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Now showing 1 - 10 of 47

Polarization control of GaN-based micro-caivty lasers with top high-contrast grating reflectors
(2019-01-01)
Chang, Tsu-Chi
;
Hong, Kuo-Bin
;
Kuo, Shiou-Yi
;
Lu, Tien-Chang
;
光電工程學系
We reported on GaN micro-cavity (MC) lasers combining one rigid TiO2 high-contrast grating (HCG) structure as the output mirror. HCG structure was made directly on the GaN without an airgap, designed to yield high reflectance for transverse magnetic (TM) or transverse electric (TE) polarized light. The laser emission was TM polarized with a degree of polarization of 99.2% and had a small divergence angle of 14 degrees (full width at half maximum), under pulsed optical pumping at room temperature. This demonstration of laser operation for the GaN-based MC with an HCG fully exhibited advantages of HCGs for applications in semiconductor lasers at the wavelength from green to ultraviolet regimes.
Plasmonic nanolasers based on graphene-insulator-metal platform
(2019-01-01)
Li, Heng
;
Hong, Kuo-Bin
;
Hsu, Chu-Yuan
;
Huang, Zhen-Ting
;
Lu, Tien-Chang
As the development of nanoscale optics, the ability of surface plasmons to break the diffraction limit receives numerous attention from researchers. In this work, we demonstrate a graphene-insulator-metal (GIM) nanolaser structure. The graphene can modify the permittivity of metal films which would further influence the nanolasers characteristics.
Low Coherence Illumination of Flexible Perovskite Random Lasers
(2018-01-01)
Wang, Yu-Chi
;
Hong, Yu-Heng
;
Hong, Kuo-Bin
;
Kao, Tsung-Sheng
;
Lu, Tien-Chang
We demonstrated that the methylammonium metal-halide perovskites can be exploited as a random laser source for the advanced speckle-free imaging Furthermore, the lasing performance can be actively controlled via the mechanical modulation of supporting substrates.
Mode-switching phenomena in periodic InGaN-based hexagon microcavity array
(2018-01-01)
Huang, Chia-Yen
;
Dai, Tzu-Ying
;
Lin, Jing-Jie
;
Chang, Tsu-Chi
;
Liu, Che-Yu
The lasing behavior of InGaN-based microcavity array was strongly relevant to the excitation area. The stronger rod-to-rod optical interaction between the fundamental axial mode resulted its dominance in the collective lasing behavior.
Full-Spectrum Analysis of Perovskite-Based Surface Plasmon Nanolasers
(2020-03-29)
Cheng, Pi-Ju
;
Zheng, Qi-Yan
;
Hsu, Chu-Yuan
;
Li, Heng
;
Hong, Kuo-Bin
We systematically studied the characteristics of hybrid perovskite-based surface plasmon nanolasers. If one changes the anion composition of perovskites, the emission wavelength can be easily tuned. We conducted in full-spectrum modeling that featured hybrid perovskite nanowires placed on different SiO2-coated metallic (Au, Ag, and Al) plates. The proposed nanocavities that supported plasmonic gap modes exhibited distinguished properties of nanolasers, such as low-transparency threshold-gain and low lasing threshold. The corresponding experimental results for the MAPbBr(3) nanolaser on Ag revealed the low-threshold operation. These superior features were attributed to enhanced light-matter interaction with strong coupling. Therefore, the proposed scheme, integrated with hybrid perovskite as gain material, provides an excellent platform for nanoscale plasmon lasing in the visible to near-infrared spectra.
Electrically Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers with TiO2 High-Index-Contrast Grating Reflectors
(2020-04-15)
Chang, Tsu-Chi
;
Hashemi, Ehsan
;
Hong, Kuo-Bin
;
Bengtsson, Jorgen
;
Gustaysson, Johan
We demonstrate the first electrically injected GaNbased vertical-cavity surface-emitting lasers (VCSELs) with a TiO2 high-index-contrast grating (HCG) as the top mirror. Replacing the top distributed Bragg reflector (DBR) with an HCG offers substantial thickness reduction, polarization-pinning, and setting of the resonance wavelength by the grating parameters. Conventional HCGs are usually suspended in the low refractive index material, such as air, in order to create the largest refractive index contrast. However, the mechanical stability of such structures can be questioned and creating free-hanging GaN-membrane on top of GaN is problematic. We have therefore fabricated TiO2-HCGs resting directly on GaN without an air-gap. No DBR layers are used below the HCG to boost the reflectivity. A VCSEL with an aperture diameter of 10 mu m shows a threshold current of 25 mA under pulsed operation at room temperature. The lasing modes locate around 400 nm and are transversely electrically -polarized with a line width of 0.5 nm. The full-width half-maximum beam divergence is 10 degrees. This demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as postgrowth setting of the resonance wavelength.
