Optics: measuring and testing – By polarized light examination – With birefringent element
Patent
1999-01-14
2000-02-08
Font, Frank G.
Optics: measuring and testing
By polarized light examination
With birefringent element
356364, 356367, 356368, 356369, G01J 400
Patent
active
06023332&
ABSTRACT:
A device for measuring birefringence in an optical data carrier has a laser light source with a polarization modifier, a beamsplitter, a polarizer, a photodetector, and a controller operatively connected to the photodetector. The laser light source illuminates various spots on the optical data carrier by means of a laser beam. The photodetector receives a reflected laser beam, converts it into an electric signal and supplies this signal to the controller, which determines a value for the birefringence in the illuminated spot on the optical data carrier. Furthermore, the device is provided with a transparent reference element with known birefringence properties, a mirror, and for directing the laser beam towards the reference element in a first calibration position; directly towards the mirror in a second calibration position; and towards the optical data carrier during non-calibration time. In the first calibration position the controller calculates a first calibration value from the signal received from the photodetector, said first calibration value corresponding to a given birefringence in the optical data carrier, and in the second calibration position the controller calculates a second calibration value, corresponding to a situation essentially without any birefringence at all in the optical data carrier. These calibration values are used for determining the birefringence in a given spot on the optical data carrier.
REFERENCES:
patent: 5227623 (1993-07-01), Heffner
patent: 5257092 (1993-10-01), Noguchi et al.
patent: 5450200 (1995-09-01), Imagawa et al.
patent: 5864403 (1999-01-01), Ajji et al.
Bergstrom Hakan
Jonsson Lars
Wilhelmson Ulf
Font Frank G.
Ifunga Test Equipment B.V.
Punnoose Roy M.
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