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Abstract This study presents an innovative methane gas sensor design based on anti-resonant hollow-core fiber (AR-HCF) technology, optimized for high-precision detection at 3.3 $$\:\:{\upmu\:}\text{m}$$ . Our numerical analysis explores the geometric optimization of the AR-HCF’s structural parameters, incorporating real-world component specifications. The proposed design features a 65 $$\:\:{\upmu\:}\text{m}$$ diameter hollow core surrounded by seven silica rings. We achieved significant improvements in confinement loss and optical power distribution through progressive structural modifications. The optimized structure demonstrated a confinement loss of $$\:1.85\times\:{10}^{-4}\:\text{d}\text{B}/\text{m}$$ and over 95% optical power confinement in the hollow core. Our model predicts a relative sensitivity of $$\:0.1745\:\text{A}\text{U}/\text{p}\text{p}\text{m}$$ , a response time of 5.4 s, and a theoretical detection threshold of 2.24 ppm. The limit of detection (LoD) was estimated to be 3.8 ppbv, and the normalized noise equivalent absorption (NNEA) coefficient was $$\:1.22\times\:{10}^{-10}\:\text{W} \; {\text{c}\text{m}}^{-1} \; {\text{H}\text{z}}^{-1/2}$$ . The sensor response exhibited excellent linearity over its operating range, with an R2 value of 0.9917 in the critical concentration range. These findings highlight the potential of our AR-HCF-based methane sensor design for real-time gas monitoring applications.

Abstract Optical encoders are widely used circuits in digital systems. One of the most critical features of an optical encoder is the power values in two logic states; low and high. The difference between these two values is expressed with the contrast ratio (CR) parameter. This research has designed and simulated an optical encoder based on a two-dimensional (2D) photonic crystal with four inputs and two outputs. The results show that the proposed structure has low power in low mode and high intensity in high mode. This difference in two logical modes has caused the proposed encoder to have CR = 19.8 dB, which is improved compared to previous works. Also, the proposed structure is very compact and its footprint is as small as 96.88 µm2. The data speed for the designed encoder is $$BR = 2{\text{ Tb/s}}$$ B R = 2 Tb/s . This encoder can be used in high-speed optical integrated circuits with low error according to the obtained values.

In this paper, a novel interference-based nanostructure was designed and simulated to realize an all-optical 2-bit reversible comparator by employing a novel technique. The plane wave expansion (PWE) method was adopted to analyze the encoder design and frequency modes. Aside from downsizing, the finite-difference time-domain (FDTD) method was utilized for the simulation and numerical analysis of the design proposed herein. An ultra-compact nanostructure with a 129.8 μm2 footprint was utilized for the all-optical 2-bit reversible comparator. One of the noteworthy characteristics of the proposed nanostructure was its excellent contrast ratio (i.e., 13.8 dB) in comparison to other nanostructures. The bitrate and delay time in this nanostructure were 3.33 Tb/s and 300 fs, respectively. Based on the findings of the simulations conducted at a central wavelength of 1.55 μm, it is recommended to employ the nanostructure proposed herein during the third telecom window. A photonic crystal nano-resonator was utilized to design the high-performance all-optical 2-bit reversible comparator, which may also be employed in integrated optical circuits (IOCs).

In this article, we present a novel approach to achieve a highly compact Si3N4 photonic crystal waveguide by incorporating air holes. This structure is developed in two functional applications that simultaneously perform the functions of generating optical frequency combs and demultiplexing them. The presence of air holes enhances control and precision in the dispersion engineering process. At the same time, the light conduction, based on the refractive index contrast between the core and cladding, along with the conduction occurring in the photonic bandgap region of the structure, leads to enhanced trapping of light within the core of the structure. As a result, a nonlinear coefficient of 4.2 m-1W−1 is obtained, which originates from the small effective mode area of 0.67 µm2. By employing four-wave mixing, a total of 40 comb lines are generated with a frequency spacing range of 10 GHz, 50 GHz, 60 GHz, and 100 GHz over a 6 mm length waveguide. The same waveguide structure is also developed for demultiplexing the comb lines, with four filters at the end which, individually extract the optical combs possessing wavelengths of 1317.8 nm, 1318.5 nm, 1319.2 nm, and 1319.9 nm. This demultiplexer has a Q-factor, average transmission efficiency, channel spacing, and spectral linewidth of 7209.35, 99.2 %, 0.7 nm, and 0.185 nm, respectively. The suggested design can significantly advance integrated photonic circuits, optical communications, and remote sensing applications requiring simultaneous information delivery, such as remote surgical operations and sensing, because of its substantial compactness.

Detection of bio-alcohol is crucial in diverse industries, including forensics, medicine, and food production. This paper presents a novel biosensor for bio-alcohol detection in water, integrating three micro-cavities with two waveguides within a hexagonal photonic crystal array. Employing a wavelength interrogation approach and finite-difference time-domain (FDTD) simulations, the proposed biosensor demonstrates a high sensitivity of 610 nm/RIU (nanometers per refractive index unit) and a low detection limit of 7 × 10-3 RIU. Simulation results validate the effectiveness of this photonic crystal biosensor for detecting organic substances in water, showcasing its potential for practical applications.

