Efficient Optical Amplification in a Sandwich-Type Active-Passive Polymer Waveguide Containing Perylenediimides

Abstract

Polymer waveguides doped with luminescent materials serve as a suitable flexible platform for active elements (lasers and amplifiers) in on-chip optical circuits. However, at present, the best parameters (lowest thresholds) achieved with these devices are obtained with the use of the stripe excitation technique in the framework of which external illumination of an active material along the whole length of the waveguide is realized that is not convenient for the waveguide on-chip integration and requires high peak energies due to the large excitation area. In the present work, an elegant method is proposed to overcome this obstacle and provide efficient active material pumping along the whole waveguide length with use of on-chip integration compatible edge-type excitation light injection. This novel type of planar active-passive polymer waveguides includes a thin (50−100 nm) active layer of poly(methyl methacrylate) (PMMA), which is heavily doped with highly luminescent perylenediimide (PDI) molecules, sandwiched between two cladding (passive) PMMA layers. This structure efficiently exploits the excellent light-emitting properties of PDIs with a confinement of both the excitation beam and the photoluminescence in the active PMMA−PDI film. In this way, the absence of losses in the PMMA claddings guarantees the propagation of the pump beam along the whole length of the structure (≈1 mm) in order to provide the required excitation to obtain stimulated emission. Geometrical parameters are optimized to demonstrate the amplified spontaneous emission with a threshold as low as 0.9 μJ and a line width as narrow as 2 nm.