Inspection of periodically poled waveguide devices by confocal luminescence microscopy

Abstract

Using confocal defect-luminescence microscopy, we investigated Er³⁺-doped periodically-poled LiNbO₃ waveguide devices and found that the Er³⁺ ion and vibrational Raman modes can be used effectively as probes to inspect and characterize the devices with high spatial resolution, non-destructively, and free of topographical artifacts. The technique is based on scanning over the sample, while simultaneously measuring and evaluating the emission or Raman spectra in terms of their moments (i.e., area, average emission wavelength, and spectral width). The contrast is observed even in tempered samples because of differences in intrinsic electric (strain) fields and defect arrangements that occur in regions inside and outside the waveguide as well as in regions in which domains have been inverted, or which are as grown. Evaluating different parts of the Er³⁺ spectra and/or using different moments, different aspects of the device can be highlighted and regions inside and outside the waveguide, in which domains have been inverted or not inverted, as well as domain walls, can be identified. Raman spectroscopy is less sensitive, but it still can identify the domain wall regions.