26 June 2017 A high-resolution optical rangefinder using tunable focus optics and spatial photonic signal processing
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Proceedings Volume 10335, Digital Optical Technologies 2017; 103350S (2017) https://doi.org/10.1117/12.2270121
Event: SPIE Digital Optical Technologies, 2017, Munich, Germany
In this paper, we present the design of a proposed optical rangefinder to determine the distance of a semi-reflective target from the sensor module. The sensor module deploys a simple Tunable Focus Lens (TFL), a Laser Source (LS) with a Gaussian Beam profile and a digital beam profiler/imager to achieve its desired operation. We show that, owing to the nature of existing measurement methodologies, previous attempts to use a simple TFL in prior art to estimate target distance mostly deliver “one-shot” distance measurement estimates instead of obtaining and using a larger dataset which can significantly reduce the effect of some largely incorrect individual data points on the final distance estimate. Using a measurement dataset and calculating averages also helps smooth out measurement errors in individual data points through effectively low-pass filtering unexpectedly odd measurement offsets in individual data points. In this paper, we show that a simple setup deploying an LS, a TFL and a beam profiler or imager is capable of delivering an entire measurement dataset thus effectively mitigating the effects on measurement accuracy which are associated with “one-shot” measurement techniques. The technique we propose allows a Gaussian Beam from an LS to pass through the TFL. Tuning the focal length of the TFL results in altering the spot size of the beam at the beam imager plane. Recording these different spot radii at the plane of the beam profiler for each unique setting of the TFL provides us with a means to use this measurement dataset to obtain a significantly improved estimate of the target distance as opposed to relying on a single measurement. We show that an iterative least-squares curve-fit on the recorded data allows us to estimate distances of remote objects very precisely. We also show that using some basic ray-optics-based approximations, we also obtain an initial seed value for distance estimate and subsequently use this value to obtain a more precise estimate through an iterative residual reduction in the least-squares sense. In our experiments, we use a MEMS-based Digital Micro-mirror Device (DMD) as a beam imager/profiler as it delivers an accurate estimate of a Gaussian Beam profile. The proposed method, its working and the distance estimation methodology are discussed in detail. For a proof-of-concept, we back our claims with initial experimental results.
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Tariq S. Khwaja, Tariq S. Khwaja, Mohsin Ali Mazhar, Mohsin Ali Mazhar, Haris Khan Niazi, Haris Khan Niazi, Syed Azer Reza, Syed Azer Reza, } "A high-resolution optical rangefinder using tunable focus optics and spatial photonic signal processing", Proc. SPIE 10335, Digital Optical Technologies 2017, 103350S (26 June 2017); doi: 10.1117/12.2270121; https://doi.org/10.1117/12.2270121

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