U.S. patent application number 09/795781 was filed with the patent office on 2003-11-27 for totally photonic switch for optical fibers.
Invention is credited to James, Kenneth A., Yee, Jonathan W..
Application Number | 20030219199 09/795781 |
Document ID | / |
Family ID | 29550486 |
Filed Date | 2003-11-27 |
United States Patent
Application |
20030219199 |
Kind Code |
A1 |
James, Kenneth A. ; et
al. |
November 27, 2003 |
TOTALLY PHOTONIC SWITCH FOR OPTICAL FIBERS
Abstract
A totally photonic switch having a pair of D-optical fibers by
which optical energy can be efficiently coupled at high speed from
one D-fiber to the other. The cores of the D-fibers are held in
close proximity to one another at opposite sides of a thin (e.g.,
film) evanescent coupling region that is fabricated from a doped
semiconductor based material (e.g., silicon dioxide). A pair of
thin metal electrodes are located between the pair of D-fibers and
the opposite sides of the evanescent coupling region by which to
cause the coupling region to become electrooptic, to bond the
fibers to the coupling region, and to receive a controlled voltage
from a DC voltage source. Optical energy is coupled (i.e.,
switched) between the D-fibers depending upon the magnitude of the
voltage applied to the electrodes. A plurality of such totally
photonic switches can be arranged to form a coupler network on a
semiconductor wafer so as to route optical signals over a selected
switch path between input and output sides of the network.
Inventors: |
James, Kenneth A.; (Pauma
Valley, CA) ; Yee, Jonathan W.; (Cypress,
CA) |
Correspondence
Address: |
MORLAND C FISCHER
2030 MAIN ST
SUITE 1050
IRVINE
CA
92614
|
Family ID: |
29550486 |
Appl. No.: |
09/795781 |
Filed: |
March 1, 2001 |
Current U.S.
Class: |
385/30 |
Current CPC
Class: |
G02B 6/357 20130101;
G02B 6/3502 20130101; G02B 6/3546 20130101; G02B 6/3536 20130101;
G02B 6/283 20130101; G02F 1/3131 20130101; G02B 6/3582 20130101;
G02F 1/3132 20130101 |
Class at
Publication: |
385/30 |
International
Class: |
G02B 006/26 |
Claims
We claim:
1. An optical switch comprising: first and second optical fibers
arranged in spaced proximity to one another and adapted to carry
optical energy; an evanescent coupling region having first and
opposite sides and running between said first and second optical
fibers; a first electrode located between said first optical fiber
and the first side of said evanescent coupling region and a second
electrode located between said second optical fiber and the
opposite side of said evanescent coupling region; and a source of
voltage connected to the first and second electrodes at the first
and opposite sides of said evanescent coupling region to apply a
voltage to said first and second electrodes and thereby control the
transfer of optical energy between said first and second optical
fibers by way of said evanescent coupling region depending upon the
magnitude of said voltage.
2. The optical switch recited in claim 1 wherein each of said first
and second optical fibers is a D-shaped fiber.
3. The optical switch recited in claim 2 wherein each of said
D-shaped optical fibers has a flat face and a core, said D-shaped
optical fibers being arranged face-to-face one another at the first
and opposite sides of said evanescent coupling region so that the
respective cores thereof are located in close proximity.
4. The optical switch recited in claim 3, wherein the flat faces of
said first and second D-shaped optical fibers are respectively
bonded to the first and opposite sides of said evanescent coupling
region by means of said first and second electrodes located
therebetween.
5. The optical switch recited in claim 2, further comprising a
semiconductor substrate having top and bottom surfaces and first
and second troughs formed in said top and bottom surfaces to
receive respective ones of said first and second D-shaped optical
fibers.
6. The optical switch recited in claim 5, wherein said first and
second troughs are axially aligned so as to share a common bottom
which forms said evanescent coupling region running between said
first and second D-shaped optical fibers, such that said first and
second D-shaped optical fibers are arranged face-to-face one
another across the common bottom of said first and second
troughs.
