Unusual techniques for absolute distance measurement

Abstract

I describe four unusual laser systems for absolute measures of linear distance. All employ the familiar techniques of multiple wavelengths, chirped wavelength, optical feedback and intensity modulation, but in somewhat unfamiliar architectures. These examples serve to illustrate the breadth of solutions to this important problem.

Laser diode self-mixing technique for sensing applications

“…By using this method, the resolution can be improved up to a factor of 8 and an overall accuracy of ±1.5 mm is achieved on a 1-2 m range using a FP LD [18]. A comparison is worthwhile with other ranging techniques such as time-of-flight [36], triangulation [36,37] and absolute distance interferometry [38]. Commercially available instruments based on time-of-flight methods (telemeters) are best suited for long-range applications: distances from tens of cm to tens of km, with resolutions (measurement error) from a few mm to a few m. The triangulation technique better applies to short-range measurements with limited dynamic: distances from a few cm to a few m, with resolutions in the Figure 14.…”

Study on the self-mixing interference in a composite four-mirror cavity laser

“…Since the self-mixing interference was first reported by King and Steward [1], it has been widely used in imaging [2][3], displacement [4][5][6], velocity measurement [7][8] and ranging [9][10]. Lots of theoretical models and experimental phenomena of self-mixing interference presented before are mainly based on a Fabry-Parot linear resonator with a external cavity [1,11].…”

Absolute positioning by multi-wavelength interferometry referenced to the frequency comb of a femtosecond laser

“…As the counterpart of IDM interferometers, absolute-type distance measurement (ADM) interferometers are intended to measure the total distance directly to the end position without incremental addition of movements of the target mirror all the way from the zero datum. In the past, relying mainly on modulation techniques of the intensity or frequency of continuous wave laser light [6][7][8], ADM interferometers provided relatively less accuracy suitable just for coarse measurements of long distances for geodetic surveying and large-scale engineering. However, during the past decade, a remarkable advance has been made with femtosecond lasers being proved as a high-potential workhorse to advance optical interferometry [9,10].…”