Optical: systems and elements – Polarization without modulation – By relatively adjustable superimposed or in series polarizers
Reexamination Certificate
2000-03-27
2001-07-24
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Polarization without modulation
By relatively adjustable superimposed or in series polarizers
C359S486010, C359S506000, C359S576000
Reexamination Certificate
active
06266188
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a polarizing beam splitter typically used on optical pickups with which information is written to or read from optical recording media such as optical recording disks and magneto-optical recording disks.
2. Related Art
A polarizing beam splitter capable of diffraction at varying efficiency with the direction of polarization is used on various kinds of optical devices. Inexpensive models using an optically isotropic substrate have been proposed by the assignee in Unexamined Published Japanese Patent Application Nos. 230140/1997 and 66598/1999.
The polarizing beam splitters disclosed in these patents have essentially the same structure as the polarizing beam splitter of the invention and, as shown in
FIG. 1
which is a schematic representation of the invention's model, has a glass substrate
11
as an optically isotropic substrate and an oriented polydiacetylene film
12
a
which is formed of a birefringent material to a predetermined thickness on the surface of the glass substrate. By patterned exposure to ultraviolet light, a periodic grating
12
b
consisting of alternating exposed and non-exposed areas of specified width is formed in the oriented polydiacetylene film
12
a.
The present inventors have found a problem with these polarizing beam splitters, that is, after the formation of the periodic grating, thermal deterioration occurs to instabilize diffraction efficiencies such as the efficiency of first-order diffraction.
A further problem occurs when the polarizing beam splitter with a periodic grating is divided into discrete units by dicing the glass substrate in a pattern of squares. Since a jet of pressurized water is applied in the dicing step, the exposed areas of the oriented polydiacetylene film come off the glass substrate.
SUMMARY OF INVENTION
An object, therefore, of the present invention is to provide a process for producing a polarizing beam splitter whose characteristics such as diffraction efficiencies are stabilized to ensure even higher quality.
There is provided a process for producing a polarizing beam splitter comprising the steps of:
forming a birefringent material layer made of an oriented film of an organic polymeric material on an optically isotropic substrate;
applying a first heat treatment to the birefringent material layer to cause a change in color or stabilize its molecular structure;
forming a periodic grating on said birefringent material layer defined by alternativly arranging exposed and non-exposed areas by applying a patterned exposure of ultraviolet light on said birefringent material layer;
applying a second heat treatment heat to stabilize said periodic grating at a temperature not higher than that for said first heat treatment after said periodic grating is formed.
According to the method of the present invention for producing a polarizing beam splitter, the formation of a periodic grating is followed by the step of second heat treatment which is performed at a temperature not higher than the temperature at which a color change occurs or the molecular structure of the grating is stabilized. In this way, the oriented film of an organic polymeric material can be thermally stabilized without causing a color change or letting the film shrink while ensuring that the film maintains the desired color. Therefore, the polarizing beam splitter produced by the process of the invention retains high values of light transmittance and the first-order diffraction efficiency.
Since the second heat treatment is conducted after forming the periodic grating by patterned exposure, the exposed areas of the periodic grating are also thermally stabilized. If the time of the second heat treatment is set with reference to the specific kind of the light source used in patterned exposure of the periodic grating, the exposed areas can be mechanically stabilized to provide better adhesion to the glass substrate with almost 100% probability. As a result, the fabricated polarizing beam splitter can safely be diced into discrete units of high quality that are free from the problem of delamination of the exposed areas.
REFERENCES:
patent: 5793733 (1998-08-01), Takeda et al.
patent: B1 5245471 (1993-09-01), Iwatsuka et al.
patent: B1 5739952 (1998-04-01), Takeda et al.
patent: 9-230140 (1997-09-01), None
patent: 11-66598 (1999-03-01), None
Kabushiki Kaisha Sankyo Seiki Seisakusho
Schuberg Darren
Sughrue Mion Zinn Macpeak & Seas, PLLC
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