We present a novel freeform lens design method for an application to LED collimating illumination. The method is derived from a basic geometric-optics analysis and construction approach. By using this method, a compact collimated lenses with Aspect Ratio = 0.219 is presented. Moreover, the utility efficiency (UE) inside the angle defined by ideal concentrator hypothesis with different lens-to-LED size ratios for both this lens and TIR lens are presented. A prototype of the collimator lens is also made to verify the practical performance of the lens, which has light distribution very compatible with the simulation results.
KEYWORDS: 3D modeling, Tolerancing, Light emitting diodes, Error analysis, 3D imaging standards, Monte Carlo methods, Ray tracing, Sun, Optical simulations, Performance modeling
This paper presented a general concentration standard index (GCSI) for 3D TIR lenses, which is introduced as a metric for analyzing the luminous intensity at certain angle, both locally and globally. A Three- Dimensional (3D) slope error tolerance model for TIR lens is constructed and the slope error sensitivities for luminous intensity for different angels are derived. How the slope error impact on the angular candela distribution is obtained with calculation of the slope error impact on the Beam angle (the Full Width at Half Maximum luminous intensity (FWHM)) and the Filed Angle (the Full Width at 10% Maximum luminous intensity). The results revealed that the Beam Angle is decreased at first and then increased with the increased slope error, whereas the Filed angle is monotonically increasing with the slope errors. According theory has been well demonstrated with Monte Carlo ray tracing due to RMS uniformity as low as 1.8% for Beam angle and 2.23% for Filed angle.
This work provides a design and optimization method for total internal reflection (TIR) lenses based on slope-error tolerance analysis. This work focuses on how the slope error impacts the central luminous intensity (CLI) of a TIR lens. The concentration standard index (CSI) is introduced as a metric for analyzing the CLI, both locally and globally. A unique design method for improved manufacturing tolerance is introduced, and a way of optimizing the TIR lens design in order to achieve a better slope-error tolerance is presented by evaluating the CSI. Using the design method, a TIR lens is fabricated and this theoretical approach is then demonstrated by a comparison between the tested contours of the TIR surfaces.
High power GaN-based LEDs with nano-structured Ga-doped ZnO (GZO) transparent conductive layer (TCL) were
fabricated by using metal-organic chemical vapor deposition (MOCVD) method. Compared with the conventional LED
with Ni/Au or ITO process, the saturation current in the LEDs with GZO TCL approximately increased up to more than
14 % and 13 %, and the light output intensity up to 57.5 % and 30.1 %, respectively. This improvement was attributed to
the high carrier concentration of GZO TCL and the planar structure at the TCL bottom, which improved the electrical
conductivity, and therefore promoted current spreading. The refractive index of GZO is similar to GaN (n ≈ 2) and
thereby results in the reduction of the reflection loss between GaN and TCL interface. In addition, the nano-structure of
GZO TCL increased the light output critical angle and enhanced surface light emitting while reducing the lateral light
loss and consequently improved light extraction efficiency of LEDs.
Terahertz (THz) emission from ZnSe and ZnTe nano dots and nano gratings is experimentally studied compared with that
from <111> orientation bulk ZnSe and <110> orientation bulk ZnTe. These nano dots and nano gratings are fabricated by
the femtosecond laser ablation technique. Three main mechanisms coexist in the THz radiation from ZnSe and ZnTe
surface nano structures as the same as from bulk sample: current surge effect (drift current), Photo Dember effect
(diffusion current), and optical rectification. Moreover, it is found that nano structures not only contribute to an
enhancement of THz emission, but also increase the threshold of polarity reversal of THz wave, and widen the spectrum
of THz radiation. We also observe a two-fold symmetry in rotating pump polarization angle from ZnTe nano gratings,
which is completely different from the three-fold symmetry observed from bulk ZnTe.
We showed a detailed thermal simulation of an Epi-down flip-chip packaged LED. Simulation results show that chip attachment defects can cause significant thermal gradients across the active layer of chip, leading to premature failures.
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