We present optimized air-clad silicon waveguides for broadband wavelength conversion spanning nearly the entire telecom band (1260–1625 nm) via degenerate-pump four-wave mixing (FWM). The waveguides with optimized design parameters are fabricated in silicon-on-insulator (SOI) platform with a device layer thickness of 220 nm for experimental demonstration. Wavelength conversion efficiency ∼−20 dB is measured for pump power <100 mW for a waveguide of length 10 mm. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.