Design Of Photonic Crystal Waveguide Research Articles

Exploring high-performance photonic crystal slow light waveguides through deep reinforcement learning

Supervised deep learning is not really suitable for automatic inverse design of photonic crystal waveguides. There are three reasons for this:(1) Pre-training of the network requires a large number of datasets, which leads to a lot of time spent in the physical simulation process. (2) The one-to-many mapping problem often arises during the reverse design process. (3) It is difficult to realize the inverse design of photonic structures beyond the performance of the dataset. These problems can be well addressed by deep reinforcement learning (DRL). Here, deep reinforcement learning is proposed for the first time for the design of complex slow-light photonic crystal waveguides. The design using DRL took less than 72 h to obtain a photonic crystal waveguide with a normalized delay bandwidth product of 0.449 and group index of 48.72. By increasing the scaling factor of bandwidth in the reward function to 0.25, the bandwidth value of the optimized slow-light waveguide increases to 50.01 nm with an NDBP value of 0.39. The slow-light performance of both structures is verified by FDTD. In addition, the NDBP value is further optimized to 0.46 if the size of the structural parameters is not constrained. Compared with deep learning, DRL can improve the sampling efficiency by more than an order of magnitude and is not plagued by the three problems mentioned above. This work confirms the effectiveness of DRL in the inverse design of energy band engineering. DRL can be widely used in the optimization of energy band related performance.

Optimised photonic crystal waveguide for chiral light–matter interactions

We present slow-light photonic crystal waveguide designs that provide a ×8.6 improvement of the local density of optical states at a fully chiral point over previous designs.

Time-reversal constraint limits unidirectional photon emission in slow-light photonic crystals.

Photonic crystal waveguides are known to support C-points-point-like polarization singularities with local chirality. Such points can couple with dipole-like emitters to produce highly directional emission, from which spin-photon entanglers can be built. Much is made of the promise of using slow-light modes to enhance this light-matter coupling. Here we explore the transition from travelling to standing waves for two different photonic crystal waveguide designs. We find that time-reversal symmetry and the reciprocal nature of light places constraints on using C-points in the slow-light regime. We observe two distinctly different mechanisms through which this condition is satisfied in the two waveguides. In the waveguide designs, we consider a modest group velocity of vg≈c/10 is found to be the optimum for slow-light coupling to the C-points.This article is part of the themed issue 'Unifying physics and technology in light of Maxwell's equations'.

Asymmetric Oval-Shaped-Hole Photonic Crystal Waveguide Design by Artificial Intelligence Optimizers

This paper proposes a new kind of photonic crystal waveguide (PCW) called asymmetric oval-shaped-hole PCW (AOPCW). In this PCW, 20 structural parameters are considered, which provides a very flexible PCW to design. The large number of variables makes the design process of this new PCW almost impossible by the current manual try and error methods. Therefore, the AOPCW is optimized automatically by the artificial intelligence optimization technique in three phases. First, the AOPCW is optimized to maximize normalized delay-bandwidth product. Second, it is optimized with respect to two objectives: averaged of group index ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\overline {n_g } $</tex-math> </inline-formula> ) and normalized bandwidth <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$(\Delta \omega /\omega _0)$</tex-math> </inline-formula> . Third, group velocity dispersion is also considered in addition to the two objectives in the second phase, so AOPCW is optimized with respect to three objectives. In all of the three phases, a band mixing avoidance mechanism is also considered and handled. The comparative study of the optimized designs proves that the proposed AOPCW is able to substantially outperform the current PCW structures in the literature. This paper also considers and discusses time-domain simulation issues of the PCW-based optical buffer.

Designing photonic crystal waveguides for broadband four-wave mixing applications.

We present photonic crystal waveguide designs which exhibit large four-wave mixing efficiencies over a wide wavelength region. These designs are identified using an optimization process taking into account sophisticated figure-of-merits that depend on the pump bandwidth and the signal/pump tunability. The obtained designs achieve up to -18.9 dB conversion efficiency, tunable over a 10nm tunability range. We also present alternative designs that are less efficient but have smaller power requirements and are far more compact.

Oval-Shaped-Hole Photonic Crystal Waveguide Design by MoMIR Framework

This letter proposes a new type of photonic crystal waveguide (PCW) called oval-shaped-hole PCW (OPCW). In the proposed structure, the circle-shaped holes are replaced by oval-shaped holes. In order to find the best possible structural parameters, the recently proposed multiobjective framework called MoMIR is employed. The calculation results show that the proposed optimized OPCWs are able to outperform the best current PCW in the literature significantly.

Sensibility of influential factors to transmittance in two-dimensional photonic crystal waveguide composed of Kerr nonlinear medium

In order to obtain the higher propagating efficiency in the photonic crystal waveguide, in this paper, a two-dimensional photonic crystal waveguide composed of Kerr nonlinear dielectric rods is considered to study the parameters influence on transmittance. The most sensitive factor on transmittance is obtained by the method of (NFDTD) according to the orthogonal numerical analysis, which may be helpful to the nonlinear Kerr medium selection in the photonic crystal waveguide design.

