Radiative energy transfer assisted amplified spontaneous emission in asymmetric-coupled-waveguide structures

Abstract

We demonstrate the efficient amplified spontaneous emission (ASE) of rhodamine 640 in asymmetric-coupled-waveguides. In these structures, two active waveguides, one doped with [2-[2-[4-(dimethylamino)phenyl]ethenyl]-6-methyl-4H-pyran-4-ylidene]-propanedinitrile (DCM) and the other with rhodamine 640, are coupled by a passive layer of polyvinyl alcohol. Under a suitable pumping wavelength of 500 nm, the DCM waveguiding layer acts as the donor and rhodamine waveguiding layer acts as the acceptor. Time-resolved fluorescence measurements are employed to confirm that radiative energy transfer is the responsible mechanism for ASE when the waveguiding layers are separated by a thickness of less than 50 nm. In this case, the ASE threshold was found to be reduced by a factor of 16, associated with an intensity enhancement of 56 times, compared to that of the rhodamine waveguiding layer. Next, we investigate the ASE properties of asymmetric-coupled-waveguides as a function of coupling layer thickness. The thickness-dependent coupling constant is simulated using the coupled-mode theory, and its behavior is applied to understand the experimental results.

Asymmetric coupling coefficients induced amplified spontaneous emission in planar coupled waveguides

“…This work investigated the fluorescence response of the acceptor pertaining to the energy transfer, and the structure required sophisticated instrumentation to introduce a metallic coating as a coupling layer. Recently, our group has demonstrated radiative energy transfer-assisted wavelength-tunable amplified spontaneous emission (ASE) of the acceptor by varying the coupling layer thickness in the coupled planar waveguides, fabricated using a more straightforward technique of spin coating [17]. As low threshold components are desired in photonic devices, the ASE threshold needs to be optimized in such coupled waveguides.…”

“…Thickness of each guiding layer was found to be 400 nm. A standard experimental setup was used for ASE experiments [10,17,22,23]. A schematic image of sample excitation and emission collection is shown in figure 3(a).…”