Planar waveguide switch and optical cross-connect
First Claim
1. An integrated optic switch capable of redirecting optical beams in a planar waveguide geometry comprising:
- an optical planar waveguide structure including a lower cladding layer, a core layer having means for introducing an incident optical beam therein to, a trench formed in said core layer, an upper cladding layer, and a temperature control element;
said trench extending at least substantially through the thickness of said core layer, said trench being filled with a liquid crystal material, said liquid crystal, and said core layer having refractive indices that are at least substantially matched at a temperature at which said liquid crystal material is in its isotropic phase, said liquid crystal filled trench being covered by said upper cladding layer, said temperature control element disposed at a location above said liquid crystal filled trench, said liquid crystal having its director aligned along the long dimension of said trench when said liquid crystal is in its nematic phase, said liquid crystal material having positive birefringence so that the ordinary refractive index of said liquid crystal material in said nematic phase is lower than said isotropic refractive index as well as said core layer refractive index, the angle of incidence of an incident optical beam passing through said core layer and onto said liquid crystal filled trench being larger than that needed for total reflection of said optical beam from the interface between said core layer and said liquid crystal material when said liquid crystal material is in said nematic phase, said temperature control element having the capability of holding said liquid crystal filled trench at said temperature at which said liquid crystal material is in said nematic phase so that said optical beam is redirected by reflection from said interface so that said optic switch is in its ON state, said temperature control element alternatively having the capability of holding said liquid crystal filled trench at said temperature at which said liquid crystal material is in said isotropic phase so that said optical beam is transmitted through said liquid crystal filled trench so that said optic switch is in its OFF state.
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Abstract
A planar waveguide integrated optic switch suitable for use in optical cross-connect applications. A narrow trench in the planar waveguide core layer is filled with a liquid crystal material possessing positive birefringence. When held at a temperature a few degrees above the clearing point, the liquids crystal'"'"'s isotropic refractive index is matched to that of the core layer allowing nearly complete optical transmission through the switch. When held at a temperature a few degrees below the clearing point, the liquid crystal'"'"'s ordinary refractive index is lower than that of the core layer and both polarizations of the incident optical radiation are totally reflected from the trench. When coupled with planar waveguide beam expanding and refocusing elements, arrays of the switches can be used to form an optical cross-connect capable of fully interconnecting linear arrays of single- or multi-mode optical fibers with very low optical loss. By controlling the liquid crystal temperature at more than one location along the trench, the switch can be configured to operate as a variable attenuator.
49 Citations
34 Claims
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1. An integrated optic switch capable of redirecting optical beams in a planar waveguide geometry comprising:
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an optical planar waveguide structure including a lower cladding layer, a core layer having means for introducing an incident optical beam therein to, a trench formed in said core layer, an upper cladding layer, and a temperature control element;
said trench extending at least substantially through the thickness of said core layer, said trench being filled with a liquid crystal material, said liquid crystal, and said core layer having refractive indices that are at least substantially matched at a temperature at which said liquid crystal material is in its isotropic phase, said liquid crystal filled trench being covered by said upper cladding layer, said temperature control element disposed at a location above said liquid crystal filled trench, said liquid crystal having its director aligned along the long dimension of said trench when said liquid crystal is in its nematic phase, said liquid crystal material having positive birefringence so that the ordinary refractive index of said liquid crystal material in said nematic phase is lower than said isotropic refractive index as well as said core layer refractive index, the angle of incidence of an incident optical beam passing through said core layer and onto said liquid crystal filled trench being larger than that needed for total reflection of said optical beam from the interface between said core layer and said liquid crystal material when said liquid crystal material is in said nematic phase, said temperature control element having the capability of holding said liquid crystal filled trench at said temperature at which said liquid crystal material is in said nematic phase so that said optical beam is redirected by reflection from said interface so that said optic switch is in its ON state, said temperature control element alternatively having the capability of holding said liquid crystal filled trench at said temperature at which said liquid crystal material is in said isotropic phase so that said optical beam is transmitted through said liquid crystal filled trench so that said optic switch is in its OFF state. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
an integrated array of independently addressable optic planar waveguide switch elements as recited in any of claims 1-20, said array of output beam collimator mirrors being aligned with said switch array so that an array of substantially point source optical inputs is transformed into an array of collimated optical beams, and an array of integrated output beam refocusing mirrors, said array of output beam refocusing mirrors being aligned with said switch element array so that said array of collimated optical beams is transformed into a corresponding array of substantially point source optical outputs, one edge of said cross connect being adapted to receive the array of point source optical inputs, another edge of the cross connect being adapted to output the array of point source optical outputs, one switch element in each tow of said switch element array being held in its ON state to direct a corresponding input beam to a corresponding optical output, all other switch elements in said switch element array being held in their OFF state.
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25. An optical cross-connect as recited in claim 24 and further comprising an additional array of output mirror elements which serve to restore the symmetry of the point source optical inputs when the collimated optical beams are refocused into said corresponding array of point source optical outputs.