7. The optical switch recited in claim 5, wherein said evanescent
coupling region running between said first and second D-shaped
optical fibers is formed from a completely oxidized semiconductor
material.
8. The optical switch recited in claim 7, wherein said evanescent
coupling region is formed from silicon dioxide
9. The optical switch recited in claim 7, wherein the oxidized
semiconductor material of said evanescent coupling region is doped
to an index of refraction that matches the index of refraction of
the cladding of said first and second D-shaped optical fibers.
10. The optical switch recited in claim 7, further comprising a
relatively thick passivation region communicating with said
evanescent coupling region and being formed from the same oxidized
semiconductor material from which said evanescent coupling region
is formed, and a thin metal layer by which to bond said passivation
region to said first and second D-shaped optical fibers.
11. The optical switch recited in claim 10, wherein the index of
refraction of said relatively thick passivation region matches the
index of refraction of the cladding of said first and second
D-shaped optical fibers.
12. The optical switch recited in claim 5, further comprising a
plurality of said optical switches arranged in a network on said
semiconductor substrate, each of said plurality of optical switches
having first and second troughs and first and second D-shaped
optical fibers received in said first and second troughs and
positioned in face-to-face alignment with one another at first and
opposite sides of an evanescent coupling region running
therebetween, at least one of said first and second D-shaped
optical fibers from at least some of said plurality of optical
switches being the same optical fiber.
13. A method for making an optical switch comprising the steps of
forming a trough in each of the top and bottom of a semiconductor
substrate such that said troughs are axially aligned one above the
other so as to establish an evanescent coupling region along a
shared bottom running between said troughs; simultaneously applying
heat and an electric field to said evanescent coupling region to
make said coupling region electrooptic in response to a voltage
applied thereto; positioning an optical fiber in each of said
troughs at the top and bottom of said semiconductor substrate so
that said optical fibers are separated from one another by said
evanescent coupling region; locating a first electrode between the
optical fiber in the trough at the top of said semiconductor
substrate and a first side of said evanescent coupling region;
locating a second electrode between the optical fiber in the trough
at the bottom of said semiconductor substrate and the opposite side
of said evanescent coupling region; and applying a voltage to said
first and second electrodes for controlling the transfer of optical
energy between the optical fibers via said evanescent coupling
region depending upon the magnitude of the applied voltage.
14. The method recited in claim 13, including the additional steps
of producing each of said optical fibers to have a flat face, and
positioning said optical fibers in said axially aligned troughs
formed in the top and bottom of said semiconductor substrate such
that the flat faces of said optical fibers are positioned against
the first and opposite sides of said evanescent coupling region in
opposing face-to-face alignment with one another.
15. The method recited in claim 13, including the additional step
of oxidizing said evanescent coupling region between said troughs
formed in the top and bottom of said semiconductor substrate.
16. The method recited in claim 15, wherein said semiconductor
substrate is formed from silicon and said evanescent coupling
region consists of silicon dioxide following said oxidizing
step.
17. The method recited in claim 15, including the additional step
of doping said evanescent coupling region prior to said oxidizing
step, such that evanescent coupling region has an index of
refraction that matches the index of refraction of the cores of
said optical fibers
18. The method recited in claim 17, including the additional steps
of oxidizing said semiconductor substrate to form a passivation
region communicating with said evanescent coupling region, and
bonding said optical fibers to said passivation region at the top
and bottom of said semiconductor substrate.
19. The method recited in claim 18, wherein said passivation region
has an index of refraction that matches the index of refraction of
the cladding of said optical fibers.
