Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1998-05-19
2001-05-22
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000, C385S020000, C385S024000, C385S129000, C359S199200
Reexamination Certificate
active
06236775
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to optical switch arrays and, more particularly, to an integrated optical switch array 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 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 three input waveguides
10
and three 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
, and that input waveguide
10
c
leads directly into output waveguide
12
c
. To allow arbitrary coupling of inputs to outputs, two auxiliary waveguides
11
a
and
11
b
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
11
a
are coupled in switches
14
d
,
14
e
and
14
f
. Waveguides
11
a and
11
b are coupled in switches
14
g
and
14
h
. Note that switches
14
d
and
14
g
actually are 1×2 switches, that switches
14
f
and
14
h
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. One drawback of known optical switch array configurations is that it is difficult to determine how to configure the switch to achieve a desired coupling of input and output channels. In general, in order to configure a switch array as desired, on the order of N! switch combinations may have to be tested computationally to find the desired combination. In large switch arrays, the time required for this computation is the rate limiting factor in switch array speed.
In the days before integrated optics, Fulenwider, in U.S. Pat. No. 3,871,743, described an optical switch array in which input optical fibers are coupled explicitly to output optical fibers. Each input optical fiber is coupled to each output optical fiber by only two “input ports”. In such a switch geometry, the amount of time needed to decide which “input ports” to activate to achieve arbitrary coupling of inputs to outputs is linear in the number of coupled channels. Unfortunately, the particular embodiment described by Fulenwider is not well-suited to fabrication as an integrated optical device.
There is thus a widely recognized need for, and it would be highly advantageous to have, an integrated optical switch array, for arbitrary coupling of input channels to output channels, in which the computational burden is linear in the number of coupled channels.
SUMMARY OF THE INVENTION
According to the present invention there is provided an optical switch array including: (a) a plurality of input waveguides; (b) a plurality of output waveguides; (c) for each of the output waveguides other than a last the output waveguide: for each of the input waveguides, a switching element coupling the each input waveguide to the each output waveguide; and (d) for each of the output waveguides, a combining mechanism for coupling all of the input waveguides to the each output waveguide; the input waveguides, the output waveguides, the switching elements and the combining mechanism all being arranged substantially in a common plane.
According to the present invention there is provided a method for switching signals from at least one input channel among a plurality of output channels, each output channel receiving signals from only one input channel, including the steps of: (a) providing an optical switch array including: (i) a plurality of input waveguides, each of the input waveguides corresponding uniquely to one of the input channels, (ii) a plurality of output waveguides, each of the output waveguides corresponding uniquely to one of the output channels, (iii) for each of the output waveguides other than a last the output waveguide: for each of the input waveguides, a switching element coupling the each input waveguide to the each output waveguide, and (iv) for each of the output waveguides, a combining mechanism for coupling all of the input waveguides to the each output waveguide, the input waveguides, the output waveguides, the switching elements and the combining mechanism all being arranged substantially in a common plane; and (b) for each of the output waveguides other than the last output waveguide: setting the switching element, that couples the each output waveguide to the input waveguide that corresponds to the input channel wherefrom a signal is to be switched to the output channel corresponding to the each output waveguide, to divert at least a portion of the signal to the each output waveguide.
According to the present invention there is provided a method for multicasting from at least one input channel to a plurality of output channels, each output channel receiving input from only one input channel, including the steps of: (a) providing an optical switch array including, for each of the output channels other than a last output channel, and for each input channel, a switching element coupling the each output channel to the each input channel; (b) for each output channel other than the last output channel: setting the switching element, that couples the each output channel to the input channel wherefrom a signal is to be switched to the each output channel, to divert at least a portion of the signal to the each output channel, at least one of the switching elements being set to divert only a portion of the signal.
The present invention is based on the realization that a switch array geometry similar to Fulenwider's can in fact be fabricated, essentially in a single plane, as an integrated optical device, for example, on a Z-cut lithium niobate substrate. As in the prior art configuration of
FIG. 1B
, one of the input waveguides continues directly into one of the output waveguides. All but one of the output waveguides is coupled
Friedman Mark M.
Lynx Photonic Networks Inc.
Sanghavi Hemang
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