Patent ID: 8345238

Claim:
A method for measuring spectrum of light, comprising: directing light under measurement through a differential group delay (DGD) device to produce output light with a DGD value representing a difference in the group delay between two orthogonal optical polarizations of the light under measurement; measuring optical polarization and a degree of polarization of the output light corresponding to the DGD value; and processing the measured optical polarization and degree of polarization for the output light to produce an optical spectrum of the light under measurement; wherein the DGD device comprises: a polarization beam splitter to split the light under measurement into a first optical beam in a first optical polarization along a first optical path and a second optical beam along a second, different optical path in a second optical polarization that is orthogonal to the first optical polarization; a first Faraday reflector in the first optical path to reflect light in the first optical path back towards the polarization beam splitter; a second Faraday reflector in the second optical path to reflect light in the second optical path back towards the polarization beam splitter; and a delay mechanism that changes a relative optical path difference between the first and second optical paths to produce the DGD values; wherein the polarization beam splitter combines reflected light in the first optical path in the second optical polarization and reflected light in the second optical path in the first optical polarization to produce a combined output beam as the output light.