Topological photonic states are important for constructing optical devices immune from structural perturbations, offering a viable solution for robust photonic integrations. Dynamically encircling exceptional points (EPs) of self-intersecting Riemann sheets gives rise to chiral mode transfer, and recently chiral mode converters capable of directionally switching topological photonic states have been constructed in optical waveguide arrays. However, the transmission efficiencies realized in previous studies are inherently low due to path-dependent losses, which hinders their practical application. Here, we proposed to realize efficient chiral topological mode conversion by dynamically encircling the moving EP of the two topological edge modes in lossy waveguide arrays mimicking the non-Hermitian Su-Schrieffer-Heeger lattice via modulation of loss along the propagation direction, which enables reduced average loss in a whole cycle while maintaining the employment of topological properties around an EP. The resultant chiral topological mode converter is highly efficient due to reduced average loss during the passage of EP encirclement, with transfer efficiency as high as $86\%$ in theory with near unity mode purity and considerable transmission $(-2.8\mathrm{dB})$ in simulation with over $92\%$ of the total output energy taken over by the transferred mode. It is also proven to be robust against mild perturbations of coupling strengths and mode mismatch. The efficient and robust chiral topological mode converter will promote the practical applications of topological photonic states, such as broadband optical switches and optical isolators.

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• Integrated optics
• Nanophotonics
• Topological effects in photonic systems
• Non-Hermitian systems
• Waveguide arrays
• PT-symmetry