Distance measurement by the wavelength shift of laser diode light

Distance Measurement Systems Using Lasers and Their Applications

“…Fig. 10 shows the operation of this interferometer, where the emitting source is a laser diode (Kikuta, Iwata, & Nagata, 1986). …”

“…The corresponding phase difference is calculated by (13.1), where λ is the wavelength of the laser light (Kikuta, Iwata, & Nagata, 1986).…”

Dimensional Metrology and Frequency Sweeping Interferometry

“…In FSI, the generation of the synthetic wavelength is based on frequency sweeping the laser source within a given sweep range. The technique is not new, has strong similarities to radar, dating back to the 80's (Kikuta et al, 1986), but it was not studied extensively until the development of tunable lasers and the emergence of External Cavity Diode Lasers (ECDL) (Hecht, 2001). As frequency sweeps, detection electronics counts synthetic wavelength fringes (temporal "synthetic fringes") without ambiguity, thus making it particularly interesting for large measurement ranges (Thiel et al, 1995;Stone, 1999;Edwards et al, 2000;Coe et al, 2004;Cabral & Rebordão, 2005;Swinkels et al, 2005).…”

The Applications of the Heterodyne Interferoemetry

“…There are many methods can construct the optical frequency shift such as rotation or moving grating method [16,17], accousto-optical modulator (AOM) [18,19], electro-optical modulator (EOM) [20,21], and modulating two slightly different wavelengths of laser diodes [22]. Suzuki and Hioki [16] proposed the idea of moving grating method for constructing the heterodyne light source in 1967.…”

“…The wavelength increased as the injection current increased. In general, the rate of the increase is about 0.005 nm/mA at 800 nm and that will be different for different types of laser diode [22]. As the wavelength of the laser diode is changed from  to + periodically, in which the injection current is periodically changed, the frequency shift of the heterodyne signal can be obtained.…”