Theoretical study of the influence of wavelength on bandwidth of newly designed multimode doubly clad W-type GI silica photonic crystal fiber

In this study, we use the power flow equation (PFE) to analyze the wavelength-dependent transmission characteristics of a newly designed multimode doubly clad W-type silica photonic crystal fiber (SPCF) structure with a graded-index (GI) core. Our results show that narrowing the inner cladding of the multimode doubly clad W-type GI SPCF boosts bandwidth by reducing number of guided modes and modal dispersion. The bandwidth rises from 0.95 GHz km at 650 nm to 9.8 GHz km at 850 nm, before decreasing to 0.38 GHz km at 1310 nm and further to 0.35 GHz km at 1550 nm. At 850 nm, the core's refractive index becomes parabolic, minimizing modal dispersion and yielding the highest bandwidth of 9.8 GHz km. In comparison, standard OM4 and OM5 multimode silica optical fibers (SOFs) have a bandwidth of 4.7 GHz km at 850 nm and significantly lower bandwidth at 650 nm (200 MHz km) and 1310/1550 nm (500 MHz km). The W-type GI SPCF achieves a higher bandwidth-length product of ∼1 GHz km at 650 nm and ∼700 MHz km at 1310 and 1550 nm. We also observe that radial offset slightly impacts bandwidth at short lengths but has minimal effect at longer lengths due to mode coupling. A key advantage of SPCFs is their tunability—air-hole diameters and pitches can be precisely adjusted without the complex doping required for standard SOFs.