  Some inflationary models predict the existence of isocurvature primordial
fluctuations, in addition to the well known adiabatic perturbation. Such mixed
models are not yet ruled out by available data sets. In this paper we explore
the possibility of obtaining better constraints on the isocurva- ture
contribution from future astronomical data. We consider the axion and curvaton
inflationary scenarios, and use Planck satellite experimental specifications
together with SDSS galaxy survey to forecast for the best parameter error
estimation by means of the Fisher information matrix formal- ism. In
particular, we consider how CMB lensing information can improve this forecast.
We found substantial improvements for all the considered cosmological
parameters. In the case of isocurvature amplitude this improvement is strongly
model dependent, varying between less than 1% and above 20% around its fiducial
value. Furthermore, CMB lensing enables the degeneracy break between the
isocurvature amplitude and correlation phase in one of the models. In this
sense, CMB lensing information will be crucial in the analysis of future data.
