Polarization independent all-fiber optical circulator

An optical circulator, comprising:

• a pair of Faraday single-mode fiber links, each Faraday fiber link having a first and a second end;
• a first pair of polarization preserving single-mode fiber links, each having a first end joined to a first end of a different Faraday fiber link, and each having an axial twist along its length;
• a first all-fiber polarization splitter having a first end joined to a second end of each of the first pair of polarization preserving single-mode fiber links, and a second end terminating in first and third fiber optic communication ports, respectively;
• a second pair of polarization preserving single-mode fiber links, each having a first end joined to a second end of a different Faraday fiber link, and each having an axial twist along its length;
• a second all-fiber polarization splitter having a first end joined to a second end of each of the second pair of polarization preserving single-mode fibers, and a second end terminating in second and fourth fiber optic communication ports, respectively;
• and
• at least one magnet disposed near the Faraday fiber links for creating a magnetic field surrounding the Faraday fiber links, such that the Faraday fiber links impart a polarization rotation to light traversing them which is dependent upon the direction of traversal of the light.

A method for providing bidirectional communication to and from a single light-transmissive fiber optic link, which comprises the steps of:

• emitting an outgoing beam of randomly polarized light from a fiber optic communication transmitter;
• dividing the outgoing beam in a first polarization splitter into two outgoing beams, one for each of two orthogonal, linearly polarized states of light;
• passing each divided outgoing beam through one or more axially twisted links of polarization preserving single-mode fiber to rotate the polarization of light in each outgoing beam;
• passing each divided outgoing beam through a Faraday single-mode fiber link in a magnetic field to rotate the polarization of light in each divided outgoing beam, whereby the polarization rotation occurring in the Faraday fiber link cancels the polarization rotation occurring in the polarization preserving fiber links and the polarization states of light in the divided outgoing beams remain unchanged after having passed through the Faraday fiber link and the polarization preserving fiber links;
• recombining the divided outgoing beams in a second polarization splitter into a single outgoing beam of randomly polarized light;
• transmitting the recombined outgoing beam into the fiber optic link;
• emitting an incoming beam of randomly polarized light from the fiber optic link;
• dividing the incoming beam in the second polarization splitter into two incoming beams, one for each of two orthogonal, linearly polarized states of light;
• passing each divided incoming beam through one or more axially twisted links of polarization preserving single-mode fiber to rotate the polarization of light in each incoming beam;
• passing each divided incoming beam through a Faraday single-mode fiber link in a magnetic field in a direction opposite that of the divided outgoing beams, to rotate the polarization of light in each divided incoming beam, whereby the polarization states of light in the divided incoming beams are completely reversed after having passed through the Faraday fiber link and the polarization-preserving fiber links;
• recombining the divided incoming beams in the first polarization splitter into a single incoming beam of randomly polarized light;
• and
• transmitting the recombined incoming beams into a fiber optic communication receiver.

An optical circulator, comprising:

• a pair of Faraday single-mode fiber links, each Faraday fiber link having a first end and a second end;
• a first pair of single-mode fiber links, each having a first end joined to a first end of a different Faraday fiber link;
• a first polarization splitter having a first end joined to a second end of each of the first pair of single-mode fiber links, and a second end terminating in first and third fiber optic communication ports, respectively;
• a pair of polarization controllers, each having a first port connected to a second end of a different Faraday fiber link;
• a second pair of single-mode fiber links, each having a first end joined to a second port of a different polarization controller;
• and
• a second polarization splitter having a first end joined to a second end of each of the second pair of single-mode fiber links and a second end terminating in second and fourth fiber optic communication ports, respectively.

