Optical switch

Details Optical switch Optical switch

2001-08-30

2003-09-23

Nguyen, Khiem (Department: 2839)

Optical waveguides

With optical coupler

Switch

Reexamination Certificate

active

06625343

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an optical switch and, more particularly, to an optical switch of the type wherein a mirror upstanding on a movable electrode plate is brought out of and into the optical path between opposed end faces of output and input optical fibers by electrostatic driving of the movable electrode plate to perform an ON-OFF operation.
A conventional optical switch will be described below with reference to
FIGS. 1A and 1B
.
FIG. 1A
is a top plan view of the optical switch and
FIG. 1B
a sectional view taken along the line
1
B—
1
B in FIG.
1
A.
Reference numeral
20
denotes a movable electrode plate
20
integrally formed with a silicon (Si) substrate through frame-shaped flexure portions
21
, and
41
denotes a mirror formed on the top of the movable electrode plate
20
. The movable electrode plate
20
, the flexure portions
21
and the substrate
10
are formed as an integral whole by subjecting a rectangular starting silicon substrate to thin-film forming, photolithographic and etching process steps. Reference numeral
10
a
denotes a hole formed through the substrate
10
. A brief description will be given of how to manufacture the conventional optical switch. The manufacture begins with the preparation of the substrate
10
whose thickness is hundreds of micrometers. The next step is to form a movable electrode plate (
20
) formation area in middle of the substrate surface and flexure part (
21
) formation areas on both sides thereof through application of thin-film forming, photolithographic and etching techniques to the top surface of the substrate
10
, followed by forming the mirror
41
in the movable electrode plate (
20
) formation area through photolithography and etching, and then by selectively etching away the substrate
10
from underneath to form the through hole
10
a
, providing the movable electrode plate
20
and the flexure portions
21
.
Following this, a stationary electrode plate
23
is attached to the underside of the substrate
10
over the through hole
10
a
in opposing relation to the movable electrode plate
20
. A voltage is applied across the movable and stationary electrode plates
20
and
23
to generate electrostatic force, by which the movable electrode plate
20
is driven toward the stationary electrode plate
23
.
Now, a description will be given of spatial optical path switching by the above optical switch.
FIGS. 1A and 1B
show that light transmitted through an output optical fiber
34
and emitted from its emitting end face is reflected by the mirror
41
and impinges on an input optical fiber
35
as indicated by L
R
. This state will hereinafter be referred to as a steady state. With voltage application across the movable and stationary electrode plates
20
and
23
, electrostatic force is generated to attract the both electrodes toward each other, by which the movable electrode
20
is driven and hence displaced downward with the flexure portions
21
deformed accordingly. With the downward displacement of the movable electrode plate
20
, the mirror
41
formed on the top of the movable electrode plate
20
is also displaced downward and brought out of the optical path of the light beam emitted from the output optical fiber
34
. As a result, the light beam emitted from the optical fiber
34
travels in a straight line and directly impinges on an input optical fiber
35
′ as indicated by L
S
.
The optical switch depicted in
FIGS. 1A and 1B
is provided with one output optical fiber
34
and two input optical fibers
35
and
35
′, and the incidence of light on the both input optical fibers is controlled reversely relative to each other; that is, when the emitted light beam is incident on the one input optical fiber, no light beam is incident on the other, whereas when the light is incident on the latter, no light is incident on the former.
FIGS. 2A
to
2
D depict operations of a 2-by-2 optical switch of the type having two output optical fibers
34
,
34
′ and two input optical fibers
35
,
35
′. The light beam emitted from the output optical fiber
34
is, in the steady state shown in
FIGS. 2A and 2B
, reflected by the mirror
41
on the movable electrode plate
20
and is incident on the input optical fiber
35
. On the other hand, a light beam emitted from the output optical fiber
34
′ is, in the steady state of
FIGS. 2A and 2B
, reflected by the mirror
41
and is incident on the input optical fiber
35
′.
In a driven state shown in
FIGS. 2C and 2D
in which a voltage is applied across the movable and stationary electrode plates
20
and
23
to attract the movable electrode plate
20
toward the stationary electrode plate
23
, the light beam emitted from the output optical fiber
34
travels in a straight line over the mirror
41
and impinges on the input optical fiber
35
′ but does not strike on the other input optical fiber
35
. On the other hand, the light beam emitted from the output optical fiber
34
′ travels in a straight line over the mirror
41
and impinges on the input optical fiber
35
but does not strike on the other input optical fiber
35
′.
In the above prior art examples there is formed on the movable electrode plate
20
only one mirror
41
which reflects or does not reflect incident light beams. Incidentally, since the mirror
41
has a certain thickness, perfect coincidence of the optical axes of incident and reflected light beans is impossible as described below with respect to
FIGS. 3A and 3B
.
FIG. 3A
shows that the light beam emitted from the output optical fiber
34
is reflected by the one surface of the mirror
41
for incidence on the input optical fiber
35
or travels in a straight line over the mirror
41
for incidence on the input optical fiber
35
′. In this state, if the optical axis of the optical fiber
34
′ is adjusted for coincidence or alignment between the optical axis of the light beam emitted from the output optical fiber
34
′ and traveling in a straight line over the mirror
41
and the optical axis of the input optical fiber
35
, the optical axis of the light beam emitted from the output optical fiber
34
′ and reflected by the other surface of the mirror is displaced out of alignment with the optical axis of the input optical fiber
35
′.
Referring next to
FIG. 3B
, in the illustrated state in which the optical axes of the input optical fibers
35
and
35
′ are aligned with the optical axes of the reflected and the straight-line traveling versions of the light beam emitted from the output optical fiber
34
, if the optical axis of the optical fiber
34
′ is adjusted for coincidence or alignment between the optical axis of the light beam emitted from the output optical fiber
34
′ and reflected by the other surface of the mirror
41
and the optical axis of the input optical fiber
35
′, the optical axis of the light beam emitted from the optical fiber
34
′ and traveling in a straight line over the mirror
41
for incidence on the optical fiber
35
is displaced out of alignment with the optical axis of the input optical fiber
35
as shown.
Thus, the use of only one mirror
41
formed on the movable electrode plate
20
permits implementation of the 1-by-2 optical switch as depicted in
FIGS. 1A and 1B
, but such a single-mirror structure cannot be applied to the 2-by-2 optical switch because of the displacement of optical axes as referred to above with reference to
FIGS. 2A
to
2
D or
FIGS. 3A and 3D
. In general, the incidence of light on one mirror from two optical fibers along optical axes crossing at right angles gives rise to the problem of misalignments of optical axes as depicted in
FIGS. 3A and 3B
. This problem arises also in the case of using, in combination, configurations that enable plural optical beams to impinge on each mirror.
Further, since the thickness of the mirror
41
, the accuracy of the position of the mirror
41
on the movable electrode plate
20
and the

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