Spectral Amplitude Coding Optical Code Division Multiple Access (SAC OCDMA) is an advanced technique in asynchronous environments. This paper proposes design and implementation of a novel quantum logic gate (QLG) code, with code construction algorithm generated without following any code mapping procedures for SAC system. The proposed code has a unitary matrices property with maximum overlap of one chip for various clients and no overlaps in spectra for the rest of the subscribers. Results indicate that a single algorithm produces the same length increment for codes with weight greater than two and follows the same signal to noise ratio (SNR) and bit error rate (BER) calculations for a higher number of users. This paper further examines the performance of a QLG code based SAC-OCDMA system with NAND and direct detection techniques. BER analysis was carried out for the proposed code and results were compared with existing MDW, RD and GMP codes. We demonstrate that the QLG code based system performs better in terms of cardinality, which is followed by improved BER. Numerical analysis reveals that for error free transmission (10−9), the suggested code supports approximately 170 users with code weight 4. Our results also conclude that the proposed code provides improvement in the code construction, cross-correlation and minimization of noises.
Spectral Amplitude Coding Optical Code Division Multiple Access (SAC OCDMA) is an advanced technique in asynchronous environments. This paper proposes design and implementation of a novel quantum logic gate (QLG) code, with code construction algorithm generated without following any code mapping procedures for SAC system. The proposed code has a unitary matrices property with maximum overlap of one chip for various clients and no overlaps in spectra for the rest of the subscribers. Results indicate that a single algorithm produces the same length increment for codes with weight greater than two and follows the same signal to noise ratio (SNR) and bit error rate (BER) calculations for a higher number of users. This paper further examines the performance of a QLG code based SAC-OCDMA system with NAND and direct detection techniques. BER analysis was carried out for the proposed code and results were compared with existing MDW, RD and GMP codes. We demonstrate that the QLG code based system performs better in terms of cardinality, which is followed by improved BER. Numerical analysis reveals that for error free transmission (10−9), the suggested code supports approximately 170 users with code weight 4. Our results also conclude that the proposed code provides improvement in the code construction, cross-correlation and minimization of noises.
This study presents the design and analysis of a hybrid multi-user quantum key distribution (QKD) system utilizing spectral amplitude coding optical code division multiple access (SAC-OCDMA) encoding techniques. By assigning unique optical codes to each user, SAC-OCDMA enables spontaneous, asynchronous data transmission without any strict synchronization, which makes it scalable and flexible for quantum networks. In the architecture, each user’s quantum signal, initially prepared as weak coherent pulses and encoded using phase or polarization bases, is further spectrally sliced by a SAC-OCDMA encoder in a zero-based cross-correlation code. The physical impairments, comprising spontaneous Raman scattering, four-wave mixing, and crosstalk, were modeled and analyzed. We report a maximum secret key rate of ∼10 5 bps over a transmission distance of ∼58km . Furthermore, our analysis demonstrates that careful selection of launch power, simultaneous users, code weight, and spectral bin width is necessary for optimizing the trade-off between multi-user capacity and security performance. In comparison with wave division multiplexing QKD, which has much better spectral efficiency but strict channel allocation, the flexibility and asynchronous access to secure communication of our OCDMA-QKD design with zero cross-correlation coding are more aligned with the needs of quantum security.
Quantum Key Distribution (QKD) has remained the provable technique of ensuring secure communication amidst the impending security threat by the emerging quantum computers. Its security guarantee is based on superposition and entanglement, which are fundamental principle of quantum mechanics. As efforts are currently underway toward actualization of QKD network, researchers have explored a number of techniques though which this could be achieved. Some of the techniques proposed are; subcarrier based QKD network, Orthogonal Frequency Division Multiplexed (OFDM) based QKD network and spectral amplitude coding optical code division multiplexed (SAC-OCDMA) based QKD network. Among the aforementioned technique, SAC-OCDMA based system has history of efficient channel management, asynchronous nature, as well as channel security. Nevertheless, the adopted Optical Orthogonal Code (OOC) which is a family of OCDMA code, has a couple of challenges which include complex architecture, as well as longer code length, both of which are capable of resulting to reduction in the secure key rate and number of simultaneous users. Thus, this work presents a new one-weight authentication code, which are assigned, uniquely to individual user in SAC-OCDMA based QKD network. The performance of the code was explored in QKD network using simulation, mathematics and laboratory experiment. Firstly, the proof of concept of plug and play (p&p) in QKD network was carried out and the concept of phase reorientation was clearly established using Optisystem simulation tool. This was followed by mathematical modelling of the secure key rate and QBER for different number of users. As observed in the obtained results, at an average mean photon number of 0.48, a 21-user network was achieved at a secure key rate of 24 bps over a distance of 5 km. The result of comparison of the proposed code with a Wavelength Division Multiplexed (WDM) system shows its security capability above the later. The code was further compared with an OOC based network and found to generate key at higher rate when the number of users is below 14. A two-user experimental result shows the real life realization of the proposed system as a transmission distance up to 40 km was achieved with secure key rate of 320 bps. Application of the proposed code in Differential Phase Shift Key – Quantum Key Distribution (DPS-QKD) environment was also established. The obtained results have shown that aside presenting a secure mechanism, the design flexibility and moderate code length exhibited by the proposed code are excellent factors that could be explored in enhancing the performance of QKD network.
