Photonics

Research

14 pages, 2993 KiB

Open AccessArticle

Tunable Near-Infrared Transparent Bands Based on Cascaded Fabry–Perot Cavities Containing Phase Change Materials

by Yuchun She, Kaichan Zhong, Manni Tu, Shuyuan Xiao, Zhanxu Chen, Yuehua An, Dejun Liu and Feng Wu

Photonics 2024, 11(6), 497; https://doi.org/10.3390/photonics11060497 - 24 May 2024

Viewed by 811

Abstract

In this paper, we construct a near-infrared Fabry–Perot cavity composed of two sodium (Na) layers and an antimony trisulfide (Sb₂S₃) layer. By cascading two Fabry–Perot cavities, the transmittance peak splits into two transmittance peaks due to the coupling between [...] Read more.

In this paper, we construct a near-infrared Fabry–Perot cavity composed of two sodium (Na) layers and an antimony trisulfide (Sb₂S₃) layer. By cascading two Fabry–Perot cavities, the transmittance peak splits into two transmittance peaks due to the coupling between two Fabry–Perot modes. We utilize a coupled oscillator model to describe the mode coupling and obtain a Rabi splitting of 60.0 meV. By cascading four Fabry–Perot cavities, the transmittance peak splits into four transmittance peaks, leading to a near-infrared transparent band. The near-infrared transparent band can be flexibly tuned by the crystalline fraction of the Sb₂S₃ layers. In addition, the effects of the layer thickness and incident angle on the near-infrared transparent band and the mode coupling are investigated. As the thickness of the Na layer increases, the coupling strength between the Fabry–Perot modes becomes weaker, leading to a narrower transparent band. As the thickness of the Sb₂S₃ layer increases, the round-trip propagating of the Sb₂S₃ layer increases, leading to the redshift of the transparent band. As the incident angle increases, the round-trip propagating of the Sb₂S₃ layer decreases, leading to the blueshift of the transparent band. This work not only provides a viable route to achieving tunable near-infrared transparent bands, but also possesses potential applications in high-performance display, filtering, and sensing. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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12 pages, 4886 KiB

Open AccessArticle

Design of a High-Gain and Tri-Band Terahertz Microstrip Antenna Using a Polyimide Rectangular Dielectric Column Photonic Band Gap Substrate

by Gaofang Li, Chenguang Huang, Renjie Huang, Bo Tang, Jingguo Huang, Jie Tan, Nenghong Xia and Haoyang Cui

Photonics 2024, 11(4), 307; https://doi.org/10.3390/photonics11040307 - 27 Mar 2024

Cited by 2 | Viewed by 1251

Abstract

A high-gain and tri-band terahertz microstrip antenna with a photonic band gap (PBG) substrate is presented in this paper for terahertz communications. Polyimide dielectric columns are inserted into the silicon substrate to form the PBG substrate to improve the gain of the antenna. [...] Read more.

A high-gain and tri-band terahertz microstrip antenna with a photonic band gap (PBG) substrate is presented in this paper for terahertz communications. Polyimide dielectric columns are inserted into the silicon substrate to form the PBG substrate to improve the gain of the antenna. The PBG substrate and polyimide substrate constituted a multilayer substrate structure and enabled the multi-band operation of the antenna. The PBG substrate antenna achieves gains of 6.28 dB, 4.84 dB, and 7.66 dB at resonant frequencies of 0.360 THz, 0.580 THz, and 0.692 THz, respectively, outperforming the homogeneous substrate THz microstrip antenna (H antenna) by 1.18 dB, 1.74 dB, and 1.82 dB, respectively. The radiation efficiencies at three operating bands are over 93%, 92%, and 88%, respectively, which are slightly higher than that of the H antenna and greater than that of the standard multi-band antenna. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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12 pages, 3049 KiB

Open AccessArticle

Effects of Plasmonic Au Nanoparticles on the Optical Nonlinearity of InAs/GaAs Quantum Dot Semiconductor Saturable Absorber Mirrors

by Hongpei Wang, Hao Dai, Menglu Lyu, Cheng Jiang, Shulong Lu and Ziyang Zhang

Photonics 2024, 11(3), 235; https://doi.org/10.3390/photonics11030235 - 5 Mar 2024

Viewed by 1384

Abstract

Au nanoparticles (NPs) were designed to be embedded into III-V semiconductors to form Au/GaAs Schottky heterostructures, which were used as top-modified cover layers for quantum dot semiconductor saturable absorption mirrors (QD-SESAMs). By harnessing the distinctive localized surface plasmon resonance (LSPR) effect exhibited by [...] Read more.

