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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 research, the angular rotation speed in a passive photonic gyroscope based on the combination of side nanoring resonators and compensating waveguides has been analyzed by creating nonlinear effects in the control factors of the rings using the Sagnac effect. This structure consists of a central waveguide, two identical square resonators, and an almost U-shaped waveguide. The U-shaped waveguide causes coupling between the two resonators in a counterclockwise (CCW) mode. In this structure, a phase shift has been created in the output from the interference of two clockwise (CW) and CCW waves inside the resonators, and according to this phase shift and the central wavelength, the angular rotation speed has been estimated. In the proposed design of the gyroscope, by managing the nonlinear effects in the radius and refractive index (RI) of the coupling and inner rods, we have been able to control the changes in power, phase, and wavelength of the output from the device. With the increase in the intensity of power, the output power has an increasing slope at first, and at the point of creating a nonlinear effect in the sensor, the output power slope decreases. Also, this nonlinear effect directly affects the output phase of the structure. The maximum angular rotation speed in this gyroscope was 6. 6 8 × 1 0 8 ∘ /s. By changing the RI of the inner rods from 3.2 to 3.7, the maximum output-to-input power ratio changes from 0.38 W/ μ m2 to 0.75 W/ μ m2. By changing the radius of the coupling rods from 93 nm to 97 nm, the maximum power ratio decreases from 0.78 W/ μ m2 to 0.55 W/ μ m2. The field distribution profile and photonic bandgap in this gyroscope have been analyzed using the finite-difference time-domain (FDTD) and plane-wave expansion (PWE) methods, respectively. Also, the gyroscope has a footprint of 163.5  μ m2. [ABSTRACT FROM AUTHOR]

In this article, the design and numerical analysis of an all-optical tunable gyroscope using photonic crystal in nonlinear nanostructures for rotation sensing applications is investigated. In this proposed structure, the lattice constant, the filling factor, footprint, the radius of the rods and the refractive index of the silicon rods are set as 528 nm, 0.2, 240 µm2, 103 nm and 3.46, respectively. In this design, according to the changes in the ratio of output power to input power, the output phase shift is estimated. Due to the creation of nonlinear effects in the coupling rods by increasing the input power to the gyroscope, the output power has decreased in the range of the appearance of the nonlinear effect. The value of nonlinear refractive index in silicon coupling rods is considered 4.47 × 10 − 18 m2/W. With the increase of input power, the phase change is almost constant and changes in the range of 120 degrees. In the situation where the nonlinear effects in the structure are activated by increasing the input power, the phase change has a decreasing trend due to the decrease in the output power. This decreasing trend changes from the range of 120° to 44°. According to this phase change, the angular rotation of the gyroscope changes in the range of 78 × 107 deg/h to 200 × 107 deg./h. [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]

The present paper examines a photonic crystal-based ring resonator created using a triangular lattice to design a biosensor with a sensing cavity based on an optical filter. Using this structure, the central wavelength of 1547 nm can be filtered with a transmission coefficient of 95%. Additionally, the maximum value of ultra-high-quality factor (Q) in the proposed structure is about 3740 at 1496 nm wavelengths. Moreover, the minimum detection limit and maximum sensitivity for the proposed structure are calculated to be 7.15 × 10–8 RIU (refractive index unit) and 561 nm/RIU, respectively. In this paper, the effects of structural parameters, including refractive index, lattice constant, and the radius of the rods in the resonator core on the central wavelength of the filter, transmission coefficient, and quality factor have been investigated. The plane wave expansion (PWE) method has been used to extract the photonic bandgap and the finite-difference time-domain (FDTD) method has been used to study the optical behavior of the photonic crystal structure. [ABSTRACT FROM AUTHOR]

In this paper, we describe a two-dimensional photonic crystal-based biosensor that consists of a waveguide and a nanocavity with high sensitivity. A new method is employed for increasing sensitivity of the biosensor. The simulation results show that biosensor is highly sensitive to the refractive index (RI) variations due to injected biomaterials, like glycated haemoglobin, into the sensing surface. The proposed biosensor is designed for the wavelength range of 1514.4–1896.3 nm. The sensitivity and the quality factor are calculated to be 3000 and 272.43 nm/RIU, respectively. The designed structure can detect a 0.002 change in the RI via resonant wavelength shift of 0.9 nm. The band diagram and transmission spectra are computed using plane wave expansion and finite difference time domain methods. [ABSTRACT FROM AUTHOR]

Efficiently use of resources for various applications requires the design of structures with multiple capabilities. Herein, we present a multi-function optical structure to compensate the dispersion of the conventional optical fibers at the third telecom window and to compress an optical pulse to an ultra-short pulse and consequence to make an ultra-high quality factor (Q) refractive index (RI) sensor at the wavelength of 1310 nm. By analyzing the obtained data using the finite-difference time-domain (FDTD) method, a high negative dispersion value is achieved as high as − 26,367 ps/nm/km at the wavelength of 1550 nm. The value of the relative dispersion slope (RDS) for the designed structure is calculated to be 0.00354 nm−1 which is closely matched to that of the conventional optical fibers. An optical pulse at the wavelength of 1310 nm is applied to the structure and the output optical pulse at the drop port with the compression factor of 9.3 is achieved after the length of only 8 mm. By applying this compressed pulse as the input pulse of the RI sensor, an ultra-high-Q equal to 4593 and a high sensitivity value equal to 1100 nm/RIU are obtained. Due to the very high negative dispersion with matched RDS to that of the conventional optical fibers, high sensitivity, and quality factor RI sensor alongside minimum-sized structure, our design has become a multifunctional structure. This feature has made it very suitable for optical integration and long-haul multi-task monitoring applications. [ABSTRACT FROM AUTHOR]

