Photonics

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13 pages, 3840 KiB

Open AccessArticle

Novel Plasmonic Metamaterials Based on Metal Nano-Hemispheres and Metal-Dielectric Composites

by Rei Niguma, Tetsuya Matsuyama, Kenji Wada and Koichi Okamoto

Photonics 2024, 11(4), 356; https://doi.org/10.3390/photonics11040356 - 12 Apr 2024

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We introduce a groundbreaking plasmonic metamaterial, the Nano-Hemisphere on Hyperbolic Metamaterial (NHoHMM), which involves the fabrication of Ag nano-hemispheres on a multilayered Ag/SiO₂ structure, achieved solely through sputtering and heat treatment. Finite Difference Time Domain (FDTD) simulations unveil the intriguing slow propagation [...] Read more.

We introduce a groundbreaking plasmonic metamaterial, the Nano-Hemisphere on Hyperbolic Metamaterial (NHoHMM), which involves the fabrication of Ag nano-hemispheres on a multilayered Ag/SiO₂ structure, achieved solely through sputtering and heat treatment. Finite Difference Time Domain (FDTD) simulations unveil the intriguing slow propagation of the localized electric field, where light travels at only 1/40th of its usual speed within this structure. These simulations reveal distinctive sharp absorption peaks in the visible spectrum, attributed to surface plasmon resonance. In practical experiments, the NHoHMM structure, characterized by random Ag nano-hemispheres, exhibits broad absorption peaks spanning the visible range, rendering it a versatile broadband optical absorber. For comparison, the optical properties of the Ag nano-hemispheres on a nanocermet (NHoNC) structure were analyzed through simultaneous sputtering of Ag and SiO₂ followed by heat treatment. Simulations employing effective medium theory and the transfer matrix method demonstrate variable optical properties dependent on the Ag filling ratio in the nanocermet structure. The results obtained differ from the spectra of the NHoHMM structure; thus, it is concluded that in the NHoHMM structure, the calculated multi-peaks are broadened due to the inhomogeneity of the nano-hemispherical structure’s size, rather than the metal/dielectric multilayer structure being altered by the heat treatment. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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9 pages, 2002 KiB

Open AccessArticle

Submilliwatt Silicon Nitride Thermo-Optic Modulator Operating at 532 nm

by Zhaoyang Wu, Shuqing Lin, Siyuan Yu and Yanfeng Zhang

Photonics 2024, 11(3), 213; https://doi.org/10.3390/photonics11030213 - 27 Feb 2024

Viewed by 843

Abstract

Optical phase control is essential for optical beam steering applications. The silicon nitride thermo-optic modulator generally suffers from high electrical power consumption. Microresonator and multipass structures could reduce the electrical power consumption of silicon nitride thermo-optic modulators, with the drawback of a narrow [...] Read more.

Optical phase control is essential for optical beam steering applications. The silicon nitride thermo-optic modulator generally suffers from high electrical power consumption. Microresonator and multipass structures could reduce the electrical power consumption of silicon nitride thermo-optic modulators, with the drawback of a narrow operating bandwidth and high insertion loss. We demonstrate a single-pass silicon nitride thermo-optic phase modulator at 532 nm with low insertion loss and low power consumption, achieving a π phase shift power consumption down to 0.63 mW in a Mach–Zehnder switch. The rise and fall time are around 1.07 ms and 0.67 ms, respectively. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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11 pages, 2799 KiB

Open AccessArticle

X-Cut Lithium Niobate Optical Waveguide with High-Index Contrast and Low Loss Fabricated by Vapor Proton Exchange

by Shicheng Rong, Xujie Wen, Ning Ding, Jia Liao and Pingrang Hua

Photonics 2023, 10(12), 1390; https://doi.org/10.3390/photonics10121390 - 18 Dec 2023

Viewed by 995

Abstract

Highly integrated and stable devices are appealing in optical communication and sensing. This appeal arises from the presence of high refractive index contrast and high-quality waveguides. In this study, we improved the vapor proton exchange (VPE) process, enabling large-scale waveguide fabrication and addressing [...] Read more.

