the use of the polarization state of photons. However, the data rates for the quantum key exchange in two-dimensional QKD are still low, while transmission distance is limited. On the other hand, it is well known that photons can carry both the spin angular momentum (SAM) and the orbital angular momentum (OAM), associated with the polarization and azimuthal phase of the complex electric field, respectively. Accordingly, we can define the combined-OAM-SAM state of a photon as |l, σ〉, where l and σ correspond to OAM and SAM indexes, respectively. Since the OAM eigenstates are orthogonal, an arbitrary number of bits per single photon can be transmitted, which could considerably increase the total secure bit rate. To improve secure data rates, we propose two types of protocols, namely, nonentangled-based (such as weak coherent state) and entanglement-assisted protocols, both employing the photon combined-OAM-SAM state, which can be used for secure key distribution over free-space optical and few-mode fiber channels. Two types of entanglement-assisted protocols are described, namely, two-basis and (D + 1)-basis protocols ( D is dimensionality of corresponding Hilbert space). We further describe how to implement the qudit gates required for implementation of these protocols. Finally, we discuss the security issues of the proposed protocols and determine both infinite and finite secret key fraction rates.
This paper proposes a novel design and analyzes security performance of quantum key distribution (QKD) protocol over free-space optics (FSO). Unlike conventional QKD protocols based on physical characteristics of quantum mechanics, the proposed QKD protocol can be implemented on standard FSO systems using subcarrier intensity modulation binary phase shift keying and direct detection with a dual-threshold receiver. Under security constraints, the design criteria for FSO transmitter and receiver, in particular, the modulation depth and the selection of dual-threshold detection, respectively, is analytically investigated. For the security analysis, quantum bit error rate, ergodic secret-key rate, and final key-creation rate are concisely derived in novel closed-form expressions in terms of finite power series, taking into account the channel loss, atmospheric turbulence-induced fading, and receiver noises. Furthermore, Monte-Carlo simulations are performed to verify analytical results and the feasibility of the proposed QKD protocol.