Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2002-03-05
2004-09-07
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S017000, C385S116000, C385S119000
Reexamination Certificate
active
06788842
ABSTRACT:
TECHNICAL FIELD
The invention described herein relates to the monitoring of movable reflectors in optical switches. In particular, the invention relates to methods and apparatus for internally monitoring and controlling the orientation of movable reflectors in an optical switch. Still more particularly, some embodiments of the invention relate to methods and apparatus for using internal auxiliary monitor light beams to determine the position and orientation of movable reflectors of the optical switch so that the movable reflectors can be positioned and maintained at a desired orientation.
BACKGROUND
In recent years there have been extensive efforts to develop commercially fill viable optical switches. Presently there are a variety of different types of optical switch architectures available on the market. One proposed optical switch architecture contemplates the use of arrays of Micro Electro-Mechanical Systems (MEMS) mirrors to accomplish the switching. Such an optical switching system is described in International (PCT) Publication Number WO99/66354, naming Herzel Laor as inventor, and entitled, “PLANAR ARRAY OPTICAL SWITCH AND METHOD,” published on Dec. 23, 1999, the entirety of which is incorporated herein by reference for all purposes. A perceived advantage of this type of optical switching system is that it is potentially scalable to many channels.
An example of a conventional MEMS mirror-based optical switching system is diagrammatically represented in
FIG. 1A
of the drawings. In the embodiment shown in
FIG. 1A
, the optical switch
100
includes an input fiber array
102
an input lens array
104
input and output reflector arrays
106
,
108
, an output lens array
110
and an output fiber array
112
. According to the configuration of
FIG. 1A
, multiple optical inputs are used with an equal number of lenses to produce an equal number of approximately collimated input optical beams. The input and output mirror arrays
106
,
108
each include a plurality of movable mirrors, such as mirror
106
a
. In the depicted embodiment, each movable mirror in the input and output mirror arrays is rotatable about two orthogonal axes so that an input beam received on any one of the input fibers can be directed towards a plurality of the output fibers by appropriately adjusting the orientation of their associated mirrors. The depicted embodiment is shown with an input optical beam
101
a
being directed through the switch into a selected output fiber as an output beam
101
b
. By changing the position of movable mirrors in the reflector arrays
106
,
108
the input optical beams (e.g.,
101
a
) can be switched to one of a plurality of output fibers as an output beam (e.g.,
101
b
). The input and output fiber blocks
102
,
112
are typically comprised of a two-dimensional array of fibers with polished end faces. The input fiber block
102
is positioned adjacent an input lens array
104
to provide collimated input beams, while the output lens array
110
is positioned adjacent to couple collimated output beams into output fiber block
112
. The input and output mirror arrays
106
,
108
each include a plurality of movable mirrors, such as mirror
106
a
. Although the depicted embodiment has movable mirrors configured to rotate in two axes, other embodiments have movable mirrors configured so that they are rotatable about a single axis.
In theory, the mirror arrays can be formed using a wide variety of techniques, and different companies have adopted different approaches in their attempts to provide suitable mirror arrays. By way of example, one approach is to create movable mirrors by forming MEMS structures on a monolithic silicon substrate. Devices such as these are commercially available from a variety of sources, including MCNC of Research Triangle Park, N.C. and Analog Devices of Cambridge, Mass.
An alternate embodiment
150
of a conventional MEMS mirror-based optical switching system is shown in
FIG. 1B
of the drawings. In this configuration, a “folded” optical path is provided by using a fixed mirror
158
that cooperates with a movable mirror array
106
so that an input beam
101
a
from fiber array
102
passes through lens array
104
to an input mirror
106
a
in movable mirror array
106
. The input beam
101
a
is reflected off a first movable mirror
106
a
and directed to the fixed mirror
158
, whereupon the beam is then reflected off of the fixed mirror
158
to an appropriate second movable mirror
106
b
which directs the beam (as output beam
101
b
) through the lens array
104
to a desired output channel in the fiber array
102
. Thus, it will be appreciated that fiber array
102
may operate as both the input array of optical fibers and the output array of optical fibers. Thus, the fiber array
102
can include an input fiber array portion and an output fiber array portion.
In general, the movable mirror arrays
106
,
112
of
FIGS. 1A and 1B
are populated with as many mirrors as fibers in the input/output fiber array; however, only two mirrors are shown for clarity. The mirrored configuration shown in
FIG. 1B
has the advantage that, in principle, any fiber can be switched to any other fiber, and so fibers do not have to be divided into sets of input fibers and output fibers.
By adjusting mirror position, optical beams can be steered from selected input fibers to selected output fibers. By monitoring and precisely adjusting the position of the movable mirrors, an optical beam from an input fiber can be switched to one of a plurality of output fibers, thereby accomplishing optical switching.
Another approach to achieving optical beam switching and mirror position control using monitor “taps” to measure a portion of optical beam power using such measurements to adjust mirror position.
FIG. 2
depicts one such approach.
FIG. 2
shows a plurality of input fibers
1
feeding input signals into an optical switching apparatus
5
. The switch directs the signals to the desired output fibers
4
where they can be transmitted through the system. The optical power of the input signals is tapped from the input fibers
1
by fiber taps that direct a portion of the signal into detectors
2
where the optical power is measured. Similarly, output optical power is tapped from the output fibers
4
and detected by detectors
3
where the optical power is measured. These measurements are compared, and using loss optimization techniques the position of movable mirrors in the switch
5
is adjusted to produce output beams of a desired power. However, such switches require complex signal processing algorithms and require the use of many expensive optical taps and optical detectors, thereby driving up the cost.
FIG. 3
is a block diagram of yet another approach. This approach is disclosed in the International Patent WO 99/67666 to H. Laor, which is hereby incorporated by reference. In the depicted optical switch, an optical signal
29
is input through an input fiber
21
. The input signal
29
is directed onto a first movable mirror
25
a
that steers the signal
29
onto the second movable mirror
25
b
, which reflects the signal
29
into the desired output fiber
24
. Additional components are used to monitor the mirror orientation (position). Arranged along the signal
29
path are a first beam splitter
31
, a second beam splitter
32
, a third beam splitter
33
, a fourth beam splitter
34
, a first lens
26
a
, and a second lens
26
b
. Also included are a first laser
27
, a second laser
28
, a first detector
22
, and a second detector
23
. The first laser
27
generates a forward propagating laser beam that is directed along the optical path toward the output fiber
24
. After passing through a plurality of beam splitters
32
,
33
, lens
26
b
, and both mirrors
25
a
,
25
b
, the beam passes through the fourth beam splitter
34
, where a portion of the beam is directed into the second detector
23
, where it is measured. Similarly, a beam generated by the second laser
28
is back propagated toward the input fiber
21
. A portion of this beam is sp
Anderson Robert
Bowers John Edward
Helkey Roger Jonathan
MacDonald Noel
Sink Robert Kehl
Beyer Weaver & Thomas LLP
Calient Networks
Lee John D.
Lin Tina M
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