Microelectromechanical Systems Scanner Research Articles

Biaxial Piezoelectric MEMS Mirrors with Low Absorption Coating for 1550 nm Long-Range LIDAR.

This paper presents the fabrication and characterization of a biaxial MEMS (MicroElectroMechanical System) scanner based on PZT (Lead Zirconate Titanate) which incorporates a low-absorption dielectric multilayer coating, i.e., a Bragg reflector. These 2 mm square MEMS mirrors, developed on 8-inch silicon wafers using VLSI (Very Large Scale Integration) technology are intended for long-range (>100 m) LIDAR (LIght Detection And Ranging) applications using a 2 W (average power) pulsed laser at 1550 nm. For this laser power, the use of a standard metal reflector leads to damaging overheating. To solve this problem, we have developed and optimised a physical sputtering (PVD) Bragg reflector deposition process compatible with our sol-gel piezoelectric motor. Experimental absorption measurements, performed at 1550 nm and show up to 24 times lower incident power absorption than the best metallic reflective coating (Au). Furthermore, we validated that the characteristics of the PZT, as well as the performance of the Bragg mirrors in terms of optical scanning angles, were identical to those of the Au reflector. These results open up the possibility of increasing the laser power beyond 2W for LIDAR applications or other applications requiring high optical power. Finally, a packaged 2D scanner was integrated into a LIDAR system and three-dimensional point cloud images were obtained, demonstrating the scanning stability and operability of these 2D MEMS mirrors.

Shaped input for reducing crosstalk of two-axis MEMS scanners

We have proposed a pre-shaped input method to minimize the crosstalk of two-axis microelectromechanical system (MEMS) scanners. The mechanical and geometrical crosstalk of a two-axis MEMS scanner was estimated to mitigate the total crosstalk of the scan pattern in an image plane. The desired scan pattern was converted into a required mechanical scan angle to compensate for the geometrical crosstalk. The device used in this study was a two-axis gimbal-less MEMS scanner, whose experimental transfer functions were obtained in terms of the mechanical scan angle. The method was evaluated for one-axis driving, reducing the total crosstalk by an average of 23.1 and 2.78 times along the x- and y -axis, respectively. The method was extended to two-axis driving, reducing the total crosstalk by an average of 18.1 and 2.49 times along the x- and y -axis, respectively. The lower reduction in the y -axis can be explained by the fact that the geometrical crosstalk appears much more on the y -axis than x -axis in the present measurement setup. In conclusion, the high suppression of crosstalk experimentally indicates that this method can effectively mitigate the total crosstalk and will be helpful to improve the performance of MEMS scanners. • Pre-shaped input was applied to obtain desirable output for two-axis MEMS scanners. • Two-axis pre-shaped input was carried out to reduce the crosstalk in MEMS scanner. • Scan pattern was improved by removing optical and mechanical crosstalk.

Capacitive Sensing for 2-D Electrostatic MEMS Scanner in a Clinical Endomicroscope.

A flexible fiber-coupled confocal laser endomicroscope has been developed using an electrostatic micro-electromechanical system (MEMS) scanner located in at distal optics to collect in vivo images in human subjects. Long transmission lines are required that deliver drive and sense signals with limited bandwidth. Phase shifts have been observed between orthogonal X and Y scanner axes from environmental perturbations, which impede image reconstruction. Image processing algorithms used for correction depend on image content and quality, while scanner calibration in the clinic can be limited by potential patient exposure to lasers. We demonstrate a capacitive sensing method to track the motion of the electrostatically driven two-dimensional MEMS scanner and to extract phase information needed for image reconstruction. This circuit uses an amplitude modulation envelope detection method on shared drive and sensing electrodes of the scanner. Circuit parameters were optimized for performance given high scan frequencies, transmission line effects, and substantial parasitic coupling of drive signal to circuit output. Extraction of phase information further leverages nonlinear dynamics of the MEMS scanner. The sensing circuit was verified by comparing with data from a position sensing detector measurement. The phase estimation showed an accuracy of 2.18° and 0.79° in X and Y axes for motion sensing, respectively. The results indicate that the sensing circuit can be implemented with feedback control for pre-calibration of the scanner in clinical MEMS-based imaging systems.

