Design and Performance Evaluation of a Fabrication-Friendly Three-Ring PCF for 980 nm EDFA Pump and Multi-Wavelength Signal Guidance

A three-ring hexagonal photonic crystal fiber (PCF), with its pitch Λ = 28 µm and airhole radius varied between 7 and 12.6 µm, was analyzed for efficient delivery of a 980 nm EDFA pump and guidance of 1.48–1.55 µm signal wavelengths. Using FEM solutions of the vector wave equation, the effective index, effective area (Aeff), and core region power fraction were obtained across all wavelengths. At 0.98 µm, the PCF exhibits tight confinement, small Aeff, and negligible confinement loss, confirming its suitability for efficient pump absorption. Increasing the airhole radius produced smooth, monotonic growth in Aeff and a slight decrease in the doped region overlap, while pump confinement remained consistently strong. Variations in the core refractive index demonstrated an effective means to control confinement, with Aeff decreasing and loss monotonically reducing as ncore increases. Mode field profiles validated a stable, centered fundamental mode at both the pump and signal wavelengths, with only moderate expansion at longer wavelengths. Overall, the PCF design showed predictable, fabrication-friendly behavior with stable confinement and very low leakage, making it highly suitable for EDFA pump delivery applications. The obtained modal characteristics and confinement behaviors indicate that the proposed structure can provide reliable pump delivery while maintaining stable guidance of signal wavelengths in the EDFA operating band. The simple three-ring geometry also offers a structural advantage for fabrication compared with more complex PCF configurations.