Broadband Profiled Eye-Safe Emission of LMA Silica Fiber Doped with Tm³⁺/Ho³⁺ Ions

LMA (Large Mode Area) optical fibers are presently under active investigation to explore their potential for generating laser action or broadband emission directly within the optical fiber structure. Additionally, a wide mode profile significantly reduces the power distribution density in the fiber cross-section, minimizing the power density, photodegradation, or thermal damage. Multi-stage deposition in the MCVD-CDT system was used to obtain the structural doping profile of the LMA fiber multi-ring core doped with Tm³⁺ and Tm³⁺/Ho³⁺ layer profiles. The low alumina content (Al₂O₃: 0.03wt%) results in low refractive index modification. The maximum concentrations of the lanthanide oxides were Tm₂O₃: 0.18wt % and Ho₂O₃: 0.15wt%. The double-clad construction of optical fiber with emission spectra in the eye-safe spectral range of (1.55-2.10 µm). The calculated LP₀₁ Mode Field Diameter (MFD) was 69.7 µm (@ 2000 nm, and 1/e of maximum intensity), which confirms LMA fundamental mode guiding conditions. The FWHM and λmax vs. fiber length are presented and analyzed as a luminescence profile modification. The proposed structured optical fiber with a ring core can be used in new broadband optical radiation source designs.