This paper presents an electrically controlled liquid-crystal (LC) interference filter in the infrared multispectral imaging system. Based on the theory of multi-beam interference, the proposed structure utilizes a pair of parallel flat plates with a reflectivity of ~95% to form a Fabry-Perot (FP) cavity, realizing constructive interferences and destructive interferences in specific wavelengths for incident infrared broad-spectra. The filtering performance of the proposed structure can be controlled by incorporating electrode layers based on the electro-optical properties of LC. We simulate the filtering characteristics of the proposed structure according to the elastic continuum theory of LC. Then the zinc selenide (ZnSe)-based LC filter with a preset cavity depth of 50 μm was fabricated with light orientation instead of the conventional friction orientation method. An infrared spectra test system was built to measure the performance of the fabricated interference filter. The experimental results successfully demonstrate the filtering characteristics covering three important infrared window bands in accordance with the simulated results by applying different root mean square (RMS) voltages. Also, the fabricated filter brings a sharper transmission peak waveform in a higher frequency infrared band. The proposed filter has a low cost and weight and is easy to install, laying the foundation for developing full-wave infrared multispectral imaging systems.
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.
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