Le Floch Sébastien, Salvadé Yves, Droz Nathalie, Mitouassiwou Rostand, Favre Patrick
Metrology and Quality Engineering Laboratory, Haute Ecole ARC Engineering, Baptiste Savoye 26, 2610 Saint-Imier, Switzerland.
Appl Opt. 2010 Feb 1;49(4):714-7. doi: 10.1364/AO.49.000714.
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 GHz, with 1 ms duration and with an accuracy of better than 1 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 m confirm the validity of this new concept, leading to a distance accuracy of +/- 50 microm for a 1 ms acquisition time.
我们提出了一种用于双波长干涉测量（TWI）的长距离测量的新型超外差技术。传统系统使用两个声光调制器来产生两个不同的外差频率，而在此处，这两个频率来自光频和射频的同步扫描。一个分布反馈激光源注入到一个以半波电压模式驱动的强度调制器中。一个射频信号施加到这个强度调制器上，以在光载波周围产生两个光边带。这个施加的射频由一个13至15 GHz之间的数字斜坡信号组成，持续时间为1 ms，精度优于1 ppm。同时，激光源通过一个与射频斜坡以及三角波形同步的电流调制进行频率调制。调制器输出处的这两个扫频光信号照射到一个迈克尔逊干涉仪上，并在光电探测器上产生两个不同的与距离相关的外差频率。然后检测超外差信号并进行带通滤波以获取绝对距离测量值。1至15米之间的实验证实了这一新概念的有效性，对于1 ms的采集时间，距离精度可达±50微米。
