All-optical hybrid active-passive waveguide selective mode converter

Waveguide-structured mode converters are essential in integrated photonics for multidimensional optical control, directly impacting the capacity and reliability of optical communication, interconnects, and mode-division multiplexing. Passive designs achieve fixed mode conversion by tailoring waveguide geometry and refractive index profile; while active control expand the flexibility through external stimuli that modulate waveguide properties for mode conversion. However, most devices confine mode conversion to the adjustment of intensity distribution under a single polarization state and lack the functionality for selective mode conversion. To address this limitation, we propose an all-optical hybrid active-passive waveguide selective mode converter that integrates a passive waveguide architecture with an active photothermal polypyrrole (PPy) material for thermally regulated mode manipulation. In the passive state, TE₀₀ converts to TE₀₁ with TM₀₀ unchanged; in the active state, TM₀₀ converts to TM₀₁ with TE₀₀ preserved, demonstrating selective mode conversion capability for both TE and TM modes. The proposed device achieves insertion losses below 0.032 dB and mode crosstalk under -21 dB, with extinction ratios exceeding 23.6 dB across all operating states at a switching power consumption of 4.79 mW. This mode converter enhances both the performance and capacity of optical communication systems and enables polarization-selective multimode control in all-optical networks.