Optical Gain at 637 nm Wavelength in Polymer Waveguide Amplifier Under Commercial LED Pumping for Planar Photonic Integration

Abstract Optical gains at 637 nm wavelength using light‐emitting diodes (LEDs) instead of traditional semiconductor lasers as pumping sources are demonstrated in the organic molecule 2,6‐bis[4‐(diphenylamino)phenyl]‐9,10‐anthracenedione (AQ(PhDPA)₂)‐doped polymethylmethacrylate (PMMA) and SU‐8 polymer waveguides. Under excitation of four blue‐violet LEDs with different central wavelengths, fluorescence in the red band is observed owing to the transition of AQ(PhDPA)₂ from the excited states to the ground state based on the thermally activated delayed fluorescence (TADF) mechanism. Channel waveguides with a cross‐section of 6 µm × 5 µm are fabricated. The relative gains of 5.0 and 4.0 dB cm⁻¹ are obtained in rectangular waveguides with active core layers as AQ(PhDPA)₂ doped PMMA and SU‐8, respectively. Optical gains have also been achieved in waveguides based on evanescent‐wave coupling. By using the vertical top pumping mode of a 450 nm LED, a gain of 2.6 dB cm⁻¹ is obtained in a passive SU‐8 waveguide with AQ(PhDPA)₂ doped PMMA as the upper cladding. In contrast, the replacement of SU‐8 with AQ(PhDPA)₂ doped SU‐8 as the active material, triples the optical gain, which reaches to 7.8 dB cm⁻¹ owing to the presence of stimulated excitation in both channel waveguide and upper cladding.