This PDF file contains the front matter associated with SPIE Proceedings Volume 12899, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

As advancing technology pushes to further miniaturize systems while increasing processing power, optical structures which offer dynamic tunability are becoming ever more valuable. Diffractive gratings popularly offer high efficiencies and can be readily designed to provide polarization sensitivity, making them useful as dynamic structured optics. Recently, slanted wire gratings compatible with fabrication by two-photon polymerization were investigated for their ability to be mechanically tuned. Potential applications for this grating may be in mechanical sensing and beam splitting. In this study, we investigate an additional degree of tunability not previously considered by exploiting the polarization sensitivity as well as the mechanical. It is observed that the population of the −1^st, 0_th, and +1_st transmitted orders are sensitive to changes between x- and y-axis polarization.

A method to calibrate multi-electrode electrowetting-driven lenses and phase-shifters based on measured wavefront feedback is presented. The aim is to compensate for wavefront errors commonly caused by processing irregularities or surface defects. The wavefront generated by the lens is measured using a Shack-Hartmann wavefront sensor to determine the surface shape. The deviation between the target surface shape is calculated and the electrode voltages are iteratively adjusted. A decentralized control algorithm is implemented which treats the meniscus height at each electrode as a variable with independent feedback control; an adaptive update condition determines which electrodes should be adjusted in each cycle.

The performance of any adaptive optics system is largely determined by the strength and number of actuators of the corrective element. Deformable phase plate (DPP) technology, recently developed by our group, allows for high order aberration correction in transmission, as it features a large number of transparent electrostatic actuators across the optical aperture. However, DPPs require high operating voltages to provide competitive stroke, which is currently provided by costly analog amplifiers. Pulse width modulation (PWM) offers a viable alternative to obtain analog operation at higher voltages without the need for analog amplifiers. It also potentially expands the library of optical liquids that can be used, as it is compatible with polar liquids acting as the dielectric. In this study we discuss the design, implementation and testing of an 8-channel PWM driver, which has 50 kHz maximum modulation frequency and 600V maximum drive voltage. A DPP variant designed to correct radial symmetric aberration is used to evaluate the performance of the manufactured PWM driver in terms of maximum deflection, stability, precision and crosstalk between actuators. Furthermore, we also demonstrate that PWM driving allows the use of polar liquids for the DPP technology, widening the library of possible optical liquids for this technology.

Highly sensitive trace-gas sensors are required in a large range of applications, such as biological, environmental, industrial, and fundamental physics. Photoacoustic spectroscopy has the advantages of compactness and robustness and is characterized by a high degree of flexibility in its configuration, in particular in the selection of the laser source and the transducer. Here we report the experimental characterization of new silicon-based Micro electro-mechanical systems (MEMS) structures to be applied as acoustic-to-voltage transducers in a photo-acoustic-based sensor. In our setup, a 4.5 μm continuous wave quantum cascade laser is used to address strong N₂O roto-vibrational transition, and the detection of MEMS oscillations is performed via a balanced interferometric readout.

Optical imaging-based remote sensing of the mechanical motion of an object is presented utilizing phase-based motion magnification (PMM) technology that amplifies subtle movement of the object invisible to the naked eye. In case that the oscillatory motion of an object is very small compared to the pixel size of optical image, the resulting motion measurement is inaccurate due to the low signal-to-noise ratio (SNR). To overcome this limitation, various vibration measurement method using phase information of the optical image is known to be more robust to noise and lighting conditions as well, however the existing PMM technology has several inherent issues to be addressed such as phase ambiguity. In this context, this paper focuses on the improvement of motion measurement accuracy by overcoming the phase ambiguity, in turn, limitation of magnification range of the remote motion sensing in existing PMM technique. The proposed PMM utilizes Gabor-like complex steerable pyramid (CSP) to expand the magnification range while retaining the local characteristics of CSP. Specifically, phase unwrapping is employed to resolve the discontinuity of the phase, and the novel envelope shift method is newly applied on the top of phase unwrapping to extend the magnification range. We verified the proposed method through the experiment of the vibrating structure. The proposed method reduces the ringing artifact and blurring of the magnified motion of the target structure. The accuracy of the proposed method was compared to the physical accelerometer measurements and previous methods. The experimental verification showed that the proposed method has accuracy of more than 90% with reduced motion artifact, while the original PMM has an accuracy of about 67% to 87% depending on the magnification factor, which demonstrate accuracy and robustness of the proposed method.

