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Optical Engineering

Laser backlight unit based on a leaky optical fiber
Author(s): Yuuto Okuda; Kousuke Onoda; Ichiro Fujieda
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Paper Abstract

A backlight unit is constructed by laying out an optical fiber on a two-dimensional plane and letting the light leak out in a controlled manner. In experiment, we formed multiple grooves on the surface of a plastic optical fiber by pressing a heated knife edge. The depth of the groove determined the percentage of the optical power leaking out. The optical fiber with multiple grooves was embedded in an acrylic plate with a spiral trench, and a diffuser sheet was placed over it. When we injected laser light into the end of the optical fiber, this configuration successfully worked as an area illuminator. However, the coherent nature of the laser light caused severe speckle noise. We evaluated the speckle contrast under darkness, and it varied from 80% to 23%, depending on the lens aperture used to capture the images of the illuminator. We glued an ultrasound generator to the optical fiber to introduce phase modulation for the light propagating inside the optical fiber. In this way, the speckle contrast was reduced by a factor of seven to four. Under room lighting, the speckle noise was made barely noticeable by turning on the ultrasound generator.

Paper Details

Date Published: 5 July 2012
PDF: 9 pages
Opt. Eng. 51(7) 074001 doi: 10.1117/1.OE.51.7.074001
Published in: Optical Engineering Volume 51, Issue 7
Show Author Affiliations
Yuuto Okuda, Ritsumeikan Univ. (Japan)
Kousuke Onoda, Ritsumeikan Univ. (Japan)
Ichiro Fujieda, Ritsumeikan Univ. (Japan)

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