Co-planar Electrode Waveguide Polarisation Modulator

The single electrode is segmented into multiple co-planar electrodes (first, second, third, and fourth electrodes) arranged in a specific pattern above the waveguide. This segmentation allows independent control of electric field components in different directions, enabling generation of any polarisation state on the Poincare sphere while maintaining a relatively simple planar structure above the waveguide.

The patent transitions from a single vertical electric field component to multiple electric field components by adding lateral dimensionality through co-planar electrodes. The first and second electrodes control one electric field component while the third and fourth electrodes control another component, allowing two-dimensional control of the polarisation state on the Poincare sphere.

The electrode system is segmented into four distinct co-planar electrodes rather than using a single electrode or simple lateral pair. This segmentation allows the first and second electrodes to optimize one electric field component while the third and fourth electrodes optimize the orthogonal component, achieving both high conversion efficiency and low switching voltage through independent optimization of each field component.

Each electrode is positioned at a specific location above the waveguide to create optimal local electric field distribution. The co-planar arrangement with specific spacing and positioning ensures that each electrode contributes maximally to its designated electric field component, achieving uniform and efficient field overlap with the optical mode throughout the interaction region.

The electrode structure is merged with the waveguide fabrication process itself, using the same semiconductor layers and processing steps. The electrodes are formed as part of the integrated optical device structure rather than as separate components requiring additional alignment steps, enabling standard fabrication processes to achieve the required positioning accuracy and facilitating integration with other waveguide devices.

The co-planar electrode configuration serves multiple functions: it provides precise polarisation control, maintains compatibility with standard semiconductor fabrication processes, and enables integration with other waveguide devices. The same electrode structure can control different polarisation states for various applications including quantum cryptography protocols requiring multiple polarisation bases.

The four co-planar electrodes are segmented into two pairs: the first and second electrodes control one electric field component while the third and fourth electrodes control the orthogonal component. This segmentation enables independent control of vertical and horizontal electric field components despite the coplanar arrangement, as each pair can be driven by independent voltage signals.

The electrodes are positioned asymmetrically relative to the waveguide centerline, with specific spacing and offset distances that create distinct electric field patterns. This asymmetric positioning ensures that each electrode pair produces primarily its designated field component with minimal cross-coupling, enabling independent control while maintaining the coplanar integrated structure.