US 5,296,913 AGranted

Polarimeter re-calibration method and apparatus

AssigneeHewlett-Packard Company

InventorBrian L. Heffner

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Abstract

A method and an apparatus to re-calibrate a polarimeter without a standard source with known polarization. An input electromagnetic wave is sequentially transformed into many electromagnetic waves, all having substantially the same degree of polarization and at least three of the electromagnetic waves having different states of polarization. All the electromagnetic waves are measured by the polarimeter. The method then calculates a calibration factor which, when applied to the measured signals, generates substantially the same calculated degree of polarization for all the electromagnetic waves. A birefringent material, such as a wave-plate, can be used to generate the electromagnetic waves from the input electromagnetic wave. If the input electromagnetic wave is an optical wave, then loops of optical fibers or an electro-optic material, such as a LiNbO.sub.3 crystal, is used as the birefringent material.

Claims20

Dependent claims

A method of re-calibrating a polarimeter, the method comprising:

measuring an input electromagnetic wave with the polarimeter to obtain raw values indicative of the state and degree of polarization of the wave;
transforming the electromagnetic wave into another electromagnetic wave having a different state of polarization but substantially the same degree of polarization after the transformation as before;
measuring the transformed electromagnetic wave with the polarimeter to obtain raw values indicative of the state and degree of polarization of the wave;
repeating the preceding two steps until at least three electromagnetic waves, each having a state of polarization differing from that of the other two, have been measured;
calculating a calibration factor by the steps of:
a. initializing the calibration factor;
b. calculating the degree of polarization of each measured electromagnetic wave by means of the initialized calibration factor, the measured raw values of the wave, and a predetermined instrument matrix;
and
c. correcting the calibration factor according to the calculated degrees of polarization of the waves;
so that the calibration factor is effective to alter the raw values such that the raw values, after alteration, indicate substantially the same degree of polarization for each of the electromagnetic waves;
and
re-calibrating the polarimeter by means of the calibration factor.

9 more elements

An apparatus for re-calibrating a polarimeter, the apparatus comprising:

means coupled to the polarimeter for receiving and transforming an input electromagnetic wave into a plurality of electromagnetic waves, all having substantially the same degree of polarization but at least three of the electromagnetic waves having different states of polarization such that the polarimeter receives the plurality of electromagnetic waves and generates a plurality of measured signals, one measured signal corresponding to the state of polarization of each electromagnetic wave;
and
means coupled to the polarimeter for calculating a calibration factor using the measured signals by the steps of:
a. initializing the calibration factor;
b. calculating the degree of polarization of each measured electromagnetic wave by means of the initialized calibration factor, the measured raw values of the wave, and a predetermined instrument matrix;
and
c. correcting the calibration factor according to the calculated degrees of polarization of the waves;
and for adjusting the polarimeter according to the calibration factor to re-calibrate the polarimeter such that when the polarimeter is re-calibrated, it indicates substantially the same degree of polarization for the plurality of electromagnetic waves.

5 more elements

Dependencies are inferred from the claim text.