In this paper, performance analysis of conventional spectral amplitude coding (CSAC) with hybrid (HSAC) for OCDMA system is investigated in local area network (LAN) environment. The CSAC is built based on arithmetic sequence with simple algebraic ways. The HSAC technique is used in which spectral amplitude coding (SAC) combined with wavelength division multiplexing (WDM) to effectively reduce multiple access interference (MAI) and mitigate the influence of phase induced intensity noise (PIIN) arising in photodetecting process. The main idea is to construct the code sequences in SAC domain then repeat it diagonally in the wavelength domain as groups which maintains the same cardinality of a given code weight. Results show that HSAC outperforms CSAC when the number of active users is high due to its better correlation properties. It has been shown that the HSAC can suppress intensity noise effectively and improve the bandwidth utilization significantly up to 4.2 nm.
Security becomes the critical issue in incoherent spectral amplitude coding optical code division multiple access (SAC-OCDMA) systems. In preventing the unintended users from decoding and extracting the data due to the cross-correlation among code sequences, an ideal detection technique is needed to enhance the security of the SAC-OCDMA systems. In this paper, we study the efficiency of the modified-AND subtraction detection technique as well as conventional AND subtraction detection technique in towards the confidentiality issue. The OptiSystem software is used to simulate the system performance of the mentioned detection approaches. Based on enhanced double weight (EDW) codes, the simulation results revealed that the modified-AND subtraction detection improves the confidentiality of SAC-OCDMA system compared to the conventional AND subtraction detection. The modified-AND subtraction detection technique manage to secured the data from the unintended users to make them only detected a noise with interferer bit-error rate (BER) = 1 and Q-factor = 0.
This paper presents security performance of spectral amplitude code OCDMA based on Modified Double Weight (MDW) OCDMA scheme. The eavesdropper probability of correctly detected Spectral Encoding Chip Bandwidth (SECB) pulses in a code word is investigated. For MDW code with code length and code weight of 9 and 4 respectively, SNR of approximately 8 dB is sufficient for an eavesdropper to detect the SECB pulses with a probability of 50%. The eavesdropper performance is based on tapping and observing the encoded transmitted signal using a tuning band pass filter followed by envelope detector. The eavesdropper measures the intensity for each intercepted pulse and calculates its corresponding sig- nal to noise ratio (SNR). Spectral Encoding Chip Bandwidth effect is investigated by simulation. The possibility of eavesdropping increases with wide SECB. Our results show that using unipolar OCDMA code schemes based on MDW code system enhances the security with a low cost implementation in comparison to the bipolar ones.
Abstract Security enhancement and bandwidth increase are requirements of ultrafast future optical code division networks that also minimise the latency at nodes without distressing the traffic performance. In OCDMA systems, eavesdropper tries to breach the optical code, and encoded/encrypted data in order to get correct code word of legitimate user. For security enhancement, an ultra high speed 4×100 Gbps two dimensional Diagonal identity matrix (2D-DIM) code and four input single output (FISO) all optical logic gate (AOLG) with private key encryption is proposed and its performance in terms of security is analyzed. Expressions for synchronous and asynchronous transmissions are derived for proposed work and it is perceived that asynchronous transmission has better security. Further performance/security analysis is carried out for different scenarios such as with/without FISO, with 1D-DIM/2D-DIM codes, using 4×1 AND gate/NOR gate in terms of correct code detection rate (CCDR), max. eye amplitude (MEA), Received Q factor, Signal to noise ratio (SNR) at different launched power levels for legitimate user and eavesdropper. Eavesdropper attacked the proposed system but due to FISO layering, private key encryption, and 2D-DIM codes, cannot get acceptable level of CCDR. To the best of author’s knowledge, proposed system is ultra high speed with enhanced security and no reported studies have investigated security enhancement at this much ultra high speed.