Shengwu Kang

Liquid-crystal microlens with focus swing and low driving voltage

A focus-swing liquid-crystal (LC) microlens with two patterned electrodes and filled in nematic liquid crystal is proposed. In order to lower the level of the applied voltage signal and effectively increase the focus-swing range, the bottom electrode is designed as a circular patterned structure. The top electrode is composed of four stripe-patterned subelectrodes, which are powered, respectively to generate expecting potential and drive the focus swing in the focal plane of the microlens. The common optical properties of the LC microlens and the swing behavior of the formed focus in the focal plane are demonstrated experimentally.

Ommatidia structure based on double layers of liquid crystal microlens array

We present a new liquid crystal (LC) microlens structure having ommatidia function, which consists of the overlapped patterned electrode layers. Each electrode layer has a circular electrode array with a different size. Two electrode layers are deposited on the surface of a glass substrate and insulated by thin SiO₂ coating, which act as controlling electrodes. A plane electrode layer deposited on the surface of another glass substrate acts as the base electrode. Two glass substrates are made into a LC cell filled with nematic LC material. When a voltage signal is applied to the controlling electrode and base electrode, each circular unit of the array can focus along the optical axis and has good focusing character, and it behaves as a common microconvex lens. The whole circular array achieves ommatidia optical characters because of many microconvex lenses imaging to the objects simultaneously. Two circular arrays can both image to the objects and have different fields of view, which have extraordinary ommatidia effects. The common optical properties of the LC microlens are also demonstrated experimentally.

The focal spot shape and point spread function of liquid crystal microlens with different pattern electrodes

In this paper, we present a new LC lens with different pattern electrodes including triangle electrode, square electrode, pentagon electrode, hexagon and octagon electrodes. We demonstrate the focusing process of LC lens, when the electrodes are driven by the voltage signal, all the LC lens with different pattern electrodes have good focusing characters along the optical axis. In addition, a LC lens with different sub-electrode pattern is also introduced, the sub-electrodes are designed to circular pattern and each sub-electrode can be driven separately. If the sub-electrodes are driven by the same voltage signal, the LC lens can focus along the axis, while they are controlled separately, it can make the focus swing off the axis over the focal plane. We show the Interference patterns of LC lens with various pattern electrodes. The different focal spot shapes and the optical properties of LC microlens are also demonstrated experimentally.

Modeling and simulation of nematic liquid crystal microlens with electrically focal-swing over focal plane

In this paper, a three-dimensional relaxation method together with a finite difference method (FDM) are used to model the dynamic response behavior of liquid crystal (LC) directors filled into a cavity with complex patterned electrodes. Simulations and analysis have been done for the focus-swing patterned electrodes structures. A new type of LC micro-structure which has an ability to swing its focus over its focal plane has been designed. The simulation shows that the new LC structure designed by us has also a strong ability of swing focus over focal plane. We can expect that the model developed by us can be utilized to design more complex LC microlenses or other functioned LC structures.

Ring patterned electrode driven by electrical signal liquid crystal microlens with focus tunable

In this paper, we present a new LC lens with multi-ring patterned electrode, it consists of two ring-shaped sub-electrodes and a circle sub-electrode, each sub-electrode can be driven separately. The two rings have different diameter but the same center, when the two ring-shaped sub-electrodes are driven independently, the LC lens can work as micro convex lens with different clear aperture and its local length can be tunable along optical axis by electrical signal. As the voltage is applied to the circle sub-electrode, it appears like concave lens. With this design, it can achieve two types microlens effect in one structure, and by applying the voltage to the different patterned electrode, it can switch between two types microlens. The optical properties of the LC microlens are also demonstrated experimentally.

Simulation of nematic liquid crystal focal-swing microlens and analysis of the disclination lines

In this paper, a three-dimensional relaxation method and a finite difference method (FDM) are used to model the dynamic response behavior of liquid crystal (LC) microlens. Simulations have been done for the focus-swing patterned electrodes structures. The formation of disclination lines in the director orientation can be accurately predicted. Based on the simulation, a careful choice of the device structure and the voltage will help to design better lens. We can expect that the model developed by us can be utilized to design more complex LC microlens or other functioned LC structure.

Addressable wide dynamic range and high precision digital control device for adaptive liquid crystal microlenses array

Optical microlenses have been developed for 30 years, and thus are widely used in various application fields including imaging, optical communication, optical interconnection, sensors, and so on. Traditional optical microlenses, which are usually fabricated by common optical materials such as typical glasses or silicon materials, have generally immobile shape and fixed focal length and focus distribution over the focal plane of the lens. But it has certain limitations because of the fixed optical properties, for example, a zoom lens for a CCD or CMOS camera need a change of the focal length or the lens power achieved by mechanical movements of several individual lenses in lens system. Current research demonstrates that liquid crystal (LC) is a kind of excellent electro-optic materials, because they have relatively large electrical and optical anisotropies, and their optical properties can easily be shifted by external electric fields applied. Compared to traditional optical microlenses, the focal length of LC microlenses can be changed according to the variance of the alternating signal voltage applied over the LC microlenses. A relatively wide range adjustable and precise output voltage signal can be utilized to perform well in the controlling LC microlenses array, because the variance of focal length can be set in a relatively large range when the voltage of the signal is varied in a relatively large dynamic region. According to the above demands, a digital control device with a wide-range adjustable precise output voltage is designed and realized for LC lens.

Three-dimensional modeling of nematic liquid crystal micro-optics structures with complex patterned electrodes

In this paper, a three-dimensional (3-D) relaxation method is used to model the dynamic response behavior of liquid crystal (LC) directors in LC micro-optics structures with complex patterned electrodes. The method is based on Frank- Oseen continuum elastic theory by using a vectorial representation. This method can deal with liquid crystal structures with arbitrary patterned electrodes, and it is quite computational stability. Different numerical results obtained according the method are as follows: (1) the nematic LC structures with complex patterned electrodes applied by a constant voltage signal, and (2) the nematic LC structures with different thickness of LC layer, and (3) the nematic LC structures with different signal voltage. The typical results include the distribution of LC directors in LC layers, the distribution of electric potential in LC layers, and the distribution of phase retardation. The results show that the method can be used to effectively predict the formation of disclination lines, which has a strong impact on the performance of LC micro-optics structures.

Liquid crystal microlens with tunable-focus over focal plane driven by low-voltage signal

A liquid crystal (LC) microlens with a new type of electrode pattern is designed. The both bottom and top ITO electrodes of LC microlens are placed face to face, and are separated by glass spacer with the thickness in micron scale, and then LC materials are injected into the cell constructed by them. Because of the two electrodes directly and closely facing the LC layer injected, the design can largely decrease the driving signal voltage for LC lens. The bottom electrode is designed with one round hole pattern. The top electrode is four circle patterns. The diameters of round hole and circle are 500μm and 160μm, respectively. Each circle pattern electrode can be used to focus incident light into different region over the focal plane of LC lens. When the four circle electrodes are driven by different signal at the same time, the focus can be moved off-axis over the focal plane of LC lens, and thus the voltage amplitude can be varied in the range from 0Vrms to 20Vrms. So, we realize a LC microlens with tunable-focus over the focal plane of LC lens driven by low-amplitude voltage signal.