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In a class of high quality (Q-) factor dielectric resonators with low radiative losses, including popular whispering-gallery mode (WGM) resonators with high azimuthal mode numbers, due to high confinement of modal field in dielectric, the Q-factor is limited by the value of inverse dielectric loss tangent of dielectric material. Metal enclosures necessary for device integration only marginally affect the Q-factor while eliminating the residual radiative loss and allowing the optimization of input and output coupling. While very high Q-factors ∼ 200 000 are available in sapphire WGM resonators in X-band, at millimeter wave frequencies increasing dielectric loss limits the Q-factor to much smaller values, e.g. ∼50000 and ∼25000 for quasi-TE and quasi-TM modes, correspondingly, at 36 GHz. The use of distributed Bragg reflection (DBR) principle allows to push modal energy outside dielectric while also isolating it from Joule losses in metallic enclosure walls. Very high Q ∼ 600 000 > --> t g δ has been demonstrated in X-band [C. A. Flory and R. C. Taber, IEEE Trans. Ultrason., Ferroelectr., Freq. Control 44, 486–495 (1997).] at the expense of impractically large dimensions. In this work, we report on the assembly and testing of a compact Ka-band sapphire distributed Bragg reflector cavity characterized with Q-factor seven times larger than one predicted by the material's dielectric loss at the frequency of interest. An intrinsic Q-factor of ∼ 200 000 is demonstrated at 36 GHz for the lowest order TM-mode of a sapphire DBR. The resonator has 50 cm 3 volume, smaller than previously demonstrated DBRs. [ABSTRACT FROM AUTHOR]

This paper presents the design of a high-efficiency spot size converter (SSC) for photonic crystal fiber (PCF) to silicon-based waveguides, utilizing composite optical waveguide structures. The SSC is composed of a series of waveguide cores, with one core progressively widening to enable all cores to collectively serve as a composite input port, while the broader core functions as the output port. Simulation results reveal that the proposed design efficiently facilitates mode and energy transfer between the waveguide and the PCF, achieving a coupling efficiency of up to 93.99% over a length of 66 μm. Additionally, the SSC exhibits polarization insensitivity, with the high circularity of the output beam enhancing vertical alignment tolerance, and maintaining excellent performance over a wide wavelength range. In sum, this SSC demonstrates excellent coupling efficiency and holds significant promise for applications in optical communication systems and optical integrated circuit systems. [ABSTRACT FROM AUTHOR]

Methane gas leakage can lead to pollution problems, such as rising ambient temperature. In this paper, the Vernier effect of a double D-shaped photonic crystal fiber (PCF) in a Sagnac interferometer (SI) is proposed for the accurate detection of mixed methane gas content in the gas. The optical fiber structure of the effective sensing in the sensing SI loop and the effective sensing in the reference SI loop are the same. Both of them adopt the polarization-maintaining photonic crystal fiber (PM-PCF) designed in this paper. The optical fiber structure of the effective sensing in the sensing SI loop deposited with the methane gas-sensitive film is polished to obtain a double-D structure. This operation makes it easier for methane gas to contact the sensitive film and realize the sensor's repeated use. The sensing capability of the methane gas sensor was evaluated utilizing the finite element method (FEM). The numerical simulation results show that when the concentration of methane gas in the environment is 0~3.5%, the average sensitivity of two parallel Sagnac loops is 409.43 nm/%. Using Vernier effect cascade SI loops, the sensitivity of the sensor for detecting methane gas increased by four times. Without considering air and humidity, we provide a practical scheme for the development and design of high-sensitivity methane gas sensors. [ABSTRACT FROM AUTHOR]

The generation of high‐coherence mid‐infrared (MIR) supercontinuum (SC) spanning over one octave in As2Se3 tapered photonic crystal fiber (As2Se3‐TPCF) is investigated through numerical simulations. Combined with the photonic crystal fiber and tapered fiber's structural characteristics, six As2Se3‐TPCFs with different tapered structures are designed. The tapered regions are the power function and cosine tapered structures, respectively, while the taper waist and the untapered region have the same structure. Moreover, the nonlinear coefficient of the taper waist is 2.23825 W−1m−1 calculated by the finite element method (FEM), and the zero‐dispersion wavelength (ZDW) in the down‐taper moves with the increase of transmission distance, shifted from 5.2 to 2.4 μm. The temporal and spectral features of the MIR SC generated in As2Se3‐TPCFs are numerically simulated by solving the generalized nonlinear Schrödinger equation (GNLSE), and the spectral broadening of As2Se3‐TPCFs is mainly caused by self‐phase modulation, Raman soliton self‐frequency shift, and dispersive wave generation. Finally, six As2Se3‐TPCFs with lengths of 0.1 m are pumped by short pulses with a center wavelength of 4.0 μm, pulse width of 40 fs, and pulse energy of 250 pJ, the results show that the linear tapered As2Se3‐TPCF and the cosine tapered As2Se3‐TPCF can achieve high‐coherence MIR spectra spanning 1.6 octaves, with spectral widths from 2.1 to 6.4 μm. [ABSTRACT FROM AUTHOR]

In this article, we present our analysis of the Raman-induced wavelength shift (RIWS) in configuring high-performance temperature sensor by employing a highly nonlinear Chalcogenide (As30S70) microstructured optical fiber (MOF) having central holes partially filled with Chloroform (CHCl3). Through precise adjustment of the device parameters, we demonstrate a sensitivity of temperature measurement of ~ 2.6262 nm/°C in the mid-infrared (MIR) wavelength range. Implementing Artificial Neural Network (ANN) analysis, this sensitivity increases to 2.7039 nm/°C yielding a temperature resolution of 0.24688 °C. To our knowledge, this is the first investigation that specifically addresses RIWS effect in temperature sensing using Chalcogenide fiber at MIR range. [ABSTRACT FROM AUTHOR]

