Refractive index profile measurement techniques by reflectivity profiling: vidicon imaging, beam scanning, and sample scanning

Abstract

The refractive index profiles of titanium-diffused LiNbO(3) planar and channel waveguides are determined directly by measuring the reflectivity of angular polished surfaces. Three measurement techniques are described and compared: (1) large area illumination of the angular polished waveguide and imaging of the reflected light to a vidicon, (2) scanning of a focused beam across the sample, and (3) scanning of the sample under a focused beam. Preference is given to the last method which provides an accuracy of Deltan/n = 10(-4) with a local resolution of the index profile of <0.1 microm in depth and ~1 microm in width.

Measurement of planar refractive index profiles with rapid variations in glass using interferometry and total variation regularized differentiation

“…These include ellipsometry using multiple angle data [1], mode measurements mediated with a prism coupler (for both guided and leaky modes) [2][3][4], reflectance analysis [5,6] and numerous interferometric methods [7][8][9][10][11][12][13]. Each method has advantages and disadvantages.…”

“…If the sample is known to support only guided modes, then a smooth monotonically decreasing index profile can be deduced without further assumptions [4]. Reflectance measurements are not limited to planar index profiles but require careful sample preparation and are sensitive only to large index differences [5,6]. Interferometric measurements on cross sections of samples require careful sample preparation and are limited to the analysis of index profiles that are deep due to the magnification of the optical system [8].…”

Index Profile Reconstruction of Ti: LiNbO3 Structures and Loss Bending Evaluation from Near-Field Measurements

“…When reconstructing the profiles we reduced the number of profile parameters by fixing b = 0 in (2), assuming a Gaussian-like index distribution in depth which is known to be a good approximation in the case of diffused waveguides in LiNbO 3 [12]. Thereby, the computation time is considerably reduced.…”

Recovery of graded index profile in planar waveguide by cubic spline function

“…In destructive approaches, samples must be processed before the measurement, such as reflectivity profiling [1], ellipsometry [2]. The non-destructive method takes advantage of intact waveguide sample.…”

“…The techniques used to solve this problem are classified to destructive and non-destructive method. In destructive approaches, samples must be processed before the measurement, such as reflectivity profiling [1], ellipsometry [2]. The non-destructive method takes advantage of intact waveguide sample.…”