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Determining Over-Modulation and Under-Modulation of Dichromated Gelatin Holographic Grating

IP.com Disclosure Number: IPCOM000115773D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Dickson, LD: AUTHOR

Abstract

For a Dichromated Gelatin (DCG) holographic polarization separation element, maximum diffraction efficiency for one polarization (P, for example) and minimum diffraction efficiency for the other polarization (S, for example) are desirable. However, in the fabrication process for CDG gratings, one often finds that the delta-n is too low or too high, resulting in less than maximum diffraction efficiency for the desired polarization. These two conditions are referred to as under-modulation and over-modulation, respectively.

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Determining Over-Modulation and Under-Modulation of Dichromated Gelatin
Holographic Grating

      For a Dichromated Gelatin (DCG) holographic polarization
separation element, maximum diffraction efficiency for one
polarization (P, for example) and minimum diffraction efficiency for
the other polarization (S, for example) are desirable.  However, in
the fabrication process for CDG gratings, one often finds that the
delta-n is too low or too high, resulting in less than maximum
diffraction efficiency for the desired polarization.  These two
conditions are referred to as under-modulation and over-modulation,
respectively.

      In order to get the desired maximum P polarization diffraction
efficiency and the minimum S polarization diffraction efficiency, the
proper processing corrections should be made.  But there is no way to
know, from a diffraction efficiency measurement alone, whether the
incorrect efficiencies are due to under-modulation or
over-modulation.

      If, when making the diffraction efficiency measurements for a
DCG grating, we rotate the HOE about an axis normal to the plane of
incidence, passing through the point of incidence on the HOE, the max
(P) diffraction efficiency of the HOE will decrease as we move away
from the maximum efficiency angle (the Bragg angle), regardless of
the modulation condition.

      However, as the DCG grating is rotated away from the Bragg
angle, the min (S) diffraction efficiency will decrease if the CDG is
...