Image sensors with electrically tunable spatial resolution based on liquid crystal microlens array with three-layered patterned electrode

The development of electrically tunable liquid crystal (LC) lenses is perspective and promising for a wide range of applications, for example, for imaging system, pico projectors, optical zoom systems, ophthalmology applications and other. Of particular note is the development of polarization-independent LC lenses, as eliminates polarizers from application devices that reduce the efficiency of light transmission through optical systems. Alignment benzaldehyde photosensitive materials, capable of changing the pretilt angles of nematic LC from 90 to 0 ºС in a controlled manner under UV exposure are developed. The anisotropy of the benzaldehyde alignment layers is generated by a two-stage treatment consisting of uniform rubbing with a cloth and subsequent non-polarized UV exposure. Inhomogeneous UV exposure of uniformly rubbed alignment layers allows formation of refractive index gradient inside the LC cell. The concept of tunable polarization-independent self-aligned LC lens based on gradient pretilt angle alignment materials with different photosensitivity is demonstrated. Self-alignment of two polarization-dependent sub-lens is achieved due to a single UV exposure act of two alignment layers, which are located on the same piece of glass on both sides, forming one common optical axis for a polarization-independent LC lens. The independence of the polarization of LC lenses is achieved by setting the azimuthal rubbing direction of the alignment layers of two polarizationdependent LC lenses perpendicular to each other. The sub-lens cells have uniform cell gap and are independently controlled using low-voltage driving. Devices based on gradient benzaldehyde alignment materials can be used in many modern optical and photonic devices.

A polarized liquid crystal (LC) lens composed of a LC layers as a polarization switch and a liquid crystal and polymer composites lens (LCPC lens) is demonstrated with electrically switching (ES) mode and optically rewritten (ORW) mode. The lens power of LCPC lens is related to a polarization state of light modulated by the LC layer whose orientations are manipulated either electrically or optically. As a result, the LC lens is not only electrically switchable, but also optically rewritable. Each mode, ES mode or ORW mode, exhibits two discrete lens powers (-1.39 Diopter and +0.7 Diopter). The demonstrated aperture size is 10 mm. The detail optical mechanism is also discussed. The Modulation Transfer Function (so-called MTF) of the lens is measured as well. In addition, the image performance and the dispersion of the LC lens are investigated. Such a polarized LC lens could be a special switch in optical systems due to dual operation modes.

Liquid crystal (LC) lenses that have hole-patterned electrodes and are driven by two voltages used as imaging devices are reported. Two different LC lenses are applied in image formation systems. One LC lens is used with a polarizer in a relay lens scope, and another LC lens that is polarization independent is used in a TV lens. Both LC lenses play roles of focusing elements in lens systems; objects are separately brought into focus by the LC lenses. Very sharp black-and-white and color images are formed by the systems.

We demonstrate a liquid crystal (LC) microlens array (MLA) fabricated by LCs possessing negative dielectric anisotropy, in conjunction with a cell with a three-electrode structure. The presented LC MLA is polarization-insensitive and can be operated in both concave and convex modes. The shortest focal length of the LC MLA is -2.54 and 2.22 mm in concave and convex mode, respectively. Disclination lines that are usually observed in conventional hole-patterned LC lens can also be avoided because of the vertical alignment treatment of LCs.

Analysis of the rotation of the polarisation direction in a cylindrical liquid crystal lens where the direction of the incident linear polarisation is not parallel to the axis of the cylindrical lens

Liquid crystal Pancharatnam-Berry phase lens with spatially separated focuses

A low-aberration hole-patterned-electrodes (HPE) liquid crystal (LC) lens with positive and negative focal lengths is demonstrated in this Letter by using four hybrid-aligned nematic LC layers filled with dual-frequency LC materials. The diopter can be controlled from the positive lens (0D∼1.1D) to the negative lens (0D∼-1.25D). The aberration is analyzed using the Zernike polynomial, and the wavefront optical path difference is improved from 2λ for the conventional one-layer HPE LC lens to less than 0.25λ for our proposed LC lens. The proposed LC lens does not require the use of a polarizer, increasing the optical efficiency two times compared with the conventional LC lens.

We demonstrated a fast response and large tunable focusing imaging system consisting of a lens module and a liquid crystal (LC) lens based on the switching of two modes of a LC lens: the negative LC lens and positive LC lens. By discarding the conventional operation of a positive LC lens only in the imaging system, large tunable focusing range can be achieve from 300 to 10 cm owning to the phase change between the positive and the negative LC lens; meanwhile, the response time is fast (∼433 ms). The potential applications are autofocused cell phones, and cameras.

