Estimation of Fiber-Waveguide Coupling Loss and Waveguide Propagation Loss by Spectral Analysis

This letter presents a non-destructive and simple method for simultaneous measurement of fiber-waveguide coupling loss and propagation loss of single-mode optical waveguides. The experiment includes the coupling of a medium bandwidth laser source to optical waveguide under test and the analysis of its transmission spectra by using a grating monochromator. The technique has been demonstrated for a 46.5-mm-long fabricated titanium-indiffused lithium niobate (Ti:LiNbO₃) waveguide for transverse magnetic polarization, and our first experiment yields a 2.18-dB fiber-waveguide coupling loss and a 0.58-dB/cm propagation loss at around 1557-nm transmitting wavelength. The measurement process needs no external perturbation, such as electric field or controlled heating, and hence is applicable for optical waveguides as-fabricated.