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Circularization of Laser Beam with Large Aspect Ratio using Single Optical Element

IP.com Disclosure Number: IPCOM000115798D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Dickson, LD: AUTHOR [+2]

Abstract

The laser used in nearly all optical storage systems today is the GaAs laser, which has a beam aspect ratio on the order of 3:1. Such a beam can be circularized by using a prism and an angle of incidence of approximately 75 degrees. However, there is a great deal of interest today in shorter wavelength lasers for optical storage applications. The most promising short wavelength laser is the GaAIInP laser, with a wavelength of 670 nm. The beam aspect ratio for this laser is on the order of 4.5:1. Circularization of such a beam with a single prism would require an angle of incidence of about 82 degrees. It would be very difficult to get the incident surface coated to the required transmission and reflection specifications for such a large angle of incidence.

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Circularization of Laser Beam with Large Aspect Ratio using Single
Optical Element

      The laser used in nearly all optical storage systems today is
the GaAs laser, which has a beam aspect ratio on the order of 3:1.
Such a beam can be circularized by using a prism and an angle of
incidence of approximately 75 degrees.  However, there is a great
deal of interest today in shorter wavelength lasers for optical
storage applications.  The most promising short wavelength laser is
the GaAIInP laser, with a wavelength of 670 nm.  The beam aspect
ratio for this laser is on the order of 4.5:1.  Circularization of
such a beam with a single prism would require an angle of incidence
of about 82 degrees.  It would be very difficult to get the incident
surface coated to the required transmission and reflection
specifications for such a large angle of incidence.

      While it would be possible to achieve circularization of a beam
with a large aspect ratio with sequential prisms, this would add to
the complexity of the design and would increase the manufacturing
costs.

      The invention described herein would allow the circularization
to be done with a single optical element by combining the effects of
a refraction at the entrance surface of the prism and a diffraction
at the exit surface.

      Assume that the incoming beam spect ratio is 4.5:1.  The angle
of incidence at the first surface can be selected to be about 72
degrees.  If the refractive index of the prism material is 1.5, then
the angle of refraction will be 39.35 degrees.  The prism is
constructed such that the angle of incidence at the second surface is
56.2 degrees.  A hologram is attached to the second surface with an
index matching adhesive.

      By proper construction of the hologram on the second surface,
one can cause the exiting beam to exit the prism perpendicular to the
second surface.  This has the sam...