We have applied a third nearest-neighbor tight binding model to investigate the optical properties of CNTs in terms of radius, chirality and magnetic field. The optical spectrum of CNTs depends strongly on the radius and chirality in the infrared region in contrast to the middle energy region. The dependence of E 22/E 11 on the radius and chirality from optical peak positions and band structure is similar. In the infrared region, by applying the magnetic field, the optical peak splitting rates show well-expressed radius and chirality dependence and family behaviors.
