In this paper, an ideal highly sensitive THz biological sensor based on a polarization-insensitive graphene absorber with three bands is designed and optimized. The concept of a polarization-insensitive sensor involves a ring of graphene and eight symmetrical ring resonators. Finite element modeling reveals that the developed absorber may be fine-tuned for a sensing capacity and an absorption efficiency of over 99.8 %. At frequencies of 3.769 THz, 5.888 THz, and 9.453 THz, respectively, three distinct narrow absorption peaks with efficiencies of 98.6 %, 99.2 %, and 99.8 % are produced as a result of field confinement induced by graphene surface plasmon resonances. This study delineates our sensitive refractive index sensor, including circular micro ring resonator and multiple graphene rings. A periodic design consisting of a center ring and eight peripheral rings that rotate pi/4 rad produces a three-band absorber arrangement independent of wave polarization. Moreover, it has been demonstrated that modifying the graphene layer's chemical potential may change the resonance frequencies while improving absorber performance. A maximum sensitivity of 3045 GHz/RIU, a Q-factor of 26.01, and a figure-of-merit of 9.18 RIU- 1 are achieved by the proposed refractive index sensor with an analyte thickness of 2.3 mu m. The suggested THz RI sensor offers an identical response for TE and TM polarizations because of its rotational symmetry. The performance of RI sensors is assessed using two biological samples: breast cancer and healthy breast cells. The findings unequivocally demonstrate the THz sensor's possible biological applications. Achieving high absorption and sensitivity is the main feature of this paper.

In this paper, a simple and compact 1 × 2 decoder based on a two-dimensional photonic crystal structure is proposed, whose operation relies on total internal reflection and photonic band gaps. The designed structure employs a square-lattice configuration of silicon dielectric rods embedded in air. The decoder consists of two input ports, one acting as a Bias port and the other as a logical input port. Numerical modeling and simulations are performed using the plane-wave expansion (PWE) method and the finite-difference time-domain (FDTD) technique. The proposed coupling-resonator structure increases the coupling efficiency at resonant frequencies. The structure has a relatively small footprint, comprising an 18 × 18 array of dielectric rods with a total area of approximately 147 µm2. A minimum contrast ratio of about 8.4 dB between logical “1” and “0” states is achieved. The decoder operates at 1.55 µm, making it suitable for photonic and optical communication applications. Due to its compact size, simple architecture, and use of a minimal number of ring resonators, the proposed decoder is well suited for high-speed photonic integrated circuits and future all-optical computing systems. The bit rate of the proposed decoder is estimated to be 2 Tb/s.

In this study, a terahertz (THz) absorptive metamaterial sensor is presented for the early detection of seven different types of cancer. The proposed absorptive metamaterial sensor is polarization-independent due to its symmetric structure. It consists of a patterned gold resonator on an intermediate Teflon dielectric layer and a gold reflector. This sensor operates within the frequency range of 4 to 6.5 THz and absorbs energy in four distinct spectral bands, with the maximum absorption of 99%. For basal cell carcinoma detection, the sensor achieves the quality factor (Q) of 213.39, sensitivity (S) of 1.68 THz/RIU, and figure of merit (FOM) of 83.31 RIU−1. In contrast to existing multi-band designs, which typically exhibit low Q-factors ranging from 8.9 to 17 and consequently limited resolution, the main advantage of the proposed quad-band structure is its ability to simultaneously achieve a high Q-factor and high sensitivity. Due to its optimized performance, the resonance frequency of the proposed sensor exhibits significant shifts even with minor changes in the surrounding refractive index (RI). Therefore, the sensor can respond to subtle differences in the refractive index between cancerous and healthy cells. Owing to its high sensitivity to environmental changes, this sensor is suitable for biomedical applications, including noninvasive detection of subtle tissue variations and early diagnosis of various diseases. Furthermore, the simple, symmetrical design and quad-band operation make this sensor a more practical and reliable option than other existing structures, as it significantly reduces manufacturing challenges, costs, and error rates.

This work introduces a metamaterial absorber sensor in the terahertz region, specifically designed in the form of a rod resonator inside two square rings to act as refractive index sensor. The structural dimensions are 50×50 micrometers squared. The underlying material between two gold layers is Teflon. The absorption coefficient for this structure is exceptionally high, measured at 99.9% and 94.6% at frequencies of 4.72 THz and 5.75 THz, respectively. This study investigates the sensing performance by analyzing refractive index values in the range of 1.3 to 1.4. The sensor performance is evaluated through precise simulations conducted using the CST software. Sensitivities of 0.55 THz/refractive index unit (RIU) and 1.75 THz/RIU are obtained for the first and second peaks, respectively. The quality factors for the absorption peaks in order are 269.17, 42.5 and the figure of merit index (FOM) is also calculated in order as 33.45 and 14.6 (RIU-1) for the first and second peaks. Given its small size, high absorption, and high sensitivity, the proposed design has the potential for use as a terahertz biosensor.

