We proposed a periodic coaxial honeycomb nanostructure array patterned in a silver film to realize the plasmonic structural color, which was inspired from natural honeybee hives. The spectral characteristics of the structure with variant geometrical parameters are investigated by employing a finite-difference time-domain method, and the corresponding colors are thus derived by calculating XYZ tristimulus values corresponding with the transmission spectra. The study demonstrates that the suggested structure with only a single layer has high transmission, narrow full-width at half-maximum, and wide color tunability by changing geometrical parameters. Therefore, the plasmonic colors realized possess a high color brightness, saturation, as well as a wide color gamut. In addition, the strong polarization independence makes it more attractive for practical applications. These results indicate that the recommended color-generating plasmonic structure has various potential applications in highly integrated optoelectronic devices, such as color filters and high-definition displays.
This paper presents the preliminary experimental studies of the influences of structural parameters, including the fill factor, device size, lattice, and nanoaperture shape, on the far-field optical transmission properties through the finite-sized two-dimensional periodic arrays of metallic nanoapertures. Both the lensing effect and the Talbot effect are observed, characterized and analyzed. Light intensity patterns of Talbot revivals at various Talbot distances containing abundant subwavelength hotspots are obtained, and the average size of the hotspots are derived and compared. Some concluding remarks are given to provide an important technological reference for the design and application of such devices according to the current experimental results.
The marriage of optics and MEMS has resulted in a new category of optical devices and systems that have unprecedented advantages compared with their traditional counterparts. As an important spatial light modulating technology, diffractive optical MEMS obtains a wide variety of successful commercial applications, e.g. projection displays, optical communication and spectral analysis, due to its features of highly compact, low-cost, IC-compatible, excellent performance, and providing possibilities for developing totally new, yet smart devices and systems. Three most successful MEMS diffraction gratings (GLVs, Polychromator and DMDs) are briefly introduced and their potential applications are analyzed. Then, three different MEMS tunable gratings developed by our group, named as micro programmable blazed gratings (μPBGs) and micro pitch-tunable gratings (μPTGs) working in either digital or analog mode, are demonstrated. The strategies to largely enhance the maximum blazed angle and grating period are described. Some preliminary application explorations based on the developed grating devices are also shown. For our ongoing research focus, we will further improve the device performance to meet the engineering application requirements.
A new MEMS-based tunable grating with programmable grating period, driven by electrostatic comb, was designed.
Finite element model was developed and finite element simulation was performed with ANSYS. Modal analysis and
static analysis were carried out. To improve the calculation efficiency, electrostatic driving force at each movable comb
was directly computed by analytical method instead of time-consuming coupled-field analysis. The results show that this
MEMS-based tunable grating functions quite well when a driving voltage is provided. To operate at its working
resonating mode much easier, thicker grating structure is needed, revealing the necessity in using the bulk
micromachining such as SOI technology to fabricate the grating. Also, larger the length of connecting beam and spring
beam, and smaller the width of spring beam, larger the deflection we can get for a specific driving voltage. The designed
MEMS-based tunable grating can be applied in many fields.
Effects of residual stresses on mechanical properties such as voltage vs. displacement response, pull-in voltage and structural resonant frequency of segmented micro deformable mirrors were investigated with both finite element method (FEM) and analytical method. A simplified model was adopted to study the structural spring constant on the existence of residual stress and two methods for imposing residual stress on structures were utilized for the purpose. Both results of analytical method and FEM show that larger structural spring constant can be obtained by introducing tensile residual stress. Consequently, mechanical properties relevant to spring constant are also greatly affected. The higher the tensile residual stress is, the stronger the structural stiffness will be. That means in order to induce the same structural displacement of mirror plate as stress-free state, higher voltage is demanded. Meanwhile, with higher tensile residual stress, larger pull-in voltage and greater structural resonant frequency are achieved. For the situation of compressive residual stress, totally the opposite influences can be observed. In conclusion, residual stress (no matter tensile or compressive) can greatly affect the mechanical properties of segmented micro deformable mirrors. Accurate control of it is needed for optimizing the structural design and improving the performance of devices.