Micromirror Array Research Articles

Considerations for a Micromirror Array Optimized for Compressive Sensing (VIS to MIR) in Space Applications

Earth observation (EO) is crucial for addressing environmental and societal challenges, but it struggles with revisit times and spatial resolution. The EU-funded SURPRISE project aims to improve EO capabilities by studying space instrumentation using compressive sensing (CS) implemented through spatial light modulators (SLMs) based on micromirror arrays (MMAs) to improve the ground sampling distance. In the SURPRISE project, we studied the development of an MMA that meets the requirements of a CS-based geostationary instrument working in the visible (VIS) and mid-infrared (MIR) spectral ranges. This paper describes the optical simulation procedure and the results obtained for analyzing the performance of such an MMA with the goal of identifying a mirror design that would allow the device to meet the optical requirements of this specific application.

HaptoFloater: Visuo-Haptic Augmented Reality by Embedding Imperceptible Color Vibration Signals for Tactile Display Control in a Mid-Air Image.

We propose HaptoFloater, a low-latency mid-air visuo-haptic augmented reality (VHAR) system that utilizes imperceptible color vibrations. When adding tactile stimuli to the visual information of a mid-air image, the user should not perceive the latency between the tactile and visual information. However, conventional tactile presentation methods for mid-air images, based on camera-detected fingertip positioning, introduce latency due to image processing and communication. To mitigate this latency, we use a color vibration technique; humans cannot perceive the vibration when the display alternates between two different color stimuli at a frequency of 25 Hz or higher. In our system, we embed this imperceptible color vibration into the mid-air image formed by a micromirror array plate, and a photodiode on the fingertip device directly detects this color vibration to provide tactile stimulation. Thus, our system allows for the tactile perception of multiple patterns on a mid-air image in 59.5 ms. In addition, we evaluate the visual-haptic delay tolerance on a mid-air display using our VHAR system and a tactile actuator with a single pattern and faster response time. The results of our user study indicate a visual-haptic delay tolerance of 110.6 ms, which is considerably larger than the latency associated with systems using multiple tactile patterns.

Single-step beam intensity and profile optimization using a 256 × 256 micromirror array and reinforcement learning

Many optical applications require accurate control over a beam’s spatial intensity profile, in particular, achieving uniform irradiance across a target area can be critically important for nonlinear optical processes such as laser machining. This paper introduces a novel control algorithm for Digital Micromirror Devices (DMDs) that simultaneously and adaptively modulates both the intensity and the spatial intensity profile of an incident beam with random and intricate intensity variations in a single step. The algorithm treats each micromirror within the DMD as an independent Bernoulli distribution characterized by a learnable parameter. By integrating reinforcement learning with fully convolutional neural networks, we demonstrate that the control of 65,536 (256 × 256) micromirrors in a DMD can be achieved with modest computational expense. Furthermore, we implement the Error Diffusion (ED) algorithm as a sampling method and show that an incident beam with random and intricate intensity variations can be modulated to a predefined shape with high uniformity in intensity, both in simulated and experimental environments.

Binary amplitude holograms for shaping complex light fields with digital micromirror devices

Abstract Digital micromirror devices are a popular type of spatial light modulators for wavefront shaping applications. While they offer several advantages when compared to liquid crystal modulators, such as polarization insensitivity and rapid-switching, they only provide a binary amplitude modulation. Despite this restriction, it is possible to use binary holograms to modulate both the amplitude and phase of the incoming light, thus allowing the creation of complex light fields. Here, a didactic exploration of various types of binary holograms is presented. A particular emphasis is placed on the fact that the finite number of pixels coupled with the binary modulation limits the number of complex values that can be encoded into the holograms. This entails an inevitable trade-off between the number of complex values that can be modulated with the hologram and the number of independent degrees of freedom available to shape light, both of which impact the quality of the shaped field. Nonetheless, it is shown that by appropriately choosing the type of hologram and its parameters, it is possible to find a suitable compromise that allows shaping a wide range of complex fields with high accuracy. In particular, it is shown that choosing the appropriate alignment between the hologram and the micromirror array allows for maximizing the number of complex values. Likewise, the implications of the type of hologram and its parameters on the diffraction efficiency are also considered.

