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17 pages, 5512 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Electrically Parallel Three-Element 980 nm VCSEL Arrays with Ternary and Binary Bottom DBR Mirror Layers

by Nasibeh Haghighi and James A. Lott

Materials 2021, 14(2), 397; https://doi.org/10.3390/ma14020397 - 14 Jan 2021

Cited by 10 | Viewed by 4196

Abstract

To meet the performance goals of fifth generation (5G) and future sixth generation (6G) optical wireless communication (OWC) and sensing systems, we seek to develop low-cost, reliable, compact lasers capable of sourcing 5–20 Gb/s (ideally up to 100 Gb/s by the 2030s) infrared [...] Read more.

To meet the performance goals of fifth generation (5G) and future sixth generation (6G) optical wireless communication (OWC) and sensing systems, we seek to develop low-cost, reliable, compact lasers capable of sourcing 5–20 Gb/s (ideally up to 100 Gb/s by the 2030s) infrared beams across free-space line-of-sight distances of meters to kilometers. Toward this end, we develop small arrays of electrically parallel vertical cavity surface emitting lasers (VCSELs) for possible future use in short-distance (tens of meters) free-space optical communication and sensing applications in, for example, homes, data centers, manufacturing spaces, and backhaul (pole-to-pole or pole-to-building) optical links. As a starting point, we design, grow by metal–organic vapor phase epitaxy, fabricate, test, and analyze 980 nm top-emitting triple VCSEL arrays. Via on-wafer high-frequency probe testing, our arrays exhibit record bandwidths of 20–25 GHz, optical output powers of 20–50 mW, and error-free data transmission at up to 40 Gb/s—all extremely well suited for the intended 5G short-reach OWC and sensing applications. We employ novel p-metal and top mesa inter-VCSEL connectors to form electrically parallel but optically uncoupled (to reduce speckle) arrays with performance exceeding that of single VCSELs with equal total emitting areas. Full article

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

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10 pages, 1879 KiB

Open AccessArticle

Novel Aggregation-Induced Emission Materials/Cadmium Sulfide Composite Photocatalyst for Efficient Hydrogen Evolution in Absence of Sacrificial Reagent

by Xi Ke, Kunqiang Wang, Chen Tu, Runda Huang, Dongxiang Luo and Menglong Zhang

Materials 2020, 13(22), 5287; https://doi.org/10.3390/ma13225287 - 22 Nov 2020

Cited by 3 | Viewed by 2499

Abstract

This work focuses on the development of a novel organic–inorganic photoactive material composited by aggregation-induced emission luminogens (AIE) and CdS. Tetraphenylethene-based AIE (TPE-Ca) is synthesized on CdS to form CdS/TPE-Ca electrode, due to its suitable band structure and potential capability of renewable energy [...] Read more.

This work focuses on the development of a novel organic–inorganic photoactive material composited by aggregation-induced emission luminogens (AIE) and CdS. Tetraphenylethene-based AIE (TPE-Ca) is synthesized on CdS to form CdS/TPE-Ca electrode, due to its suitable band structure and potential capability of renewable energy production. The CdS/TPE-Ca electrode presents over three-fold improved photocurrent density and dramatically reduced interfacial resistance, compared with the pure CdS electrode. In addition, the engineering of the band alignment allows the holes to accumulate on the valance band of TPE-Ca, which would partially prevent the CdS from photo-corrosion, thus improving the stability of the sacrificial-free electrolyte photoelectrochemical cell. Full article

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

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14 pages, 6888 KiB

Open AccessArticle

Challenges in a Hybrid Fabrication Process to Generate Metallic Polarization Elements with Sub-Wavelength Dimensions

by Stefan Belle, Babette Goetzendorfer and Ralf Hellmann

Materials 2020, 13(22), 5279; https://doi.org/10.3390/ma13225279 - 22 Nov 2020

Cited by 3 | Viewed by 2392

Abstract

We report on the challenges in a hybrid sub-micrometer fabrication process while using three dimensional femtosecond direct laser writing and electroplating. With this hybrid subtractive and additive fabrication process, it is possible to generate metallic polarization elements with sub-wavelength dimensions of less than [...] Read more.