Au nanoparticles (NPs) were designed to be embedded into III-V semiconductors to form Au/GaAs Schottky heterostructures, which were used as top-modified cover layers for quantum dot semiconductor saturable absorption mirrors (QD-SESAMs). By harnessing the distinctive localized surface plasmon resonance (LSPR) effect exhibited by Au NPs, a remarkable enhancement in photogenerated carrier concentration is achieved at the heterojunction interface. Consequently, this leads to a significant improvement in the nonlinear optical characteristics of the device. The modulation depth (MD) and saturation fluence of the device are optimized from the initial 2.2% and 16.1 MW/cm² to 2.8% and 8.3 MW/cm², respectively. Based on the optimized device, a Q-switched laser has been developed with an impressive output power of 17.61 mW and a single pulse energy of 274.9 nJ. These results unequivocally showcase the exceptional advantages offered by utilizing Au NPs to optimize the nonlinear optical characteristics of III-V semiconductor devices, thereby highlighting its immense potential for practical applications in various fields. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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13 pages, 11259 KiB

Open AccessArticle

Modulation of the Multiple Bound States in the Continuum of the All-Dielectric Metasurface

by Suxia Xie, Jingcheng Yang, Guang Tian, Weiwei Shen and Chongjun Bai

Photonics 2023, 10(4), 418; https://doi.org/10.3390/photonics10040418 - 7 Apr 2023

Cited by 2 | Viewed by 2232

Abstract

Based on the ideas of modulation of multiple BICs, ultrahigh Q-factor resonance has been realized by array of planar metasurfaces with H-shaped nanoholes, perforated on a Si₃N₄ photonic crystal slab surrounded by a silica medium. Multiple BICs of both at [...] Read more.

Based on the ideas of modulation of multiple BICs, ultrahigh Q-factor resonance has been realized by array of planar metasurfaces with H-shaped nanoholes, perforated on a Si₃N₄ photonic crystal slab surrounded by a silica medium. Multiple BICs of both at Γ BICs and off Γ BICs are obtained. Two BICs at the Γ point show up in the lower band of the visible light, and they can be tuned by the center position and hole size of each part of the H-shaped, the refractive index of the surrounding medium, and the lattice constant. In detail, they move apart from each other or shift together with a fixed distance, with the structure parameters changing. On the other hand, the off Γ BICs behave only in the form of monotonously shifting. The at Γ BICs transform from BICs to quasi-BICs obviously with the broken symmetry of the H-shaped nanohole; however, its influence on off Γ BICs is insignificant. BICs in both types are ultra-sensitive to the surrounding medium, and the Q-factor of the BICs reaches a value more than 10⁶. The results here are helpful in the design of photonic filters and sensors. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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8 pages, 1633 KiB

Open AccessCommunication

Broadband Second Harmonic Generation in a z-Cut Lithium Niobate on Insulator Waveguide Based on Type-I Modal Phase Matching

by Changwen Wang, Haozong Zhong, Minghao Ning, Bin Fang, Lin Li and Ya Cheng

Photonics 2023, 10(1), 80; https://doi.org/10.3390/photonics10010080 - 10 Jan 2023

Cited by 10 | Viewed by 3191

Abstract

We numerically investigate a second harmonic generation (SHG) in a z-cut lithium niobate on insulator (LNOI) waveguide based on type-I mode phase matching (MPM) between two fundamental modes. A mode overlap factor that is close to unity is achieved and the normalized SHG [...] Read more.