In this study, we investigate the (3+1) q-deformed tanh-Gordon equation due to its importance in the context of mathematical physics. It describes solitonic solutions in quantum field theory; it can sometimes be used in condensed matter physics to describe interactions between particles in magnetic materials or superconductors; it can model light propagation in nonlinear optical fibers or photonic crystals where the refractive index has a q-deformed structure; and it also can be applied in studying shock waves, turbulence and rogue waves where the deformation introduces corrections to classical wave phenomena. Utilizing the ( G ′ ω G ′ + G + r) -expansion technique, we derive novel analytical solutions that enhance our understanding of the underlying dynamics. Additionally, we employ a finite element method (extended cubic B-spline method) to validate our analytical findings and explore the behavior of the q-deformed equation under different parameter regimes. Our results demonstrate the versatility of the q-deformed framework in generating rich optical phenomena, paving the way for future research in both theoretical and applied physics. [ABSTRACT FROM AUTHOR]

In this study, we propose a novel approach to enhance the sensitivity of salinity measurement using photonic crystal fiber. Our method involves filling the first ring of holes in the fiber with seawater, which serves as the analyte, and embedding it in a single-material silica substrate. This design allows for precise tuning of sensitivity to even minimal changes in salinity concentration. Through numerical simulations, we explore the influence of different geometrical parameters on the photonic crystal fiber's (PCF) characteristics. We calculate the sensitivity for two wavelengths, 1.3µm and 1.55µm, and achieve a highest salinity sensitivity of 0.017966 ps/(nm·km)/PSU and 0.021818 ps/(nm·km)/PSU, respectively. Our proposed sensor not only demonstrates excellent performance in salinity sensing but also holds promise for applications in the field of communication, thanks to its satisfactory and impressive sensing capabilities. [ABSTRACT FROM AUTHOR]

This paper presents the results of a detailed theoretical study of the bending properties of all-glass leakage channel microstructured optical fibers (LC MOFs) with a polymer coating over a bending radius range from 4.8 cm to 10 cm. The dependencies of the effective refractive indices of the LC MOF modes on the bending radius have a number of crossings and anticrossings for different mode pairs. A detailed analysis showed that eight modes for each polarization have to be considered to correctly calculate the bending losses. These modes can be classified into relatively strong modes (three for each polarization) and relatively weak modes. The three strong modes have the most direct effect on the loss calculation. However, the relatively weaker modes also play a role through their coupling with the stronger modes, resulting in the appearance of local loss maxima in the loss dependencies for the strong modes. At a bending radius of 10 cm, the final leakage loss of the LC MOFs with a polymer coating is approximately four times lower than that of the LC MOFs without a coating. The significant reduction in losses paves the way for further optimization of the LC MOF geometric structure, leading to a reduction in the allowable bending radius. [ABSTRACT FROM AUTHOR]

The editorial on fiber-optic sensors highlights their significance in modern technology, utilizing light transmission through optical fibers to detect physical, chemical, or environmental changes. These sensors are lightweight, compact, immune to electromagnetic interference, and can operate in harsh conditions, making them pivotal in industries such as telecommunications, aerospace, and medical diagnostics. Recent research has focused on advancements in fiber Bragg gratings, graphene-based sensors, 2D magnetic field sensing, Fabry-Perot pressure sensors, and air-gap fiber Bragg grating sensors, showcasing the transformative potential of fiber-optic technology in various applications. The continuous progress in fabrication techniques and materials like graphene underscores the ongoing innovation in fiber-optic sensors, offering high sensitivity, multi-parameter measurements, and adaptability to diverse environments. [Extracted from the article]

The paper presents a thorough investigation into the design of a Modified Core Hexa–Deca Photonic Crystal Fiber (MHD-PCF) with adjustable features to regulate dispersion and birefringence. At the target wavelength of 1550 nm, the suggested MHD-PCF exhibits extraordinary optical properties, including an ultra-high negative dispersion coefficient of − 7755 ps/(nm km) and significant birefringence of 1.905 × 10−2. The analysis entails regular changes in lattice constants and center air hole parameters, which provide insights into optical property trends. The MHD-PCF regularly exceeds existing benchmarks across a wide range of parameter adjustments. Notably, this fiber has strong nonlinearity (59.12 W−1 km−1) and low confinement loss (2.896 × 10−3 dB/cm), as well as an enhanced numerical aperture (0.5144), demonstrating its potential for efficient light coupling and supercontinuum production. These results put the Modified Core Hexa–Deca Photonic Crystal Fiber at the forefront of contemporary communication systems, and its optical enhancements and flexible features present exciting opportunities for novel Terahertz technology breakthroughs, especially in the areas of communication systems and sensing applications. [ABSTRACT FROM AUTHOR]

We design and simulate a near-zero flat dispersion As2S3 photonic crystal fiber (PCF) with a circular shape to generate a broad and smooth supercontinuum (SC). A near-zero flattened dispersion in the all-normal dispersion PCF is maintained in the 4–6.2 μ m wavelength range. A 6 μ m hyperbolic pulse is injected into this fiber, producing a flat spectrum from 2.45 to 8.4 μ m at a peak power of 5 kW. The generated SC in anomalous dispersion PCF can cover multi-octaves by a pump laser with a 6500 nm wavelength, 10 kW of peak power, and a 90 fs duration in 10 cm of the proposed fiber structure. These results are achieved by optimizing the fiber structure through the core size. In general, the proposed structures could be used for broadband smooth low-cost SC generation. [ABSTRACT FROM AUTHOR]

Polarization filters based on surface plasmon resonance (SPR) have undergone rapid development in recent years. In this work, a dual D-type PCF polarization filter based on SPR is designed and analyzed. The filter improves the limiting loss of the core mode by gilding the semi-circular split ring and inlaying amethyst. The influence of the structural parameters of the filter on the filtering characteristics is analyzed by the finite element method. The results show that the core mode losses of the x and y polarized light are 32 dB/cm and 910.56 dB/cm at 1.55 μ m, respectively. For a fiber length of 1000 μ m, the crosstalk and bandwidth are 763.11 dB and 700 nm, respectively. In addition, the impact of manufacturing errors in the structural parameters on the filter performance is discussed. The filter has excellent filtering characteristics and large potential in optical communication and optical sensing. [ABSTRACT FROM AUTHOR]