We report on the challenges in a hybrid sub-micrometer fabrication process while using three dimensional femtosecond direct laser writing and electroplating. With this hybrid subtractive and additive fabrication process, it is possible to generate metallic polarization elements with sub-wavelength dimensions of less than 400 nm in the cladding area. We show approaches for improving the adhesion of freestanding photoresist pillars as well as of the metallic cladding area, and we also demonstrate the avoidance of an inhibition layer and sticking of the freestanding pillars. Three-dimensional direct laser writing in a positive tone photoresist is used as a subtractive process to fabricate free-standing non-metallic photoresist pillars with an area of about 850 nm × 1400 nm, a height of 3000 nm, and a distance between the pillars of less than 400 nm. In a subsequent additive fabrication process, these channels are filled with gold by electrochemical deposition up to a final height of 2200 nm. Finally, the polarization elements are characterized by measuring the degree of polarization in order to show their behavior as quarter- and half-wave plates. Full article

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

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10 pages, 2309 KiB

Open AccessArticle

Precise Method for Measuring the Quadratic Electro-Optic Effect in Noncentrosymmetric Crystals in the Presence of Natural Birefringence

by Marek Izdebski, Rafał Ledzion and Włodzimierz Kucharczyk

Materials 2020, 13(18), 3942; https://doi.org/10.3390/ma13183942 - 6 Sep 2020

Cited by 1 | Viewed by 2006

Abstract

The application of the improved dynamic polarimetric method for the measurement of the quadratic electro-optic effect in NH₄H₂PO₄ (ADP) crystal with the light beam propagating perpendicularly to its optical axis is presented. This technique can be applied in [...] Read more.

The application of the improved dynamic polarimetric method for the measurement of the quadratic electro-optic effect in NH₄H₂PO₄ (ADP) crystal with the light beam propagating perpendicularly to its optical axis is presented. This technique can be applied in noncetrosymmetric crystals in the presence of natural birefringence even when the fast and slow rays diverge slightly, causing them to only partially interfere. The method allows for minor errors in cutting and orientation of the crystal samples, resulting in deviations from configurations in which the crystal symmetry vetoes the linear electro-optic effect. The occurring contribution of the linear effect, if it is not too large, not only does not exclude the measurement of the quadratic effect, but increases its accuracy. The method does not require any prior compensation for the natural birefringence. Its sensitivity allows for quadratic electro-optic effect measurements in ferroelectrics in temperatures significantly different from the phase transition temperature or in paraelectric crystals, for which this effect is relatively small. Full article

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

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11 pages, 2712 KiB

Open AccessArticle

Double Electromagnetically Induced Transparency and Its Slow Light Application Based on a Guided-Mode Resonance Grating Cascade Structure

by Guofeng Li, Junbo Yang, Zhaojian Zhang, Yuyu Tao, Lingjun Zhou, Huimin Huang, Zhenrong Zhang and Yunxin Han

Materials 2020, 13(17), 3710; https://doi.org/10.3390/ma13173710 - 21 Aug 2020

Cited by 11 | Viewed by 2849

Abstract

In recent years, the achievement of the electromagnetically induced transparency (EIT) effect based on the guided-mode resonance (GMR) effect has attracted extensive attention. However, few works have achieved a double EIT-like effect using this method. In this paper, we numerically achieve a double [...] Read more.

In recent years, the achievement of the electromagnetically induced transparency (EIT) effect based on the guided-mode resonance (GMR) effect has attracted extensive attention. However, few works have achieved a double EIT-like effect using this method. In this paper, we numerically achieve a double EIT-like effect in a GMR system with a three-layer silicon nitride waveguide grating structure (WGS), using the multi-level atomic system model for theoretical explanation. In terms of slow light performance, the corresponding two delay times reach 22.59 ps and 8.43 ps, respectively. We also investigate the influence of wavelength detuning of different GMR modes on the transparent window and slow light performance. Furthermore, a wide-band flat-top transparent window was also achieved by appropriately adjusting the wavelength detuning between GMR modes. These results indicate that the EIT-like effect in the WGS has potential application prospects in low-loss slow optical devices, optical sensing, and optical communications. Full article

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

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11 pages, 1810 KiB

Open AccessArticle

Realization of Deep UV Plasmonic Enhancement to Photo Response through Al Mesh

by Gaoming Li, Jingwen Zhang, Yaoting Hu and Yongning He

Materials 2020, 13(15), 3252; https://doi.org/10.3390/ma13153252 - 22 Jul 2020

Cited by 1 | Viewed by 2070

Abstract

High-performance UV detectors are of great significance for various applications. Plasmonic structures enable great improvement of the performance of detectors. However, to push the plasmonic enhancement to photo response into the deep-UV region presents some challenges. In this work, we found that the [...] Read more.

