Photonic Crystal Waveguide Research Articles

Study, simulation and detection of glucose concentrations through a biochip based on two-dimensional photonic crystals

A biochip is made from a two-dimensional photonic crystal waveguide and a rhombus shape that acts as a resonator. This biochip is a sensor that can detect different concentrations of glucose with amounts of 10, 20 and 60% in water. Here, we studied and simulated the concentrations of glucose, which have a refractive index n of 1.3477, 1.3635 and 1.4394, respectively. To identify these quantities, we have proposed a square lattice structure formed by silicon rods with a n = 3.46. With the help of these dielectric rods immersed in the air, it was possible to analyze the detection characteristics. Our results are examined according to COMSOL software by using the PWE method and the finite element method in order to have the PBG and which helped us to create the structure and extract the propagation at resonance, the field norm, the total energy density (TED), the power flow norm (PFN), the transmission and the sensitivity. The concentrations of glucose in water answered yes to the variations for each of the E-field, the TED, the PFN and the sensitivity. These variations are due to the radius r and refractive index n of each concentration used. This structure can help with diabetes self-monitoring.

Modal analysis of planar waveguides by the immersed interface method

Modal analysis of optical waveguides is a basic task in the design of advanced waveguide devices and optical circuits. How to deal with the problem of electromagnetic heterogeneous interface and absorption boundary condition are two major difficulties in implementing efficient numerical analysis of optical waveguides. Existing high-order accurate finite-difference modal analysis methods do not take into consideration the absorption boundary problem, which, thus, makes it difficult to accurately simulate leakage and radiation modes. Based on the immersed interface method and perfectly matched layer absorption boundary condition, a finite-difference method with the second- and fourth-order accuracy is proposed in this work. By using this method, the single-interface plasmonic waveguide mode, planar symmetric waveguide mode, and one-dimensional photonic crystal waveguide mode are analyzed. Numerico-experimental results show that the convergence rate of the second- and fourth-order algorithm are consistent with the anticipated order of the guided mode, leakage mode and radiation mode. The second-order algorithm provides an ultimate accuracy of about <inline-formula><tex-math id="M5">\begin{document}$10^{-9}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230595_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230595_M5.png"/></alternatives></inline-formula> for the relative error of effective refractive index, when the normalized step size is <inline-formula><tex-math id="M6">\begin{document}$10^{-4}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230595_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230595_M6.png"/></alternatives></inline-formula>. The fourth-order algorithm provides an ultimate accuracy of about <inline-formula><tex-math id="M7">\begin{document}$10^{-10}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230595_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230595_M7.png"/></alternatives></inline-formula> for the relative error of effective refractive index, when the normalized step size is <inline-formula><tex-math id="M8">\begin{document}$10^{-3}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230595_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230595_M8.png"/></alternatives></inline-formula>. Through the study of field distribution of guided mode and cladding mode in a one-dimensional photonic crystal waveguide, we show that the continuity of the field of transverse electric mode and its first derivative across the interface, and the continuity of the field of transverse magnetic mode and the discontinuity of its first derivative across interface, can be analyzed accurately. The method proposed in this paper can be used to calculate any mode for any refractive index profile, only by using the value of refractive index, independent of the specific functional representation of modal fields. The method provides a simple and efficient tool for implementing the modal analysis of step-index planar waveguides.

A road toward zero-spacing photonic waveguides and circuits

Like their electronic counterparts, photonic integrated circuits face the challenge of further integration and miniaturization. One of the fundamental limitations comes from waveguide spacing, which leads to serious crosstalk between the neighboring waveguides when it is less than half a wavelength. Here we demonstrate a potential approach to remove this limitation and realize zero-spacing photonic waveguides with extreme compactness. This is achieved by designing pure-dielectric photonic crystal waveguides with shifted spatial dispersion and arranging them with normal dielectric waveguides alternately. Amazingly, the coupling and crosstalk between the two types of waveguides are negligible despite the zero spacing between them. Through proper designs, zero-spacing photonic bending waveguides and circuits can also be realized in practice. Such a finding opens a new avenue for ultra-compact photonic waveguides and circuits with 100% space utilization efficiency.

