Tuning the index of a waveguide structure
First Claim
1. An optical waveguide coupler having a tunable coupling coefficient, said coupler comprising:
- a first waveguide and a second waveguide comprising first and second cores respectively, said first and second cores separated by cladding in an evanescent coupling region, said first and second waveguides supporting respective first and second spatial modes, wherein said first and second waveguides are comprised of semiconductor having a distribution of free carriers, and said cladding comprises a dielectric material that electrically isolates the first and second waveguides from each other, said first waveguide comprising an optical path in a resonant cavity;
a first electrode electrically connected to said first waveguide;
a second electrode electrically connected to said second waveguide; and
a variable voltage source connected between first and second electrodes;
wherein the distributions of free carriers are responsive to application of said voltage such that index of refraction variations can be introduced in said first waveguide to increase or decrease confinement of said first spatial mode and alter overlap of said first and second spatial modes in said cladding of said coupling region thereby changing the coupling coefficient between said waveguides from a first value to a second value.
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Abstract
The index of refraction of waveguide structures can be varied by altering carrier concentration. The waveguides preferably comprise semiconductors like silicon that are substantially optically transmissive at certain wavelengths. Variation of the carrier density in these semiconductors may be effectuated by inducing an electric field within the semiconductor for example by apply a voltage to electrodes associated with the semiconductor. Variable control of the index of refraction may be used to implement a variety of functionalites including, but not limited to, tunable waveguide gratings and resonant cavities, switchable couplers, modulators, and optical switches.
266 Citations
50 Claims
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1. An optical waveguide coupler having a tunable coupling coefficient, said coupler comprising:
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a first waveguide and a second waveguide comprising first and second cores respectively, said first and second cores separated by cladding in an evanescent coupling region, said first and second waveguides supporting respective first and second spatial modes, wherein said first and second waveguides are comprised of semiconductor having a distribution of free carriers, and said cladding comprises a dielectric material that electrically isolates the first and second waveguides from each other, said first waveguide comprising an optical path in a resonant cavity; a first electrode electrically connected to said first waveguide; a second electrode electrically connected to said second waveguide; and a variable voltage source connected between first and second electrodes; wherein the distributions of free carriers are responsive to application of said voltage such that index of refraction variations can be introduced in said first waveguide to increase or decrease confinement of said first spatial mode and alter overlap of said first and second spatial modes in said cladding of said coupling region thereby changing the coupling coefficient between said waveguides from a first value to a second value. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 35, 36)
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2. A method of tuning the coupling coefficient of an optical waveguide coupler, comprising:
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providing a first waveguide comprising semiconductor containing a distribution of free carriers, said first waveguide comprising an optical path in a resonant cavity; providing a second waveguide separated from and electrically isolated from said first waveguide, said second waveguide comprising semiconductor containing a distribution of free carriers, said first and second waveguides supporting first and second spatial modes respectively; and applying a voltage between said first and second waveguides to alter the free carrier distribution in said semiconductor so as to reduce confinement of said first spatial mode in said first waveguide and increase overlap between said first and second spatial modes, thereby changing the coupling coefficient of said optical waveguide coupler from a first value to a second value. - View Dependent Claims (28, 29, 37, 38)
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3. A capacitor comprising:
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a first capacitor electrode comprising a first semiconductor optical waveguide; a second capacitor electrode comprising a second semiconductor optical waveguide, the second semiconductor waveguide comprising a portion of a resonant cavity; a dielectric comprising cladding disposed between said first and second optical waveguides, wherein the first and second semiconductor optical waveguides are sufficiently close to permit evanescent optical coupling therebetween, said coupling changeable with application of a voltage between said first and second capacitor electrodes. - View Dependent Claims (4, 30, 31, 32, 33, 39, 40)
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5. A method of optically switching, comprising:
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applying a voltage across first and second electrodes of a capacitor comprising respective first and second waveguides separated from each other by an inter-electrode dielectric wherein at least one of the first and second waveguides comprises at least a portion of a resonant cavity; wherein application of said voltage induces storage of charge on said first and second electrodes thereby altering coupling of optical modes in said first waveguide to said second waveguide. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 34, 41, 42)
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43. An optical waveguide coupler having a tunable coupling coefficient, said coupler comprising:
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a first waveguide and a second waveguide comprising first and second cores respectively, said first and second cores separated by cladding in an evanescent coupling region, said first and second waveguides supporting respective first and second spatial modes, wherein said first waveguide is comprised of semiconductor having a distribution of free carriers, and said cladding comprises a dielectric material that electrically isolates the first and second waveguides from each other, said first waveguide comprising an optical path in a resonant cavity; a first electrode electrically connected to the first waveguide; and a variable voltage source coupled to the first electrode so that a voltage is applied to the first waveguide via the first electrode; wherein the distributions of free carriers are responsive to application of said voltage such that index of refraction variations can be introduced in said first waveguide to increase or decrease confinement of said first spatial mode and alter overlap of said first and second spatial modes in said cladding of said coupling region thereby changing the coupling coefficient between said waveguides from a first value to a second value. - View Dependent Claims (44, 45, 46)
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47. A method of tuning the coupling coefficient of an optical waveguide coupler, comprising:
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providing a first waveguide comprising semiconductor containing a distribution of free carriers, said first waveguide comprising an optical path in a resonant cavity;
providing a second waveguide separated from and electrically isolated from said first waveguide, said first and second waveguides supporting first and second spatial modes respectively; andapplying a voltage to said first waveguide to alter the free carrier distribution in said semiconductor so as to reduce confinement of said first spatial mode in said first waveguide and increase overlap between said first and second spatial modes, thereby changing the coupling coefficient of said optical waveguide coupler from a first value to a second value. - View Dependent Claims (48, 49, 50)
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Specification