Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-10-25
2003-07-29
Kim, Ellen E. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000
Reexamination Certificate
active
06600850
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 in to, 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”.
Optomechanical switches can employ any of a variety of configurations. One configuration commonly used is a pop-up or flip-up mirror, as shown in FIG.
1
. In a pop-up mirror switch
100
, the mirror
120
is attached to a structure
130
which allows the mirror to be moved from a lowered position, where the mirror is held out of the beam of light B
1
(as shown by the dashed lines), to a raised position, where the mirror has been rotated up into the beam B
1
(as shown by solid lines). As can be seen, the mirror
120
rotates about a hinge
140
when being moved between the lowered and raised positions. The hinge
140
is positioned at the surface
110
of the switch
100
. The mirror is raised by actuators
150
. In its raised position, the mirror
120
is at an angle Al to the beam B
1
.
It has been found that pop-up mirrors like that shown in
FIG. 1
, generally have difficulties keeping the angle Al within the necessary tolerances. This is especially true the more the switch
100
is used. Maintaining the alignment of the mirror with the light beam is critical to the operation of any such mirror. Changing the mirror position, even a few tenths of a degree, can result in the reflected beam failing to be sufficiently aligned with the receiving fiber. That is, if the mirror is positioned at an angle which is outside its operating limits, the light beam will no longer be properly aligned with the receiving fiber, and as such, the reflected beam will not continue to the receiving fiber. This will cause not only the specific switch to fail, but will effectively make the entire switching device (i.e. an array of switches) useless.
Another problem with pop-up mirrors has been the inherent limited displacements provided by the comb (lateral) actuators they use. Sufficient displacement is critical as it is necessary to move the pop-up mirror completely into and out of the path of the light beam.
Another actuator which has been used with pop-up mirrors are scratch drive actuators. While these types of actuators can provide longer travel distances, they have large contact areas which are susceptible to stiction and charging. This causes repeatability problems in long term cycling.
To overcome the inherent problems of pop-up mirrors, switches have been constructed which position the mirror in a fixed upright position and move the mirror vertically into and out of the light beam. An example of such a switch is shown in FIG.
2
. As can be seen, the switch
200
has a mirror
220
, an actuator structure
230
and an actuator hinge
240
. The switch
200
is positioned on surface
210
. The mirror
220
is attached to the actuator structure
230
at a mirror hinge
260
and is supported by a latch
270
. With the switch
200
in the lower position, the mirror
220
is held down near the surface
210
and in the light beam B
2
. Then, when the switch
200
is in its upward position, the mirror
220
is raised up out of the light beam B
2
.
In this configuration, the mirror
220
is kept in a position where the angle A
2
of the mirror relative to the beam B
2
, is kept constant as the mirror
220
is moved from its raised position to its lowered position. This provides the advantage that, unlike with the pop-up switches, the angle A
2
is not changed during the operation of the switch
200
. This keeps angle A
2
from departing from its allowable range during repetitive use of the switch. As such, the likelihood of failure of the switch due to misalignment of the mirror is greatly reduced.
As shown in
FIG. 2
, the mirror
220
is supported and held in place by the latch
270
. During construction of the switch
200
the mirror
220
is raised from a horizontal position by rotating the mirror
220
about the hinge
260
. The mirror
220
is retained in its upright or vertical position with latch
270
. A typical configuration for latch
270
is shown in FIG.
3
.
As set forth in
FIGS. 2
,
3
a
and
b
, the latch
270
has cut-outs
272
which are received in the catches
222
of the mirror
220
, when the mirror is raised up to its operating position. As further shown in the enlarged view in
FIG. 4
, the engagement of catches
222
with cut-outs
272
causes the mirror
220
to become “locked” into a fixed vertical position relative to the actuator structure
230
. The positioning of the cut-outs
272
along the length of the latch
270
will determine the angle of the mirror relative to the actuator structure
230
and consequently will determine the angle A
2
of the mirror relative to the light beam B
2
.
Unfortunately, mirrors and latches with cut-outs, as shown in
FIGS. 2-4
, have had relatively large variations in the positioning of the mirror from switch to switch. These variations have resulted in corresponding variations in the angle of the mirror relative to the light beam. As a result, these switches have had a high occurrence of failures from improper alignment of the reflected light beams with the receiving fibers. The variations in the mirror positioning are due to the fact that there exists a relatively large range in the possible location of the contact points between the latch and the mirror structure. That is, the location where the mirror structure contacts the latch varies from switch to switch.
As shown
FIG. 4
, both the cut-out
222
of the mirror
220
and the cut-out
272
of the latch
270
have rounded corners
224
and
272
, respectively. With rounded corner
224
contacting rounded corner
274
, a large variation of the possible location of the contact point between the corners exists. As noted above, this positional range of the contact point produces a corresponding range in the possible positioning angle of the mirror
220
.
The rounded corners
224
and
274
are produced when each device is etched during fabrication. When etching small corners, particularly small inside corners, of small thin film structures, rounded corners typically result.
As a result, the angle A
2
of the mirror relative to the beam B
2
, can vary significantly, as shown in FIG.
2
. Thus, there exists a corresponding large range in the positioning of the reflected beam B
2
′. This, in turn, causes a greater number of switches to fail since the reflected light beam B
2
′ is not properly aligned with the receiving optical fiber. With the reflected beam B
2
′ so misaligned, the receiving fiber cannot further transmit the light beam. That is, the misalignment of the reflected beams B
2
′ due to the rounded corners
224
and
274
, causes failure of not just the particular misaligned switch, but effectively the failure of the entire optical switching device.
Therefore, a need exists for an apparatus which couples mircomachine structures together more precisely and which minimizes the range of possible positions between coupled structures.
SUMMARY
In at least one embodiment, a thin film structure havin
Aagaard Eric J.
Aagaard & Balzan LLP
Ferrell Arien C. T.
Kim Ellen E.
OMM, Inc.
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