Augmented reality (AR), which use computer-aided projected information to augment our sense, has important impact on human life, especially for the elder people. However, there are three major challenges regarding the optical system in the AR system, which are registration, vision correction, and readability under strong ambient light. Here, we solve three challenges simultaneously for the first time using two liquid crystal (LC) lenses and polarizer-free attenuator integrated in optical-see-through AR system. One of the LC lens is used to electrically adjust the position of the projected virtual image which is so-called registration. The other LC lens with larger aperture and polarization independent characteristic is in charge of vision correction, such as myopia and presbyopia. The linearity of lens powers of two LC lenses is also discussed. The readability of virtual images under strong ambient light is solved by electrically switchable transmittance of the LC attenuator originating from light scattering and light absorption. The concept demonstrated in this paper could be further extended to other electro-optical devices as long as the devices exhibit the capability of phase modulations and amplitude modulations.

In this paper, we present a novel design concept for determining the depth map of three-dimensional (3D) scenes based on an electrically controlled liquid crystal (LC) lens. The advantages of the proposed method are that it does not need any mechanical movements and a large amount of computations to acquire a depth map of a 3D scene in a relatively short amount of time. The tunable-focus LC lens doped with multi-walled carbon nanotubes is to become a key optical component for determining a depth map system. Sequenced two-dimensional images of slightly different perspectives are recorded in a short time, and the depth map of the 3D scene, according to a proposed depth estimation method and a focusing evaluation function, can be acquired in a simple way. This new method to acquire a depth map based on a doped LC lens maximizes the use of the proposed LC lens. The proposed system is novel in its compact, simple, and fast features, so we believe the proposed method can open a new creative dimension in image analysis and imaging systems and can also overcome the limitations of the conventional imaging mode.

In this paper, we present a relatively simple method to acquire a 3D image based on an electrically controlled liquid crystal (LC) lens. Its advantage is that this proposed method does not need any mechanical movements to acquire a 3D image. The tunable-focus LC lens combined with a high-resistance layer (PEDOT) is applied by an overdrive method to become a key optical component for use in a 3D imaging system. Multiple 2D images of slightly different perspectives are recorded, respectively, and 3D images, according to a proposed mapping and projection method, can be reconstructed. This is the first report, to the best of our knowledge, on using an LC lens to reconstruct 3D images. The proposed 3D imaging system is novel for its compact and smart features, so it is attractive for some compact 3D imaging systems.

Mobile video and gaming are now widely used, and delivery of a glass-free 3D experience is of both research and development interest. The key drawbacks of a conventional 3D display based on a static lenticular lenslet array and parallax barriers are low resolution, limited viewing angle and reduced brightness, mainly because of the need of multiple-pixels for each object point. This study describes the concept and performance of pixel-level cylindrical liquid crystal (LC) lenses, which are designed to steer light to the left and right eye sequentially to form stereo parallax. The width of the LC lenses can be as small as 20-30 μm, so that the associated auto-stereoscopic display will have the same resolution as the 2D display panel in use. Such a thin sheet of tunable LC lens array can be applied directly on existing mobile displays, and can deliver 3D viewing experience while maintaining 2D viewing capability. Transparent electrodes were laser patterned to achieve the single pixel lens resolution, and a high birefringent LC material was used to realise a large diffraction angle for a wide field of view. Simulation was carried out to model the intensity profile at the viewing plane and optimise the lens array based on the measured LC phase profile. The measured viewing angle and intensity profile were compared with the simulation results.

This paper proposes a newly developed optical design and an active compensation method for a Blu-ray pickup head system with a liquid crystal (LC) element. Different from traditional pickup lens design, this new optical design delivers performance as good as the conventional one but has more room for tolerance control, which plays a role in antishaking devices, such as portable Blu-ray players. A hole-pattern electrode and LC optics with external voltage input were employed to generate a symmetric nonuniform electrical field in the LC layer that directs LC molecules into the appropriate gradient refractive index distribution, resulting in the convergence or divergence of specific light beams. LC optics deliver fast and, most importantly, active compensation through optical design when errors occur. Simulations and tolerance analysis were conducted using Code V software, including various tolerance analyses, such as defocus, tilt, and decenter, and their related compensations. Two distinct Blu-ray pickup head system designs were examined in this study. In traditional Blu-ray pickup head system designs, the aperture stop is always set on objective lenses. In the study, the aperture stop is on the LC lens as a newly developed lens. The results revealed that an optical design with aperture stop set on the LC lens as an active compensation device successfully eliminated up to 57% of coma aberration compared with traditional optical designs so that this pickup head lens design will have more space for tolerance control.

The microscope system in combination with a digital image processing is developed for determining all-focused images and depth mapping properties of microscopic objects by using a liquid crystal (LC) lens with variable focal length. Three-dimensional distributions of the microscopic objects are determined by applying voltages to the electrodes of the LC lens and tuning a focal plane in a depth direction.

We propose a liquid-crystal (LC) micro-lens array with a flat external electrode in addition to two-divided and square-shaped electrodes for electrically controlling cylindrical or spherical lens properties in each LC cell of the lens array. The LC micro-lens array is useful for tuning optical properties such a focal length and deflection angle of a light emitting diode illumination system.