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Manufacturable, High Directivity Input/Output for Coupler For Integrated Optics

IP.com Disclosure Number: IPCOM000119228D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 3 page(s) / 112K

Publishing Venue

IBM

Related People

Agrawal, N: AUTHOR [+2]

Abstract

Several proposals have been made to produce heads for optical storage drives using integrated optics (1). They have the advantages of being small, robust and simpler to fabricate than heads made of conventional optical components. One of the key issues in optical heads is the process of coupling light from the integrated head to the optical disk and back again. It is important that this process be very efficient and that it not distort the wavefront or the beam polarization.

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Manufacturable, High Directivity Input/Output for Coupler For Integrated
Optics

      Several proposals have been made to produce heads for
optical storage drives using integrated optics (1).  They have the
advantages of being small, robust and simpler to fabricate than heads
made of conventional optical components.  One of the key issues in
optical heads is the process of coupling light from the integrated
head to the optical disk and back again.  It is important that this
process be very efficient and that it not distort the wavefront or
the beam polarization.

      Current proposals use grating couplers for the input and output
coupling.  These couplers have several limitations for optical
storage in terms of their efficiency, induced aberrations, and
polarization sensitivity.  The efficiency of a simple grating coupler
is limited by the fact that, typically, half the light is diffracted
into the substrate where it is lost.  We refer to the ratio of the
light coupled out of the waveguide in the radiation mode to the total
diffracted intensity as the directivity of the coupler.  Thus,
typical couplers will have a directivity of roughly one-half, whereas
directivities close to unity will be required for optical storage
applications.  To overcome this, one can resort to blazed grating
structures.  However, these are difficult to manufacture and control
accurately, especially for cases where the grating period is varying,
as is the case in a focussing grating coupler that would be desirable
for optical storage.  Furthermore, once the period is selected, the
entire structure is fixed.  This means that the coupling coefficient
and the polarization properties are fixed and the structure cannot be
optimized for these parameters.

      Many of these limitations can be overcome by using a reflective
dielectric stack on the substrate to reflect the light diffracted
toward the substrate back up out...