High-performance UV detectors are of great significance for various applications. Plasmonic structures enable great improvement of the performance of detectors. However, to push the plasmonic enhancement to photo response into the deep-UV region presents some challenges. In this work, we found that the optical properties of the supporting layer play important roles in achieving the optimal plasmonic enhancement. Therefore, we fully considered the dependence of the optical constants of the MgZnO supporting layer, which is a promising material to realize deep-UV photodetectors, on microstructure and crystalline quality, which are related to the fabrication method. Based on the optical constants, we designed an Al mesh plasmonic structure and fabricated it with a polystyrene monolayer as a mask. Finally, we demonstrated a three-times enhancement to photo response with UV radiation at 254 nm. Full article

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

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17 pages, 6168 KiB

Open AccessArticle

A Four Green TM/Red TE Demultiplexer Based on Multi Slot-Waveguide Structures

by Dror Malka

Materials 2020, 13(14), 3219; https://doi.org/10.3390/ma13143219 - 20 Jul 2020

Cited by 27 | Viewed by 2802

Abstract

A four green transverse magnetic (TM)/red transverse electric (TE) light wavelength demultiplexer device, based on multi slot-waveguide (SW) structures is demonstrated. The device aims to demultiplex wavelengths in the green/red light range with wavelengths of 530, 540, 550, and 560 nm; 630, 640, [...] Read more.

A four green transverse magnetic (TM)/red transverse electric (TE) light wavelength demultiplexer device, based on multi slot-waveguide (SW) structures is demonstrated. The device aims to demultiplex wavelengths in the green/red light range with wavelengths of 530, 540, 550, and 560 nm; 630, 640, 650, and 660 nm. This means that the device functions as a 1 × 4 demultiplexer for each polarization mode (TE/TM). The controlling of the light switching between two closer segment SWs under the TM/TE polarization mode was studied by designing a suitable SW structure and setting the right segment length to fit the coupling lengths of the operating wavelengths. The device is composed of six-segment SW units and six S-bends (SB) SW. The key SW and SB parameters were optimized and determined by a full vectorial beam propagation method (FV-BPM). Results show power losses better than 0.138 dB, crosstalk better than −21.14 dB, and an optical spectrum smaller than 9.39 nm, with an overall compact size of 104.5 µm. The device can be integrated in wavelength division multiplexing (WDM) for increasing data bit rate in a visible light communication (VLC) system. Full article

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

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13 pages, 1060 KiB

Open AccessArticle

Impact of an Antiresonant Oxide Island on the Lasing of Lateral Modes in VCSELs

by Marta Więckowska, Robert P. Sarzała, Rafał Ledzion and Maciej Dems

Materials 2020, 13(9), 2195; https://doi.org/10.3390/ma13092195 - 11 May 2020

Cited by 3 | Viewed by 2733

Abstract

Use of antiresonant structures is a proven, efficient method of improving lateral mode selectivity in VCSELs. In this paper, we analyze the impact of a low-refractive antiresonant oxide island buried in a top VCSEL mirror on the lasing conditions of lateral modes of [...] Read more.

Use of antiresonant structures is a proven, efficient method of improving lateral mode selectivity in VCSELs. In this paper, we analyze the impact of a low-refractive antiresonant oxide island buried in a top VCSEL mirror on the lasing conditions of lateral modes of different orders. By performing comprehensive thermal, electrical, and optical numerical analysis of the VCSEL device, we show the impact of the size and location of the oxide island on the current-crowding effect and compute threshold currents for various lateral modes. If the island is placed close to the cavity, the threshold shows strong oscillations, which for moderate island distances can be tuned to increase the side mode discrimination. We are therefore able to pinpoint the most important factors influencing mode discrimination and to identify oxide island parameters capable of providing single-lateral-mode emission. Full article

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

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16 pages, 4637 KiB

Open AccessArticle

Numerical Investigation of the Impact of ITO, AlInN, Plasmonic GaN and Top Gold Metalization on Semipolar Green EELs

by Maciej Kuc, Łukasz Piskorski, Maciej Dems, Michał Wasiak, Adam K. Sokół, Robert P. Sarzała and Tomasz Czyszanowski

Materials 2020, 13(6), 1444; https://doi.org/10.3390/ma13061444 - 22 Mar 2020

Cited by 9 | Viewed by 2690

Abstract

In this paper, we present the results of a computational analysis of continuous-wave (CW) room-temperature (RT) semipolar InGaN/GaN edge-emitting lasers (EELs) operating in the green spectral region. In our calculations, we focused on the most promising materials and design solutions for the cladding [...] Read more.

