Mr. Wing Shing Cheung Profile

Wing Shing Cheung

at Univ of Hong Kong

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Proceedings Article | 8 March 2016 Paper

Emission characteristics of light-emitting diodes by confocal microscopy

W. S. Cheung, H. W. Choi

Proceedings Volume 9768, 97680K (2016) https://doi.org/10.1117/12.2213111

KEYWORDS: Light emitting diodes, Confocal microscopy, Microscopes, Goniophotometry, Spatial resolution, Objectives, Light sources, Distance measurement, Near field optics, Sensors, Optical testing, Optical microscopy

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The emission profiles of light-emitting diodes have typically be measured by goniophotometry. However this technique suffers from several drawbacks, including the inability to generate three-dimensional intensity profiles as well as poor spatial resolution. These limitations are particularly pronounced when the technique is used to compared devices whose emission patterns have been modified through surface texturing at the micrometer and nanometer scales,. In view of such limitations, confocal microscopy has been adopted for the study of emission characteristics of LEDs. This enables three-dimensional emission maps to be collected, from which two-dimensional cross-sectional emission profiles can be generated. Of course, there are limitations associated with confocal microscopy, including the range of emission angles that can be measured due to the limited acceptance angle of the objective. As an illustration, the technique has been adopted to compare the emission profiles of LEDs with different divergence angles using an objective with a numerical aperture of 0.8. It is found that the results are consistent with those obtained by goniophotometry when the divergence angle is less that the acceptance angle of the objective.

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