Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-03-03
2002-09-10
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C359S199200, C385S017000, C385S024000
Reexamination Certificate
active
06449407
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to optical communications. More particularly, the invention relates to switches for fiber optic communications systems.
BACKGROUND ART
Silicon-micromachining technology has been used to fabricate micro-optical devices such as movable micromirrors in order to build miniaturized optical components and communications subsystems. Using silicon-micromachining and silicon optical bench technologies, extremely compact optical components and systems incorporating fiber optic technologies can be built for communication and test-and-measurement instrumentation applications.
Microelectromechanical systems (MEMS) are miniature mechanical devices manufactured using the techniques developed by the semiconductor industry for integrated circuit fabrication. Such techniques generally involve depositing layers of material that form the device, selectively etching features in the layer to shape the device and removing certain layers (known as sacrificial layers, to release the device. Such techniques have been used, for example, to fabricate miniature electric motors as described in U.S. Pat. No. 5,043,043.
Recently, MEMS devices have been developed for optical switching. Such systems typically include an array of mechanically actuatable mirrors that deflect light from one optical fiber to another. The mirrors are configured to translate or rotate into the path of the light from the fiber. Mirrors that rotate into the light path generally rotate about a substantially horizontal axis, i.e., they “flip up” from a horizontal position into a vertical position. MEMS mirrors may be actuated by magnetic interaction, electrostatic interaction, or some combination of both.
Modern fiber optic communication networks utilize fiber cable trunk lines containing a plurality of fiber optic strands for routing the traffic in the fibers to designated destinations. The number of fibers or optical ports continues to grow as the traffic load increases. Consequently multiple (>2) port fiberoptic components and subsystems are becoming more popular. Of particular interest are optical add/drop multiplexers (OADMs) that can be constructed using a micromirror array in conjunction with fiber arrays for optical inputs and outputs. As the number of add/drop/pass channels increases, the arrangement of the fibers in the array becomes critical as a proportional scaling of component size with channel count does not make an ideal solution for all applications.
A typical component of an optical communications system is an optical crossbar switch. Optical crossbar switches that utilize a single movable mirror are described, for example, in U.S. Pat. No. 4,932,745.
FIG. 1A
shows a typical 2×2 crossbar switch
100
of the prior art. The switch
100
optically couples light signals between inputs IN
1
, and outputs Out
1
, Out
2
. The switch
100
generally comprises a mirror
102
movable disposed on a substrate
104
. The mirror
102
includes reflecting surfaces on a front side
106
and a back side
108
. The mirror
102
translates horizontally between a first position and a second position. In the first position the mirror
102
blocks direct optical paths between inputs IN
1
, IN
2
and outputs Out
2
, Out
1
respectively. Light from IN
1
reflects off the back surface
108
to Out
1
. Light from IN
2
reflects off the front surface
106
to Out
2
. In the second position, mirror
102
is removed from the direct path of light between the inputs and the outputs such that light from IN
1
travels directly to Out
2
and light from IN
2
travels directly to Out
1
.
Switch
100
requires very precise alignment between the inputs and the outputs. Because the inputs are not parallel to each other, alignment of the inputs with the outputs is difficult. Furthermore, it is difficult, if not impossible to scale up the basic 2×2 crossbar switch to larger numbers of inputs and outputs. Furthermore, the input and output fibers have to be assembled individually, which is not conducive to the construction of large port-count components.
An alternative crossbar switch is described in U.S. Pat. No. 5,841917.
FIGS. 2A-2B
depict a crossbar switch
200
that is compatible with parallel arrays of inputs and outputs. The switch
200
generally comprises a 2×2 array of movable mirrors
2021
,
2022
,
2023
, and
2024
. The movable mirrors selectively couple two parallel inputs IN
1
and IN
2
to two parallel outputs Out
1
and Out
2
that are oriented at right angles to IN
1
and IN
2
. Each mirror is oriented at an angle of approximately 45° with respect to the orientation of both the inputs and the outputs. Consequently mirrors
202
deflect the path of light beams from the inputs by 90° to direct them towards the outputs. As in the crossbar switch
100
of
FIG. 1
, two switching states are possible. For example, in
FIG. 2A
mirrors
2021
and
2024
are in an “up” position and mirrors
2022
and
2023
are in a “down” position. Mirror
202
1
deflects light from input IN
1
toward output Out
1
while mirror
2024
deflects light from input IN
2
toward output Out
2
. Alternatively, in
FIG. 2B
, mirrors
202
1
and
202
4
are in the “down” position and mirrors
202
2
and
202
3
are in the “up” position. Mirror
202
2
deflects light from input IN
1
toward output Out
2
while mirror
202
3
deflects light from input IN
2
toward output Out
1
.
Because the inputs IN
1
, IN
2
are parallel to each other and outputs Out
1
, Out
2
in switch
200
, alignment is greatly simplified. Furthermore, switch
200
may be readily scaled up to accommodate any number of fibers M in an MXM array, where M is an integer greater than 2. However, because the input fiber array and the output fiber array are oriented at an angle with respect to each other, alignment of the inputs and outputs with the mirrors is problematic. Furthermore, as the number of fibers M becomes large, the number of mirrors and the area they occupy, scales as M
2
. Thus, for very large-scale arrays the switch occupies a large amount of space, which can be a serious disadvantage when the space available for the switch is limited.
There is a need, therefore, for an optical switching apparatus that is easier to align, uses fewer mirrors, and occupies less space.
OBJECTS AND ADVANTAGES
Accordingly, it is a primary object of the present invention to provide a layout for micromachined mirrors that facilitates the optimal arrangement of the mirrors. It is a further object of the invention to provide a layout that facilitates alignment of the input and output ports. It is an additional object of the invention to provide a layout for an optical switching module that facilitates miniaturization the dimensions of the resulting components or subsystems.
SUMMARY
These objects and advantages are achieved by the present invention of an optical switch module, comprising at least two fixed mirrors and at least one movable mirror. In a first embodiment, the movable mirror is typically disposed between the two fixed mirrors with all three mirrors aligned parallel to each other in a linear array to form a crossbar switch. The mirrors couple optical signals between two or more inputs and two or more outputs. The movable mirror is movable between a first position and a second position. In the first position, a first fixed mirror and the movable mirror deflect light from a first input to a first output and light from a second input to a second output. The movable mirror and a second fixed mirror deflect light from a second input to a second output. In the second position, the first and second fixed mirrors deflect light from the first input to the second output and light from the second input travels straight to the second output.
In a second embodiment, the basic switch module may be scaled up to form an apparatus that incorporates N movable mirrors and N+1 fixed mirrors, where N is an integer greater than zero. Such an apparatus can accommodate 2N fiber inputs and 2N fiber outputs. According
Behin Behrang
Daneman Michael
Kiang Meng-Hsiung
Lau Kam Yin
Isenberg Joshua D.
JDI Patent
Lee John D.
Orix Microsystems, Inc.
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