Demonstration of Optical Gain at 1535 nm Based on Er^III Complex‐Doped Polymer Waveguides Under Light‐Emitting Diode Excitation

Abstract A near‐infrared luminescent complex Er(DBTTA)₃(DBFDPO) [where DBTTA = dibenzotetrathienoacene; DBFDPO = 4,6‐bis (diphenylphosphoryl) dibenzofuran] is synthesized. Based on the intramolecular energy transfer between organic ligands and Er³⁺ ions, optical gains at 1535 nm are demonstrated in Er(DBTTA)₃(DBFDPO)‐doped polymer waveguides under the excitation of light‐emitting diodes (LEDs) instead of laser pumping. Relative gains of 6.4, 8.2, and 10.6 dB are obtained in 1 cm long waveguides with cross‐sectional dimensions of 6 × 4, 4 × 4, and 2 × 3 µm² respectively, using the vertical top‐pumping mode of a 365 nm LED with 462 mW. Incorporating an ≈100 nm thick aluminum reflector grown under the lower cladding, enhanced the optical gain to 11.6 dB cm⁻¹ in a waveguide with a cross‐section of 4 × 4 µm², and an internal gain of ≈7.4 dB cm⁻¹ is achieved. By relying on the intramolecular energy transfer and LED top‐pumping technology, the upconversion luminescence of Er³⁺ ions and thermal damage to polymer waveguides caused by the high power density of laser pumping can be effectively reduced. The complex Er(DBTTA)₃(DBFDPO)‐doped polymer can be spin‐coated on different types of waveguides to compensate for optical losses at 1.5 µm and is expected to have a critical role in planar photonic integration.