A novel cyclic olefin copolymer (COC)-based terahertz (THz) polarization beam splitter (PBS) employing photonic crystal fiber (PCF) with cascade hexagonal porous two-core structure is proposed. The porous two-core is achieved by replacing the original two large air holes with three layers of small air holes. The mode coupling characteristics between the even and odd modes in the x- and y-polarization directions for the proposed THz PBS are explored using the time-domain finite difference (FDTD) method. The influence of PBS structural parameters on its coupling length is investigated. Numerical analysis results indicate that the bandwidths of 227.8 GHz (ranging from 1.8970 to 2.1248 THz) and 147 GHz (ranging from 1.928 to 2.075 THz) are acquired for the x- and y-polarization fundamental modes, respectively. The highest extinction ratios (ERs) are 114.5 dB and 72.3 dB, and the minimum insertion losses (ILs) are 0.0142 dB and 0.0369 dB for the x- and y-polarization fundamental modes, respectively. Moreover, the length of the proposed PBS is merely 11.655 mm. The proposed PBS will find potential applications in polarization-diverse THz systems, including broadband line-of-sight communication, real-time security checks, and high-resolution imaging. [ABSTRACT FROM AUTHOR]

A Fresnel mirror is introduced at a hollow-core photonic bandgap fiber end by fusion splicing a short single-mode fiber segment, to reflect the light backward to an optical frequency domain reflectometry. The backward Fresnel reflection is used as a probe light to achieve light speed measurement with a high resolution and a high signal-to-noise ratio. Thus, its group velocity is obtained with the round-trip time delay as well as the beat frequency at the reflection peak. Multiple Fresnel peaks are observed from 2180.00 Hz to 13,988.75 Hz, corresponding to fusion-spliced hollow-core fiber segments with different lengths from 0.2595 m to 1.6678 m, respectively. The speed of light in the air guidance is calculated at 2.9753 × 108 m/s, approaching that in vacuum, which is also in good agreement with 2.9672 × 108 m/s given by the numerical analysis with an uncertainty of 10−3. Our demonstration promises a key to hollow-core waveguide characterization for future wide-bandwidth and low-latency optical communication. [ABSTRACT FROM AUTHOR]

This study introduces a novel photonic crystal fiber designed with several zero-dispersion wavelengths with exceptional characteristics for dispersion compensation in telecommunication applications. Two distinct photonic crystal fibers were designed and compared: one with periodic arrangement of air holes, the other with 12 extra air holes. The performance metrics of the fibers were analyzed, revealing a notable advantage for the designed fiber with supplementary air holes. Moreover, the dispersion curve analysis provides an intriguing insight into the behavior of zero-dispersion wavelengths (ZDWs), showcasing the PCF with extra air holes as a potentially rich source of multiple ZDWs. This innovative PCF design holds the potential to advance dispersion compensation capabilities, enhancing the efficiency and quality of optical signal transmission in telecommunication systems. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrated a method of filling the air holes of a photonic crystal fiber (PCF), coated with gold film, with magnetic fluid (MF) to enhance the Surface Plasmon Resonance (SPR). The simulation results show that at the wavelength of 1260–1675 nm, the minimum loss coefficient of the y-polarization mode is 4.7 times that before filling with MF, and the x-polarization mode is 0.45 times greater. Then, based on this method, we designed a polarizing filter with a core diameter of 9 µm. The numerical simulation results indicate that it not only maintains the same core diameter as the single-mode fiber, but also has a larger bandwidth and a higher extinction ratio (ER). Additionally, we can optimize its ER at a specific wavelength by adjusting the magnetic field. [ABSTRACT FROM AUTHOR]

A photonic lantern is a low-loss device that connects a single multimode waveguide to multiple single-mode waveguides and can enhance the beam quality of a fiber laser by adaptively controlling the optical parameters (amplitude, phase, polarization) at the input. In this work, we combined the gains and losses of individual modes within the fiber amplifier and introduced a mode content parameter at the amplifier's output as an evaluation function to simulate mode control effects. Mode competition within the gain fiber can degrade the control effect of the fundamental mode and lead to it taking a longer time for the control to converge. Optimal parameters, such as the gain fiber length and pumping method, were identified to improve control effectiveness. Specifically, an optimal gain fiber length of 8 m was determined, and backward pumping was found to achieve higher pumping efficiency and better control results. The system demonstrated significant power amplification potential and could stabilize mode control under different pumping powers ranging from 50 W to 5 kW. In conclusion, our research demonstrates that an adaptive fiber amplifier based on a photonic lantern can achieve a stable, high-power, large-mode-field, near-fundamental-mode output from the gain fiber. Although mode competition within the gain fiber can degrade the control effect of the fundamental mode and cause the control to take a longer time to converge, these aspects should be further studied to improve the control's effectiveness. These findings contribute to the development of advanced simulation models that guide high-power mode control experiments and deepen our understanding of physical processes in science and technology. [ABSTRACT FROM AUTHOR]

The Perturbed Gerdjikov–Ivanov Equation (PGIE) describes optical solitons in nonlinear fiber optics and photonic crystal fibers. It was currently studied in the literature. Here, we consider a new complex field equation, the PGIE with fourth-order dispersion. The exact solutions of the aforementioned equation are obtained by implementing the unified method. These solutions are evaluated numerically and they are shown in graphs. Our objectives, here, are to inspect the onset of self- steepening and self-phase modulation and investigate the structures of solitons produced. It is found that these phenomena are launched for high values of the relevant coefficients, and they may be overlapped. Multiple solitons shapes are observed; M-shaped solitons, rhombus shapes, solitons with tunneling, 2D-lumps vector, and solitons- cascade. Further, the analysis of modulation instability (MI) and global bifurcation are carried out. It is established that the MI triggers when the coefficient of Raman scattering exceeds a critical value. It is worth mentioning that two kinds of bifurcations can be studied, namely local and global bifurcations. Here, we are concerned with studying global bifurcation. This is based on constructing the phase portrait via Hamiltonian function. [ABSTRACT FROM AUTHOR]

