Interferometric method for determining the losses of spatially multi-mode nonlinear waveguides based on second harmonic generation.

Abstract

The characterisation of loss in optical waveguides is essential in understanding the performance of these devices and their limitations. Whilst interferometric-based methods generally provide the best results for low-loss waveguides, they are almost exclusively used to provide characterization in cases where the waveguide is spatially singlemode. Here, we introduce a Fabry-Pérot-based scheme to estimate the losses of a nonlinear (birefringent or quasi-phase matched) waveguide at a wavelength where it is multi-mode. The method involves measuring the generated second harmonic power as the pump wavelength is scanned over the phasematching region. Furthermore, it is shown that this method allows one to infer the losses of different second harmonic spatial modes by scanning the pump field over the separated phase matching spectra. By fitting the measured phasematching spectra from a titanium indiffused lithium niobate waveguide sample to the model presented in this paper, it is shown that one can estimate the second harmonic losses of a single spatial-mode, at wavelengths where the waveguides are spatially multi-mode. arXiv:1910.07300v2 [physics.optics]

Omni‐functional crystal: Advanced methods to characterize the composition and homogeneity of lithium niobate melts and crystals

“…Santandrea et al. [ 125 ] introduced a method to estimate the loss of nonlinear waveguides at multimode wavelengths. By fitting the phase‐matched spectra of different titanium‐diffused LN waveguides to their model, a single spatial second‐harmonic loss of the mode at the spatial multimode wavelength was obtained.…”

“…[120] Sattibabu et al [124] proposed a non-destructive and simple spectroscopic method to measure a single-mode optical waveguide's coupling and transmission losses, and they demonstrated this technique using a fabricated Ti:LN waveguide. Santandrea et al [125] introduced a method to estimate the loss of nonlinear waveguides at multimode wavelengths. By fitting the phase-matched spectra of different titanium-diffused LN waveguides to their model, a single spatial second-harmonic F I G U R E  Four-inch LN wafer thickness uniformity characterization: (A) before device processing and (B) after device processing.…”

Waveguide Resonator with Integrated Phase Modulator for Second Harmonic Generation

“…As is often the case, these benefits do not come without a cost. Waveguides typically have higher losses than their bulk counterparts, are more often strongly impacted by production errors, and are sometimes susceptible to photothermal and/or photorefractive effects [8,9,10]. Furthermore, these issues are typically exacerbated when using optical fields at higher frequencies, making processes such as high power and/or efficient second harmonic generation (SHG) particularly difficult.…”