In order to optimize modulator linearity and thereby maximize the linear dynamic range of optical waveguide devices, the phase angle is important. Normally, the phase angle in optical waveguide devices must be precise for optimum performance, e.g., directional couplers require phase matching and a precise coupling length for proper performance and Mach-Zehnder interferometers require an optical phase difference of 90.degree. between the arms of the interferometer for linear operation. The precise achievement of the required phase angle is very hard to obtain since phase velocity in optical devices depends on material indices and waveguide geometry.
Currently, the manufacture of optical waveguide devices having a plurality of arms or paths is imprecise. Because the lengths of the arms or paths form a balanced or unbalanced bridge for providing a built-in phase bias, the desired phase relationships between the paths or arms is difficult to obtain during fabrication due to the differences in phase velocity along the paths. Currently utilized methods to tune optical waveguide devices by phase velocity adjustment, e.g., lithographic oxide cladding of the areas over certain parts of the structure and annealing by a CO.sub.2 laser beam, are relatively slow and of limited accuracy because the preciseness of control is lacking. These processes are cumbersome, do not provide for instantaneous observation of the results and small changes in the waveguide cross-section are difficult to achieve. Manufacture of optical waveguides can currently take weeks, and the final product's accuracy is limited because in situ measurement and correction are not possible.
As the utilization of optical waveguide devices becomes more prevalent in the optical-electronic industry, it is desirable that procedures to overcome the lack of precision control over the quality of the manufactured product be developed.
USPTO Backgrounds
USPTO Backgrounds