Numerous techniques and technologies have been proposed for the detection and identification of hazardous chemicals that can harm the lungs and respiratory system as well as the central nervous system and kidneys when inhaled. Most practical techniques can be carried out by extraordinary professionals in well-equipped facilities. A reliable, simple, highly sensitive, and feasible sensing technique is still required. A potential sensor for these harmful chemicals is the photonic crystal fiber (PCF), which achieves several unique properties. A square-core PCF sensor is proposed in this work for the detection of detrimental gases (tetra-chloro silane, tetra-chloro methane, turpentine, and tin terra-chloride) in the THz region. The cladding region is divided into three rings, and each ring has rectangular and square air holes. Within the operating region, we have found a relatively high sensitivity of 96.185% along with 95.407% core power fraction, 0.2211 numerical aperture, and a low effective area of 154 470 μm2 at 1.9 THz frequency. Ignorable confinement loss of 3.071 × 10−14 cm−1 and effective material loss of 0.007 72 cm−1 have been also found. Additionally, the current manufacturing techniques guarantee the viability of the proposed PCF sensor's manufacture. These obtained results demonstrate that the proposed sensor can be effectively employed for applications involving hazardous chemical compounds, gases, and biosensing. [ABSTRACT FROM AUTHOR]

3D printing, also known as additive manufacturing technique, has recently found applications in various engineering fields due to its ability to produce freeform 3D structures beyond the ability of traditional subtractive manufacturing methods. In this respect, the field of THz photonics is no exception. The adoption of 3D printing technique resulted in a revolution in THz optics and device manufacturing and will continue advancing this field for years to come. In this Perspective paper, we consider, in particular, the fabrication of guided optics devices for the THz operation range using additive manufacturing. We first introduce the technical characteristics of various 3D printing techniques as well as the advantages, disadvantages, and main performance parameters. Then, various 3D printed THz waveguides and fibers and functional devices, such as metalized/metallic/dielectric rectangular waveguides, photonic crystal waveguides, hollow-core anti-resonant/Bragg waveguides, hybrid metal/dielectric waveguides, plasmonic waveguide, porous fibers, magic tee, and serpentine waveguide traveling-wave circuits, are discussed. We also highlight practical applications of 3D printed waveguides/fibers in manipulating THz waves, especially in the fields of sensing and communication, including the analyte thickness and refractive index sensors, subwavelength/suspended core fiber communication links, dispersion compensators, and add-drop multiplexers. Finally, the prospects of 3D printing techniques in the THz field are summarized. [ABSTRACT FROM AUTHOR]

Most of the spectral bandwidths of previous publications are still limited by high input powers making them economically less than ideal. By using a benzene core (C6H6) photonic crystal fiber (PCF) as a new supercontinuum (SC) light source, it is possible to achieve a very large spectral broadening with hundreds of times lower peak power. Due to the change in the diameter of air holes in the first ring near the core, near-zero flattened dispersion, high nonlinearity and small attenuation can be achieved for spectral broadening. The structural geometries of two C6H6-PCFs are optimized to generate wide SC at low input energy. The SC spectrum produced in 1 cm long of all dispersion fiber extends from a part of visible light to the near-infrared range at 1.3 μ m wavelength and a small pulse energy of 18 pJ (or 450 W of electrical input). The second PCF shows wide soliton-induced SC from 0.8 to 4.2 μ m with 71 pJ pulse energy (or input power approximately 790 W) at 1.5 μ m wavelength within a fiber of 12 cm. The proposed structures have the potential to become a new class of microstructured optical fibers for low-cost, broad-spectrum SC generation. [ABSTRACT FROM AUTHOR]

The article delves into the process of drawing shear-thinning or shear-thickening fluid threads with internal holes, examining the influence of axial drawing, inertia, and surface tension. It highlights how surface tension forces impact the hole size and outer radius, particularly affecting shear-thinning fluids more than shear-thickening fluids. The study also analyzes the stability of drawing holey fibers, revealing that factors like surface tension, inertia, and hole size play crucial roles in determining the critical draw ratio for stability. Overall, the research sheds light on the behavior of different fluids during fiber drawing and their significance for stability and fiber quality. [Extracted from the article]

In this study, a simple air-silica microstructure based on circular-lattice geometry is designed and analyzed to achieve an ultra-large negative dispersion coefficient and high birefringence simultaneously for dispersion compensation. The fiber design has been analyzed numerically by utilizing finite difference mode convergence technique. The influences of varying various geometrical parameters on the dispersion as well as on the birefringence properties have been examined. Through a systematic analysis, the geometrical parameters of the design have been optimized for achieving the desired results. Finally, two photonic crystal fiber designs for narrowband and another design for broadband dispersion compensation have been proposed. The proposed narrowband designs exhibit high negative dispersion of −10,388 and −4,542 ps/nm/km, with birefringence values of 4 × 10−3 and 5.4 × 10−3 at a wavelength of 1.55 μm, respectively. The computed FWHM of the dispersion curves of these designed fibers are found to be 30 and 100 nm, respectively. For the broadband design, dispersion coefficient between −452 and −1,408 ps/nm/km has been achieved over the wide wavelength range of 1.4 to 1.7 μm. Additionally, the compensation ratio and relative dispersion slope of the proposed broadband design have been computed. It is observed that the design provides a negative dispersion coefficient of −932 ps/nm/km and a relative dispersion slope of 0.0036 nm−1 at 1.55 μm wavelength with a birefringence value of 1.23 × 10−2. [ABSTRACT FROM AUTHOR]

For high birefringence photonic crystal fibres (PCF) operating in terahertz (THz) regime, an outstanding model of slotted porous core with triangular lattice-based hexagonal shape cladding has been presented in this study. In this proposed THz-PCF, a five-layer circular air holes arranged in hexagon configuration have been placed in the cladding area, and five rectangular air holes have been positioned in core region for investigating the THz-PCF in polarization maintaining applications. The asymmetrical rectangular slots in core area creates difference between x and y polarized THz waves to offer high birefringence. The compact geometry of hexagonal structure in cladding offers more useful power confinement. The designed PCF offers high birefringence of 0.0866, low effective material loss of 0.0786 cm−1, core power fraction of 42.7%, less confinement loss of 0.02598 cm−1, low dispersion of 0.0963 ps/THz/cm and very less effective area of 0.03 µm2 in a broad frequency range of 0.1–2.3 THz, according to the Finite Element Method based simulation results in COMSOL Multiphysics software. These features enable the proposed PCF to be a better choice for numerous applications like polarization filtering, sensing, short distance communication, etc. in THz photonic integrated circuits. [ABSTRACT FROM AUTHOR]

