Dispersion-Engineered SOI Ridge Waveguides for Broadband Nonlinear Photonics and Polarization-Insensitive Transport

Sub-micron silicon-on-insulator (SOI) strip waveguides face a well-known dilemma: strong optical confinement comes at the price of steep normal disper- sion, high sidewall scattering, and severe modal birefrin- gence. Here, we show how partial etching into a ridge geometry resolves these constraints across two distinct operating regimes. We combine calibrated full-vector modal solvers, layout synthesis, beam-propagation elec- trodynamics, and nonlinear pulse propagation into a unified computational model. For nonlinear applications, Platform A (W = 480 nm, H = 220 nm, hslab = 65 nm) flattens the group-velocity dispersion, delivering anoma- lous values (D = +18.0 ps/(nm·km), β2 = −23 ps 2 /km at 1550 nm) across 1420–1680 nm inside a broad |D| ≤ 18 ps/(nm·km) window (1400–1700 nm). This profile supports a 267-nm four-wave mixing gain bandwidth at P p = 650 mW, near-octave supercontinuum genera- tion (1150–2200 nm) under 100-fs pulse pumping, and single-soliton Kerr combs (79 lines across 17.7 THz, FSR = 227.2 GHz) at P in = 12.5 mW when accounting for carrier kinetics and cavity heating via the Lugiato– Lefever equation. Conversely, Platform B (W = 570 nm, H = 400 nm, h slab = 127 nm) addresses polariza- tion sensitivity. It suppresses phase birefringence be- low |∆neff| < 10−6 and limits group birefringence to |∆ng| < 1.5 × 10−5 , holding differential group delay under 0.50 fs/cm with single-mode guidance throughout the C-band. Tapered mode converters maintain inser- tion losses below 0.15 dB with reflections under −42 dB. Three-dimensional volume current calculations indicate a 58% drop in sidewall scattering relative to wire base- lines (αscat = 1.14 ± 0.08 dB/cm vs. 2.70 ± 0.15 dB/cm). Both cross-sections tolerate standard lithographic er- rors (∆W = ±10 nm, ∆h slab = ±5 nm) and align with air-clad silicon manufacturing.