Simulation of Broadband Transmission Photonic Crystal Waveguide Crossing with Linear Taper

A novel design of photonic crystal waveguide crossing with taper structure is proposed. Simulations are performed by finite-difference time-domain method. The results show the proposed design has both high transmission and low cross talk characteristics. The transmission band and low cross talk band can be tuned to match each other by adjusting the taper structure..

Design of a highly sensitive photonic crystal waveguide platform for refractive index based biosensing

In this paper, a photonic crystal waveguide platform on silicon-on-insulator substrate is proposed in order to realize a highly sensitive refractive index based biosensor. Following the design, the analysis of the sensor structure are made by using the three dimensional Finite Difference Time Domain method. The principle of sensing is based on the change in refractive index, which in turn changes the output spectrum of the waveguide. Results show that the sensitivity of the sensor depends mainly on the geometrical properties of the defect region of the photonic crystal structure. The phenomenon is verified for various samples having refractive index ranging from 1 (air) to 1.57 (Bovine serum albumin). Further, the structure is compared with few other conventional photonic crystal waveguide designs to analyze the sensing performance. The estimated value of sensitivity of the sensor is found to be 260 nm/RIU with a detection limit of 0.001 RIU. This high sensitivity can enhance the performance of low-concentration analytes detection.

Multimode-Interference-Based Waveguide Crossing in Two-Dimensional Cubic Photonic Crystal

A novel design of photonic crystal waveguide crossing based on multimode-interference (MMI) structure is proposed. Two structures of difference device lengths are simulated and studied. The proposed structures have high transmission efficiency for a wide bandwidth. The crosstalk is -26dB with device length of 12 lattice periods and -39dB with device length of 24 lattice periods. The plane wave expansion method and finite-difference time-domain method are used to calculate the modal dispersion curve and field propagation, respectively. The proposed MMI-based waveguide crossing has the potential to be practical in high-density optical integrated circuits.

Improved design of photonic crystal waveguides with elliptical holes for enhanced slow light performance

We propose a new design for slow-light photonic crystal W1 waveguide, which uses a combination of circular and elliptical air holes arranged in a hexagonal lattice with background material of refractive index n = 2.84. Large value of normalized delay bandwidth product (NDBP = 0.3708) is obtained. We have also analyzed dispersion property for the structure and achieved nearly zero-dispersion for a very large bandwidth. Our proposed photonic crystal waveguide has slow light applications such as reduction in length and power consumption of all-optical and electro-optic switches at optical frequency.

Semi-analytic method for slow light photonic crystal waveguide design

We present a semi-analytic method to calculate the dispersion curves and the group velocity of photonic crystal waveguide modes in two-dimensional geometries. We model the waveguide as a homogenous strip, surrounded by photonic crystal acting as diffracting mirrors. Following conventional guided-wave optics, the properties of the photonic crystal waveguide may be calculated from the phase upon propagation over the strip and the phase upon reflection. The cases of interest require a theory including the specular order and one other diffracted reflected order. The computational advantages let us scan a large parameter space, allowing us to find novel types of solutions.

Loss-Relevant Structural Imperfections in Substrate-Type Photonic Crystal Waveguides

Substrate-type planar 2-D photonic crystal (PhC) waveguides suffer from large experimental propagation losses compared to membrane-type PhC waveguides. Numerical simulations can give insight into the quantitative contribution to the propagation losses originating from fabrication imperfections and nonideal designs of the waveguide or the vertical layer structure. Many numerical studies have been performed in the past addressing only a part of the question. All of them lack the general overview, which is essential to identify the main source for the large propagation losses. Since those studies are performed with various numerical methods on many different PhC waveguide designs, a general overview cannot be reliably assembled from the literature. Therefore, we (re-)performed a comprehensive set of numerical experiments with the 3-D finite-difference time-domain method to investigate the influences of imperfections, such as the finite etch depth, a conical hole shape, the finite number of lateral layers of holes, the asymmetric vertical layer structure, lattice disorder, and variations of the hole radius. A major result of this paper is a list of requirements to be met by the process technology for the fabrication of a W1 PhC waveguide in the low-index contrast system (InP/InGaAsP/InP). Furthermore, we were able to identify the angled sidewalls to be responsible for the main fabrication-related propagation loss contribution. Finally, we show the potential of new, alternative low-loss waveguide designs for the weak index contrast system and emphasize the importance of using realistic hole shapes in this search process.

All-optical controllable trapping and transport of subwavelength particles on a tapered photonic crystal waveguide

We propose that a tapered photonic crystal waveguide design can unify optical trapping and transport functionalities to advance the controllability of optical manipulation. Subwavelength particles can be trapped by a resonance-enhanced field and transported to a specified position along the waveguide on demand by varying the input wavelength. A simulated transport ability as high as 148 (transport distance/wavelength variation) is obtained by the waveguide with 0.1° tilted angle. Stable trapping of a 50 nm polystyrene particle can be achieved with input power of 7 mW. We anticipate that this design would be beneficial for future life science research and optomechanical applications.

