Broadband effective-loss characterization and application bounds of compact silicon nitride spiral waveguides

We report a wavelength-resolved, family-level characterization of four oxide-clad Si ₃ N ₄ spiral waveguides with a 20- μ m centerline pitch, a 70- μ m minimum bend radius, and total lengths derived from the Graphic Design System II (GDSII) layouts, ranging from 1.43 to 9.83 cm. Absolute fiber-to-fiber transmission was measured from 1520 to 1630 nm, and the effective length-dependent loss was extracted over 1540–1600 nm. The median wavelength-resolved ordinary-least-squares slope is 2.93 dB cm ⁻¹ and differs by less than 1% from the corresponding Theil–Sen estimate. Using a modeled quasi-transverse-electric (quasi-TE) group index of 1.93, the four layouts correspond to nominal delays of 92–633 ps and distributed penalties of 4.2–28.8 dB. The resulting power-budget map identifies compact sub-nanosecond delay and interaction-length functions as the credible operating range of the present process, whereas meter-scale waveguide coils require a loss reduction of several orders of magnitude.