Highly Sensitive Dispersion Characterization of Silicon Nitride Waveguides Using Femtosecond Time-of-Flight Measurements

The field of photonic integrated circuits has experienced significant growth over the past several decades. A key parameter of on-chip waveguides is their dispersion, as it governs, amongst others, the temporal and phase evolution of optical pulses and the phase matching conditions for nonlinear-optical processes. In view of the short length of on-chip waveguides, accurately measuring their dispersive properties remains challenging, especially at wavelengths approaching the zero-dispersion wavelength (ZDW) where the dispersion-length product becomes very small. Ideally, the dispersion should be measured with a highly sensitive technique that “directly” provides the dispersion value without the need for frequency derivative calculations nor the addition of interferometric or resonator structures on chip. To address this challenge, we here introduce a dispersion characterization technique that combines ultrafast time-of- flight measurements with advanced spatial light modulator (SLM) technology [1]. We show that this new “direct” and highly sensitive technique enables us to characterize the dispersion of mm-length on-chip silicon nitride waveguides around the ZDW.