Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1992-11-06
1994-11-29
Turner, Samuel A.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
G01C 1972
Patent
active
053694872
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an arrangement for determining the amplitudes of spectral lines contained in the phase-modulated output signal of an optical ring interferometer which are suited to determine the angular velocity with which the ring interferometer is rotated, for which a digital evaluation circuit is utilized.
Such a method is disclosed in DE 31 40 110 A1. Two light waves moving in opposite directions are propagated in the fiber-optical wave guide, forming a ring-shaped light path, of the ring interferometer and interfere with each other when they exit. The interference is a function of the angular velocity with which the fiber-optical wave guide, which forms at least one coil, is rotated. The phase difference between the two light waves which have travelled through the fiber-optical wave guide in opposite directions is proportional to the angular velocity. As can be gathered from DE 31 40 110 A1, this phase difference, which is called a Sagnac phase, can be determined from the amplitudes of the spectral lines of the interference light exiting the fiber-optical wave guide.
The light waves exiting at one end from the fiber-optical wave guide are phase-modulated in order to obtain an output signal of the fiber ring interferometer suitable for determining the Sagnac phase. Evaluation of the analog output signal is advantageously performed by means of digital signal processing to determine the Sagnac phase. Since the analog output signal has a disadvantageously high frequency level for subsequent digital signal processing because of the required high phase modulation frequency, according to DE 31 40 110 A2 either the output of the light fed into the fiber ring interferometer is pulsed with a suitable frequency or the output signal is reduced by means of a mixer to a lower frequency level. Both solutions involve additional circuit expenditures. A further disadvantage of the mixing process is that undesired mixing products are created which must be suppressed by additional analog filtering so that the scanning theorem is satisfied and therefore no impermissible spectral convolution products are created which would greatly distort the signal to be evaluated.
It is therefore the object of the invention to recite an arrangement of the previously mentioned type which determines, with a small technical expenditure in circuits, as exactly as possible the amplitudes of desired spectral lines from the output signal of a ring interferometer.
The above and other objects are achieved, according to the present invention, in a digital evaluation circuit for determining the amplitudes of spectral lines contained in a digitized phase-modulated output signal of an optical ring interferometer which is being rotated, wherein the spectral lines contain information indicating the angular velocity with which the ring interferometer is being utilized, by the improvement wherein the circuit comprises: a frequency-selective filter connected for splitting the digitized output signal of the ring interferometer into first and second signal portions, the first signal portion containing spectral lines corresponding to odd-numbered multiples of a given frequency which is one of the phase modulation frequency and a frequency derived from the phase modulation frequency and the second signal portion containing spectral lines corresponding to even-numbered multiples of the given frequency, wherein the spectral lines contained in the first and second signal portions are available by selective frequency separation; and two digital filters each connected to receive a respective signal portion and to filter out of the respective signal portion a signal element at the frequency of one selected spectral line in order to allow determination of the amplitude of the filtered spectral line.
Advantageous embodiments and features of the invention will be described below.
Because of the employment of a frequency-selective filter in accordance with the invention, no great demands need to be made on the subsequent digital filters in respect to
REFERENCES:
patent: 4796993 (1989-01-01), Sonobe et al.
patent: 4883358 (1989-11-01), Okada
patent: 5048962 (1991-09-01), Kurokawa et al.
patent: 5127732 (1992-07-01), Gockler
"Fiber Optic Gyro with Digital Data Processing", Bohm et al, Conference Proceedings OFS '84, Sep. 1984, pp. 251-258.
ANT Nachrichtentechnik GmbH
Turner Samuel A.
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