6 December 2002 Eye-safe collimated laser emitter for optical wireless communications
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Proceedings Volume 4873, Optical Wireless Communications V; (2002) https://doi.org/10.1117/12.455517
Event: ITCom 2002: The Convergence of Information Technologies and Communications, 2002, Boston, MA, United States
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).
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Pablo Benitez, Juan Carlos Minano, Francisco J. Lopez, Dioen Biosca, Ruben Mohedano, Mabel Labrador, Fernando Munoz, Kazutoshi Hirohashi, Masahisa Sakai, "Eye-safe collimated laser emitter for optical wireless communications", Proc. SPIE 4873, Optical Wireless Communications V, (6 December 2002); doi: 10.1117/12.455517; https://doi.org/10.1117/12.455517
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