Polarization decomposition device

Provided is a polarization decomposition device. The polarization decomposition device includes a polarization beam splitter configured to split an optical signal into a first polarized light having a first polarization direction and a second polarized light having a second polarization direction different from the first polarized light, a phase shifter configured to delay a phase of the first polarized light, a polarization rotator configured to rotate the second polarized light so that the polarization direction of the second polarized light is changed, and an interference beam splitter configured to allow the first polarized light in which the phase is delayed and the second polarized light in which the polarization direction is rotated to interfere with each other and split them into a third polarized light and a fourth polarized light.