In this paper, we present the results of a computational analysis of continuous-wave (CW) room-temperature (RT) semipolar InGaN/GaN edge-emitting lasers (EELs) operating in the green spectral region. In our calculations, we focused on the most promising materials and design solutions for the cladding layers, in terms of enhancing optical mode confinement. The structural modifications included optimization of top gold metalization, partial replacement of p-type GaN cladding layers with ITO and introducing low refractive index lattice-matched AlInN or plasmonic GaN regions. Based on our numerical findings, we show that by employing new material modifications to green EELs operating at around 540 nm it is possible to decrease their CW RT threshold current densities from over 11 kA/cm² to less than 7 kA/cm². Full article

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

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11 pages, 2306 KiB

Open AccessArticle

Nanowire Ring Embedded in a Flexible Substrate for Local Strain Detection

by Shengkun Li, Yue Qin, Xin Li and Yuejin Zhao

Materials 2020, 13(2), 347; https://doi.org/10.3390/ma13020347 - 12 Jan 2020

Cited by 1 | Viewed by 2631

Abstract

Optical sensing has attracted more and more attention in recent years with the advance in planar waveguide fabrication processes. The photon, as a carrier of information in sensing areas, could have a better performance than electrons. We propose a novel end-to-end ring cavity [...] Read more.

Optical sensing has attracted more and more attention in recent years with the advance in planar waveguide fabrication processes. The photon, as a carrier of information in sensing areas, could have a better performance than electrons. We propose a novel end-to-end ring cavity to fabricate sensitive units of a strain sensor. We then propose a method of combining a flexible substrate with an end-to-end semiconductor nanowire ring cavity to fabricate novel strain sensors. We used a tuning resonant wavelength detected by a homebuilt excitation and detection system to measure applied strain. The resonant wavelength of the strain gauge was red-shift and linear tuned with increasing strain. The gauge factor was about 50, calculated through experiments and theory, and Q was 1938, with structural parameters L = 70 µm and d = 1 µm. The high sensitivity makes it possible to measure micro deformation more accurately. End-to-end coupling active nanowire waveguides eliminate the shortcomings of side by side coupling structures, which have the phasing shift with no minor optical density loss. This resonator in flexible substrates could be used not only as on-chip strain sensors for micro or nano deformation detecting but also as tunable light sources for photonic integrated circuits. Full article

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

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16 pages, 3788 KiB

Open AccessArticle

Random Voids Generation and Effect of Thermal Shock Load on Mechanical Reliability of Light-Emitting Diode Flip Chip Solder Joints

by Jiajie Fan, Jie Wu, Changzhen Jiang, Hao Zhang, Mesfin Ibrahim and Liang Deng

Materials 2020, 13(1), 94; https://doi.org/10.3390/ma13010094 - 23 Dec 2019

Cited by 11 | Viewed by 3640

Abstract

To make the light-emitting diode (LED) more compact and effective, the flip chip solder joint is recommended in LED chip-scale packaging (CSP) with critical functions in mechanical support, heat dissipation, and electrical conductivity. However, the generation of voids always challenges the mechanical strength, [...] Read more.

To make the light-emitting diode (LED) more compact and effective, the flip chip solder joint is recommended in LED chip-scale packaging (CSP) with critical functions in mechanical support, heat dissipation, and electrical conductivity. However, the generation of voids always challenges the mechanical strength, thermal stability, and reliability of solder joints. This paper models the 3D random voids generation in the LED flip chip Sn96.5–Ag3.0–Cu0.5 (SAC305) solder joint, and investigates the effect of thermal shock load on its mechanical reliability with both simulations and experiments referring to the JEDEC thermal shock test standard (JESD22-A106B). The results reveal the following: (1) the void rate of the solder joint increases after thermal shock ageing, and its shear strength exponentially degrades; (2) the first principal stress of the solder joint is not obviously increased, however, if the through-hole voids emerged in the corner of solder joints, it will dramatically increase; (3) modelling of the fatigue failure of solder joint with randomly distributed voids utilizes the approximate model to estimate the lifetime, and the experimental results confirm that the absolute prediction error can be controlled around 2.84%. Full article

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

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9 pages, 2599 KiB

Open AccessArticle

Linear Tuning of Phase-Matching Temperature in LiNbO₃:Zr Crystals by MgO Co-Doping

by Tengfei Kong, Hongde Liu, Liyun Xue, Weiwei Wang, Shahzad Saeed, Dahuai Zheng, Shiguo Liu, Shaolin Chen, Ling Zhang, Yongfa Kong and Jingjun Xu

Materials 2019, 12(24), 4155; https://doi.org/10.3390/ma12244155 - 11 Dec 2019

Cited by 3 | Viewed by 2206

Abstract

We grew a series of co-doped LiNbO₃ crystals with fixed 1.5 mol % ZrO₂ and various MgO concentrations (1.0, 3.0, 4.0, 6.0 mol %), and investigated their optical properties and defect structures. By 3.0 mol % MgO co-doping, the optical damage [...] Read more.

