Three-port circulator

#Optical circulators are commonly used in optical communication systems and optical measurement systems. FIG. 1 shows a three-port circulator 10 that has ports 1, 2, and 3. Each of ports 1, 2, and 3 can be coupled to a Polarization Maintenance (“PM”) fiber. As shown in FIG. 1, a polarized optical signal SI entering port 1 exits from port 2 as a polarized optical signal S2. A polarized optical signal S2′ entering port 2 exits from port 3 as a polarized optical signal S3.

#In one aspect, the invention provides a three-port circulator. The three-port circulator includes a non-reciprocal rotating element, a first birefringent wedge, and a second birefringent wedge. The non-reciprocal rotating element has a rotation axis and is adapted to rotate a polarization of light passing therethrough by a predetermined angle. The first birefringent wedge has a first optical axis substantially perpendicular to the rotation axis. The second birefringent wedge has a second optical axis substantially perpendicular to both the rotation axis and the first optical axis. The second birefringent wedge is optically coupled between the non-reciprocal rotating element and the first birefringent wedge. The three-port circulator can also include a first lens optically coupled to the first wedge. The three-port circulator can also include a second lens optically coupled to the second wedge. The non-reciprocal rotating element in the three-port circulator can be a Faraday rotator.

#In another aspect, the invention provides a method for constructing a three-port circulator having a first port, a second port and a third port. The method includes the step of providing a non-reciprocal rotating element for rotating a polarization of light passing therethrough by a first angle with respect to a rotation axis. The method includes the step of providing a first birefringent wedge having a first optical axis. The method includes the step of providing a second birefringent wedge having a second optical axis forming a second angle with the first optical axis. The method includes the step of directing an input polarized optical signal received from the first port to pass sequentially through the first birefringent wedge, the second birefringent wedge, and the non-reciprocal rotating element, to provide an output polarized optical signal directed to the second port. The method includes the step of directing an input polarized optical signal received from the second port to pass sequentially through the non-reciprocal rotating element, the second birefringent wedge and the first birefringent wedge, to provide an output polarized optical signal directed to the third port.

#FIG. 1 illustrates a three-port circulator 10 including ports 1, 2, and 3.

#FIG. 2a illustrates an implementation of a three-port circulator.

#FIG. 2b illustrates a specific configuration of the birefringent wedges and the Faraday rotator shown in FIG. 2a.

#The present invention relates to an improvement in optical technology. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the invention will be readily apparent to those skilled in the art and the generic principals herein may be applied to other implementations. Thus, the present invention is not intended to be limited to the implementations shown, but is to be accorded the widest scope consistent with the principals and features described herein.

#The present invention will be described in terms of a three-port circulator having specific components having specific configurations. Similarly, the present invention will be described in terms of components having specific relationships, such as distances or angles between components. However, one of ordinary skill in the art will readily recognize that the devices and systems described can include other components having similar properties, other configurations, and other relationships between components.

#FIG. 2a illustrates an implementation of a three-port circulator 200. Three-port circulator 200 includes a birefringent wedge 230, a birefringent wedge 240, and a non-reciprocal rotating element such as Faraday rotator 250. Three-port circulator 200 can includes lens 220 for optically coupling PM fibers 201 and 203 to birefringent wedge 230, and lens 260 for optically coupling a PM fiber 202 to Faraday rotator 250. The positions of PM fibers 201 and 203 can be fixed with a capillary 220. The position of PM fiber 202 can be fixed with a capillary 270.