Highly integrated and stable devices are appealing in optical communication and sensing. This appeal arises from the presence of high refractive index contrast and high-quality waveguides. In this study, we improved the vapor proton exchange (VPE) process, enabling large-scale waveguide fabrication and addressing the issue of liquid exchange during cooling. Additionally, we have prepared and characterized planar waveguides on X-cut lithium niobate (LN) crystals. The exchanged samples exhibit α and k1 phases, refractive index contrasts as high as 0.082, and exceptional refractive index uniformity. Furthermore, we utilized the same process to fabricate channel waveguides and Y-branch waveguides. We achieved low propagation losses in channel waveguides, accompanied by small mode sizes, and low-loss Y-branch waveguides with a highly uniform beam splitting ratio. All waveguides exhibited consistent performance across multiple preparations and tests, remaining free from aging effects for three months. Our results underscore the promising potential of VPE for creating Y-branch splitters and modulators in LN crystals. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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13 pages, 5859 KiB

Open AccessArticle

The Amplification and Polarization Control of Transmitted Radiation by a Graphene-Containing Photonic Cell

by Svetlana V. Eliseeva, Pavel A. Itrin and Dmitrij I. Sementsov

Photonics 2023, 10(12), 1318; https://doi.org/10.3390/photonics10121318 - 29 Nov 2023

Viewed by 734

Abstract

The transformation of the transmission spectra of linearly polarized radiation passing through a symmetric photonic cell is studied based on numerical analysis. The cell consists of two layers of magnetic semiconductor with a graphene monolayer on each and a central dielectric layer located [...] Read more.

The transformation of the transmission spectra of linearly polarized radiation passing through a symmetric photonic cell is studied based on numerical analysis. The cell consists of two layers of magnetic semiconductor with a graphene monolayer on each and a central dielectric layer located between the graphene monolayers. It is possible to achieve amplification in the near terahertz range in graphene layers due to charge carrier drift. Control of transmission spectra and polarization of transmitted radiation can be achieved by changing the Fermi energy of graphene layers, by changing the external magnetic field, and by changing the thickness of the dielectric layer and the orientation of the incident radiation polarization plane. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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12 pages, 2364 KiB

Open AccessCommunication

Room–Temperature Terahertz Detector Based on Monolayer Graphene Integrated with an Asymmetric Bowtie Antenna

by Zicheng Guo, Chaojun Ma, Hai Ou, Ximiao Wang, Shaojing Liu, Huanjun Chen, Shaoyong Zheng and Shaozhi Deng

Photonics 2023, 10(5), 576; https://doi.org/10.3390/photonics10050576 - 15 May 2023

Cited by 1 | Viewed by 1522

Abstract

Terahertz (THz) technology has great potential for applications in various fields, such as security imaging detection, optical communication, environmental quality monitoring, and life sciences. Most of these applications require THz detectors with high sensitivity, fast response, and a miniaturized size that can operate [...] Read more.

Terahertz (THz) technology has great potential for applications in various fields, such as security imaging detection, optical communication, environmental quality monitoring, and life sciences. Most of these applications require THz detectors with high sensitivity, fast response, and a miniaturized size that can operate at room temperature. In this study, we present a graphene THz detector integrated with an asymmetric bowtie antenna. The asymmetric antenna confines the incident THz waves into the graphene active layer, leading to photocurrent generation and its directional flow. The maximum responsivity of this device can reach 19.6 V/W at 2.52 THz, with a noise–equivalent power (NEP) of 0.59 nW /Hz^0.5. Additionally, the response time is less than 21 μs, with an active area of less than 1500 μm². Such a small device enables THz imaging with a spatial resolution as small as 200 μm. These results provide a feasible way to design miniaturized and integrable two–dimensional material–based THz detectors. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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12 pages, 2185 KiB

