Effective electro-optical coefficient determination of low finesse periodically poled lithium niobate waveguide...

Lithium niobate (LiNbO₃), as a second-order nonlinear crystal, possesses sufficient linear electro-optic strength, making it a suitable substrate for integrated optical modulators. Waveguides fabricated by titanium diffusion into lithium niobate (Ti:LN) can guide both TE and TM polarizations. Thus, a single-channel waveguide of suitably periodically poled Ti:PPLN can be used as a polarization converter for a desired wavelength. Consequently, the effective electro-optic coefficient of the Ti:PPLN waveguide for a specified polarization is of interest. This paper proposes a novel, compatible method to determine the effective electro-optic coefficient of a Ti:PPLN channel waveguide. The proposed technique, which has been experimentally investigated, is based on the phase difference induced by illuminating a low-finesse waveguide resonator from both end facets. By measuring the resulting difference in resonance wavelengths along with the residual last PPLN domain at both ends of the waveguide, the electro-optic coefficient [Formula: see text] is determined to be [Formula: see text] for a 15 mm-long Ti:PPLN channel waveguide. The in situ characterization method developed in this work enables direct measurement of electro-optic coefficients in integrated photonic circuits, providing essential performance parameters for optimizing phase modulators, polarization converters, and nonlinear frequency mixing devices while maintaining device integrity.