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Proceedings Paper

Eye-safe collimated laser emitter for optical wireless communications
Author(s): Pablo Benitez; Juan Carlos Minano; Francisco J. Lopez; Dioen Biosca; Ruben Mohedano; Mabel Labrador; Fernando Munoz; Kazutoshi Hirohashi; Masahisa Sakai
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Paper Abstract

In this work we present laser-based novel devices that maximize the emitted power for constant eye safety level and beam divergence angle, i.e., without affecting the eye safety classification or the necessary tracking accuracy. This is achieved by breaking the spatial coherence of the beam, which allows the system to be considered as an extended light source. The system comprises a laser, a diffuser, a collimator and, sometimes, other optical elements. As an example, one of the devices is composed of a laser, a Lambertian reflective-type diffuser, and a single-piece reflective-refractive collimator of 20 mm aperture and ultra-high numerical aperture (NA = 1.43), which re-collimates the radiation into 3.5 deg. (full angle). According to the IEC 60825-1:1993 (amendment 2, 2001-01), the Accessible Emission Limit (AEL) (Class 1, wavelength λ = 780 nm, exposure T = 30000 s) for this device is 35.9 times greater than that of a laser with the same divergence angle (15.6 dB), i.e., this device is allowed to emit 35.9 times more power than that of the laser alone with the same divergence angle. The switching time, the beam divergence and the eye safety classification remain the same. This power gain varies with the design conditions. In the cases analyzed it goes from = 8.4 (9.24dB) to 551.3 (27.4 dB).

Paper Details

Date Published: 6 December 2002
PDF: 11 pages
Proc. SPIE 4873, Optical Wireless Communications V, (6 December 2002); doi: 10.1117/12.455517
Show Author Affiliations
Pablo Benitez, Univ. Politecnica de Madrid (Spain)
Juan Carlos Minano, Univ. Politecnica de Madrid (Spain)
Francisco J. Lopez, Univ. Politecnica de Madrid (Spain)
Dioen Biosca, Univ. Politecnica de Madrid (Spain)
Ruben Mohedano, Univ. Politecnica de Madrid (Spain)
Mabel Labrador, Univ. Politecnica de Madrid (Spain)
Fernando Munoz, Univ. Politecnica de Madrid (Spain)
Kazutoshi Hirohashi, HITS Labs., Inc. (Japan)
Masahisa Sakai, HITS Labs. (Japan)


Published in SPIE Proceedings Vol. 4873:
Optical Wireless Communications V
Eric J. Korevaar, Editor(s)

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