Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-10-26
2001-09-04
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000
Reexamination Certificate
active
06285809
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to optical switch matrices and, more particularly, to an improved optical switch matrix with wraparound architecture
FIG. 1
illustrates the prior art optical switch matrix
10
of which the present invention is an improvement. This prior art optical switch matrix also is described as prior art in U.S. Pat. No. 4,852,958, to Okuyama et al. Matrix
10
connects four input waveguides
18
to four output waveguides
20
via four rows (a, b, c, d) of switches. Each row includes a 1×2 switch
12
, two 2×2 switches
14
and a 2×1 combiner
16
. Each 1×2 switch
12
has a single input port
40
and two output ports: an upper output port
22
and a lower output port
24
. Each 2×2 switch has two input ports and two output ports: an upper input port
26
, a lower input port
28
, an upper output port
30
and a lower output port
32
. Each 2×1 combiner has two input ports: an upper input port
34
and a lower input port
36
; and a single output port
42
. Input waveguides
18
are connected to corresponding input ports
40
. Output waveguides
20
are connected to corresponding output ports
42
. In each row, lower output ports
24
and
32
are connected by intermediate waveguides
38
to lower input ports
28
and
36
of the immediately succeeding switches
14
or
16
; whereas upper output ports
22
and
30
are connected by intermediate waveguides
38
to upper input ports
26
or
34
of respective switches
14
or
16
in the cyclically succeeding row. Cyclical succession means that the connection topology is as though the rows were fabricated on the periphery of a cylinder, parallel to the axis of the cylinder: row b is the successor of row a, row c is the successor of row b, row d is the successor of row c and row a is the successor of row d. So, for example, an intermediate waveguide
38
connects upper output port
22
of switch
12
d
to upper input port
26
of switch
14
aa
. In Okuyama et al., rows a and d are shown connected by intermediate waveguides
38
that cross other intermediate waveguides
38
. For illustrational clarity, this wraparound of the connectivity between rows a and d is represented in
FIG. 1
by the circled terminations A, B and C on intermediate waveguides
38
that connect output ports
22
and
30
in row d to input ports
26
and
34
in row a.
Several implementations of 2×2 switches
14
are known in the prior art, including, among others, directional coupler switches and Mach-Zehnder interferometer switches. A 2×2 switch
14
can be in one of two states: a straight-through state (also called the “bar” state or the “=” state), in which optical energy, that enters switch
14
via upper input port
26
, exits switch
14
via upper output port
30
, and in which optical energy, that enters switch
14
via lower input port
28
, exits switch
14
via lower output port
32
; and a crossover state (also called the “cross” state or the “X” state”) in which optical energy, that enters switch
14
via upper input port
26
, exits switch
14
via lower output port
32
, and in which optical energy, that enters switch
14
via lower input port
28
, exits switch
14
via upper output port
30
. Switch
14
is switched from one state to another by the application of a voltage to an internal component of switch
14
. With no voltage applied, switch
14
is “OFF” in one of its two states. With the switching voltage applied, switch
14
is “ON” in the other of its two states. Two variants of switch
14
thus are possible. In the first variant, switch
14
is in its=state when OFF and in its X state when ON. In the second variant, switch
14
is in its X state when OFF and in its=state when ON. In the context of the present invention, the first variant of switch
14
is preferred.
2×2 switch
14
is turned into a 1×2 switch
12
simply by making one of the input ports an idle port, ie., leaving this input port disconnected. For example, if lower input port
28
is idle, then upper input port
26
serves as input port
40
, upper output port
30
serves as upper output port
22
and lower output port
32
serves as lower output port
24
. In the preferred variant of such a 1×2 switch
12
, when this switch
12
is OFF, it is in its=state, so that optical energy entering via input port
40
leaves via upper output port
22
; and when this switch
12
is ON, it is in its X state, so that optical energy entering via input port
40
leaves via lower output port
24
. Alternatively, if input port
26
is idle, then lower input port
28
serves as input port
40
. In the preferred variant of this alternative 1×2 switch
12
, when this switch
12
is OFF, it is in its=state, so that optical energy entering via input port
40
leaves via lower output port
24
, and when this switch
12
is ON, it is in its X state, so that optical energy entering via input port
40
leaves via upper output port
22
.
2×1 combiners
16
may be either passive or active. 2×2 switch
14
is turned into a 2×1 active combiner
16
simply by malting one of the output ports an idle port, i.e., leaving this output port disconnected. For example, if lower output port
32
is idle, then upper input port
26
serves as upper input port
34
, lower input port
28
serves as lower input port
36
, and upper output port
30
serves as output port
42
. In what follows, an active 2×1 combiner usually is referred to as a “2×1 switch”. In the preferred variant of such a 2×1 switch
16
, when this 2×1 switch
16
is OFF, it is in its=state, so that only optical energy entering via upper input port
34
leaves via output port
42
; and when this 2×1 switch
16
is ON, it is in its X state, so that only optical energy entering via lower input port
36
leaves via output port
42
. Alternatively, if upper output port
30
is idle, then lower output port
32
serves as output port
42
. In the preferred variant of this alternative 2×1 switch
16
, when this 2×1 switch
16
is OFF, it is in its=state, so that only optical energy entering via lower input port
36
leaves via output port
42
, and when this 2×1 switch
16
is ON, it is in its X state, so that only optical energy entering via upper input port
34
leaves via output port
42
. Although 2×1 combiners
16
are most simply implemented as passive combiners, such as y-junction combiners, the preferred 2×1 combiners of the present invention are active 2×1 combiners, both because passive 2×1 combiners are inherently lossy and for a second reason describe below.
By turning appropriate switches
12
and
14
ON and OFF, any input waveguide
18
may be connected to any output waveguide
20
. For example, let 1×2 switches
12
be 2×2 switches with idle lower input ports, let 1×2 switches
12
and 2×2 switches
14
be in their=states when OFF and in their X states when ON, and let 2×1 combiners
16
be passive. With all switches
12
and
14
OFF, input waveguide
18
a
is connected to output waveguide
20
d
, input waveguide
18
b
is connected to output waveguide
20
a
, input waveguide
18
c
is connected to output waveguide
20
b
, and input waveguide
18
d
is connected to output waveguide
20
c
. Turning switch
12
a
ON connects input waveguide
18
a
to output waveguide
20
a
. Turning switch
14
ba
ON connects input waveguide
18
a
to output waveguide
20
b
. Turning switch
14
cb
ON connects input waveguide
18
a
to output waveguide
20
c.
By using active 2×1 combiners
16
, optical switch matrix
10
may be configured so that no input waveguide
18
is connected to any output waveguide
20
unless a switch
12
,
14
or
16
is turned ON. For example, let 1×2 switches
12
and 2×2 switches
14
be as above, and let 2×1 combiners
16
be 2×2 switches, with idle upper output ports, that are in their&equ
Duer Reuven
Nir David
Friedman Mark M.
Lynx Photonic Networks Inc.
Palmer Phan T. H.
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