Scalable TM0-to-TM3 mode-order conversion using all-dielectric perturbations in near-infrared and mid-infrared regions

Abstract Scalable mode-order conversion across different wavelength regimes is a fundamental requirement for advanced photonic integration. In this work, we design two compact TM 0 -to-TM 3 converters operating in both the near-infrared (NIR) and mid-infrared (MIR) bands. The first design employs a series of shallowly-etched rectangular slots that progressively reshape the input TM 0 mode into the four-lobe TM 3 distribution. In the NIR regime, it achieves a conversion efficiency (CE) of 94.4%, crosstalk (CT) of − 19.2 dB, insertion loss (IL) of 1.37 dB, and wavelength-dependent loss (WDL) of 0.278 dB over a 70 nm bandwidth, with a device length of 17.63 μm. In the MIR regime, the same structural concept delivers CE of 96.8%, CT of − 19.5 dB, IL of 0.42 dB, and WDL of 2.6 dB over a 1000 nm bandwidth, with a device length of 24.72 μm. The second design combines elliptical perturbations with rectangular features to enhance modal splitting. In the NIR band, it achieves CE of 88%, CT of − 11.5 dB, and IL of 2.9 dB, with a compact device length of 13.12 μm and WDL of 0.64 dB over a 70 nm bandwidth. Comparable performance is maintained in the MIR regime, where CE reaches 91.04%, CT is − 13.6 dB, IL is 1.48 dB, and WDL is 2.05 dB over a 1000 nm bandwidth, with a device length of 22.4 μm. These results highlight not only the efficiency of the individual devices but also their scalability, demonstrating that a single design approach can be extended across multiple spectral regimes. Moreover, the all-dielectric configuration ensures low optical loss and fabrication practicality, strengthening the potential of these converters for wideband and polarization-diverse silicon photonic platforms.