Model Selection Under Limited Information Using a Value-of-Information-Based Indicator

Designers are continuously challenged by complexity, as well as by the excessive instantiation and execution times of models, particularly in the context of integrated product and materials design. In order to manage these challenges, a systematic strategy for evaluating and selecting models is presented in this paper. The systematic strategy is based on value-of-information for design decision making. It consists of a (i) process performance indicator (PPI) to quantify the impact of model refinement from a decision-centric perspective and (ii) a method involving model evaluation. Using this method, a least complex but valid model is evaluated, and, only if necessary, gradually refined it until the most appropriate one is selected. The systematic approach is particularly well suited for integrated product and materials design, and all other scenarios where the perfect knowledge of the true system behavior and bounds of error are not available throughout the design space. The proposed strategy is applied to the design of photonic crystal waveguides for use in a next-generation optoelectronic communication system. In this paper, it is shown that the systematic strategy based on the PPI is useful for evaluating and selecting models particularly when accuracy of the prediction or the associated error bounds are not known.

Hexagonal array photonic crystal with photonic quasi-crystal defect inclusion

The central region of a hexagonal array photonic crystal is replaced with the central region of a higher rotational order photonic quasi-crystal pattern. The quasi-crystal, with band gaps and defect states now acts as the defect region of the hexagonal array. For the model system examined, different types of “defect” states are identified, and the modal properties examined. The higher degree of defect state control provided by the mixing of photonic crystal types can find applications in resonator design for laser cavities and WDM as well as assist in the formation of non-conventional photonic crystal waveguide designs. Results are presented specifically for the hexagonal array and 12-fold quasi-crystal and can be extended to other photonic crystal combinations.

Highly dispersive micro-ring resonator based on one dimensional photonic crystal waveguide design and analysis

We propose and analyze a novel design of a hybrid micro-ring resonator and photonic crystal device. The proposed device is based on a micro-ring resonator with the addition of a series of periodic defects that are introduced to the microring. When the wavelength of operation approaches the band-gap of the periodic structure, the modal dispersion is significantly increased. The huge dispersion leads to narrowing of the spectral linewidth of the resonator. We predict an order of magnitude linewidth narrowing for a microring radius of the order of 10mum. The proposed hybrid device is analyzed theoretically and numerically using finite-elements calculations and finite-difference-time-domain calculations. We also present as well as the design and analysis of add-drop and notch filters based on the highly dispersive ring resonator.

Directional emission from photonic crystal waveguides

We propose a novel photonic crystal waveguide design with defects at the termination to provoke directional emission. Because the resulting optical field distribution at the waveguide exit resembles a triple point source, the light can emit with low angular divergence. This phenomenon appears both in photonic crystal structures formed by dielectric rods as well as by air holes.

Design of photonic crystal waveguides for evanescent coupling to optical fiber tapers and integration with high-Q cavities

We describe a novel scheme based on evanescent guided-wave coupling for optically interfacing between conventional fiber-optic and planar photonic crystal devices such as waveguides and resonant cavities. By considering the band structure of bulk photonic crystal slabs, we analyze the k space properties of a linear defect waveguide and establish a set of design rules to ensure efficient evanescent coupling with optical fiber tapers. These rules are used to design a waveguide in a square-lattice photonic crystal. The coupling efficiency is calculated with a coupled-mode theory incorporating the finite-difference time-domain-calculated uncoupled modes of the fiber taper and photonic crystal waveguide. On the basis of this coupled-mode theory, 95% power transfer from the fiber taper to the photonic crystal waveguide is possible over a coupling length of 80 lattice periods and with a bandwidth of 1.5% of the center wavelength. The integration of this waveguide with a photonic crystal defect resonant cavity is also presented, thus showing the usefulness of the combined fiber taper and photonic crystal waveguide system for efficient, optical fiber-based probing of optical elements based on planar photonic crystal technologies.

Three-dimensional photonic crystals operating at optical wavelength region

Three-dimensional photonic crystals operating at optical wavelength region are developed with III–V semiconductors, where micron-to-submicron-scale large-contrast refractive index change with an asymmetric face-centered cubic structure is formed by a method based on a wafer fusion and a very precise alignment technique. A considerable band-gap effect is successfully demonstrated in infrared-to-near-infrared wavelengths. It is pointed out for this method that the introduction of arbitrary defects states and/or efficient light emitters can be possible. For the example of the introduction of light-emitting element, a surface-emitting laser with a two-dimensional photonic crystal structure is developed, and very unique lasing characteristics are demonstrated. These results encourage us for the development of various quantum optical devices and circuits including not only passive but also active devices. Some ultra-small optical integrated circuits are proposed, and a guideline for the design of photonic crystal waveguides is successfully demonstrated.