Effect of PMMA Temperature on Optical Performances of 1 x 2 Hybrid Photonic Crystals Waveguide Beam Splitters

Effect of PMMA Temperature on Optical Performances of 1 x 2 Hybrid Photonic Crystals Waveguide Beam Splitters

Local density of optical states calculated by the mode spectrum in stratified media

The local density of optical states (LDOS) is an important physical concept, which can characterize the spontaneous emission of microcavities. In order to calculate the LDOS, the relationship between the mode spectrum and the LDOS is established. Then, based on the transfer matrix method and the effective resonator model, the leaky loss of the leaky mode and the mode spectrum in the one-dimensional photonic bandgap crystal waveguide are calculated, results of which indicate that the mode spectrum can characterize the leaky loss of the leaky mode. At last, the density of optical states (DOS), and the LDOS in each layer are calculated. The partial DOS and the partial LDOS in the quantum well, related to the fundamental leaky mode, can be used to find out the optimal location of the quantum well in the defect layer to couple more useful photons into the lasing mode for lasers.

Large-Area and High-Precision Milling of Focused Ion Beam Based on the Integration of Nanoscale Machine Vision and Compensation Control

Abstract Focused ion beam (FIB) is a high-precision technology for micro/nanofabrication that can be used to fabricate micro/nanoscale structures and electronic devices, such as waveguide gratings, resonators, and photonic crystals. In this study, a novel FIB processing system was developed using machine vision coupled with a piezoelectric motor, which compensates the process periodically and automatically. The FIB system is controlled by a computer program that enables automatic processing, automatic recognition, and provides feedback to control the movement of the stage. The results show that ring arrays with a diameter of 2 μm can be detected automatically under the field of view (FOV) of 114 × 114 μm2 with relative errors of less than 6%. The FOV can be larger than 400 × 400 μm2 after the splicing function of automatic compensation control is applied to the same ring arrays. Structurally, the average splicing errors in the X- and Y-directions decreased one order of magnitude, which are from 1.49 to 0.15 μm and 1.47 to 0.37 μm, respectively. This paves the way for the mass production of nanoholes in a large area with high precision and high speed for semiconductor manufacturing and research.

20 dB improvement utilizing custom-designed 3D-printed terahertz horn coupler.

Terahertz band is envisaged to provide substantially higher capacity and much lower latency for wireless communications in contrast to microwave frequencies. Moving to higher frequencies comes with its own unique challenges to be addressed, such as poor coupling efficiency from free space into and out of planar air-core waveguides. Here, we propose a framework for rapid design and low-cost fabrication of terahertz horn couplers. The horn couplers are first designed by maximizing the field overlap integral on apex and aperture interfaces, then fabricated exploiting 3D printing technique, and finally sputtered with a thin layer of gold. A 28~μm standard deviation of the surface roughness height of the 3D printed horn couplers is calculated. Experimental demonstrations show that the proposed horn coupler improves the transmittance of a hybrid photonic crystal waveguide by 20 dB in comparison with the previous pinhole-based coupling configuration. This work provides a fast, convenient and economical approach for design and fabrication of customized couplers for any waveguide size, with a cost of only 5% of commercially available counterparts, and could be integrated in 3D-printed terahertz devices during fabrication.

Design and analysis of all-optical 1 × 4 demultiplexer based on 2D photonic crystal

Abstract In this paper, an all-optical 1 × 4 demultiplexer (DEMUX) has been designed by employing 2D photonic crystal (PhC) waveguides for use in optical networking and signal processing. The proposed structures consist of four T-shaped and one Y-shaped waveguide using 15a × 15a rectangular lattice silicon rods in ambient air. All-optical DEMUX has been simulated using the finite-difference-time-domain (FDTD) method and the results have been verified by distributing the optical field at a wavelength of 1.90 μm. Analysis of the device has been carried out for distinctive crystal and lattice designs with the achievement of a transmission ratio of more than 2.05 in presence of select input.

