Optical Amplification at 1.5 µm in Er^III Coordination Polymer‐Doped Waveguides Based on Intramolecular Energy Transfer

Abstract 9,9‐bis (diphenylphosphorylphenyl) fluorene (FDPO) and dibenzotetrathienoacene (DBTTA), are synthesized as the neutral and anionic ligands, respectively, to prepare the Er^III coordination polymer [Er(DBTTA)₃(FDPO)]_n. Based on the intramolecular energy transfer, optical gains at 1.5 µm are demonstrated in [Er(DBTTA)₃(FDPO)]_n‐doped polymer waveguides under excitations of low‐power light‐emitting diodes (LEDs) instead of laser pumping. A ligand‐sensitization scheme between organic ligands and Er³⁺ ions under an excitation of an ultraviolet (UV) LED is established. Relative gains of 10.5 and 8.5 dB cm⁻¹ are achieved at 1.53 and 1.55 µm, respectively, on a 1‐cm‐long SU‐8 channel waveguide with a cross‐section of 2 × 3 µm² and a 1.5‐µm‐thick [Er(DBTTA)₃(FDPO)]_n‐doped polymethylmethacrylate (PMMA) as upper cladding. The Er^III coordination polymer [Er(DBTTA)₃(FDPO)]_n can be conveniently integrated with various low‐loss inorganic waveguides to compensate for optical losses in the C‐band window. Moreover, by relying on the intramolecular energy transfer and UV LED top‐pumping technology, it is easy to achieve coupling packaging of erbium‐doped waveguide amplifiers (EDWAs) with pump sources in planar photonic integrated chips, effectively reducing the commercial costs.