Photonic Crystal Refractive Index Research Articles

Pair of optical solitons in parallel planar waveguides coupled by linear photonic crystal

We propose a simple optical model, which consists of two Kerr nonlinear parallel planar waveguides sandwiching a one-dimensional photonic crystal for demonstrating the phenomenon of spontaneous symmetry breaking in optics. We study the shape and stability of soliton pairs propagating in two planar waveguides and the spontaneous symmetry breaking of the power distribution of solitons in the two waveguides. The results of numerical simulation show that there is supercritical type of spontaneous symmetry breaking in this system. More optical power P and smaller refractive index of photonic crystals [Formula: see text] make soliton solutions more prone to spontaneous symmetry breaking bifurcation. Asymmetric soliton solutions and symmetric soliton solutions correspond to different dispersion relations. Under the given total power P, for the symmetric soliton solutions, the propagation constant k increases linearly with [Formula: see text], and for asymmetric soliton solutions, the propagation constant k decreases nonlinearly with [Formula: see text]. The minimum point of [Formula: see text] is just the demarkation between the symmetric soliton solutions and the asymmetric soliton solutions. If [Formula: see text] is fixed, the minimum point of the Hamiltonian of the system, [Formula: see text], is also the critical point of the two different kinds of soliton solutions. We also study stable and unstable distributions of two kinds of soliton solutions.

Consequence of Fibonacci quasiperiodic sequences in 1-D photonic crystal refractive index sensor for the blood plasma and cancer cells detections

We present the consequences of different Fibonacci quasiperiodic sequences on the sensing performance of a one-dimensional (1D) photonic crystal (PC) based sensor to detect the blood plasma and cancer cells. We demonstrate that the sensitivity and figure of merit (FOM) of the sensor can be modulated, respectively, from 427.5 nm/RIU to 530 nm/RIU and from 162.5 RIU−1 to 2983.33 RIU−1 by utilizing the pertinent sensor structures with Fibonacci generation and structural parameters for the analyte refractive index from 1.31 to 1.41. We have also shown that the operational sensing wavelengths and sensitivity can be changed significantly by introducing the different Fibonacci sequences in the proposed sensor. The sensing peaks separation, FWHM, and sensitivity can also be tuned by changing the analyte and PC stacked layers' thicknesses. We also introduce the sensing performances for the Blood plasma and Cancer cells detection using the proposed Fibonacci quasiperiodic PC sensor. We observe that the maximum sensitivities and FOM of the proposed sensor are 552.5 nm/RIU and 2986.93 RIU−1 for cancer cells and 553.55 nm/RIU and 2214.21 RIU−1 for blood plasma, respectively. The proposed structure reveals the tunable sensing performances and stimulates the fabrication interest.

Highly sensitive refractive index sensor based on photonic crystal ring resonators nested in a Mach–Zehnder interferometer

Today, with the rapid development of photonics, optical sensors are being considered as efficient tools for detecting environmental variations and have been regarded as one of the most important fields in photonic research. In this study, we have proposed a two-dimensional photonic crystal refractive index sensor using a combination of Mach–Zehnder interferometers and two ring resonators. Our goal is to increase the sensitivity and figure of merit of the sensor, so that the output transmission spectrum can be considerably shifted by changing the refractive index of the simulated analytes. The proposed photonic crystal sensor consists of a hexagonal array of silicon rods on a SiO2 substrate. The finite difference time domain method is used for the numerical simulation of the structure. In this regard, to validate the simulation results, two different commercial software have been used. The quality-factor and the sensitivity of the proposed structure are 1535 and 1658 nm/RIU, respectively, where RIU stands for the refractive index unit. In general, the structure has advantages such as low fabrication cost, high sensitivity to changes in refractive index and a high Q-factor.

Design of a highly sensitive photonic crystal refractive index sensor incorporating ring-shaped GaAs cavity

Two highly sensitive optical sensor topologies are proposed and simulated in this paper. The proposed structures are optimized to provide better performance characteristics such as sensitivity, detection limit, and quality factor. They are based on two-dimensional photonic crystals consisting of rectangular arrays of GaAs rods in SiO 2 substrates. Such lattices have bandgaps for transverse magnetic modes. Two-dimensional finite difference time domain and plane wave expansion methods are used for the simulation and analysis of the refractive index sensors and particle swarm optimization method is used to optimize the structural parameters. The designed structures show a high sensitivity to refractive index variations. They are able to detect refractive indices from 1.33 to 1.5. An excellent figure of merit equal to 737 RIU −1 is observed for the proposed structure and a significant improvement is observed compared to the structures reported in the literature.

High-sensitivity silicon-based photonic crystal refractive index biosensor based on defect-mode coupling

A high-sensitivity, high-resolution, multi-working-channel and real-time-detection typed one-dimensional photonic crystal biosensor is proposed in this paper. Through changing the slit’s width between two adjacent silicon layers, multiple defects with different resonant wavelengths are designed. Based on the air-typed defect mode whose light energy is greatly localized in the lower refractive index region and the coupling interaction between different defects, a subtle alteration of the liquid’s refractive index can make the resonant wavelength and light transmittance change significantly. Different liquid samples can flow freely within respective channels, and they can be measured in real time and at the same time. Through analyzing the alteration of the wavelengths and transmittances, the concentration information of a variety of liquid samples can be measured through a wide transmission spectrum measurement. When the working wavelength λres is about 1559.0 nm, the bulk refractive index sensitivity as high as ∼810 nm/RIU is obtained with the quality factor of ∼9679 and the detection limit of ∼4.18×10−6.