We numerically investigate a second harmonic generation (SHG) in a z-cut lithium niobate on insulator (LNOI) waveguide based on type-I mode phase matching (MPM) between two fundamental modes. A mode overlap factor that is close to unity is achieved and the normalized SHG efficiency reaches up to 72.1% W⁻¹cm⁻² at the telecommunication band, together with a large spectral tunability of 2.5 nm/K. Moreover, a bandwidth of about 100 nm for the broad SHG in a 5 mm-long LNOI ridge waveguide is demonstrated with this scheme. This stratagem will inspire new integrated nonlinear frequency conversion methods for versatile applications. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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9 pages, 2782 KiB

Open AccessCommunication

Near-Perfect Narrow-Band Tunable Graphene Absorber with a Dual-Layer Asymmetric Meta-Grating

by Junfang Liang, Jinhua Hu, Xiuhong Liu and Jijun Zhao

Photonics 2023, 10(1), 14; https://doi.org/10.3390/photonics10010014 - 23 Dec 2022

Cited by 5 | Viewed by 1795

Abstract

A near-perfect narrow-band graphene-based absorber was fabricated using a resonant system integrated with an asymmetric meta-grating at a wavelength of 1550 nm. By optimizing the gap between the two grating strips, the absorption of monolayer graphene can be increased to 99.6% owing to [...] Read more.

A near-perfect narrow-band graphene-based absorber was fabricated using a resonant system integrated with an asymmetric meta-grating at a wavelength of 1550 nm. By optimizing the gap between the two grating strips, the absorption of monolayer graphene can be increased to 99.6% owing to the strong field confinement of the bottom zero-contrast grating (ZCG). The position of the absorption spectrum could be adjusted by tailoring the grating period or the thickness of the waveguide layer. Interestingly, absorption spectrum linewidth can be tailored by changing the thickness of the spacer layer. The accidental bound states in the continuum (BICs) are then demonstrated in the structure. Moreover, the designed structure realizes the dynamic adjustment of the absorption efficiency at a specific wavelength, which has excellent potential in integrated optical devices and systems. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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17 pages, 45276 KiB

Open AccessArticle

Investigation of Optical-Switching Mechanism Using Guided Mode Resonances

by Atiq Ur Rehman, Yousuf Khan, Muhammad Irfan and Muhammad A. Butt

Photonics 2023, 10(1), 13; https://doi.org/10.3390/photonics10010013 - 23 Dec 2022

Cited by 4 | Viewed by 2216

Abstract

Recently, photonic crystals have paved the way to control photonic signals. Therefore, this research numerically investigated the design of the optical switch using the guided-mode resonances in photonic crystals operating in a communication window around 1.55 μm. The design of the device is [...] Read more.

Recently, photonic crystals have paved the way to control photonic signals. Therefore, this research numerically investigated the design of the optical switch using the guided-mode resonances in photonic crystals operating in a communication window around 1.55 μm. The design of the device is based on a dielectric slab waveguide to make it compatible with optical waveguides in photonic circuits. Moreover, two signals are used and are termed as the data signal and control signal. The data signal is coupled into the optical waveguide using an out-of-the-plane vertical coupling mechanism, whereas the control signal is index-guided into the optical waveguide to amplify the data signal. The switching parameters of the optical switch are adjusted by changing the number of the photonic crystal periods and implementing a varying radius PhC-cavity within the middle of the PhC-lattice, where the optical characteristics in terms of resonant wavelength, reflection peaks, linewidth, and quality factor of the data signal can be adjusted. The numerical simulations are carried out in open-source finite difference time domain-based software. Congruently, 7% optical amplification is achieved in the data signal with a wavelength shift of 0.011 μm and a quality factor of 12.64. The amplification of the data signal can be utilized to implement an optical switching mechanism. The device is easy to implement and has great potential to be used in programmable photonics and optical integrated circuits. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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10 pages, 2184 KiB

Open AccessCommunication

Investigation of InGaN-Based Green Micro-Photonic-Crystal- Light-Emitting-Diodes with Bottom, Nanoporous, Distributed Bragg Reflectors

by Kuo-Bin Hong, Wei-Ta Huang, Wen-Cheng Hsu, Chang-Ching Tu and Hao-Chung Kuo

Photonics 2022, 9(12), 939; https://doi.org/10.3390/photonics9120939 - 5 Dec 2022

Cited by 4 | Viewed by 2162

Abstract

In this work, an InGaN-based, green micro-photonic crystal-light-emitting-diode (µ-PCLED), which incorporates a nanoporous, GaN-distributed Bragg reflector (DBR) to form a Fabry–Perot (FP) cavity, was fabricated and characterized. Simulations for the µ-PCLED’s optical features were systematically performed and analyzed. Numerical results revealed that the [...] Read more.

