Asymmetric coupling coefficients induced amplified spontaneous emission in planar coupled waveguides

Abstract

We demonstrate the role of coupling coefficients in asymmetric coupled waveguides towards delivering a low threshold amplified spontaneous emission (ASE). A theoretical investigation in four different coupled waveguides possessing varying order of symmetry that arises from the bounding media refractive indices shows that the coupling coefficient carries the asymmetry in accordance with the nature of symmetry of the investigating structure. That is, a symmetric coupled waveguide is characterized with identical and asymmetric coupled waveguides, with, unlike coupling coefficients. The effect of unequal coefficients designating the electromagnetic energy transfer from one waveguide to the other and vice versa are experimentally demonstrated on the ASE of the acceptor (Rhodamine 640) by flipping the positions of the donor [[2-[2-[4-(dimethylamino) phenyl] ethenyl]-6-methyl-4H-pyran-4-ylidene]-propanedinitrile (DCM) and acceptor molecules that exist in the opposite waveguides of an asymmetric coupled waveguide. We also correlate the value of the coupling coefficient with the observed threshold of the acceptor ASE towards the optimization of a coupled waveguide as an efficient optical amplifier.