Two-dimensional Photonic Crystal Waveguide Research Articles

Two-dimensional thin film lithium niobate photonic crystal waveguide for integrated photonic chips

The photonic crystal waveguide (PCW) possesses remarkable capabilities in manipulating light beams and light–matter interactions within the subwavelength range. This property renders it a highly promising structure for the miniaturization of optical devices. We delve into the mode characteristics in two-dimensional PCWs on thin film lithium niobate, establish the correlation between the single-mode region in the PCW and its photonic crystal duty cycle, and observe mode hybridization in the waveguide. A lithium niobate PCW with sidewall angles can realize single-mode transmission or mode conversion by adjusting the width of its defective waveguides, and it is theoretically and experimentally verified that a change in the width of the waveguide shifts the operating wavelength. The results of the mode analysis are useful in the design of waveguide structures for photonic crystal-based electro-optical modulators and optical sensors.

2D FDTD Electromagnetic Simulation of an Ultracompact All Optical Logic Gate Based on 2D Photonic Crystal for Ultrafast Applications

In this paper, the concept of photonic crystals (PhCs) is fundamental to designing and simulating an all-optical logic gate device. We proposed an all-optical switch composed of two-dimensional (2D) photonic crystal waveguides with a central photonic crystal ring resonator (PCRR). The new all-optical NAND logic gate device comprises two linear waveguides coupled to each other through a single compact PCRR. The plane wave expansion (PWE) and finite-difference time-domain (FDTD) methods are applied to simulate the properties of the system. The structure is implemented on the operational wavelength of 1700 nm on an air wafer of only 12 μm × 12 μm. Indeed, the simulation results show that the proposed all-optical NAND gate is a strong candidate for ultrafast photonic integrated circuits (PICs) for applications in optical communications, being advantageous with high transmitting power, with simple design, and without the use of optical amplifiers and nonlinear materials.

Ultra compact, high contrast ratio all optical NOR gate using two dimensional photonic crystals

An all-optical NOR gate is implemented using a two-dimensional photonic crystal waveguide. The paper provides a structure of an all-optical NOR gate constructed by introducing a line and point defect. The proposed NOR gate uses a hexagonal lattice structure with E shaped waveguide. The contrast ratio, response time and bit rate of three input NOR gate are 29.59 dB, 0.8 ps and 1.19 Tbps, respectively. The proposed gate is constructed with the operating wavelength of 1550 nm. The structure has been simulated and analyzed using Finite Difference Time Domain (FDTD) and Plane Wave Expansion (PWE) methods. It offers high contrast ratio, better response time with ultra-compact size. Hence it is suitable for high speed optical integrated circuits and switching devices.

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.

Ultra-slow light with high normalized delay–bandwidth product and refractive-index sensing in photonic crystal coupled-cavity waveguide

Ultra-slow light can enhance light–matter interactions and effectively realize all-optical buffering and modulation. In this paper, we present an efficient design for a two-dimensional square-lattice photonic crystal coupled-cavity waveguide, which can realize multi-frequency band slow-light transmission in the near-infrared band (1500–1640 nm).Through adjusting intercavity spacing N and structural parameters of elliptical air holes, high group index ng (202.46) within the bandwidth of 5.04 nm and improved normalized delay–bandwidth​ product of 0.6583 can be obtained at the wavelength of 1550.05 nm. Moreover, the designed devices can effectively function as a slow light sensor with the wavelength sensitivity of 585 nm/RIU. Multiple functions can be achieved synchronously in only one structure, which is essential in complex optical integrated circuits.

Tunable propagation of waveguide modes in multichannel two-dimensional photonic crystal waveguide

Photonic Hall effect (PHE) can be realized in the multiple-channel photonic crystal waveguide. By modulating the polarization state of the incident light, the light can propagate in any one or more of the four channels of the waveguide, while the light energy in the other channels is very weak. Its fascinating behavior can be explained by the theory of interference of the two component waves. We believe that our results will have important applications in photonic integrated circuits.