In this paper, a novel method for simultaneous ultra-broadband and ultrashort femtosecond laser pulse generation in silica photonic crystal fibers is investigated analytically using the fully vectorial effective index method (FVEIM). By reducing the impact of fifth and lower-order dispersions, the method produces narrower laser pulses and wider supercontinuum using a fixed soliton order over a specific distance of the fiber. Additionally, the larger effective areas utilized in this approach make the manufacturing process simpler compared to other samples. These simultaneous features represent the primary innovations of this study.

This paper reveals special design features of the proposed highly nonlinear circular-lattice-silicon-core and silica-doped-with-fluorine (1%) cladding-composite photonic crystal fiber (PCF) in the Mid-infrared region of the spectrum. A region of small negative group velocity dispersion (GVD), managed higher order dispersions (HODs), and unique nonlinearity of silicon have been used to demonstrate a supercontinuum broadening from 1500 nm to 4700 nm with consumption of low input power of 400 W over short fiber distances. It will be also shown that the fiber’s high-level engineered structure finally results in a simple manufacturing process compared with other designed nano-sized silicon PCFs. The designed fiber could have massive potential in gas sensing, soliton effect pulse compression, spectroscopy, material processing, etc.

An optical comparator is an important logic circuit used in digital designs. Photonic crystals are among the platforms for implementing different kinds of gates and logic circuits, and they are structures with alternating refractive indices. In this paper, an optical comparator is designed and simulated based on a square lattice photonic crystal. In the design of this comparator, a small-sized structure is used. The simulation results show that in the proposed comparator, there is a high difference between logical values “0” and “1”, which are defined based on the optical power level. Due to the small size of this comparator and the adequate difference between logical values “0” and “1”, this structure suits photonic integrated circuits with high accuracy. The proposed structure footprint is 149.04 µm2, and the calculated rise time for this circuit is less than 0.4 ps.

Efficiency has been known to be one of the most important factors in a solar cell. This article presents the results of a simulation performed on a perovskite/CIGS dual-junction solar cell. In this report, first, a top solar cell consisting of a perovskite absorber layer is simulated using the pn-junction; the separation and transfer of carriers in this structure are done by the internal electric field. The pn-junction has a discharge area smaller than the pin-junction, which increases carrier recombination and reduces optical losses. The perovskite band gap of 1.9 eV is considered, and the efficiency is 21.65% using the Au electrode. Then, the bottom solar cell is fabricated with a CIGS absorbent layer with a 1.4 eV band gap and an efficiency of 11.46%. After simulating and evaluating the performance of the top and bottom solar cells independently, both cells were simulated and examined for the dual-junction state. Since the perovskite and CIGS band gaps are both adjustable, these two materials can act as a proper partner for an absorbent layer in a dual-junction solar cell. In this structure, instead of the usual connection of p-i-n and n-i-p perovskite, n-type and p-type homojunction perovskite connection is used, in which the transfer and separation of carriers are done by an internal electric field. Due to the fact that in this structure, the discharge area is smaller, the recombination of carriers is increased, and the light losses are reduced, which will increase the absorption and efficiency of the cell. The results show that in the tandem design, we encounter an increase in Voc (2.25 V), thus increasing the efficiency of the solar cell (30.71%).

Jones matrix computation is one of the widely used methods in nonlinearitycalculation in laser interferometers. In this paper, the nonlinearity error in developedthree-longitudinal mode heterodyne interferometer (DTLMI) has been mathematicallymodeled at various speeds, by using Jones matrix calculations. This review has been donedespite the fact that simultaneously the main factors including non-ideal polarization ofthe laser beam and the non-ideal PBS produce nonlinearity. According to the results, itwas found that although nonlinearity error is a pure sinusoid in low velocities, it isn't asingle-sinus and increases in amplitude in high velocities. It was also observed that theeffect of non-ideal PBS on nonlinearity error is less than that of non-ideal laser beam andfrequency of nonlinearity error caused by it is twice more.

Abstract In this paper, we have proposed a metal-insulator-metal (MIM) pressure sensor which consists of two plasmonic waveguides and a double square ring resonator. The two square rings are connected via a rectangular patch located between the two of them. The surface plasmon polaritons (SPPs) can be transferred from a square ring to the other through this patch. The finite-difference time-domain method (FDTD) has been used to simulate the device. Applying a pressure on the structure, it deforms, and a red shift of 103 nm in the resonance wavelength has been calculated. The deformation is linearly proportional to the wavelength shift in a wide range of wavelength. The proposed optical plasmonic pressure sensor has a sensitivity of 16.5 nm/MPa which makes it very suitable for using in biological and biomedical engineering.

