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THE PHASE LOCKING SYSTEM FOR THE FREQUENCY LOCKING OF LASERS FOR GEOINFORMATICS

Vadim Zhmud

Abstract

Lasers are the most accurate measure of distance increment. Therefore, they are used to detect ultra-small oscillations of rock under the influence of tidal forces [1?6]. This allows identifying the accumulated tensions in the earth's crust. The change in the type of such fluctuations indicates the possibility of earthquakes in the near future, which allows reducing the damage from such catastrophic events, to save the lives of many people. Currently, such systems use frequency locking of two or more lasers to each others. This locking must be carried out to within phase accuracy [7?9]. It is extremely difficult to ensure a complete coincidence of the frequencies of the two lasers, and this is not required. It is sufficient to ensure that the difference frequency of the radiation of two lasers is equal to the reference frequency to error not more than some restricted phase difference. The creation of such systems is also a rather difficult task. The problem lies in the choice of the type of phase detector. A phase detector based on a signal multiplier does not allow reliable locking due to the small signal existence band at its output. The phase detector of a pulsed type has a large band of signal existence, but it requires a very high signal-to-noise ratio at its input, since it uses the transformation of harmonic signals into pulsed ones. The slightest noise at its input generates its incorrect work. To solve this problem, it is proposed to use a following filter on the basis of a phase detector based on a signal multiplier with the subsequent use of a pulsed phase detector for a phase locked loop.

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DOI resolver: doi.org/10.5593/sgem2018/2.2/s08.062

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