  Photonic integrated circuits currently use platform intrinsic thermo-optic
and electro-optic effects to implement dynamic functions such as switching,
modulation and other processing. Currently, there is a drive to implement field
programmable photonic circuits, a need which is only magnified by new
neuromorphic and quantum computing applications. The most promising
non-volatile photonic components employ phase change materials such as GST and
GSST, which had their origin in electronic memory. However, in the optical
domain, these compounds introduce significant losses potentially preventing a
large number of applications. Here, we evaluate the use of two newly introduced
low loss phase change materials, Sb2S3 and Sb2Se3, on a silicon nitride
photonic platform. We focus the study on Mach-Zehnder interferometers that
operate at the O and C bands to demonstrate the performance of the system. Our
measurements show an insertion loss below 0.04 dB/um for Sb2S3 and lower than
0.09 dB/um for Sb2Se3 cladded devices for both amorphous and crystalline
phases. The effective refractive index contrast for Sb2S3 on SiNx was measured
to be 0.05 at 1310 nm and 0.02 at 1550 nm, whereas for Sb2Se3, it was 0.03 at
1310 nm and 0.05 at 1550 nm highlighting the performance of the integrated
device.
