Semiconductor device manufacturing: process – Chemical etching – Liquid phase etching
Reexamination Certificate
2001-11-29
2004-04-20
Thai, Luan (Department: 2827)
Semiconductor device manufacturing: process
Chemical etching
Liquid phase etching
C438S694000, C438S719000, C438S756000
Reexamination Certificate
active
06723659
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micromirror unit used in optical apparatus for the purposes of changing the direction of light. In particular, it relates to a micromirror unit of the type which is advantageously incorporated in an optical switching apparatus (for selectively connecting one optical fiber to another to provide a light passage), an optical disk apparatus (for writing to or reading data from an optical disk), etc.
2. Description of the Related Art
In recent years, optical communications techniques have been widely used in various fields. In optical communications, optical signals are transmitted through optical fibers. In general, use is made of an optical switching device for changing the transmission path of optical signals from one fiber to another. To attain proper data transmission, the operation of the switching device needs to meet several requirements, such as a large data-handling capacity, high-speed data transmission, high stability, etc. In light of these requirements, it is preferable that an optical switching device incorporates a micromirror unit fabricated by a micro-machining technique. With the use of a micromirror unit, there is no need to convert an optical signal to an electrical signal in performing the switching operation between the data input path and the data output path of the switching device. This feature enables a micromirror unit to meet the above-mentioned requirements.
An optical switching device incorporating a micromirror unit fabricated by a micro-machining technique is disclosed for example in a PCT application WO 00/20899 and a treatise titled “Fully Provisioned 112×112 Micro-Mechanical Optical Crossconnect with 35.8 Tb/sec Demonstrated Capacity (Proc. 25th Optical Fiber Communication Conf. Baltimore. PD12 (2000)).
FIG. 39
of the accompanying drawings shows the basic structure of a typical optical switching device. The switching device
200
includes a pair of micromirror arrays
201
-
202
, an input fiber array
203
and an output fiber array
204
. The input fiber array
203
includes a predetermined number of input fibers
203
a
each of which corresponds to a micromirror unit
201
a
of the micromirror array
201
. Likewise, the output fiber array
204
includes a predetermined number of output fibers
204
a
each of which correspond to a micromirror unit
202
a
of the micromirror array
202
. A plurality of micro lenses
205
are arranged in facing relation to the ends of the respective input fibers
203
a
, while a plurality of micro lenses
206
are arranged in facing relation to the ends of the respective output fibers
204
a.
In the optical data transmission, light beams L
1
emitted from the input fibers
203
a
are collimated by the micro lenses
205
and strike upon the respective micromirror units
201
a
. Reflected on these units, the light beams are directed toward the second micromirror array
202
. Each of the micromirror units
201
a
has a mirror surface which is adjustable in orientation for causing the reflected light to be properly directed toward a corresponding one of the micromirror units
202
a
. Likewise, each of the micromirror units
202
a
has a mirror surface which is adjustable in orientation. In this arrangement, the light beam L
1
emitted from an input fiber
203
a
can be caused to enter a selected one of the output fibers
204
a
by changing the orientation of the micromirror units
201
a
and
202
a.
FIG. 40
shows the basic structure of another optical switching device. The illustrated device
300
includes one micromirror array
301
, a stationary mirror
302
and an input/output fiber array
303
. The fiber array
303
includes a predetermined number of input fibers
303
a
and a predetermined number of output fibers
303
b
. The micromirror array
301
includes a plurality of micromirror units
301
a
disposed correspondingly to the respective fibers
303
a
,
303
b
. The switching device
300
also includes a plurality of micro lenses
304
each of which is arranged in facing relation to the end of a corresponding fiber
303
a
or
303
b.
In the device
300
again, the respective micromirror units
301
a
are adjustable in orientation to change the path of a light beam. Specifically, in the optical data transmission, a light beam L
2
emitted from an input fiber
303
a
passes through the micro lens
304
and strikes upon a micromirror unit
301
a
(the “first micromirror unit”
301
a
) Reflected on the first micromirror unit
301
a
, the light beam L
2
is directed toward the stationary mirror
302
, and reflected on the mirror
302
to be directed back toward the micromirror array
301
. As readily understood, the returned light beam can be caused to strike upon a selected micromirror unit
301
a
(the “second micromirror unit”
301
a
) by adjusting the orientation of the first micromirror unit
301
a
. With the second micromirror unit
301
a
properly oriented, the reflected light beam L
2
is caused to enter a selected one of the output fibers
303
b.
In the above-described switching devices
200
and
300
, the structure of each micromirror unit influences the overall performance of the switching device. For instance, the switching accuracy or switching speed may be altered by structural change in the switching device. Further, the control method of adjusting the inclination angle of the mirror surface of a micromirror unit depends on the structure of the micromirror unit. If the control method can be simplified, it is possible to increase the control accuracy. In addition, the simplification of the control method will reduce the burden on a control/drive circuit of the device, thereby making it possible to downsize the switching device as a whole. Furthermore, optical monitoring and prevention of cross talk will also be simplified.
FIG. 41
shows a conventional two-axis type micromirror unit that can be incorporated in the above-described optical switching device
200
or
300
. The illustrated micromirror unit
400
includes a mirror substrate
410
and a base substrate
420
. The mirror substrate
410
is arranged above the base substrate
420
with non-illustrated spacers provided therebetween. The mirror substrate
410
includes a mirror forming base
411
, an inner frame
412
and an outer frame
413
. The mirror forming base
411
is connected to the inner frame
412
by a pair of first torsion bars
414
. The inner frame
412
is connected to the outer frame
413
by a pair of second torsion bars
415
. The first torsion bars
414
define a rotation axis about which the mirror forming base
411
is rotated relative to the inner frame
412
. Similarly, the second torsion bars
415
define another rotation axis about which the inner frame
412
(and hence the mirror forming base
411
) is rotated relative to the outer frame
413
.
The lower surface of the mirror forming base
411
is provided with a pair of first conductive strips or electrodes
411
a
and
411
b
, while the upper surface of the base
411
is provided with a mirror surface (not shown) for reflecting light. The lower side of the inner frame
412
is provided with a pair of second conductive plates or electrodes
412
a
and
412
b.
The base substrate
420
is provided with a pair of third conductive plates or electrodes
420
a
and
420
b
arranged in facing relation to the first electrodes
411
a
and
411
b
, respectively. In addition, the base substrate
420
is provided with a pair of fourth conductive plates or electrodes
420
c
and
420
d
arranged in facing relation to the second electrodes
412
a
and
412
b
, respectively. In the micromirror unit
400
, the mirror forming base
411
is driven about the first or second torsion bars
414
or
415
by generating electrostatic force between the above-mentioned electrodes.
With the above arrangement, the mirror forming base
411
undergoes rotation in an M3-direction (called “M3-rotation” below) about the first torsion bars
414
, for example when the first electrode
411
a
is charge
Kouma Norinao
Mizuno Yoshihiro
Okuda Hisao
Sawaki Ippei
Tsuboi Osamu
Armstrong Kratz Quintos Hanson & Brooks, LLP
Fujitsu Limited
Thai Luan
LandOfFree
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