Time-of-flight telemeter based on a ring-laser
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Time‑of‑flight telemeter based on a ring‑laser G. Aromataris1 · L. Lombardi1 · A. Scirè1 · V. Annovazzi‑Lodi1 Received: 25 February 2020 / Accepted: 11 August 2020 © The Author(s) 2020
Abstract We propose a new telemeter scheme for absolute distance measurements, based on a semiconductor ring laser, working in the bistability regime. The optical feedback provided by two external reflectors (a fixed one at short distance, and a moveable one defining the measuring arm) generates commutations of the propagation direction (clockwise, counterclockwise) inside the ring laser, the period of which is linearly related to the distance of the measure arm reflector. A convenient electrical output signal can be easily obtained by a photodiode located behind the (partially reflecting) fixed mirror. This telemeter, which combines time-of-flight and optical injection, is very simple to implement, since, in addition to the laser, it only requires mirrors and collimation or focusing optics. Also electronic driving and processing are straightforward. Differently from most time-of-flight telemeters, this scheme does not require special provisions or processing to tackle the ambiguity problem. Simulations are performed by mathematical models based on rate-equations. This telemeter has been evaluated in the range 10 cm–32 m of round trip distance, with a fixed arm of 10 μm–10 cm, assuming typical literature parameters for a 1 mW ring laser. Keywords Ring laser · Laser diode · Distance measurements · Optical injection
1 Introduction Optical methods for distance measurement include many schemes, most of which are based on lasers (Berkovic and Shafir 2012; Donati 2004). Telemeters are indeed one of the most successful applications of this device, since 1970, just after its invention. Among different options, time-of-flight telemeters (Donati 2004) are based on the measurement of the time required by the laser radiation to cover the round trip distance to a * V. Annovazzi‑Lodi [email protected] G. Aromataris [email protected] L. Lombardi [email protected] A. Scirè [email protected] 1
Department of Electrical, Computer and Biomedical Engineering, University of Pavia, Pavia, Italy
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target. Both pulsed and sine-wave time-of-flight telemeters require proper design and processing to tackle the ambiguity problem in distance measurement. Moreover, pulsed telemeters require fast laser power switching, fast electronic circuits and possibly the implementation of gating and optimum filtering techniques to get high resolution. Even though the basic principles of pulsed telemeters are well-known, recent contributions can be found in the literature, especially on electronic detection and processing (Kurti 2018; Norgia et al. 2016). Telemeters based on optical injection have been also designed: in these schemes, the laser power is modulated by the optical power reflected or diffused back by a target (Donati 1978, 2004; Donati et al.
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