A numerical investigation of the impact of fourth-order dispersion in the dynamics of Gaussian pulse propagation in photonic crystal fiber is presented. Considering the importance of waveguide dispersion in photonic crystal fiber, higher-order dispersion, especially fourth-order dispersion, is found to be crucial and significantly affects the dynamics. To study the evolution of various pulse parameters during propagation, we adopt the generalized projection operator method to derive the pulse parameter equation. It is observed that the fourth-order dispersion is found to be critical and, hence, remarkably influences the dynamics. A detailed discussion is presented to give further insight into the impact of Fourth order dispersion. Different ansatz-like methods are also considered alongside the Gaussian ansatz. [ABSTRACT FROM AUTHOR]

The ability to transmit data at a high transmission rate is one of the main challenges that has limited the performance of visible light networking systems. In this paper, we present an eight-core photonic crystal fiber designed for multiplexing (MUX) operations at wavelengths of 1.32, 1.3, 1.54, 1.19, 1.4, 0.98, 1.35, and 1.1 µm to overcome this issue. Various MUX parameters, such as transmission rate and normalized power, are examined in this numerical study. A multiplexer is a device that enables multiple messages or signals to be conveyed simultaneously through a single communication channel. A specific type of optical fiber, called photonic crystal fiber (PCF), is used in this context, which has a cladding made of photonic crystals surrounding the fiber core. The fiber features a periodic arrangement of tiny air holes along its length, creating a low-loss periodic dielectric material known as a photonic crystal. In this new design, silica rods are employed instead of multiple air-hole zones along the fiber's length to adjust the coupling length between adjacent channels. The results indicate that after 5.5 mm of light propagation, the operating wavelengths can be effectively multiplexed. [ABSTRACT FROM AUTHOR]

In this work, we propose a novel dual guided PCF design capable of supporting the transmission of 68 OAM modes. The innovative design features a specialized structure with multiple layers composed of pure silica and SF57 material arranged alternately. To enhance physical strength and minimize loss, the fiber is enclosed by a perfectly matched layer (PML). Air holes are strategically added and optimized in the third and fifth layers. Through numerical analysis, we observed that the proposed design yields excellent results across all evaluated parameters. The maximum confinement loss recorded is 10–12 dB/m. The effective refractive index values range from 1.444 to 1.8, with effective refractive index difference values in the order of 10–2. Furthermore, the modal purity and power fraction values exceed 99% for all modes. Dispersion values are maintained below 9.87 ps/THz/cm, and crosstalk values are less than − 12 dB. These results demonstrate the potential of our dual guided PCF design in meeting the increasing demands for high-speed and reliable communicating systems. [ABSTRACT FROM AUTHOR]

In this study, we present a novel design for a photonic crystal fiber (PCF) biosensor utilizing a quadruple silica channel configuration, specifically engineered for highly sensitive external sensing through surface plasmon resonance (SPR). In order to take advantage of the interaction between the surface plasmon polariton (SPP) and core-guided modes within the fiber, the silica channels are carefully positioned to generate an H-shaped PCF. The suggested sensor is designed and completely characterized by the finite element method-based COMSOL Multiphysics program, taking into account the refractive index (RI) variation in the analyte channels. A noticeably performance is achieved with a maximum wavelength sensitivity (WS) of 20,000 nm/RIU and amplitude sensitivity (AS) of - 1367.62 R I U - 1 in the wide RI range of 1.33 to 1.41. The proposed research aids in the early identification of certain cancer cells. Due to the variation in RI between cancer-affected and normal cell samples, the resonance wavelength of cancer-affected cell samples differs from their normal cell samples. The study demonstrates the sensor's specific sensitivities, AS of - 792.8853, - 422.7596, and - 985.2674 R I U - 1 and WS of 5000, 4000, and 7857.14 nm/RIU for HeLa, Basal, and MDA-MB-231 cell lines, respectively. The proposed SPR sensor is a strong contender in a variety of refractive index detection applications due to its high sensing performance and fabrication viability that is evident in this study. [ABSTRACT FROM AUTHOR]

This paper presents a photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor designed to achieve precise malaria detection in blood samples. The sensor's innovative architecture incorporates carefully optimized layers of plasmonic materials, including gold and TiO2, to attain sensitivity and specificity. Extensive assessment of this sensor's performance has been carried out through rigorous finite element analysis using COMSOL Multiphysics v5.6. The sensor's configuration features a gold-coated PCF with a thin analyte layer, enabling the external detection of malaria parasites within blood samples. The air-hole configuration of the PCF sensor resembles the shape of a "barred spiral galaxy". It has undergone comprehensive testing across various stages of infected blood cells (ring, trophozoite, schizont), as well as normal red blood cells, each with their distinct refractive indices (RI). Through meticulous adjustments to the sensor's geometric parameters, remarkable wavelength sensitivity of 17,857.14 nm/RIU and amplitude sensitivity of 442.92 RIU−1 have been achieved for the ring phase, 10,210.53 nm/RIU and 392.72 RIU−1 for the trophozoite phase, and 8758.62 nm/RIU and 352.86 RIU−1 for the schizont phase. The numerical investigation also shows that the sensor possesses a low confinement loss of 50.25 dB/cm, 34.97 dB/cm, 28.74 dB/cm, and 25.47 dB/cm for normal RBC, ring phase RBC, trophozoite phase RBC, and schizont phase RBC, respectively. The results confirm the potential of the proposed sensor to detect malaria compared to existing methods. Hence, this sensor holds significant promise for advancing malaria detection and monitoring in blood samples, potentially leading to improved diagnostic and management strategies for this disease. [ABSTRACT FROM AUTHOR]

This article recommends a photonic crystal fiber (PCF) with a square hollow core sensor for detecting blood cells effectively. To achieve improved relative sensitivity with low confinement loss (CL), the suggested PCF has been explored in the terahertz (THz) band from 2.0 to 4.0 THz. The Full-Vectorial Finite Element Method (FV-FEM) is used to solve the electromagnetic formula and perform numerical computations on the structure in the THz frequency range domain. At optimal frequency f = 3.2 THz, considerable variations in the relative sensitivity of 91.38%, 92.25%, 93.20%, and 95.48% for glucose, plasma, white blood cell (WBC), and red blood cell (RBC) are revealed. At 3.2 THz, the PCF sensor has a relative sensitivity of 95.5% and CL of 2.3698 × 10−08 dB/m. Furthermore, the photonic crystal fiber has an effective area of 2.9435 × 10−08 m2, a very small EML of 0.00803 cm−1, and a spot size of 1.6626 × 10−04 µm. The relatively small confinement loss (CL), excellent effective mode area, and substantial sensitivity at operating frequency in the THz band (2 THz–4 THz) for each blood component are also investigated in this research. [ABSTRACT FROM AUTHOR]

