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The purpose of this study is to design and investigate very compact waveguide with high-performance capabilities. This waveguide consists of a silicon core with a hexagonal photonic crystal structure consisting of air holes. This engineered dispersion structure has a high nonlinearity coefficient, enabling it to simultaneously generate frequency combs and perform their demultiplexing. The small effective mode area of 0.195 μm2 and its large nonlinear coefficient of 103. 9 5 m - 1 w - 1 are achieved due to the high optical confinement within the core. Frequency combs with adjustable frequency spacing of 5 nm (620 GHz), 1 nm (120 GHz), and 0.2 nm (25 GHz) are generated by injecting two continuous wave laser pumps with powers of 20 w to the initial section of the proposed waveguide with a length of 4 mm. In the second stage of the waveguide, the demultiplexing process is accomplished by propagating these combs, effectively separating five distinct comb lines with a wavelength spacing of 1 nm. It is possible to create resonance in the second part of the structure, which is a continuation of the first part, and as a result, separate the comb lines. As a result, this part of the waveguide has the average transmission efficiency, Q factor, spectral line width, and channel spacing, which are approximately 98.08%, 6863.6, 0.222 nm, and 1 nm, respectively. The proposed structure is suitable for optical integrated circuits and in applications that require simultaneous information transmission due to its great compactness. [ABSTRACT FROM AUTHOR]

In the present study, a photonic crystal fiber with a simple design and low losses in the range of terahertz broadband pulse was designed. The proposed structure of this study consisted of a large central air core arranged by three rings of air holes in a regular hexagonal pattern in a uniform Teflon matrix. The refractive index of Teflon, which was made of polymer, was 1.44. The conduction in this fiber was achieved using photonic band gap (PBG) only for a certain range of non-zero values. The simulation results showed that at the wavelength of 174 µm with a central hole diameter of 2.9Ʌ (Ʌ = 300 µm), the lowest confinement losses equal to 0.2 dB/m occurred and the dispersion parameter was 1.2 ps/nm km. [ABSTRACT FROM AUTHOR]

In this work, we study the generation of ultrashort femtosecond laser pulses in photonic crystal fibers through the widely used symmetric split-step Fourier method (S-SSFM). The results are compared with the method of fourth-order Runge-Kutta method (RK4) as the most recognized and powerful method in the analysis of the evolution of ultrashort femtosecond laser pulses. The results show that although S-SSFM is a widely used method, its accuracy decreases for the selected relatively large step sizes of ∆𝑧 in comparison with RK4. In contrast, the accuracy of the mentioned methods becomes closer to each other by selecting relatively small step sizes of ∆𝑧. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, the design and simulation of an ultra-fast 4 × 2 encoder have been optimized in a new and unique way using the wave interference technique based on two-dimensional photonic crystal structures. To create the given structure, nano-resonators (NR) were used in combination with curved 2-branch waveguides to take advantage of wave interference as well as reduce losses and light scattering in the structure to achieve the desired results. Due to its special design, the proposed structure has been symmetrical with a structural size of about 149 µm2. This symmetry caused the same results to be obtained in different states of the used encoder. The results from the structure simulation indicated a contrast ratio of 7.88 dB, a delay time of 0.21 ps, and a bit rate of 4.761 Tbit/s. All simulations were performed with a central wavelength of 1550 nm and an input power intensity of about 1 mW/µm2. To optimize the structure and evaluate the results obtained from it, the changes were made in the structural parameters such as the size of the radius of dielectric rods, the size of NRs, and the value of lattice constant, and the effects of wavelength, operating frequency, and input power intensity on the simulation results were investigated. The analysis of the results of simulations and optimizations indicated the design of a completely principled and logical structure with very suitable results in comparison with other structures proposed in this field so that it can be used appropriately in integrated optical circuits and can be considered as the basic structure for other designs. In the present research, the plane-wave expansion method was used to extract and analyze the photonic bandgap and the finite-difference time-domain method to obtain the results of the output spectrum of the proposed structure. [ABSTRACT FROM AUTHOR]

Supercontinuum spectrum generation is a process in which laser beam in femtoseconds and high power (kilowatts) is converted into a broad-spectrum beam of light after passing through a specific environment. Of course, achieving this range comes with many limitations. In this paper, photonic crystal fibers are used as a substrate for input pulse due to the ability to control dispersion and loss, and creating single-mode operating conditions. One of the main factors for the formation of supercontinuum spectra of injection pulses is maintaining the nonlinear performance of this type of fiber by controlling the effective mode area and also using chalcogenides (nonlinear coefficients about 100 times higher than silica) in their structure. In the proposed structure, a photonic crystal fiber with silica base element and air cavities with hexagonal structure with the center of Ge11.5As24Se64.5 chalcogenide element have been used to provide the nonlinear property of the structure. Also, in this structure, a ring of Ge20Sb15Se65 chalcogenide elements has been used to reduce the effective mode region and create a flat dispersion curve at a wavelength of 1300 nm (second telecommunication window). The input pulse power is 10 kW and its width is 50 femtoseconds, which has caused the range of the supercontinuum from 800 to 1900 nm. This structure can be used to provide the required wavelengths as a carrier in a wavelength division multiplexing. [ABSTRACT FROM AUTHOR]

