Browsing by Author "Tu, C. W."

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Composite metal substrate for thin film AlGaInP LED applications
(2019-04-15)
Horng, R. H.
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Sinha, Shreekant
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Lee, C. P.
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Feng, H. A.
;
Chung, C. Y.
The fabrication and feasibility assessment of n-side up, thin-epilayer, AlGaInPbased vertical light-emitting-diodes (LEDs; emitting area: 1 mm x 1 mm) with a copperinvar-copper-composite metal (CIC) substrate was obtained by wafer bonding and epilayer transferring technologies. The structure of CIC substrate is a top Cu layer of 20 mu m, a middle Invar layer of 64 mu m, and a bottom Cu layer of 20 mu m. The invar layer consists of Fe and Ni at a ratio of 70% to 30%. The coefficient of thermal expansion for CIC is about 6.1 x 10(-6) /K, which is similar to that of the GaAs substrate (5.7 x 10(-6)/K) and AlGaInP epilayers. Due to the high thermal conductivity (160 W/m-K) of 10(4)-mu m-thick CIC, the high performances of the packaged LEDs are obtained. They present a low red shift phenomenon (from 623 to 642 nm for 100 mA to 1 A) and a high output power 212 mW at 800 mA. The CIC substrate can be extended to fabricate high-efficiency thin film LEDs with conventional vertical electrodes. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Exploring elliptical vortex beams with the spatial damping effect
(2019-02-15)
Chen, Y. F.
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Hsieh, M. X.
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Lai, Y. H.
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Hsieh, Y. H.
;
Tu, C. W.
A general integral formula is analytically derived to represent the wave function of elliptical vortex modes. The derived formula can be straightforwardly employed to take account of spatial damping to explore vortex structure. Spatial damping is found to cause the central degenerate singularity of the circular vortex mode to be split into several singularities with different topological charges. For the non-circular vortex beam, the influence of spatial damping on the distribution of singularities is not significant. Theoretical analyses are confirmed to agree very well with the experimental measurements. (C) 2019 Optical Society of America
Wave representation for asymmetric elliptic vortex beams generated from the astigmatic mode converter
(2019-04-15)
Chen, Y. F.
;
Lai, Y. H.
;
Hsieh, M. X.
;
Hsieh, Y. H.
;
Tu, C. W.
An analytical wave representation is derived to express the asymmetric elliptic vortex beams generated by using an astigmatic mode converter to transform the asymmetric Hermite-Gaussian modes. The effect of the spatial asymmetry on the elliptic vortex beam can be straight forwardly considered in the analytical wave representation. A detailed comparison with experimental intensity patterns and phase structures is made. The good agreement between experimental results and theoretical analyses confirms the characterization and generation of the asymmetric elliptic vortex beams. (C) 2019 Optical Society of America