Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1992-03-23
1995-04-04
Turner, Samuel A.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
G01C 1966
Patent
active
054042232
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a readout apparatus for a ring laser gyro according to the preamble of one of the independent claims.
In contrast to a passive Sagnac interferometer at which a light source is arranged outside of a ring resonator and at which the phase difference at a rotation of the ring resonator is evaluated a ring laser gyro is an active interferometer, at which the frequency of two counter-propagating waves is shifted in the event where the resonating cavity is rotated and where said frequency shift may be evaluated by means of a readout apparatus.
Hitherto known readout devices (see e.g. F. Aronowitz "The Laser Gyro" published in Laser Applications, Vol. 1, 1971, pages 137 to 140, Academic Press. Inc., New York and London) use a triple prism behind of a partially transmissive readout mirror whereat one beam directly propagates with an according refraction through said mirror and the opposite laser beam is superimposed to the laser beam by means of a triple total reflection and the provision of a small opening angle within said triple prism. For readout purposes the interference modulation of both superimposed counterpropagating laser beams is converted into electrical signals by means of the receiving surfaces of a double diode. The interference fringe width is given by the opening angle between both superimposed laser beams. The optical components effective in the beam path have an influence on the interference fringe distance due to the angle distortions to be tolerated. Furtheron the depth of modulation of the interference fringe pattern is influenced by the choice of the reflective factor of the backside reflective coating and the transmission losses of the triple prism.
The evaluation of the intensity modulation by means of said double diode results in quadrature signals necessary for the sign determination. The amplitude of the signal corresponds to the intensity integral of the light on the receiving surface. The phase of the signal is determined by the effective width of the gap between the receiving surfaces. A reduction of the beam intensity of the laser emission results in a reduction of the average constant light value and therefore to a not realizable migration of the reference point for the rotation of the electrical pointer which is defined by the pair of photodiode signals. This results in errors at the electrical evaluation of the interference phase. Therefore the signal characteristic of both signals depends on a plurality of manufacturing tolerances and the readout apparatus used until now rarely effects optimum signal conditions. Furtheron the known readout apparatus due to its non-symmetrical design is prone to vibrations and temperature changes, the modulation depth is small and occurence of error pulses cannot be precluded.
It is therefore the object of the present invention to devise an improved readout apparatus which is insensitive to vibrations and temperature changes which comprises a large modulation depth and which allows to adjust the phase shift between the signals exactly to 90.degree. so that occurence of error pulses is precluded to a large extent.
The solution of this object is achieved according to the characterizing features of the independent claims. Further advantageous embodiments of the inventive reatout apparatus may be taken from the dependent claims.
Herewith the inventive readout apparatus makes use of known polarizing beam splitting and phase shifting means as they are shown and described in the doctor thesis "Photoelektrische Messung der Anderung von Langen oder Winkelpositionen mit Hilfe von Beugungsgittern", Stuttgart 1976, author: Dipl-Phys. Fromund HocK. The present invention is to be seen in the use of such means in a strictly symmetrical design for superimposing both counter-propagating laser beams within an active ring laser gyro.
With respect to the figures of the attached drawings embodiments of the inventive readout apparatus shown there shall be further described in the following. It shows:
FIG. 1 a first embodiment of an inve
REFERENCES:
patent: 4582429 (1986-04-01), Callaghan
patent: 4865452 (1989-09-01), Ljung et al.
Honeywell Inc.
Lervick Craig J.
Turner Samuel A.
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