Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2003-06-19
2004-08-10
Tsai, H. Jey (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S042000, C438S460000
Reexamination Certificate
active
06773942
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to an optical switch array, and more particularly, is related to an optical micro-electro-mechanical switch array.
BACKGROUND OF THE INVENTION
Optical switches can replace electrical switches in electro-optical systems, because of their low weight and immunity to electromagnetic interference, and because they eliminate the need for optical-to-electrical and electrical-to-optical conversion at the switch.
The importance of fiber-optic switches has been increasing due to the rapid growth of optical fiber networks. Recently, there has been a growing demand to make fiber-optic switches based on micro-electro-mechanical system (MEMS) technology. The use of MEMS techniques to make fiber-optic switches offers several advantages such as miniaturization, high performance and batch production or low cost.
One type of a conventional micromachined free-space optical matrix switch uses electrostatically actuated torsion mirrors, as shown in FIG.
1
. The optical matrix switch includes a first base member
101
, a plurality of bonding pads and interconnections
104
, a second base member
105
, and a plurality of optical fibers
108
. The first base member
101
has an array of bores
103
formed therethrough and arranged in a plurality of columns and rows. The torsion mirror has a reflective panel member
102
and a torsion bar connected to the reflective panel member
102
by a connector section.
Each of bores
103
is sized to receive a respective one of the torsion mirrors. Each of the torsion mirrors is mounted onto the first base member by embedding opposite distal ends of the torsion bar into the first base member so that the torsion mirrors can pivot between a reflective state and a non-reflective state.
The second base member
105
includes an array of cavities
106
. The first base member
101
and the second base member
105
are connected to each other with the cavities
106
disposed in a manner to receive an end portion of the reflective panel member
102
when the reflective panel member
102
is in the reflective state. A support wall
107
retains the reflective panel member
102
at an appropriate position for redirecting a beam of light traveling in a first direction to a second direction.
One problem with the optical matrix switch described above is that the insertion loss between the fibers is quite high due to a fact that there are no lenses for collimating the light between them.
Another problem is that precision alignment is required to connect the first base member and the second base member together so that the support wall is properly oriented to retain the reflective panel member properly in its reflective state.
Additionally, electrostatic torque causes the reflective panel member to move between the reflective state and the non-reflective state. Electrostatic torque is a complicated area of the art and there is limited data to determine when mechanical fatigue might be expected over the lifetime of the conventional optical matrix switch.
As shown in
FIG. 2
, another type of a conventional micromachined free-space optical matrix switch includes a base member
201
, a plurality of reflective panels
202
,
203
, a plurality of microlenses
204
, a plurality of optical fibers
205
, and an actuator. Each reflective panel is pivotally connected to the base member and is unbiasedly movable between a reflective state and a non-reflective state. The actuator is connected to the base member
201
and the reflective panels and causes the reflective panels to move between the reflective state and the non-reflective state.
Each reflective panel includes at least one hinge pin member and at least two hinge pin connecting members. A staple member having a channel sized to receive at least one hinge pin member is connected to the base member
201
with at least one hinge pin member disposed within the channel so that the reflective panel can pivotally move about a pivot axis that extends through at least one hinge pin member.
The actuator includes a hinge assembly and a translation plate. The hinge assembly has at least one connecting rod with a first end pivotally connected to the reflective panel and an opposite second end pivotally connected to the translation plate. The translation plate is slidably connected to the base member and moves between a first position and a second position.
The actuator is a scratch drive actuator mechanism or a comb drive mechanism. One of these mechanisms is connected to the translation plate and is operated in conjunction with the base member to cause the translation plate to move to and between the first and second positions.
This type of optical matrix switch does not include any microstructures for receiving optical fibers and lenses. It is impossible to realize passive alignment between the optical fibers, the mirrors and the lenses.
The optical matrix switch of
FIG. 2
is fabricated using a three-layer polysilicon process that can only be offered by a few MEMS technology centers. Since the three-layer polysilicon process is still not in a definition manner, even though all the mirrors go through the same processes, they still have quite different natural frequencies.
A reflection position of the optical matrix switch is established by placing at least four separated movable components in place. Any vibration may change position of the movable components and cause the switch to go out of the reflection position.
The optical matrix switch has a mirror-to-mirror distance greater than 175 micrometers. It has been shown that the mirror-to-mirror distance more than 175 micrometers results in an insertion loss between the two mirrors greater than 2.5 dB which exceeds the allowable maximum insertion loss for practical applications.
SUMMARY OF THE INVENTION
In order to solve the aforementioned problems and other problems, an optical switch array has been developed by the present invention. The optical switch array at least possesses the following features:
The reflection mirrors of the optical switch array are self-oriented to the vertical direction of its operation plane.
The reflection mirrors and their supporting flexural strips are orthogonal to each other so that bending of the strips can be turned into the vertical movement of the mirrors.
The supporting flexural strips are formed from single crystal silicon with excellent mechanical properties.
The reflection mirrors are formed from (111) silicon crystal planes with excellent optical properties.
The reflection mirrors are double-sided mirrors to increase switching density.
The optical switch array has a plurality of microchannels capable of holding optical fibers therein and realizing passive alignment between the reflection mirrors and the optical fibers.
The optical switch array has a plurality of cylindrical lenses capable of realizing passive alignment with the optical fibers and the reflection mirrors.
With the aforementioned features, the present invention provides an optical switch array comprising a plurality of (111) silicon planar plates formed in a (110) silicon substrate, bonded by two opposite (111) crystal planes vertical to the surface of the (110) silicon substrate and arranged in columns and rows. Each (111) silicon planar plate is supported by a flexural silicon strip that is anchored to the (110) silicon substrate at least at its one side. An air gap separates each silicon strip from the (110) silicon substrate and allows the silicon strip to bend up and down. Two stop shoulders are used to guide the (111) silicon planar plate vertically moving up and down and halt the (111) silicon planar plate precisely at a lifted vertical position.
The optical switch array further comprises a plurality of microchannels formed in the (110) silicon substrate. The longitudinal axis of each microchannel is oriented to a (111) silicon crystal plate at an angle of 135 or 45 degrees so that they are parallel or orthogonal to each other.
Each microchannel holds a cylindrical lens or an optical fiber therein. The optical fiber has one end
Johnsonbaugh Bruce H.
Tsai H. Jey
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