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

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.