This paper introduces the first integrated three-stage design including a semiconductor optical amplifier (SOA), an erbium-doped fiber amplifier (EDFA), and a noise suppression loop. This system effectively mitigates amplified spontaneous emission (ASE) noise in fiber Bragg grating (FBG)-based strain and temperature sensing applications. The proposed configuration addresses the persistent challenge of a low signal-to-noise ratio (SNR), which limits the sensitivity and precision of FBG sensors. The system consists of an SOA-based modulator, an EDFA pre-amplifier with feedback control, and a fast photodetector within a noise-suppression module. Previous interrogation methods have achieved SNRs approaching 30 dB. Our design exceeds this threshold, delivering an output SNR improvement of 35.34 dB compared to conventional single-stage architectures. Simulation results validate the effectiveness of the proposed design in enhancing signal quality. They also demonstrate its strong potential for deployment in high-precision sensing applications, including structural health monitoring, aerospace systems, and biomedical diagnostics.

Surface plasmon resonance (SPR) is a technique utilized for the label-free detection of cancer cells. In this analysis, we introduce a photonic crystal fiber (PCF) designed with an open D-channel, featuring a layer of gold (Au) and titanium dioxide (TiO2) as the plasmonic material. This effectively reduces the gap between the fiber core and the gold layer, resulting in improved performance. Additionally, incorporating TiO2 between the gold and the silica substrate enhances their adhesion and contributes to a more robust structure. We conducted a comprehensive numerical analysis of the suggested biosensor utilizing the finite element method (FEM) integrated with perfectly matched layers (PML) within the COMSOL Multiphysics simulation tool. The design of this sensor is specifically intended for the detection of molecules with a refractive index (RI) varying from 1.25 to 1.43, achieving an impressive peak spectral sensitivity of 47,000 nm/RIU. For this purpose, we investigated RI values from 1.36 to 1.401 concerning six different cancer cell types. The highest spectral sensitivity is 5214.285 nm/RIU, while the amplitude sensitivity is -1481.1 RIU− 1, which has been recorded for MCF-7 and HeLa cells. This proposed sensor shows improved amplitude sensitivity, signal-to-noise ratio (SNR), full width at half maximum (FWHM), figure of merit (FOM), and detection limit (DL) compared to existing biosensors, highlighting its potential for biosensing applications. Additionally, it is significant that according to the results, HeLa cells have a maximum resolution of 1.19 × 10− 5 RIU and a FOM of 350 RIU− 1.

Plasmonic biosensors based on photonic crystal fibers (PCF-SPR) have emerged as promising candidates for highly sensitive and real-time biomedical detection. In this study, we propose and numerically investigate a novel D-shaped PCF-based plasmonic biosensor incorporating a thin gold layer as the plasmonic medium and an optimized titanium dioxide (TiO2) dielectric interlayer. This configuration significantly enhances light-metal interaction, improves mode confinement, and strengthens surface plasmon resonance (SPR) coupling efficiency. Three-dimensional finite element method (FEM) simulations are employed to examine the influence of critical design parameters, including the thicknesses of Au and TiO2 layers, air-hole diameters and arrangement, and analyte refractive index (RI) variations, on resonance wavelength and confinement loss. The proposed sensor achieves an outstanding wavelength sensitivity (Sλ) of 14,000 nm/RIU, amplitude sensitivity (SA) of 610 RIU−1, and a resolution of 1.4 × 10−2 RIU within the analyte RI range of 1.33–1.40. These performance metrics enable the discrimination of blood constituents such as water, plasma, hemoglobin, and red and white blood cells, even under conditions of closely matched refractive indices. The findings highlight the remarkable potential of PCF-SPR biosensors for rapid and precise blood analysis, offering new avenues for the advancement of next-generation biomedical diagnostic platforms.

