Advanced characterization techniques of photonic devices with frequency combs

Doktorsavhandling, 2023

Integrated photonics has witnessed remarkable progress in the last decades.
Measuring photonic devices in amplitude and phase provides insight into
their performance. Swept wavelength interferometry is a prominent technique
for the broadband characterization of the complex response. It
leverages continuous advances in rapidly tunable laser sources but is
prone to systematic errors associated with frequency calibration. This
thesis focuses on the non-destructive measurement of ultralow-loss photonic
devices using swept wavelength interferometric technique. We overcome
issues associated with nonlinear tuning by calibrating the frequency
of the laser on the fly with the aid of a frequency comb. We apply the
concept to diverse components of relevance including microresonators
and spiral waveguides. This technique enables diagnosing waveguides
for the loss and potential defects and is instrumental in optimizing device
fabrication ecosystems. The measured phase response of microresonators
allows for untangling the coupling condition and provides insight
into microresonator-waveguide systems. The later part of this thesis
covers the linear (stepped and multi-heterodyne) methods for spectral
and temporal characterization of frequency combs. The linear heterodyne
method provides unprecedented sensitivity and bandwidth range
of measurement. In addition, we provide an overview and comparative
assessment of the state-of-the-art in the field.