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13 pages, 6462 KiB

Open AccessArticle

Study on Transmission Characteristics and Bandgap Types of Plasma Photonic Crystal

by Yichao Liang, Zhen Liu, Jun Peng, Liguang Lin, Rubing Lin and Qi Lin

Photonics 2021, 8(9), 401; https://doi.org/10.3390/photonics8090401 - 20 Sep 2021

Cited by 7 | Viewed by 2165

A plasma photonic crystal (PPC) was formed using an array of discharge plasma tubes. The transmission spectra and bandstructure of PPCs with different lattice types under different polarization modes were studied through simulation and measurement. To study the types of bandgap in PPCs, [...] Read more.

A plasma photonic crystal (PPC) was formed using an array of discharge plasma tubes. The transmission spectra and bandstructure of PPCs with different lattice types under different polarization modes were studied through simulation and measurement. To study the types of bandgap in PPCs, the bandstructure of the PPC is calculated using symplectic finite difference time domain (SFDTD), a modified plane wave expansion (PWE) method, and a finite element method (FEM) based on weak form equations. The bandstructure of the PPC is compared with the transmission curve results. The results show that the bandgap is stable in the PPC, and the experimental and numerical results of the transmission spectra agree well. There are different types of bandgap in the PPC; the bandgap under TE-like polarization is caused by localized surface plasmon (LSP) and Bragg scattering. The bandgap under TM-like polarization is caused by the cutoff effect of plasma on the electromagnetic wave and Bragg scattering. The lattice type also affects the position and number of the bandgap. The three methods have their advantages and disadvantages when calculating bandstructure. Therefore, it is necessary to combine the results of three methods and experimental results to accurately determine the bandgap type of the PPC. Full article

(This article belongs to the Special Issue Photonic Devices and Systems)

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17 pages, 10083 KiB

Open AccessArticle

Substrate Cleaning Threshold for Various Coated Al Alloys Using a Continuous-Wave Laser

by Xudong Sun, Qiansong Yu, Xiaoyu Bai, Guangyong Jin, Jixing Cai and Boshi Yuan

Photonics 2021, 8(9), 395; https://doi.org/10.3390/photonics8090395 - 16 Sep 2021

Cited by 6 | Viewed by 2296

Abstract

In this study, different coatings (gray epoxy primer, white epoxy varnish and red alkyd paint) of 7075 aluminum alloy are cleaned with a 500 W continuous-wave (CW) fiber laser. We analyzed the influence of the laser power density on the temperature evolution and [...] Read more.

In this study, different coatings (gray epoxy primer, white epoxy varnish and red alkyd paint) of 7075 aluminum alloy are cleaned with a 500 W continuous-wave (CW) fiber laser. We analyzed the influence of the laser power density on the temperature evolution and target surface morphology. Under the condition of continuous laser irradiation for 1 s, the experimental results indicated that the suitable cleaning thresholds of epoxy primer, epoxy primer and epoxy varnish, as well as epoxy primer, epoxy varnish and alkyd paint were 177.74, 192.89 and 147.44 W/mm². The results show that the cleaning threshold of thicker three-layer paint target was smaller than the single-layer paint layer, and we analyze the mechanism of this phenomenon. Full article

(This article belongs to the Special Issue Photonic Devices and Systems)

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8 pages, 3829 KiB

Open AccessArticle

Fabrication of 2 kW-Level Chirped and Tilted Fiber Bragg Gratings and Mitigating Stimulated Raman Scattering in Long-Distance Delivery of High-Power Fiber Laser

by Xiaofan Zhao, Xin Tian, Meng Wang, Binyu Rao, Hongye Li, Xiaoming Xi and Zefeng Wang

Photonics 2021, 8(9), 369; https://doi.org/10.3390/photonics8090369 - 02 Sep 2021

Cited by 5 | Viewed by 2062

Abstract

Chirped and tilted fiber Bragg gratings (CTFBGs) have attracted a lot of attention in stimulated Raman scattering (SRS) suppression of high-power fiber lasers. However, the laser power handling capacity seriously limits their applications. In this paper, by optimizing the inscription parameters and post-processing [...] Read more.

