The direct detection of gravitational waves has ushered in a new epoch for the observation of the universe, making it possible to investigate its hidden mysteries. In order to be able to see sources from ever more distant regions of the universe, gravitational wave detectors must be further improved. So far, a total of 90 coalescence events have been revealed, most of which are black hole collisions, two black hole-neutron stars coalescences and a two neutron stars coalescence. The latter allowed the beginning of the so-called multi-messenger astronomy. During the last O3 data take LIGO and Virgo detectors revealed one coalescence event per week. During O4, the sensitivity of Virgo will increase from 60 Mpc to about 100 Mpc, increasing the amount of observable events thanks to the reduction of several sources of noise. Among them, it is necessary to reduce quantum noise over the entire detection band by introducing frequency-dependent squeezed quantum vacuum states in the interferometer. The ellipse angle of the squeezed states needs to be rotated at the frequency where shot noise and radiation pressure noise have the same amplitude, i.e. 25 Hz for Virgo, to provide a broadband quantum noise reduction. During O3, the introduction of frequency-independent states improved Virgo’s sensitivity at high frequencies by 3 dB. However, it was not possible to inject all the squeezing produced in order to avoid worsening the low-frequency sensitivity. To avoid this, it is necessary to introduce a filter cavity that rotates the squeezed states as a function of the frequency. This also makes it possible to increase low-frequency sensitivity if there are no other limiting noises. One of these noises is the scattered light from the optics on the suspended benches that re-couples with the interferometer’s main beam. This noise source was studied, projecting its effect on Virgo’s sensitivity curve.