Open AccessArticle

Multiplexing Linear and Nonlinear Bragg Diffractions through Volume Gratings Fabricated by Femtosecond Laser Writing in Lithium Niobate Crystal

by Pailin Lai, Chun Chang, Xinyu Liu and Dunzhao Wei

Photonics 2023, 10(5), 562; https://doi.org/10.3390/photonics10050562 - 11 May 2023

Cited by 1 | Viewed by 1238

Abstract

The femtosecond-laser-writing technique provides a flexible method for fabrication of nonlinear photonic crystals in three dimensions, providing structures that enable efficient complex nonlinear wave interactions and modulation for applications including nonlinear holography, nonlinear beam shaping, and waveguide-integrated wavelength conversion. However, the tightly focused [...] Read more.

The femtosecond-laser-writing technique provides a flexible method for fabrication of nonlinear photonic crystals in three dimensions, providing structures that enable efficient complex nonlinear wave interactions and modulation for applications including nonlinear holography, nonlinear beam shaping, and waveguide-integrated wavelength conversion. However, the tightly focused laser pulse inevitably causes structural modification and then changes the local refractive index, resulting in additional linear modulation of the interacting waves. Here, we use the same periodic distributions of the refractive index and the second-order nonlinear coefficient for grating arrays engineered in lithium niobate crystals by femtosecond laser writing to achieve polarization-dependent linear and nonlinear Bragg diffractions simultaneously. The experimental results show that the linear and nonlinear diffraction efficiencies range up to 31% and 2.9 × 10⁻⁵, respectively, for grating arrays with dimensions of 100 μm (x) × 100 μm (y) × 100 μm (z). This work paves the way toward the realization of the multiplexing of linear and nonlinear optical modulations in a single structure for potential applications that include multidimensional optical data storage and optical coding. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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7 pages, 1772 KiB

Open AccessCommunication

High-Efficiency Integrated Color Routers by Simple Identical Nanostructures for Visible and Near-Infrared Wavelengths

by Rongxuan Zhong, Xiayuan Xu, Yongle Zhou, Haowen Liang and Juntao Li

Photonics 2023, 10(5), 536; https://doi.org/10.3390/photonics10050536 - 06 May 2023

Cited by 2 | Viewed by 1307

Abstract

Imaging in both the visible and the near-infrared ranges has various applications in computational photography and computer vision. Comparing it with the traditional imaging system, integrating pixel-level metasurfaces on the imaging sensor is effective to plot the route of visible and near-infrared light [...] Read more.

Imaging in both the visible and the near-infrared ranges has various applications in computational photography and computer vision. Comparing it with the traditional imaging system, integrating pixel-level metasurfaces on the imaging sensor is effective to plot the route of visible and near-infrared light to the right pixels, while the previously reported nanostructures were complicated to design and fabricate. Here, a pixel-level color router based on metalens, which provides a much simpler construction to improve the visible and near-infrared imaging efficiencies to 59% and 60%, is designed. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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10 pages, 3632 KiB

Open AccessCommunication

Versatile Tunning of Compact Microring Waveguide Resonator Based on Lithium Niobate Thin Films

by Qijing Lin, Yuanzhi Hu, Yang Li, Huajiang Chen, Runhao Liu, Gang Tian, Wentao Qiu, Tiefeng Yang, Heyuan Guan and Huihui Lu

Photonics 2023, 10(4), 424; https://doi.org/10.3390/photonics10040424 - 09 Apr 2023

Cited by 4 | Viewed by 1878

Abstract

With the advancement of modulation technology and the requirement for device miniaturization and integration, lithium niobate on insulator (LNOI) can be a versatile platform for this pursuit, as it can confine the transmitted light at the nanoscale, leading to a strong light–matter interaction, [...] Read more.

