Analysis of the relationship between the facet phases and the vertical radiation profile of second order CC-DFB lasers

Summary form only given. Complex coupling (CC) in distributed feedback (DFB) lasers can lead to high-quality modal properties such as high monomode yield, stable narrow linewidth, high side-mode suppression ratio (SMSR) and strong immunity to feedback without the use of AR coatings. We fabricate second order DFB lasers with strong vertical emission to create the complex coupling by a simple and reliable method. The vertical radiation also presents the potential advantage of high power, high brightness and low diffraction angles. In this paper, we use a 2-dimensional model of the laser cavity to describe the relations between the facet phases and the vertical radiation profile of as-cleaved second order DFB lasers. We demonstrate a method that uses the radiation profile to derive the left and right facet phases. Previously, Morthier et al. (1995) proposed a method based on numerical fits of subthreshold spectra to determine the coupling coefficients and the facet phases. However, this method requires high-resolution spectra and precise relative intensity measurements of the modal peaks below threshold. It is preferential to measure the facet phases under actual lasing conditions. Our new method requires only one measurement of the surface near-field emission profile.