20. A method for making an optical switch comprising the steps of:
locating a first electrode at a first side of an optical coupling
region manufactured from a semiconductor material; locating a
second electrode on the opposite side of said optical coupling
region; simultaneously applying heat and an electric field to said
optical coupling region for making said coupling region
electrooptic in response to a voltage applied thereto; connecting a
first optical fiber to the first side of said optical coupling
region; connecting a second optical fiber to the opposite side of
said optical coupling region such that at least some of said first
and second optical fibers are aligned one above the other with said
optical coupling region extending therebetween; and applying a
voltage to said first and second electrodes for controlling the
transfer of optical energy between said first and second optical
fibers via said optical coupling region depending upon the
magnitude of the applied voltage.
21. The method recited in claim 20, including the additional step
of applying the electric field to said optical coupling region by
means of applying another voltage to said first and second
electrodes at the first and opposite sides of said optical coupling
region at the same time that said heat is applied for making said
coupling region electrooptic.
22. The method recited in claim 20, including the additional steps
of connecting said first and second optical fibers to the first and
opposite sides of said optical coupling region by applying heat to
said first and second electrodes and thereby bonding said first and
second optical fibers to said coupling region by means of said
first and second electrodes.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a totally photonic switch having a
pair of D-optical fibers separated by an evanescent coupling region
and a pair of thin metal electrodes to which a voltage is applied
for causing optical signals to be transferred between the pair of
optical fibers in a predictable and controllable manner.
[0003] 2. Background Art
[0004] The totally photonic switch which forms the present
invention uses principles that are characteristic of a conventional
passive 3 db fiber coupler. Such a conventional fiber coupler is
typically fabricated by twisting two identical fibers together
under high heat and tension. The tension under heat deforms the
fibers to reduce the thickness of their cladding, whereby an
optical signal is evanescently coupled from one fiber to the other.
This twisting of the fibers effectively compresses the length of
the coupling or interactive region therebetween so that the coupler
can be accommodated according to known packaging techniques,
especially in situations where half the optical energy is to be
coupled between the fibers.
[0005] Doubling the half energy coupling length will permit all of
the optical signal to be evanescently coupled, while quadrupling
the half energy coupling length will cause the signal to couple
completely from one fiber to the other and then completely back to
the original fiber. If the evanescent coupling could be controlled
(i.e., varied by a factor of 2) over a fixed coupling length, an
input optical signal could be switched between two optically
coupled fibers.
[0006] However, it is difficult to achieve optimal and predictable
evanescent coupling in an optical switch by using the conventional
technique of twisting together a pair of optical fibers. Firstly,
the twisted fibers are bulky and would consume a large area,
particularly if a switch network were contemplated using
conventional planar semiconductor processing techniques. Moreover,
it would be unlikely that the fibers from different couplers could
be identically twisted, such that some of the optical switches
would have different physical characteristics that vary slightly
from one to the other and, consequently, mismatched optical
characteristics. What is more, a twisted fiber switch is not
electrically controllable, whereby the maximum switching (i.e.,
coupling) speed would be undesirably limited. In addition, the
twisted fiber construction is not compatible with modern
photolithographic and microelectronic fabrication processes.
[0007] Fiber coupling structures are known in which direct
fiber-to-fiber coupling is not possible. Some fiber coupling
structures interrupt the fiber path and use a wave guide which
correspondingly results in a space consuming fiber-to-wave
guide-to-fiber optical path. Other fiber coupling structures
require the inefficient use of liquids, mirrors and similar
mechanical reflective devices (e.g., including baffles, flexures
and the like) which slows the speed in which optical energy can be
coupled from one transmission path to another and makes the optical
coupling difficult to control. Examples of known optical couplers
like those described above are available by referring to one or
more of the following Untied States patents:
1 5,253,094 12 Oct. 1993 5,504,607 2 Apr. 1996 5,729,641 17 Mar.
1998 5,768,462 16 Jun. 1998 5,854,864 29 Dec. 1998 6,047,095 4 Apr.
