In order to overcome the difficulty in imaging detection of high-speed moving targets under complex environments, and to get more comprehensive image information of the target, there is a urgent need to develop new high-performance optical imaging components. Compared to traditional lenses which have fixed shapes and immutable focal length, liquid-crystal microlens (LCMs) can not only adjust the focal length without changing the external shape, but also realize many practical functions such as swinging focus, spectral selection, depth of field adjustment, etc. The physical properties of spatial electric fields constructed between electrode plates of the LCMs are directly related to the light-field adjusting performances of LCMs, such as the polarity of electric field, the frequency and amplitude of applied voltage signal. In other words, the optical behaviors of LCMs will be affected remarkably by the parameters of driving voltage signal mentioned above. To implement these important functions flexibly and effectively, the driving voltage signal must be powerful and flexible. It had better to have multiple channels to control the direction of swinging focus, with relatively wide variance range to spread spectrum selection range, and with high precision to ensure accurately controlling LCMs. In addition, special waveforms may be required to support special functions of LCMs. Therefore a digital control device, which meet the requirements mentioned above, is designed, and then LCMs with it can realize imaging detection of targets in complex environment.
We present the results of numerical simulations and preliminary experiments to investigate the nano-focusing effect of incident light based on the surface plasmon polaritons (SPPs) on the nano-metallic-planar-apex metamaterials (NMPAM). The NMPAM are prepared by Focused Ion Beam lithography (FIB), a nanoscale fabrication tool. The NMPAM can be used to remarkably enhance the strength of the surface evanescent and lead to the excitation of several SPP modes on the metal surface. The interaction of different SPPs result in unique near-field optical properties for imaging and optical storage, so as to focus light into a nano-size point and thus enhance the light power greatly. The energy flow and electromagnetic field distribution is calculated by finite-difference time-domain (FDTD) method. The nano-spot position and intensity is experimentally shown to be controlled by the array of the apex. In our experiments, we fabricate a 10×10 array by FIB, and then the scanning near-field optical microscopy (SNOM) is used to observe the optical power distribution in nano-scale at the air-metal interface in the infrared region. we find that the light can be focus into ~100nm-scale and consequently enhance the light power up to several times than before common focusing method. The principle of nano-focusing based on nano-planar-apex is theoretically explained. The NMPAM can be utilized for coupling with infrared pixels to enhance the incident light converging so as to improve signal to noise ratio of infrared detection.
Polarization-independent microlens array based on liquid crystal (PI-LCMLA) has been an interesting and important topic in optoelectronic application. In this study, a polarization-independent microlens array using double layered nematic liquid crystals (LC) with orthogonal alignment is proposed and demonstrated. Two orthogonal LC layers are separated by a double-sided indium-tin oxide silica. Further optical experiments and investigations reveals that the PILCMLA can work in polarization and polarization-insensitive mode by operating the driving voltages. The normalized focusing intensity is no polarization dependence on the incident light. Several raw images at different working modes are obtained through by utilizing this novel configuration with low applied voltages. With advantages in high optical efficiency, simple manufacture, electrically tunable focal length, low power consumption, polarization independence and multi operation modes, this device can not only be used for imaging application but also has many potential applications in optical systems.