Fiber optic polarizer with error signal feedback
AssigneeLitton Systems, Inc.
InventorGeorge A. Pavlath
Life of this patent
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Abstract
This invention provides apparatus and methods for converting a lightwave of an arbitrary polarization propagating in a single mode optical fiber into a wave having a single linear polarization state. A polarization couples light of an undesired polarization out of the fiber, and a photodetector produces an error signal responsive to light coupled from the fiber. Control circuitry processes the error signal to produce control signals which are input to a polarization of light input to the polarizer to null the error signal. With the error signal maintained at a minimum value the light input to the polarizer and, hence, the light ouput therefrom is a wave having only the desired linear polarization.
Claims21
A system for producing light having a selected polarization state, comprising:
- a fiber optic waveguide having an interaction region;
- a fiber optic polarizer for coupling light of a first polarization out of said fiber optic waveguide at the interaction region while leaving light of a second polarization within said fiber optic waveguide;
- and
- processing means for processing light of the first polarization coupled out of said fiber optic waveguide to control the polarization of light before incidence upon said polarizer.
A system for producing light having a selected polarization state, comprising:
- a fiber optic waveguide having an interaction region formed thereon;
- a fiber optic polarizer including a birefringent crystal having a portion thereof positioned within the evanescent field of light propagating in the fiber optic waveguide at the interaction region, said birefringent crystal having a first index of refraction which couples light of a first selected polarization out of said fiber optic waveguide and a second index of refraction which causes light of a second selected polarization to remain guided by said fiber optic waveguide:
- detector means positioned to receive light coupled out of said fiber optic waveguide for forming an error signal;
- signal processing means for receiving the error signal and producing a control signal in response thereto;
- and
- polarization controller means responsive to the control signal for adjusting the polarization of light incident upon said polarizer to null the error signal and to provide an output signal from said polarizer guided by said fiber optic waveguide and having a selected polarization state.
A method for producing light having a selected polarization state, comprising the steps of:
- supplying a light input to a fiber optic waveguide having an interaction region;
- coupling light of a first polarization out of the fiber optic waveguide with a fiber optic polarizer at the interaction region while retaining light of a second polarization within the fiber optic waveguide;
- detecting light of the first polarization coupled out of the fiber optic waveguide;
- forming an error signal proportional to the detected light;
- and
- adjusting the polarization of light within the fiber optic waveguide to null the error signal.
A method for producing light of a selected polarization, comprising the steps of:
- forming an interaction region in a fiber optic waveguide wherein a light wave propagated by the fiber optic waveguide has an evanescent field extending out of said fiber optic waveguide;
- placing a birefringent material adjacent the interaction region such that a portion of the evanescent field extends into the birefringent material, the birefringent material having a pair of refractive indicies that cooperate at the interaction region, to couple light of a first polarization from the fiber optic waveguide into a bulk wave in the birefringent material while light of a second polarization is guided by the fiber optic waveguide past the interaction region;
- and
- processing light of the first polarization coupled from the fiber optic waveguide at the interaction region to maximize the intensity of the second polarization before incidence of light of said first polarization upon said interaction region.
A system for producing light having a selected polarization in an optical fiber without removing light of the selected polarization from the fiber, comprising:
- a fiber optic waveguide;
- a fiber optic polarizer for removing light of an undesired polarization from the fiber optic waveguide while permitting light of the selected polarization to be guided by the fiber optic waveguide;
- means responsive to the intensity of the undesired polarization coupled from the fiber optic waveguide for controlling the polarization of light before input to said polarizer to produce a signal of constant intensity and the selected polarization output from said polarizer.
A system for producing light having a selected polarization state in a pair of light waves that propagate in opposite directions in an optical fiber, comprising:
- an interaction region formed on the optical fiber;
- a fiber optic polarizer for coupling light of a first polarization in both light waves out of the optical fiber at the interaction region while leaving light of a second polarization in both light waves within the optical fiber;
- means for detecting light from a first one of the light waves that has been coupled out of the fiber;
- first processing means for processing light from the first wave coupled out of said fiber optic waveguide to control the polarization of light incident upon said polarizer;
- means for detecting light from a second one of the light waves that has been coupled out out of the fiber;
- and
- second processing means for processing light from the second wave coupled out of said fiber optic waveguide to control the polarization of light before incidence upon said polarizer.
A method for producing light having a selected polarization state in a pair of light waves that propagate in opposite directions in an optical fiber, comprising:
- forming an interaction region on the optical fiber;
- coupling light of a first polarization in both light waves out of the optical fiber with a fiber optic polarizer at the interaction region while leaving light of a second polarization in both light waves within the optical fiber;
- detecting light from a first one of the light waves that has been coupled out out of the fiber;
- processing light from the first wave coupled out of said fiber optic waveguide to control the polarization of light incident upon said polarizer;
- detecting light from a second one of the light waves that has been coupled out out of the fiber;
- and
- processing means for processing light from the second wave coupled out of said fiber optic waveguide to control the polarization of light before incidence upon said polarizer.
Dependencies are inferred from the claim text.