Distance meter utilizing the intermode beat of a He–Ne laser

Abstract

A distance meter was built utilizing the intermode beat of a He-Ne laser instead of an optical modulater. Its performance was tested at distances between 10 and 1300 m on a 300-m baseline in a tunnel. The resolution was about 20 microm and the total uncertainty was within 0.1 mm, if the air was stable. The length of the tunnel was measured by a distance meter, and the annual periodic strain of the tunnel was observed with submillimeter precision.

Blade tip clearance measurement of the turbine engines based on a multi-mode fiber coupled laser ranging system

“…18,19 The wavelength of the laser is 632 nm and the optical power is 1 mW. The split ratio of the fiber splitter is 80:20.…”

Intermodal beat frequency stability in a polarization stabilized HeNe laser with an optical switch

“…The measured changes of the beat frequency versus time were reported in some sources [1,4,8]. The variation of the beat frequency with a change in the cavity length has to be noticed.…”

“…Optical distance measurement methods can be, in general, divided into two categories: interferometric [1][2] and time of flight TOF. The methods from the first category are very accurate but difficult in use.…”

“…The former method is superior for measurement of longer distances. The latter seems more suitable in short to medium distance ranges [1]. The phase and frequency stability of the modulation signal is of indisputable importance in both methods [2].…”

Development of a calibration system for electronic distance measuring instruments

“…In these ways the aforementioned problems were minimised and the standard deviations achieved over 80 m were ± 18 µm. Some other methods for the construction and calibration of base-lines using interferometric techniques are found in the literature [2][3][4][5][6][7] .…”