Dual-Axis MEMS Resonant Scanner Using 128∘Y Lithium Niobate Thin-Film

The micro-electro-mechanical systems (MEMS) resonant scanners are in great demand for numerous light scanning applications. Recently, the development of LiDAR in micro-robotics and mobile devices has led to the requirement of ultra-small systems with low driving voltage, low power, compact size and high performance. We have first proposed the dual-axis MEMS scanner using the lithium niobate (LN) thin-film platform, which is expected to fulfill the requirement. This paper describes the actuation principle and scanner structure, meanwhile develops the analytical model for the scanner. The analytical model is later validated by the finite element analysis. The performance of the proposed scanner is improved with the optimization of the orientation of LN and layer thickness. The proposed scanner achieves the θopt·D·f up to 937.8∘·mm·kHz in simulation. The simulated optical angle in the x-axis and y-axis are 50∘ and 42∘ at 1 V, corresponding to resonant frequencies of 79.9 kHz and 558.2 kHz, respectively. With the superior performance of large deflection, high scanning frequency, high figure of merit and low voltage, the proposed MEMS scanner is a promising candidate for fast scanner applications (e.g., wavelength-selective switches and submicron biomedical system), especially the application of LiDAR in mobile devices or micro-robotics.

Modeling and Optimization of a Novel ScAlN-Based MEMS Scanning Mirror with Large Static and Dynamic Two-Axis Tilting Angles.

The piezoelectric MEMS (micro-electro-mechanical systems) scanning mirrors are in a great demand for numerous optoelectronic applications. However, the existing actuation strategies are severely limited for poor compatibility with CMOS process, non-linear control, insufficient mirror size and small angular travel. In this paper, a novel, particularly efficient ScAlN-based piezoelectric MEMS mirror with a pupil size of 10 mm is presented. The MEMS mirror consists of a reflection mirror plate, four meandering springs with mechanical rotation transformation, and eight right-angle trapezoidal actuators designed in Union Jack-shaped form. Theoretical modeling, simulations and comparative analysis have been investigated for optimizing two different device designs. For Device A with a 1 mm-length square mirror, the orthogonal and diagonal static tilting angles are ±36.2°@200 VDC and ±36.2°@180 VDC, respectively, and the dynamic tilting angles increases linearly with the driving voltage. Device B with a 10 mm-length square mirror provides the accessible tilting angles of ±36.0°@200 VDC and ±35.9°@180 VDC for horizontal and diagonal actuations, respectively. In the dynamic actuation regime, the orthogonal and diagonal tilting angles at 10 Hz are ±8.1°/Vpp and ±8.9°/Vpp, respectively. This work confirmed that the Union Jack-shaped arrangement of trapezoidal actuators is a promising option for designing powerful optical devices.

Intraoperative Label‐Free Photoacoustic Histopathology of Clinical Specimens

AbstractDuring cancer resection surgeries, intraoperative histopathologic examination of the surgical specimen is crucial for tumor margin identification. A conventional frozen‐section analysis requires complex tissue processing, which prolongs surgery and potentially introduces interpretation errors. Here, as a novel approach to label‐free intraoperative histopathology, a high‐speed reflection‐mode ultraviolet photoacoustic microscopy (UV‐PAM) system employing a waterproof 1‐axis microelectromechanical systems scanner is demonstrated. Label‐free nuclear imaging is photoacoustically verified using tissue sections excised from mice and humans. Moreover, by imaging clinical specimens from cancer patients and numerically quantifying the histopathologic results, it is successfully demonstrated that the proposed UV‐PAM system has great potential as an alternative intraoperative histopathology method with minimal tissue preparation processes.

Real-time variable field-of-view scanning of LiDAR by controlling the drive voltage of MEMS micromirror

As the new generation of 3D imaging Lidar is being more and more miniaturized, low-cost and high-precision, micro-electromechanical systems(MEMS) are being considered as core components due to their unique characteristics. In practice, according to the distance of the measured objects, it is necessary to change the field-of-view scanning in real-time to achieve the best imaging effect. In this paper, we attempt to establish a nonlinear dynamic model of the MEMS scanning micromirror, and thereby determine the nonlinear relationship between the driving voltage and the scanning angle. The field-of-view scanning in the range of 0–40° can be achieved by controlling the drive voltage of the MEMS scanning micromirror.

MEMS enabled miniaturized light-sheet microscopy with all optical control

We have designed and implemented a compact, cost-efficient miniaturised light-sheet microscopy system based on optical microelectromechanical systems scanners and tunable lenses. The system occupies a footprint of 20 × 28 × 13 cm3 and combines off-the-shelf optics and optomechanics with 3D-printed structural and optical elements, and an economically costed objective lens, excitation laser and camera. All-optical volume scanning enables imaging of 435 × 232 × 60 µm3 volumes with 0.25 vps (volumes per second) and minimum lateral and axial resolution of 1.0 µm and 3.8 µm respectively. An open-top geometry allows imaging of samples on flat bottomed holders, allowing integration with microfluidic devices, multi-well plates and slide mounted samples, with applications envisaged in biomedical research and pre-clinical settings.

