Broadband C  +  L-band waveguide amplifier enabled by co-doping with dual-size PbS/CdS quantum dots

In this work, we propose and demonstrate a broadband waveguide amplifier based on dual-size core–shell PbS/CdS quantum dot (QD) co-doping. PbS/CdS QDs with emission peaks at 1508 and 1604 nm, respectively, were dispersed in SU-8 photoresist at a 1:1 mass ratio to serve as the core material. We fabricated the devices using photobleaching combined with precision UV lithography and systematically characterized the propagation loss and gain performance of single-size and dual-size QD-doped waveguide amplifiers. The results verify that the dual-size co-doping strategy effectively extends the gain bandwidth. The co-doped waveguide amplifier covers a gain spectrum of 1450–1630 nm, with a full width at half maximum spanning 1490–1630 nm, fully covering the C + L-band, which achieves a maximum gain of 11.9 dB at 1540 nm. Within the entire C + L-band, gain fluctuation is kept below 3 dB, and the gain remains over 9 dB across all operating wavelengths. This work provides an effective route to realize broadband on-chip optical amplifiers.