▎ 摘　　要

We simulate electron transport through graphene nanoribbons of realistic size containing a p-n junction patterned by electrostatic gates. For a sharp p-n interface, Klein tunneling leads to refocusing of a divergent beam forming a Veselago lens. Wider transition regions allow only electrons with near-perpendicular incidence to pass the junction, forming a Klein collimator. Using a third nearest neighbor tight binding description we explore the influence of interface roughness and bulk disorder on guiding properties. We provide bounds on disorder amplitudes and p-n junction properties to be satisfied in order to experimentally observe the focusing effect and compare our predictions to very recent realizations.