Similar to Fig. 15, but including simulations of the performances of future observations with the CTA array (50 h observations) and different spectral corrections for photon-photon absorption. Cyan and red datapoints as in the previous figure. Here we assume the existence of a diffuse excess background in the near-IR from very high redshift sources (Population III objects), on top of our estimated EBL in the present paper. The figure includes a simulation of future observations of a similar gamma-ray source observed at the redshift z = 1.8 with the CTA array, to show how sensitive the instrument will be in constraining truly diffuse background signals from un-resolved high-redshift source population.