Electro-optic interface for ultrasensitive intra-cavity electric field sensing

We demonstrate a fibre-coupled, fully monolithic electro-optic coherent interface on the silicon-photonics platform that senses terahertz electric fields with sub-cycle resolution by means of nonlinear coupling with photons at telecom frequencies. A strong confinement of the terahertz field to a cavity mode enables a coupling strength to sense fields as low as 20 V/m. We discuss the opportunities such platforms provide for sensing of cavity-confined terahertz states at the quantum limit.