Abstract

We present a new superheterodyne technique for long-distance measurements by two-wavelength interferometry (TWI). While conventional systems use two acousto-optic modulators to generate two different heterodyne frequencies, here the two frequencies result from synchronized sweeps of optical and radio frequencies. A distributed feedback laser source is injected in an intensity modulator that is driven at the half-wave voltage mode. A radio-frequency signal is applied to this intensity modulator to generate two optical sidebands around the optical carrier. This applied radio frequency consists of a digital ramp between 13 and $15\mathrm{GHz}$, with $1\mathrm{ms}$ duration and with an accuracy of better than $1\mathrm{ppm}$. Simultaneously, the laser source is frequency modulated by a current modulation that is synchronized on the radio- frequency ramp as well as on a triangle waveform. These two frequency-swept optical signals at the output of the modulator illuminate a Michelson interferometer and create two distinct distance-dependent heterodyne frequencies on the photodetector. The superheterodyne signal is then detected and bandpass filtered to retrieve the absolute distance measurement. Experiments between 1 and $15\mathrm{m}$ confirm the validity of this new concept, leading to a distance accuracy of $\pm 50\mathrm{\mu m}$ for a $1\mathrm{ms}$ acquisition time.

© 2010 Optical Society of America

Radio frequency controlled synthetic wavelength sweep for absolute distance measurement by optical interferometry

Sébastien Le Floch, Yves Salvadé, Rostand Mitouassiwou, and Patrick Favre
Appl. Opt. 47(16) 3027-3031 (2008)

Absolute distance measurement by two-point-diffraction interferometry

Hyug-Gyo Rhee and Seung-Woo Kim
Appl. Opt. 41(28) 5921-5928 (2002)

High-accuracy absolute distance measurement using frequency comb referenced multiwavelength source

Yves Salvadé, Nicolas Schuhler, Samuel Lévêque, and Sébastien Le Floch
Appl. Opt. 47(14) 2715-2720 (2008)

Improvement of speckle statistics in double-wavelength superheterodyne interferometry

R. Dändliker, M. Geiser, C. Giunti, S. Zatti, and G. Margheri
Appl. Opt. 34(31) 7197-7201 (1995)

Absolute distance measurements by variable wavelength interferometry

F. Bien, M. Camac, H. J. Caulfield, and S. Ezekiel
Appl. Opt. 20(3) 400-403 (1981)