We grew a series of co-doped LiNbO₃ crystals with fixed 1.5 mol % ZrO₂ and various MgO concentrations (1.0, 3.0, 4.0, 6.0 mol %), and investigated their optical properties and defect structures. By 3.0 mol % MgO co-doping, the optical damage resistance at 532 nm reached 6.5 × 10⁶ W/cm², while the phase-matching temperature for doubling 1064 nm was only 29.3 °C—close to room temperature—which was conducive to realizing the 90° phase matching at room temperature by slightly modulating the incident angle of the fundamental beam. Notably, we found that the phase-matching temperature increased linearly with the increase of MgO doping, and this linear dependence helped us to grow the high-quality crystal for room temperature 90° phase matching. Moreover, the defect analysis indicated that the linear tuning of phase-matching temperature might be attributed to

{Mg}_{Li}^{+}

+

{Zr}_{Nb}^{-}

neutral pairs in crystals. Full article

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

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8 pages, 912 KiB

Open AccessArticle

Highly Deep Ultraviolet–Transparent h-BN Film Deposited on an Al_0.7Ga_0.3N Template by Low-Temperature Radio-Frequency Sputtering

by Guo-Dong Hao, Manabu Taniguchi and Shin-ichiro Inoue

Materials 2019, 12(24), 4046; https://doi.org/10.3390/ma12244046 - 5 Dec 2019

Cited by 5 | Viewed by 3219

Abstract

Hexagonal boron nitride (h-BN) is an attractive wide-bandgap material for application to emitters and detectors operating in the deep ultraviolet (DUV) spectral region. The optical transmittance of h-BN in the DUV region is particularly important for these devices. We report on the deposition [...] Read more.

Hexagonal boron nitride (h-BN) is an attractive wide-bandgap material for application to emitters and detectors operating in the deep ultraviolet (DUV) spectral region. The optical transmittance of h-BN in the DUV region is particularly important for these devices. We report on the deposition of thick h-BN films (>200 nm) on Al_0.7Ga_0.3N templates via radio-frequency sputtering, along with the realization of ultrahigh transmittance in the DUV region. The fraction of the gas mixture (Ar/N₂) was varied to investigate its effects on the optical transmittance of BN. DUV light transmittance of as high as 94% was achieved at 265 nm. This value could be further enhanced to exceed 98% by a post-annealing treatment at 800 °C in a N₂ ambient for 20 min. The phase of the highly DUV–transparent BN film was determined to be a purely hexagonal structure via Raman spectra measurements. More importantly, these deposition processes were performed at a low temperature (300 °C), which can provide protection from device performance degradation when applied to actual devices. Full article

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

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13 pages, 916 KiB

Open AccessArticle

Influence of Various Bottom DBR Designs on the Thermal Properties of Blue Semiconductor-Metal Subwavelength-Grating VCSELs

by Robert P. Sarzała, Łukasz Piskorski, Tomasz Czyszanowski and Maciej Dems

Materials 2019, 12(19), 3235; https://doi.org/10.3390/ma12193235 - 2 Oct 2019

Cited by 6 | Viewed by 3315

Abstract

In this paper, we consider several designs for nitride-based vertical-cavity surface-emitting lasers (VCSELs) with a top semiconductor-metal subwavelength grating (SMSG) as the facet mirror. The constructions of the bottom distributed Bragg reflectors (DBRs) used in the VCSEL designs were inspired by devices demonstrated [...] Read more.

In this paper, we consider several designs for nitride-based vertical-cavity surface-emitting lasers (VCSELs) with a top semiconductor-metal subwavelength grating (SMSG) as the facet mirror. The constructions of the bottom distributed Bragg reflectors (DBRs) used in the VCSEL designs were inspired by devices demonstrated recently by several research groups. A multiparameter numerical analysis was performed, based on self-consistent thermal and electrical simulations. The results show that, in the case of small aperture VCSEL designs, dielectric-based DBRs with metallic or GaN channels enable equally efficient heat dissipation to designs with monolithically integrated DBRs. In the case of broad aperture designs enabled by SMSGs, monolithically integrated DBRs provide much more efficient heat dissipation in comparison to all other considered designs. Full article

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

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17 pages, 3246 KiB

Open AccessFeature PaperArticle

Delay-Differential-Equation Modeling of Mode-Locked Vertical-External-Cavity Surface-Emitting Lasers in Different Cavity Configurations

by Eugene A. Avrutin and Krassimir Panajotov

Materials 2019, 12(19), 3224; https://doi.org/10.3390/ma12193224 - 1 Oct 2019

Cited by 12 | Viewed by 2774

Abstract

A simple, versatile model for the dynamics of electrically and optically pumped vertical-external-cavity surface-emitting lasers, which are mode locked by a semiconductor saturable-absorber mirror, is presented. The difference between the laser operation in the linear and folded cavity, as well as the potential [...] Read more.