High efficiency regulation method to generate an illumination source by adopting the micromirror array in DUV lithography

Source and mask optimization (SMO) is an important lithography resolution enhancement technique for 22 nm technology nodes and beyond in lithography. This technique generates freeform sources by adjusting the inclination angle of the micromirror array (MMA). In this paper, a high efficiency regulation method to generate an illumination source by adopting the micromirror array in DUV lithography is proposed. The number and inclination angles of micromirrors required for adjustment to convert the initial source into any illumination source are quickly and accurately obtained by using the proposed method. The illumination source is obtained on the pupil plane by adjusting the inclination angles of some micromirrors. The simulation results show that the initial source is converted into another illumination source with different complexities by adjusting some micromirrors. Compared with the traditional MMA allocation method, when the initial source is the freeform source, the regulation efficiency of micromirrors has been improved by at least 20%. The method reduces the regulation time of micromirrors and the number of micromirrors required for adjustment. Moreover, the number of micromirrors required for adjustment is positively correlated with the coherence coefficient. The results illustrate that this method is effective and has significant engineering implications.

A novel quasi-static MEMS piezoelectric micromirror array with a high fill factor and three degrees of freedom

This paper presents the design of a novel 3×3 piezoelectric micromirror array (PMMA) with an 84.6 % fill factor and describes a three-dimensional hidden fabrication platform. The fabricated device operates with quasi-static mode in 3-degree-of-freedom, namely tip, tilt, and piston. In order to achieve a high fill factor, a three-dimensional hidden micromirror array structure is introduced, and is realized through multi-layer bonding. In addition, a double-stop-layer’s glass cover for optical device was employed to realize transparent wafer-level packaging. The device testing result achieves a mechanical tilting angle of 4.4 mrad at 82.5 VDC with over 99.5 % linearity. This design has the potential to achieve a larger size of micromirror arrays.

Extended depth-of-field wide-field fluorescence microscopy with a micro-mirror array lens system for versatile cellular examination.

We present a versatile extended depth-of-field (EDOF) wide-field fluorescence microscopy using a new, to the best of our knowledge, active device, micro-mirror array lens system (MALS) for calibration-free and orientation-insensitive EDOF imaging. The MALS changed the focal plane during image acquisition, and the system could be operated in any orientation. Two EDOF imaging modes of high-speed accumulation and low-speed surface sectioning were implemented. The performance was demonstrated in non-contact imaging of conjunctival goblet cells in live mice and depth-resolved cellular examination of ex-vivo human cancer specimens. MALS-based EDOF microscopy has potential for versatile cellular examination.

Omnidirectional mid-air image system using micro-mirror array plates

We proposed and implemented an omnidirectional mid-air image optical system that suppresses stray light and transmitted light. When micro-mirror array plates (MMAP) are integrated with view control films and rotated these optical elements at high speed, stray and transmitted light are effectively suppressed. This enables the visibility of omnidirectional mid-air image. We evaluated the effects of the view control film and high-speed rotation on the luminance and resolution of mid-air images, respectively. Our system facilitates the simultaneous viewing of mid-air images by multiple users, expanding the accessibility of mid-air image content to a large audience.

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.

Micromirror Array with Adjustable Reflection Characteristics Based on Different Microstructures and Its Application.

The conventional reflective optical surface with adjustable reflection characteristics requires a complex external power source. The complicated structure and preparation process of the power system leads to the limited modulation of the reflective properties and difficulty of use in large-scale applications. Inspired by the biological compound eye, different microstructures are utilized to modulate the optical performance. Convex aspheric micromirror arrays (MMAs) can increase the luminance gain while expanding the field of view, with a luminance gain wide angle > 90° and a field-of-view wide angle close to 180°, which has the reflective characteristics of a large gain wide angle and a large field-of-view wide angle. Concave aspheric micromirror arrays can increase the luminance gain by a relatively large amount of up to 2.66, which has the reflective characteristics of high gain. Industrial-level production and practical applications in the projection display segment were carried out. The results confirmed that convex MMAs are able to realize luminance gain over a wide spectrum and a wide range of angles, and concave MMAs are able to substantially enhance luminance gain, which may provide new opportunities in developing advanced reflective optical surfaces.