Development of an Electrostatic Comb-Driven MEMS Scanning Mirror for Two-Dimensional Raster Scanning.

Microelectromechanical System (MEMS)-based scanning mirrors are important optical devices that have been employed in many fields as a low-cost and miniaturized solution. In recent years, the rapid development of Light Detection and Ranging (LiDAR) has led to opportunities and challenges for MEMS scanners. In this work, we propose a 2D electrostatically actuated micro raster scanner with relatively large aperture. The 2D scanner combines a resonant scanning axis driven by an in-plane comb and a quasistatic scanning axis driven by a vertical comb, which is achieved by raising the moving comb finger above the fixed comb finger through the residual stress gradient. The analytic formula for the resonant axis frequency, based on the mechanical coupling of two oscillation modes, is derived and compared with finite element simulation. A prototype is designed, fabricated, and tested, and an overall optical Field-of-View (FoV) of about 60° × 4° is achieved. Finally, some possibilities for further improvement or optimization are discussed.

MEMS Scanning Mirrors for Optical Coherence Tomography

This contribution presents an overview of advances in scanning micromirrors based on MEMS (Micro-electro-mechanical systems) technologies to achieve beam scanning for OCT (Optical Coherence Tomography). The use of MEMS scanners for miniaturized OCT probes requires appropriate optical architectures. Their design involves a suitable actuation mechanism and an adapted imaging scheme in terms of achievable scan range, scan speed, low power consumption, and acceptable size of the OCT probe. The electrostatic, electromagnetic, and electrothermal actuation techniques are discussed here as well as the requirements that drive the design and fabrication of functional OCT probes. Each actuation mechanism is illustrated by examples of miniature OCT probes demonstrating the effectiveness of in vivo bioimaging. Finally, the design issues are discussed to permit users to select an OCT scanner that is adapted to their specific imaging needs.

A Silicon Optical Bench-Based Forward-View Two-Axis Scanner for Microendoscopy Applications.

Optical microendoscopy enabled by a microelectromechanical system (MEMS) scanning mirror offers great potential for in vivo diagnosis of early cancer inside the human body. However, an additional beam folding mirror is needed for a MEMS mirror to perform forward-view scanning, which drastically increases the diameter of the resultant MEMS endoscopic probe. This paper presents a new monolithic two-axis forward-view optical scanner that is composed of an electrothermally driven MEMS mirror and a beam folding mirror both vertically standing and integrated on a silicon substrate. The mirror plates of the two mirrors are parallel to each other with a small distance of 0.6 mm. The laser beam can be incident first on the MEMS mirror and then on the beam folding mirror, both at 45°. The MEMS scanner has been successfully fabricated. The measured optical scan angles of the MEMS mirror were 10.3° for the x axis and 10.2° for the y axis operated under only 3 V. The measured tip-tilt resonant frequencies of the MEMS mirror were 1590 Hz and 1850 Hz, respectively. With this compact MEMS design, a forward-view scanning endoscopic probe with an outer diameter as small as 2.5 mm can be made, which will enable such imaging probes to enter the subsegmental bronchi of an adult patient.

Dynamic measurement of beam divergence angle of different fields of view of scanning lidar* *Project supported by the National Key Scientific Instrument and Equipment Development Projects of China (Grant No. 62027823), the Shenzhen Fundamental Research Program (Grant No. JCYJ2020109150808037), and the National Natural Science Foundation of China (Grant No. 61775048).

The laser beam divergence angle is one of the important parameters to evaluate the quality of the laser beam. It can not only accurately indicate the nature of the beam divergence when the laser beam is transmitted over a long distance, but also objectively evaluate the performance of the laser system. At present, lidar has received a lot of attention as a core component of environment awareness technology. Micro-electromechanical system (MEMS) micromirror has become the first choice for three-dimensional imaging lidar because of its small size and fast scanning speed. However, due to the small size of the MEMS micromirror, the lidar scanning system has a small field of view (FOV). In order to achieve a wide range of scanning imaging, collimating optical system and wide-angle optical system are generally added to the system. However, due to the inherent properties of the optical lens, it is impossible to perfect the imaging, so the effects of collimating and expanding the beam will be different at different angles. This article aims to propose a measurement system that dynamically measures the divergence angles of MEMS scanning lidar beams in different fields of view to objectively evaluate the performances of scanning lidar systems.

Image processing metrics for phase identification of a multiaxis MEMS scanner used in single pixel imaging.

