System of angular displacement control for micro-mirrors

Details System of angular displacement control for micro-mirrors System of angular displacement control for micro-mirrors

2001-06-15

2003-06-10

Epps, Georgia (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S291000, C359S290000

Reexamination Certificate

active

06577431

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical switch device that controls the angular displacement of micro mirror structures, eliminates the interference of magnetic field from other optical switch device and controls the horizontal displacement of micro mirror structures to prevent vibration and collision in the optical switch device transportation. Further, the present invention is directed to control the displacement and eliminate the interference of micro mirror structures or a plurality of optical switch devices. Alternatively, the present invention also improves the reliability of transporting optical switch devices.
2. Description of the Related Art
Recently several researchers have spurred an increasing development of microstructures in optical communication and micro electro-mechanical systems (MEMS). The microstructures that were not performed in the past are fabricated by a combination of silicon deposition, surface micromachining and bulk-micromachining. A typical optical communication system requires a number of small-sized, high-speed, and highly reliable optical switches for the line switching operation in any applications. The optical switch devices are discussed in detail in Transducers, 1995, entitled “An electrostatically operated torsion mirror for optical switching device” by Hiroshi Toshiyoshi and Hiroyuki Fujita and in Solid-state sensor and actuator, 1998, entitled “Parallel assembly of hinged microstructures using magnetic actuation” by Yang Yi and Chang Liu. Recently, U.S. Pat. Nos. 6,094,293 and 5,960,132 have been disclosed the related information.
The optical switch devices as mentioned previously use electrostatic or magnetic force to control the angular displacement of individual mirror. The incident light is transmitted and passed only when mirror is in the non-reflection state (OFF-state). On the other hand, the incident light is reflected and changed the origin route when the mirror moves between the non-reflection state and the reflection state (On-state). A problem associated with the typical optical switch devices is that precision alignment of mirror is required to control the reflective light's route. The mirror achieves large angular displacements (over 90°) under a torque provided by applying an external magnetic or electrostatic force because the mirror is influenced by the inertia.
FIG.
1
and
FIG. 2
show the 3D views and cross-section views of the micro mirror in the prior art. A torsion mirror device
10
is formed on a flat surface of a silicon substrate
11
(or glass substrate). The torsion mirror device
10
includes a bump
15
, a reflective mirror
14
and a torsion bar
121
connected the reflective mirror
14
with the first connector section
12
a
and the second connector section
12
b.
Alternatively, first connector section
12
a
, second connector section
12
b
, the torsion bar
121
, the reflective mirror
14
, and the bump
15
are formed by the elastic poly-silicon in the lithography process. The first connector section
12
a
and second connector section
12
b
are performed on the silicon substrate
11
and separated by the torsion bar
121
. The reflective mirror
14
is formed on the extension part of the middle of the torsion bar
121
. A magnetic material
141
(so called permalloy) is performed on the top of the reflective mirror
14
. The permalloy
141
is deposited by the way of sputtering or electroplating. The reflective mirror
14
contains a reflective area
142
. The reflective area
142
is performed by a smooth plane, which makes the incident light to change the route of the incident light when the incident light approaches the reflective area
142
. The bump
15
fixed under the reflective mirror
14
is a square or a rectangle. Furthermore, the height of the bump
15
is suitable for the reflective mirror
14
placed on the bump
15
when the reflective mirror
14
is in the horizontal level. An actuator
16
under the silicon substrate
11
could provide repulsive force to raise the reflective mirror
14
.
The conventional rotation mechanism of the reflective mirror
14
is introduced in
FIGS. 3-5
. As shown in
FIG. 3
, the torsion mirror device
10
is at rest and the external magnetic field is just applied to the actuator
16
.
FIG. 4
shows that a torque provided by the actuator
16
makes the torsion mirror device
10
rotate from the horizontal level to vertical level. Thereafter,
FIG. 5
shows that the torsion mirror device
10
achieves large angular displacements (over 90°) and doesn't keep stable at the vertical position under the influence of the inertia.
As shown in
FIG. 3
, when the actuator
16
applying magnetic field results in flux density
161
and the permalloy
141
induces magnetization
163
. The positive pole of the flux density
161
and the positive pole of the magnetization
163
result in repulsive force
164
. The repulsive force
164
raises the reflective mirror
14
away from silicon substrate
11
. Alternatively, the torsion bar
121
which connects with the reflective mirror
14
, first connector section
12
a
and second connector section
12
b
. When the reflective mirror
14
rotates from the horizontal level to the vertical level, the torsion bar
121
is provided with elasticity to distort under the repulsive force
164
. Furthermore, the repulsive force
164
achieves the maximum when the distance between the positive pole of the flux density
161
and the positive pole of the magnetization
163
is shortest.
As shown in
FIG. 4
, the repulsive force
164
achieves smaller when the distance between the positive pole of the flux density
161
and the positive pole of the magnetization
163
is farther. The torsion bar
121
is so elastic that the reflective mirror
14
moves forward to the vertical position.
As shown in
FIG. 5
, when the reflective mirror
14
approaches the vertical position, the distance between two positive poles increases further and the repulsive force
164
decreases substantially. The repulsive force
164
approaches zero when the reflective mirror
14
is at a vertical position
17
. In the influence of the inertia, the reflective mirror
14
stops at a static position
18
after the orientation mirror
14
rotates over the vertical position
17
. The repulsive force
164
is continuously applied to retain the reflective mirror
14
at the static position
18
.
FIG. 6
illustrates a cross-section view that the conventional mirror device stays at the static position
18
. Although the actuator
16
is not provided by applying external magnetic field anymore, the induced magnetic filed of the permalloy
141
disappears and the reflective mirror
14
influenced by resilience moves back to horizontal level form the static position
18
.
FIG. 7
shows a cross-section view that the conventional torsion mirror device
10
moves back to the horizontal level. A problem with a reflective mirror
14
similarly described above is that the reflective mirror
14
couldn't retain the horizontal level for the inertia when the reflective mirror
14
moves back. The bump
15
overcomes the problem because the height of the bump
15
is suitable for the reflective mirror
14
stopped on the bump
15
.
As shown in
FIG. 7
, the torsion mirror device
10
isn't fixed by the bump
15
in the horizontal level when the torsion mirror device
10
or an array of torsion mirror devices is transported.
FIG. 8
illustrates the cross-section view of an array of torsion mirror devices
20
in prior art. The array of torsion mirror devices
20
are composed by the sixteen micro mirrors labeled
211
,
212
,
213
,
214
,
221
,
222
,
223
,
224
,
231
,
232
,
233
,
234
,
241
,
242
,
243
and
244
. Among these mirrors, the mirrors labeled
213
,
221
,
232
and
244
are in the vertical level (reflective state), and therefore beams of incident light
20
A,
20
B,
20
C and
20
D are individually reflected by the mirrors labeled
213
,
221
,
232
and
244
to sensors of
20

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