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Coupling a LED Array to Optical Fibers

IP.com Disclosure Number: IPCOM000087450D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Lean, EG: AUTHOR

Abstract

One of the limitations in coupling light from a GaAs light-emitting diode (LED) to an optical fiber is the trapping of the light within the LED by total internal reflection at the interface. In discrete devices, the interface has been formed with a hemispherical surface to increase the emission and to more or less collimate the exiting light.

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Coupling a LED Array to Optical Fibers

One of the limitations in coupling light from a GaAs light-emitting diode (LED) to an optical fiber is the trapping of the light within the LED by total internal reflection at the interface. In discrete devices, the interface has been formed with a hemispherical surface to increase the emission and to more or less collimate the exiting light.

If the diodes are to be fabricated as a matrix array on a common substrate, it is extremely difficult to form an individual lens on each LED by mechanical or chemical means because the lens is not a planar structure.

Therefore, a Fresnel grating is fabricated in the planar interface surface between the air and each of the individual LED junctions. The geometry of the grating is chosen such that substantially all of the light impinging on the grating is either collimated or converged to fill the core of the optical fiber to which it is to be coupled. This not only increases the total emission of the LED by surface roughening, but also by providing a controlled periodic roughening, viz, Fresnel grating, the numerical aperture of the LED may be matched to that of the optical fiber for maximum coupling efficiency.

The grating may be etched through use of masks and preferential chemical etching to control the grating geometry.

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