Thermally actuated optical add/drop switch

Details Thermally actuated optical add/drop switch Thermally actuated optical add/drop switch

2000-02-09

2002-05-28

Sanghavi, Hemang (Department: 2874)

Optical waveguides

With optical coupler

Switch

C385S018000, C385S019000

Reexamination Certificate

active

06396972

ABSTRACT:

TECHNICAL FIELD
The invention relates generally to optical switching arrangements and more particularly to arrangements of thermally actuated switching units for selectively manipulating optical signals from input and add ports to output and drop ports.
BACKGROUND ART
While signals within telecommunications and data communications networks have been traditionally exchanged by transmitting electrical signals via electrically conductive lines, an alternative mode of data exchange is the transmission of optical signals through optical fibers. Information is exchanged in the form of modulations of laser-produced light. The equipment for efficiently generating and transmitting the optical signals has been designed and implemented, but the design of optical switches for use in telecommunications and data communications networks is problematic. As a result, switching requirements within a network that transmits optical signals is sometimes satisfied by converting the optical signals to electrical signals at the inputs of a switching network, and then reconverting the electrical signals to optical signals at the outputs of the switching network.
Recently, reliable optical switching systems have been developed. U.S. Pat. No. 5,699,462 to Fouquet et al., which is assigned to the assignee of the present invention, describes a switching matrix that may be used for routing optical signals from any one of a number of parallel input optical fibers to any one of a number of parallel output optical fibers. An isolated switching unit
10
is shown in FIG.
1
. The switching unit includes planar waveguides that are formed by layers on a substrate. The waveguide layers include a lower cladding layer
14
, an optical core
16
, and an upper cladding layer, not shown. The optical core is primarily silicon dioxide, but with other materials that achieve a desired index of refraction for the core. The cladding layers are formed of a material having a refractive index that is substantially different than the refractive index of the core material, so that optical signals are guided along the core.
The layer of core material
16
is patterned into waveguide segments that define a first input waveguide
20
and a first output waveguide
26
of a first optical path and define a second input waveguide
24
with a second output waveguide
22
of a second optical path. The upper cladding layer is then deposited over the patterned core material. A gap is formed by etching a trench
28
through the core material, the upper cladding layer, and at least a portion of the lower cladding layer
14
. The first input waveguide
20
and the second output waveguide
22
intersect a sidewall of the trench
28
at an angle of incidence greater than the critical angle of total internal reflection (TIR) when the crosspoint
30
of the waveguides is filled with a vapor or gas. Thus, TIR diverts light from the input waveguide
20
to the output waveguide
22
, unless an index-matching fluid resides within the crosspoint
30
between the aligned input and output waveguides
20
and
26
. The trench
28
is positioned with respect to the four waveguides such that one sidewall of the trench passes through or is slightly offset from the intersection of the axes of the waveguides.
The above-identified patent to Fouquet et al. describes a number of alternative approaches to switching the optical switching unit
10
between a transmissive state and a reflective state. One approach is illustrated in FIG.
1
. The switching unit
10
includes a microheater
38
that controls formation of a bubble within the fluid-containing trench. While not shown in the embodiment of
FIG. 1
, the waveguides of a switching matrix are typically formed on a waveguide substrate and the heaters and heater control circuitry are integrated onto a heater substrate that is bonded to the waveguide substrate. The fluid within the trench has a refractive index that is close to the refractive index of the core material
16
of the four waveguides
20
-
26
. Fluid fill-holes
34
and
36
may be used to provide a steady supply of fluid, but this is not critical. In the operation of the switching unit, the heater
38
is brought to a temperature sufficiently high to form a bubble. Once formed, the bubble can be maintained in position by maintaining power to the heater. In
FIG. 1
, the bubble is positioned at the crosspoint
30
of the four waveguides. Consequently, an input signal along the waveguide
20
will encounter a refractive index mismatch upon reaching the sidewall of the trench
28
. This places the switching unit in a reflective state, causing the optical signal along the waveguide
20
to be redirected to the second output waveguide
22
. However, even in the reflective state, the second input waveguide
24
is not in communication with the first output waveguide
26
.
If the heater
38
at crosspoint
30
is deactivated, the bubble will quickly condense and disappear. This allows index-matching fluid to fill the crosspoint
30
of the waveguides
20
-
26
. The switching unit
10
is then in the transmissive state, since input signals will not encounter a significant change in refractive index at the interfaces of the input waveguides
20
and
24
with the trench
28
. In the transmissive state, the optical signals along the first input waveguide
20
will propagate through the trench to the first output waveguide
26
, while optical signals that are introduced via the second input waveguide
24
will propagate through the trench to the second output waveguide
22
.
Matrices of the switching elements
10
may be used to form complex switching arrangements., A switching matrix may have any number of input ports (N) and any number of output ports (M), With each port being connected to an optical fiber. The fluid-controlled switching units allow the arrangement to be a strictly “non-blocking” matrix, since any free input fiber can be optically coupled to any free output fiber without rearrangement of existing connections.
Another type of switching matrix is an add/drop multiplexer that includes add ports and drop ports in addition to the input and output ports. Such multiplexers are utilized in telecommunications applications in which signals are passed through a series of nodes, with each node being able to introduce additional signals and being able to extract those signals that identify that node as a target. For example, each node may be a switching facility of a long distance carrier that supports calls to and from a number of cities. Calls that originate in a city are introduced using add ports within the switching facility of that city. On the other hand, data and voice information for calls directed to a telephone supported by that switching facility are extracted via drop ports. A known switching arrangement
42
that can be used as a rearrangeable add/drop switch is shown in FIG.
2
. The arrangement includes a 4×4 matrix of optical switching units for selectively coupling any one of four input ports
44
,
46
,
48
and
50
to any one of four output ports
52
,
54
,
56
and
58
. In
FIG. 2
, each of the switching units that is in a reflective state is shown as having a bubble at the area of the intersection of input and output waveguides to that switching unit. Thus, switching units
60
,
62
,
64
and
66
are in reflective states. The remaining twelve switching units are in the transmissive state, since there are no bubbles present at the intersections of the input and output waveguides to those switching units.
Optical fibers are connected to each of the input ports
44
-
50
and each of the output ports
52
-
58
. An optical signal that is introduced at the input port
44
will be reflected at the switching unit
62
and will be output via the output port
54
. Similarly, an optical signal from the input port
46
will reflect at the switching unit
64
for output at the port
56
. An optical signal from input port
48
reflects at the switching unit
66
for output via the port
58
. Finally, an optical signal on port
50
is

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