  We demonstrate power-efficient, thermo-optic, silicon nitride waveguide phase
shifters for blue, green, and yellow wavelengths. The phase shifters operated
with low power consumption due to a suspended structure and multi-pass
waveguide design. The devices were fabricated on 200-mm silicon wafers using
deep ultraviolet lithography as part of an active visible-light integrated
photonics platform. The measured power consumption to achieve a $\pi$ phase
shift (averaged over multiple devices) was 0.78, 0.93, 1.09, and 1.20 mW at
wavelengths of 445, 488, 532, and 561 nm, respectively. The phase shifters were
integrated into Mach-Zehnder interferometer switches, and $10- 90$\% rise(fall)
times of about 570(590) $\mu$s were measured.