A method for providing bidirectional communication to and from a single light-transmissive fiber optic link, which comprises the steps of:

• emitting an outgoing beam of randomly polarized light from a fiber optic communication transmitter;
• dividing the outgoing beam in a first polarization splitter into two outgoing beams, one for each of two orthogonal, linearly polarized states of light;
• passing each divided outgoing beam through a polarization controller to rotate the polarization of light in each outgoing beam;
• passing each divided outgoing beam through a Faraday single-mode fiber link in a magnetic field to rotate the polarization of light in each divided outgoing beam, whereby the polarization rotation occurring in the Faraday fiber link cancels the polarization rotation occurring in the polarization controller and the polarization states of light in the divided outgoing beams remain unchanged after having passed through the Faraday fiber links and the polarization controllers;
• recombining the divided outgoing beams in a second polarization splitter into a single outgoing beam of randomly polarized light;
• transmitting the recombined outgoing beam into the fiber optic link;
• emitting an incoming beam of randomly polarized light from the fiber optic link;
• dividing the incoming beam in the second polarization splitter into two incoming beams, one for each of two orthogonal, linearly polarized states of light;
• passing each divided incoming beam through a polarization controller to rotate the polarization of light in each incoming beam;
• passing each divided incoming beam through a Faraday single-mode fiber link in a magnetic field in a direction opposite that of the divided outgoing beams, to rotate the polarization of light in each divided incoming beam, whereby the polarization states of light in the divided incoming beams are completely reversed after having passed through the Faraday fiber links and the polarization controllers;
• recombining the divided incoming beams in the first polarization splitter into a single incoming beam of randomly polarized light;
• and
• transmitting the recombined incoming beams into a fiber optic communication receiver.

An optical circulator, comprising;

• a first pair of single-mode fiber links, each having a first end and a second end, wherein at least a portion of each of the first pair of single-mode fiber links is exposed to a magnetic field such that the first pair of single-mode fiber links impart a polarization rotation to light traversing the first pair of single-mode fiber links in a first direction, and a different rotation to light traversing the first pair of single-mode fiber links in a second, opposite direction;
• a first polarization splitter having a first end joined to the first end of each of the first pair of single-mode fiber links, and a second end terminating in first and third fiber optic communication ports, respectively;
• a pair of polarization controllers, each having a first port connected to the second end of each of the first pair of single-mode fiber links;
• a second pair of single-mode fiber links, each having a first end joined to a second port of a different polarization controller;
• and
• a second polarization splitter having a first end joined to a second end of each of the second pair of single-mode fiber links;
• and a second end terminating in second and fourth fiber optic communication ports, respectively.

A method for providing bidirectional communication to and from a single light-transmissive fiber optic link, which comprises the steps of:

• emitting an outgoing beam of randomly polarized light from a fiber optic communication transmitter;
• dividing the outgoing beam in a first polarization splitter into two outgoing beams, one for each of two orthogonal, linearly polarized states of light;
• passing each divided outgoing beam through a polarization controller to rotate the polarization of light in each outgoing beam;
• passing each divided outgoing beam through a single-mode fiber link outside of a magnetic field;
• passing each divided outgoing beam through a single-mode fiber link in the magnetic field to rotate the polarization of light in each divided outgoing beam, whereby the polarization rotation occurring in the single-mode fiber link in the magnetic field cancels the polarization rotation occurring in the polarization controller and in the single-mode fiber link outside the magnetic field and the polarization states of light in the divided outgoing beams remain unchanged after having passed through the fiber links in and outside of the magnetic field and the polarization controllers;
• recombining the divided outgoing beams in a second polarization splitter into a single outgoing beam of randomly polarized light;
• transmitting the recombined outgoing beam into the fiber optic link;
• emitting an incoming beam of randomly polarized light from the fiber optic link;
• dividing the incoming beam in the second polarization splitter into two incoming beams, one for each of two orthogonal, linearly polarized states of light;
• passing each divided incoming beam through a polarization controller to rotate the polarization of light in each incoming beam;
• passing each divided incoming beam through a single-mode fiber link outside of the magnetic field;
• passing each divided incoming beam through a single-mode fiber link in the magnetic field in a direction opposite that of the divided outgoing beams, to rotate the polarization of light in each divided incoming beam, whereby the polarization states of light in the divided incoming beams are completely reversed after having passed through the fiber links in and outside of the magnetic field and the polarization controllers;
• recombining the divided incoming beams in the first polarization splitter into a single incoming beam of randomly polarized light;
• and
• transmitting the recombined incoming beams into a fiber optic communication receiver.