Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-08-08
2002-11-26
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S318000
Reexamination Certificate
active
06487000
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention refers to a microelectromechanical structure comprising distinct parts mechanically connected through a translation-to-rotation motion converting assembly.
2. Description of the Related Art
As is known, optical devices formed by microelectromechanical structures (MEMs) are currently studied for guiding laser light beams. These optical devices in general comprise switches that have the function of deflecting the laser light beams and are controlled by electronic circuitry, preferably integrated circuits, associated to the devices.
FIG. 1
is a schematic representation of an optical device
1
of the indicated type, which comprises a first optical transmission element
2
, a second optical transmission element
3
, and a third optical transmission element
4
. The optical transmission elements may be of any type, for example optical fibers, waveguides, etc. The second optical transmission element
3
is arranged at 90° with respect to the first optical transmission element
2
, whereas the third optical transmission element
4
is arranged at preset angle, different from 90°, with respect to the first optical transmission element
2
.
An optical switch
7
is arranged between the optical transmission elements
2
-
4
to direct an incident light ray, which traverses the first optical transmission element
2
, selectively towards the second optical transmission element
3
or the third optical transmission element
4
. The optical switch
7
comprises a mirror element
8
and a control structure (not shown) which rotates the mirror element
8
between a first position (indicated by the solid line) and a second position (indicated by the dashed line). In the first position, the mirror element
8
is arranged at 45° with respect to the first optical transmission element
2
and the second optical transmission element
3
, so that an incident ray
9
, supplied by the first optical transmission element
2
, is reflected towards the second optical transmission element
3
(reflected ray
10
represented by a solid line), whilst in the second position, the mirror element
8
is arranged at an angle different from 45° with respect to the first optical transmission element
2
and the second optical transmission element
3
, and the incident ray
9
is reflected towards the third optical transmission element
4
(reflected ray
11
represented by a dashed-and-dotted line).
The third optical transmission element
4
may not be present. In this case, the optical switch
7
operates as an on/off switch, which enables or disables transmission of the light ray
9
.
Rotation of the mirror element
8
is obtained by applying a twisting moment lying in the plane of the mirror element
8
, which is suspended from a bearing structure through spring elements (two or four, according to the number of desired freedom degrees). At present, the twisting moment necessary for rotating the mirror element
8
is generated in two ways: via electrostatic forces acting directly on the mirror element
8
, or via a mechanical conversion assembly which converts a translation of a linear actuator into a rotation.
FIG. 2
is a schematic representation of an electrostatic actuation system. The mirror element
8
is formed by a platform
15
of semiconductor material suspended from a frame
18
through two spring elements
17
a
extending in the X direction starting from two opposite sides of the platform
15
. The frame
18
is in turn supported by a first wafer
16
of semiconductor material through two spring elements
17
b
extending in the Y direction starting from two opposite sides of the platform
15
. The spring elements
17
a,
17
b
of each pair are aligned to one another and are sized in order to be substantially rigid to tension/compression and to be compliant to torsion, so as to form pairs of axes of rotation of the platform
15
. Specifically, the spring elements
17
a
define an axis of rotation parallel to the X axis, and the spring elements
17
b
define an axis of rotation parallel to the Y axis. In the vicinity of its four comers, the platform
15
has, on the underside, electrodes
20
facing corresponding counterelectrodes
21
arranged on a second wafer
22
, arranged underneath. When appropriate differences of potential are applied between one pair of electrodes
20
and the respective counterelectrodes
21
, one side of the platform
15
is subjected to an attractive force (arrows F in FIG.
2
), which generates a twisting moment M about two opposed spring elements (in this case the spring elements
17
a
), so causing rotation of the platform
15
in the desired direction and with the desired angle.
FIG. 3
is a schematic representation of a mechanical actuation system. Also in this case, the mirror element
8
is formed by a platform
15
made of semiconductor material supported by the first wafer
16
through spring elements
17
a,
17
b
and through the frame
18
.
On the underside of the platform
15
is arranged an element having the shape of a frustum of a pyramid integral with the platform
15
and defining a lever
25
. The lever
25
is engaged by four projecting elements, in this case four walls
26
extending vertically upwards starting from a plate
27
and each arranged perpendicular to the adjacent walls
26
. The plate
27
(illustrated in greater detail in
FIG. 4
) is suspended from a frame
30
through two spring elements
28
extending in the X direction starting from two opposite sides of the plate
27
. The frame
30
is in turn supported by the second wafer
22
through two spring elements
31
extending in the Y direction starting from two opposite sides of the frame
30
. The spring elements
28
,
31
are sized in such a way as to be compliant, respectively, in the Y direction and in the X direction, and to be more rigid to rotation.
According to what is illustrated in
FIG. 5
, the plate
27
is suspended above a cavity
34
present in one protection layer
36
(for instance, a layer of silicon dioxide) which overlies a substrate
35
belonging to the second wafer
22
and in which there are formed integrated components belonging to the control circuitry. The plate
27
is conveniently made in a third wafer
37
bonded between the first wafer
16
and the second wafer
22
.
The plate
27
may translate as a result of the electrostatic attraction between actuating electrodes
38
,
39
. For this purpose, on the underside of the plate
27
there are present mobile electrodes
38
facing fixed electrodes
39
formed on the bottom of the cavity
34
. In use, the mobile electrodes
38
and the fixed electrodes
39
are biased in such a way as to generate a translation of the plate
27
in the X direction or in the Y direction or in a vector combination of the two directions, exploiting the elastic compliance of the spring elements
28
and
31
in both directions.
The walls
26
-lever
25
ensemble form a conversion assembly
40
that converts the translation of the plate
27
into a rotation of the platform
15
, as illustrated in
FIG. 5
, which illustrates the effect of a displacement in the X direction of the plate
27
. This displacement determines, in fact, a corresponding displacement of the walls
26
, in particular, of the wall
26
on the left in
FIG. 5
; this wall
26
, by engaging the lever
25
, draws it towards the right, thus determining a rotation of the platform
15
by an angle &thgr; about the spring elements
17
b
(one of which may be seen in FIG.
3
), which are represented by the axis
17
in FIG.
5
.
The linear actuation of the plate
27
thus enables rotation of the platform
15
about the axes defined by the spring elements
17
a
or
17
b
or both, so enabling the platform
15
to assume a plurality of angular positions that may be controlled through the actuation electrodes
38
,
39
.
The described conversion assembly
40
is affected by hysteresis, which limits the precision in the control of the platform
15
and causes part of the movement of the plate
27
to be ineffe
Mastromatteo Ubaldo
Murari Bruno
Epps Georgia
Iannucci Robert
Jorgenson Lisa K.
Seed IP Law Group PLLC
Seyrafi Saeed
LandOfFree
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