A FETD scheme and analysis for photonic crystal waveguides comprising third-order nonlinear and linear materials

In this paper, we design a time-domain finite element (FETD) algorithm for solving Maxwell’s equations in third-order nonlinear media. The Cardano’s method is used to solve the nonlinear constitutive equation. At the same time, we also establish the continuous stability of the third-order nonlinear model and the numerical stability of the FETD scheme. In order to reduce the wave reflection from the truncated domain boundary, the anisotropic perfectly matched layer model is developed and solved. Extensive numerical simulations are carried out and they demonstrate that bistable transmission switches depending on the incident wave’s intensity can be obtained if a number of rods made of Kerr-type nonlinear materials are inserted around the bend of the linear bent photonic crystal waveguides.

A hybrid photonic-plasmonic resonator based on a partially encapsulated 1D photonic crystal waveguide and a plasmonic nanoparticle

In this paper, a hybrid photonic-plasmonic resonator is proposed. The device consists of a partially encapsulated 1D photonic crystal waveguide and a plasmonic nanoparticle to yield high radiation efficiency for integrated photonic platforms, owing to a high Q-factor and a small mode volume. The design of the resonator is accomplished in two consecutive steps: first of all, a partially encapsulated photonic crystal nanobeam with a robust mechanical stability and a high-Q factor is prepared; secondly, a plasmonic nanoparticle is placed on the surface of the nanobeam to interact the optical mode with the localized surface plasmons of the gold nanoparticle which is being present in the vicinity of the radiating dipole. Strongly enhanced electromagnetic field, regenerated through the optical mode field inside the hybrid resonator, enables to reduce the optical mode volume of the device and significantly enhance the Purcell factor.

Information preservation of two qubits in a structured environment

The environment-induced decoherence of a quantum open system makes it fundamentally import to preserve the initial quantum information of the system in its steady state. Here we study information preservation of two maximally entangled qubits lying inside a photonic-crystal waveguide with semi-infinite cavity-array structure. We generalize our study to arbitrary position and arbitrary frequency detuning of the qubits. We find that for weak qubits-waveguide couplings, the information preservation greatly depends on the position and the frequency detuning of the qubits, while for strong couplings, both of these dependence is significantly weakened. Interestingly, by suitably choosing the position and the frequency of the qubits, high information preservation could be achieved for both weak and strong couplings, irrespective to Markovian or non-Markovian dynamics. Physically, we analytically verify that the ability of information preservation is indeed determined by the existence of the bound states of the entire system, but the probability of information preservation is closely related to the probability of the initial state of the qubits in the bound states. Our results provide an alternative route getting high information preservation without any external controls of the system.

Eigenfunction and eigenmode-spacing statistics in chaotic photonic crystal graphs.

The statistical properties of wave chaotic systems of varying dimensionalities and realizations have been studied extensively. These systems are commonly characterized by the statistics of the eigenmode spacings and the statistics of the eigenfunctions. Here, we propose photonic crystal (PC) defect waveguide graphs as a physical setting for chaotic graph studies. Photonic crystal waveguides possess a dispersion relation for the propagating modes, which is engineerable. Graphs constructed by joining these waveguides possess junctions and bends with distinct scattering properties. We present numerically determined statistical properties of an ensemble of such PC graphs including both eigenfunction amplitude and eigenmode-spacing studies. Our proposed system is compatible with silicon nanophotonic technology and opens chaotic graph studies to a new community of researchers.

Waveguide-Integrated MoTe2 p-i-n Homojunction Photodetector.