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26. An optical cross-connect as recited in claim 24 wherein the temperature control elements are integrated into a single structure which is associated with at least on eof said upper cladding layer and said lower cladding layer.
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27. An optical cross-connect as recited in claim 24 wherein groups of the switch elements are interconnected to each other and to through holes in the upper cladding layer by channels within the core layer for the purpose of filling the trenches with the liquid crystal material.
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28. An optical cross-connect as recited in claim 24 wherein a second switch element is employed at each node within the cross-connect which serves to both reduce cross-talk and to restore the symmetry of said point source optical inputs when said collimated optical output beams from said switch element are refocused into said corresponding array of said substantially point source optical outputs.
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29. An optical cross-connect as recited in claim 24 wherein optical absorber elements are positioned within the cross-connect to remove residual or stray optical radiation.
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30. An optical cross-connect as recited in claim 24 wherein each switch element is sufficiently curved so that any lateral diffraction and/or spreading of the optical input and output beams is compensated for by reflection from the curved front wall of the switch element when the switch element is in the ON state.
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31. A 2×
- 2 optical cross-connect building block capable of dynamically switching two input beams into two output beams in either a cross state or a bar state comprising;
four independently addressable integrated optic planar waveguide switch elements as recited in any of claims 1-20, said switch elements being oriented so that when all of said switch elements are held in the ON state, said input beams are directed by reflection from said switch elements into said output beams and said building block is in said cross state, and when all of said switch elements are held in said OFF state, said input beams are transmitted through said switch elements into said output beams and said building block is in said bar state.
- 2 optical cross-connect building block capable of dynamically switching two input beams into two output beams in either a cross state or a bar state comprising;
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32. An optical cross-connect as recited of claim 24 wherein each said switch element has a curved front wall sufficiently curved so that any lateral diffraction and/or spreading of said optical input and output beams is largely compensated for by reflection from the curved front wall of the switch elements when the switch elements are in said ON state.
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33. An integrated optic planar waveguide switch as recited in claim 1-20 in which said switch is configured for operation as a variable attenuator by employing a plurality of individually addressable temperature controlled elements respectively positioned in sequence along said liquid crystal filled trench, said individually addressable temperature controlled elements being operable to control both a corresponding fraction of the incident optical beam that is reflected from said liquid crystal filled trench into said output or attenuated beam, and the fraction of said incident optical beam that is transmitted through said liquid crystal filled trench into said alternate output or compliment attenuated beam.
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34. An optical cross-connect as recited in claim 24 wherein at least one switch element is configured for operation as a variable attenuator, said variable attenuator employing a plurality of individually addressable temperature controlled elements respectively positioned in sequence along a corresponding liquid crystal filled trench, said individually addressable temperature controlled elements being operable to control both a corresponding fraction of the incident optical beam that is reflected from said liquid crystal filled trench into said output or attenuated beam, and the fraction of said incident optical beam that is transmitted through said liquid crystal filled trench into said alternate output or compliment attenuated beam.
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13. An integrated optic switch capable of redirecting an optical beam in a planar waveguide geometry comprising
a substrate, a core layer, a trench formed in said core layer and including front and back walls, a superstrate, and a temperature control element, said trench extending through the thickness of said core layer, said trench being filled with a liquid crystal material, said liquid crystal material and said core layer having refractive indices of approximately 1.5350 at an optical wavelength of 1550 nm and at a temperature of 63° - C., said core layer having a thickness of 7.0 microns, and said substrate and superstrate having refractive indices of approximately 1.5318, said liquid crystal filled trench being covered by said superstrate, said temperature control element being bonded to said superstrate at a location above said liquid crystal filled trench, said liquid crystal filled trench having a length of 1.5 cm, said optic switch further including means for causing the angle of incidence of said optical beam on said liquid crystal filled trench to be substantially 80 degrees, the distance between the front and back walls of said liquid crystal filled trench being 10 microns, said temperature control element being of the thermoelectric type, and having the capability of holding said liquid crystal filled trench at a temperature of 53°
C. wherein said liquid crystal material is in its nematic phase with its director aligned with the long dimension of said trench causing said optic switch to be in its ON state, whereby said optical beam is redirected by total reflection from said liquid crystal filled trench, said temperature control element also having the capability of alternatively holding said liquid crystal filled trench at a temperature of 63°
C. wherein said liquid crystal material is in its isotropic phase causing said optic switch is in its OFF state optical beam is transmitted through said liquid crystal filled trench. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
- C., said core layer having a thickness of 7.0 microns, and said substrate and superstrate having refractive indices of approximately 1.5318, said liquid crystal filled trench being covered by said superstrate, said temperature control element being bonded to said superstrate at a location above said liquid crystal filled trench, said liquid crystal filled trench having a length of 1.5 cm, said optic switch further including means for causing the angle of incidence of said optical beam on said liquid crystal filled trench to be substantially 80 degrees, the distance between the front and back walls of said liquid crystal filled trench being 10 microns, said temperature control element being of the thermoelectric type, and having the capability of holding said liquid crystal filled trench at a temperature of 53°
Specification