Multibeam scanning exposure device

Details Multibeam scanning exposure device Multibeam scanning exposure device

1999-03-05

2001-01-23

Schuberg, Darren (Department: 2872)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S566000, C359S569000, C359S575000

Reexamination Certificate

active

06178028

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a multibeam scanning exposure device that forms a plurality of scanning beam spots to form a drawing pattern on a photosensitive medium. Particularly, the present invention relates to the device that includes a multiple beam splitting element to divide a single light beam from a light source into a plurality of light beams.
U.S. Pat. No. 5,798,784 discloses a multibeam scanning exposure device, for example. The disclosed device is provided with an Argon laser as a light source, a half mirror to divide a light beam from the Argon laser into two beams, a pair of a multiple beam splitting elements for each of the divided light beams to further split the divided light beam into eight beams respectively and a scanning optical system that forms sixteen scanning beams on the photosensitive medium.
FIG. 8
is a perspective view showing the multiple beam splitting element that is used in an optical system of the device disclosed in the publication. The multiple beam splitting element consists of first and second right angle prisms
71
and
72
at both ends and first through seventh parallel plate prisms
73
a
through
73
g
arranged between the right angle prisms
71
and
72
. These prisms are cemented with each other using organic adhesive such as epoxy resin adhesive.
Beam splitting films
74
a
through
74
g
are formed at the boundary between the first right angle prism
71
and the first parallel plate prism
73
a
and at the boundaries among the parallel plate prisms
73
a
through
73
g.
A reflection film
75
is formed at the boundary between the seventh parallel plate prism
73
g
and the second right angle prism
72
.
An incident beam into the first parallel plate prism
73
a
from the rear side in
FIG. 8
is divided into eight beams by the beam splitting films
74
a
through
74
g
, and then the parallel eight beams are exited from the first right angle prism
71
and the parallel plate prisms
73
a
through
73
g.
Since the conventional multiple beam splitting element consists of the plurality of prisms cemented to each other, it is difficult to align the prisms in high-precision because it may include both of processing error of each prism and assembling error among the prisms. The error of the element has a bad influence on the parallelism of the exit beams, resulting in disorder of the arrangement of the scanning spots on the photosensitive medium, which deteriorates printing quality.
Further, the irradiation energy of the laser beam carbonizes the organic adhesive among the prisms of the multiple beam splitting element, lowering transmittances of the boundaries among the prisms, which loses the power balance among the eight exit beams. The conventional multiple beam splitting element has, therefore, short life span, which requires frequent exchanges of the multiple beam splitting element. Moreover, the intensity of the incident beam into the multiple beam splitting element should be controlled in low level in order to extend the life span of the multiple beam splitting element.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved multibeam scanning exposure device, which is capable of accurately aligning the scanning bead spots on the photosensitive medium and increasing a power resistance of the multiple beam splitting element.
For the above object, according to the present invention, there is provided a multibeam scanning exposure device, which includes:
a light source for emitting a light beam;
a multiple beam splitting element that is provided with a diffractive grating for dividing the light beam from the light source into a plurality of beams, the diffractive grating having a corrugated surface having a plurality of periodical patterns arranged in parallel at a predetermined fixed pitch;
a deflector for deflecting exit beams from the multiple beam splitting element; and
a scanning lens for converging the deflected beams onto the photosensitive medium to form a plurality of scanning beam spots.
With this construction, since the incident light beam in the multiple beam splitting element from the light source is divided into a plurality of beams at once, there are no influence of the assembling error and therefore the arrangement of the beam spots on the photosensitive medium can be controlled accurately.
The phase pattern may have a shape that causes non-linear phase difference to the beam passing therethrough within one pitch and the adjacent phase patterns may be, connected without phase gaps at the boundaries therebetween.


REFERENCES:
patent: 5210635 (1993-05-01), Nagata et al.
patent: 5574597 (1996-11-01), Kataoka
patent: 5798784 (1998-08-01), Nonaka et al.
patent: 10-26706 (1997-07-01), None
patent: 10-78504 (1997-07-01), None
Pp. 3456-3464 of Optical Engineering, vol. 34 No. 12, published in Dec., 1995.
Pp. 2540-2547 of Applied Optics, vol. 34, No. 14, published in May 1995.

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