2000
SUMMARY OF THE INVENTION
[0008] A totally photonic switch is disclosed for the high speed,
efficient fiber-to-fiber coupling of optical signals between a pair
of D-shaped optical fibers. A pair of axially aligned troughs are
formed in the top and bottom of a semiconductor (e.g., silicon)
substrate. The axially aligned troughs are preferably etched in the
substrate so as to have a trapezoidal shape and a thin silicon
coupling region that is shared by the troughs as a common bottom.
The D-fibers are received within respective troughs and laid
face-to-face one another against opposite sides of the coupling
region so that the cores of the fibers are arranged in close
proximity.
[0009] The silicon coupling region that is shared by the bottoms of
the troughs is completely oxidized to form a thin film silicon
dioxide evanescent coupling region extending between the fiber
cores. Prior to oxidizing, the silicon coupling region may be doped
to an index of refraction that is similar to the cores of the
D-fibers. An ultra thin metal film is applied along the top and
bottom of the silicon dioxide evanescent coupling region to create
a pair of electrodes. By poling the electrodes during fabrication
of the switch (i.e., applying a DC voltage to the electrodes at the
same time that the semiconductor substrate is heated), the silicon
dioxide evanescent coupling region will be polarized so as to
become electrooptic. Following fabrication, another DC voltage is
applied to the electrodes to selectively control the switch and the
coupling of optical energy between the cores of the D-fibers. By
applying localized heat, the thin metal film electrodes can also be
used to bond the opposing flat faces of the D-fibers to the top and
bottom of the silicon dioxide evanescent coupling region. Ultra
thin metal films and the aforementioned localized heating can also
be employed to bond the D-fibers to the relatively thick silicon
dioxide passivation region. As in the case of the thin film silicon
evanescent coupling region, the index of refraction of the
relatively thick passivation region can be chosen to match that of
the cladding of the D-fibers. Accordingly, the cores of the
D-fibers received within the axially aligned troughs are separated
only by the required cladding thickness along the flat faces
thereof, the thin silicon dioxide electrooptic evanescent coupling
region running between the flat faces, and the ultra-thin metal
electrodes bonded to the top and bottom of the coupling region.
[0010] Optical signals are switched between the cores of a pair of
the D-shaped optical fibers of a single photonic switch or a
plurality of photonic switches arranged on a semiconductor wafer to
form a fiber coupler network. That is, by driving the electrodes
which extend along the top and bottom of the evanescent coupling
region of the photonic switch to a first DC voltage (e.g., ground),
an optical signal is transferred from one of the pair of optical
fibers to the other. However, by driving the electrodes of the
photonic switch to a second DC voltage (e.g., 3.0 volts), an
optical signal is transferred from one of the pair of optical
fibers to the other and then back to the first fiber so that the
optical signal carried on the first fiber is preserved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 illustrates the top of a semiconductor substrate
within which the totally photonic switch which forms the present
invention is fabricated;
[0012] FIG. 2 shows the totally photonic switch of FIG. 1 having a
pair of D-fibers aligned one above the other and separated by an
evanescent coupling region;
[0013] FIG. 3 shows the face-to-face alignment of the D-fibers of
FIG. 2 within oppositely and axially aligned trapezoidal shaped
troughs formed in the semiconductor substrate; and
[0014] FIG. 4 shows a 4.times.4 fiber coupler network by which
optical signals are coupled between respective pairs of D-fibers
from a plurality of the totally photonic switches of this
invention.
DETAILED DESCRIPTION
[0015] The totally photonic switch which forms the present
invention is initially described while referring to FIG. 1 of the
drawings, where there is shown an optical fiber coupler 1. Fiber
coupler 1 is formed on a semiconductor (e.g., silicon, or the like)
substrate 3. A pair of long and narrow, preferably trapezoidal,
troughs (designated 5-1 and 5-2 and best shown in FIG. 3) are
formed in the opposite sides of the substrate 3. Each trough (e.g.,
5-1) is formed by a conventional technique such as, but not limited
to, chemical (KOH) or ion mill etching methods. As is best shown in
FIG. 3, the pair of trapezoidal troughs 5-1 and 5-2 are axially
aligned bottom-to-bottom one another by means of a standard
semiconductor photolithographic process. The bottoms of the
oppositely aligned troughs 5-1 and 5-2 are sized to match the
diameters of a pair of optical D-fibers (designated 7-1 and 7-2 and
best shown in FIGS. 2 and 3) that are to be received therein and
aligned face-to-face one another.