The continuous demand for faster processing systems, driven by the rise of artificial intelligence, has exposed limitations in traditional transistor-based electronics, including quantum tunneling, heat dissipation, and switching delays due to challenges in further miniaturization. This study explores optical systems as a promising alternative, leveraging the speed of photons over electrons. Specifically, we design and simulate optical NAND and NOR logic gates using a two-dimensional photonic crystal structure with a square lattice. Symmetrical waveguides are used for the input paths to make the structure relatively more straightforward to fabricate. A key innovation is the ability to realize both gates within a single structure by adjusting the phases of the input sources. To optimize the phase parameters efficiently, we employ the ML-FOLD (Meta-Learning and Formula Optimization for Logic Design) optimization formula, which outperforms traditional methods and machine learning approaches in terms of computational efficiency and data requirements. Through finite-difference time-domain (FDTD) simulations, the proposed optical structure demonstrates successful implementation of NAND and NOR gate logic, achieving high contrast ratios of 4.2 dB and 4.8 dB, respectively. The results validate the effectiveness of the ML-FOLD method in identifying optimal configurations, offering a streamlined approach for the design of all-optical logic devices.

In this article, a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) has been presented for use in detecting the concentration of sucrose solution. This sensor is expertly designed, drawing on the vertical pupil pattern found in the eyes of certain animals to optimize the concentration of the electromagnetic field at the center of the structure. The primary objective is achieving superior amplitude sensitivity (AS) while minimizing losses. To ensure this, we have applied the Nelder-Mead algorithm for precise optimization of the structural parameters. For the analysis of this structure, the finite element method based on the mode solver has been used. After analyzing and optimizing the sensor, maximum wavelength sensitivity (WS) of 12,000 nm/RIU, AS of -5430.24 RIU-1, and maximum figure of merit (FOM) of 315.9077 RIU-1 were obtained. Finally, in order to investigate the application of this sensor as a sensor for determining the concentration of sucrose solution, it has shown the values ​​of 13,000 nm/RIU, -6202.62 RIU-1, and 356.93 RIU-1 for WS, AS, and FOM respectively related to the concentration of 45%, which shows its excellent performance in refractive index (RI) detection applications. Due to the absence of structural complications and being immune to manufacturing errors caused by small air holes, this design is considered to be an excellent impression of natural elements by providing ultra-high sensitivity.

In this paper, we present the design, investigation, and optimization of a surface plasmon resonance (SPR) biosensor using a D-shaped photonic crystal fiber (PCF) with layers of gold and titanium oxide (TiO₂). The TiO₂ layer is applied on top of the gold layer to enhance sensitivity. This biosensor aims to simplify the manufacturing process while achieving optimal performance through effective coupling. We improved the design by thoroughly analyzing and optimizing various structural parameters to enhance performance. Our biosensor demonstrated exceptional diagnostic accuracy when tested on multiple samples, including cancer cells (Basal, MDA-MB-231, Jurkat, PC-12, and HeLa). The biosensor achieved a maximum wavelength sensitivity (WS) of 42,000 nm/RIU, a maximum amplitude sensitivity (AS) of - 1862.72 RIU, and a maximum figure of merit (FOM) of 1393.128 RIU⁻¹ across the wavelength range from visible to near-infrared and within a refractive index (RI) range of 1.3-1.4. The results indicate that this optimized biosensor exhibits reliable and accurate detection capabilities, capable of measuring minute changes in RI with high precision.

This paper investigates the bit error rate (BER) changes for a free space optical (FSO) communication system. The performance of BER in 4th-order pulse position modulation (4-PPM), pulse width modulation (PWM), non-return to zero (NRZ), return to zero (RZ), SISO, and MIMO binary phase shift keying (BPSK) is compared in three models of Log-Normal, Gamma-Gamma, and Kim distribution. Also, pointing error for free-space optical channels with atmospheric turbulence for various transmitter beam divergence angle values and different transmitter and receiver aperture diameters are considered. After generating, sending, and receiving random bits with Gaussian white noise in MATLAB, the receiver's optical power is calculated by applying the channel factors for each distribution model for all selected modulations. Then, the received optical power is converted to an electrical signal. Finally, the changes in BER regarding the signal-to-noise ratio (SNR) are simulated for the intended free-space optical communication channel. The Log-Normal model shows lower BER for SNR values less than 15 dB, while the BER in the Gamma-Gamma distribution model reduces as SNR increases. Also, MIMO_BPSK modulation shows better performance compared to the other used modulations in reducing BER per distribution model with the same channel conditions.