Two-dimensional (2D) materials, featuring distinctive electronic and optical properties and dangling-bond-free surfaces, are promising for developing high-performance on-chip photodetectors in photonic integrated circuits. However, most of the previously reported devices operating in the photoconductive mode suffer from a high dark current or a low responsivity. Here, we demonstrate a MoTe2 p-i-n homojunction fabricated directly on a silicon photonic crystal (PC) waveguide, which enables on-chip photodetection with ultralow dark current, high responsivity, and fast response speed. The adopted silicon PC waveguide is electrically split into two individual back gates to selectively dope the top regions of the MoTe2 channel in p- or n-types. High-quality reconfigurable MoTe2 (p-i-n, n-i-p, n-i-n, p-i-p) homojunctions are realized successfully, presenting rectification behaviors with ideality factors approaching 1.0 and ultralow dark currents less than 90 pA. Waveguide-assisted MoTe2 absorption promises a sensitive photodetection in the telecommunication O-band from 1260 to 1340 nm, though it is close to MoTe2's absorption band-edge. A competitive photoresponsivity of 0.4 A/W is realized with a light on/off current ratio exceeding 104 and a record-high normalized photocurrent-to-dark-current ratio of 106 mW-1. The ultrasmall capacitance of p-i-n homojunction and high carrier mobility of MoTe2 promise a high dynamic response bandwidth close to 34.0 GHz. The proposed device geometry has the advantages of employing a silicon PC waveguide as the back gates to build a 2D material p-i-n homojunction directly and simultaneously to enhance light-2D material interaction. It provides a potential pathway to develop 2D material-based photodetectors, laser diodes, and electro-optic modulators on silicon photonic chips.

Discrete exterior calculus for photonic crystal waveguides

AbstractThe discrete exterior calculus (DEC) is very promising, though not yet widely used, discretization method for photonic crystal (PC) waveguides. It can be seen as a generalization of the finite difference time domain (FDTD) method. The DEC enables efficient time evolution by construction and fits well for nonhomogeneous computational domains and obstacles of curved surfaces. These properties are typically present in applications of PC waveguides that are constructed as periodic structures of inhomogeneities in a computational domain. We present a two‐dimensional DEC discretization for PC waveguides and demonstrate it with a selection of numerical experiments typical in the application area. We also make a numerical comparison of the method with the FDTD method that is a mainstream method for simulating PC structures. Numerical results demonstrate the advantages of the DEC method.

Revolution of optical computing logic gates based on its applications: an extensive survey

Nowadays, communication has grown into a key area with a rapidly growing user community. The existing broadband users are overcrowded, and its faster speed has now become an essential parameter to meet the consumer’s expectations in the growing technology. As a result of our growth in computer technologies, high-speed processors are necessary, which provide simultaneous data computing with lower costs and a performance of more than 10,000 times quicker than electrical computers. Optics has become a more feasible alternative to electronics because of its greater speed. In this study, various methods of photonic crystals (PhCs) have been thoroughly examined, with essential properties and their benefits explained over previously identified methods (semiconductor optical amplifier and nonlinear waveguides) utilized to construct all-optical logic circuits. Particularly, evaluated a number of articles that covered topics including self-collimation effects, PhC waveguide intersection, and multi-mode interference with nonlinear effects. The merits and demerits of each technology are analyzed. Finally, concluded the major difficulties and the potential usage of every method. PhCs are used in logic circuits and devices for high data transmission. The performances of different types of logic gates based on PhC are studied.

All-optical switch with ultrahigh switching efficiency and ultralow threshold energy based on a one-dimensional PT-symmetric ring optical waveguide network

In this work, we propose an all-optical switch based on one-dimensional (1D) parity-time-symmetric (PT-symmetric) ring optical waveguide network (PTSROWN). By use of the resonant coupling effect of the PT-symmetric structure, the all-optical switch based on our designed 1D PTSROWN generates an ultrahigh transmissivity of 1.42×1018 at ON state, which breaks the bottleneck of the transmissivity of 1 at ON state produced by the all-optical switches made of dielectric optical waveguide networks, photonic crystals, microring resonators, and meanwhile, creates an ultralow transmissivity of 1.01×10−18 at OFF state. It causes our designing all-optical switch reproducing extraordinary large switch efficiency of 1.41×1036, which is 10 orders of magnitude greater than the optimal results reported yet. On the other hand, the super resonant coupling effects can also make the all-optical switch generate ultrastrong photonic localization at ON state, and then drastically reduce the threshold energy. In addition, we have deeply optimized the PT-symmetric optical waveguide network and obtain better extremum spontaneous PT-symmetric breaking points. On this condition, our designing all-optical switch can produce an ultralow threshold energy of 4.3×10−34 J, which is 12 orders of magnitude smaller than the best reported results. This not only provides a better choice for developing all-optical switching devices with better performance, but also possesses a broad application prospect in designing high-efficiency optical amplifiers, optical energy saver devices, etc.