A compact and simple structure is designed to create an all-optical XOR logic gate using a two-dimensional, photonic crystal lattice. The structure was implemented using three waveguides connected by two nano-resonators. The plane wave expansion method was used to obtain the photonic band gap and the finite-difference time-domain method was used to investigate the behavior of the electromagnetic field in the photonic crystal structure. Examining the high contrast ratio and high-speed cascade, all-optical XOR on a chip, the effects of fabrication error and the changes in the input optical power showed that the structure could be used in optical integrated circuits. The contrast ratio and data transfer rate of the cascade XOR logic gate were respectively obtained as 44.29 dB and 1.5 Tb/s. In addition, the designed structure had very small dimensions at 158.65 μm2 and required very low power to operate, which made it suitable for low-power circuits. This structure could also be used as a NOT logic gate. Therefore, an XNOR logic gate can be designed using XOR and NOT logic gates.

Waveguides with low confinement loss, low chromatic dispersion, and low nonlinear effects are used in optical communication systems. Optical fibers can also be employed in such systems. Besides optical fibers, photonic crystal fibers are also highly suitable transmission media for optical communication systems. In this paper, we introduce two new designs of index-guiding photonic crystal fiber (IGPCF) with characteristics appropriate for optical communications. In the first proposed design with a hexagonal structure having a defect at the center, the chromatic dispersion at the wavelength of 1550 nm is less than 1 ps/(nm.km). In the second design with a hexagonal structure having air holes with unequal diameters, nearly zero dispersion at the wavelength range of 1370 to 1380 nm is achieved. At the same time, for the latter design, at the wavelength of 1550 nm, the chromatic dispersion slope is1 ps/(km.nm), the confinement loss is less than 10-9 dB/km, and the nonlinear coefficient reaches 3.690 W-1.km-1.

Vertical nanowire (NW) arrays are a promising candidate for the next generation of the optoelectronics industry because of their significant features. Here, we investigated the InP NW array solar cells and obtained the optoelectronic properties of the structure. To improve the performance of the NW array solar cells, we placed a metal layer of Au at the bottom of the NWs and considered their top part to be a conical-shaped parabola. Using optical and electrical simulations, it has been shown that the proposed structure improves the absorption of light in normal incidence, especially at wavelengths near the bandgap of InP, where photons are usually not absorbed. Under inclined radiation, light absorption is also improved in the middle part of the solar spectrum. Increased light absorption in the cell led to the generation of more electron–hole pairs, resulting in an increase in short circuit current density from 24.1 mA/cm2 to 27.64 mA/cm2, which is equivalent to 14.69% improvement.

Abstract: In this paper, a method for determination of refractive index in membrane of fuel cell on basis of three-longitudinal-mode laser heterodyne interferometer is presented. The optical path difference between the target and reference paths is fixed and phase shift is then calculated in terms of refractive index shift. The measurement accuracy of this system is limited by nonlinearity error. In this study, nonlinearity error is modeled by multi-layer perceptrons (MLPs) and stacked generalization method (Stacking), using two learning methods; back propagation (BP) and genetic algorithm. Training neural networks with genetic algorithm, improves modeling of nonlinearity error in this system. In the proposed technique, a real code version of genetic algorithm is used. Parameters and genetic operators are set and designed accurately. The results indicate that the nonlinearity error can be effectively modeled by training the stacking with the genetic algorithm which has minimum mean square error (MSE). Keywords: Fuel cell, Genetic algorithm, Heterodyne interferometer, Multi-layer perceptrons, Nonlinearity error, Refractive index, Stacked Generalization.

The interaction of light with plasmonic nanostructures can induce electric field intensity either around or at the surface of the nanostructures. The enhanced intensity of the electric field can increase the probability of light absorption in the active layer of solar cells. The absorption edge of perovskite solar cells (PSCs), which is almost 800 nm, can be raised to higher wavelengths with the help of plasmonic nanostructures due to their perfect photovoltaic characteristics. We placed plasmonic nanoparticles (NPs) with different radii (20–60 nm) within the bulk of the perovskite solar cell and found that the Au nanoparticles with a radius of 60 nm increased the absorption of the cell by 20% compared to the bare one without Au nanoparticles. By increasing the radius of the nanoparticles, the total absorption of the cell will increase because of the scattering enhancement. The results reveal that the best case is the PSC with the NP radius of 60 nm.

In this paper, we present a high accuracy laser range finder and velocimeter using ultra-fast time-to-digital converter (TDC). The system operation is based on the measuring the round-trip time of a narrow laser pulse. A low-dark current high-speed PIN photodiode is used to detect the triggered laser beam and to produce start signal. The pulsed laser diode generates 45W optical power at 30ns duration time and 905nm wavelength. A high-responsivity avalanche photodiode (APD) detects the reflected beam from the target. An optical head including beam splitter, lenses and optical filters is also designed and implemented. The signal conditioner of the system includes pre- and post-amplifiers, comparator, opto-isolators and monostable. By using a 3MV/W reach-through structure avalanche photodiode and a wideband pre-amplifier, the pre-amplifier output reaches 15.9mV, resulting from the minimum detectable optical power. The APD temperature and as a result its responsivity is controlled by a thermoelectric controller unit. The start and stop signals from PIN and APD are led to the time-to-digital converter to count the round-trip time of the laser beam. The system is tested by a retro-reflector as a target for 30-1200m distances. The resolutions of the distance and velocity measurement are limited to 18.75mm and 1.2m/s, respectively. In the worst condition, the minimum reflected optical power is limited to about 5.3nW in 1.2km distance.