Ever since discovered, graphene has brought in high-energy relativistic quantum mechanics to low-energy condensed matter system. Exploiting its unique relativistic characters and electrostatic tunability, ballistic graphene has a great potential leading us to novel electronic optical quantum devices. When electrons tunnel p-n barriers, that is called Klein tunneling, they exhibit negative refraction in order to conserve their pseudo-spins. Based on this unique phenomenon, Veselago’s lens was demonstrated in the graphene heterostructure of two sharp p-n barriers. We will also discuss a quantum switch based on Dirac-fermion optics, where strong angle dependence of Klein tunneling probability enabled collimators and mirrors for electrons. Through systematic measurements, we isolated the net optical contribution and extracted a full set of transmission coefficient, demonstrating clear evidences of Dirac fermions’ optical characteristics. Lastly, we will also discuss how electrons can be focused by using external magnetic field or abortive pinhole structures, and their interaction with superconductivity.