Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-10-25
2003-04-29
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C359S874000
Reexamination Certificate
active
06556741
ABSTRACT:
BACKGROUND
Microelectrical mechanical systems (MEMS) are electro-mechanical structures typically sized on a millimeter scale or smaller. These structures are used in a wide variety of applications including for example, sensing, electrical and optical switching, and micron scale (or smaller) machinery, such as robotics and motors. Because of their small size, MEMS devices may be fabricated utilizing semiconductor production methods and other microfabrication techniques such as thin film processing and photolithography. Once fabricated, the MEMS structures are assembled to form MEMS devices. The fabrication and assembly of MEMS devices is typically called “micromachining”.
For optical switching, structures can be built which have a mirrored surface for reflecting a light beam from a sending input optical fiber to a separate receiving output fiber. By constructing a mirrored surface onto a movable structure, the mirror can be moved into, or out of, the path of a beam of light. With more than one switch aligned in the beam path, the beam can be directed to one of several receiving fibers. These types of structures are generally known as “optomechanical switches”.
With optomechanical switches a common technique for moving mirrors and other structures is to employ one or more micromachined hinges. These hinges allow one structure to be rotated relative to another. With the use of a electrode, or other actuator, the movable structure attached to the hinge can be moved between two or more positions. For a structure with a movable mirror, the mirror is typically mounted out on an actuator arm which is hinged at its base. The mirror may use latches to fix it into a desired position.
With the actuator arm rotating about the hinge, the mirror can be moved into and out of a beam of light. As such, the hinge, by allowing the mirror to move between defined positions, enables the light beam to be switched between receiving devices such as various optical fibers, other mirrors, sensors and the like.
Another use for micromachined hinges is to facilitate the fabrication of MEMS structures. Hinges allow components built in common planes to one another, to be rotated to positions where the components are angled to one another. That is, by employing hinges, various non-planar structures can be created. The hinges also act to keep the base of the component in generally a fixed location while the component is rotated during construction. This results in a simpler construction process. An example of a construction hinge is a mirror set at a fixed angle to the actuator arm it is attached to. During the fabrication of this type of mirror, the mirror, actuator arm and latch are all etched out of aligned planar thin film layers. The mirror and the actuator arm are attached by a hinge. After the etching is complete, the mirror can be raised by placing a probe under the mirror and rotating it about the hinge until the latch is engaged and the mirror is locked into an upright or vertical position. After fabrication the mirror will not rotate about the hinge, but the hinge will continue to maintain the base of the mirror in a generally fixed position relative to the actuator arm.
Hinges can also be constructed both to enable construction of a structure and to allow rotational movement of the structure. One example of such a hinge use is with an actuator arm having a backflap which limits upward movement. The hinge is initially employed to allow the actuator arm to be raised and locked to the backflap at an angle relative to the backflap. Thereafter, the hinge operates to allow the actuator arm/backflap structure to rotate about the hinge. This results in a device that not only can move the actuator arm up and down, but limits the upward displacement of the arm.
In most cases, proper operation of MEMS devices are highly dependent on the specific positioning of the device's components. For example, with optomechanical switches, the positioning of the mirror must be within specific limits to allow the light beam to be properly switched. Improper mirror positioning can cause the reflected light beam to not sufficiently align with the receiving device (e.g. an output optical fiber), cause only a portion of the beam to contact the mirror, or even cause the beam to miss the mirror all together. Any of these events can easily result in the failure of the switch and effectively of the entire switching device (array of switches).
With hinges it is desirable to limit any non-hinge-aligned rotational movements as much as possible. That is, to keep the components of the device positioned correctly, translational movements of the device along and/or lateral to the hinge are sought to be minimized. The more the components can slide or slip about the hinge, the greater the potential for failure of the switch. Further, if the component can move both along and lateral to the hinge, then it will most probably be able to rotate in a direction not aligned with the hinge (e.g. in a yawing motion). Such rotational movements can also easily cause switch failure.
One type of prior hinge is shown in FIG.
1
. This type of hinge is set forth in “Microfabricated hinges”, by K. S. J. Pister, M. W. Judy, S. R. Burgett and R. S. Fearing, in Sensors and Actuators, Vol. 33, pp. 249-256, 1992, which is herein incorporated by reference in its entirety. Referring to
FIG. 1
, the switch
100
has an actuator arm
110
which rotates about a hinge
120
. The hinge
120
includes a hinge axis
122
and a hinge opening
124
, a clasp
126
having supports
128
and a bridge
130
. In this hinge the axis
122
is position between the supports
128
. When the actuator arm
110
is in its lowered position (as shown in FIG.
1
), one support
128
extends up through the opening
124
. Extending between each support
128
and over the axis
122
is the bridge
130
. The supports
128
and bridge
130
define a duct
132
and enclose the axis
122
. The axis
122
is free to rotate within the duct
132
as the actuator arm
110
is raised and lowered.
The hinge
120
has play in it which is partly a result of using a sacrificial layers to separate the elements during the fabrication process. The play is also a result of limits due to process resolution and design rules. The play is further necessary to provide enough space for the square shaped axis
122
to rotate within the duct
132
.
Although undesired movements of the actuator arm
110
are limited to some extent by the hinge
120
structure, the amount of movement is typically still sufficient to allow misalignment of the actuator arm
110
. That is, the play existing in the hinge
120
allows the actuator arm
110
to slide either, or both, along the axis
122
or laterally towards one of the supports
128
. Also, with the axis
122
moving in the duct
132
the actuator arm
110
can pivot in a yawing manner. Any of these undesired movements can produce a failure of the switch
100
due to misalignment of the mirror (not shown) mounted on the actuator arm
110
. Failure can also occur in such a switch as the contact between the axis
122
and the clasp
126
will cause premature wear and breakage.
Another hinge switch is shown in FIG.
2
. With switch
200
, the actuator arm
210
is attached by hinge
220
. The hinge
220
includes an anchor
222
and couplings
224
. Because the couplings
224
have a relatively thin and elongated structure (shaped in an extended arch), the couplings
224
., are sufficiently deformable to allow the actuator to rotate about the hinge
220
. The hinge
220
is etched from the same layer of material as the actuator arm
210
and the anchor
222
extends downward and connects to the surface
205
of the switch
200
.
While the hinge
220
is simpler to construct than the hinge
120
, it retains at least some of the unwanted play of the hinge
120
. Specifically, in addition to allowing the actuator arm
210
to rotate, the couplings
224
also allow the actuator arm
210
to move in a lateral direction away from the anchor
222
. That is, the couplings are f
Aagaard & Balzan LLP
Ferrell Arien
OMM, Inc.
Rahll Jerry T
Ullah Akm E.
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