Comparison of three inverse Fourier transform techniques to determine the second-order optical nonlinearity profile of thin films

Abstract

We compare the predictions of three inverse Fourier transform (IFT) Maker fringe techniques that we have developed over the last 2 years to measure uniquely and accurately the second-order nonlinearity spatial profile of thin films. These techniques involve clamping two wafers with unknown nonlinearity profiles together to form a sandwich structure and measuring its Maker fringe (MF) spectrum. As a result of interference between the two nonlinear films, these spectra contain information on both the magnitude and phase of the FT of the two unknown profiles. These FT magnitude and phase can be processed numerically and the full FT is inverted to recover the profiles. In the first method the samples are different, in the second one they are identical, and in the third technique one of the two wafers has a known profile. The latter methods are advantageous because they require a single MF measurement, and consequently, their algorithms are simpler, and data processing is much faster. We present experimental evidence using thermally poled silica samples showing that when all three techniques are applied to the same sample, they yield very similar profiles, which gives credence to all three techniques.