Design of a label-free photonic crystal refractive index sensor for biomedical applications

Two photonic crystal optical refractive index sensors have been proposed in this paper. These sensors can be used for detection of basal cell cancer. A rod-type square lattice of GaAs is used for this purpose. The sensor topologies are based on a photonic crystal ring-shaped resonator coupled to two and waveguides respectively. Instead of using ultra-high quality factor cavities for improving the sensitivity, the resonance profile is localized and concentrated on the analyte to achieve good distinction. A 13 nm cavity resonance frequency shift for normal and cancer cells is obtained for detection of basal cell carcinoma. Finite difference time domain method and plane wave expansion methods are used to simulate and analyze the structures. The proposed biosensors have a sensitivity equal to 720 and 638 nm/RIU. The simplicity of the design and its high sensitivity make it a suitable choice for bio-sensing applications.

Photonic crystal microcavity as a highly sensitive platform for RI detection

In this paper, we propose a new design principle of two-dimensional photonic crystal refractive index sensors with high transmission and sensitivity simultaneously. The proposed sensor is made of two waveguide couplers and one microcavity which is obtained by varying the radius of one air hole in the center of PC structure. The microcavity is separated from the input and output waveguides by many holes of the PC. It is shown that by injecting an analyte such as gas or a liquid into a sensing hole, and thus changing its refractive index, a shift in the resonant wavelength may occur. The transmission spectra, quality factor and sensitivity of the sensor have been analyzed numerically by the finite difference time domain (FDTD) method. The sensitivity value of the sensor has been found to be 668 nm/(RIU with minimum detection limit of 0.002 RIU), which proves the ability of the structure to produce biosensor PhC.

Mesoporous anodic aluminum oxide photonic crystalline films and its applications

We have calculated the optical characteristics of mesoporous photonic crystalline film of aluminum oxide. We obtained the dispersion relation for electromagnetic waves in the film, calculated an effective refractive index of photonic crystal, worked out group velocities and effective masses of photons and polaritons in mesoporous medium. The results of theoretical analysis are in the good agreement with the measured reflection spectrum. It is shown that the mesoporous photonic crystalline films are good as the radiation amplifiers and highly efficient selective mirrors and filters.

Design of simultaneous high-Q and high-sensitivity photonic crystal refractive index sensors

Sensitivities (S) and quality factors (Q) have been trade-offs in label-free optical resonator sensors, and optimal geometry that maximizes both factors is under active development. In this paper, we demonstrate that the nanoslotted parallel multibeam cavity possesses unexplored high S and high Q. We achieve S>800  nm/RIU (refractive index unit) and Q>107 in liquid at telecom wavelength range when absorption is neglected. To the best of our knowledge, this is the first geometry that features both high S and Q factors, and thus is potentially an ideal platform for refractive index-based biochemical sensing.

Effective refractive index of the photonic crystal deduced from the oscillation model of the membrane

The oscillation model of the circular membrane is used to calculate the effective refractive index of the two-dimensional triangular photonic crystal at normal incidence within the second photonic band. Negatively effective refractive indices deduced from this model match those calculated by equifrequency surfaces very well. The result reveals that the field distribution has relation with the effective refractive index at certain frequency regions. Besides, the field distribution described by the Bessel function is more compact than the Fourier series expansion.

Photonic crystal refractive index sensing based on sandwich structure

An ultracompact refractive index sensing based on the sandwich structure of photonic crystal is presented and demonstrated with solutions of water, methylsilicone and silicone. The performances of the sensor are analyzed theoretically by using Fabry–Perot cavity mode, the change in opposite direction between the transmission of the refractive index sensing and its quality factor is derived. The experimental results are consistent with the results of theoretical analysis.

Direct observations for the superprism effect in photonic crystals utilizing negative refraction

In this work, we experimentally explored the negative-refraction superprism effect in photonic crystals by investigating the frequency-dependent negative refractive index of photonic crystals at microwave frequencies from 8.2to8.4GHz. By detecting the spatially distributed intensity of a transmitted microwave whose incident angle is well controlled, we determined the propagating path, the refractive angle, and the refractive index of the transmitted microwave. The highly dispersive relationship between the negative refractive index and the frequency of microwave observed indicates potential applicability of this method for being used in a microwave wavelength demultiplexer by utilizing the negative-refraction superprism effect in photonic crystals.

On the relationship between Bloch modes and phase-related refractive index of photonic crystals

It has previously been shown that the phase-related refractive index is positive in photonic crystals that display negative refraction at higher bands. We hypothesize that the phase velocity is governed by a wave that can be related to the dominant Bloch mode. This dominant wave can be identified from an approximate solution of Maxwell Equations using a homogeneously averaged dielectric constant and the dominant wavevector is related to the fundamental wavevector and the reciprocal lattice vectors. We validate this hypothesis by numerical Fourier decomposition of the field in the entire simulation domain. It confirms that for negative refraction at higher bands, the phase-related refractive index is indeed positive and differs significantly from the negative value of effective refractive index calculated from the band structure.