Coherent light generators – Particular beam control device – Scanning
Reexamination Certificate
2000-04-26
2002-10-29
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
Scanning
C372S100000, C372S101000, C372S102000, C372S103000, C365S037000
Reexamination Certificate
active
06473443
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for generating a grating image and, more particularly to a method which can generate a grating image in an improved speed.
DESCRIPTION OF THE RELATED ART
In general, a grating image is formed by arranging and combining various micro-gratings. Gratings which have different pitch, orientation and different diffraction efficiencies, will generate various diffraction effects on different wavelength of light. Therefore, it is understood that in order to generate a grating image, it is necessary to control the pitch of each grating, the orientation, the diffraction efficiency and the scale of the gratings as well.
FIG. 1
is a conventional method to generate a grating. A laser beam “a” and a coherent laser beam “b” intersect and form an interferenced standing wave at the intersection area. By placing photosensitive material at the plane A—A, a grating can be formed by recording the interferenced standing waves.
FIG.
2
and
FIG. 3
show another method to generate a grating. It can be seen from
FIG. 2
that a pair of parallel coherent laser beams “a
1
” and “b
1
” irradiate onto a lens (
51
) in the vertical direction. After being refracted by the lens (
51
), the pair of laser beams “a
1
” and “b
1
” intersect at the focus point of the lens (
51
) and form a standing wave. By placing a photosensitive material (
6
) at the focal plane of the lens (
51
), a grating can be obtained by recording the standing wave. If the locations where the laser beams “a
1
” and “b
1
” incidence the lens (
51
) are adjusted, the pitch and orientation of the gratings will be changed. Alternatively, by adjusting the exposure, the diffraction efficiency of the gratings will be changed. Also, by adjusting the beam size and the divergence angle of the laser beams “a
1
” and “b
1
” the size of the generated gratings will be changed.
FIG. 4
is a previous art for generating a grating image. A laser source (
11
) is used for sending out a laser beam “L”. An acusto-optic modulator (
21
) (called “AOM” hereinafter) is utilized for controlling the exposure. At the beginning, the laser beam “L” is emitted from the laser source and passes through the AOM (
21
) and a beam expander “
3
a
”. The beam expander “
3
a
” is composed of the first lens (
31
) and the first lens (
31
) or the second lens (
32
), the divergence angle of the laser beam “L” can be adjusted, therefore the size of the generated gratings can be adjusted. The first reflector (
111
) is located behind the beam expander “
3
a
” to reflect and change direction of the laser beam “L” through the beam expander “
a
”. Then the laser beam “L” enters a beam splitting and beam guiding device “
4
a
”. The beam splitting and beam guiding device “
4
a
” includes a beam splitter (
41
) which is provided for splitting the laser beam “L” into two beams “a
2
” and “b
2
”. The second reflector (
42
) and the third reflector (
44
) are arranged within the beam splitting and guiding device “
4
a
” for changing direction of the beam “a
2
” and allow it to vertically irradiate onto the lens (
51
A). The fourth reflector (
43
) is also arranged within the beam splitting and guiding device “
4
a
” for changing direction of the beam “b
2
” and allow it to vertically irradiate onto the lens (
51
). After that, the beams “a
2
” and “b
2
” intersect at the focus of the lens (
51
A) and forms an interferenced standing wave. By placing a photosensitive material (
6
A) at the focal plane of the lens (
51
A), the standing wave can be recorded and generate a grating. It is obvious that by moving the beam splitter (
41
) and the second reflector (
42
), the distance between two beams “a
2
” and “b
2
” will be changed. Therefore, the pitch of the gratings can be changed accordingly. Alternatively, if the beam splitting and beam guiding device (
4
a
) is rotated along the direction of the incident optical axis of the laser beam “L”, the orientation of the generated gratings will be changed. A precise translation stage (
71
) is provided for supporting and moving the photosensitive material (
6
A). It can be understood that different grating can be combined upon displacement of the photosensitive material (
6
) so as to form a grating image. In this method, the AOM (
21
), the beam expander “
3
a
”, the beam splitting and beam guiding device “
4
a
” and the precise translation stage (
71
) can be controlled by computer and realize automation. The method of using the beam splitting and beam guiding device “
4
a
” and the lens (
51
A) is mirrored from the known Laser Doppler Anemometer (hereinafter called “LDA”) technology. The speed of generating grating images may be limited due to a slow dynamic response of the beam splitting and guiding device “
4
a
” and the precise translation stage (
71
). This is a main shortcoming of the previous arts of generating grating images.
SUMMARY OF THE INVENTION
A main object of the present invention is to provide an improved method for generating grating images which is able to greatly increase the speed of the grating image generation by utilizing the technique of beams guiding, symmetrical beams forming and local scan.
In accordance with one aspect of the present invention, a method for generating a grating image comprises a step of generating a coherent beam, a step of controlling exposure of the coherent beam, a step of guiding the coherent beam to a required location, a step of splitting the coherent beam into two symmetrical coherent beams, a step of local scanning, allowing the symmetrical coherent beams to intersect and form an interferenced standing wave at different position in a small local scan area, a photoactive step for recording a grating on a photosensitive material, and a step of changing the position of the the photosensitive material, combining different local scan areas which are full with gratings and forming a large scale grating image.
In accordance with another aspect of the present invention, a system for generating a grating image, comprises a coherent light source for providing a coherent beam “L”,
an exposure control device for the coherent beam “L” to pass therethrough and control the exposure of the coherent beam “L”, a beam guiding device for controlling the pitch and the orientation of each grating, a symmetrical beam generating device for splitting the coherent beam “L” into two symmetrical coherent beams, a local scan device for allowing the two coherent beams to intersect and form a standing wave at different position in a small local scan area, a photosensitive material for recording the standing wave, and
a supporting device for supporting and moving the photosensitive material so as to combine different local scan areas which are full with gratings.
REFERENCES:
patent: 6084998 (2000-07-01), Straayer
Kuo Chi-Wang
Lin Shyh-Tsong
Ip Paul
Jackson Walker L.L.P.
Kutai Electrical Industrial Co., Ltd.
Rodriguez Armando
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