We investigate the optical response of graphene nanoribbons (GNRs) using the broadband nonlinear generation and detection capabilities of nanoscale junctions created at the LaAlO3/SrTiO3 interface. GNR nanoclusters measured to be as small as 1–2 GNRs in size are deposited on the LaAlO3 surface with an atomic force microscope tip. Time-resolved nonlinear optical probes of GNR nanoclusters reveal a strong, gate-tunable second and third harmonic response, as well as strong extinction of visible to near-infrared light at distinct wavelengths, similar to previous reports with graphene.