Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-03-04
2004-07-20
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S291000, C310S309000
Reexamination Certificate
active
06765711
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application Nos. 2001-10916 and 2001-10917, both filed Mar. 2, 2001, in the Korean Patent Office, the disclosures of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micromirror driver, and more particularly, to a micromirror driver which controls a resonant frequency and an amplitude of a micromirror as the micromirror rotates due to electrostatic forces, and increases a rotation angle of the micromirror using a lower voltage, and to a method of controlling the micromirror driver.
2. Description of the Related Art
micromirror drivers are operated by electrostatic forces and switch a path, along which light beams are reflected, using a rotation angle of a micromirror.
Referring to
FIG. 1
, a conventional micromirror driver comprises a frame
5
, a trench
10
formed in the frame
5
, a micromirror
20
received in the trench
10
and having a base electrode
15
, a torsion spring
25
which supports the micromirror
20
in rotation, and an electrode
30
which interacts with the base electrode
15
to rotate the micromirror
20
.
The micromirror
20
rotates about the torsion spring
25
due to electrostatic forces generated between the base electrode
15
and the electrode
30
, as shown in FIG.
2
. If the micromirror sufficiently rotates with a predetermined rotation angle, the micromirror
20
is restored to a horizontal state due to elastic restoring forces of the torsion spring
25
. The micromirror
20
repeatedly rotates in the above-described manner. It is possible to allow a rotating body, such as the micromirror
20
, to rotate with a greater rotation angle with a use of less voltage, taking advantage of resonance characteristics of an oscillating body. In other words, it is possible to effectively operate an oscillating body with less driving forces if the oscillating body is operated with a frequency, which is the same as a resonant frequency of the oscillating body.
A conventional method of adjusting the resonant frequency of a micromirror increases or decreases a mass of the micromirror and a spring constant of a torsion spring. However, such a mass of the micromirror and the spring constant of a torsion spring are set in accordance with manufacturing conditions and may vary according to an environment, in which the micromirror is manufactured or is driven. Accordingly, it is difficult to obtain a precise resonant frequency of the micromirror due to variations in the manufacture of the micromirror. Thus, various efforts have been made to control the resonant frequency of a micromirror after manufacturing the micromirror.
The resonant frequency f of an oscillating body can be expressed by Equation (1).
f
=
1
2
π
K
t
I
(
1
)
In Equation (1), K
t
represents a spring constant, and I represents an inertia moment.
The equation of motion concerning the micromirror
20
rotating with a predetermined rotation angle (&thgr;) is shown below as Equation (2).
I
θ
¨
+
C
t
θ
.
+
K
t
θ
=
τ
(
θ
,
V
)
=
1
2
ⅆ
ⅆ
θ
(
CV
2
)
(
2
)
In Equation (2), I represents an inertia moment, C
t
represents capacitance between the base electrode
15
of the micromirror
20
and the electrode
30
, K
t
represents the spring constant of the torsion spring
25
, and &tgr; represents a rotation moment (torque). Where V
0
, &agr;, and V represent an initial voltage of the electrode
30
, an arbitrary coefficient and a driving voltage of the electrode
30
, respectively, and V=(V
0
+&agr;&thgr;), Equation (2) can be rearranged into Equation (3)
I
θ
¨
+
C
t
θ
.
+
K
t
θ
=
1
2
ⅆ
C
ⅆ
θ
V
2
+
1
2
C
(
2
V
)
ⅆ
V
ⅆ
θ
=
1
2
ⅆ
C
ⅆ
θ
(
V
0
2
+
2
V
0
αθ
+
a
2
θ
2
)
+
1
2
C2
(
V
0
+
α
θ
)
α
(
3
)
by substitution of V=(V
0
+&agr;&thgr;).
The capacitance C
t
is linearly varied with respect to the rotation angle &thgr; of the micromirror
20
, as shown in FIG.
3
. In other words, as the rotation angle &thgr; of the micromirror
20
increases, the distance between the base electrode
15
and the electrode
30
increases, and thus the capacitance C
t
linearly decreases. Accordingly, a variation of the capacitance C
t
with respect to a variation of the rotation angle &thgr; becomes a constant &ggr;.
The constant &ggr; can be expressed as
ⅆ
C
ⅆ
θ
=
γ
.
Accordingly, C=C
0
+&ggr;&thgr; where C
0
represents a capacitance value when &thgr;=0. Equation (3) can be rearranged into Equation (4) by substitutions of
ⅆ
C
ⅆ
θ
=
γ
and C=C
0
+&ggr;&thgr;.
I
θ
¨
+
C
t
θ
.
+
K
t
θ
=
1
2
[
(
γ
V
0
+
2
αC
0
)
V
0
+
(
4
γ
α
V
0
+
2
α
2
C
0
)
θ
+
3
γα
2
θ
2
]
(
4
)
In the right side of Equation (4), (&ggr;V
0
+2&agr;C
0
) affects the rotation amplitude of the micromirror
20
, (4&ggr;&agr;V
0
+2&agr;
2
C
0
) affects the resonant frequency ƒ of the micromirror
20
, and 3&ggr;&agr;
2
affects both the amplitude and the resonant frequency of the micromirror
20
. Here, if the resonant frequency ƒ of the micromirror
20
is controlled by adjusting &agr;, the voltage V of the driving voltage of the electrode
30
is varied because V=(V
0
+&agr;&thgr;). If the initial voltage V
0
of the electrode
30
is varied, &agr; is also varied. Thus, it is impossible to simultaneously control the frequency ƒ and the amplitude of the micromirror
20
. In other words, elements required to control the frequency ƒ and the amplitude of the micromirror
20
are dependent on each other, and thus if one of the elements is controlled, the other element is affected by the controlled element and cannot be controlled simultaneously or independently.
SUMMARY OF THE INVENTION
To solve the above-described problems, it is an object of the present invention to provide a micromirror driver, in which a frequency controlling electrode and an amplitude controlling electrode operate independently and thus a resonant frequency and an amplitude of a micromirror are independently and simultaneously controllable, allowing the micromirror to rotate with a larger rotation angle by decreasing a spring constant of a rotation axis of the micromirror. Another object of the present invention is to provide a method of controlling a micromirror driver.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects of the invention, according to one aspect of the present invention, there is provided a micromirror driver. The micromirror driver comprises a micromirror having at least one groove, an elastic body which supports the micromirror in rotation, and at least one electrode which receives a voltage to generate electrostatic forces to rotate the micromirror through interaction of the electrostatic forces with the micromirror. The amplitude and frequency of the micromirror are controlled by varying one of a magnitude and a waveform of the voltage of the at least one electrode.
Each groove is formed in a respective peripheral area of the micromirror and is arranged near a rotation axis of the micromirror.
Preferably, a first electrode controls the frequency of the micromirror during rotation of the micromirror, a second electrode controls the amplitude of the micromirror during the rotation of the micromirror, and the second electrod
Choi Hwan-young
Lee Jeong-kwan
Min Young-hun
Shin Hyung-jae
Epps Georgia
Hasan M.
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
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