Abstract This paper introduces an optimized multistage design approach for multipump distributed Raman amplifiers (MP-DRAs) in future multiband wavelength division multiplexing (MB-WDM) systems. Wideband system increases transmission capacity of the transmission but results in extreme nonuniformity of gain and asymmetric noise accumulation. To limit these impairments, three single-stage configurations are systematically explored in the C+L band: copropagating, counterpropagating, and bidirectional. The bidirectional configuration provides the optimum C+L performance. It has a peak gain of 17.57 dB, a minimal gain ripple of 1.97 dB, an average noise figure of 7.077 dB (average), and a transmission reach of 206 km. This was the starting point for the implementation of a dual-stage cascaded bidirectional DRA in the same system of 8 channels C+L. This configuration increased the maximum common transmission reach to 274 km, an extra 68 km. The optimization framework is then extended to 110 nm S+C+L band (1,515–1,625 nm). Two different configurations are assessed; single-stage gain-flatting filter (SS-GFF)- and dual-stage (DS-GFF)-based DRA. The SS-GFF yields a 14.12 dB peak gain, a 4.125 dB ripple, and 188 km reach. Importantly, the DS-GFF architecture extends the range of transmission reach to be 236 km, an improvement of 25.5 %. The results provided a strong, simple path toward optimizing transmissions in broad band optical infrastructure.
Abstract Direct-detection DWDM links combining dispersion compensating fiber (DCF) with chirped fiber Bragg gratings have been studied mainly at 10 Gb/s per channel and low channel counts. This paper examines how such compensation scales when rate and channel count increase together. A 64-channel, 50 GHz-grid system using DCF with a square-root chirped fiber Bragg grating (SR-CFBG) is analyzed at 25 and 40 Gb/s per channel (1.6 and 2.56 Tb/s aggregate) with NRZ, RZ, and PAM-4. An analytical Q-factor framework combines ASE-, ISI-, and receiver-limited contributions, and its OSNR model matches a 32-channel, 10 Gb/s reference within 0.08 dB over 100–2,000 km. With compensation fixed, the maximum FEC-compliant reach (Q ≥ 6; SMF distance only) falls from 2,433 km at 10 Gb/s to 405 km (25 Gb/s) and 160 km (40 Gb/s) for NRZ, whereas PAM-4 reaches 652 and 297 km. NRZ and RZ remain dispersion-limited, but PAM-4 becomes OSNR-limited: lowering launch power from −5 to −10 dBm shortens its reach by about half. Relative to the 10 Gb/s reference, the capacity–distance product is 0.83 and 0.53 times for NRZ but 1.34 and 0.98 times for PAM-4. Results are trend-level: the ISI term is calibrated at one operating point, and the PAM-4 advantage depends on the assumed rate scaling.
Abstract Accurate optical communication monitoring is essential for distinguishing optical transmission failures from physical-layer attacks that produce similar signal degradation characteristics. This study proposes a class-specific validation–optimized DNN–LSTM (CSVO-DL) framework for joint optical failure diagnosis and physical-layer attack detection. The framework considers seven operating states, comprising normal operation, three optical failure conditions, and three physical-layer attacks. Physically constrained attack scenarios are constructed from optical measurements, with corresponding bit-error rates estimated using a quality-of-transmission model. Unlike conventional fixed-weight fusion, the proposed framework integrates DNN and LSTM predictions through class-specific weights optimized using validation data to improve multiclass discrimination. Experimental evaluation on a balanced dataset of 910,000 samples, including an independent test set of 210,000 samples, achieved 91.190 % accuracy, 91.600 % macro-precision, and 91.056 % macro-F1 score, outperforming the evaluated standalone machine-learning and deep-learning baselines. The framework achieved macro-recall values of 98.468 % for optical failures and 80.553 % for physical-layer attacks. Ablation analysis demonstrated an improvement in macro-F1 from 90.819 % with fixed-weight fusion to 91.056 %, while introducing only 0.019 s of additional fusion overhead for the complete test set. These findings highlight the potential of class-specific deep-learning fusion for integrated optical performance monitoring, failure diagnosis, and physical-layer security.
Abstract In this work, the design and evaluation of a hybrid optical modulation technique for wavelength division multiplexing (WDM) technology is presented. The proposed optical system consists of 21 channels, with each channel generating a data rate of 45 Gbps, using advanced modulation techniques such as binary phase shift keying (BPSK) and modified duobinary return-to-zero (MDRZ). The performance of the hybrid modulation format is evaluated at a channel spacing of 100 GHz. The key performance parameters, including spectral efficiency, signal quality, optical signal-to-noise ratio (OSNR), eye opening factor (EOF) spectral efficiency, receiver sensitivity, and BER (bit error rate), are investigated using the proposed hybrid optical modulation technique. The results demonstrate that employing MDRZ with BPSK can improve the performance of the WDM system, making it suitable for noise-resistant and long-haul optical communication systems. The highest values of OSNR, signal quality, and spectral efficiency achieved are 49.6 dB, 47.77, and 11.157 bit/s/Hz, respectively. The obtained results indicate enhanced WDM system performance, which can further be utilized in high-data-rate communication systems.
