Frequency‐Resolved Optical Gating in Transverse Geometry for On‐Chip Optical Pulse Diagnostics

Abstract A new on‐chip diagnostic tool is developed, allowing for real‐time full characterization of waveguided ultrashort optical pulses. This technique, called transverse frequency‐resolved optical gating (T‐FROG), relies on second harmonic generation (SHG) in a transverse (surface emitting) geometry. The T‐FROG is implemented on a thin‐film lithium niobate (LN) platform, demonstrating its versatility and consistency in accurately characterizing waveguided femtosecond pulses, including information about chirp and self‐phase modulation. In contrast to traditional FROG techniques, T‐FROG represents a significant improvement as it provides temporal amplitude and phase profiles of ultrafast optical pulses directly inside photonic integrated circuits. The real‐time in situ characteristics and dynamics of optical pulses offered by T‐FROG show promise for their potential applications in the design, testing, and optimization of ultrafast photonic integrated circuits.