Abstract Free Space Optical (FSO) communication is a highly efficient wireless communication technology owing to its high capacity and improved security features. In this manuscript, a dual-hop FSO communication system is considered that employs Amplify-and-Forward (AF) protocol at the relay. Channel State Information (CSI)-assisted relaying is utilized for enhancing the performance of the network by taking advantage of the information about the channel conditions. The dual-hop FSO system is assumed to be degraded by Malaga ($\mathcal{M}$) turbulence fading and pointing errors. Closed-form expressions for Outage Probability (OP), Bit Error Rate (BER) and Ergodic Capacity (EC) are formulated using Meijer-G function. OP is examined under varying turbulence strengths, pointing errors, link lengths and rate threshold values, and BER is presented for various modulation schemes. Asymptotic OP expression is also derived which illustrates and validates OP at high SNRs. Additionally, Monte-Carlo simulations are performed to check the validity of the obtained analytical results.

Abstract The present work simulates and evaluates a novel lead-free double perovskite absorber in combination with various transport layers to achieve a high-performance solar cell with optimized efficiency. The lead-free PSCs are configured with ITO as the transparent conducting oxide, Cs2PtI6 as the absorber, PDINO, PCBM, IGZO, PFN-Br, C60 as Electron transport layers (ETLs), CuI, CuSCN, NiO, PEDOT:PSS, Spiro-OMeTAD, CZTSe, CFTS as hole transport layers (HTLs), and carbon as the back electrode. A total of 35 distinct PSC configurations were designed by combining different ETLs and HTLs, and their performance characteristics were thoroughly analyzed and evaluated. Among all possible combinations, CuSCN used as the HTL exhibited the best performance compared to the other HTLs. Accordingly, five superior device configurations incorporating CuSCN as the HTL, various ETLs, and Cs2PtI6 as the absorber were thoroughly investigated. Their performance was analyzed under different input parameters, including the thickness and defect density of the perovskite absorber layer (PAL), ETL thickness, PAL bandgap, back-contact work function, series resistance, temperature, and shunt resistance. The best performance is achieved with the architecture ITO/PDINO/Cs2PtI6/CuSCN/C, delivering a VOC of 1.3 V, JSC of 32.17 mA/cm2, FF of 73.71%, and a PCE of 30.95%.

The Monte Carlo Method is a powerful statistical technique for propagating uncertainty in photometric measurements, particularly when models are nonlinear or input variables deviate from Gaussian distributions. This study explores the application of MCM to luminous flux measurements using Type C goniophotometers, with comparisons to the conventional Root Sum of Squares Method. Three distinct Monte Carlo models were implemented. The first classified uncertainties as Type A or Type B, assigning corresponding probability distributions. The second employed Shannon information theory to derive distributions based on available knowledge, while the third exploratory model randomized distribution selection among normal, uniform, and triangular forms. Sensitivity analysis, guided by the Pareto principle, identified the key variables contributing to $$80 \%$$ of overall variability. Results showed that Root Sum of Squares Method yielded an expanded uncertainty of $$3.4\%$$ , whereas the first, second, and third Monte Carlo models achieved $$3.0 \%$$ , $$2.5\%$$ , and $$2.3\%$$ , respectively. Importantly, the Pareto-based reduction strategy preserved accuracy while lowering computational complexity. These findings demonstrate that Monte Carlo Method provides a more effective framework for uncertainty evaluation in photometry than traditional approaches, with the information theory-based model offering the best balance between accuracy and efficiency. The proposed methodology enhances the reliability of luminaire characterization and supports practical adoption in industrial measurement contexts.

Abstract Motivated by recent experiments, the theoretical study of wave propagation in time-varying materials is of current interest. Although significant in nearly all such experiments, material dispersion is commonly neglected in theoretical studies. Yet, as we show here, understanding the precise microscopic model for the material dispersion is crucial for predicting experimental outcomes. Here we study the temporal scattering coefficients of four different time-varying Drude–Lorentz models, exploring how an incident continuous wave splits into forward and backward waves due to an abrupt change in plasma frequency. The differences in the predicted scattering are unique to time-varying media, and arise from the exact way in which the time variation appears in the various model parameters. We verify our results using a custom finite difference time domain algorithm, concluding with a discussion of the limitations that arise from using these models with an abrupt change in plasma frequency.