In this work, an InGaN-based, green micro-photonic crystal-light-emitting-diode (µ-PCLED), which incorporates a nanoporous, GaN-distributed Bragg reflector (DBR) to form a Fabry–Perot (FP) cavity, was fabricated and characterized. Simulations for the µ-PCLED’s optical features were systematically performed and analyzed. Numerical results revealed that the p-GaN photonic crystal (PC) with a filling factor of 0.3 is beneficial for improving the coupling constants of the first- and second-order Bragg diffractions. In addition, based on the product of quantum well (QW) and PC confinement factors, four to six pairs of InGaN QWs should be the preferable design. In order to achieve single-wavelength emission and small full-width at half-maximum (FWHM), the thickness of the n-GaN layer was controlled to be thinner than 920 nm, leading to more than 20 nm wavelength separation between two adjacent FP modes. Experimentally, the fabricated InGaN-based µ-PCLED with a mesa diameter of 30 µm can emit 545 nm green light with FWHM of about 10 nm and negligible blue-shift of about 3 nm in spontaneous emission under the injection current of 1 to 10 mA. Our simulation and experimental results demonstrate that the p-GaN PC design can effectively resolve the wavelength instability issue. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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8 pages, 1349 KiB

Open AccessCommunication

Dual Optical and Acoustic Negative Refraction in Phoxonic Crystals

by Shuyi Zhao, Linlin Lei, Qin Tang, Feng Xin and Tianbao Yu

Photonics 2022, 9(12), 908; https://doi.org/10.3390/photonics9120908 - 28 Nov 2022

Cited by 1 | Viewed by 1506

Abstract

We report dual optical and acoustic negative refraction based on a defect-free phoxonic crystal within a triangular lattice. The phoxonic negative refraction is achieved based on abnormal dispersion effect, by intentionally creating convex equal-frequency contours for both photonic and phononic modes. As a [...] Read more.

We report dual optical and acoustic negative refraction based on a defect-free phoxonic crystal within a triangular lattice. The phoxonic negative refraction is achieved based on abnormal dispersion effect, by intentionally creating convex equal-frequency contours for both photonic and phononic modes. As a potential application, negative refraction imaging for both photonic and phononic modes is also achieved. Numerical simulations based on the finite element method demonstrate the coexistence of negative refraction and the resultant imaging for electromagnetic and acoustic waves. Compared with the defect-based bandgap effects that need low fault tolerance, phoxonic negative refraction relying on passbands has considerable advantages in realizing controllable propagation of waves. The new scheme for the simultaneous control of electromagnetic and acoustic waves provides a potential platform for designing novel phoxonic devices. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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9 pages, 4011 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Ultra-Wideband Polarization Insensitive Angle Filter Based on ENZ Characteristics and Dynamic Antireflection Structures

by Baofei Wan, Haining Ye and Haifeng Zhang

Photonics 2022, 9(11), 854; https://doi.org/10.3390/photonics9110854 - 12 Nov 2022

Cited by 4 | Viewed by 1956

Abstract

Bandwidth expansion has always been an important dimension in investigating angle filters (AFs) and is critical for optical communication and radar detection. In this paper, the AF with strong selectivity is realized by using the epsilon-near-zero (ENZ) jump characteristic of YaBa₂Cu [...] Read more.

