Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-08-09
2003-06-10
Zarroli, Michael C. (Department: 2839)
Optical waveguides
With optical coupler
Switch
Reexamination Certificate
active
06577785
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to optical waveguides, and in particular to an optical waveguide switch formed from III-V compound semiconductor layers. The optical waveguide switch can be used, for example, to form an optical waveguide switching network for signal routing in fiber optic communications and data transfer.
BACKGROUND OF THE INVENTION
There is currently a need for low-insertion-loss gangable optical switches to provide signal routing for fiber optics communications and data transfer. Many approaches have been recently proposed to fill this need, based primarily on silicon micromachining of tiltable mirrors or deflectable cantilevered waveguides (see e.g. E. Ollier et al, “Micro-Opto Mechanical Switch Integrated on Silicon,”
Electronics Letters
, vol. 31, pp. 2003-2005, Nov. 9, 1995; and E. Ollier et al, “Integrated Electrostatic Micro-Switch for Optical Fiber Networks Driven by Low Voltage,”
Electronics Letters
, vol. 32, pp. 2007-2009, Oct. 10, 1996).
The present invention represents an advance in the art of optical waveguide switching compared to previous optical waveguide switches formed from polycrystalline silicon (also termed polysilicon) by providing a moveable optical waveguide formed from a plurality of epitaxially-deposited and patterned III-V compound semiconductor layers.
An advantage of the present invention is that the III-V compound semiconductor layers are of high quality, being epitaxially grown as single crystals with atomically flat interfaces and well-controlled layer thicknesses; whereas polycrystalline silicon comprises a plurality of microcrystals with random orientation.
Another advantage is that the III-V compound semiconductor layers wherefrom the optical switch of the present invention is formed, can be epitaxially deposited with very low residual stress to limit any vertical deflection of the moveable optical waveguide therein; whereas polycrystalline silicon can have substantial residual stress which must be reduced by annealing at high temperature.
These and other advantages of the present invention will become evident to those skilled in the art.
SUMMARY OF THE INVENTION
The present invention relates to an optical waveguide switch that comprises a moveable optical waveguide formed from a plurality of III-V compound semiconductor layers epitaxially deposited on a substrate, with the moveable optical waveguide having a portion thereof cantilevered above the substrate, and with an end of the cantilevered portion being moveable in the plane of the substrate. The optical waveguide switch further comprises an electrostatic actuator operatively coupled to the moveable optical waveguide to move the end of the cantilevered portion in the plane of the substrate and into optical alignment with one of a plurality of fixed optical waveguides formed on the substrate from the same plurality of epitaxially-deposited III-V compound semiconductor layers.
The plurality of epitaxially-deposited III-V compound semiconductor layers used to form the optical waveguide switch include a high-refractive-index compound semiconductor layer sandwiched between a pair of lower-refractive-index compound semiconductor layers. The high-refractive-index III-V compound semiconductor layer can comprise gallium arsenide (GaAs), gallium arsenide antimonide (GaAsSb) or indium gallium arsenide (InGaAs). The lower-refractive-index III-V compound semiconductor layer can comprise aluminum gallium arsenide (AlGaAs), aluminum arsenide antimonide (AlAsSb) or indium aluminum arsenide (InAlAs). The substrate can comprise GaAs or indium phosphide (InP), with the substrate being lattice matched to the III-V compound semiconductor layers epitaxially deposited thereon.
The electrostatic actuator can comprise one or more pairs of meshed electrostatic combs, with each pair of the meshed electrostatic combs further comprising a fixed electrostatic comb supported on the substrate, and a moveable electrostatic comb attached to the cantilevered portion of the moveable optical waveguide. Each electrostatic comb comprises a plurality of spaced fingers which are interconnected.
A plurality of stops can be formed on the substrate to limit motion of the cantilevered portion of the moveable optical waveguide to facilitate precise optical alignment with the fixed optical waveguides. An anti-reflection coating can be deposited on the end of the cantilevered portion of the moveable optical waveguide to reduce an optical loss in coupling light between the moveable optical waveguide and each fixed optical waveguide. Another anti-reflection coating can be provided on the end of each fixed optical waveguide proximate to the end of the cantilevered portion of the moveable optical waveguide for reduced optical coupling loss.
The present invention further relates to an optical waveguide switch that comprises a III-V compound semiconductor substrate, a pair of fixed optical waveguides formed on the substrate from a plurality of III-V compound semiconductor layers including a pair of cladding layers sandwiched about a core layer, and a moveable optical waveguide formed on the substrate from the plurality of III-V compound semiconductor layers, with the moveable optical waveguide having a cantilevered end thereof which is electrostatically moveable into alignment with one or the other of the pair of fixed optical waveguides. The cantilevered end of the moveable optical waveguide can optionally include an anti-reflection coating formed thereon to reduce an optical coupling loss between the moveable optical waveguide and each fixed optical waveguide.
In the optical waveguide switch, the core and cladding layers can comprise, for example, gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs), respectively, when the substrate comprises gallium arsenide (GaAs). When the substrate comprises indium phosphide (InP), the core and cladding layers can comprise respectively gallium arsenide antimonide (GaAsSb) and aluminum arsenide antimonide (AlAsSb), or indium gallium arsenide (InGaAs) and indium aluminum arsenide (InAlAs).
The optical waveguide switch preferably further includes an electrostatic actuator operatively coupled to electrostatically move the cantilevered end of the moveable optical waveguide into alignment with one of the pair of fixed optical waveguides. The electrostatic actuator can comprise one or more pairs of meshed electrostatic combs, with each pair of the meshed electrostatic combs further comprising a fixed electrostatic comb supported on the substrate, and a moveable electrostatic comb attached to the cantilevered end of the moveable optical waveguide.
The present invention also relates to a plurality of optical waveguide switches formed on a common substrate and interconnected to form an optical switching network that can be electronically reconfigured to route optical signals (i.e. comprising light with information encoded therein) between one or more input optical fibers and a plurality of output optical fibers.
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Garcia Ernest J.
Spahn Olga B.
Sullivan Charles T.
Hohimer John P.
Sandia Corporation
Zarroli Michael C.
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