[0016] As will be known to those skilled in the art, each D-fiber
7-1 and 7-2 is produced by extruding or otherwise machining away a
portion of the outer cladding of the fiber to about a micron of the
core, thereby forming a flat polished face on one side thereof.
This process creates a fiber having a D-shaped cross section. Such
a D-fiber 7-1 and 7-2 can be manufactured in either multimode or
single mode form and adapted to be polarization maintaining, if
required.
[0017] As is best shown in FIG. 3 of the drawings, the pair of
D-fibers 7-1 and 7-2 are received within the trapezoidal troughs
5-1 and 5-2 formed in the semiconductor substrate 3, such that the
flat faces of the fibers are disposed one above the other with the
fiber cores held in close proximity. By virtue of an accurate
sizing and alignment of the opposing toughs 5-1 and 5-2, the cores
of D-fibers 7-1 and 7-2 will be automatically and correspondingly
aligned with one another to enable efficient evanescent coupling
therebetween, as well as the ability to electrically alter the
coupling so as to create the photonic switch/coupler 1 of this
invention. As will soon be explained, the photonic switch herein
disclosed allows more reliable optical coupling and switching and
much faster switch speeds than would otherwise be available by
using conventional coupling and switching techniques, such as where
a pair of optical fibers are twisted and deformed to bring their
cores into close proximity, and other conventional optical
switching devices including MEMS, LCD switches, and the like.
[0018] Turning now to FIG. 2 of the drawings, it will be recognized
that the opposing trapezoidal troughs 5-1 and 5-2 formed in the
semiconductor substrate 3 effectively share a common bottom which
establishes a thin silicon evanescent coupling region 10 between
the opposing faces of the D-fibers 7-1 and 7-2. Known semiconductor
processing techniques may be employed to assure a uniform
evanescent coupling region 10. In addition, an ion implanted etch
stop may be placed at the same depth in opposite sides of the
silicon substrate 3 by which to define the thickness of coupling
region 10 and provide for an accurate bottom-to-bottom alignment of
the troughs 5-1 and 5-2.
[0019] The silicon coupling region 10 running between fibers 7-1
and 7-2 is then completely oxidized to form a thin silicon dioxide
film which functions as the shared bottom of troughs 5-1 and 5-2.
Doping the silicon coupling region 10 prior to oxidizing to an
index of refraction that is similar to that of the cores of the
D-fibers 7-1 and 72 can be used to alter the optical index of
refraction of the oxidized coupling region along the shared bottom
of troughs 5-1 and 5-2.
[0020] An ultra thin metal film is applied by a standard
metalization process along the top and bottom of the silicon
dioxide evanescent coupling region 10 in order to create a pair of
electrodes 14-1 and 14-2. The electrodes 14-1 and 14-2 perform
three important functions. First, during fabrication of the coupler
1, the electrodes 14-1 and 14-2 are used as poling electrodes. More
particularly, after the metal electrodes 14-1 and 14-2 are applied
to the evanescent coupling region 10, the substrate 3 is placed in
an oven for approximately one hour and heated to a temperature that
lies in a range of temperatures between 300-400 degrees C. At the
same time that the substrate is heated, a voltage that lies in a
range of voltages between 50-70 volts DC is applied to the
electrodes. The fabrication step of poling (i.e., simultaneously
applying significant heat while subjecting the evanescent coupling
region 10 to an electric field) is believed to cause a permanent
electrooptic effect in coupling region 10. Such an electrooptic
effect will cause a change in the index of refraction of coupling
region 10 in a particular direction in response to an applied
voltage. Accordingly, by using electrodes 14-1 and 14-2 as poling
electrodes, the normally non-electrooptic silicon dioxide
evanescent coupling region 10 can be converted to an electrooptic
coupling region which is essential to being able to selectively
control the switch 1 and the coupling of optical energy between the
D-fibers 7-1 and 7-2.
