Electro-optic modulators with internal impedance matching
View Patent ↗A resonant optical modulator includes an electro-optical substrate, an optical waveguide formed in the substrate and having a variable index of refraction, and an active modulator electrode formed on the substrate in relation to the waveguide to effect electro-optical variation of the index of refraction upon application to the electrode of a modulating signal. An interface port formed on the substrate provides the modulating signal to the electrode from a signal source and has an impedance. An electrical structure, formed on the substrate and coupled to the interface port and the electrode, makes an impedance of the optical modulator substantially equal to the impedance of the signal source. The electrical structure includes a delay line and a stub formed on the substrate.
1. An electrode structure for an optical modulator disposed on an electro-optical substrate having an optical waveguide extending therethrough, comprising:
a first electrode symmetrically disposed between first and second portions of a ground plane, and having a width decreasing from an edge of the substrate to a node;
a second electrode extending in one direction from the node and connecting to the first portion of the ground plane;
a third electrode extending in another direction from the node and having an end near the optical waveguide; and
a fourth electrode connected to the end of the third electrode near the optical waveguide, extending parallel to the optical waveguide, and connecting to the second portion of the ground plane.
2. An electrode structure as recited in claim 1 , wherein an impedance of the electrode structure, viewed from an input to the first electrode, is substantially equal to an impedance of a signal source connected to the input of the first electrode.
3. An electrode structure as recited in claim 2 , wherein a total impedance of the second, third, and fourth electrodes, viewed from the node, is substantially equal to the impedance of the signal source connected to the input of the first electrode.
4. An electrode structure as recited in claim 1 , wherein the third electrode includes at least two orthogonal portions.
5. An electrode structure as recited in claim 1 , wherein a modulating signal in the fourth electrode modulates an optical signal traveling through the optical waveguide.