Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1992-09-01
1994-10-25
Turner, Samuel A.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
356359, 356356, 356352, G01B 1102
Patent
active
053594150
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an interferometer for determining the position or displacement travel of a movable measuring mirror or the like comprising an interferometer head, to the housing or carrier of which are rigidly connected a beam divider for dividing the laser light into a measuring beam and a reference beam, and a recombination device, wherein the measuring beam which is passed by way of the movable measuring mirror or the like and the reference beam which is passed by way of a fixed reference section interfere in the recombination device forming at least one optical interference signal, a laser light source arranged outside the interferometer head, wherein at least one flexible optical fiber for the laser light feed is arranged between the laser light source and the beam divider of the interferometer head, and a photoelectric detector device for evaluation of the interference signal or signals coming from the recombination device.
Interferometers for length measurement purposes are already known. Typically, in such interferometers, a measuring beam is passed by way of a movable measuring mirror whose displacement travel or position is to be detected. The reference beam passes through a fixed reference section. The measuring beam returning from the measuring mirror and the reference beam coming from the reference section interfere in a recombination device which can be formed for example by a beam divider. With a known laser light wavelength, the displacement travel or measuring mirror data which is correlated therewith can be ascertained from the interference signal.
In order to achieve thermal decoupling between the laser light source and the central optical components of the interferometer (in particular the beam divider, the reference section and the recombination device), it has already been suggested that those central interferometer components should be combined together in an interferometer head and the laser light source should be arranged outside the interferometer head, wherein one or more successively connected optical fibers feed laser light from the laser light source to the interferometer head. However the use of flexible optical fibres for the laser light feed is not without its difficulties. On the contrary, it has been found that the interference signal or signals depends or depend not only on the position of the measuring mirror or the like but also, and this is undesirable, on the position and the loadings of the laser light-feeding optical fiber or fibers.
Therefore the object of the present invention is to provide an interferometer of the kind set forth in the opening part of this specification, in which at least one flexible optical fiber is used for the laser light feed and wherein the position or loadings of the optical fibers do not interfere with the measurement result, thus permitting reliable and interference-free operation.
In accordance with a first variant of the invention, that is achieved in that arranged downstream of the flexible optical fiber or fibers for the laser light feed and upstream of the beam divider is a polarisation means which is connected to the interferometer housing or carrier for establishing a defined, preferably linear polarisation of the laser light at the entrance of the beam divider.
The reference to "defined" polarisation in accordance with the invention means a given polarisation condition (linear, elliptical or left-hand or right-hand circular) of the laser light and, in respect of the linear and elliptical cases, a given spatial orientation of the polarised laser light with respect to the beam divider of the actual interferometer. In the case of linear polarisation, the spatial orientation is determined by the spatial position of the direction of oscillation of the light vector, while in the case of elliptical polarisation it is given by the spatial position of the long and short semiaxes of the ellipse. For reliable and interference-free operation of an interferometer, maintenance of a defined condition of polarisation of the laser light
REFERENCES:
patent: 4420260 (1983-12-01), Martinelli
patent: 4909629 (1990-04-01), Yokokura et al.
Keesee LaCharles
Turner Samuel A.
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