Free-space optical hybrid

A free-space optical hybrid comprising:

• a polarizing beam splitter splitting the light beams S and L into horizontal polarization light beams Sx, Lx and orthogonal polarization light beams Sy, Ly respectively;
• and
• at least one birefringent crystal splitting the horizontal polarization light beams Sx, Lx and orthogonal polarization light beams Sy, Ly into light beams Sxo, Sxe, Lxo, Lxe, Syo, Sye, Lyo, Lye;
• a light combiner combining the light beams Sxo+Lxo, Sxo−Lxo, Sxe+jLxe, Sxe−jLxe, Syo+Lyo, Syo−Lyo, Sye+jLye, Sye−jLye and outputting the light beams at ports;
• wherein the light beams Syo+Lyo, Sye+jLye, Syo−Lyo and Sye−jLye are the hybridized beams of beam S and beam L at X polarization status, and the phase relations of the beam S and beam L of four beams are pi—0+0, pi—0+pi/2, pi—0+pi, pi—0+pi3/2;
• the beams Syo+Lyo, Sye+jLye, Syo−Lyo, Sye−jLye are the hybridized beams of beam S and beam L at Y polarization status, and the phase relations of the beam S and beam L of four beams are pi—0+0, pi—0+pi/2, pi—0+pi, pi—0+pi3/2;
• wherein the polarizing beam splitter is PBS or a birefringent crystal;
• a quarter-wave plate is configured between the polarizing beam splitter and the birefringent crystal, the quarter-wave plate transforms the light beam emitted from the polarizing beam splitter into circular polarization light;
• the free-space optical hybrid further comprises a plurality of phase shifters configured between the birefringent crystal and the light combiner and for regulating the phase of each light;
• the phase shifters are glass plates or silicon plates;
• the birefringent crystal is a rutile, sapphire, yttrium orthovanadate crystal, MgF2 crystal, a-BaB2O4 crystal, lithium niobate or quartz crystal;
• wherein the at least one birefringent crystal comprising a first birefringent crystal for receiving the light beams Sx and Lx split by the beam splitter, and splitting the light beams Sx and Lx into the light beams Sxo, Sxe, Lxo and Lxe;
• wherein the at least one birefringent crystal comprising a second birefringent crystal for receiving the light beams Sy and Ly split by the light-splitter, and splitting the light beams Sx and Lx into the light beams Syo, Sye, Lyo and Lye;
• wherein a first light combiner is provided at the right side of birefringent crystal, the first light combiner combines the light beams Sxo, Sxe, Lxo and Lxe which transmit through the birefringent crystal into light beams Sxo+Lxo, Sxo−Lxo, Sxe+jLxe, Sxe−jLxe;
• wherein a second light combiner is provided at the right side of birefringent crystal, the second light combiner combines the light beams Syo, Sye, Lyo and Lye which transmit through the birefringent crystal into light beams Syo+Lyo, Syo−Lyo, Sye+jLye, Sye−jLye;
• wherein the light beams Sxo+Lxo, Sxe+jLxe, Sxo−Lxo, Sxe−jLxe, Syo+Lyo, Sye+jLye, Syo−Lyo, Sye−jLye converge on a corresponding photo detector via reflectors or lenses.