Abstract Distributed feedback (DFB) lasers with narrow linewidths are vital in high-coherence photonics. However, the quarter-wave phase shift (QWPS) that enforces single-mode emission drives a non-uniform photon density distribution and longitudinal spatial hole burning (LSHB) effect, broadening the linewidth. Here, we propose a step apodized coupling surface grating DFB (SAC-DFB) laser that divides the cavity into two segments with distinct coupling coefficients and evaluates it using a time-domain traveling wave model within a linewidth analysis framework.Co-optimizing the coupling coefficient distribution and segment length ratio flattens the photon density distribution under different facet coatings.To relate the grating structure, optical field, and LSHB effect induced linewidth (Δν NN ), we define three physics-based parameters: the photon density distribution uniformity factor f, carrier dynamics parameter U K (w) ,its optical field intensity weighted counterpart U H (w) . The ordinary least squares fit identify U H (w) as the dominant correlate of Δν NN . Relative to QWPS-DFB lasers matched in cavity length and facet coatings, optimized SAC-DFB lasers reduce Δν NN by up to approximately 68% and decrease the total linewidth by more than 35%; extending the cavity to 1500 μm yields a total linewidth of 85.85 kHz at 150 mA with high-reflection/anti-reflection facet coating. A neural network predicts f from grating parameters with a coefficient of determination exceeding 99.5%, thereby enabling manufacturing-oriented screening. Collectively, this study establishes a general, physics-guided framework that relates grating structure and optical field modulation to linewidth, both qualitatively and quantitatively, and demonstrates a fabrication tolerant SAC architecture that suppresses the LSHB effect and achieves narrow linewidths.

Abstract A tunable Brillouin multi-wavelength mode-locked fiber laser (BMMFL) is proposed, predominantly based on a nonlinear optical loop mirror (NOLM) and assisted by nonlinear polarization rotation (NPR). The system employs 10 km of dispersion-shifted fiber (DSF) as the Brillouin gain medium to generate multiple wavelengths. The DSF, together with the polarization controller (PC1) and the optical coupler (OC1), forms the NOLM; the combined NOLM-NPR action functions as an equivalent saturable absorber (SA) to enable mode-locked pulse generation. By adjusting the PCs, the BMMFL generated 69 Brillouin multi-wavelength lines (BMLs) with a 10.9 GHz Brillouin frequency shift, when the pump power, Brillouin pump (BP) power, and BP central wavelength were fixed at 250 mW, 6 dBm, and 1546.5 nm, respectively. Under these conditions, no stably repeating mode-locked pulses were observed. A multi-wavelength tuning range of 30 nm was also obtained at different BP central wavelengths. Subsequently, by further adjusting the PCs, the BMMFL achieved a mode-locked pulse train with a pulse width of 236 ns and a fundamental frequency repetition rate of 19.92 kHz, with only 13 BMLs retained. At a pump power of 350 mW, the maximum average output power of the mode-locked pulse reached 1.29 mW. Moreover, harmonic mode locking up to the fifth order was achieved. This BMMFL offers broad application prospects in dense wavelength division multiplexing (DWDM) systems, laser processing and optical fiber communications.

Abstract In this paper, a compact and high-performance dual-channel all-silicon polarizer (DCASP) is proposed, optimized, and validated experimentally. Device optimization is carried out via the finite-difference time-domain method and a simulated-annealing-particle-swarm-optimization hybrid strategy, enabling compact size, low insertion loss, high polarization extinction ratio, and wide bandwidth for both channels. Our presented DCASP is only 13.6 × 7.6 μ m 2 in size. From 1520 to 1600 nm, the insertion loss below 0.72 dB, polarization extinction ratio exceeding 24.67 dB, and crosstalk (CT) lower than −17.70 dB are measured for TE-pass channel, while the measured insertion loss is below 0.49 dB and the measured polarization extinction ratio exceeds 33.87 dB, and the measured CT is less than −22.05 dB for TM-pass channel.

Abstract In this paper, a dual-layer metamaterial structure which is composed of polytetrafluoroethylene (PTFE) substrate and copper was designed. The mechanism underlying the generation of multi-band analogous electromagnetically induced transparency (EIT) effect in the structure is analyzed by the finite integration time-domain (FITD) method and equivalent circuit method (ECM). Additionally, the influence of the structural parameters of the structure on transmission is also investigated. A detection approach utilizing the structure to detect the thickness and permittivity of solid plate structures is formulated, which can be employed in solid sensing. The results indicate that the structure holds potential applications in refractive index sensing and multi-band filter.

Abstract This paper presents the design of a novel reflective linear-to-circular polarization conversion metasurface (PCM) and its application to a wideband high-gain circularly polarized (CP) antenna. The proposed PCM efficiently converts incident linearly polarized (LP) waves into CP waves within an ultra-wideband range of 11.8-28.6 GHz, thereby laying a solid foundation for the design of the wideband CP antenna. By adding an LP microstrip antenna as the feed source above the PCM, the metasurface leverages its polarization conversion capability to reflect CP waves, simultaneously enhancing the antenna gain, and thus yields a wideband high-gain CP antenna. The designed CP antenna exhibits an impedance bandwidth and a 3-dB axial ratio (AR) bandwidth both spanning from 13.2 to 18.6 GHz, corresponding to a relative bandwidth of 34%. Notably, the 3-dB AR bandwidth perfectly matches the impedance bandwidth. Meanwhile, the antenna maintains a stable high gain exceeding 11 dBi across the entire operating bandwidth. Excellent agreement is achieved between the measured and simulated results, confirming that the proposed antenna simultaneously achieves a wide CP operating bandwidth, full-band 3-dB AR coverage, and high gain. Such characteristics make it highly valuable for potential applications requiring both wideband CP operation and high gain, such as microwave communications, precision radar, and satellite navigation systems.