Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2002-01-14
2004-11-23
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S018000, C385S052000, C398S012000, C398S019000
Reexamination Certificate
active
06823101
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the field of fiber optic communications and in particular, to a method for calibrating a micro-electromechanical (MEMS) device.
BACKGROUND ART
In fiber optic communication systems, signal routing is the ability to direct a signal received from one of a plurality of input fibers or ports to any of a plurality of output fibers or ports without regard to the frequency and polarization of the optical signal. Signal routing is essential for directing an optical signal carrying data to an intended location.
Free-space optical crossconnects allow interconnecting among input and output ports in a reconfigurable switch fabric. An example of such an optical crossconnect utilizes an array of MEMS tilting mirror devices as the fabric. By adjusting the tilt angles of the MEMS mirror devices, optical signals can be directed to various destinations, i.e., to numerous output fibers.
Arrays of two-axis tilt mirrors implemented using micro-electromechanical systems (MEMS) technology allow for the construction of large scale optical crossconnects for use in optical systems. Optical crossconnects are commonly employed to connect a number of input optical paths to a number of output optical paths. A typical requirement of optical crossconnects is that any input be capable of being connected to any output. One example of a MEMS device is the MEMS mirror array
10
depicted in FIG.
1
. The mirror array
10
includes a plurality of tilt mirrors
12
formed on a substrate
11
, mounted to springs
14
and controlled by electrodes (not shown). Each mirror
12
is approximately 100-500 microns across, may be shaped as square circular or elliptical, and is gimbaled with the tilt angle being selectively determined by the amount of voltage applied to the control electrodes. Gimbaled mirrors are capable of operatively rotating or tilting about at least two axes, for example, orthogonal X-Y axes of rotation. With two axes, one axis is termed the mirror axis, the other axis (typically orthogonal to the mirror axis) is the gimbaled axis. Gimbaled mirror configurations are described in U.S. Pat. No. 6,201,631 to Greywall. Other mirrors, with only one axis, are also known in the art.
Further details of the operation of the MEMS mirror array
10
are found in copending U.S. patent application Ser. No. 09/415,178, filed Oct. 8, 1999. Utilizing two or more such tilt mirror arrays
10
to form an optical crossconnect is disclosed in copending U.S. patent application Ser. No. 09/410,586 filed Oct. 1, 1999. Techniques associated with monitoring mirror position are disclosed in copending U.S. patent application Ser. No. 09/414,621 filed Oct. 8, 1999. Techniques for detecting mirror position are disclosed in copending U.S. patent application Ser. No. 09/518,070 filed Mar. 3, 2000. The entire contents of each of the above-mentioned patent applications are hereby incorporated by reference.
The use of one or more MEMS tilt mirror arrays in conjunction with a lens array is disclosed in co-pending U.S. patent application Ser. No. 09/512,174, filed Feb. 24, 2000, the entire content of which is also incorporated herein by reference. As disclosed in that application, various optical crossconnect configurations of compact size (i.e. minimal spacing between crossconnect components) and exhibiting minimal optical power loss can be realized. One such optical crossconnect
100
discussed in the aforementioned application is depicted in FIG.
2
. Crossconnect
100
receives input optic signals
108
through a plurality of optic fibers
112
a
,
112
b
,
112
c
,
112
d
, preferably formed in an array
112
as is well known in the art. For ease of illustration, fiber array
112
is shown as a one-dimensional array having four fibers
112
a
,
112
b
,
112
c
,
112
d
. It is in any event to be understood that fiber array
112
, as well as other fiber arrays discussed herein are preferably two-dimensional arrays such as, for example, N×N arrays.
Fiber array
112
transmits the optical signals
108
to an array of lenses
114
that function as collimating lenses. The lens array
114
is positioned relative to fiber array
112
so that each lens communicates with a corresponding fiber for producing beams
116
from the optic signals
118
. Thus, beam
116
a
is produced from a signal carried by fiber
112
a
, beam
116
b
is produced from a signal carried by fiber
112
b
, etc.
A first MEMS tilt mirror array
10
a
, also referred to as the input array, is positioned in alignment with the lens array
114
so that each mirror element
12
a
will receive a corresponding beam
116
. The mirror elements
12
a
are operatively tilted, in a manner discussed in application Ser. No. 09/415,178, to reflect the respective beams
116
to a second or output MEMS mirror array
10
b
positioned in optical communication with MEMS array
10
a
. Depending on the tilt angle of each mirror element
12
a
in input MEMS array
10
a
, the reflected signals can be selectively directed to specific mirror elements
12
b
in output MEMS array
10
b.
To illustrate this principle, beam
116
a
is shown in
FIG. 2
generating reflection beams
120
a
and
120
a
′ and beam
116
d
is shown generating reflection beams
120
d
and
120
d
′. The particular trajectory of the reflection beams is determined by the tilt angle of the mirrors in the MEMS array
10
a
, on which the beam
116
is incident. These beams are received by mirror elements
12
b
in the output MEMS array
10
b
and are directed as beams
124
a
to an output lens array
126
. An output fiber array
128
is aligned with lens array
126
to receive and transmit output optical signals
129
. Thus, lens array
126
couples beams
124
into the output fiber array
128
.
MEMS devices
10
a
and
10
b
, and in particular, tilting mirror devices
12
a
and
12
b
, are fairly sensitive devices which may be moved by the application of a force and may require fairly precise positioning. Knowledge of the devices'
10
a
and
10
b
response to an applied force is important to controlling the position of the mirrors
12
a
and
12
b
. Further, acquiring this knowledge as quickly as possible is also an important criterion.
SUMMARY OF THE INVENTION
The present invention is directed to a method of calibrating a MEMS device such that the response of each of the elements of the MEMS device to the applied force is known.
The present invention is directed to a method of calibrating a MEMS device such that the MEMS device is calibrated quickly and accurately.
In the present invention, various voltages are applied via electrodes to create potentials between mirrors of the MEMS device and the electrodes to move the mirrors. The potentials cause the mirrors to rotate. The relationship between the applied voltage and the mirror rotation (in angle or position) is recorded as a calibration curve. In one embodiment, this relationship is determined for every mirror in the MEMS device. Next, the trajectory of a beam reflected by a mirror is determined as a function of mirror position. Determining the trajectory of the beam determines where the beam is directed by the mirror. In an optical cross-connect the beam is directed to a location on another component (e.g. another moving mirror in a different array, a non-moving optical element, an output fiber, etc.) In one embodiment, raytracing is used to determine where a beam will be directed as a function of mirror position. The angles of the mirrors associated with directing the beam to a particular location are determined from the ray tracing. In one embodiment, this relationship is determined for every mirror in the MEMS device. The calibration curve and the raytraces provide the voltages to be applied to move mirrors in a perfectly aligned cross-connect to direct a beam to desired locations.
Once this information is obtained, the optical interconnect is actually physically assembled. A subset of the mirrors are tested to determine the voltages that are actually needed to move the mirrors to direct the beams to t
Gates, II John V.
Holland William R.
Kim Jungsang
Pau Stanley
Agere Systems Inc.
Rahll Jerry T.
Ullah Akm Enayet
LandOfFree
Method for calibrating a MEMS device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for calibrating a MEMS device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for calibrating a MEMS device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3307415