Chirped and tilted fiber Bragg gratings (CTFBGs) have attracted a lot of attention in stimulated Raman scattering (SRS) suppression of high-power fiber lasers. However, the laser power handling capacity seriously limits their applications. In this paper, by optimizing the inscription parameters and post-processing strategy, we fabricate a large-mode-area double-cladding CTFBG with a thermal slope of ~0.015 °C/W due to the low insertion loss of about 0.15 dB, which make it possible for direct kilowatt-level application. A 2 kW-level fiber laser oscillator is employed to test the CTFBG, and a series of experiments have been carried out to compare the effect of SRS mitigation in high-power fiber laser long-distance delivery. In addition, the influence of CTFBGs on laser beam quality is studied for the first time. Experimental results indicated that the CTFBG could effectively mitigate SRS and has no obvious influence on laser beam quality. This work opens a new opportunity for further power scaling and the delivery of high-power fiber lasers over longer distances. Full article

(This article belongs to the Special Issue Photonic Devices and Systems)

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12 pages, 5783 KiB

Open AccessArticle

Multispectral Photonic Jet Shaping and Steering by Control of Tangential Electric Field Component on Cuboid Particle

by Cheng-Yang Liu, Wei-Yu Chen, Oleg V. Minin and Igor V. Minin

Photonics 2021, 8(8), 317; https://doi.org/10.3390/photonics8080317 - 06 Aug 2021

Cited by 4 | Viewed by 1796

Abstract

In this study, we present the simulations and experimental observations of photonic jet (PJ) shaping by control of tangential electric field components at illuminating wavelengths of 405 nm, 532 nm, and 671 nm. The PJs are generated by a single dielectric 4-micrometer cube [...] Read more.

In this study, we present the simulations and experimental observations of photonic jet (PJ) shaping by control of tangential electric field components at illuminating wavelengths of 405 nm, 532 nm, and 671 nm. The PJs are generated by a single dielectric 4-micrometer cube that was fabricated from polydimethylsiloxane (PDMS). The dielectric cube is deposited on a silicon substrate and placed on two aluminum masks with a width equal to the side length of the cube. Due to the appearance of the metal masks, the focal length and decay length of the generated PJs decreased almost twice, while the PJ resolution increased 1.2 times. Thus, PJ shaping can be controlled by the presence of the metal mask along the lateral surface of the cube without changing the external shape or internal structure of the cube. This effect is based on the control of the tangential components of the electric field along the lateral surface of the cube. In the case of a one-sided metal mask, the effect of optical deflection and bending is predicted to form a photonic hook. Due to the low cost of these dielectric cubes, they have potential in far-field systems to better meet the requirements of modern optical integration circuits and switches. Full article

(This article belongs to the Special Issue Photonic Devices and Systems)

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11 pages, 4015 KiB

Open AccessCommunication

Compact Photonic Crystal Polarization Beam Splitter Based on the Self-Collimation Effect

by Geyu Tang, Huamao Huang, Yuqi Liu and Hong Wang

Photonics 2021, 8(6), 198; https://doi.org/10.3390/photonics8060198 - 04 Jun 2021

Cited by 5 | Viewed by 2352

Abstract

We propose a new compact polarization beam splitter based on the self-collimation effect of two-dimensional photonic crystals and photonic bandgap characteristics. The device is composed of a rectangular air holes-based polarization beam splitting structure and circular air holes-based self-collimating structure. By inserting the [...] Read more.

We propose a new compact polarization beam splitter based on the self-collimation effect of two-dimensional photonic crystals and photonic bandgap characteristics. The device is composed of a rectangular air holes-based polarization beam splitting structure and circular air holes-based self-collimating structure. By inserting the polarization beam splitting structure into the self-collimating structure, the TE and TM polarized lights are orthogonally separated at their junction. When the number of rows in the hypotenuse of the inserted rectangular holes is 5, the transmittance of TE polarized light at 1550 nm is 95.4% and the corresponding polarization extinction ratio is 23 dB; on the other hand, the transmittance of TM polarized light is 88.5% and the corresponding polarization extinction ratio is 37 dB. For TE and TM polarized lights covering a 100 nm bandwidth, the TE and TM polarization extinction ratios are higher than 18 dB and 30 dB, respectively. Compared with the previous polarization beam splitters, our structure is simple, the size is small, and the extinction ratio is high, which meets the needs of modern optical communications, optical interconnection, and optical integrated systems. Full article

(This article belongs to the Special Issue Photonic Devices and Systems)

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21 pages, 11649 KiB

Open AccessArticle

Experimental Investigation on the Sputtering Process for Tantalum Oxynitride Thin Films

by Chuan Li, Jang-Hsing Hsieh and Y. R. Chuang

Photonics 2021, 8(2), 53; https://doi.org/10.3390/photonics8020053 - 15 Feb 2021

Cited by 3 | Viewed by 2676

Abstract

Metal oxynitrides are compounds between nitrides and oxides with a certain level of photocatalytic functions. The purpose of this study is to investigate an appropriate range of oxygen flow rate during sputtering for depositing tantalum oxynitride films. The sputtering process was carried out [...] Read more.

