Responsive photonic crystals have attracted much attention due to their strong capability to manipulate the propagation of light in the visible region, but it is still a big challenge to invisibility and mechanical stability. Here, the novel Poly(ether sulfone)/Poly(acrylic acid) inverse opal photonic crystals, which have high mechanical stability and can release visible patterns after wetting with water, are discussed. The Poly(ether sulfone)/Poly(acrylic acid) inverse opal photonic crystals are also responsive to the concentration of ethanol, and the structural color response times increase with increasing ethanol concentration. This design uses the selective infiltration, hydrogen bonding and capillary action of solvent to realize the spectral diversity of reflectance. Owing to the high polarity and hydrogen bonding ability of carboxyl groups, water molecules are adsorbed easily by the poly(acrylic acid) gel. Subsequently, the encrypted information is decrypted due to the redshift of the structural color. Because of its lower polarity and hydrogen bonding ability relative to water, ethanol can impede the absorption of solvent by gel. Therefore, the ethanol concentration can be identified based on the structural color response time. Furthermore, reliable information decryption methods make Poly(ether sulfone)/Poly(acrylic acid) inverse opal photonic crystals potentially uesful as trusted encryption devices.

The novel all-optical unidirectional wavelength filters are studied by the finite-difference time-domain method, which are based on the two-dimensional square-lattice photonic crystal with the rectangular defects. Owing to the modes’ match and mismatch between the defect and the adjacent waveguides, the unidirectional propagation of the fundamental-mode light beam resonant at a certain frequency is obtained. Through merely altering the coupling region between the defect and the input waveguide, a unidirectional dual-branch waveguide filter is designed. This kind of devices has both the abilities of wavelength filtering and unidirectional light propagation, and may be potentially applied in the future all-optical complex integrated circuits.

The exponential growth of information and data processing has led to bottlenecks in the continuous improvement of performance for traditional electronic hardware processors.¹ To address this problem, all-optical computing using photons as information carriers has become a promising solution.^{2 – 6} Compared with traditional electronic hardware computing, optical computing offers several advantages, including ultrafast computing speed,^7,8 ultralow energy consumption,⁹ and significant potential for parallel computing.^10,11 In recent years, with the rapid development of deep learning,¹² optical computing based on deep learning with different implementation schemes has been increasingly applied to various tasks,¹³ such as vowel recognition,⁹ image classification,^{11,14 – 17} mathematical operations,⁷ and matrix operations.^{18 – 25}

In this paper, we provide a detailed insight on InGaAs/InAlAs separate absorption, grading, charge, and multiplication avalanche photodiodes (SAGCM APDs) and a theoretical model of APDs is built. Through theoretical analysis and two-dimensional (2D) simulation, the influence of charge layer and tunneling effect on the APDs is fully understood. The design of charge layer (including doping level and thickness) can be calculated by our predictive model for different multiplication thickness. We find that as the thickness of charge layer increases, the suitable doping level range in charge layer decreases. Compared to thinner charge layer, performance of APD varies significantly via several percent deviations of doping concentrations in thicker charge layer. Moreover, the generation rate (G btt ) of band-to-band tunnel is calculated, and the influence of tunneling effect on avalanche field was analyzed. We confirm that avalanche field and multiplication factor (M n ) in multiplication will decrease by the tunneling effect. The theoretical model and analysis are based on InGaAs/InAlAs APD; however, they are applicable to other APD material systems as well.

The unidirectional light transmission characteristics of a two-dimensional square-lattice photonic crystal heterostructure consisting of rectangular metal rods and air holes immersed in silicon are studied by the finite-difference time-domain method. Compared with all-optical photonic crystal diodes based on the directional bandgap mismatch, this kind of diode can be designed to confine the light wave to travel along a certain direction owing to self-collimation behavior. The working frequencies of this diode are within the photonic crystal's passband, so a higher light transmittance can be obtained. This wideband high-contrast diode has the advantages of combination with other functional devices in the complex integrated optical circuits.

The sensitivities of the octagonal quasi-periodic photonic crystal (QPC) defective modes are theoretically studied. The octagonal QPC biosensors are composed of silicon columns arranged in a liquid background. By designing a defect structure, a variety of localized modes with different spatial symmetries and field profiles are obtained, and a maximum refractive index sensitivity 800 nm/RIU is achieved around 1500 nm transmission peak when the central rod’s size equals 100 nm, and the corresponding detection limit reaches 0.00042. The liquid can flow freely among the rods through the entire structure, so it is convenient to monitor the concentration of protein in the liquid environment dynamically. The influence of the protein’s thickness to the shift of the resonant wavelength is also studied, where a minimum protein’s thickness of less than 10 nm can be detected by optimizing the central column’s size to be 400 nm, and the spatial field profiles of different resonant modes are analyzed to explain the corresponding sensitivities.