With the advancement of modulation technology and the requirement for device miniaturization and integration, lithium niobate on insulator (LNOI) can be a versatile platform for this pursuit, as it can confine the transmitted light at the nanoscale, leading to a strong light–matter interaction, which can sensitively capture external variations, such as electric fields and temperature. This paper presents a compact microring modulator with versatile tuning based on X-cut LNOI. The LNOI modulator equipped with electrodes with a coverage angle of 120

^{\circ}

achieved a maximum electro-optic (EO) tuning efficiency of 13 pm/V and a maximum extinction ratio of 11 dB. The asymmetry in the static or quasi-static electro-optic tuning of the microring modulator was also analyzed. Furthermore, we measured the thermal-optic effect of the device with a sensitivity of 26.33 pm/

^{\circ}

C, which can potentially monitor the environment temperature or compensate for devices’ functional behavior. The demonstrated efficient and versatile compact microring modulator will be an important platform for on-chip active or passive photonic components, microring-based sensor arrays and integrated optics. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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13 pages, 1972 KiB

Open AccessCommunication

Intensity Modulation of Two Weakly Coupled Stimulated Oscillating Mechanical Modes in an Optomechanical Microbubble Resonator

by Xiayuqi Yu, Lei Xu and Liying Liu

Photonics 2023, 10(4), 365; https://doi.org/10.3390/photonics10040365 - 24 Mar 2023

Viewed by 1267

Abstract

We report that when two stimulating mechanical modes in an optomechanical microbubble resonator are weakly coupled to each other, strong oscillation intensity modulation occurs. The modulation was theoretically expected and experimentally observed. We theoretically derived the expressions of the coupling coefficient between the [...] Read more.

We report that when two stimulating mechanical modes in an optomechanical microbubble resonator are weakly coupled to each other, strong oscillation intensity modulation occurs. The modulation was theoretically expected and experimentally observed. We theoretically derived the expressions of the coupling coefficient between the mechanical modes and calculated the region where weak coupling happens. We found that weak coupling exists when the optical quality factor of the microcavity is high and the detuning of the pump laser is close to the beat frequency of the two mechanical modes. Experimentally, we observed that when two mechanical modes are both in stimulated oscillation, they undergo strong intensity modulation as the optical pump power changes, and the coupling coefficient of the two modes is estimated to be 0.962 at the pump power when one mode is in the stimulated region and the other mode is at a stimulating threshold; this proves that the two mechanical modes are weakly coupled. Our results extended the weak coupling conclusion in multimode laser emission to stimulated oscillation in multiple mechanical modes. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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15 pages, 6129 KiB

Open AccessArticle

Structural Color of Multi-Order Fabry–Perot Resonator Based on Sc_0.2Sb₂Te₃ Enhanced Saturated Reflection Color

by Yangbo Lian, Yongzhi Zhang, Furong Liu, Qingyuan Chen, Lulu Zhang and Boshuo Yin

Photonics 2023, 10(1), 70; https://doi.org/10.3390/photonics10010070 - 09 Jan 2023

Cited by 1 | Viewed by 1405

Abstract

The structural color based on the Fabry–Perot (F–P) resonator has been extensively applied lithography-free and tunable color displays. Conventional F–P cavity-based structural color technology exhibits a wide half maximum full width (fwhm), thus causing low color saturation. In this study, a Sc_0.2 [...] Read more.

The structural color based on the Fabry–Perot (F–P) resonator has been extensively applied lithography-free and tunable color displays. Conventional F–P cavity-based structural color technology exhibits a wide half maximum full width (fwhm), thus causing low color saturation. In this study, a Sc_0.2Sb₂Te₃(SST) based structure of multi-order F–P cavity resonance was proposed to obtain high-saturation colors. The surface absorber of the multi-order F–P resonator structure was coated with an SST film, such that the reflection effect at nonresonant wavelengths was reduced. Moreover, ITO layer stacking served as F–P cavity resonance for multi-level modulation, and only a resonant wavelength was allowed to reflect. On that basis, the fwhm of nearly 25 nm and a peak reflectance of 90 was achieved. With the above structure, the color saturation can be dynamically regulated by the phase state of the SST. It is noteworthy that 60% sRGB color gamut space and 50% aRGB color gamut space can be currently achieved. The proposed modulation subsurface is expected to expand the color range of high-level and micro-nano display technology. Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

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