Optical polarimeter having four channels

Claim 3

A method according to claim 1, in which all four said beam portions are equally attenuated prior to the determination of the intensities thereof.

Claim 4

Apparatus for determining the state of polarization of an incoming collimated beam of electromagnetic radiation, which apparatus comprises: a beam expander to increase the effective diameter of said incoming collimated beam of electromagnetic radiation; means dividing the expanded beam into four channels and for mounting a set of filters in the optical paths of the channels, which said set of filters comprises first and second filters being linear polarizers with their respective planes of polarization lying at an angle to one another, a third filter being a combination of a linear polarizer and a phase retardation plate, and a fourth channel being insensitive to polarization whereby four portions of said expanded beam are directed along the four channels respectively and filtered accordingly; four intensity detectors one associated with each of said channels respectively, and disposed to detect the intensity of the respective beam portion and to produce an output dependent therefrom and means for analyzing the determined intensity to yield an indication of the polarization state of said incoming beam.

Claim 5

Apparatus for determining the state of polarization of an incoming collimated beam of electromagnetic radiation, which apparatus comprises: a beam expander to increase the effective diameter of said incoming collimated beam of electromagnetic radiation; means dividing the expanded beam into four channels and for mounting a set of filters in the optical paths of the channels, which said set of filters comprises first and second filters being linear polarizers with their respective planes of polarization lying at an angle to one another, a third filter being a combination of a linear polarizer and a phase retardation plate, and a fourth channel being insensitive to polarization whereby four portions of said expanded beam are directed along the four channels respectively and filtered accordingly; four intensity detectors one associated with each of said channels respectively, and disposed to detect the intensity of the respective beam portion and to produce an output dependent therefrom and means for analyzing the determined intensity to yield an indication of the polarization state of said incoming beam.

Claim 6

Apparatus according to claim 3, in which said set of filters are grouped together and lie substantially in the same plane.

Claim 7

Apparatus according to claim 4, in which each said filter is circular and is assembled within an aperture in a carrier such that all four said filters are symmetrically disposed with respect to the apparatus optical axis.

Claim 8

Apparatus according to claim 3, in which each said intensity detector comprises a lens mounted on the optical path of the respective beam portion, together with a photosensitive element on to which said lens focuses the beam portion passing therethrough, the photosensitive element producing an electrical signal corresponding to the intensity of said beam portion.

Claim 9

Apparatus according to claim 6, in which an amplifier is associated with each said photosensitive element respectively, each said amplifier producing an electrical signal which is fed to an analogue-to-digital converter, thereby to yield four digital signals corresponding to the four outputs of the intensity detectors.

Claim 10

Apparatus according to claim 3, in which there is provided a fibre optic coupler having associated therewith a lens to produce from light emerging from a connected fibre optic a collimated beam projected to the beam expanded on the optical axis thereof.

Claim 11

Apparatus according to claim 3, in which attenuation means is provided uniformly to attenuate all four said beam portions following the passage thereof through the respective filter of the set thereof.

Claim 12

Apparatus according to claim 9, in which said attenuation means comprises an adjustable iris diaphragm.

Claim 13

A method according to claim 1, in which the fourth beam portion passes freely along the fourth channel without attenuation or polarizing filtration.