A simple, versatile model for the dynamics of electrically and optically pumped vertical-external-cavity surface-emitting lasers, which are mode locked by a semiconductor saturable-absorber mirror, is presented. The difference between the laser operation in the linear and folded cavity, as well as the potential for a colliding pulse operation, are studied. Full article

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

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15 pages, 7350 KiB

Open AccessArticle

A Terahertz (THz) Single-Polarization-Single-Mode (SPSM) Photonic Crystal Fiber (PCF)

by Tianyu Yang, Can Ding, Richard W. Ziolkowski and Y. Jay Guo

Materials 2019, 12(15), 2442; https://doi.org/10.3390/ma12152442 - 31 Jul 2019

Cited by 35 | Viewed by 4092

Abstract

This paper presents a novel approach to attain a single-polarization-single-mode (SPSM) photonic crystal fiber (PCF) in the terahertz (THz) regime. An initial circular hole PCF design is modified by introducing asymmetry in the first ring of six air holes in the cladding, i.e., [...] Read more.

This paper presents a novel approach to attain a single-polarization-single-mode (SPSM) photonic crystal fiber (PCF) in the terahertz (THz) regime. An initial circular hole PCF design is modified by introducing asymmetry in the first ring of six air holes in the cladding, i.e., epsilon-near-zero (ENZ) material is introduced into only four of those air holes and the other two remain air-filled but have different diameters. The resulting fundamental X-polarized (XP) and Y-polarized (YP) modes have distinctly different electric field distributions. The asymmetry is arranged so that the YP mode has a much larger amount of the field distributed in the ENZ material than the XP mode. Since the ENZ material is very lossy, the YP mode suffers a much higher loss than the XP mode. Consequently, after a short propagation distance, the loss difference (LD) between the XP and YP modes will be large enough that only the XP mode still realistically exists in the PCF. To further enhance the outcome, gain material is introduced into the core area to increase the LDs between the wanted XP mode and any unwanted higher order (HO) modes, as well as to compensate for the XP mode loss without affecting the LD between the XP and YP modes. The optimized PCF exhibits LDs between the desired XP mode and all other modes greater than 8.0 dB/cm across a wide frequency range of 0.312 THz. Consequently, the reported PCF only needs a length of 2.5 cm to attain an SPSM result, with the unwanted modes being more than 20 dB smaller than the wanted mode over the entire operational band. Full article

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

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14 pages, 3782 KiB

Open AccessArticle

Multicolor and Warm White Emissions with a High Color Rendering Index in a Tb³⁺/Eu³⁺-Codoped Phosphor Ceramic Plate

by Haggeo Desirena, Jorge Molina-González, Octavio Meza, Priscilla Castillo and Juan Bujdud-Pérez

Materials 2019, 12(14), 2240; https://doi.org/10.3390/ma12142240 - 11 Jul 2019

Cited by 3 | Viewed by 3069

Abstract

A series of Tb³⁺/Eu³⁺-codoped phosphor ceramic plates with a high color rendering index (CRI) for a near-ultraviolet light emitting diode (LED) were fabricated. Color emission can be tuned from green to reddish as a function of Eu³⁺ concentration. [...] Read more.

A series of Tb³⁺/Eu³⁺-codoped phosphor ceramic plates with a high color rendering index (CRI) for a near-ultraviolet light emitting diode (LED) were fabricated. Color emission can be tuned from green to reddish as a function of Eu³⁺ concentration. By doping only 0.15 mol% of Eu³⁺ concentration, a comfortable warm white emission is promoted as a result of simultaneous emissions of Tb³⁺ and Eu³⁺ ions. A theoretical model is proposed to calculate the contributions of the emitted color of the donor (Tb³⁺) and acceptor (Eu³⁺) ions in terms of europium concentration. The energy transfer from Tb³⁺ to Eu³⁺ ions is corroborated by the luminescence spectra and decay time of Tb³⁺, with a maximum energy transfer efficiency of 76% for 28 mol% of Tb³⁺ and 14 mol% of Eu³⁺. Warm white LEDs were constructed using a 380 nm UV chip and showed a CRI of 82.5, which was one of highest values reported for Tb³⁺/Eu³⁺-codoped samples. Color-correlated temperature (CCT), color coordinate (CC), and luminous efficacy (LE) were utilized to know the potentials as a phosphor converter in solid-state lighting. Full article

