Graphene, a 2-dimensional crystal of carbon, can absorb 2.3% of light over a very broad spectrum. Doped graphene, however has a gap in optical absorption due to the Pauli blocking principle. For doped graphene, the interband optical transitions with energy less than 2EF are not allowed, therefore the consequent optical absorption is expected to fall down to zero for energies below 2EF threshold. In this thesis, we investigated the optical residual absorption of graphene in Pauli-blocked region. Optical absorption of the monolayer graphene transferred on transparent substrates was analyzed via optical spectroscopy. We used electrostatic and chemical doping methods to shift Fermi energy of graphene. The observed residual absorption of 0.5% which is due to chemical impurities reduced slightly by increasing doping level.