Bandwidth expansion has always been an important dimension in investigating angle filters (AFs) and is critical for optical communication and radar detection. In this paper, the AF with strong selectivity is realized by using the epsilon-near-zero (ENZ) jump characteristic of YaBa₂Cu₃O₇ material. At the same time, for both the TE and the TM waves in the range of 237~1000 THz, the transmissivity of the AF is stronger than 0.9 by using dynamic antireflection structures (AFSs). The transfer matrix method is suitable for theoretical calculation, and the impedance matching theory is introduced to analyze the features of the AF. The increment of the thickness of superconductor material can effectively enhance the selectivity of the AF structure, and the consequence is the attenuation of transmission performances. If the temperature is covered from 0 K to 85 K, the filtering performance higher than 0.9 can still be maintained for two polarization waves. For these explicit performances, the proposed design may provide a new idea for widening the frequency bandwidth of the AF. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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9 pages, 6768 KiB

Open AccessCommunication

Nanoparticle Shape Optimization for Tamm-Plasmon-Polariton-Based Organic Solar Cells in the Visible Spectral Range

by Rashid G. Bikbaev, Stepan Ya. Vetrov, Ivan V. Timofeev and Vasily F. Shabanov

Photonics 2022, 9(11), 786; https://doi.org/10.3390/photonics9110786 - 23 Oct 2022

Cited by 3 | Viewed by 1723

Abstract

The effect of the shape of the nanoparticles and the polarization of incident light on the surface current density and the efficiency of an organic solar cell based on the Tamm plasmon polariton is investigated. In the cases of both elongated and flattened [...] Read more.

The effect of the shape of the nanoparticles and the polarization of incident light on the surface current density and the efficiency of an organic solar cell based on the Tamm plasmon polariton is investigated. In the cases of both elongated and flattened nanoparticles, it is shown that the efficiency of such a solar cell is increased when the electric field vector is parallel to the largest axis of the spheroid. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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16 pages, 7500 KiB

Open AccessArticle

A Novel Design of Optical Switch Based on Guided Mode Resonances in Dielectric Photonic Crystal Structures

by Atiq Ur Rehman, Yousuf Khan, Muhammad Irfan, Muhammad A. Butt, Svetlana N. Khonina and Nikolay L. Kazanskiy

Photonics 2022, 9(8), 580; https://doi.org/10.3390/photonics9080580 - 17 Aug 2022

Cited by 8 | Viewed by 2843

Abstract

In this work, a novel idea of optical switch design based on guided mode resonance in the photonic crystal structure is numerically investigated. The designed switching device work on the principle of optical amplification and wavelength shift of data signal with the help [...] Read more.

In this work, a novel idea of optical switch design based on guided mode resonance in the photonic crystal structure is numerically investigated. The designed switching device work on the principle of optical amplification and wavelength shift of data signal with the help of a control signal. The data signal can be coupled into the waveguide using guided-mode resonance, whereas, a control signal is index-coupled into the waveguide to influence the data signal. The optical switching action is optimized by introducing a photonic crystal cavity and varying the number of photonic crystal elements, where the resonant wavelength, reflection peaks, linewidth, and quality factor of the data signal can be adjusted. The device is based on low refractive index contrast dielectric materials compatible with fiber optic communication and can operate in a near-infrared range of around 1.55 μm. The numerical simulations are carried out in an open source finite-difference time-domain-based software. An optical switching action is achieved with 7% amplification in the data signal at a central wavelength of 1.55 µm with a maximum shift of the wavelength of 0.001 µm. The proposed device can be easily implemented in cascade designs of programmable photonic and optical switching circuits. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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13 pages, 1885 KiB

Open AccessArticle

One-Dimensional Photonic Crystals with Different Termination Layer Thicknesses and Very Narrow Bloch Surface Wave and Guided Wave Based Resonances for Sensing Applications

by Tomas Fort, Roman Kanok, Petr Hlubina, Pavel Pokorny and Jaroslav Sobota

Photonics 2022, 9(8), 561; https://doi.org/10.3390/photonics9080561 - 10 Aug 2022

Cited by 8 | Viewed by 1853

Abstract

We demonstrate an efficient sensing of both gaseous and aqueous analytes utilizing Bloch surface waves (BSWs) and guided waves (GWs) excited on a truncated one-dimensional photonic crystal (1DPhC) composed of six TiO

_{2}

/SiO

_{2}

bilayers with a termination layer of TiO

_{2}

[...] Read more.

