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High Numerical Aperture Optical Head using an Ellipsoidal Reflector

IP.com Disclosure Number: IPCOM000107594D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Lean, EG: AUTHOR

Abstract

Disclosed is a high numerical aperture (NA) optical head arrangement based on an ellipsoidal reflector. The concept of the ellipsoidal reflector, as shown in Fig. 1 (only the elliptical cross section in the xy plane is shown), is based on the definition that the sum of the distance from each point in the ellipsoidal surface to the foci is a constant. Each ray from one of the focal points will be reflected by the surface and ends at the other focal point after having travelled a constant path length. This eliminates spherical aberration for all the rays inside the ellipsoidal reflector. The application of this ellipsoidal reflector to an optical storage head results in unexpected advantages in getting an aberration-free, high NA, and low profile, focusing and bending optical element for the head design.

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High Numerical Aperture Optical Head using an Ellipsoidal Reflector

       Disclosed is a high numerical aperture (NA) optical head
arrangement based on an ellipsoidal reflector.  The concept of the
ellipsoidal reflector, as shown in Fig. 1 (only the elliptical cross
section in the xy plane is shown), is based on the definition that
the sum of the distance from each point in the ellipsoidal surface to
the foci is a constant. Each ray from one of the focal points will be
reflected by the surface and ends at the other focal point after
having travelled a constant path length.  This eliminates spherical
aberration for all the rays inside the ellipsoidal reflector.  The
application of this ellipsoidal reflector to an optical storage head
results in unexpected advantages in getting an aberration-free, high
NA, and low profile, focusing and bending optical element for the
head design.

      As shown in Fig. 2, a beam with a divergent angle P1 is
reflected by a mirror located in the bottom of the head, back to the
ellipsoidal surface.  The location of the focus of the input beam is
put in the mirror image of one of the foci of the ellipsoid above the
horizontal mirror.  This arrangement allows the input beam to enter
from above.  The rays reflected by the ellipsoidal surface is then
focused with an angle P2 at the other focal point of the ellipsoid. A
MO disk is located in the horizontal axes of the ellipsoid (parallel
to the bottom of the head) to be addressed by the focused spot.

      The input beam to the ellipsoidal reflector head can be
collimated be...