Chalcogenide-based photonic crystal fibers (PCFs), due to their nonlinear properties, are capable of producing supercontinuum spectra, which can be used in the wavelength division multiplexing (WDM). These types of fibers highly absorb telecommunication wavelengths and hence cannot be used to transmit information over the corresponding wavelengths. We have studied the dispersion engineered chalcogenide PCF numerically, which is important to produce ultra-flat broadband supercontinuum (SC) spectra in all-normal dispersion areas. A 1 mm long, hexagonal chalcogenide PCF made from As2S3/Ge20Sb15Se65 and silica glass pumped at 1550 nm provided a SC bandwidth of 5000 nm with pump power of 1 kW. Here, we have reached zero-dispersion wavelength (ZDW) at third telecommunication window, which in turn has given us a broad spectrum at this window with reasonable efficiency. [ABSTRACT FROM AUTHOR]

In this article, a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) is simulated and analyzed by finite element method (FEM). Gold and titanium oxide (TiO2) are used as plasmonic layers. The TiO2 layer is placed under the gold layer to increase the sensitivity of this sensor. The sensor's top and bottom surfaces are polished, and the plasmonic layer is placed on both these surfaces. Unlike sensors with typical external circular coating, less plasmonic material is used. Additionally, unlike internal coating sensors, there is no issue of partial air holes coating and achieving a uniform thickness of the plasmonic layer. Also using two plasmonic levels can expand the range of refractive index (RI) detection. The sensor's structure creates birefringence, allowing complete coupling between the core mode and both plasmonic layers. This results in more reliable detection ability. By optimizing the dimensions and arrangement of air holes and the sensor's structure, the ability to detect unknown analytes in the ultra-wide range of refractive index of 1.21–1.41 with the maximum wavelength sensitivity (WS) of 61,000 nm / RIU , the maximum amplitude sensitivity (AS) of 1294.29 RIU - 1 , the maximum figure of merit (FOM) of 657.14 RIU - 1 and the sensor resolution (SR) of 4.35 × 10–6 RIU have been obtained. This sensor operates in the visible to near-infrared wavelength range. During its design, feasibility in construction was taken into consideration, along with reducing the complexity and multiplicity of structural parameters. As a result, the sensor delivers excellent performance in detection parameters and is a suitable option for RI detection applications like organic chemicals and biosensing. [ABSTRACT FROM AUTHOR]

We theoretically analyze the detection of a cancer cell in the one-dimensional photonic crystal by infiltrating different sample cells in the cavity layer. The defect modes appear in their transmission spectra only if the nanocomposite layers are included on either side of the cavity layer. This analysis is carried out by a dielectric constant and the transmittance peak of the cancer cell is compared with the normal cell. The transmittance peak shifts are analyzed with various filling factors for optimization purposes. Through the shifting spectrum, the sensitivity of cancer cell from the normal cell is obtained from a minimum of 42 nm/RIU to a maximum of 43 nm/RIU. [ABSTRACT FROM AUTHOR]

In this paper, a photonic-crystal fiber based plasmonic biosensor in which gold is used as the plasmonic material is proposed. The introduced sensor is designed in such a way that the plasmonic metal layer and the sensing layer are placed outside the fiber structure so that the fabrication process and the numerical analysis has become comparatively much easier. The proposed plasmonic biosensor properties are calculated numerically using the finite element method. Amongst the parameters affecting the performance of the biosensor are the thickness of the gold layer and the diameter of the central cavity. By applying the wavelength interrogation method, the maximum sensitivity and the resolution of the proposed biosensor are computed as 5723.5 nm/RIU and 1.74 × 10−5 RIU, respectively. The proposed structure with the above properties is suitable for detecting biological molecules, organic chemicals and analytes. [ABSTRACT FROM AUTHOR]

Optical fibers are widely used in optical communication systems as waveguides with low confinement loss, low chromatic dispersion, and low nonlinear effects. Besides conventional optical fibers, photonic crystal fibers can be also used in transmission media for optical communication systems. In this paper, we present two new designs of index-guiding photonic crystal fiber (IGPCF) with characteristics appropriate for optical communications. In the first proposed design with a hexagonalcircular structure (HC-IGPCF), the chromatic dispersion and the confinement loss at the wavelength of 1550 nm are 0.4 ps/(nm.km) and 1.2×10-10 dB/cm, respectively. In the second design with a squarehexagonal structure (SH-IGPCF) having air holes with unequal diameters, nearly zero dispersion at the wavelength range of 1540 to 1550 nm is achieved. For the latter design, at the wavelength of 1550 nm, the chromatic dispersion slope is -0.05 ps/(km.nm), the confinement loss is less than 10-12 dB/cm and the nonlinear coefficient reaches 8.380 w-1.km-1. [ABSTRACT FROM AUTHOR]

