A new fabrication method for enhancing the yield of linear micromirror arrays assisted by temporary anchors.

As one of the most common spatial light modulators, linear micromirror arrays (MMAs) based on microelectromechanical system (MEMS) processes are currently utilized in many fields. However, two crucial challenges exist in the fabrication of such devices: the adhesion of silicon microstructures caused by anodic bonding and the destruction of the suspended silicon film due to residual stress. To solve these issues, an innovative processing method assisted by temporary anchors is presented. This approach effectively reduces the span of silicon microstructures and improves the Euler buckling limit of the silicon film. Importantly, these temporary anchors are strategically placed within the primary etching areas, enabling easy removal without additional processing steps. As a result, we successfully achieved wafer-level, high-yield manufacturing of linear MMAs with a filling factor as high as 95.1%. Demonstrating superior capabilities to those of original MMAs, our enhanced version boasts a total of 60 linear micromirror elements, each featuring a length-to-width ratio of 52.6, and the entire optical aperture measures 5 mm × 6 mm. The linear MMA exhibits an optical deflection angle of 20.4° at 110 Vdc while maintaining exceptional deflection flatness and uniformity. This study offers a viable approach for the design and fabrication of thin-film MEMS devices with high yields, and the proposed MMA is promising as a replacement for digital micromirror devices (DMDs, by TI Corp.) in fields such as spectral imaging and optical communication.

Column coded scanning aperture hyperspectral imaging system.

The line scanning hyperspectral imaging system (LS-HIS), which relies on a mechanical slit or spatial light modulation device for single channel spatial scanning, is widely used in various fields such as biomedical imaging and remote sensing. However, in scenes that require low light illumination, a decrease in luminous flux will increase exposure time, leading to a significant decrease in scanning efficiency and signal-to-noise ratio (SNR). To address this issue, we present a flexible column coded scanning aperture hyperspectral imaging system (CCSA-HIS) using a spatial light modulator digital micromirror device (DMD). By introducing the concept of multiplex and constructing a multiplexing encoding matrix, we form a one-dimensional multi-column coded scanning aperture, which greatly improves scanning efficiency. Experimental comparisons demonstrate that this approach achieves higher SNR and equivalent spatial and spectral resolution in significantly less sampling time compared to LS-HIS. In short, our scheme provides a new imaging technology for the field of hyperspectral imaging with good theoretical value and engineering significance.

Non-paraxial diffraction analysis for developing DMD-based optical systems.

We propose a non-paraxial diffraction model of the digital micromirror device (DMD) by combining the conventional Fraunhofer diffraction and a simple method of coordinative mapping. It is equivalent to adding aberrations of diffracted wave fields to the aberration-free Fraunhofer diffraction instead of complex integral calculations, allowing the simulated diffraction patterns to be consistent with the actual experimental counterparts. Moreover, it is verified by the experiments and literature that the diffraction angles, orders, and efficiency can all be well predicted for arbitrary incident angles and wavelengths. Especially for diffracted zenith angles within 50°, the predicted values reveal ∼1% error, and in a broader range, the predicted errors of diffracted azimuth angles are less than 4%. To the best of our knowledge, it is the first model capable of describing the non-paraxial diffraction behavior of the DMD. The proposed model with universality and effectiveness will help users to optimally construct DMD-based optical systems by guiding optical layouts, selection of light sources, and utilization and suppression of diffraction effects.

MEMS-based linear micromirror array with a high filling factor for spatial light modulation.

A smart digital micromirror device (DMD) was employed to realize the on-chip scanning in versatile hyperspectral imaging (HSI) systems in our previous research. However, the rotation manner around the diagonal of the DMD makes the imaging subsystem and the spectral dispersion subsystem unable to be in the same horizontal surface. This leads to the difficulty in designing the opto-mechanical structures, system assembly and adjustment of the light path to a certain extent. On the other hand, the HSI system also needs a larger space to accommodate the two subsystems simultaneously since either of them has to incline against the horizontal surface. Moreover, there exists the interference of the reflected light between the adjacent micromirrors during the scanning process performed by the DMD, causing the loss of optical information about the object. Here, a novel linear micromirror array (MMA) based on the microelectromechanical system process that rotates around one lateral axis of the micromirror is developed, which is helpful to simplify the optical system of HSI and obtain more optical information about the detected target. The MMA has 32 independent linear micromirrors across an aperture of 5mm×6.5mm, under which there are dimple structures and a common bottom electrode. Finally, the MMA with a 98.6% filling factor is successfully fabricated by employing the bulk micromachining process. The experimental results show that the maximum rotational angle is 5.1° at a direct current driving voltage of 30 V. The proposed micromirror array is promising to replace the DMD and shows potential as a spatial light modulator in the fields of hyperspectral imaging, optical communication, and so on.

DMD-based hyperspectral microscopy with flexible multiline parallel scanning.

As one of the most common hyperspectral microscopy (HSM) techniques, line-scanning HSM is currently utilized in many fields. However, its scanning efficiency is still considered to be inadequate since many biological and chemical processes occur too rapidly to be captured. Accordingly, in this work, a digital micromirror device (DMD) based on microelectromechanical systems (MEMS) is utilized to demonstrate a flexible multiline scanning HSM system. To the best of our knowledge, this is the first line-scanning HSM system in which the number of scanning lines N can be tuned by simply changing the DMD's parallel scanning units according to diverse applications. This brilliant strategy of effortless adjustability relies only on on-chip scanning methods and totally exploits the benefits of parallelization, aiming to achieve nearly an N-time improvement in the detection efficiency and an N-time decrease in the scanning time and data volume compared with the single-line method under the same operating conditions. To validate this, we selected a few samples of different spectral wavebands to perform reflection imaging, transmission imaging, and fluorescence imaging with varying numbers of scanning lines. The results show the great potential of our DMD-based HSM system for the rapid development of cellular biology, material analysis, and so on. In addition, its on-chip scanning process eliminates the inherent microscopic architecture, making the whole system compact, lightweight, portable, and not subject to site constraints.

DMD-based hyperspectral imaging system with tunable spatial and spectral resolution.

Pushbroom hyperspectral imaging (HSI) has been used in many areas from air to land. However, its inherent operational drawback of the bulky slit leads to a limited field of view (FOV) and high energy consumption. Accordingly, a new and versatile HSI system is proposed by employing a smart digital micromirror device (DMD) to replace the mechanical scanning component. Moreover, tunable spatial and spectral resolution is implemented through adjusting the on-chip scanning linewidth and adopting the pixel fusion method, respectively. Meanwhile, three scanning modes including rough scanning, fine scanning, and regional scanning are achieved. These multiple choices increase the system's flexibility, universality, and intelligence, which is attractive for practically different applications, especially for military and remote sensing fields in need of a large FOV, and medical and food fields in need of tunable resolution for various samples.