Silicon optical modulator, method for making the same

A method for forming a silicon optical modulator comprising:

• providing a silicon layer in a silicon-on-insulator substrate;
• forming a first linear waveguide of a length in the silicon layer, the first linear waveguide comprising a ridge-shape having a central portion of a height of the silicon layer sandwiched in a nominal width direction by a first side portion and a second side portion throughout the length of the first linear waveguide;
• forming a second linear waveguide substantially the same as and in parallel at a side of the first linear waveguide to form two branches of a Mach-Zehnder interferometer with a common input end and a common output end;
• and
• forming an irregular shaped PN junction in the central portion throughout the length of the at least one of the first linear waveguide and the second linear waveguide, the irregular shaped PN junction in each cross-section plane of the central portion having a p-region and a n-region separated by a continuous border line, the continuous border line being configured to have at least one section-line with a sloped angle relative to the nominal width direction and having a total border-length substantially longer than the height of the central portion, the p-region at least partially being in contact with the first side portion and the n-region at least partially being in contact with the second side portion.