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Browse Prior Art Database

Retro-Directive Prism for an Optical Storage Head

IP.com Disclosure Number: IPCOM000102271D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 47K

Publishing Venue

IBM

Related People

Grant, D: AUTHOR [+2]

Abstract

Disclosed is an optical system employing a retro-directive prism for use in an optical storage head. The use of this prism provides a constant angular deviation of the sensing beam in the plane of the prism retro-reflection angle. This reduces the angular alignment accuracy required in this plane as well as allowing a more compact opto-mechanical design than might otherwise be possible

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Retro-Directive Prism for an Optical Storage Head

       Disclosed is an optical system employing a
retro-directive prism for use in an optical storage head. The use of
this prism provides a constant angular deviation of the sensing beam
in the plane of the prism retro-reflection angle. This reduces the
angular alignment accuracy required in this plane as well as allowing
a more compact opto-mechanical design than might otherwise be
possible

      A schematic of the optical system is shown above. Light from a
laser-collimator source S enters the prism at face R1 at an incidence
angle i. It is refracted through the prism and exits towards a high
numerical aperture objective and optic disk surface beyond R2.  After
reflection and optical modification, the light returns to the prism
by nearly the same path. Upon reentering the prism, it is totally
internally reflected at surfaces R3 and R4 which are at 90 degrees to
each other. (Note: If desired, optical thin film coatings can be
applied to surfaces R1/R3 and R4 in order to optimize the
polarization transmission and reflection properties of the system.)
By constructing the prism such that the included angle is 90 degrees,
it serves as a retro- reflector in the x-z plane. The incident and
emergent light paths at the prism hypotenuse remain parallel to each
other even if the prism is rotated in the x-z plane. This aids
greatly in relaxing the alignment requirements for positioning the
sensing detector D. Due to the re...