A wavelength-switchable polarization mode filter (PMF) based on a graphene-coated D-shaped photonic crystal fiber (DPCF) is proposed. Due to the different coupling properties between the two polarized core modes and surface plasmon polariton (SPP) modes, the PMF is designed for y-polarized mode filtering. In order to enhance the interaction between the graphene and fiber, gold is coated on top of graphene. Finite element method is applied to analyze the performance. Results show that the filtering wavelength can be modulated by adjusting the chemical potential (μc) of graphene. Especially, a single-wavelength PMF can be switched to a dual-wavelength or a three-wavelength filter by increasing the value of μc. The extinction ratio is higher than 25 dB with a small device length of 100 μm over the wavelength range of 1.0~1.4 μm. The wavelength-switchable PMF has a great potential in polarization modulation, WDM communication system, and multi-parameter sensing. [ABSTRACT FROM AUTHOR]

A terahertz photonic crystal fiber with two sensing channels was designed. Graphene coated on the micro-grooves in the cladding was used as plasma material to introduce tunability. The dispersion relation, mode coupling, and sensing characteristics of the fiber were studied using the finite element method. Ultrahigh sensitivity of 2.014 THz/RIU and 0.734 GHz/°C were obtained for analytes with refractive index in the range of 1.33 to 1.4 and environment temperature in the range of 10–60 °C, respectively. Refractive index resolution can reach the order of 10−5. The dual parameter simultaneous detection, dynamic tunable characteristics, and working in the low-frequency range of terahertz enable the designed photonic crystal fiber to have application prospects in the field of biosensing. [ABSTRACT FROM AUTHOR]

Photonic crystal fiber is a category of optical fibers, getting great attention by its promise to offer a range of optical characteristics that are not achievable in conventional optical fibers. Engineered dispersion and nonlinear characteristics of photonic crystal fiber (PCF) make it an attractive candidate for nonlinear optics and advanced optical networking in the all-optical domain. An optical network consists of different optical components such as laser sources, amplifiers, regenerators, and convertors for proper signal transmission over long distances. In recent years, the performance of the components has been improving by employing the appealing properties of PCF. The PCF's application on such components is discussed, and the simulated results on gain amplification, regeneration, conversion, fiber laser are reviewed. These developments reveal that the enhanced performance provided by PCF makes it suitable for different optics applications. [ABSTRACT FROM AUTHOR]

This paper presents the results of a detailed theoretical study of the bending properties of original all-glass leakage channel microstructured optical fibers (LC MOFs) over a bending radius range from 3 cm to 11 cm. These LC MOFs contain two layers of fluorine-doped silica glass elements with reduced refractive index, different diameters, and different distances between them. We determined the spatial distributions of the electric field components of different modes in addition to the usual parameters such as effective refractive indices, bending losses, and spatial intensity distributions. A detailed analysis showed that three modes for each polarization have to be considered to correctly calculate the bending losses. Two pairs of these three modes couple in two distinct bending radius ranges, specifically near 3.68 cm and near 5.95 cm, and the mode coupling in these pairs is resonant. The resulting bending losses of the LC MOF for two polarizations are very close to each other and have two maxima at bending radii of 3.68 cm and 5.95 cm. However, the nature of these maxima is not resonant; they are caused by the combined influence of all three modes, each of which has specific dependencies of losses and other parameters on the bending radius that exhibit quasi-resonant behavior near the corresponding bending radii. [ABSTRACT FROM AUTHOR]

In this paper, we design and demonstrate an all-fiber-sensitive refractive index (RI) sensor based on the Mach–Zehnder interferometer (MZI). It is constructed by splicing two no-core fibers (NCFs) and a photonic crystal fiber (PCF) between two single-mode fibers (SMFs) to obtain an SMF–NCF–PCF–NCF–SMF composite structure (SNPNS). A study of the effect of varying PCF lengths on the RI reveals that the shorter the length, the higher the sensitivity. The maximum RI sensitivity of 176.9 nm/RIU is attained within the RI range of 1.3365–1.3767 when the PCF length in the SNPNS structure is 3 cm. Meanwhile, the sensor exhibits a high stability in water, with an RSD of only 0.0019% for the interference trough over a duration of two hours. This proposed sensing structure offers the advantages of a large extinction ratio, small size, low temperature sensitivity, and simple fabrication, exhibiting a great potential in RI measurements. [ABSTRACT FROM AUTHOR]

The mode coupling in a graded-index polymer photonic crystal fiber (GI PPCF) with a solid core has been investigated using the Langevin equation. Based on the computer-simulated Langevin force, the Langevin equation is numerically integrated. The numerical solutions of the Langevin equation align with those of the time-independent power flow equation (TI PFE). We showed that by solving the Langevin equation, which is a stochastic differential equation, one can successfully treat a mode coupling in GI PPCFs, which is an intrinsically stochastic process. We demonstrated that, in terms of effectiveness, the Langevin equation is preferable compared to the TI PFE. The GI PPCF achieves the equilibrium mode distribution (EMD) at a coupling length that is even shorter than the conventional GI plastic optical fiber (POF). The application of multimode GI PCFs in communications and optical fiber sensor systems will benefit from these findings. [ABSTRACT FROM AUTHOR]

Photonic Crystal Fiber (PCF) constructions, controlled light propagation for measuring amplitude, phase, polarization and wavelength of the spectrum, and PCF-incorporated interferometry techniques are the foundations upon which sensors operate. But the existing PCF techniques have very large stretching that tends to be difficult to align due to the cross-polarization mode of the optical fiber structure. Hence, the novel Polymer graphene-based Hexagonal cladding is designed by using a hexagonal hollowed core and a cladding material of Polymethyl methacrylate reinforced with gyroidal graphene which increases confinement strength. Once the crystal structure is designed, normally the presence of substrate the Q-factors is degraded. On substrates, Q-factors are enhanced by fine-tuning the position of the neighboring holes. Hence, the novel Bilayer Grating Stratum solves the degrading issues in Q-factors, which utilizes a Silicon polyamide-coated FBG in the crystal that is incorporated using the Femto-laser technique thereby increasing the wavelength tenability. To identify the electric field pattern, the designed structure is simulated in COMSOL software. Thus, the proposed system has a high sensitivity of 22 with a low material loss of 0.1% and a low response time of 0.2 s. [ABSTRACT FROM AUTHOR]