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 ⋀1 = 3μm and ⋀2 =18μm , 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 super-continuum generation. The nonlinear coefficient of the proposed PCF is 1.5 W-1m-1 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. [ABSTRACT FROM AUTHOR]

Abstract: Flammable and/or toxic gas sensors can be used as safety measuring in gas production facilities, especially in oil rigs. The gas sensors detect gas leaks capable of causing fire, explosion, and toxic exposure. Here we proposed an index-guiding photonic crystal fiber for gas sensing that have a broad spectral transmission band and so is capable to detect more gas condensate components. The dependence of relative sensitivity and confinement loss on the fiber parameters is numerically investigated by finite element method (FEM). Introducing a hollow high index ring with an air hole in the center of fiber simultaneously enhances the relative sensitivity and achieves low confinement loss. In addition, we prove that increasing the diameter of holes located in the inner rings, improve the relative sensitivity and increasing the ring diameter holes located in the outer rings, greatly reduces the confinement loss. Placing hexagonal holes instead of circular holes in the innermost ring, the relative sensitivity is effectively enhanced. The relative sensitivity at wavelength of λ =1.33μm that is in the Methane absorption line is enhanced to value of 13.23%. The confinement loss is also improved to 3.77×10−6. [Copyright &y& Elsevier]

A hollow-core photonic bandgap fiber for gas sensing with high sensitivity was designed. Some undesirable parameters like mode interference and propagation losses can deteriorate the performance of PBF. By selecting an accurate and reasonable size of the fiber core, consequently modification the shape and size of the first row of holes surrounding the hollow-core, we could improve light intensity profile in the fiber core. According to the simulation results, at a reasonable core radius the relative sensitivity of gas sensor was improved to 96.57%. In addition, by mode interference suppression, we could minimize the effect of mode mismatch. Furthermore, by optimization of fiber structural parameters like lattice constant and air holes diameter, the PBF was single-mode. Considering the operation wavelength λ = 1.55 µm which is approximately equal to the acetylene gas absorption line, this fiber is suitable to be a high sensitivity gas sensor to detect absorbing gases. [ABSTRACT FROM AUTHOR]

• An ultra-compact multifunctional structure is presented based on the photonic crystal structures. • Simultaneous application of logic gates of AND, XOR, half-adder, 1-bit comparator, reversible Feynman logic gate along with desirable and suitable function are some of the proposed nanostructure properties. • In the proposed multifunctional nanostructure, ultra-fast and ultra-compact logic gates with a maximum time delay of about 280 fs, an area of 104 μm2, and a bit rate of 3.57 Tb/s are provided. • In addition to the proposed ultra-compact logic gate, achieving the appropriate contrast ratio is another advantage of the proposed multifunctional nanostructure. All-optical multifunctional structures are at the beginning of the growth and development path to achieve an all-optical integrated circuit (AOIC). The main challenge of designing multifunctional all-optical nanostructures is to maintain the overall function of the structure compared to single-function nanostructures. Simultaneous application of logic gates of AND, XOR, half-adder, 1-bit comparator, reversible Feynman logic gate along with desirable and suitable function are some of the proposed nanostructure properties. The propagation modes in the structure are extracted by the plane wave expansion (PWE) method. The overall operation of the nanostructure, simulation, and numerical analysis of the proposed nanostructure for the submitted applications are performed using the numerical method finite-difference time-domain (FDTD). In the proposed multifunctional nanostructure, ultra-fast and ultra-compact logic gates with a maximum time delay of approximately 280 fs, an area of 104 μm2, and a bit rate of 3.57 Tb/s are provided. In addition to the proposed ultra-compact logic gate, another advantage of the proposed multifunctional nanostructure is achieving the appropriate contrast ratio. [ABSTRACT FROM AUTHOR]

• In this review, we examine various types of photonic crystal sensors. • A variety of challenges for the construction of label-free diagnostic biosensors are examined. • Important parameters of photonic crystal sensors are compared. Photonic crystals are nanoscale structures that affect the motion of photons. The strong light limitation in photonic crystals and the adjustment of its structural parameters have led to the emergence of photonic crystal biosensors. Moreover, the use of holes as a feature of photonic crystals has resulted in sensors that are very sensitive to low refractive index changes with a small sensing area, which offers flexibility and integration on single-chip systems. Using emerging optofluidic technology, label-free biosensors are on the rise. In this review, we examine various types of photonic crystal sensors, such as waveguides, nanoresonators, LX resonators, holes, multi-channel resonators, nano RINGS resonators, and fibers. These sensors are based on the measurement of biomolecules and the refractive index properties that have been identified. Finally, a variety of challenges and guidelines for the construction of label-free diagnostic biosensors are examined. [ABSTRACT FROM AUTHOR]