Fabrication of High‐Density Micro‐Bump Arrays for 3D Integration of MEMS and CMOS

Cu‐Sn transient‐liquid‐phase bonding has a limit in achieving small diameter/high‐density bumps due to the extrusion of the melted Sn layer during bonding. This paper report a new method that can fabricate small diameter Cu‐Sn bumps with 5 μm diameter and 25 μm pitch based on a new thermal reflow and pre‐bonding method that enables solid‐state Cu‐Sn reaction for avoiding Sn extrusion. Using the new method, 3D integration of a 640 × 480 MEMS array on a CMOS circuit chip has been demonstrated. This method can be used in 3D integration of MEMS arrays and CMOS circuits such as micromirror arrays. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

State-of-the-Art Materials Used in MEMS Micromirror Arrays for Photonic Applications

This work provides an overview on micromirror arrays based on different material systems such as dielectrics, element silicon, compound semiconductors, metals, and novel 2D materials. The goal is to work out the particular strength of each material system to enable optimum performance for various applications. In particular, this review is intended to draw attention to the fact that MEMS micro-mirrors can be successful in many other material systems besides silicon. In particular, the review is intended to draw attention to two material systems that have so far been used less for MEMS micromirror arrays, that have been less researched, and of which fewer applications have been reported to date: metallic heterostructures and 2D materials. However, the main focus is on metallic MEMS micromirror arrays on glass substrates for applications like personalized light steering in buildings via active windows, energy management, active laser safety goggles, interference microscopy, and endoscopy. Finally, the different micromirror arrays are compared with respect to fabrication challenges, switching speed, number of mirrors, mirror dimensions, array sizes, miniaturization potential for individual mirrors, reliability, lifetime, and hinge methodology.

Spatial Mode Division Multiplexing of Free-Space Optical Communications Using a Pair of Multiplane Light Converters and a Micromirror Array for Turbulence Emulation

Multi-plane light converters (MPLC) are a means of deconstructing a wavefront into constituent modes that are focused at specific spatial locations, and the reverse—that specific inputs result in controlled modal output. We have used a pair of MPLCs with 21 Hermite–Gaussian modes to represent a free-space optical connection. The effects of strong atmospheric turbulence (Cn2 = 10−13 m−2/3) are emulated using a micromirror array producing a time sequence of aberrating frames. The modal crosstalk between transmitter and receiver modes induced by the turbulence is presented by measuring the intensity in receiver channels for the same turbulence. Six receiver modes are used for optical communication channels with a rate of 137 Gbits/s displaying the benefits of single input multiple output (SIMO) operation for overcoming the deleterious effects of turbulence.

Temporary Protective Packaging for Vertical Integration of Optical-Window-Free TSV-Based Micromirror Array

Temporary Protective Packaging for Vertical Integration of Optical-Window-Free TSV-Based Micromirror Array

Single-pixel Fresnel incoherent correlation holography for 3D imaging

Fresnel incoherent correlation holography (FINCH) is an incoherent, non-scanning, and high-precision 3D imaging technique, but its area imaging characteristics limit the application of FINCH to some extent. Accordingly, we developed a single-pixel imaging method based on FINCH to realize 3D imaging. We utilized spatial light modulators (SLM) and loaded a measurement matrix on a digital micromirror array (DMD), thereby achieving phase modulation and compressed encoding simultaneously; one-dimensional data acquisition was achieved using a single-pixel camera. Finally, we combined the single-pixel reconstruction and phase-shifting algorithm to achieve incoherent correlation holography imaging with subsampling. The experimental results demonstrated that the proposed method could achieve comparable quality results at a sampling rate of 20 % compared to a 100 % sampling rate, and the method had good noise immunity. This not only avoided the limitations of area array sensors but also enabled high-fidelity imaging with a small data volume, which broadened the scope of research on the application of FINCH in the field of 3D imaging.

Angle monitor of micromirror array for freeform illumination in lithography systems