A novel surface plasmon resonance (SPR) refractive index (RI) sensor based on the D-type dual-mode photonic crystal fiber (PCF) is proposed. The sensor employs a side-polished few-mode PCF that facilitates the transmission of the fundamental and second-order modes, with an integrated microfluidic channel positioned directly above the fiber core. This design minimizes the distance to the analyte and maximizes the interaction between the optical field and the analyte, thereby enhancing the SPR effect and resonance loss for improved sensing performance. Au-TiO2 dual-layer material was coated on the surface of a microfluidic channel to enhance the penetration depth of the core evanescent field and tune the resonance wavelength to the near-infrared band, meeting the special needs of chemical and biomedical detection fields. The finite element method was utilized to systematically investigate the coupling characteristics between various modes and surface plasmon polariton (SPP) modes, as well as the impact of structural parameters on the sensor performance. The results indicate that the LP11b_y mode exhibits greater wavelength sensitivity than the HE11_y mode, with a maximum sensitivity of 33,000 nm/RIU and an average sensitivity of 8272.7 nm/RIU in the RI sensing range of 1.25–1.36, which is higher than the maximum sensitivity of 16,000 nm/RIU and average sensitivity of 5666.7 nm/RIU for the HE11b_y mode. It is believed that the proposed PCF-SPR sensor features both high sensitivity and high resolution, which will become a critical device for wide RI detection in mid-infrared fields. [ABSTRACT FROM AUTHOR]

To optimize the use of hollow‐core photonic crystal fibers (HC‐PCF), their cores are filled with an atomic gas for an ultra‐enhanced interaction with an incident laser beam in applications such as atomic vapor microcells. One challenge in these gas‐filled HC‐PCFs is to control the physiochemical interactions between the gas medium and the silica inner surface of the fiber core surround. In this work, thus, the processing of ceramic coatings on glass substrates by chemical solution deposition is focused on. Also, the successful implementation of an original coating procedure for a deposition inside hollow‐core fibers with complex microstructures is described. It is indeed possible to form a thin, dense, inorganic, and amorphous layer with a low thickness, low roughness, and high transparency. To obtain such a result, several parameters must be controlled, including the concentration of the solution, the technique and the deposition time, as well as the heat treatment undergone by the fiber. In particular, the selected aluminosilicate coatings, which are nonporous and present a 20–30 nm thickness, demonstrate a considerable improvement of the lifetime properties of the fibers filled with rubidium vapor, without modifying its original guiding properties. [ABSTRACT FROM AUTHOR]

Chikungunya virus (CHIKV) poses a significant public health threat due to its capacity to cause widespread and debilitating outbreaks. The virus is responsible for CHIKV fever, a disease characterized by severe joint pain, sudden onset of fever, headache, muscle pain, and rash. The virus has been reported in various regions globally, with outbreaks occurring in parts of Africa, Asia, the Americas, and the Indian subcontinent. Consequently, the scientific community expends substantial efforts in developing dependable, rapid, highly sensitive, and cost-effective techniques in order to identify the CHIKV virus. In this study, an innovative biomedical sensor using photonic crystal fiber technology enables precise detection of the CHIKV virus through uric acid, normal and infected plasma, red blood cells, and platelets in the blood. The introduced sensor identifies those kinds with extremely increased relative sensitivity and minimal losses in contrast to alternative photonic crystal fiber-based biosensors. The introduced sensor showcases a minimal confinement loss of 2.25 × 10− 13 cm− 1, a relative sensitivity of 99.37%, an effective area of 1.36 × 105 µm2, with a minimal effective material loss of 0.001966 cm–1, a numerical aperture of 0.1874, and low dispersion of 0.06. Also, the demonstrated sensor is able to function within the terahertz spectrum, covering a substantial span from 0.8 to 2.6 THz. Furthermore, an extensive comparison analysis is performed between the showcased sensor and related literature on photonic crystal fibers to verify the reliability and effectiveness of the introduced structure. [ABSTRACT FROM AUTHOR]

We report the design and theoretical study of a Ga‐Sb‐S chalcogenide glass‐based photonic crystal fiber (PCF) structure for mid‐infrared supercontinuum generation. The proposed design is engineered by adjusting the diameter of air holes in the cladding region and pitch, giving us control over the dispersion characteristics of the fiber. The optimized structure design offers the Zero Dispersion Wavelength of 5.2 μm. When pumped with 50 fs secant hyperbolic pulses of peak power 4.9 kW, for a fiber of length 8 mm at pump wavelength of 5 μm, the proposed structure design produces an ultra‐broadband supercontinuum spectrum spanning 1.5–14 μm. Proposed PCF design should be helpful in, biomedical imaging, supercontinuum sources, biosesning, and optical coherence tomography. [ABSTRACT FROM AUTHOR]

Skin cancer is a disorder marked by inappropriate skin cell proliferation, which is frequently brought on by UV radiation exposure from tanning booths or the sun. It can present as melanoma, squamous cell carcinoma, or basal cell carcinoma, with varying levels of malignancy and available therapies. Our newly developed photonic crystal fiber (PCF) has exceptional efficacy in the identification of skin cancer. The proposed US model has a heptagonal core and a clad surface with a heptagonal pattern. The PCF analyzer that has just been released shows a maximum relative sensitivity (RS) of 95.35% as well 94.29% for the basal (cancer) alongside basal (normal), respectively. For the aforementioned cells, we also looked at the confinement loss (CL) of 1.74 × 10–14 dB/m, 5.98 × 10–13 dB/m, plus the effective material loss (EML) of 0.0077 cm−1, 0.0088 cm−1. Rapid identification in skin cancer allows for improved results, tailored treatment, and prompt intervention. Early detection of cancer makes milder medications available, which lessens the need for aggressive treatment. Moreover, increasing the treatment of patients and simplifying the continual sickness monitoring process. Accurate evaluation also helps with research into developments that enhance global recognition as well as treatment options. The new PCF, with its exceptional detecting capacity, may have been instrumental in the prompt discovery of such harmful organisms. In summary, there are a lot of opportunities in the medical field. [ABSTRACT FROM AUTHOR]

