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Integrated Optic Head With a Gradient-Index Coupler

IP.com Disclosure Number: IPCOM000037210D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Rubin, KA: AUTHOR [+2]

Abstract

A waveguide output coupler for an integrated optical head is disclosed in which the efficiency of coupling and diffraction angle across the aperture are independently adjustable. This creates a more desirable distribution of illumination across the focusing coupler aperture and permits more nearly diffraction-limited performance.

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Integrated Optic Head With a Gradient-Index Coupler

A waveguide output coupler for an integrated optical head is disclosed in which the efficiency of coupling and diffraction angle across the aperture are independently adjustable. This creates a more desirable distribution of illumination across the focusing coupler aperture and permits more nearly diffraction-limited performance.

Integrated optical pickup devices using optical waveguides and focusing grating couplers are being considered for use in optical storage files. The couplers are typically fabricated by forming gratings in a layer on top of the waveguide layer, for example, in a SiN layer on a 7059 glass waveguide, by either electron beam or holographic exposure of a photoresist and subsequent development and etching. This process creates a surface relief grating. The angle into which the light is diffracted is governed by the spacing of the grating grooves, and the efficiency of the diffraction into that angle is governed by the depth of the grooves and the refractive index difference between the grating material and the surrounding medium, which is usually air. Devices which have been made to date have constant index difference and a constant groove depth which results from etching through the thickness of the grating layer. Therefore, the coupling of light out of the waveguide is essentially constant across the aperture, resulting in an effective nonuniform illumination of the aperture; that is, the illumination exiting any given point in the aperture is a function of the illumination reaching that point which decreases with distance from the leading edge. Control of the illumination distribution is desired so the spot can be focused into a more circularly symmetric and smaller size spot. It is well known that if the groove depth could be varied, then the diffraction efficiency along the grating could be controlled in a predetermined manner. No techniques have been reported to date to produce and control a variation in the depth of the grooves.

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