# Bi-directional top hat D-Scan: single beam accurate characterization of nonlinear waveguides

## TL;DR

This paper introduces a novel single-beam method using top-hat D-Scan for precise characterization of third-order nonlinear waveguides, including TPA and Kerr coefficients, validated on silicon waveguides with high accuracy.

## Contribution

It presents the first application of top-hat D-Scan for third-order nonlinear waveguide characterization, enabling accurate measurement with a single beam and dual-directional transmission.

## Key findings

- Accurately measures TPA and Kerr coefficients within ±10%
- Validates the technique on silicon waveguides
- Provides a new method for nonlinear waveguide analysis

## Abstract

The characterization of a third order nonlinear integrated waveguide is reported for the first time by means of a top-hat Dispersive-Scan (D-Scan) technique, a temporal analog of the top-hat Z-Scan. With a single laser beam, and by carrying two counter-directional nonlinear transmissions to assess the input and output coupling efficiencies, a novel procedure is described leading to an accurate measurement of the TPA figure of merit, the effective Two-Photon Absorption (TPA) and optical Kerr (including the sign) coefficients. The technique is validated in a silicon strip waveguide for which the effective nonlinear coefficients are measured with an accuracy of $\pm 10~\%$