Patent ID: 7376310

Claim:
Optical waveguide element, comprising 1) a cladding layer formed on a substrate, 2) two optical waveguides formed in the cladding layer, 3) first and second heater sections, each of said heater sections comprising a heater section on one of the waveguides for shifting a phase of an optical signal that is transmitted via the waveguide; and 4) means to control, adjust, and balance overall birefringence, shift the phases of the optical signals transmitted via the waveguides and induce birefringence of opposite signs in each of said heater sections, said means comprising the first and second heater sections having different designs including: a) the first heater having a first material, and the second heater having a second material, where a thermal expansion coefficient of the first material is different from that of the second material; b) the first heater having a different width and thickness than that of the second heater, whereby a larger width and thickness of the heater increases the influence on the stress in the waveguide area; c) the first heater having trenches next the heater that are different from those of the second heater, whereby the trenches next to the heaters allow a lateral stress field to relax, and d) the trenches next to the first heater differ in separation and depth from the trenches next to the second heater; and 5) two optical couplers being interconnected by the two waveguides.