Highly Sensitive Dispersion Characterization of mm-Length Silicon Nitride Waveguides and Their Couplers Around the Zero-Dispersion Wavelength

In the fast-growing field of integrated photonics, quantifying the dispersive characteristics of the optical components integrated on chip is of key importance. The short length of on-chip components, however, makes it challenging to measure their dispersive properties. Hence, experimental data are relatively scarce, especially at wavelengths close to the zero-dispersion wavelength (ZDW) where the dispersion-length product becomes very small. Ideally, the dispersion should be characterized with a technique that, besides being highly sensitive, "directly" yields the dispersion value without frequency derivative calculations nor the addition of dedicated on-chip measurement structures. To fulfill these requirements, a dispersion characterization technique is presented relying on femtosecond-resolution time-of-flight measurements combined with advanced spatial light modulator (SLM) technology. With this new "direct" technique, suitable for measuring dispersion-length products down to 5 x 10-5 ps nm-1, the dispersion of mm-length silicon nitride waveguides is characterized, both in the weakly dispersive (close to the ZDW) and strongly dispersive regimes. Furthermore, dispersion data are presented for sub-mm-length trident couplers and inverted taper couplers connected to the waveguides. The resulting insights into the waveguides' and couplers' dispersive properties, and the wide applicability of the technique, will benefit the development of advanced photonic integrated circuits (PICs) in silicon nitride and other waveguide material platforms.