Optical waveguides – With optical coupler – Input/output coupler
Patent
1996-10-18
1998-08-18
Ngo, John
Optical waveguides
With optical coupler
Input/output coupler
385 43, 385901, 385146, G02B 626
Patent
active
057968926
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a waveguide for the transmission of guided radiation from a medium with a high refraction index to a medium with a lower refraction index, in particular to delivery of concentrated sunlight into a solar receiver. It may be also used in radio telescopes, fiber optics waveguides, etc.
BACKGROUND OF THE INVENTION
The concentration of radiation, for example in the context of solar energy utilization, is limited by the conservation of space law (W. T. Welford and R. Winston High Collection Non-Imaging Optics Chapter 3, Academic Press, New York, 1989). Thus rotationally symmetric optical systems can achieve a maximum concentration ratio of ##EQU1## where .theta. is the maximum angle to the optical axis subtended by the incoming radiation and n is the index of refraction of the medium. In a high index transparent material such as glass or fused silica (n.apprxeq.1.45) the maximum concentration is therefore roughly twice as high as in air (n.apprxeq.1). However, if finally this radiation is to be extracted into air, this advantage is lost due to total internal reflection at the interface. Total internal reflection, on the other hand, can be used to guide part of this maximally concentrated radiation in a waveguide. If however, the light guide is terminated simply by a cut perpendicular to the axis, again part of the radiation undergoes total internal reflection and is lost. There thus exists a problem to extract the light from the light guide, without increasing its diameter, in such a manner that losses are minimized. The diameter should not be increased in order to be able to use the light guide to deliver radiation into a cavity receiver of given aperture.
When radiation is delivered from a source to the receiver, it is often desirable, especially in the field of solar energy, to provide on the receiver an as high as possible power density so as to maximize the efficiency of energy transfer from or energy conversion by the receiver. It is, therefore, advantageous to use a relatively small receiver chamber with a relatively small aperture, in association with suitable optical concentration systems and waveguides for transferring the concentrated radiation from a source to a receiver.
It is accordingly the object of the present invention to provide an improved wave guiding method and means for the effective extraction of radiation from a transparent delivery medium with a high index of refraction into a receiving medium with a lower index of refraction.
SUMMARY OF THE INVENTION
In the following description and claims the term "guided radiation" means a radiation propagating in a controllable fashion. The term "receiver chamber" is used to designate a chamber into which concentrated radiation is delivered by extraction from a waveguide regardless of the manner in which the extracted radiation behaves inside the chamber. The term "transparent" means that a given medium transmits the radiation under consideration.
In accordance with the invention there is provided a method of delivering guided radiation arriving via a first transparent medium having a first refraction index n.sub.1,into a second transparent medium having a second refraction index n.sub.2 that is smaller than n.sub.1,comprising providing a transparent radiation delivery waveguide having a longitudinal axis and a third refraction index n.sub.3 substantially equal to or greater than n.sub.1 and adapted to guide said radiation along said longitudinal axis, said waveguide having a tapered radiation delivery portion of non-circular cross-sectional shape, mounting said waveguide in optical contact with said first transparent medium and so that said radiation delivery portion projects inside said second transparent medium, and causing said first transparent medium to take up radiation whereby radiation transmitted by the waveguide is extracted therefrom through the radiation delivery portion into the second transparent medium.
The guided radiation delivered in accordance with the invention from a first
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Karni Jacob
Krupkin Vladimir
Ries Harald
Segal Akiba
Yogev Amnon
Ngo John
Yeda Research and Development Co. Ltd.
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