Metal oxynitrides are compounds between nitrides and oxides with a certain level of photocatalytic functions. The purpose of this study is to investigate an appropriate range of oxygen flow rate during sputtering for depositing tantalum oxynitride films. The sputtering process was carried out under fixed nitrogen but variable oxygen flow rates. Post rapid thermal annealing was conducted at 800 °C for 5 min to transform the as-deposited amorphous films into crystalline phases. The material characterizations of annealed films include X-ray diffraction and Raman spectroscopy for identifying crystal structures; scanning electron microscope for examining surface morphology; energy-dispersive X-ray spectroscopy to determine surface elemental compositions; four-point probe and Hall effect analysis to evaluate electrical resistivity; UV-visible-NIR spectroscopy for quantifying optical properties and optical bandgaps. To assess the photocatalytic function of oxynitride films, the degradation of methyl orange in de-ionized water was examined under continuous irradiation by a simulated solar light source for six hours. Results indicate that crystalline tantalum oxynitride films can be obtained if the O₂ flow rate is chosen to be 0.25–1.5 sccm along with 10 sccm of N₂ and 20 sccm of Ar. In particular, films deposited between 0.25 and 1.5 sccm O₂ flow have higher efficiency in photodegradation on methyl orange due to a more comprehensive formation of oxynitrides. Full article

(This article belongs to the Special Issue Photonic Devices and Systems)

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11 pages, 1023 KiB

Open AccessArticle

Photonic Nanojets and Whispering Gallery Modes in Smooth and Corrugated Micro-Cylinders under Point-Source Illumination

by Ibrahim Mahariq, Thabet Abdeljawad, Abdullah S. Karar, Shadi A. Alboon, Hamza Kurt and Alexey V. Maslov

Photonics 2020, 7(3), 50; https://doi.org/10.3390/photonics7030050 - 21 Jul 2020

Cited by 16 | Viewed by 3304

Abstract

We numerically investigate the generation of photonic nanojets (PNJs) and the excitation of whispering gallery modes (WGMs) supported by both smooth and corrugated dielectric micro-cylinders under point-source illumination. Results show that the location of the point-source defines the location and properties of PNJs, [...] Read more.

We numerically investigate the generation of photonic nanojets (PNJs) and the excitation of whispering gallery modes (WGMs) supported by both smooth and corrugated dielectric micro-cylinders under point-source illumination. Results show that the location of the point-source defines the location and properties of PNJs, whereas stability of WGMs exists in smooth micro-cylinders but vanishes in corrugated ones. It is shown that the location of the point-source acts as an additional degree of freedom for controlling the characteristics of the generated PNJs for both smooth and corrugated dielectric micro-cylinders. Furthermore, the influence of the point-source location on the stability of the excited WGMs was diminished for the smooth micro-cylinders, while being fully pronounced for their corrugated counterparts. Full article

(This article belongs to the Special Issue Photonic Devices and Systems)

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10 pages, 3607 KiB

Open AccessLetter

Silicon Photonic Mode-Division Reconfigurable Optical Add/Drop Multiplexers with Mode-Selective Integrated MEMS Switches

by Vinh Huu Nguyen, In Ki Kim and Tae Joon Seok

Photonics 2020, 7(4), 80; https://doi.org/10.3390/photonics7040080 - 24 Sep 2020

Cited by 8 | Viewed by 2737

Abstract

Mode-division multiplexing (MDM) is an attractive solution for future on-chip networks to enhance the optical transmission capacity with a single laser source. A mode-division reconfigurable optical add/drop multiplexer (ROADM) is one of the key components to construct flexible and complex on-chip optical networks [...] Read more.

Mode-division multiplexing (MDM) is an attractive solution for future on-chip networks to enhance the optical transmission capacity with a single laser source. A mode-division reconfigurable optical add/drop multiplexer (ROADM) is one of the key components to construct flexible and complex on-chip optical networks for MDM systems. In this paper, we report on a novel scheme of mode-division ROADM with mode-selective silicon photonic MEMS (micro-electromechanical system) switches. With this ROADM device, data carried by any mode-channels can be rerouted or switched at an MDM network node, i.e., any mode could be added/dropped to/from the multimode bus waveguide flexibly and selectively. Particularly, the design and simulation of adiabatic vertical couplers for three quasi-TE modes (TE₀, TE₁, and TE₂ modes) based on effective index analysis and mode overlap calculation method are reported. The calculated insertion losses are less than 0.08 dB, 0.19 dB, and 0.03 dB for the TE₀ mode, TE₁ mode, and TE₂ mode couplers, respectively, over a wavelength range of 75 nm (1515–1590 nm). The crosstalks are below −20 dB over the bandwidth. The proposed device is promising for future on-chip optical networks with flexible functionality and large-scale integration. Full article

(This article belongs to the Special Issue Photonic Devices and Systems)

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