Two-dimensional photonic crystal waveguide 1×5 beam splitter reversely designed by downhill-simplex algorithm

Beam splitter, whose main function is to achieve the splitting, combining and routing of optical signals, is an important component of photonic integrated circuits, passive optical network and other fields. Compared with the conventional beam splitter, photonic crystal beam splitter, which has the virtues of smaller size and higher transmission efficiency, is very suitable for high-density and large-scale integration. The traditional control variable method often used in the optimal design of photonic crystal beam splitter is time-consuming and inefficient. When parameter variables are large, it is difficult for beam splitter to achieve the optimal splitting performance. In addition, it is hard to realize flexible design of beam splitting ratio when optimizing multi-channel photonic crystal beam splitter by this method. In this paper, a novel photonic crystal 1×5 beam splitter, in which two special Y-junction waveguides are introduced into a completely two-dimensional square lattice silicon, is proposed and optimally designed by using downhill-simplex algorithm. Firstly, to determine the optimization range of each variable, the influences of the radius of the dielectric rod in the coupling region and the radius and the lateral offset of the regulating dielectric rod in the center of the two Y-junction waveguides on the five output ports of the 1×5 beam splitter are explored respectively by the plane wave expansion method and finite difference time domain method. The results show that the optical energy coupled from the main waveguide W<sub>1</sub> to the upper Y-junction waveguide and lower Y-junction waveguide can be controlled by optimizing the radius of the dielectric rod in the coupling region. The transmittance of the five output ports can be controlled in proportion by optimizing the lateral offset of the regulating dielectric rods. The total transmittance of the five output ports can be improved, and the output of each port can be adjusted by optimizing the radius of the regulating dielectric rod. Then, according to the specific target of the splitting ratio, using downhill-simplex algorithm, the 1×5 beam splitter with different splitting ratio can be reversely designed by optimizing the radius of the coupling dielectric rod and the radius and the lateral offset of the regulating dielectric rod within the selected optimization range. The total transmittance of the 1×5 beam splitter is above 99%, the additional loss is less than 0.044 dB, and the response time is less than 1ps. Besides, to determine the allowable error range of each optimization variable in actual processing, the machining error of the 1×5 beam splitter is analyzed, which provides a theoretical reference for fabricating the device. Owing to the advantages of flexible splitting ratio design, high optimization efficiency, small size and excellent performance, the proposed 1×5 beam splitter will have broad application prospects in the field of photonic integrated circuits and so on.

Photonic crystal-based biosensor for detection of human red blood cells parasitized by plasmodium falciparum

In this paper, a biosensors based on a two-dimensional photonic crystal (2D PhC) waveguide including a ring resonator is designed and simulated based on refractive index changes of red blood cells. The proposed biosensor structure consists of an elliptical photonic crystal ring resonator and two linear waveguides containing silicon nitride rods in a 2D rectangular lattice with circular rods. The biosensor is utilized to detect the stages of the Plasmodium falciparum cycle in red blood cells and to diagnose malaria disease. The proposed design distinguishes with high sensitivity between normal red blood cells and cells infected with Plasmodium falciparum. This biosensor is very compact, consists of gold rods in the air background and works very well at two input central wavelengths of 0.514 and 1.55 μm. The finite-difference time-domain (FDTD) method is used to simulate and investigate the device. The biosensor is extremely compact which is very suitable for lab-on-chip applications and exhibits higher sensitivity at both input central wavelengths compared with that of previously reported sensors.

Photon Hall effect in two-dimensional photonic crystal waveguide

The finding of Photon Hall effect (PHE) on metal surface is an important progress in photonics, but it will be more practical if PHE can be realized in line-type waveguide. In this paper, we suggested a way to realize PHE in two-dimensional photonic crystal (PC) waveguide. Numerical simulation results show that the propagating direction and strength of light in the PC waveguide can be controlled by the polarization state of incident light. Different from the PHE on metal surface, the PHE in PC waveguide can be driven not only by circularly polarized light, but also by linearly polarized light. The PHE in PC waveguide can be attributed to the interference of the two component waves excited by the incident light.

