High frequency optical modulator with laterally displaced conduction plane relative to modulating electrodes
Optical modulators are described having a Mach-Zehnder interferometer and a pair of RF electrodes interfaced with the Mach-Zehnder interferometer in which the Mach-Zehnder interferometer comprises optical waveguides formed from semiconductor material. The optical modulator also comprises a ground plane spaced away in a distinct plane from transmission line electrodes formed from the association of the pair of RF electrodes interfaced with the Mach-Zehnder interferometer. The ground plane can be associated with a submount in which an optical chip comprising the Mach-Zehnder interferometer and the pair of RF electrodes is mounted on the submount with the two semiconductor optical waveguides are oriented toward the submount. Methods for forming the modulators are described.
1. A method of forming an optical modulator, the method comprising:
bonding an inverted optical chip comprising a Mach-Zehnder interferometer with optical waveguides, two RF electrodes each associated with a distinct arm of the Mach-Zehnder interferometer, and electrical contact points for each RF electrode, to a submount comprising electrical contacts aligned with the electrical contact points for the RF electrodes to form conduction pathways between distinct electrical contacts on the submount through respective RF electrodes on the optical chip, wherein the submount comprises a ground plane spaced away from a mounting surface of the submount and electrically separate from the inverted optical chip.
2. The method of claim 1 wherein the ground plane is within the submount.
3. The method of claim 1 wherein the ground plane is on a surface of the submount oriented away from the optical chip.
4. The method of claim 1 wherein the optical modulator further comprises insulating posts between locations on the optical chip and the submount that stabilize the optical modulator and wherein the submount electrical contacts are electrically connected to an RF source.
5. The method of claim 1 wherein the Mach-Zehnder interferometer comprises an optical splitter connected to an optical input waveguide, two optical waveguide arms optically connected to the optical splitter and an optical combiner optically connected to the two optical waveguides and to an output waveguide, wherein the optical waveguides comprise semiconductor material, an electrical contact is located on portions of the optical waveguide arms surface, and each RF electrode of the pair comprising transmission line electrodes connected by additional electrodes to electrical contacts on respective optical waveguides.
6. The method of claim 1 wherein the optical modulator comprises two coupled pairs of Mach-Zehnder interferometers and an optical splitter that is configured to combine optical signals from the four Mach-Zehnder interferometers where the two output waveguides are optically coupled by a polarization combining element to generate a polarization multiplexed signal, wherein each pair of Mach-Zehnder interferometers comprises two Mach-Zehnder interferometers and two pair of RF electrodes with each pair associated with a corresponding Mach-Zehnder interferometer, wherein each Mach-Zehnder interferometer comprises an optical splitter connected to an optical input waveguide, two optical waveguide arms optically connected to the optical splitter and an optical combiner optically connected to the two optical waveguides and to an output waveguide, the two input waveguides of each of the Mach-Zehnder interferometer are connected through a splitter to a single optical input, the two output waveguides of each of the Mach-Zehnder interferometer are connected by a combiner to a single optical output, wherein the optical waveguides comprise a semiconductor optical material, an electrical contact is located on portions of the optical waveguide arms surface, and each RF electrode of the pair comprising transmission line electrodes connected by additional electrodes to electrical contacts on respective optical waveguides and a ground plane spaced away in a distinct plane from the transmission line electrodes.
7. The method of claim 1 wherein the optical chip is free of any ground electrodes.