â€å“laser Ranging a Critical Review of Usual Techniques for Distance Measurement
Increasing the operating distance of a phase-shift laser range-finding system by using an active reflector
Abstract
A new phase-shift light amplification by stimulated emission of radiation ranging method is developed by combining the conventional phase-shift ranging and the concept of transponder, in which the passive mirror in a phase-shift laser range-finding system is replaced with an active reflector whose light source power is the same as that at the measurement final. As a result, the power of the returned light is inversely proportional to the second instead of the 4th power of the distance being measured. Section 3 bespeak that by using the active reflector, the operating distance is dramatically increased without increasing the light amplification by stimulated emission of radiation power or lens aperture. With a transmitted power of 20 mW and an aperture of 100 mm, the operating distance increased from one.five km to nine.iv km, and a 15-fold range gain can be forecasted for a transmitted ability of 1 W. This strongly confirms the suitability of the adult phase-shift method with an active reflector for measuring longer distances.
Introduction
Laser range finding is ane of the fundamental techniques used in cases such every bit assembly of large-scale equipment, formation flight of spacecraft, and space exploration. More often than not, information technology can be further divided into pulse ranging, frequency-modulated-continuous-wave (FMCW) ranging, phase-shift ranging, and interferometry [1], [ii], [three], [4]. Pulse ranging tin can exist applied to mensurate distances of more 100 km, with a resolution of millimeter-level [4], [5], [half-dozen]. By comparing, better resolutions can be accomplished by using the other three methods based on continuous-moving ridge (CW). More precisely, FMCW [4], [vii], [viii], [9] and phase-shift ranging [four], [x], [eleven], [12], [xiii] tin be used to accomplish a resolution of several tens of microns or even several microns, while a nanometer-level resolution can exist achieved by using interferometry [14], [15]. However, long distance (>1 km) measurement is all the same a great challenge to a CW ranging system, because of the very depression returned light power which is inversely proportional to the 4th power of the altitude beingness measured [1], [16].
Therefore, an increase in the transmitted laser power or the optical lens area of the range-finding organization proportional to the 4th power of the operating distance could be a possible way to improve the measurement range of a CW ranging organisation, but it is very expensive in most cases and sometimes even infeasible to practise then. For example, inter-satellite baseline measurements of hereafter synthetic aperture radar (SAR) systems require a measurement range of more 100 km and a resolution of millimeter-level or higher [17], [18], [19], [xx]; still, the transmitted laser power and the lens discontinuity of the range-finding system are greatly express past the volume and the load of the small satellite. Therefore, conventional CW methods will not be effective in such cases.
In addition, in order to ameliorate the measurement range, a transponder had been introduced into an interferometer to realize the "active metrology" [21], in which the target detects the phase of an incoming measuring beam and sends back a locally generated light amplification by stimulated emission of radiation axle whose stage is referenced to the phase of the incoming beam. This makes the returned calorie-free power inversely proportional to the 2d instead of the quaternary ability of the distance being measured [xvi], [21], [22]. Similar bidirectional interferometers have been used in GRACE follow-on missions [23], [24] and LISA [25], [26], [27] to measure distances of more than than 100 km or even 5 million km. Although a resolution of nanometer-level or even picometer-level can be accomplished, such a arrangement is extremely complex and expensive due to the light-wave phase lock between both lasers used.
In this newspaper, a new phase-shift laser ranging method is adult past combining the conventional stage-shift ranging and the concept of transponder. The passive mirror in a phase-shift laser ranging system is replaced with an "active reflector" which measures the modulation betoken and generates new modulated lite whose stage is referenced to the original low-cal. As a result, the ability of the returned calorie-free (the light received at the measurement terminal) is inversely proportional to the 2nd instead of the fourth power of the distance being measured. This results in a substantial increase in the returned light ability and enables measurements of much longer distances without increasing the light ability or lens discontinuity of a phase-shift range-finding system.
Section snippets
Principle
In the phase-shift method adult, the mirror at the target terminal is replaced with an active reflector, every bit shown in Fig. one. Compared to transponder applications, there is no distinction betwixt master and slave lasers considering the structures between the measurement final and the active reflector are the aforementioned, which is more than reasonable for systems similar SAR. The light transmitted by laser 1 is modulated and so divided by beam splitter (BS) 1: part of the light is received by the avalanche
Experimental results
Indoor equivalent comparative experiments were performed to identify the operating altitude and measurement precision of the proposed method past comparing to the conventional method. In the experiments, the operating distances of the phase-shift laser ranging organization with or without the agile reflector were experimentally faux indoor. The agile reflector would certainly innovate noise into the ranging system considering of the actress circuit and light path, which results in distance errors.
Conclusions
The passive mirror in a stage-shift light amplification by stimulated emission of radiation range-finding arrangement is replaced with an active reflector whose light source power is the same as that at the measurement terminal. As a issue, the power of the returned light is inversely proportional to the 2nd instead of the 4th power of the distance being measured. Comparative measurements indicate that the operating distance of a phase-shift ranging organization is dramatically increased by using the active reflector. With a transmitted calorie-free power of 20
Acknowledgments
This research was financially supported by National Natural Science Foundation of Red china (Grant no. 51105114) and Fundamental Enquiry Funds for the Key Universities (Grant no. HIT.NSRIF.20168)
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