This paper applies image processing metrics to tracking of perturbations in mechanical phase delay in a multi-axis microelectromechanical system (MEMS) scanner. The compact mirror is designed to scan a laser beam in a Lissajous pattern during the collection of endoscopic confocal fluorescence images, but environmental perturbations to the mirror dynamics can lead to image registration errors and blurry images. A binarized, threshold-based blur metric and variance-based sharpness metric are introduced for detecting scanner phase delay. Accuracy of local optima of the metric for identification of phase delay is examined, and relative advantages for processing accuracy and computational complexity are assessed. Image reconstruction is demonstrated using both generic images and sample tissue images, with significant improvement in image quality for tissue imaging. Implications of non-ideal Lissajous scan effects on phase detection and image reconstruction are discussed.

Multiscale high-speed photoacoustic microscopy based on free-space light transmission and a MEMS scanning mirror.

The conventional photoacoustic microscopy (PAM) system allows trade-offs between lateral resolution and imaging depth, limiting its applications in biological imaging in vivo. Here we present an integrated optical-resolution (OR) and acoustic-resolution (AR) multiscale PAM based on free-space light transmission and fast microelectromechanical systems (MEMS) scanning. The lateral resolution for OR is 4.9 µm, and the lateral resolution for AR is 114.5 µm. The maximum imaging depth for OR is 0.7 mm, and the maximum imaging depth for AR is 4.1 mm. The imaging speed can reach 50 k Alines per second. The high signal-to-noise ratios and wavelength throughput are achieved by delivering light via free-space, and the high speed is achieved by a MEMS scanning mirror. The blood vasculature from superficial skin to the deep tissue of a mouse leg was imaged in vivo using two different resolutions to demonstrate the multiscale imaging capability.

An imaging analysis and reconstruction method for multiple-micro-electro-mechanical system mirrors-based off-centre scanning optical coherence tomography probe

An endoscopic optical coherence tomography (OCT) probe that can perform full circumferential scans using a circular array of six micro-electro-mechanical system (MEMS) mirrors has been developed. Inside the OCT probe, each of the six MEMS mirrors forms an independent scanning unit; circumferential OCT images are acquired by off-centre scanning and combining the image data from the individual multiple scanning units. Here, an imaging analysis and reconstruction (IAR) method is proposed to construct endoscopic OCT volumetric images from the multiple individual MEMS scanning unit. Imaging procedures of six-MEMS mirrors-based, eight-MEMS mirrors-based and twelve-MEMS mirrors-based OCT probes have been analyzed theoretically. All the data sets are in the Cartesian coordinate system and need to be transformed as fan-shaped images located in the polar coordinate system. The 3-D volume rendering is employed for visualizing the endoscopic data. Typically, this method is used into the image reconstruction of a six-MEMS mirrors-based endoscopic probe. The imaging area is also appropriate for scanning large-scale biological tissue through qualitative and quantitative evaluation. The proposed IAR method using the multiple-MEMS mirrors-based endoscopic off-centre scanning OCT probe has been verified in an experiment of imaging a swine small intestines. This method can be used to analyze the imaging of the multi-MEMS mirrors-based endoscopic OCT probe, which can image the large-scale gastrointestinal tracts in the future.

A Survey on LiDAR Scanning Mechanisms

In recent years, light detection and ranging (LiDAR) technology has gained huge popularity in various applications such as navigation, robotics, remote sensing, and advanced driving assistance systems (ADAS). This popularity is mainly due to the improvements in LiDAR performance in terms of range detection, accuracy, power consumption, as well as physical features such as dimension and weight. Although a number of literatures on LiDAR technology have been published earlier, not many has been reported on the state-of-the-art LiDAR scanning mechanisms. The aim of this article is to review the scanning mechanisms employed in LiDAR technology from past research works to the current commercial products. The review highlights four commonly used mechanisms in LiDAR systems: Opto-mechanical, electromechanical, micro-electromechanical systems (MEMS), and solid-state scanning. The study reveals that electro-mechanical scanning is the most prominent technology in use today. The commercially available 1D time of flight (TOF) LiDAR instrument is currently the most attractive option for conversion from 1D to 3D LiDAR system, provided that low scanning rate is not an issue. As for applications with low size, weight, and power (SWaP) requirements, MEMS scanning is found to be the better alternative. MEMS scanning is by far the more matured technology compared to solid-state scanning and is currently given great emphasis to increase its robustness for fulfilling the requirements of ADAS applications. Finally, solid-state LiDAR systems are expected to fill in the gap in ADAS applications despite the low technology readiness in comparison to MEMS scanners. However, since solid-state scanning is believed to have superior robustness, field of view (FOV), and scanning rate potential, great efforts are given by both academics and industries to further develop this technology.