Early cancer detection is vital for improving treatment outcomes, addressing a global health challenge with approximately 10 million cancer-related deaths in 2020. We propose a novel Surface Plasmon Resonance (SPR)-based Photonic Crystal Fiber (PCF) biosensor featuring a gold nanowire embedded in a U-shaped open channel, designed for label-free, high-throughput detection of cancer cells. This innovative structure addresses the critical need for cost-effective, scalable biosensors by simplifying fabrication compared to traditional SPR-PCF designs, facilitating analyte injection, and enabling precise nanowire placement. Using Finite Element Method (FEM) numerical analysis, the sensor demonstrates high sensitivity for detecting six cancer cell types within a refractive index range of 1.360–1.401 and a near-infrared spectral window of 870–1100 nm. The biosensor achieves a maximum wavelength sensitivity (WS) of 7857.14 nm/RIU and an amplitude sensitivity (AS) of -1893.08 RIU⁻1 for MCF-7 breast cancer cells. These results highlight its excellent potential for real-time, high-sensitivity cancer detection without requiring fluorescent or chemical labels, positioning it as a strong candidate for clinical diagnostics and lab-on-chip systems.

In recent years, many studies have been conducted on OFDM-based optical wireless communications to develop a 6G communication infrastructure to improve data transmission and reduce the BER. Real-time optimal power management can enhance the data transmission speed and received power in an optical wireless channel under various conditions. This paper discusses implementing a real-time optimal power allocation system using a neural network for OFDM-based optical wireless communications. The system is designed to manage transmitter power, enhancing data transmission rates in optical wireless channels. In system design, data concerning power allocation for various types of OFDM-based optical wireless channels are calculated analytically, including the BER, SNR, fog effects, and fading types in the channel model. Next, a DNN neural model is trained using data generated from the analytical method. The trained model is finally integrated into wireless optical communication transmitter hardware. The experimental results indicate that the embedded power allocation system processes power allocation quickly. The proposed system achieves an average accuracy of 98% in power allocation, surpassing the analytical method. When used in wireless optical communication transmitters, this embedded system enhances speed and accuracy in power management, optimizing the data transmission rate up to 16 Gbps for a 500 m channel.

A surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) for the detection of various analytes through surface plasmon has been proposed in this study. In this biosensor, the main workmanship of the structure is based on the coupling between the fundamental mode of the photonic crystal fiber and the plasmonic mode, which creates the resonance wavelength at different refractive index (RI) of the analyte. In this design, the plasmonic material silver (Ag) is deposited between the PCF and the analyte to detect the RI changes of the analyte, and considering that silver oxidizes quickly, a thin layer of titanium dioxide (TiO2) is placed between the silver and the PCF; this solves the problem and strengthens the adhesion of silver on the fiber. For the optimal and suitable analysis of the performance of the proposed biosensor, the thickness of the structure layers, the lattice constant, and the diameter of the air holes of the structure have been analyzed. In this proposed biosensor, the maximum wavelength sensitivity is 10,000 nm/RIU, and the amplitude sensitivity is 250 RIU−1, and this structure has provided a maximum resolution of 2 × 10−5 RIU in the RI of an analyte, which ranges from 1.32 to 1.37. According to these results, the proposed biosensor emerges as an exemplary candidate for applications in medical and chemical assays, as well as various assessments reliant on the RI of different analytes.

This study introduces a waveguide design capable of generating supercontinuum spectrum and frequency combs within the mid-infrared range. The proposed structure consists of an As2Se3 core and cladding layers of MgF2 and SiO2, exhibiting two zero-dispersion wavelengths at 2100 nm and 2850 nm. Theoretical modeling and numerical simulations demonstrate the generation of a supercontinuum spanning a wavelength range of 4500 nm, from 1000 to 5500 nm, at a − 30 dB level, as well as frequency combs featuring up to 44 comb lines with a flatness of 15 dBm. The supercontinuum was generated in the maximum range of 30 dB using a 1 kW input pulse and 1 and 4 mm long waveguides. The generated frequency combs cover the wavelength range of 2073.1–2159.8 nm, making them suitable for applications such as gas sensing, industrial process monitoring, and medical diagnostics. The proposed waveguide design offers advantages over existing methods in terms of the number of comb lines, flatness, and effective area while operating in the mid-infrared region.

In recent studies on free-space optical communication, researchers have focused on improving data transmission speed. Optimizing resource management, including power allocation, in free-space optical communication enhances the number of bits received at the receiver. To calculate the optimal transmitter power, consider a power range. Allocation of different power values is followed by balancing with bit error rate (BER) and signal-to-noise ratio (SNR) values for all free-space optical communication scenarios. Channels with high BER values and low SNR are allocated higher powers. Channels with low fading and BER are assigned low transmitter powers. A real-time power allocation system is necessary due to the complex analytical equations and changing atmospheric conditions in FSO channels. Therefore, a fuzzy inference system is designed to allocate optimal power in real-time, eliminating the need to calculate and analyze all states for the free-space optical channel. The results indicate that fuzzy power allocation achieves an accuracy of 90% with an SNR input and over 95% with a BER input. With the fuzzy power allocation method, the number of received bits was optimized accurately.