Anti-guiding and guiding effects in GaN-based vertical-cavity surface-emitting lasers
(2020-02-01)
Chen, Lih-Ren
;
Chen, Bo-Yan
;
Kuo, Shiou-Yi
;
Hong, Kuo-Bin
;
Lu, Tien-Chang
We study the lateral optical confinement effect on the performance and lasing characteristics of GaN-based vertical-cavity surface-emitting lasers (VCSELs). The anti-guiding and guiding structures are designed by calculating the effective refractive index difference of active and cladding regions. By varying the compensation layer configuration and thickness, the designed effective refractive index of the active region is 0.44% higher than peripheral for the guiding structure. The threshold current density of VCSEL with the guiding structure is 25.4 kA/cm(2), which is almost half of that with the anti-guiding structure showing 53.5 kA/cm(2). For the anti-guiding structure, the signals from both active and cladding regions are observed by the far-field angle-resolved spectrum at 1.4 x I-th driving current, which agrees well with our simulation. Throughout the study, we show the advantage of the guiding structure both theoretically and experimentally. Moreover, an effective guiding structure is obtained by a proper design and simple device process, which will be very promising for mass production.
Low threshold current photonic crystal surface emitting lasers with beam modulation capability
(2019-01-01)
Chen, Lih-Ren
;
Chiu, Han-Lun
;
Hong, Kuo-Bin
;
Lu, Tien-Chang
;
交大名義發表
We proposed a GaAs-based photonic crystal surface emitting laser with naturally formed periodic structures on the ITO top cladding layer. Low threshold current density and ability of beam modulation have been demonstrated. (C) 2019 The Author(s)
Plasmonic Nanolasers Enhanced by Hybrid Graphene-Insulator-Metal Structures
(2019-08-01)
Li, Heng
;
Li, Jhu-Hong
;
Hong, Kuo-Bin
;
Yu, Min-Wen
;
Chun, Yi-Cheng
Graphene is a two-dimensional (2D) structure that creates a linear relationship between energy and momentum that not only forms massless Dirac fermions with extremely high group velocity but also exhibits a broadband transmission from 300 to 2500 nm that can be applied to many optoelectronic applications, such as solar cells, light-emitting devices, touchscreens, ultrafast photodetectors, and lasers. Although the plasmonic resonance of graphene occurs in the terahertz band, graphene can be combined with a noble metal to provide a versatile platform for supporting surface plasmon waves. In this study, we propose a hybrid graphene-insulator-metal (GIM) structure that can modulate the surface plasmon polariton (SPP) dispersion characteristics and thus influence the performance of plasmonic nanolasers. Compared with values obtained when graphene is not used on an Al template, the propagation length of SPP waves can be increased 2-fold, and the threshold of nanolasers is reduced by 50% when graphene is incorporated on the template. The GIM structure can be further applied in the future to realize electrical control or electrical injection of plasmonic devices through graphene.
Flexible Organometal-Halide Perovskite Lasers for Speckle Reduction in Imaging Projection
(2019-05-01)
Wang, Yu-Chi
;
Li, Heng
;
Hong, Yu-Heng
;
Hong, Kuo-Bin
;
Chen, Fang-Chung
Disorder is emerging as a strategy for fabricating random laser sources with very promising materials, such as perovskites, for which standard laser cavities are not effective or too expensive. We need, however, different fabrication protocols and technologies for reducing the laser threshold and controlling its emission. Here, we demonstrate an effectively solvent-engineered method for high-quality perovskite thin films on a flexible polyimide substrate. The fractal perovskite thin films exhibit excellent optical properties at room temperature and easily achieve lasing action without any laser cavity above room temperature with a low pumping threshold. The lasing action is also observed in curved perovskite thin films on flexible substrates. The lasing threshold can be further reduced by increasing the local curvature, which modifies the scattering strengths of the bent thin film. We also show that the curved perovskite lasers are extremely robust with respect to repeated deformations. Because of the low spatial coherence, these curved random laser devices are efficient and durable speckle-free light sources for applications in spectroscopy, bioimaging, and illumination.

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