Electro-optic grating modulator
First Claim
1. An optical modulator structure comprising:
- an RF waveguide having a first longitudinal axis; and
at least one optical grating waveguide having a second longitudinal axis located within the RF waveguide, the first longitudinal axis being parallel with and substantially coincident with the second longitudinal axis such that, in use, an RF field propagating in the RF waveguide and an optical field propagating in the optical grating waveguide propagate in substantially parallel directions, the at least one optical grating waveguide having a grating adapted to provide a notch in a transmission spectrum for the optical field propagating in the optical grating waveguide and having an operating wavelength of the optical field propagating in the optical grating waveguide wherein the operating wavelength is selected to occur at a transition from a substantially maximum transmission to greater than minimum transmission in said optical grating waveguide, the optical field propagating, in use, in the optical grating waveguide having an optical group velocity at the operating wavelength;
wherein the RF field propagating, in use, in the RF waveguide has a RF group velocity sufficiently equal to the optical group velocity to obtain a desired amount of amplitude modulation of the optical field propagating in the optical grating waveguide by said optical modulator.
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Abstract
An optical-waveguide grating modulator is compatible with high-frequency electrical modulation signals of limited bandwidth. The modulator comprises an optical grating formed in an optical waveguide constructed from electro-optic (EO) material and an electrode that is an RF waveguide or RF transmission line that conducts a traveling-wave electromagnetic (EM) field and that contains a portion of the optical-grating waveguide with a continuous grating. The RF input modulation signal is coupled into an RF EM field that propagates through the RF waveguide or transmission line in a direction that is parallel to the direction the light propagates in the optical-grating waveguide and that EM field overlaps the optical-grating waveguide. The light travels along the optical-grating waveguide preferably at the same velocity as the RF EM field travels along the RF waveguide or transmission line.
77 Citations
35 Claims
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1. An optical modulator structure comprising:
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an RF waveguide having a first longitudinal axis; and at least one optical grating waveguide having a second longitudinal axis located within the RF waveguide, the first longitudinal axis being parallel with and substantially coincident with the second longitudinal axis such that, in use, an RF field propagating in the RF waveguide and an optical field propagating in the optical grating waveguide propagate in substantially parallel directions, the at least one optical grating waveguide having a grating adapted to provide a notch in a transmission spectrum for the optical field propagating in the optical grating waveguide and having an operating wavelength of the optical field propagating in the optical grating waveguide wherein the operating wavelength is selected to occur at a transition from a substantially maximum transmission to greater than minimum transmission in said optical grating waveguide, the optical field propagating, in use, in the optical grating waveguide having an optical group velocity at the operating wavelength; wherein the RF field propagating, in use, in the RF waveguide has a RF group velocity sufficiently equal to the optical group velocity to obtain a desired amount of amplitude modulation of the optical field propagating in the optical grating waveguide by said optical modulator. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. An optical modulator structure comprising:
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a substrate; and at least one optical grating waveguide formed of an electro-optic material, the at least one optical grating waveguide having a first longitudinal axis disposed within the substrate and an RF waveguide having a second longitudinal axis disposed on the substrate, the first longitudinal axis being parallel with and substantially coincident with the second longitudinal axis such that, in use, an electric field propagating in the RF waveguide and an optical field propagating in the at least one optical grating waveguide propagate in substantially parallel directions, wherein the at least one optical grating waveguide includes a grating adapted to provide a notch for the optical field propagating, in use, in the optical grating waveguide and the at least one optical grating waveguide having an operating wavelength wherein the operating wavelength is selected to occur at a transition from substantially maximum transmission to greater than minimum transmission, so that as the electro-optic material of the at least one optical grating waveguide reacts to the electric field propagating in the RF waveguide, its transmission spectrum changes in response thereto resulting in amplitude modulation of the optical field propagating, in use, in the at least one optical grating waveguide. - View Dependent Claims (16, 17, 18, 19)
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20. An RF photonic transmitter comprising:
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an RF waveguide formed at least in part of an electro-optic material, the RF waveguide having a first end and a first longitudinal axis and at least one optical grating waveguide with a second end and a second longitudinal axis, wherein the first end is coincident with the second end and the first longitudinal axis is parallel with and substantially coincident with the second longitudinal axis such that an RF field propagating in the RF waveguide overlaps the optical grating waveguide, the optical grating waveguide having a grating adapted to provide a notch in a transmission spectrum of an optical field propagating in the at least one optical grating waveguide and wherein the optical field has an operating wavelength, the operating wavelength being selected to occur at a transition from substantially maximum transmission to greater than minimum transmission; for each of the at least one optical grating waveguide, an associated laser emitting laser light at the operating wavelength of the at least one optical grating waveguide with which it is associated, the laser light of the associated laser entering its associated optical grating waveguide at the second end and being amplitude modulated as an edge of the notch in the transmission spectrum of the optical field propagating in the associated optical grating waveguide shifts frequency in response to a changing refractive index of said electro-optic material; and wherein the RF waveguide is adapted to receive an RF signal at the first end for changing the refractive index of said electro-optic material. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
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32. A method of modulating the intensity of an optical field propagating in an optical modulator structure with an RF field, the optical modulator structure including:
- an RF waveguide for propagating said RF field, the RF waveguide having a first longitudinal axis; and
at least one optical grating waveguide having a second longitudinal axis located within the RF waveguide, the first longitudinal axis being parallel with and substantially coincident with the second longitudinal axis such that the RF field propagating in the RF waveguide and an optical field propagating in the optical grating waveguide propagate in substantially parallel directions, the at least one optical grating waveguide having a grating adapted to provide a notch in a transmission spectrum for the optical field propagating in the optical grating waveguide and having an operating wavelength of the optical field propagating in the optical grating waveguide wherein the operating wavelength is selected to occur at a transition from a substantially maximum transmission to greater than minimum transmission in said optical grating waveguide, the optical field propagating in the optical grating waveguide having an optical group velocity at the operating wavelength;wherein the RF field propagating in the RF waveguide has a RF group velocity sufficiently equal to the optical group velocity to obtain a desired amount of amplitude modulation of the optical field. - View Dependent Claims (33, 34, 35)
- an RF waveguide for propagating said RF field, the RF waveguide having a first longitudinal axis; and
Specification