[0021] The thin metal film electrodes 14-1 and 14-2 are also used
to bond the opposing flat faces of D-fibers 7-1 and 7-2 to the top
and bottom of the silicon dioxide evanescent coupling region 10 by
applying localized heating to essentially weld the fibers 7-1 and
7-2 to the shared bottom of the troughs 5-1 and 5-2 in which the
fibers are received. Following fabrication, and as will be
described when referring to FIG. 4, the electrodes 14-1 and 14-2
are connected to a source of DC voltage by which to control the
operation of coupler 1 by causing the aforementioned index of
refraction change in the silicon dioxide evanescent coupling region
10 along the common bottom of troughs 5-1 and 5-2. Accordingly, the
cores of D-fibers 7-1 and 7-2 of coupler 1 will be held in close
proximity, separated only by the remaining cladding along their
respective flat faces, the thin eletrooptic silicon dioxide
coupling region 10, and the ultra thin metal electrodes 14-1 and
14-2.
[0022] The D-fibers 7-1 and 7-2 can be bonded to the relatively
thick silicon dioxide passivation layers 16-1 and 16-2 by means of
very thin metal films 17-1 and 17-2 and the previously described
localized heating/welding step by which the fibers are also bonded
to the relatively thin silicon dioxide evanescent coupling region
10. As in the case of the thin coupling region 10, the thick
silicon dioxide passivation layers 16-1 and 16-2 can be made to
have an index of refraction that is similar to that of the cladding
of the D-fibers 7-1 and 7-2. Since the D-fibers 7-1 and 7-2 are not
perfectly flexible, some air gaps 18 may occur between the fibers
and the passivation layers 16-1 and 16-2. It can be appreciated
that the index of refraction of air is considerably lower than that
of the core or cladding of the D-fibers 7-1 and 7-2 so that little
energy will be lost to air gaps 18.
[0023] FIG. 4 of the drawings shows the fiber coupler 1 of FIGS.
1-3 used to form a 4.times.4 fiber coupler network 20. In this
case, fiber coupler network 20 includes an arrangement of five
photonic switches 21-1, 21-2, 21-3, 21-4, and 21-5, each of which
being identical to the fiber coupler photonic switch 1. Although
FIG. 4 illustrates only the top surface of a semiconductor wafer 24
and the first of a pair of actually aligned trapezoidal troughs
26-1, 26-2, 26-3, 26-4, and 26-5 formed therein, it is to be
understood that the bottom of wafer 24 having the second of the
pair of trapezoidal troughs (not shown) is identical to that shown
in FIG. 3, but for the orientation of the optical fiber received
therein.
[0024] More particularly, a total of six D-optical fibers 27, 28,
29, 30, 31 and 32, are required to implement the 4.times.4 coupler
network 20 of FIG. 4 Photonic switch 26-5 functions as a central
routing switch and is located between origination switches 21-1 and
21-2 at the input side of network 20 and terminus switches 21-3 and
21-4 at the output side of network 20. A first optical fiber runs
between input and output sides of network 20 through the troughs
26-1, 26-5, and 26-4 of origination switch 21-1, central routing
switch 21-5, and terminus switch 21-4 at the top of the
semiconductor wafer 24. The second optical fiber 28 runs between
the input and output sides of network 20 through the troughs (not
shown) that are formed at the bottom of the semiconductor wafer 24
below the troughs 26-2, 26-5 and 26-3 of origination switch 21-2,
central routing switch 21-5 and terminus switch 21-3. The third
optical fiber 29 runs from the input side of network 20 to and
stops at the trough (not shown) that is formed in the bottom of the
semiconductor wafer 24 below the trough 26-1 of origination switch
21-1. The fourth optical fiber 30 runs from the input side of
network 20 to and stops at the trough 26-2 of origination switch
21-2 that is formed in the top of the semiconductor wafer 24. The
fifth optical fiber 31 runs from the trough 36-3 of the terminus
switch 21-3 that is formed in the top of the semiconductor wafer 24
to the output side of network 20. Lastly, the sixth optical fiber
32 runs from the trough (not shown) of the terminus switch 21-4
that is formed in the bottom of the semiconductor wafer 24 below
the trough 26-2 to the output side of network 20.