A novel highly sensitive D-shaped photonic crystal fiber-based surface plasmon resonance (PCF-SPR) sensor for dual parameters of refractive index and temperature detecting is proposed. A PCF cladding polishing provides a D-shape design with a gold (Au) film coating for refractive index (RI) sensing (Core 1) and a composite film of silver (Ag) and polydimethylsiloxane (PDMS) for temperature sensing (Core 2). Comsol Multiphysics 5.5 is used to design and simulate the proposed sensor by the finite element method (FEM). The proposed sensor numerically provides results with maximum wavelength sensitivities (WSs) of 51,200 and 56,700 nm/RIU for Core 1 and 2 as RI sensing while amplitude sensitivities are −98.9 and −147.6 RIU−1 with spectral resolution of 1.95 × 10−6 and 1.76 × 10−6 RIU, respectively. Notably, wavelength sensitivity of 17.4 nm/°C is obtained between −20 and −10 °C with resolution of 5.74 × 10−3 °C for Core 2 as temperature sensing. This sensor can efficiently work in the analyte and temperature ranges of 1.33–1.43 RI and −20–100 °C. Due to its high sensitivity and wide detection ranges, both in T and RI sensing, it is a promising candidate for a variety of applications, including chemical, medical, and environmental detection. [ABSTRACT FROM AUTHOR]

In this work, a flat-top and broadband supercontinuum (SC) generation in photonic crystal fibers (PCFs) infiltrated with carbon tetrachloride ( CCl 4) with different air hole diameters in the cladding has been introduced. The optical properties of the fundamental mode are analyzed by numerical simulation. Based on the obtained results, two optimized PCFs with small dispersion are proposed and verified against SC generation in detail. The first fiber has an all-normal dispersion of −9.376 ps.nm − 1 .km − 1 at the pump wavelength of 0.98 μ m, generating broadband of 768 nm and flat-top with only 0.3 nJ of input energy and time duration of 90 fs. In the meantime the dispersion property of the second fiber is anomalous, which equals 1.105 ps ⋅ nm − 1 ⋅ km − 1 at 1.3 μ m pump wavelength. The second fiber generates a SC spectrum of 1,751.1 nm with input energy and time duration of 0.55 nJ and 55 fs, respectively. Proposed fibers are suitable for all-fiber SC sources which could lead to new low-cost all-fiber optical systems. [ABSTRACT FROM AUTHOR]

This paper uses numerical investigation to present an efficient photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor. The proposed sensor is simulated and modelled by the finite element method (FEM). The plasmonic and analyte layers are utilized on the fiber's exterior to ease practical implementation. Additionally, the designed sensor contains all the circular air holes, making it simpler and easier to fabricate using currently available techniques. Silver (Ag) and tantalum pentaoxide (Ta2O5) are used as plasmonic materials for surface plasmon generations and to achieve smooth coupling. The sensor achieves the maximum wavelength sensitivity of 22860 nm/RIU and amplitude sensitivity of 1758 1/RIU. Moreover, the sensor shows a wide refractive range of chemical sensing capabilities within 1.375-1.400. Due to the broad RI detection range, the proposed sensor can detect various biological cells, biochemicals, and food additives, making this sensor applicable in medical applications and food quality control. [ABSTRACT FROM AUTHOR]

This paper presents a photonic crystal fiber (PCF) sensor that can be used to measure the temperature and magnetic field simultaneously, and to monitor the changes in them in the environment. When we designed the fiber structure, two circular channels of the same size were added to the fiber to facilitate the subsequent addition of materials. A gold film is added to the upper channel (ch1), and the channel is filled with a magnetic fluid (MF). The sensor can reflect changes in the temperature and magnetic field strength. The two channels containing MF and PDMS in the proposed fiber are called ch1 and ch2. The structure, mode and properties (temperature and magnetic field) were analyzed and discussed using the finite element method. By using the control variable method, the influence of Ta2O5 or no Ta2O5, the Ta2O5 thickness, the diameter of the special air hole, the distance from the fiber core and the distance between them in the displacement of the loss spectrum and the phase-matching condition of the coupling mode were studied. The resulting maximum temperature sensitivity is 6.3 nm/°C (SPR peak 5), and the maximum magnetic field sensitivity is 40 nm/Oe (SPR peak 4). Because the sensor can respond to temperature and magnetic field changes in the environment, it can play an important role in special environmental monitoring, industrial production and other fields. [ABSTRACT FROM AUTHOR]

As an essential biomarker for diagnosing and treating various diseases, low-cost, quantitative detection methods for complementary DNA (cDNA) have received much attention. The surface plasmon resonance (SPR) sensing technique is an effective measurement scheme, but the ambient temperature and pH variations have a non-negligible impact. In this work, we developed a triple-probe SPR sensing system for detecting cDNA concentration, temperature, and pH. In order to satisfy the triple parameter measurements, we used a microstructured optical fiber as the sensing platform, silver and gold films as the excitation layer, and a MoS2 film as the modulation layer. First, we explore the modulation mechanism of SPR and the conditions for excitation of triple SPR and demonstrate that the carrier concentration is a crucial factor affecting the resonance wavelength. Then, the feasibility of the sensing system for triple-probing is theoretically analyzed. Finally, in the experiment, the optimal parameters of the sensor were determined, and the triple parameter detection was successfully realized. The experimental results show that the three probes can work independently, and the hybridized DNA probe can realize the selective detection of cDNA with a sensitivity of 0.249 nm/(nmol/l). The maximum sensitivity of the pH probe and the temperature probe are 51.5 nm/pH and 6.14 nm/°C. In addition, the experimental results show that the sensing probes have excellent reproducibility. This paper's innovation is using the fiber optic SPR effect to achieve quantitative detection for cDNA, temperature detection, and pH detection. Therefore, the sensor has a promising future in early diagnosis and biosensing. [ABSTRACT FROM AUTHOR]