Programmable THz pulse shaping and frequency shifting using a cascade of spatial and temporal boundaries

The ability to manipulate ultrafast pulses has been at the heart of major technological advances, including chirp pulse amplification, pulse compression, and frequency conversion. At terahertz (THz) frequencies, precise control of pulse dispersion and frequency is key to next-generation high-speed wireless communication and sensing applications, yet such control remains difficult owing to inefficient nonlinear materials and the fundamental constraints of passive devices. Here, to overcome these limitations, we introduce a time-varying semiconductor waveguide platform with a cascade of temporal and spatial boundaries and demonstrate programmable control of THz pulse waveforms with efficient frequency conversion. By precisely timing optical pulses at multiple temporal boundaries to control the THz intra-pulse frequency shifts, we generate tailored positive, negative, and non-monotonic chirp pulses, as well as tunable frequency upconversion. These results open a way toward programmable THz pulse manipulation for time-varying photonics.