[0025] Switching (i.e., the optical coupling of energy between the
top and bottom D-fibers 7-1 and 7-2) of the switch 1 of FIGS. 1-3
and any of the switches 21-1 . . . 21-5 of the network 20 of FIG. 4
is controlled by applying a low power DC voltage to the thin
elecrooptic silicon dioxide evanescent coupling region 10 by way of
the electrodes (designated 14-1 and 14-2 of FIGS. 1-3). A suitable
DC voltage for controlling the optical coupling between the fibers
may be CMOS logic level voltages (e.g., 3.0 volts and ground). Most
typically, when an optical switch/coupler is passive and no power
is applied to the electrodes 14-1 and 14-2 thereof, optical energy
is transmitted from one of the pair of top or bottom fibers 7-1 or
7-2 to the other. When an optical switch/coupler is active such
that a voltage is applied across the electrodes, optical energy is
transmitted from one of the pair of D-fibers 7-1 or 7-2 to the
other and then back to the first fiber so that the optical energy
on the first fiber is preserved. That is to say, the poled
electrooptic silicon dioxide coupling region 10 causes an optical
signal to be coupled back and forth between a pair of D-fibers in a
switch/coupler of the network 20 of FIG. 4. Of course, the active
and passive states of an optical switch/coupler and the
corresponding voltages applied thereto could be reversed if the
bias of the electrooptic effect in coupling region 10 were reversed
during fabrication of coupler 1.
[0026] By way of example, an input optical signal at the input side
of the switch network 20 of FIG. 4 is selectively transmitted to
the output side over a particular switch path, as follows: The
input signal is initially received by the optical fiber 30. By
maintaining the origination optical switch 21-2 at a passive switch
condition, the optical signal will be transmitted from optical
fiber 28 to optical fiber 30. By driving the central routing
optical switch 21-5 to an active switch condition, the optical
signal is transmitted from optical fiber 28 to optical fiber 27 and
then back to optical fiber 28. By driving terminus optical switch
21-3 to a passive switch condition, the optical signal is
transmitted from optical fiber 28 to optical fiber 31 where the
optical signal is carried to a suitable output terminal (not shown)
at the output side of switch network 20.
[0027] In this same regard, the electrodes of the same and/or
different photonic switches 21-1 . . . 21-5 of the 4.times.4
coupler network 20 (or any other coupler network) can be
selectively driven by suitable processing electronics between
active and passive switch conditions to rapidly and reliably route
a plurality of optical signals between input and output sides of
the network without consuming excessive power or space so as to
make the network ideally suited for data transmission by employing
conventional semiconductor fabricating techniques.
[0028] It may now be appreciated by those skilled in the art that
the mode structure of the closely spaced fibers is optimized in the
switch/coupler herein disclosed which enables both a direct and
highly efficient D-fiber-to-D-fiber optical coupling without using
a space consuming wave guide structure. What is more, the
switch/coupler of this invention can be fabricated entirely
according to available photolithographic and microelectronic
processes in a completely optical fiber based environment, while
avoiding the addition of liquids, mirrors, LCD reflectors, and the
like. By virtue of the electrooptic evanescent coupling region, it
is possible to actively and selectively control the direction in
which optical energy is transferred between a pair of D-fibers in a
single switch/coupler as well as a network of switch/couplers.
* * * * *