Optical: systems and elements – Deflection using a moving element – By moving a reflective element
Reexamination Certificate
2001-10-11
2004-04-27
Robinson, Mark A. (Department: 2872)
Optical: systems and elements
Deflection using a moving element
By moving a reflective element
C359S298000
Reexamination Certificate
active
06728017
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micromirror actuator, and more particularly, to a micromirror actuator which is capable of effectively preventing a mirror from abnormally operating due to abnormal variation of a torsion bar.
2. Description of the Related Art
Micromirror actuators are optical switching devices used in optical communication devices and holographic optical information recorders. In holographic optical information recorders, mirrors are required to be placed at exact positions for correctly changing an optical path, that is, for switching. A plurality of micromirror actuators are installed in an array in a holographic optical information recorder and must show the same mirror operational characteristics.
FIG. 1
illustrates a conventional micromirror actuator, in which two posts
2
a
and
2
b
are installed a predetermined distance apart on a substrate
1
, and torsion bars
3
a
and
3
b
are formed to extend from a mirror
3
. The torsion bars
3
a
and
3
b
are connected at one end to the two posts
2
a
and
2
b,
respectively. In addition, magnets
4
a
and
4
b
are placed at two opposite sides of the mirror
3
.
Referring to
FIG. 1
, the mirror
3
inclines over the substrate
1
by a predetermined angle due to a vertical magnetic field emanating from the substrate
1
. Here, one edge of the mirror
3
is in contact with the surface of the substrate
1
, and thus the inclination angle of the mirror
3
with respect to the substrate
1
can be maintained. When the mirror inclines over the substrate
1
, the torsion bars
3
a
and
3
b
having predetermined elastic forces are twisted.
FIG. 2
illustrates the conventional micromirror actuator of
FIG. 1
in a state where there is no magnetic field. If the magnetic field affecting the micromirror actuator of
FIG. 1
is removed, as illustrated in
FIG. 2
, the mirror
3
rotates about the torsion bars
3
a
and
3
b
so as to be parallel with the surface of the substrate
1
due to the elastic restoring force of each of the torsion bars
3
a
and
3
b.
As shown in
FIG. 1
, when the mirror
3
is inclined over the substrate
1
by 45 degrees, light, which enters the micromirror actuator of
FIG. 1
parallel to the surface of the substrate
1
, is reflected perpendicular to the substrate
1
by the mirror
3
. On the other hand, light, which enters the micromirror actuator of
FIG. 2
, directly passes over the surface of the mirror
3
without being reflected by the mirror
3
. The operation of the micromirror actuator is controlled by the external magnetic field mentioned above. In most cases, an electromagnet is attached on the bottom surface of the substrate
1
in order to form such a vertical magnetic field.
As shown in
FIG. 3
, when an external magnetic field is formed, the mirror
3
can rotate about the torsion bars
3
a
and
3
b
against the elastic forces of the torsion bars
3
a
and
3
b
so as to form a predetermined angle with the substrate
1
. On the other hand, when there is no external magnetic field, the mirror
3
rotates so as to be parallel with the surface of the substrate
1
due to the elastic restoring forces of the torsion bars
3
a
and
3
b.
However, as shown in
FIG. 4
, if a strong external magnetic field is applied to the micromirror actuator after one edge of the mirror
3
contacts the surface of the substrate
1
, the torsion bars
3
a
and
3
b
cannot maintain their straight shapes and are inevitably bent due to their flexibility. Here, the fact that the torsion bars
3
a
and
3
b
cannot maintain their straight shapes, means that the rotation center of the mirror
3
changes and accordingly, the rotation angle of the mirror
3
exceeds a desired level. The torsion bars
3
a
and
3
b
are supported at one end by the posts
2
a
and
2
b
, respectively. Accordingly, it becomes difficult to obtain a normal inclination angle of the mirror
3
in the conventional actuator, in which the mirror
3
and the torsion bars
3
a
and
3
b
are connected to one another. Dotted lines
3
a′
and
3
b′
in
FIG. 4
indicate the original shapes of the torsion bars
3
a
and
3
b
, respectively, before the lower edge of the mirror
3
contacts the substrate
1
and the torsion bars are abnormally deformed. Solid lines in
FIG. 4
indicate the shapes of the torsion bars
3
a
and
3
b
, respectively, abnormally deformed due to the rotation of the mirror
3
.
As described above, if the mirror
3
is sufficiently rotated until one edge of the mirror contacts the surface of the substrate
1
and thus the torsion bars
3
a
and
3
b
are deformed, the rotation center of the mirror changes, and the rotation angle of the mirror
3
exceeds a designed angle range. Accordingly, it is impossible to reflect light in a desired direction in an apparatus using the conventional micromirror actuator as an optical switching device.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a micromirror actuator which is capable of precisely controlling the rotation angle of a mirror and preventing light from being reflected into an abnormal path due to abnormal rotation of the mirror.
Accordingly, to achieve the above object, there is provided a micromirror actuator including a substrate; two posts having predetermined heights and installed a predetermined distance apart on the substrate; a element, such as a torsion bar both ends of which are fixed to the posts; a stopper extending from a portion of the torsion bar and contacting or coming apart from the surface of the substrate, e.g., contacting or not contacting a surface of the substrate depending on a state of the torsion bar; a mirror connected to a portion of the torsion bar such as its middle; a driving element, such as parallel elements, connected to the torsion bar being isolated from the mirror and causing the torsion bar to be distorted; and a magnetic component, such as a magnet providing a rotation force to the driving element via an external magnetic field.
Preferably, the mirror is connected to the middle portion of the torsion bar via a connecting portion. Preferably, the parallel elements are symmetrically installed at two opposite sides of the mirror and the magnet is installed on each of the parallel elements. Preferably, the parallel elements are connected to each other via a connecting element and thus are kept in alignment with each other, and the magnet is formed on at least one of the parallel elements.
Preferably, the stopper is formed at the middle portion of the torsion bar and is opposite to a connecting portion connecting the mirror and the torsion bar.
REFERENCES:
patent: 6044705 (2000-04-01), Neukermans et al.
patent: 6046840 (2000-04-01), Huibers
patent: 6147790 (2000-11-01), Meier et al.
patent: 6172797 (2001-01-01), Huibers
patent: 6307169 (2001-10-01), Sun et al.
patent: 6353492 (2002-03-01), McClelland et al.
Burns Doane , Swecker, Mathis LLP
Robinson Mark A.
Samsung Electronics Co,. Ltd.
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