A new and effective nonintrusive method for characterization of N coupled waveguides is presented. The method is able to furnish readily the coupling parameters of most significance, and furnishes in addition, a way of assessment of overall device quality and performance. The procedure is based on a semi-empirical implementation of coupled mode theory, by means of which different functions are defined for different input configurations. In a well-functioning device, all these function should attain a common single minimum, out of which the coupling coefficient and additional parameters of the device are deduced. Devices were fabricated on Z-cut LiNbO3 crystals by in-diffusion of Titanium. The method was applied in order to measure the wavelength and polarization dependence of the coupling coefficient.
Arkady Kaplan and Shlomo Ruschin, "Characterization and Performance Evaluation of Coupled Multiwaveguide Arrays," J. Lightwave Technol. 17, 1884- (1999)