Add and drop circulator

An optical signal bidirectional transmission system comprising:

• a bi-directional port configured to receive an eastward beam and output a westward beam;
• an input port configured only as an input port to receive the westward beam;
• an output port configured only as an output port to output the eastward beam;
• only one birefringent crystal including a first side and a second side opposite of the first side;
• a first beam manipulation system coupled to the bi-directional port and the first side of the birefringent crystal, and configured to receive the eastward beam from the bi-directional port, adjust a polarization of the eastward beam, and direct the eastward beam from the bi-directional port to the first side of the birefringent crystal;
• and
• a second beam manipulation system coupled to the input port, the output port, and the second side of the birefringent crystal, and configured to receive the westward beam from the input port, adjust a polarization of the westward beam, and direct the westward beam from the input port to the second side of the birefringent crystal;
• wherein the birefringent crystal is configured to:
• receive, at the first side, the eastward beam from the first beam manipulation system;
• direct the eastward beam, according to the polarization of the eastward beam, toward the second beam manipulation system such that the eastward beam may exit the second beam manipulation system through the output port;
• receive, at the second side, the westward beam from the second beam manipulation system;
• and
• direct the westward beam, according to the polarization of the westward beam, toward the first beam manipulation system such that the westward beam may exit the first beam manipulation system through the bi-directional port.