Patent ID: 7265836

Claim:
A device, comprising: a base comprising a groove and four through holes located at four different sampling positions along the groove; three optical linear polarization analyzers mounted in three of the four different sampling positions in the groove to define an optical path in free space to split three sample beams with three different states of linear polarization from an input optical beam propagating along the optical path, each optical linear polarization analyzer transmitting a majority of the input optical beam along the optical path and splitting a fraction of the input beam in a predetermined linear polarization as a respective sample beam into a respective through hole in the base; a quarter-wave plate mounted in the groove before a fourth sampling position along the groove that is not occupied by any of the three optical linear polarization analyzers; a fourth optical linear polarization analyzer mounted in the groove at the fourth sampling position to receive light transmitted through the quarter-wave plate along the optical path and to split a fraction of the received light in a fourth linear polarization to produce a fourth sample beam into a fourth through hole in the base, wherein the fourth optical linear polarization analyzer and the quarter-wave plate form a circular polarization analyzer; and four optical detectors respectively positioned in the four through holes in the base to receive the four sample beams, respectively, and to convert the four sample beams into four detector signals indicative of optical power levels of the four sample beams, respectively.