The refractive index n(lambda), and optical absorption coefficient alpha(lambda), of thin polycrystalline silicon films (Si-poly), undoped or heavily doped in-situ with boron 8.10(20) cm(-3) or phosphorus 6.10(20) cm(-3), deposited inside a new kind of reactor, called sector reactor (a reduced model of an annular reactor). The optical constants of undoped Si-poly are obtained by a simple procedure which is based on the use of the fringe pattern in the transmission spectrum. For heavily B-or P-doped polysilicon films, the optical absorption coefficient become not negligible at near infrared and we deduced the optical constants from both the measured transmission T(lambda) and reflection R(lambda) for film-substrate structures. In the infrared, the index of refraction decreases systematically and the absorption coefficient increases systematically with wavelength. This variation of the optical parameters is attributed to the presence of free carriers. Drude’s theory was used in order to calculate the free-carrier concentration and the mobilities, and these results compared well with those obtained by Hall-effect measurements.