the optical/ultraviolet light and reradiates in the FIR/sub-mm. Dust emission makes up the CIB, which contains about half of the extragalactic background radiation (excluding the cosmic microwave background), i.e. the total power originated from stars and AGN throughout the cosmic history (Puget et al. 1996; Fixsen et al. 1998; Lagache et al. 1999). The *Herschel[^2] Space Observatory* (Pilbratt et al. 2010) has carried out imaging surveys with unprecedented size and depth at FIR/sub-mm wavelengths. Thanks to its sensitivity and mapping speed, it allows us for the first time to probe the bolometric power of DSFGs at high redshifts in large volumes.

This paper is organised as follows. In Section 2, we give an overview of the *Herschel*-SPIRE maps and SDSS DR7 and DR9 QSO catalogues used in our analysis. In Section 3, we first describe the estimator used to calculate the cross-correlation signal between the QSOs and the CIB. We then investigate the potential contamination of Galactic dust emission by explicitly calculating the cross-correlation signal between our quasar samples and the IRAS 100 $\micron$ data in our fields. Finally, we present the cross-correlation results between various quasar samples and the SPIRE maps at 250, 350 and 500 $\micron$. In Section 