A method for fast laser beam spot focus using electrically tunable lenses

Abstract

Various applications in optics and photonics employ a Tunable Focus Lens (TFL) to obtain a minimum beam spot of a laser beam at different locations along the direction of beam propagation. Using a TFL to achieve a minimum beam spot size at different planes is critical for several optical imaging and sensing applications. As focal length of TFLs is generally controlled through the amplitude of an input voltage or the current signal, the response time of a TFL-based sensor or imaging system depends on the time required produces a minimum beam spot in the observation plane. Therefore, the system response time or sampling rate depends on the number of voltage/current samples to ascertain a correct focal length value which yields a minimum beam spot. Due to a partial or a total lack of knowledge of the ideal voltage/current value that would produce a minimum beam spot, starting at a corner or a random voltage/current value and incrementally increasing or reducing it would be highly inefficient as converging to a minimum spot might require several steps. We propose an efficient method which results in a significant reduction in the number of voltage/current steps and experimentally validate our claims.