Application of the yellow laser based on the Dy-doped ZBLAN fiber for the treatment of the retinal diseases

Yellow lasers emitting in the 565–590 nm wavelength range are gaining increasing importance due to their wide range of applications in ophthalmology, dermatology, advanced imaging techniques, and display technologies. In particular, they are highly suitable for the treatment of retinal diseases, owing to the strong absorption of yellow light by retinal pigments. This selective absorption enables localized coagulation while minimizing damage to surrounding healthy tissue. Currently, yellow emission is primarily obtained through second harmonic generation. However, direct emission is possible by using Dysprosium-doped (Dy) specialty fibers, such as ZBLAN or phosphate fibers. Monolithic integration of all-fibers offers many advantages, including robustness due to the absence of critical alignments and distributed thermal management, higher energy efficiency due to direct emission, and superior beam quality, given the possibility of single-mode operation. One of the main challenges is maximizing the slope efficiency of these fiber lasers: indeed, while the theoretical maximum slope efficiency of Dy-doped fiber lasers approaches 78%, experimental results have so far demonstrated no more than 33%. In this work, a numerical model of a Dy-doped fiber laser was developed to optimize performance through parametric analysis. Key parameters, such as doping concentration, fiber length, and background losses, were systematically varied to optimize output efficiency. Simulation results show a significant improvement in slope efficiency, demonstrating the potential for highly energy-efficient laser systems for medical applications. The experimental realization of a yellow fiber laser based on a Dy-doped ZBLAN fiber is also discussed, and preliminary characterization results are presented to validate the simulation outcomes. In addition, a COMSOL-based thermal analysis of the eye under laser exposure was performed to assess the thermal impact on retinal and adjacent tissues. The model simulates heat distribution and tissue response, ensuring that laser parameters remain within safe limits to avoid thermal damage while maintaining therapeutic efficacy. The combination of an optimized laser design and rigorous thermal management provides a solid foundation for the development of safe and effective treatment protocols for retinal diseases.