Mach-Zehnder optical modulator
First Claim
1. An optical modulator comprising:
- a substrate having an electro-optical effect;
first and second branch optical waveguides formed in a first major surface of said substrate;
an optical branching structure for splitting an input optical signal into two split signals and supplying said split signals to said first and second branch optical waveguides, respectively; and
a 3-dB directional coupler which is connected to said first and second branch optical waveguides and which couples outputs of said first and second branch optical waveguides;
wherein a ratio of nonuniformity, which is represented by a difference between propagation constants of two optical waveguides constituting said 3-dB directional coupler, to a coupling coefficient of said 3-dB directional coupler is 1 to at least 5.
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Abstract
An optical modulator is provided that not only can realize a suitable initial operating point without using dc voltage for control, but that has little optical loss and can obtain an excellent extinction ratio. The optical modulator comprises: a substrate having an electro-optical effect, first and second branch optical waveguides formed in a first major surface of the substrate; an optical branching structure for splitting input optical signal and supplying the split signals to the branch optical waveguides; and a 3-dB directional coupler that couples the outputs of the first and second branch optical waveguides. The ratio of nonuniformity, which is represented by the difference in propagation constants of the two optical waveguides in 3-dB directional coupler, to the coupling coefficient of the 3-dB directional coupler is 1 to at least 5, preferably 1 to at least 15, and still more preferably, 1 to at least 20.
82 Citations
24 Claims
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1. An optical modulator comprising:
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a substrate having an electro-optical effect;
first and second branch optical waveguides formed in a first major surface of said substrate;
an optical branching structure for splitting an input optical signal into two split signals and supplying said split signals to said first and second branch optical waveguides, respectively; and
a 3-dB directional coupler which is connected to said first and second branch optical waveguides and which couples outputs of said first and second branch optical waveguides;
wherein a ratio of nonuniformity, which is represented by a difference between propagation constants of two optical waveguides constituting said 3-dB directional coupler, to a coupling coefficient of said 3-dB directional coupler is 1 to at least 5. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
an optical buffer layer for containing light waves provided over said first and second branch optical waveguides; and
a film of a same thickness and a same material as said optical buffer layer, said film provided on a second major surface of said substrate.
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9. An optical modulator according to claim 2 wherein said ratio is 1 to at least 15.
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10. An optical modulator according to claim 9 wherein said ratio is 1 to at least 20.
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11. An optical modulator according to claim 1 wherein said ratio is 1 to at least 15.
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12. An optical modulator according to claim 11 wherein said ratio is 1 to at least 20.
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13. An optical modulator comprising:
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a substrate having an electro-optical effect;
first and second branch optical waveguides formed in a first major surface of said substrate;
an optical branching structure for splitting an input optical signal into two split signals and supplying said split signals to said first and second branch optical waveguides, respectively;
a 2-input 2-output multi-mode interference optical waveguide connected to output ends of said first and second branch optical waveguides, wherein said multi-mode interference optical waveguide converts received light waves from single-mode to multi-mode;
a first ground electrode provided over said first branch optical waveguide;
a signal electrode provided over said second branch optical waveguide; and
a second ground electrode provided in a position that is symmetrical to said first ground electrode such that said signal electrode is interposed between said first and second ground electrodes. - View Dependent Claims (14, 15, 16, 17, 18)
an optical buffer layer for containing light waves provided over said first and second branch optical waveguides; and
a film of a same thickness and a same material as said optical buffer layer, said film provided on a second major surface of said substrate.
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18. An optical modulator according to claim 13, further comprising connectors which are provided on both ends of said signal electrode and configured to lead out in a same direction.
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19. An optical modulator comprising:
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a substrate having an electro-optical effect;
first and second branch optical waveguides formed on a first main surface of said substrate;
an optical branching structure for splitting an input optical signal into two split signals and supplying said split signals to said first and second branch optical waveguides, respectively;
a 3-dB directional coupler which is connected to said first and second branch optical waveguides and which couples outputs of said first and second branch optical waveguides;
a first ground electrode provided over said first branch optical waveguide;
a signal electrode provided over said second branch optical waveguide; and
a second ground electrode provided in a position that is symmetrical to said first ground electrode such that said signal electrode is interposed between said first and second ground electrodes. - View Dependent Claims (20, 21, 22, 23, 24)
an optical buffer layer for containing light waves provided over said first and second branch optical waveguides; and
a film of a same thickness and a same material as said optical buffer layer, said film being provided on a second major surface of said substrate.
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24. An optical modulator according to claim 20, further comprising connectors which are provided on both ends of said signal electrode and configured to lead out in a same direction.
Specification