Background: As an important optical element, concave microlens arrays are utilized in many applications. How to fabricate a mass of concave microlens arrays efficiently at a low cost is a key problem to be solved.
Aim: We propose a method of fabricating a concave microlens array based on single mask ultraviolet (UV)-photolithography and dual-step potassium hydroxide (KOH) etching, which has proven to be efficient.
Approach: An arrayed silicon-based concave microlens utilized in the infrared wavelength range was designed and fabricated based on single mask UV-photolithography and dual-step KOH etching. Combining the computation simulation and the evolving microstructural mechanism based on the silicon anisotropic corrosion characteristics in a common KOH solution with several control factors such as the solution concentration, temperature, and corrosion period, an arrayed concave microlens with a spherical profile over a silicon wafer with the required crystal orientation was simulated, designed, and fabricated effectively.
Results: Both the scanning electron microscopy and the surface profile measurements indicate that the fabricated concave microlens arrays present a high filling-factor of more than 80% and a small surface roughness with a root mean square value in several tens of nanometer scale. The common optical measurements demonstrate that the fabricated silicon-based concave microlens presents a good infrared beam divergence performance.
Conclusions: The method highlights the prospect of the industrial production of large-area silicon-based concave microlens arrays for infrared beam shaping and control light applications.
Traditional imaging based on common optical lens can only be used to collect intensity information of incident beams, but actually lightwave also carries other mode information about targets and environment, including: spectrum, wavefront, and depth of target, and so on. It is very important to acquire those information mentioned for efficiently detecting and identifying targets in complex background. There is a urgent need to develop new high-performance optical imaging components. The liquid-crystal microlens (LCMs) only by applying spatial electrical field to change optical performance, have demonstrated remarkable advantages comparing conventional lenses, and therefore show a widely application prospect. Because the physical properties of the spatial electric fields between electrode plates in LCMs are directly related to the light-field performances of LCMs, the quality of voltage signal applied to LCMs needs high requirements. In this paper, we design and achieve a new type of digital voltage equipment with a wide adjustable voltage range and high precise voltage to effectively drive and adjust LCMs. More importantly, the device primarily based on field-programmable gate array(FPGA) can generate flexible and stable voltage signals to cooperate with the various functions of LCMs. Our experiments show that through the electronic control system, the LCMs already realize several significant functions including: electrically swing focus, wavefront imaging, electrically tunable spectral imaging and light-field imaging.
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.
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