Optical gain at 1.55 µm of Er(TMHD)₃ complex doped polymer waveguides based on the intramolecular energy transfer...

Based on the intramolecular energy transfer mechanism between organic ligand TMHD (2, 2, 6, 6-tetramethyl-3, 5-heptanedione) and central Er³⁺ ions, optical gains at 1.55 µm were demonstrated in three structures of polymer waveguides using complex Er(TMHD)₃-doped polymethylmethacrylate (PMMA) as the active material. With the excitation of two low-power UV light-emitting diodes (LEDs) instead of 980 or 1480 nm lasers, relative gains of 3.5 and 4.1 dB cm^-1 were achieved in a 1-cm-long rectangular waveguide with an active core of Er(TMHD)₃-doped PMMA polymer. Meanwhile, relative gain of 3.0 dB cm^-1 was obtained in an evanescent-field waveguide with cross-section of 4 × 4 µm² using passive SU-8 polymer as core and a ∼1-µm-thick Er(TMHD)₃-doped PMMA as upper cladding. By growing a 100 nm thick aluminum mirror and active lower cladding, the optical gain was doubled to 6.7 dB cm^-1 in evanescent-field waveguides because of the stimulated excitation of Er³⁺ ions in the upper and lower cladding and the improved absorption efficiency.