Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1989-07-24
1991-08-20
Turner, Samuel
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
356345, 372 32, G01B 902
Patent
active
050408968
ABSTRACT:
A method and apparatus for wavelength stabilization of an optical source uses three birefrigent crystals that are temperature-compensated as a whole to function as the two arms of a reference interferometer. Only phase differences resulting from shifts in the wavelength of the optical source are measured. Synchronous detection of a light intensity signal representative of the phase difference between light waves of orthogonal polarization is made possible by making one of the three crystals an electro-optic material and applying a modulating voltage to it. The remaining two crystals are a pair of different passive birefringent crystals. The three interferometer crystals are cut and polished to prescribed lengths and orientations; optical path length changes with temperature in one crystal are compensated for by opposite and equal optical path length changes in the other two. To maximize the sensitivity of the interferometer to variations in the source wavelength the three-crystal system is designed to function as a quarter-wave plate at the effective source emission wavelength. For a linearly polarized input lightwave at this wavelength with its polarization axis aligned at 45 degrees with respect to the crystal axes, the two component lightwaves having orthogonal polarizations suffer a phase difference of .pi./2 radians and the output light is circularly polarized. An analyzer with its axis aligned at 45 degrees with respect to the axis of the three-crystal quarter-wave plate passes a fraction of the light intensity incident on it which varies with deviations from the nominal source emissions wavelength. Changes in the light intensity passed by the analyzer are used to generate an error signal which is then converted to a control signal and fed back to the source to stabilize the emission wavelength.
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patent: 4842358 (1989-06-01), Hall
patent: 4887900 (1989-12-01), Hall
patent: 4890922 (1990-01-01), Wilson
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