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

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13 pages, 4667 KiB

Open AccessArticle

Efficient 1 µm Laser Emission of Czochralski-Grown Nd:LGSB Single Crystal

by Catalina-Alice Brandus, Stefania Hau, Alin Broasca, Madalin Greculeasa, Flavius-Marian Voicu, Cristina Gheorghe, Lucian Gheorghe and Traian Dascalu

Materials 2019, 12(12), 2005; https://doi.org/10.3390/ma12122005 - 22 Jun 2019

Cited by 10 | Viewed by 4971

Abstract

A 5.0-at.% Nd-doped La_0.64Gd_0.41Sc_2.95(BO₃)₄ (Nd:LGSB) borate laser crystal was successfully grown by the Czochralski method, for the first time to our knowledge. The spectroscopic properties of the grown crystal are discussed and 1 µm [...] Read more.

A 5.0-at.% Nd-doped La_0.64Gd_0.41Sc_2.95(BO₃)₄ (Nd:LGSB) borate laser crystal was successfully grown by the Czochralski method, for the first time to our knowledge. The spectroscopic properties of the grown crystal are discussed and 1 µm laser emission, under end-pumping with a fiber-coupled diode laser at 807 nm, is reported. A c-cut Nd:LGSB medium yielded 1.35 W continuous-wave output power at 0.63 overall optical-to-optical efficiency, with respect to the absorbed pump power, together with the high 0.68 slope efficiency. With an a-cut Nd:LGSB sample, 0.81 W output power at 0.52 optical-to-optical efficiency was obtained. The laser emission performances under quasi-continuous wave pumping are presented as well, for both c-cut and a-cut crystals. Passive Q-switching was investigated with a semiconductor saturable absorber mirror (SESAM). Laser pulses with 2.2 µJ energy and 32.8 ns durations were recorded from a-cut Nd:LGSB. The average output power reached 0.36 W at 1.55 W absorbed pump power. Passive mode-locking with SESAM was achieved in a long Z-type resonator. Ultrashort pulses with 0.19 W average power, 1.63 nJ energy, and 1.43 ps pulse duration, at 118 MHz repetition rate, are demonstrated for the a-cut Nd:LGSB medium. Full article

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

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12 pages, 25446 KiB

Open AccessArticle

Design of a 2 × 4 Hybrid MMI-MZI Configuration with MMI Phase-Shifters

by Boris B. Niraula and Conrad Rizal

Materials 2019, 12(9), 1555; https://doi.org/10.3390/ma12091555 - 12 May 2019

Cited by 3 | Viewed by 4608

Abstract

This paper reports design of a 2 × 4 hybrid multimode interferometer-Mach-zehnder interferometer (MMI-MZI) configuration consiting of compact thermo-optical switches on the silicon-on-insulator (SOI) platform. The device consists of two identical MMI slab waveguides as power splitters and couplers that are connected with [...] Read more.

This paper reports design of a 2 × 4 hybrid multimode interferometer-Mach-zehnder interferometer (MMI-MZI) configuration consiting of compact thermo-optical switches on the silicon-on-insulator (SOI) platform. The device consists of two identical MMI slab waveguides as power splitters and couplers that are connected with two identical MMI-based phase shifters, and linear tapers at both ends of the MMIs to minimize the power coupling loss. A thin Al pad is used as a heating element and a trench is created around this pad to prevent heat from spreading, and to minimize loss. The calculated average thermo-optical switching power consumption, excess loss, and power imbalance are 1.4 mW, 0.9 dB, and 0.1 dB, respectively. The overall footprint of the device is 6 × 304

μ m^{2}

. The new heating method has advantages of compact size, ease of fabrication on SOI platform with the current CMOS technology, and offers low excess loss and power consumption as demanded by devices based on SOI technology. The device can act as two independent optical switches in one device. Full article

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

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16 pages, 8781 KiB

Open AccessArticle

Applications of Copolymers Consisting of 2,6-di(9H-carbazol-9-yl)pyridine and 3,6-di(2-thienyl)carbazole Units as Electrodes in Electrochromic Devices

by Chung-Wen Kuo, Jui-Cheng Chang, Yu-Ting Huang, Jeng-Kuei Chang, Li-Ting Lee and Tzi-Yi Wu

Materials 2019, 12(8), 1251; https://doi.org/10.3390/ma12081251 - 16 Apr 2019

Cited by 11 | Viewed by 2921

Abstract

A series of carbazole-based polymers (PdCz, P(dCz2-co-dTC1), P(dCz2-co-dTC2), P(dCz1-co-dTC2), and PdTC) were deposited on indium tin oxide (ITO) conductive electrodes using electrochemical polymerization. The as-prepared P(dCz2-co-dTC2) displayed a high ΔT (57.0%) and multichromic behaviors [...] Read more.

