In-line all-fiber polarimeter

An in-line optical fiber polarimeter comprising a set of at least four gratings, disposed in any order, along the optical fiber, each fiber grating for out-coupling a separate one of a set of four polarization states from an incoming optical signal into an associated set of at least four detectors oriented at azimuthal angles θ1, θ2, θ3 and θ4 with respect to the propagation direction;

• and
• at least one elliptical phase retarder element disposed at a predetermined location along the optical fiber with respect to the set of gratings, said phase retarder defined by two principle polarization states S1 and S2, and a retardation angle Γ, said elliptical phase retarder disposed between any two of the gratings such that S1 and S2 are different from the polarizations out-coupled by at least one adjacent grating on each side, wherein the combination of the at least one elliptical phase retarder element with the set of at least four gratings provides an arrangement such that the linear polarization state out-coupled by each grating represents a unique state of polarization at the input of the polarimeter and the detector values allow for determination of the state of polarization.