Proof-of-concept demonstration of smart optical imaging systems

Abstract

This thesis focuses on the proof-of concept demonstration of smart optical imaging systems. Two systems have been investigated: first, a three-channel multi-resolution imaging system and in second place, a refocusing imaging system. The three-channel multi-resolution optical imaging system (Static System) has already been investigated by Ir. Gebirie. Y. Belay. The system possesses three optical channels with different resolutions and fields of view. The first channel has the highest resolution and the lowest field of view; the third optical channel has contrary properties, that is, the widest field of view and the lowest resolution. The second optical channel has intermediate properties. The experiments accomplished show that the system performs according to the expectations (simulations) and the quality of the images captured by the system is good. It has been observed two phenomena: distortion in the second optical channel and crosstalk in the third optical channel. The influence of misalignment errors of the components has been analyzed as well. The system is robust to longitudinal movements of the components, especially the first optical channel. Nevertheless, the system is less sensitive to rotational movements, becoming important the achievement of a good angular alignment. The refocusing system is a voltage-tunable refocusing optical imaging system. The voltage applied to an electrically tunable liquid lens allows obtaining a sharp image for a large range of object positions. This fact is an added value with respect to the Static System, where the object distances range is limited. The refocusing optical imaging system (Dynamic System) was designed by Lien Smeesters (et al.) and consists of two optical channels. The first channel is the third optical channel of the Static System and the second channel is the refocusing channel. This channel is compound of two passive lenses and the voltage-tunable liquid lens (Varioptic Arctic 320) in-between the two passive lenses. Each passive lens is composed of two aspheric surfaces (concave and convex). The lenses have been fabricated in PMMA by ultraprecision diamond tooling and they have been characterized (surface profile) by means of a measurement coordinate machine (Werth UA 400). After the characterization of the lenses, a setup of the channel with refocusing capability has been built up. In this setup it has been necessary to modify the distance between the tunable lens and the second passive lens, and between the second lens and the image sensor (uEye CMOS camera detector) with regards to the design specifications. Indeed, the fabricated lenses are not identical to the designed lens surfaces; there is one surface that has not been fabricated with the parameters of the design. The mounted refocusing channel performs well and the quality (contrast and ability to resolve fine details) of the captured images is high. In the experiments realized the working distances (object position) go from 0.15 m to 3 m, which is similar to the distance span obtained in the simulations for almost all the voltage values considered (from 51.1 Vrms to 60. The depth of field and depth of focus for different object distances and detector distances has been measured founding that the largest depth of field are obtained for low voltage values. In the experiments has been also observed that the tunable lens behaves hysterically (the optimal distance position where the image is sharp varies depending on the turning direction of the voltage, i.e., from higher to lower voltages values or viceversa.