A series of carbazole-based polymers (PdCz, P(dCz2-co-dTC1), P(dCz2-co-dTC2), P(dCz1-co-dTC2), and PdTC) were deposited on indium tin oxide (ITO) conductive electrodes using electrochemical polymerization. The as-prepared P(dCz2-co-dTC2) displayed a high ΔT (57.0%) and multichromic behaviors ranging from yellowish green, greenish gray, gray to purplish gray in different redox states. Five organic electrochromic devices (ECDs) were built using dCz- and dTC-containing homopolymers and copolymers as anodic materials, and poly(3,4-(2,2-dimethylpropylenedioxy)thiophene) (PProdot-Me₂) as the cathodic material. The P(dCz2-co-dTC2)/PProdot-Me₂ ECD presented remarkable electrochromic behaviors from the bleached to colored states. Moreover, P(dCz2-co-dTC2)/PProdot-Me₂ ECD displayed a high optical contrast (ΔT, 45.8%), short switching time (ca. 0.3 s), high coloration efficiency (528.8 cm² C⁻¹) at 580 nm, and high redox cycling stability. Full article

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

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Review

Jump to: Research, Other

15 pages, 938 KiB

Open AccessEditor’s ChoiceReview

A Review of Polarization-Sensitive Materials for Polarization Holography

by Yueyang Zhai, Li Cao, Ying Liu and Xiaodi Tan

Materials 2020, 13(23), 5562; https://doi.org/10.3390/ma13235562 - 6 Dec 2020

Cited by 45 | Viewed by 4332

Abstract

Polarization holography has the unique capacity to record and retrieve the amplitude, phase, and polarization of light simultaneously in a polarization-sensitive recording material and has attracted widespread attention. Polarization holography is a noteworthy technology with potential applications in the fields of high-capacity data [...] Read more.

Polarization holography has the unique capacity to record and retrieve the amplitude, phase, and polarization of light simultaneously in a polarization-sensitive recording material and has attracted widespread attention. Polarization holography is a noteworthy technology with potential applications in the fields of high-capacity data storage, polarization-controlled optical elements, and other related fields. The choice of its high-performance materials is particularly important. To further develop polarization holography applications and improve the quality of the information recorded (i.e., material sensitivity and resolution), a deeper understanding of such materials is needed. We present an overview of the polarization-sensitive materials, which introduced polarization holographic technology and the development of polarization holographic materials. The three main types of polarization holographic materials are described, including azopolymer materials, photopolymer material, and photorefractive polymer material. We examine the key contributions of each work and present many of the suggestions that have been made to improve the different polarization-sensitive photopolymer materials. Full article

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

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Other

Jump to: Research, Review

7 pages, 1367 KiB

Open AccessLetter

A 33.2 W High Beam Quality Chirped-Pulse Amplification-Based Femtosecond Laser for Industrial Processing

by Zhenao Bai, Zhenxu Bai, Xiaolong Sun, Yong Liang, Kun Wang, Duo Jin and Zhongwei Fan

Materials 2020, 13(12), 2841; https://doi.org/10.3390/ma13122841 - 24 Jun 2020

Cited by 9 | Viewed by 3123

Abstract

A photonic crystal fiber-based chirped pulse amplification delivering 272 fs pulses of 66.4 µJ energy at a repetition rate of 500 kHz is presented, resulting in an average/peak power of 33.2 W/244 MW. A single grating is adopted for the pulse width stretching [...] Read more.

A photonic crystal fiber-based chirped pulse amplification delivering 272 fs pulses of 66.4 µJ energy at a repetition rate of 500 kHz is presented, resulting in an average/peak power of 33.2 W/244 MW. A single grating is adopted for the pulse width stretching and compression, which leads to high-compactness and low cost of the system. The output beam is near-diffraction-limited (M² = 1.1 ± 0.05) with a power stability better than 0.5%. The cutting of alumina ceramic substrate and flexible printed circuit are demonstrated by using the laser system. The results indicate that the laser is competent for industrial applications. Full article

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

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