Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-04-07
2002-08-06
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000, C385S020000
Reexamination Certificate
active
06430329
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to optical switch arrays and, more particularly, to an optical switch array, of particularly compact geometry, in which arbitrary combinations of the inputs and outputs are explicitly addressable.
Integrated optical switches are well-known. For an early review of the art, see Lars Thylen, “Integrated optics in LiNbO
3
: recent developments in devices for telecommunications”,
Journal of Lightwave Technology
vol. 6 no. 6 (June 1988), pp. 847-861. Waveguides are created in a lithium niobate substrate by processing the substrate locally to increase the index of refraction. For example, the index of refraction of lithium niobate may be increased locally by diffusing titanium into the substrate. To divert light from one waveguide to another, the waveguides are coupled by local optoelectrical manipulation of their indices of refraction. Well-known examples of optoelectrical switches include directional couplers, BOA couplers, digital-optical-switches and x-switches. Depending on the voltage applied to such a switch, light is thus partly or completely diverted from an input waveguide to an output waveguide.
By appropriately combining waveguides and switches, a switch array is formed to switch light from a plurality of input waveguides among a plurality of output waveguides. A variety of switch array geometries are known.
FIG. 1A
is a conceptual illustration of a switch of one such geometry: crossbar geometry. A set of input waveguides
10
crosses a set of output waveguides
12
. At the crossing points, the waveguides are coupled by 2×2 switches
14
. For simplicity, only four input
5
waveguides
10
and four output waveguides
12
are shown in FIG.
1
A. Typically the numbers of input waveguides
10
and output waveguides
12
are equal powers of 2, up to a practical maximum of 32.
FIG. 1B
shows, schematically, the actual layout of the switch array of FIG.
1
A. Switches
14
are shown as directional couplers, in which parallel segments of the waveguides are flanked by electrodes (not shown) to which the coupling voltages are applied. Note that input waveguide
10
a
leads directly into output waveguide
12
a
, that input waveguide
10
b
leads directly into output waveguide
12
b
, that input waveguide
10
c
leads directly into output waveguide
12
c
, and that input waveguide
10
d
leads directly into output waveguide
12
d
. To allow arbitrary coupling of inputs to outputs, three auxiliary waveguides
11
a
,
11
b
and
11
c
are provided. Waveguides
10
a
-
12
a
and
10
b
-
12
b
are coupled in switch
14
a
. Waveguides
10
b
-
12
b
and
10
c
-
12
c
are coupled in switches
14
b
and
14
c
. Waveguides
10
c
-
12
c
and
10
d
-
12
d
are coupled in switches
14
d
,
14
e
and
14
f
. Waveguides
10
d
-
12
d
and
11
a
are coupled in switches
14
g
,
14
h
,
14
i
and
14
j
. Waveguides
11
a
and
11
b
are coupled in switches
14
k
,
14
l
and
14
m
. Waveguides
11
b
and
11
c
are coupled in switches
14
n
and
14
o
. Note that switches
14
g
,
14
k
and
14
n
actually are 1×2 switches, that switches
14
j
,
14
m
and
14
o
actually are 2×1 switches, and that there is no switch corresponding to the lowermost 2×2 switch
14
of FIG.
1
A. (A 1×2 switch is a 2×2 switch with one input deactivated; a 2×1 switch is a 2×2 switch with one output deactivated.)
Switch arrays based on geometries such as the crossbar geometry of
FIGS. 1A and 1B
can be used to divert input signals to output channels arbitrarily. Signals from any input channels can be directed to any output channel, and even to multiple output channels, in broadcast and multicast transmission modes.
Despite the conceptual simplicity of the crossbar geometry of
FIGS. 1A and 1B
, this geometry has been found inferior, in practice, to two other geometries, the tree geometry, illustrated in
FIG. 2
, and the double crossbar geometry, illustrated in FIG.
3
.
FIG. 2
shows the tree geometry, for four input waveguides
20
and four output waveguides
22
. Waveguides
20
lead into a binary tree of 1×2 switches
24
. Waveguides
22
emerge from a complementary binary tree of 2×1 switches
26
. The highest order branches of the binary trees are connected by intermediate waveguides
28
.
FIG. 3
shows the double crossbar geometry, for four input waveguides
30
and four output waveguides
32
. Each input waveguide
30
traverses four 1×2 switches
34
a
,
34
b
,
34
c
and
34
d
. Each output waveguide
32
traverses four 2×1 switches
36
a
,
36
b
,
36
c
and
36
d
. The remaining outputs of switches
34
are connected to respective inputs of switches
36
by intermediate waveguides
38
. Note that, in principle, switches
34
d
and
36
a
are not needed, because input waveguides
30
could lead directly to switches
36
d
and output waveguides
32
could emerge directly from switches
36
a
; but, in practice, the illustrated configuration has been found to reduce cross-talk.
The tree and double crossbar geometries require larger numbers of switches than the equivalent crossbar geometry. Nevertheless, the tree and double crossbar geometries have certain advantages over the crossbar geometry:
1. The tree and double crossbar geometries have lower worst-case crosstalk than the crossbar geometry.
2. In general, the path from a particular input waveguide to a particular output waveguide through a crossbar switch array is not unique. Therefore, computational resources must be devoted to reconfiguring a crossbar switch array in real time. In a tree switch array or in a double crossbar switch array, the path from any particular input waveguide to any particular output waveguide is unique, so it is trivial to compute how to reconfigure such a switch array in real time.
3. To prevent loss of optical power by radiation, the intermediate waveguides of an optical switch array must have gentle curvature. In the case of the crossbar geometry, this requires that the switches be arranged in a diamond pattern, as illustrated in
FIGS. 1A and 1B
. This is a less efficient packing of the switches than, for example, the rectangular matrix pattern of the double crossbar switch as illustrated in FIG.
3
.
SUMMARY OF THE INVENTION
According to the present invention there is provided an optical switch array including: (a) at least three output waveguides; (b) a first group of at least three input waveguides; (c) for each of the input waveguides of the first group: for each of the output waveguides, a combining element coupling the each output waveguide only to the each input waveguide; and (d) for each of the input waveguides of the first group, a switching mechanism for coupling all of the output waveguides to the each input waveguide; the output waveguides, the input waveguides, the combining elements and the switching mechanism all being arranged substantially in a common plane; all of the output waveguides traversing successively respective the combining elements in a common order relative to the input waveguides of the first group.
According to the present invention there is provided a method for switching signals to at least one of at least three output channels from at least one of at least three input channels, each input channel providing signals to only one output channel, including the steps of: (a) providing an optical switch array including: (i) at least three output waveguides, each of the output waveguides corresponding uniquely to one of the output channels, (ii) at least three input waveguides, each of the input waveguides corresponding uniquely to one of the input channels, (iii) for each of the input waveguides: for each of the output waveguides, a combining element coupling the each output waveguide only to the each input waveguide, and (iv) for each of the input waveguides, a switching mechanism for coupling all of the output waveguides to the each input waveguide, the output waveguides, the input waveguides, the combining elements and the switching mechanism all being
Friedman Mark M.
Lynx Photonix Networks Inc.
Sanghavi Hemang
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