Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-07-16
2003-09-09
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S050000, C385S016000
Reexamination Certificate
active
06618519
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to integrated optical components and, in particular, to optical components capable of switching and/or attenuating at least one optical channel and performing add or drop functions for optical channels. Particularly preferred implementations facilitate switching and/or attenuating arrays of optical channels.
2. Description of the Related Art
Optical networks are used for wide area and long distance communication, including for the backbone of the Internet. Demand for additional bandwidth in short haul (i.e., metro) and long haul applications continues to grow and a variety of different strategies have been adopted to make optical networks less expensive and more flexible. Optical networks use a variety of components, including add/drop modules, attenuators and optical switches. Generally these components are bulky, expensive and have low levels of integration. The lack of adequate, reliable and cost-effective components has retarded the implementation of optical networks and has limited optical networks to very high traffic systems.
Conventional optical switching proceeds by various methods that include completely mechanical switching, polarization controlled switching, interferometric switching and MEMS switching.
Completely mechanical switching physically moves an input channel and/or an output channel (usually in the form of an optical fiber) with a microelectromagnetic switch (
FIG. 1
) to alter the state of a switch or to change the coupling between channels. Referring to
FIG. 1
, a first switching state is indicated at
10
in which fibers representing input channels
1
and
2
are coupled to corresponding fibers representing output channels
1
and
2
. The assembly can be switched between the state indicated at
10
in which input
1
is coupled to output
1
and input
2
is coupled to output
2
to either of the states indicated by
12
and
14
. State
12
couples input
1
to output
2
and input
2
to output
1
and illustrates the use of the
FIG. 1
assembly as a 2×2 switch. Switching is accomplished, for example, by rotating the two input fibers using a microelectromagnetic element. State
14
couples input
1
to output
2
and does not connect output
1
or input
2
to another channel. This 2×2 add-drop switching is accomplished, for example, by linearly translating the two input fibers using a similar microelectromagnetic element. The physical movements required to alter the states or coupling make the switches schematically illustrated in
FIG. 1
slow and preclude scaling the switches into an array.
A second type of switching is polarization controlled switching and is illustrated in FIG.
2
. Polarization controlled switching uses a polarization rotator whose light transmission is attenuated if followed by a polarizing filter. Polarization controlled switching is polarization dependent. It is preferable for any optical switch to accept light input having an arbitrary polarization. Consequently, polarization controlled switches include components to make the switch insensitive to the polarization of the input light.
A polarization controlled variable optical attenuator (VOA) switch that is insensitive to input light polarization is shown in FIG.
2
. Input light
16
passes through a polarizing beam-splitter
18
that separates the input light into two non-overlapping beams of orthogonal polarization light. Each of the separated beams passes through a polarization controlled light switch
20
,
22
adapted to the polarization of the separated beams to apply polarization controlled switching to each beam. The beams are provided to another polarizing beam splitter
24
that combines the two beams into a single output. The complexity required to eliminate the polarization sensitivity adds expense. In addition, the polarizing beam splitter and combiner are usually bulk components that are not readily integrated into an array.
FIG. 3
shows an interferometric switch that uses a Mach-Zehnder type interferometer. The illustrated interferometric switch is usually formed as a planar waveguide circuit and includes 2×2 couplers on either end of a pair of interferometric arms. One of the arms has an optical element that is switched thermally or electro-optically to vary the phase delay between the two arms of the interferometer. The 2×2 couplers on both ends of the interferometer arms are precisely fabricated to ensure an exact 50/50% coupling, since any imbalance between the arms manifests itself as an insertion loss as well as a poor extinction ratio or crosstalk. Typical interferometric switches have an extinction ratio or crosstalk of worse than 20 dB. It is difficult to manufacture such interferometric switches economically, especially scaling such switches into an array with many channels.
Another type of optical switch uses microelectromechanical (MEMS) structures to switch optical channels. A common MEMS 2×2 switch is illustrated in
FIG. 4
, where the input and output channels are optical fibers. A more specific description of this 2×2 switch formed on a silicon on insulator (SOI) substrate is shown in C. Marxer, et al., “Vertical Mirrors Fabricated by Deep Reactive Ion Etching for Fiber-Optic Switching Applications,”
IEEE/ASME Journal of Microelectromechanical Systems,
Vol. 6, No. 3, pp. September 1997. Referring to
FIG. 4
, a MEMS mirror
26
is shown in a first switch position in which input
1
is coupled to output
1
and input
2
is coupled to output
2
. In the second switch position indicated by MEMS mirror
28
withdrawn from between the optical fibers, input
1
is coupled to output
2
and input
2
is coupled to output
1
.
The MEMS switch system of
FIG. 4
is limited in that the diameter of the optical fibers prevents the fibers from being placed close to each other and to the MEMS switching blade. If the fiber tips are not positioned closely together, the light from an input fiber diverges unacceptably before it is captured by the output fiber, resulting in a high insertion loss. It is difficult to taper the ends of fibers consistently. Variations in the taper of the fiber makes the dispersion and the coupling between fibers unpredictable. Another limitation of the illustrated system is that the input and output channels and MEMS structures are oriented in various directions, making it difficult to scale the switch into a linear array on a single wafer.
Single mode optical channels in either optical fibers or planar channels on substrates are usually small, on the order of several micrometers, so that precise positional alignment is required to couple light into and out of such channels. Also, light emitted from such waveguides diverges in a few tens of micrometers so that the working distance between the emitting waveguide and the receiving waveguide is short. The working distance between emitting and receiving channels often needs to be extended to provide sufficient room for switching components between the channels. The conventional method to extend the working distance for switching components is to expand the light beam from the emitting fiber followed by collimating the expanded light with lenses. This not only adds to the complexity and cost of the system but also aggravates the receiving channel's susceptibility to angular misalignment. In general, the collimator of the receiving channel is precisely aligned positionally and angularly to both the switching mirror and the emitting channel's collimator. In an array of switches, the tight position and angular tolerances are maintained across the array. Also the pitches of the waveguide and mirror arrays have to be matched to a micrometer or better.
SUMMARY OF THE PREFERRED EMBODIMENTS
An aspect of the present invention provides an optical component including a waveguide substrate having an edge and having first and second waveguides formed within the waveguide substrate, the first waveguide having a first end on the edge and the second waveguide having
Chang Tallis Y.
Lam Leo
Martin Graham
Chromux Technologies, Inc.
Lee John D.
Valencia Daniel
LandOfFree
Switch and variable optical attenuator for single or arrayed... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switch and variable optical attenuator for single or arrayed..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switch and variable optical attenuator for single or arrayed... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3109621