Dual-wavelength narrowband wavelength division multiplexer operating in the O + E + S bands for BDFA applications

Bismuth-doped fiber amplifiers (BDFA) exhibit efficient gain coverage across the full O + E + S bands, making them a core technical choice for tapping into the underutilized bandwidth windows in single-mode fibers. However, existing wavelength division multiplexers (WDM) struggle to simultaneously match ultra-broadband signal light and narrowband pumping that partially overlaps with the ultra-broadband signal. Aiming at the demand of BDFA for wavelength division multiplexing of ultra-broadband signals and narrowband pumping, this paper proposes a WDM based on silicon strip metasurfaces, combined with grating design theory. Using finite element method (FEM) simulations, the dimensions of silicon strips embedded in a fused silica substrate and the spacing between these silicon strips are adjusted. Through this adjustment, wavelength-division multiplexing function of ultra-broadband signals in the 1200-1530 nm range and narrowband pumping at two wavelengths are achieved. By means of mathematical fitting, a relational formula between the central wavelength of the narrowband pump and the model parameters is derived, thereby realizing the simple and rapid design of key performances. The average error of the simple and rapid design of key performances is 1.3375 nm. This work provides a new solution for WDM devices designed for BDFA and offers new ideas for the design of metasurface devices.