Abstract: Compared with electronics that is already at nanoscale today, photonic circuits remain rather bulky due to optical diffraction limit. I will discuss physics in scaling down of photonics that is important for both optical sciences and modern information technology. We proposed a new optical cavity design using indefinite medium that exhibits an anomalous scaling law than conventional cavities which was confirmed experimentally. I will further present nanoscale waveguide and laser circuits using hybrid plasmons that can be multiplexed into a single waveguide-an effort towards integrated photonics at nano-scale. Finally, I will discuss non-Hermitian optics that is capable to sort color simultaneously at nano-scale for potential ultrahigh resolution camera.