By using a special design of electrode pattern and the differential biased circuit, the gradient of the electric field distribution inside the liquid crystal sample cell can be achieved through the adjustment of driving voltage. The characteristics of positive or negative types of lens can be converted by changing the polarity of gradient within the sample cell which posses the homogeneous alignment. The liquid crystal lens with a variable focal length and the tunable types of focusing is demonstrated by utilizing the controllable distribution of electric field. This special design incorporating with the fabrication technology of TFT has a potential to develop a large scale of liquid crystal lens.

We fabricated the liquid crystal cell which had the property of the diffraction optical element. The concentric electrode had been fabricated on an indium-tin-oxide (ITO) substrate by etching technology. With the application of a proper voltage, it produces an inhomogeneous grating-like electric field in space to form phase Fresnel liquid crystal lens. Because of liquid crystals (LCs) are excellent electro-optic materials with electrical and optical anisotropies. Their optical properties can easily be modulated by the external electric field. Hence based on the electro-optic properties, the function of the as-constructed phase Fresnel liquid crystal lens has been studied in this paper. In this study, we discuss the diffraction efficiency of Fresnel LC lenses and collocated plano-convex to form dual focal length optical element.

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L'acquisition de la profondeur d'une scène en plus de son image est une caractéristique souhaitable pour de nombreuses applications qui dépendent de l'environnement proche. L'état de l'art dans le domaine de l'extraction de profondeur propose de nombreuses méthodes, mais très peu sont réellement adaptées aux systèmes embarqués miniaturisés. Certaines parce qu'elles sont trop encombrantes en raison de leur système optique, d'autres parce qu'elles nécessitent une calibration délicate, ou des méthodes de reconstructions difficilement implantables dans un système embarqué. Dans cette thèse nous nous concentrons sur des méthodes a faible complexité matérielle afin de proposer une solution algorithmique et optique pour réaliser un capteur permettant à la fois d'extraire la profondeur de la scène, de fournir une évaluation de pertinence de cette mesure et de proposer des images focalisées en tout point. Dans ce sens, nous montrons que les algorithmes du type Depth from Focus (DfF) sont les plus adaptés à ces contraintes. Ce procédé consiste à acquérir un cube d'images multi-focus d'une même scène pour différentes distances de focalisation. Les images sont analysées afin d'annoter chacune des zones de la scène d'un indice relatif à sa profondeur estimée. Cet indice est utilisé pour reconstruire une image nette en tout point.Nous avons travaillé sur la notion de netteté afin de proposer des solutions peu complexes, uniquement basées sur des additions et comparaisons, et de fait, facilement adaptables pour un portage sur une architecture matérielle. La solution proposée effectue une analyse bidirectionnelle de contraste local puis combine les meilleures estimations de profondeur en fin de traitement. Elle se décline en trois approches avec une restriction de la complexité de plus en plus forte et ainsi une aptitude de plus en plus marquée pour l'embarqué. Pour chaque méthode, des cartes de profondeurs et de confiances sont établies, ainsi qu'une image totalement focalisée constituée d'éléments issus de l'ensemble du cube multi-focus. Ces approches sont comparées en qualité et en complexité à d'autres méthodes de l'état de l'art de complexité similaire. Une architecture est proposée pour une implantation matérielle de la solution la plus prometteuse. La conception de ces algorithmes soulève le problème de la qualité d'image. Il est en effet primordial d'avoir une évolution remarquable du contraste ainsi qu'une invariance de la scène lors de la capture du cube multi-focus. Un effet très souvent négligé dans ce type d'approche est le zoom parasite provoqué par la lentille responsable de la variation de focus. Ce zoom de focalisation fragilise l'aspect invariance de la scène et provoque l'apparition d'artefacts sur les trois informations Profondeur, Image et Confiance. La recherche d'optiques adaptées au DfF constitue donc un second axe de ces travaux. Nous avons évalué des lentilles liquides industrielles et des lentilles modales expérimentales à cristaux liquides nématiques conçues durant cette thèse. Ces technologies ont été comparées en termes de rapidité, de qualité d'image, d'intensité de zoom de focalisation engendré, de tension d'alimentation et enfin de qualité des cartes de profondeur extraites et des images totalement focalisées reconstruites.La lentille et l'algorithme répondant le mieux à cette problématique DfF embarqué ont ensuite été évalués via le portage sur une plateforme de développement CPU-GPU permettant l'acquisition d'images et de cartes de profondeurs et de confiances en temps réel. / Acquiring the depth of a scene in addition to its image is a desirable feature for many applications which depend on the near environment. The state of the art in the field of depth extraction offers many methods, but very few are well adapted to small embedded systems. Some of them are too cumbersome because of their large optical system. Others might require a delicate calibration or processing methods which are difficult to implement in an embedded system. In this PhD thesis, we focus on methods with low hardware complexity in order to propose algorithms and optical solutions that extract the depth of the scene, provide a relevance evaluation of this measurement and produce all-in-focus images. We show that Depth from Focus (DfF) algorithms are the most adapted to embedded electronics constraints. This method consists in acquiring a cube of multi-focus images of the same scene for different focusing distances. The images are analyzed in order to annotate each zone of the scene with an index relative to its estimated depth. This index is then used to build an all in focus image. We worked on the sharpness criterion in order to propose low complexity solutions, only based on additions and comparisons, easily adaptable on a hardware architecture. The proposed solution uses bidirectional local contrast analysis and then combines the most relevant depth estimations based on detection confidence at the end of treatment. It is declined in three approaches which need less and less processing and thus make them more and more adapted for a final embedded solution. For each method, depth and confidence maps are established, as well as an all-in-focus image composed of elements from the entire multi-focus cube. These approaches are compared in quality and complexity with other state-of-the-art methods which present similar complexity. A hardware implementation of the best solution is proposed. The design of these algorithms raises the problem of image quality. It is indeed essential to have a remarkable contrast evolution as well as a motionless scene during the capture of the multi-focus cube. A very often neglected effect in this type of approach is the parasitic zoom caused by the lens motion during a focus variation. This "focal zoom" weakens the invariance aspect of the scene and causes artifacts on the depth and confidence maps and on the all in focus image. The search for optics adapted to DfF is thus a second line of research in this work. We have evaluated industrial liquid lenses and experimental nematic liquid crystal modal lenses designed during this thesis. These technologies were compared in terms of speed, image quality, generated focal zoom intensity, power supply voltage and finally the quality of extracted depth maps and reconstructed all in focus images. The lens and the algorithm which best suited this embedded DfF issue were then evaluated on a CPU-GPU development platform allowing real time acquisition of depth maps, confidence maps and all in focus images.