We demonstrate an efficient sensing of both gaseous and aqueous analytes utilizing Bloch surface waves (BSWs) and guided waves (GWs) excited on a truncated one-dimensional photonic crystal (1DPhC) composed of six TiO

_{2}

/SiO

_{2}

bilayers with a termination layer of TiO

_{2}

. For the gaseous analytes, we show that 1DPhC can support the GW excited by an s-polarized wave and the theoretical shift of the resonance wavelength is linear for small changes in the analyte refractive index (RI), giving a constant RI sensitivity of 87 nm per RI unit (RIU). In addition, for the aqueous analytes, the GW excited by s-polarized and BSW by p-polarized waves can be resolved and exploited for sensing applications. We compare two designed and realized 1DPhCs with termination layer thicknesses of 60 nm and 50 nm, respectively, and show experimentally the differences in their very narrow reflectance and phase responses. An RI sensitivity and figure of merit as high as 544.3 nm/RIU and 303 RIU

^{- 1}

, respectively, are obtained for the smaller thickness when both s- and p-polarized BSWs are excited. This is the first demonstration of both very deep BSW-based resonances in two orthogonal polarizations and a very narrow resonance in one of them. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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10 pages, 1716 KiB

Open AccessArticle

Photonic Bandgaps of One-Dimensional Photonic Crystals Containing Anisotropic Chiral Metamaterials

by Qian Wei, Jiaju Wu, Zhiwei Guo, Xiaotian Xu, Ke Xu, Yong Sun, Yunhui Li, Haitao Jiang and Hong Chen

Photonics 2022, 9(6), 411; https://doi.org/10.3390/photonics9060411 - 10 Jun 2022

Cited by 2 | Viewed by 2403

Abstract

Conventional photonic bandgaps (PBGs) for linear polarization waves strongly depend on the incident angle. Usually, PBGs will shift toward short wavelengths (i.e., blue-shifted gaps) as the incident angle increases, which limits their applications. In some practices, the manipulation of PBGs for circular polarization [...] Read more.

Conventional photonic bandgaps (PBGs) for linear polarization waves strongly depend on the incident angle. Usually, PBGs will shift toward short wavelengths (i.e., blue-shifted gaps) as the incident angle increases, which limits their applications. In some practices, the manipulation of PBGs for circular polarization waves is also important. Here, the manipulation of PBGs for circular polarization waves is theoretically investigated. We propose one-dimensional photonic crystals (1DPCs) containing anisotropic chiral metamaterials which exhibit hyperbolic dispersion for left circular polarization (LCP) wave and elliptical dispersion for right circular polarization (RCP) wave. Based on the phase variation compensation effect between anisotropic chiral metamaterials and dielectrics, we can design arbitrary PBGs including zero-shifted and red-shifted PBGs for LCP wave. However, the PBGs remain blue-shifted for RCP wave. Therefore, we can design a high-efficiency wide-angle polarization selector based on the chiral PBGs. Our work extends the manipulation of PBGs for circular polarization waves, which has a broad range of potential applications, including omnidirectional reflection, splitting wave and enhancing photonic spin Hall effect. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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10 pages, 4085 KiB

Open AccessCommunication

Laser Diffraction Zones and Spots from Three-Dimensional Graded Photonic Super-Crystals and Moiré Photonic Crystals

by Noah Hurley, Steve Kamau, Khadijah Alnasser, Usha Philipose, Jingbiao Cui and Yuankun Lin

Photonics 2022, 9(6), 395; https://doi.org/10.3390/photonics9060395 - 3 Jun 2022

Cited by 4 | Viewed by 2915

Abstract

The laser diffraction from periodic structures typically shows isolated and sharp point patterns at zeroth and ±nth orders. Diffraction from 2D graded photonic super-crystals (GPSCs) has demonstrated over 1000 spots due to the fractional diffractions. Here, we report the holographic fabrication of three [...] Read more.

