Direct spatial-temporal discrimination of modes in a photonic lightwave circuit using photon scanning tunnelling microscopy

Multi-mode photonic lightwave circuits (PLCs) provide new avenues for extending the performance of single mode systems. As an example, they can potentially provide increased bandwidth by multiplexing information into different waveguide modes. For practical applications of multi-mode PLCs to be developed, a measurement technique is required to investigate detailed mode profiles and propagation constants in complex circuits. Photon scanning tunnelling microscopy (PSTM) provides a means of experimentally tracking the femtosecond inter-modal delays observed in PLCs with the ability to discriminate modes by their spatial profiles inside the waveguide.