This dissertation proposes, studies and experimentally demonstrates novel liquid crystal (LC) optics to solve challenging problems in RF and photonic signal processing, freespace and fiber optic communications and microscopic imaging. These include free-space optical scanners for military and optical wireless applications, variable fiber-optic attenuators for optical communications, photonic control techniques for phased array antennas and radar, and 3-D microscopic imaging. At the heart of the applications demonstrated in this thesis are LC devices that are non-pixelated and can be controlled either electrically or optically. Instead of the typical pixel-by-pixel control as is custom in LC devices, the phase profile across the aperture of these novel LC devices is varied through the use of high impedance layers. Due to the presence of the high impedance layer, there forms a voltage gradient across the aperture of such a device which results in a phase gradient across the LC layer which in turn is accumulated by the optical beam traversing through this LC device. The geometry of the electrical contacts that are used to apply the external voltage will define the nature of the phase gradient present across the optical beam. In order to steer a laser beam in one angular dimension, straight line electrical contacts are used to form a one dimensional phase gradient while an annular electrical contact results in a circularly symmetric phase profile across the optical beam making it suitable for focusing the optical beam. The geometry of the electrical contacts alone is not sufficient to form the linear and the quadratic phase profiles that are required to either deflect or focus an optical beam. Clever use of the phase response of a typical nematic liquid crystal (NLC) is made such that the linear response region is used for the angular beam deflection while the high voltage quadratic response region is used for focusing the beam. Employing an NLC deflector, a device that uses the linear angular deflection, laser beam steering is demonstrated in two orthogonal dimensions whereas an NLC lens is used to address the third dimension to complete a three dimensional (3-D) scanner. Such an NLC deflector was then used in a variable optical attenuator (VOA), whereby a laser beam coupled between two identical single mode fibers (SMF) was mis-aligned away from the output fiber causing the intensity of the output coupled light to decrease as a function of the angular deflection. Since the angular deflection is electrically controlled, hence the VOA operation is fairly simple and repeatable. An extension of this VOA for wavelength tunable operation is also shown in this dissertation. A LC spatial light modulator (SLM) that uses a photo-sensitive high impedance electrode whose impedance can be varied by controlling the light intensity incident on it, is used in a control system for a phased array antenna. Phase is controlled on the Write side of the SLM by controlling the intensity of the Write laser beam which then is accessed by the Read beam from the opposite side of this reflective SLM. Thus the phase of the Read beam is varied by controlling the intensity of the Write beam. A variable fiber-optic delay line is demonstrated in the thesis which uses wavelength sensitive and wavelength insensitive optics to get both analog as well as digital delays. It uses a chirped fiber Bragg grating (FBG), and a 1xN optical switch to achieve multiple time delays. The switch can be implemented using the 3-D optical scanner mentioned earlier. A technique is presented for ultra-low loss laser communication that uses a combination of strong and weak thin lens optics. As opposed to conventional laser communication systems, the Gaussian laser beam is prevented from diverging at the receiving station by using a weak thin lens that places the transmitted beam waist mid-way between a symmetrical transmitter-receiver link design thus saving prime optical power. LC device technology forms an excellent basis to realize such a large aperture weak lens. Using a 1-D array of LC deflectors, a broadband optical add-drop filter (OADF) is proposed for dense wavelength division multiplexing (DWDM) applications. By binary control of the drive signal to the individual LC deflectors in the array, any optical channel can be selectively dropped and added. For demonstration purposes, microelectromechanical systems (MEMS) digital micromirrors have been used to implement the OADF. Several key systems issues such as insertion loss, polarization dependent loss, wavelength resolution and response time are analyzed in detail for comparison with the LC deflector approach. A no-moving-parts axial scanning confocal microscope (ASCM) system is designed and demonstrated using a combination of a large diameter LC lens and a classical microscope objective lens. By electrically controlling the 5 mm diameter LC lens, the 633 nm wavelength focal spot is moved continuously over a 48 [micro]m range with measured 3-dB axial resolution of 3.1 [micro]m using a 0.65 numerical aperture (NA) micro-objective lens. The ASCM is successfully used to image an Indium Phosphide twin square optical waveguide sample with a 10.2 [micro]m waveguide pitch and 2.3 [micro]m height and width. Using fine analog electrical control of the LC lens, a super-fine sub-wavelength axial resolution of 270 nm is demonstrated. The proposed ASCM can be useful in various precision three dimensional imaging and profiling applications.