Bragg-grating engineering enables deterministic resonance control in an on-chip THz filter

On-chip filters are important for integrated terahertz (THz) communication and sensing systems. Deterministic control of resonance multiplicity in compact devices enables flexible spectral filtering. Here, we experimentally demonstrate an on-chip silicon THz filter based on a Bragg-grating-assisted Fabry–Pérot cavity, in which the resonance multiplicity is governed by the relation between the Bragg stopband and the cavity free spectral range (FSR). By engineering this stopband–FSR relation, single-, double-, and triple-resonance states are achieved within the 360–390 GHz band, with a packaged insertion loss of approximately 6 dB. The single-resonance device exhibits a through-port transmission minimum approaching −40 dB and a loaded quality factor of QL = 809.5. This work provides a compact strategy for deterministic spectral-state engineering in integrated THz filters.