Fig. 4. (a) Power transmission of light with a center wavelength of 1560 nm (TM polarization) measured for different waveguide lengths (2.30 cm, 3.89 cm, 6.90 cm, and 10.48 cm) and waveguide depths (0.8 $_{m}$m (blue circles), 1.0 $_{m}$m (red squares), and 1.2 $_{m}$m (black triangles)). The waveguide width varies between 0.7 $_{m}$m and 0.9 $_{m}$m. The graph has been corrected for the coupling losses, which vary between 13 to 15 dB in total. (b) Simulated bending losses of the quasi-TM mode at a wavelength of 1550 nm for various bending radii. Simulations were performed for cross sections and depths of w = 0 . 5$_{m}$ m and d = 0 . 8$_{m}$ m (red triangles), w = 0 . 8$_{m}$ m and d = 0 . 8 $_{m}$m (blue squares), w = 0 . 5 $_{m}$m and d = 1 . 2 $_{m}$m (black circles), and w = 0 . 8 $_{m}$m and d = 1 . 2 $_{m}$m (green diamonds). ranged from 0.7 to 0.9 $_{m}$m. No variation in the propagation loss was observed for the range of waveguide widths investigated. The propagation losses are believed to be mainly due to scattering losses since absorptive losses have been reported to amount to values of below 0.055 dB/cm in Si$_{3}$N$_{4}$ waveguides [18]. We address the comparably high losses for a d of 1.2 $_{m}$m to higher scattering losses resulting from the small gap in the center of the Si$_{3}$N$_{4}$ core, as shown in Fig. 3(c). Another important performance parameter is the bending loss, as this indicates how densely devices can be packed on a wafer. In our measurements we found that the bending losses are so low that we could not experimentally distinguish these from the differences in coupling efficiencies from waveguide to waveguide. To quantify bend- ing losses for thick Si$_{3}$N$_{4}$ waveguides, we simulated them using a finite element solver (FieldDesigner, PhoeniX BV). The simulated bending losses for a quasi-TM mode at a wavelength of 1550 nm are shown in Fig. 4(b) as a function of the radius of the bend for waveguide cross sections of d = 0 . 8 $_{m}$m and 1.2 $_{m}$m and w = 0 . 5 $_{m}$m and 0.8 $_{m}$m, respectively. As a result of the high confinement, the bending losses of the guided mode 0 2 4 6 8 10 −15 −10 −5 0 Propagation (cm) Transmission (dB) a) 0 20 40 60 10 −6 10 −4 10 −2 10 0 Bending radius (µm) Loss (dB/cm) b)