Analyzing two-dimensional tunable photonic crystal waveguides for communication band optical filter applications

Analyzing two-dimensional tunable photonic crystal waveguides for communication band optical filter applications

Design of photonic crystal based compact all-optical 2 × 1 multiplexer for optical processing devices

Through this work, an all-optical 2 ​× ​1 multiplexer (MUX) is realized for optical networking and optical signal processing using two-dimensional photonic crystal waveguides. The structure consists of two T-shaped and one Y-shaped waveguide using square lattice silicon rods with a background of air. The all-optical MUX is designed without using any nonlinear material like Kerr material to overcome the problems of low gain and nonlinear susceptibility. This design works on the principle of beam-interference phenomena. The performance all-optical MUX is simulated with the help of the finite-difference-time-domain method and resultant outputs are verified using the distribution of the optical field at a wavelength of 1.55 ​μm. The proposed circuit occupies less area 7.8 ​μm ​× ​9 ​μm and provides a transmission ratio of more than 92%, a contrast ratio of 29.66 ​dB in presence of select input and 23.2 ​dB in absence of select input and it can operate with a bit rate of 1.56 Tbps.

Design of all-optical reversible logic gates using photonic crystal waveguides for optical computing and photonic integrated circuits.

Reversible logic gates are capable of designing lossless digital systems, which have received a great deal of attention in photonic integrated circuits due to their advantages, such as less heat generation and low power dissipation. In this paper, all-optical reversible Feynman and Toffoli logic gates are designed for optical computing devices and low-power integrated circuits. Proposed designs of all-optical reversible logic gates are implemented with two-dimensional photonic crystal waveguides without using any nonlinear material. The finite-difference time-domain method is used to simulate and verify the proposed design, and it is operated at a wavelength of 1550 nm. The structure of all-optical reversible logic gates requires much less area, and Feynman logic gates offer a contrast ratio (CR) of 12.4 dB, transmittance of 0.96, and less insertion loss of -0.015dB, while Toffoli logic gates offer a CR of 32.5 dB, transmittance of 0.9, and less insertion loss of -0.04dB.

Numerical investigation of highly efficient and tunable terahertz-wave generation using a low-group-velocity and low-dispersion two-dimensional GaAs photonic crystal waveguide

Efficient terahertz (THz)-wave generation via difference frequency generation (DFG) in a GaAs-based two-dimensional photonic crystal waveguide (PhC-WG) was proposed and investigated through numerical simulations. A PhC-WG with a low-group-velocity and low-dispersion mode (LVLD PhC-WG) was designed, and THz–DFG spanning sub- to several THz in frequency was obtained. Electric field enhancement and phase-matching between two fundamental light pulses in the LVLD PhC-WG generated THz–DFG approximately 280 times that in a GaAs strip waveguide. This method is applicable to highly efficient and tunable small-footprint THz-emitting devices based on semiconductor materials.

Exception point induced flat-band and waveguide laser

In order to study the exceptional point (EP) properties in the photonic crystal waveguide, we construct the two-dimensional photonic crystal waveguide with the parity–time symmetry configuration. With the calculation of the eigen frequencies, the evolution of the waveguide mode bands discloses two EP-induced flat bands. The transmittance and reflectance at the two flat bands show a huge amplification property and the structure become a waveguide laser. The waveguide lasing is due to the common properties of the EP and the flat band. The results have been demonstrated by the transmission spectra, Poynting vector distribution and simulations of field propagation.

TE band structure in a photonic waveguide with triangular holes

This study determines the TE band structures in a two-dimensional photonic crystal waveguide with triangular dispersers in a hexagonal lattice in a GaAs background. Using the plane-wave expansion method and the supercell technique, a defective mode propagating in the direction of the linear defect was numerically identified within the photonic band gap. In addition, this study reports that this defective mode may be tuned to higher frequencies by increasing the applied hydrostatic pressure. However, when the triangular dispersers are rotated, no noticeable change is observed in the defective mode within the photonic band gap.