Slow-Light Enhanced Liquid and Gas Sensing Using 2-D Photonic Crystal Line Waveguides—A Review

Photonic crystals (PhCs) are periodically structured dielectric materials that have attracted significant research interest in the last two decades for their ability to slow down the group velocity of a propagating pulse envelope with promising sensing applications. This review article discusses the properties of 2-D PhCs including the slow-light phenomenon, bandgap generation, and application of these properties for gas and liquid sensing. Waveguide generation by introducing defects with light guiding and confinement is discussed. In addition, for 2-D PhC line waveguides, a comprehensive review on the slow-light principle and phenomenon of slow-light enhanced sensing for gases and liquids is discussed. 1-D and 3-D PhCs are also reviewed for bandgap generation and defects in PhCs along with present fabrication challenges and future trends. Our study highlights an increase in the detection capabilities of PhC-based sensors paving way for high-sensitivity detectors with applications in ubiquitous monitoring of gases and liquids.

Subradiant states for two imperfect quantum emitters coupled by a nanophotonic waveguide

Coherent interactions between quantum emitters in tailored photonic structures is a fundamental building block for future quantum technologies, but remains challenging to observe in complex solid-state environments, where the role of decoherence must be considered. Here, we investigate the optical interaction between two quantum emitters mediated by one-dimensional waveguides in a realistic solid-state environment, focusing on the creation, population and detection of a sub-radiant state, in the presence of dephasing. We show that as dephasing increases, the signatures of sub-radiance quickly vanish in intensity measurements yet remain pronounced in photon correlation measurements, particularly when the two emitters are pumped separately so as to populate the sub-radiant state efficiently. The applied Green's tensor approach is used to model a photonic crystal waveguide, including the dependence on the spatial position of the integrated emitter. The work lays out a route to the experimental realization of sub-radiant states in nanophotonic waveguides containing solid-state emitters.

Design and analysis of passive and phase insensitive all-optical isolator in linear optical platform

In this work a very simple all-optical isolator, based on 2D holes in slab Photonic Crystal (PhC) waveguide, has been proposed and its performance has been investigated by Finite-Difference Time-Domain (FDTD) method. The unidirectional characteristic of the waveguide is phase independent in nature and no extra bias signal has been used. The structure is basically a ‘W1’ pyramid shaped waveguide having a 120° -bend in it and the unidirectional property has been achieved by making some structural modification in the bend region. This design is capable of providing a high forward transmittance of 72%, very low backward transmission of 10% and high contrast ratio 8.57 dB. Due to its simple structure, small footprint (416μm2), high forward transmission and high contrast ratio altogether make the isolator suitable for upcoming photonic integrated circuits.

Slow-light effect in symmetry-reduced non-defect photonic crystals

In this study, a two-dimensional low-symmetric photonic crystal (PC) configuration with elliptical geometry is presented and its slow-light (SL) effect is investigated. Reducing the symmetry in the PC unit cell provides slow modes at the higher transverse electric bands. The calculated group index and the corresponding normalized bandwidth equal to {ng, BW}={63.56, 0.0065}. That corresponds to a value of figure of merit (FOM)=0.4344 defined by the product of the average group index and the normalized bandwidth, FOM=〈ng〉BW, which is comparable to the values available in literature. Tracing the whole edges of the Brillouin zone, strongly excited SL modes are observed only along Γ-X but not along Γ-X’ or Γ-M. That condition allows for the design of low-symmetric PC waveguides with finite thicknesses at the expense of lowering group index value. The SL effect is still obtained for the proposed low-symmetric PCs having finite thicknesses, which is numerically proved via finite-difference time-domain methods. It is important to note that non-dispersive SL Bloch modes exist through the non-zero k-vector components of Brillouin zone. Hence, such a defect-free (without either point- or line- defect) SL PC design may have a great potential for the use of compact photonic devices such as in optical switching and biochemical sensing applications.