In this paper, a biosensor is designed and optimized based on photonic crystal nano-ring resonator. The ring resonator is formed by two consecutive curves and is sandwiched by two waveguides. For analyzing this biosensor, two-dimensional finite-difference time-domain method and plane-wave expansion approach are applied. Sensing mechanism of the biosensor is based on the intensity variation scheme. When the sensing hole has different refractive indices, output transmission spectrum is shifted. Intensity variations occurred at the wavelength of 1,482.7 nm. The results show that in this biosensor for a unit change in the refractive index, intensity of the transmission spectrum is reduced by 14.26 units. [ABSTRACT FROM AUTHOR]

In this article, an octagonal photonic crystal fiber is proposed, in which the core region and four air holes in the inner ring have a refractive index of 1.43. Compared with the hexagonal photonic crystal fiber, the octagonal photonic crystal fiber has less confinement loss. To study the propagation characteristics of the proposed photonic crystal fiber, the finite-difference time-domain method with perfectly matched layer boundary conditions has been used. By properly optimizing the design parameters of the proposed octagonal photonic crystal fiber, an ultra-flattened nearly zero dispersion of 0 ± 0.1 ps/nm.km in the wavelength range of 1.25 μm to 1.65 μm is made feasible, and for wavelengths shorter than 1.65 μm, confinement losses of less than 7 × 10−7 dB/km have been achieved. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present an interferometry method for refractive index determination in membranes of fuel cells. This technique is based on the use of an improved laser heterodyne interferometer. The photocurrents of the avalanche photodiodes, resulting from reflected beams of the optical head, are led to the signal conditioner and digital signal processing sections. The optical path difference between the target and reference paths is fixed, and as a result, the phase shift is calculated in terms of the refractive index shift. In addition, nonlinearity of this system is analyzed and modeled with different neural networks and adaptive filter algorithms. For neural networks, the radial basis function (RBF), the multi-layer perceptron (MLP), and the stacked generalization method are simulated. In adaptive filter algorithms, the least mean square (LMS), the normalized least mean square (NLMS), the recursive least squares (RLS), and the affine projection algorithm (APA) are applied. The simulation results indicate that the RLS method is faster and contains minimum mean square error (MSE) compared to the other approaches. Also, comparison between two main approaches shows that the nonlinearity of refractive index determination can be effectively modeled with adaptive filter algorithms. [Copyright &y& Elsevier]

In this paper a sensing platform based on nano-cavity photonic crystal resonator (NC-PCR) is proposed for seawater salinity concentration detection. It has been demonstrated that the proposed NC-PCR has high sensitivity and selectivity for various concentrations of seawater salinity. The sensitivity is computed to be as high as 544 nm/RIU (nm per refractive index unit) and the quality factor (Q) is 3860. Also it has been shown that the figure of merit for the proposed structure calculated to be as high as ~ 1.234 × 103 RIU−1 which is very appropriate for sensing applications. Moreover, the minimum detection limit for the presented structure is obtained as 8.1 × 10−5 RIU. The finite-difference time-domain method is employed to investigate the transmission characteristics of the device for a verity of refractive indices. It should also be mentioned that our design is comparatively easy to fabricate and certainly the advantages of our design justify its usage in sensing applications. [ABSTRACT FROM AUTHOR]

This paper investigates a 2-bit all-optical analog-to-digital converter (AO-ADC) using the photonic crystal (PhC) structure. The proposed structure comprises a 27 × 27 grid of silicon rods in air with a refractive index of 3.6. In the design of this converter, a linear demultiplexer and an optical encoder are used. The optical demultiplexer has one input and three outputs. Optical coding has three inputs and two outputs. In general, this converter consists of one input and two outputs, and according to the output light power from the structure and the threshold level of the converter, two logical 0 and 1 states are created in the output. The footprint of the proposed AO-ADC is as small as 118.5 µm2 making it more suitable for use in the optical integrated circuits (OICs) compared to the previous structures. The proposed AO-ADC works at an operating wavelength of 1550 nm with a response time of about 0.6 ps and also works with lower optical intensity. [ABSTRACT FROM AUTHOR]

We have proposed a novel 2D zinc monoxide photonic sensor for detecting the components in urine samples. The proposed structure consists of linear waveguide and diamond-shaped 3 × 3 ZnO rods inside the ring resonator. To avoid a sharp bend of light at the corners of the linear waveguide region, the ZnO rods are shifted in the middle of the two rods for high transmission over a wide wavelength range and help to improve the characteristics parameters of the sensor. Further, we have evaluated the real part from the imaginary part of the refractive index using the Kramers–Kronig relationship for the different components of urine sample. The plane wave expansion (PWE) method is employed to calculate the band structure at the optimized rod radius and lattice constant. The finite-difference time-domain method is applied to observe the transmission characteristics and calculate the resonance wavelength. We have obtained an impressive sensitivity for the glucose concentration of 0.625 gm/dl, which is 28,820 nm/RIU. The highest quality factor and full-width at half maximum of 1663.52 and 1.002 nm, respectively, have been obtained for a glucose concentration of 15 gm/dl. The highest figure of merit and the lowest limit of detection are observed for the 2.5 gm/dl of urea concentration. To verify the linearity of the sensor, we have drawn fitted line for the glucose and urea concentration and obtained correlation coefficient of 0.944 and 0.998, respectively. Our calculated values of performance parameters found a considerable improvement over other existing structures, which shows the ability of the proposed sensor. [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]