COMPARATIVE ANALYSIS OF GRADED-INDEX AND STEP-INDEX OPTICAL FIBERS FOR STED MICROSCOPY

Stimulated Emission Depletion (STED) microscopy is a super-resolution technique that uses structured light to break through the diffraction limit of traditional optical microscopy.A key part of STED is producing and delivering a donut-shaped depletion beam, typically achieved using optical vortex modes.This paper compares two types of optical fibers, step-index and parabolic graded-index (GRIN) fibers, in their ability to support and deliver the specific mode profiles needed for STED, such as Gaussian-like and vortex beams.Step-index fibers are simpler but have higher intermodal dispersion, modal degeneracy, and are more sensitive to perturbations.In contrast, GRIN fibers reduce modal dispersion, enhance mode stability, and improve spatial confinement because of their smooth refractive index profile.By constructing and analyzing mode field intensity distributions for specific fiber parameters, we demonstrate that GRIN fibers more effectively support dual-mode propagation and stable beam delivery for excitation and depletion wavelengths.These traits make them more suitable for compact, fiber-integrated STED microscopy systems.The findings aid in selecting and optimizing fibers for high-resolution imaging applications.