Polarization decomposition device

A polarization decomposition device comprising:

• a polarization beam splitter configured to split an optical signal into one or both of a first polarized light having a first polarization direction and a second polarized light having a second polarization direction different from the first polarization direction;
• a phase shifter configured to delay a phase of the second 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 split the first polarized light and the second polarized light in which the phase is delayed and the polarization direction is rotated into a third polarized light and a fourth polarized light, split the optical signal having a third polarization direction which is different from at least part of the first and second polarization directions into the third polarized light, and split the optical signal having a fourth polarization direction different from the third polarization direction into the fourth polarized light, and
• wherein the polarization rotator configured to rotate the second polarized light so that the polarization direction of the second polarized light is changed from the second polarization direction to the first polarization direction.

A polarization decomposition device comprising:

• a beam splitter unit configured to split an optical signal into a first polarized light having a first polarization direction, a second polarized light having a second polarization direction different from the first polarization direction, a first split polarized light having the first polarization direction, and a second split polarized light having the second polarization direction;
• a phase shifter configured to delay a phase of the first split polarized light or the second split polarized light;
• a polarization rotator configured to rotate the first split polarized light or the second split polarized light so that a polarization direction of the first split polarized light or the second split polarized light is changed;
• and
• an interference beam splitter configured to split the first split polarized light and the second split polarized light in which the phase is delayed, the polarization direction is rotated, or both, into a third polarized light and a fourth polarized light, split the optical signal having a third polarization direction which is different from at least part of the first and second polarization directions into the third polarized light, and split the optical signal having a fourth polarization direction different from the third polarization direction into the fourth polarized light, and,
• wherein the polarization rotator configured to:
• rotate the first split polarized light so that a polarization direction of the first split polarized light is changed from the first polarization direction to the second polarization direction;
• or
• rotate the second split polarized light so that a polarization direction of the second split polarized light is changed from the second polarization direction to the first polarization direction.