Source and mask optimization is a critical technique for further resolution enhancement in immersion lithography systems, wherein the optimal illumination source shape is widely generated by the micromirror array. Accordingly, the accurate achievement of the allocated angles of micromirrors is a key prerequisite for the implementation of arbitrary illumination patterns. In this paper, we propose an angle monitor to ensure the high-precision tilting of thousands of biaxial micromirrors. As one of the critical modules for closed-loop control of the two-dimensional micromirror array, the online monitor feeds the monitored high-precision tilt angle back to the processing system. The angle monitor mainly consists of the spot scanning module and the angle detection module. Among them, an f-θ lens and a Fourier transform lens with satisfied performances are designed and evaluated by CODE V. Furthermore, a galvanometer and the designed f-θ lens are adopted for the generation of the spot array irradiated on the electrostatic actuated mirrors. Meanwhile, the designed Fourier transform lenses are employed to detect the corresponding tilt angles. In addition, the performance of the proposed system is identified by simulations and experiments individually. It is demonstrated that the monitorable biaxial tilt range of the system is (−2.5°, +2.5°) with a repeatability of better than 0.005°. The large-format micromirror array can be monitored completely without optical cross-talk. Through the device, a 16 × 16 micromirror array is monitored, where the initial angle with no bias voltage applied is captured and the voltage–angle relation for individual micromirrors is obtained. In general, the proposed system can be utilized in the illumination system, providing an efficient and reliable method for complex source shape generation.

Easily scalable multi-color DMD-based structured illumination microscopy.

Structured illumination microscopy (SIM) achieves super-resolution imaging using a series of phase-shifted sinusoidal illumination patterns to down-modulate high spatial-frequency information of samples. Digital micromirror devices (DMDs) have been increasingly used to generate SIM illumination patterns due to their high speed and moderate cost. However, a DMD micromirror array's blazed grating structure causes strong angular dispersion for different wavelengths of light, thus severely hampering its application in multicolor imaging. We developed a multi-color DMD-SIM setup that employs a diffraction grating to compensate the DMD's dispersion and demonstrate super-resolution SIM imaging of both fluorescent beads and live cells samples with four color channels. This simple but effective approach can be readily scaled to more color channels, thereby greatly expanding the application of SIM in the study of complex multi-component structures and dynamics in soft matter systems.

Micromirror Arrays as Optical Phase Modulators for Free-Space Beam Steering

Micromirror Arrays as Optical Phase Modulators for Free-Space Beam Steering

Multi-Parameter Model-Based Polarimetric Calibration for Dual-Coded Spectral Polarization Imaging System

A polarization analysis method based on a multi-parameter model is proposed to address the polarization effect analysis and calibration requirements of a dual-coded snapshot spectral polarization imaging system. A full-link polarization effect model for a spectral polarization imaging system is established that includes a digital micromirror array (DMD), prism grating prism (PGP), micro-polarizer array detector (MPA), and multi-film. The influence of parameters such as the refractive index, incident angle, grating refractive index, constant, prism refractive index, vertex angle, multi-layer film complex refractive index, and film thickness on the optical transmittance of the system are analyzed. Using a dynamic data exchange mechanism to perform full-link, full-FOV, and full-pupil ray tracing on the optical system, the polarization effect distribution of the system under different degrees of polarization (DOP) and wavelengths is obtained. A calibration experiment for the controllable incident wavelength and DOP using narrowband filters and glass stacks is established. The experimental results show that in the 420 nm, 532 nm, and 635 nm wavelength bands, the MSEs of the calibrated values are 1.3924 × 10−4, 1.6852 × 10−4, and 1.6735 × 10−4, respectively. It is proven that the calibration method based on a multi-parameter model is feasible. Finally, the spectral polarization image at 532 nm is calibrated. The contrast ratio of metallic aluminum is calibrated from 7.13 to 15.33. This study provides a theoretical basis for the analysis and calibration of polarization effects in a dual-coded snapshot spectral polarization imaging system.

3D‐Printed Electrostatic Microactuators for Flexible Microsystems

AbstractDeveloping small‐scale, lightweight, and flexible devices with integrated microactuators is one of the critical challenges in wearable haptic devices, soft robotics, and microrobotics. In this study, a novel fabrication process that leverages the benefits of 3D printing with two‐photon polymerization and flexible printed circuit boards (FPCBs) is presented. This method enables flexible microsystems with 3D‐printed electrostatic microactuators, which are demonstrated in a flexible integrated micromirror array and a legged microrobot with a mass of 4 mg. 3D electrostatic actuators on FPCBs are robust enough to actuate the micromirrors while the device is deformed, and they are easily integrated with off‐the‐shelf electronics. The crawling robot is one of the lightest legged microrobots actuated without external fields, and the legs actuated with 3D electrostatic actuators enable a locomotion speed of 0.27 body length per second. The proposed fabrication framework opens up a pathway toward a variety of highly integrated flexible microsystems.