Low-cost, ultracompact handheld optical coherence tomography probe for in vivo oral maxillofacial tissue imaging.

.Significance: Optical coherence tomography (OCT) has proven useful for detecting various oral maxillofacial abnormalities. To apply it to clinical applications including biopsy guidance and routine screening, a handheld imaging probe is indispensable. OCT probes reported for oral maxillofacial imaging were either based on a bulky galvanometric mirror pair (not compact or long enough) or a distal-end microelectromechanical systems (MEMS) scanner (raised safety concerns), or adapted from fiber-optic catheters (ill-suited for oral cavity geometry).Aim: To develop a handheld probe featuring great compactness and excellent maneuverability for oral maxillofacial tissue imaging.Approach: A dual-axis MEMS scanner was deployed at the proximal end of the probe and the scanned beam was relayed to the distal end through a 4f configuration. Such design provides both a perfect dual-axis telecentric scan and excellent compactness.Results: A handheld probe with a rigid part 70 mm in length and 7 mm in diameter and weighing 25 g in total was demonstrated through both ex vivo and in vivo experiments, including structural visualization of various oral maxillofacial tissues and monitoring the recovery process of an oral mucosa canker sore.Conclusions: The proposed probe exhibits excellent maneuverability and imaging performance showing great potential in clinical applications.

Design and Fabrication of a Kirigami-Inspired Electrothermal MEMS Scanner with Large Displacement.

Large-displacement microelectromechanical system (MEMS) scanners are in high demand for a wide variety of optical applications. Kirigami, a traditional Japanese art of paper cutting and folding, is a promising engineering method for creating out-of-plane structures. This paper explores the feasibility and potential of a kirigami-inspired electrothermal MEMS scanner, which achieves large vertical displacement by out-of-plane film actuation. The proposed scanner is composed of film materials suitable for electrothermal self-reconfigurable folding and unfolding, and microscale film cuttings are strategically placed to generate large displacement. The freestanding electrothermal kirigami film with a 2 mm diameter and high fill factor is completely fabricated by careful stress control in the MEMS process. A 200 μm vertical displacement with 131 mW and a 20 Hz responsive frequency is experimentally demonstrated as a unique function of electrothermal kirigami film. The proposed design, fabrication process, and experimental test validate the proposed scanner’s feasibility and potential for large-displacement scanning with a high fill factor.

Real-time Lissajous imaging with a low-voltage 2-axis MEMS scanner based on electrothermal actuation.

Laser scanning based on Micro-Electro-Mechanical Systems (MEMS) scanners has become very attractive for biomedical endoscopic imaging, such as confocal microscopy or Optical Coherence Tomography (OCT). These scanners are required to be fast to achieve real-time image reconstruction while working at low actuation voltage to comply with medical standards. In this context, we report a 2-axis Micro-Electro-Mechanical Systems (MEMS) electrothermal micro-scannercapable of imaging large fields of view at high frame rates, e.g. from 10 to 80 frames per second. For this purpose, Lissajous scan parameters are chosen to provide the optimal image quality within the scanner capabilities and the sampling rate limit, resulting from the limited A-scan rate of typical swept-sources used for OCT. Images of 233 px × 203 px and 53 px × 53 px at 10 fps and 61 fps, respectively, are experimentally obtained and demonstrate the potential of this micro-scannerfor high definition and high frame rate endoscopic Lissajous imaging.

Single-Pixel MEMS Imaging Systems.

Single-pixel imaging technology is an attractive technology considering the increasing demand of imagers that can operate in wavelengths where traditional cameras have limited efficiency. Meanwhile, the miniaturization of imaging systems is also desired to build affordable and portable devices for field applications. Therefore, single-pixel imaging systems based on microelectromechanical systems (MEMS) is an effective solution to develop truly miniaturized imagers, owing to their ability to integrate multiple functionalities within a small device. MEMS-based single-pixel imaging systems have mainly been explored in two research directions, namely the encoding-based approach and the scanning-based approach. The scanning method utilizes a variety of MEMS scanners to scan the target scenery and has potential applications in the biological imaging field. The encoding-based system typically employs MEMS modulators and a single-pixel detector to encode the light intensities of the scenery, and the images are constructed by harvesting the power of computational technology. This has the capability to capture non-visible images and 3D images. Thus, this review discusses the two approaches in detail, and their applications are also reviewed to evaluate the efficiency and advantages in various fields.