Power allocation (PA) is a significant and challenging real-time optimization problem in the management of optical-radio wireless networks. Analytical methods involve numerous calculations and require an extended processing time. Therefore, DNNs are employed to design a fast, real-time PA system with the required accuracy. In this paper, the innovation of a real-time optimal PA system is presented, enabling two separate three-layer DNNs to perform FSO-RF PA in parallel. The WMMSE algorithm is utilized on various RF channel models, including fading and user priorities, to produce training data. Additionally, the analytical algorithm for calculating BER is used to adjust the transmitter power interval for different FSO channel models, accommodating various modulation schemes and transmitter and receiver sizes. Finally, the DNNs were implemented on Jetson Nano, and the results were compared and validated with analytical methods. The implemented system shows 1.6 Gbps for the sum rate and an average accuracy of 97.82% for the RF channel with 10, 20, and 30 users, while the FSO channel achieves 1.6 Gbps for the data rate and an average accuracy of 98.87%. The implemented system exhibits suitable accuracy and speed in comparison to analytical algorithms for real-time optimal PA in FSO-RF wireless networks.

In this paper, we report a new design of As2Se3‎ chalcogenide glass photonic crystal fiber (PCF) with ultra-flattened dispersion at mid-infrared wavelength range. We have used the plane wave expansion method (PWE) for designing the structure of As2Se3‎ glass PCF at different wavelength windows. In the proposed structure with hole to hole spacing and , the negative dispersion is -1025 ps/nm/km at the wavelength of 1.55µm and also an ultra-flattened dispersion is achieved at the wavelength range of 3.5-18μm. Hence such PCFs have a high potential to be used as dispersion compensating fibers at 1.55µm wavelength in optical communication systems. The ultra-flattened dispersion at the wavelength range of 3.5-18μm can be employed to achieve high power supercontinuum generation. The nonlinear coefficient of the proposed PCF is at the wavelength of 1.55µm. Chalcogenide glasses are known to have both high transparency and nonlinearity in a wide range of infrared wavelengths compared to silica glasses.

Perovskite solar cells (PSCs) have gained a lot of attention due to their high power conversion efficiency (PCE), low-cost materials, and simple manufacturing process. These cells can be improved further by using photonic crystals (PCs) which can increase light absorption. A PC-based perovskite solar cell was designed and simulated in this study using FDTD and CHARGE solvers of the Lumerical software, and its components showed better values compared to other solar cell structures. The study investigated the effect of a two-dimensional PC structure on the solar cell’s light absorption. The materials used as photonic crystals were perovskite/rutile TiO 2 and perovskite/InAs, and various radii and lattice constants were examined. A comparison between each type of PC with the flat structure was conducted. The simulation results indicate that the most efficient structure was found to be the perovskite/InAs structure with a radius of 40 nm and a lattice constant of 200 nm, resulting in an improvement in the performance of the perovskite solar cell. The flat solar cell structure exhibited a short-circuit current of 24.01 mA/cm 2 and an efficiency of 17.34%. However, by adding a rutile TiO 2 photonic crystal structure, the short circuit current and efficiency increased to 27.12 mA/cm 2 and 19.94%, respectively. The efficiency and short circuit current could be further improved by adding an InAs photonic crystal structure, resulting in values of 20.97% and 28.03 mA/cm 2 , respectively. The improved performance of PC-based perovskite solar cells compared to PSC was due to the slow photon effect that occurred around the photonic bandgap, causing light to be trapped, and resulting in more electron-hole pairs being produced. In summary, this study demonstrates the potential to improve the performance of perovskite solar cells by utilizing photonic crystals.

This study aims to design and simulate a two-dimensional all-optical nonlinear analog-to-digital converter (ADC) using a set of power splitters, U-shaped, add/drop, and bus waveguides. In this work, the transmission and wavelength of output ports are managed by the length of the waveguide, number of coupling rods, nonlinear effects, and also the radius and refractive index of coupling and scattering rods. In this design, according to the nonlinear effects and the controlling parameters we can approximate the logic 0 and 1 states using the power transmission at the output ports. The finite-difference time-domain (FDTD) method is employed to investigate the transmission characteristics of the device for a variety of refractive indices. The output efficiency of the 2-bit converter is estimated as 80% and the footprint of the proposed structure is obtained to be 741 mu m2. The minimum quantized pulse width of the proposed structure is 0.7 ps. Considering this time delay, the conversion rate is estimated as much as 1430 Gb/s.