The laser diffraction from periodic structures typically shows isolated and sharp point patterns at zeroth and ±nth orders. Diffraction from 2D graded photonic super-crystals (GPSCs) has demonstrated over 1000 spots due to the fractional diffractions. Here, we report the holographic fabrication of three types of 3D GPSCs through nine beam interferences and their characteristic diffraction patterns. The diffraction spots due to the fractional orders are merged into large-area diffraction zones for these three types of GPSCs. Three distinguishable diffraction patterns have been observed: (a) 3 × 3 Diffraction zones for GPSCs with a weak gradient in unit super-cell, (b) 5 × 5 non-uniform diffraction zones for GPSCs with a strong modulation in long period and a strong gradient in unit super-cell, (c) more than 5 × 5 uniform diffraction zones for GPSCs with a medium gradient in unit super-cell and a medium modulation in long period. The GPSCs with a strong modulation appear as moiré photonic crystals. The diffraction zone pattern not only demonstrates a characterization method for the fabricated 3D GPSCs, but also proves their unique optical properties of the coupling of light from zones with 360° azimuthal angles and broad zenith angles. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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10 pages, 6609 KiB

Open AccessCommunication

High-Efficiency Grating Couplers for Pixel-Level Flat-Top Beam Generation

by Zhong-Tao Tian, Ze-Peng Zhuang, Zhi-Bin Fan, Xiao-Dong Chen and Jian-Wen Dong

Photonics 2022, 9(4), 207; https://doi.org/10.3390/photonics9040207 - 22 Mar 2022

Cited by 4 | Viewed by 4219

Abstract

We demonstrate a kind of grating coupler that generates a high quality flat-top beam with a small beamwidth from photonic integrated circuits into free-space. The grating coupler is designed on a silicon-on-insulator wafer with a 220-nm-thick silicon layer and consists of a dual-etch [...] Read more.

We demonstrate a kind of grating coupler that generates a high quality flat-top beam with a small beamwidth from photonic integrated circuits into free-space. The grating coupler is designed on a silicon-on-insulator wafer with a 220-nm-thick silicon layer and consists of a dual-etch grating (DG) and a distributed Bragg reflector (DBR). By adjusting the structural parameters of DG and DBR, a pixel-level (6.6 µm) flat-top beam with a vertical radiation of −0.5 dB and a mode match of 97% at 1550 nm is realized. Furthermore, a series of high-efficiency grating couplers are designed to create a flat-top beam with different scales. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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13 pages, 3336 KiB

Open AccessArticle

Wide-Angle Absorption Based on Angle-Insensitive Light Slowing Effect in Photonic Crystal Containing Hyperbolic Metamaterials

by Feng Wu, Xiaoqing Li, Xiufeng Fan, Ling Lin, Sofyan A. Taya and Abinash Panda

Photonics 2022, 9(3), 181; https://doi.org/10.3390/photonics9030181 - 12 Mar 2022

Cited by 1 | Viewed by 2351

Abstract

Light-slowing effect at band edges in photonic crystals (PCs) is widely utilized to enhance optical absorption. However, according to the Bragg scattering theory, photonic bandgaps (PBGs) in traditional all-dielectric one-dimensional (1-D) PCs shift towards shorter wavelengths as the incident angle increases. Therefore, light-slowing [...] Read more.

Light-slowing effect at band edges in photonic crystals (PCs) is widely utilized to enhance optical absorption. However, according to the Bragg scattering theory, photonic bandgaps (PBGs) in traditional all-dielectric one-dimensional (1-D) PCs shift towards shorter wavelengths as the incident angle increases. Therefore, light-slowing effect in traditional all-dielectric 1-D PCs is also angle-sensitive. Such angle-sensitive property of light-slowing effect in traditional all-dielectric 1-D PCs poses a great challenge to achieve wide-angle absorption. In this paper, we design an angle-insensitive PBG in a 1-D PC containing hyperbolic metamaterials based on the phase-variation compensation theory. Assisted by the angle-insensitive light-slowing effect at the angle-insensitive band edge, we achieve wide-angle absorption at near-infrared wavelengths. The absorptance keeps higher than 0.9 in a wide angle range from 0 to 45.5 degrees. Besides, the wide-angle absorption is robust when the phase-variation compensation condition is slightly broken. Our work not only provides a viable route to realize angle-insensitive light slowing and wide-angle light absorption, but also promotes the development of light-slowing- and absorption-based optical/optoelectronic devices. Full article

(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)

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