The adjustable band gap structure and transmission characteristics for the two-dimensional function photonic crystal waveguide

In this paper, we have studied band gap structure, light field distribution, and the propagating direction in the two-dimensional function photonic crystal waveguide. For the two-dimensional function photonic crystal waveguide, the dielectric constant of dielectric column is the space coordinate function, which can be realized by the electro-optic effect and the Kerr effect. The dielectric constant function form of the dielectric column is ɛr = kr + b, the parameters k and b can be adjusted by changing the applied electric field. By changing the dielectric constant parameters k or b, we found the two-dimensional function photonic crystal waveguide transmission characteristics have the adjustability, i.e., band gap and position, defects mode number and position, the propagating direction, and light field distribution can be changed by adjusting the dielectric constant parameters k or b. It can be used to conveniently design the band gap structure, light field distribution, and the propagating direction that we need. It provides a new designed methods for optical device, such as dynamic optical device, optical switch and so on.

Unique band coalescence and exceptional points from two-dimensional photonic crystal waveguide

The exceptional points (EPs) in photonic crystals (PCs) with PT-symmetry involve the band coalescence at which the real bands are transformed into conjugate complex bands. The PC EPs are usually in the extended bands and cannot be excited in a guided form. To achieve some guided EPs, we design a two-dimensional photonic crystal waveguide with localized PT-symmetry. The waveguide edges are made of balanced gain and loss materials. With the increasing of material gain or loss coefficient, the coupled mode bands clearly undergo dynamical evolution. An interesting band attraction and coalescence behavior occurs, which leads to the formation of the first-order EP and the second-order EP. The second-order EP can be locally excited with multiple field distributions which is dependent on the line source position. In contrast to the other modes whose frequencies clearly change with material parameter, the EPs in this structure have unique frequency stability against the change of material parameters.

Asymmetric and dynamic waveguide propagation based on localized parity-time symmetry

The asymmetric or unidirectional light propagation has attracted enormous research interest in optical communication system. Most of these waveguides are static and cannot be modulated. In order to achieve a dynamic and tunable asymmetric waveguide, we propose a two-dimensional photonic crystal waveguide with a localized PT-symmetry. With the band coalesce, the structure achieves a unique waveguide mode band. With an excitation of line source the light in the waveguide undergoes an asymmetric or symmetric propagation in the two opposite directions of the waveguide, dependent on the source position and frequency. For a frequency in the waveguide mode band, the contrast of the field amplitudes in the two directions change periodically with the displacement of the source; whereas for the fixed source, the contrast can be modulated by the source frequency.

InP-based polarization rotator-splitter for mid-infrared photonic integration circuits

We design and experimentally demonstrate the propagation loss of waveguides and the operation of a single-step etched polarization rotator-splitter (PRS) in low index contrast InGaAs-InP material system at 6.15 μm. Propagation losses 4.19 dB/cm for TM mode and 3.25 dB/cm for TE mode are measured. The designed PRS can achieve near 100% conversion efficiency. This study enables the possibility of monolithic integration of quantum cascade devices with TM-polarized characteristics and TE-guiding two-dimensional slotted photonic crystal waveguide gas sensors for on-chip monolithic absorption spectroscopy.

High-sensitivity temperature sensor by coupling two-dimensional photonic crystal waveguide with dual microcavities

We propose a photonic crystal dual-resonant microcavity and waveguide-coupled temperature sensor structure. The resonant characteristics of photonic crystal microcavities are simulated by finite-difference time-domain method. Due to the positive thermo-optic effect of silicon and the negative thermo-optic effect of SU-8 photoresist, a resonant wavelength shift is detected for temperature sensing in the opposite direction, which significantly improves the sensitivity of the sensor. Simulation results highlight that the sensitivity of the temperature sensor is 124.69 pm / ° C, the temperature measuring range is ∼150 ° C, and the limitation of the temperature sensing area is reduced. The sensor can be integrated to lab-on-chip and system-on-chip to achieve real-time temperature measurement in different microregions.