The ability to actively control the perceived color of objects is highly desirable for a variety of applications, such as camouflage, sensing, and displays. We report a completely new flexible, high-contrast metastructure (HCM) whose color can be varied by stretching the membrane. This is accomplished by annihilating the 0th order diffraction while enhancing the-1st order, a new phenomenon made possible with a large index contrast. The color perception of the HCM can thus be changed by varying its period. The structure is fabricated using silicon metastructures embedded in a flexible membrane. We experimentally demonstrate brilliant colors and change the color from green to orange (39 nm wavelength change) with a stretch of 25 nm period change. The same effect can be used for steering a laser beam, with more than 36 resolvable beam spots being demonstrated.
The nonlinear response and strong coupling of control channels in micromachined membrane deformable mirror (MMDM) devices make it difficult for one to control the MMDM to obtain the desired mirror surface shapes. A closed-loop adaptive control algorithm is developed for a continuous-surface MMDM used for aberration compensation. The algorithm iteratively adjusts the control voltages of all electrodes to reduce the variance of the optical wave front measured with a Hartmann-Shack wave-front sensor. Zernike polynomials are used to represent the mirror surface shape as well as the optical wave front. An adaptive experimental system to compensate for the wave-front aberrations of a model eye has been built in which the developed adaptive mirror-control algorithm is used to control a deformable mirror with 19 active channels. The experimental results show that the algorithm can adaptively update control voltages to generate an optimum continuous mirror surface profile, compensating for the aberrations within the operating range of the deformable mirror.
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