Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-06-27
2003-05-13
Bovernick, Rodney (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S018000, C385S040000, C349S196000
Reexamination Certificate
active
06563973
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to optical switching devices. More particularly, the present invention relates to a liquid crystal cross-connect for an optical waveguide and to optical prisms.
2. Technical Background
One of the current trends in telecommunications is the use of optical fibers in place of the more conventional transmission media. One advantage of optical fibers is their larger available bandwidth handling ability that provides the capability to convey larger quantities of information for a substantial number of subscribers via a media of considerably smaller size. Further, because lightwaves are shorter than microwaves, for example, a considerable reduction in component size is possible. As a result, a reduction in material, manufacturing, and packaging costs is achieved. Moreover, optical fibers do not emit electromagnetic or radio frequency radiation of any consequence and, hence, have negligible impact on the surrounding environment. As an additional advantage, optical fibers are much less sensitive to extraneous radio frequency emissions from surrounding devices and systems. With the advent of optical fiber networks, flexible switching devices are needed to direct light signals between fibers to all-optical domain fiber networks. Commonly assigned U.S. patent application Ser. No. 09/431,430, entitled “LIQUID CRYSTAL PLANAR NON-BLOCKING N×N CROSS-CONNECT,” and filed on Nov. 1, 1999 on behalf of Thomas M. Leslie et al. discloses a non-blocking N×N cross-connect having an array of liquid crystal (LC) switches in a grid of planar optical waveguides within a light optical circuit (LOC). The disclosed LC switches include rectangular trenches or canals formed in a planar optical waveguide that are filled with an LC material. The various LC switches disclosed can function as a waveguide polarization splitter, a transverse electric (TE) switch cross-point, a transverse magnetic (TM) switch cross-point, a waveguide polarization combiner, a filter, variable optical attenuator, or a signal splitter. The disclosed cross-connect system is formed by combining these elements. The disclosed LC switches can be electrically addressed to create an index change that can either match the waveguide conditions or create a total internal reflection condition.
FIG. 1
shows an example of the cross-connect system disclosed in the above U.S. patent application Ser. No. 09/431430 the disclosure of which is incorporated by reference herein. The cross-connect system includes an input port
10
, a polarization splitter
20
, a TM switch array
30
, a TE switch array
40
, a polarization combiner
50
, and an output port
60
. The input port
10
is a linear array of planar waveguides to which an array of fibers can be pigtailed. Similar to the input port
10
, the output port
60
is a linear array of planar waveguides to which an array of fibers can be pigtailed. Light from the fibers enters the input port
10
and is passed to the polarization splitter
20
.
FIG. 2
shows a more detailed schematic diagram of the cross-connect system shown in
FIG. 1
with the exemplary cross-connect being a 4×4 cross-connect. The polarization splitter
20
, the switching arrays
30
,
40
, and polarization combiner
50
are disclosed in the above U.S. patent application Ser. No. 09/431,430 as being formed with the same fundamental LC switch element, which is an LC-filled trench or canal in a planar waveguide, as generally shown in
FIGS. 3A and 3B
.
The LC switches disclosed in the above U.S. patent application Ser. No. 09/431,430 are polarization dependent and thus, the TE and TM waves are handled separately. Light from the input port
10
enters the polarization splitter
20
, which separates the TE and TM waves by reflecting the TE waves to the TE switch array
40
while passing the TM waves to the TM switch array
30
. Each switch array
30
,
40
has a plurality of LC switch elements
35
,
45
in each path
31
-
34
and
41
-
44
, respectively. A single LC switch element in each path is set to a reflecting state to pass the light onto the polarization combiner
50
. The path difference for the TE and TM waves is substantially identical. The polarization combiner
50
allows the TE wave to pass while reflecting the TM wave to recombine. Thus, the beams are recombined and passed to the appropriate path in the output port
60
.
FIGS. 3A and 3B
show a top view of an LC switch element as disclosed in the above U.S. patent application Ser. No. 09/431,430 in two different states. As shown in
FIG. 3A
, the LC switch element includes a trench
70
formed at the intersection of a first waveguide
75
and a second waveguide
77
. The front sidewall
74
and rear sidewall
76
of trench
70
have an alignment layer disposed thereon and trench
70
is filled with an LC material
72
. LC material
72
has a plurality of elongated molecules that align perpendicular to the alignment layers on surfaces
74
and
76
when no electric field is applied through the LC material. Thus, the molecules would be aligned as illustrated in FIG.
3
A. As disclosed in the above U.S. Pat. No. 09/431,430, the waveguides
75
and
77
have a refractive index of approximately 1.7 while the ordinary refractive index n
o
of LC material
72
is approximately 1.5 and the extraordinary refractive index n
e
of LC material
72
is approximately between 1.6 to 1.8.
When a TM wave propagates through first waveguide
75
in the direction corresponding to arrow A in FIG.
3
A and when the LC molecules are aligned as shown in
FIG. 3A
, the TM waves pass through trench
70
and continue to propagate along waveguide
75
in the direction indicated by arrow C. A TE wave, however, propagating in the direction indicated by arrow A along waveguide
75
couples directly into the ordinary ray in the LC material
72
, which has an index of no (~1.5). This index is considerably lower than the effective refractive index of waveguide
75
, thus resulting in total internal reflection at front surface
74
of trench
70
. Thus, the TE wave is reflected into second waveguide
77
and propagates through that waveguide in the direction indicated by arrow D. Thus, if both TE waves and TM waves are concurrently propagating through waveguide
75
in direction A, the LC switch splits the TE and TM waves from one another while directing the TM wave through first waveguide
75
in the direction indicated by arrow C and transmitting the TE wave through second waveguide
77
in the direction indicated by arrow D. Conversely, if a TM wave is propagating through second waveguide
77
in the direction indicated by arrow B while a TE wave is concurrently propagating through first waveguide
75
in the direction indicated by arrow A, the LC switch functions as a beam combiner by allowing the TM wave to be transmitted through trench
70
and continue to propagate down second waveguide
77
in the direction indicated by arrow D while also redirecting the TE wave through second waveguide
77
in the direction indicated by arrow D.
Referring to
FIG. 3B
, the LC material
72
in trench
70
is illustrated in an alternate orientation, which would occur when a voltage is applied between two electrodes that are provided on the bottom of the trench and the top of the trench. When the voltage is applied, the molecules of LC material
72
align themselves in parallel with sidewalls
74
and
76
in a vertical orientation.
When the LC molecules are aligned as illustrated in
FIG. 3B
, a TM wave propagating through first waveguide
75
in the direction indicated by arrow A is reflected from the first surface
74
of trench
70
into second waveguide
77
in the direction indicated by Arrow D. A TE wave propagating through first waveguide
75
in the direction indicated by arrow A would propagate through the LC-filled trench
70
and continue to transmit along first waveguide
75
in the direction indicated by arrow C. The LC switch may thus also function as a polarization beam splitter and beam comb
Caracci Stephen J.
Leslie Thomas M.
Lindquist Robert G.
Ma Rui-Qing
Suggs James V.
Bean Gregory V.
Bovernick Rodney
Corning Incorporated
Stahl Mike
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