Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1998-11-20
2001-03-27
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Switch
C385S017000, C385S018000, C385S019000
Reexamination Certificate
active
06208778
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to optical switching arrangements and more particularly to switching arrangements for inhibiting crosstalk among optical waveguides.
BACKGROUND ART
While signals within telecommunications and data communications networks have been traditionally exchanged by transmitting electrical signals via electrically conductive lines, an alternative medium 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 often satisfied by converting the optical signals to electrical signals at the inputs of a switching network, 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 one of a number of parallel input optical fibers to any one of a number of parallel output optical fibers. Another such matrix of switching elements is described in U.S. Pat. No. 4,988,157 to Jackel et al. An isolated switching element
10
is shown in
FIG. 1
, while a 4×4 matrix
32
of switching elements is shown in FIG.
2
. The optical switch of
FIG. 1
is formed on a substrate. The substrate may be a silicon substrate, but other materials may be used. The optical switch
10
includes planar waveguides defined by a lower cladding layer
14
, a core
16
, and an upper cladding layer, not shown. The core is primarily silicon dioxide, but with other materials that achieve a desired index of refraction for the core. The cladding layers should be formed of a material having a refractive index that is substantially different from the refractive index of the core material, so that optical signals are guided along the waveguides.
The material core
16
is patterned to form an input waveguide
20
and an output waveguide
26
of a first optical path and to define a second input waveguide
24
and a second output waveguide
22
of a second optical path. The upper cladding layer is then deposited over the patterned core material. A gap
28
is formed by etching a trench through the core material and the two cladding layers to the substrate. The waveguides intersect the trench at an angle of incidence greater than the critical angle of total internal reflection (TIR) when the location
30
aligned with 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 location
30
between the aligned 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 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 switching element
10
between a transmissive state and a reflective state. The element includes at least one heater that can be used to manipulate fluid within the gap
28
. One approach is illustrated in FIG.
1
. The switching element
10
includes two microheaters
50
and
52
that control the position of a bubble within the fluid-containing gap. The fluid within the gap 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
54
and
56
may be used to provide a steady supply of fluid, but this is not critical. In the operation of the switching element, one of the heaters
50
and
52
is brought to a temperature sufficiently high to form a gas bubble. Once formed, the bubble can be maintained in position with a reduced current to the heater. In
FIG. 1
, the bubble is positioned at the location
30
of the intersection of the four waveguides. Consequently, an input signal along the waveguide
20
will encounter a refractive index mismatch upon reaching the gap
28
. This places the switching element in a reflecting state, causing the optical signal along the waveguide
20
to be redirected to the output waveguide
22
. However, even in the reflecting state, the second input waveguide
24
is not in communication with the output waveguide
26
.
If the heater
50
at location
30
is deactivated and the second heater
52
is activated, the bubble will be attracted to the off-axis heater
52
. This allows index-matching fluid to fill the location
30
at the intersection of the waveguides
20
-
26
. The switching element
10
is then in a transmitting state, since the input waveguide
20
is optically coupled to the collinear waveguide
26
.
In the 4×4 matrix
32
of
FIG. 2
, any of the four input waveguides
34
,
36
,
38
and
40
may be optically coupled to any one of the four output waveguides
42
,
44
,
46
and
48
. The switching matrix is sometimes referred to as a “non-blocking” matrix, since any free input fiber can be connected to any free output fiber regardless of which connections have already been made through the switching matrix. Each of the sixteen optical switches has a gap that causes TIR in the absence of a fluid at the location between collinear waveguides, but collinear waveguides of a particular waveguide path are optically coupled when the locations between the waveguides are filled with the fluid. Trenches that are in the transmissive state are represented by fine lines that extend at an angle through the intersections of the optical waveguides in the matrix. On the other hand, trenches of switching elements in a reflecting state are represented by broad lines through points of intersection.
In
FIGS. 1 and 2
, the input waveguide
20
is in optical communication with the output waveguide
22
, as a result of TIR at the empty location
30
of the gap
28
. Since all other cross points for allowing the input waveguide
34
to communicate with the output waveguide
44
are in a transmissive state, a signal that is generated at input waveguide
34
will be received at output waveguide
44
. In like manner, the input waveguide
36
is optically coupled to the first output waveguide
42
, the third input waveguide
38
is optically coupled to the fourth output waveguide
48
, and the fourth input waveguide
40
is optically coupled to the third output waveguide
46
.
One concern with optical switching elements
10
of this type is that in the transmissive state, there is a small but potentially objectionable amount of reflection. If the index of refraction of the fluid is different than that of the core material
16
, reflections occur. A precise match between the indices of refraction is problematic, since there are other considerations in the selection of a fluid. For example, since the fluid is manipulated using thermal energy, the thermal properties of the liquid must be considered. The greater the mismatch between the index of refraction of the fluid and the index of refraction of the core material
16
, the greater the intensity of leakage to the second output waveguide
22
when the switching element is in the transmissive state for optically coupling the collinear waveguides
20
and
26
. This leakage will cause crosstalk among the waveguides.
What is needed is a switching arrangement that achieves greater isolation among waveguides of an optical switch. Particularly, what is needed is a switching arrangement that inhibits crosstalk among waveguides.
SUMMARY OF THE INVENTION
A crosstalk-inhibiting arrangement for a switching cell includes using more than one fluid-manipulable switching mechanism within the cell. An input wavegu
Agilent Technologie,s Inc.
Font Frank G.
Natividad Phil
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