InGaAs NIR photodetectors are widely used due to their high responsivity, low noise, low dark current, fast response time, and large spectral range, which covers a range of 900 to 1700 nm and can be extended up to a 2600 nm cutoff. However, thermal drift is a major challenge that can affect the responsivity of these photodetectors, especially in miniaturized systems, where the thermal management problem is challenging. InGaAs photodetectors exhibit a highly nonlinear increase in responsivity near the cutoff, with an increase of about 4%/°C and a nonlinear reduction of about 0.25%/°C in the middle of the spectral range. This nonlinear drift cannot be corrected by common pre-processing methods used in spectroscopy. The change in responsivity near the cutoff is due to thermal-assisted bandgap reduction, while the change in responsivity in the middle of the spectral range is not well described in the literature. To address this issue, we applied the Urbach tail formula to model the nonlinear reduction of responsivity in the middle of the spectral range. The model showed an accuracy of approximately 90% compared to experimental thermal drift, allowing us to deduce the root causes of this phenomenon. Finally, we proposed compensation methods for the thermal drift, which were investigated using MOEMS FTIR spectral sensors as a case study. Some of these methods successfully reduced the drift that occurs due to a 60°C temperature change to less than 3%.

Calibration is an important step in the construction of traditional spectrometers to ensure the accuracy of the obtained spectrum. Recent advancements in computational spectroscopy have also spurred the need for calibration with the aid of machine learning to enable the recovery of spectrums, but they generally require large datasets. In this paper, we present an arbitrary spectrum generation engine (ASGE) using a digital micromirror device (DMD) that can be configured to work in a broad wavelength range from visible to the near-infrared. The DMD allows for the independent modulation of spectral elements to output arbitrary spectrums and provide the large datasets required for training and calibration of computational spectrometers. The ASGE can also double as a normal spectrometer if a sampling accessory and a detector are included.

Light Detection and Ranging (LiDAR) sensors often encounter challenges with ambient light interference in outdoor settings, leading to depth measurement distortions. Traditional solutions involve additional hardware, causing cost, size, and optimization issues. This paper introduces a hardware-free approach: the multi-tap parallel-phase demodulation method with MEMS scanning LiDAR. Using on-off pulse-waveform modulation based on the amplitude-modulated continuous wave (AMCW) principle, the proposed method suppresses ambient light by multiplying sections of the received laser signal corresponding to off-modulation clock timing by zero. Controlling the duty ratio of the modulation signal drastically reduces ambient light, ideally reaching 1/10 to 1/100. To address harmonics error, this paper utilizes 20 taps to increase the dominant order of harmonics, naturally reducing depth errors. Experimental results demonstrate the efficacy of the method, reducing the original 8 mm depth standard deviation to less than 5 mm at 2.5 m. The cm-scale harmonics error is also reduced to the mm scale within the depth range of 1 m to 4 m. This method proves effective for suppressing ambient light interference in outdoor LiDAR applications.

In this paper, a novel 6-Dimensional (3 positions and 3 orientations) pose estimation system using indirect Time-of- Flight (ToF) region-scanning LiDAR is proposed for long-distance space object recognition. Specifically, the targeted space object detection algorithm with an IR amplitude image, and 6D pose estimation algorithm with high-resolution 3D data are performed with the region-scanning LiDAR. The proposed system is verified with a self-collected dataset of space objects in space simulation environments. The proposed pose estimation algorithm shows a maximum position error of 1% and orientation error of 5° in robust experiment conditions. Moreover, the proposed system outperformed the other conventional space object 6D pose estimation system with previous depth sensors in terms of the detection rates and 6D pose accuracy at long distances.

This paper reports a new water-immersible single-axis scanning mirror using hybrid polymer and elastomer hinges to achieve both high scanning resonance frequencies and large tilting angles for high-speed and wide-field 3D ultrasound imaging. To demonstrate the concept, a prototype scanning mirror is designed, fabricated, and characterized. The fast- and slow-scanning were achieved by integrating stiff BoPET (biaxially oriented polyethylene terephthalate) and soft elastomer PDMS (Polydimethylsiloxane) hinges, respectively. The testing results have shown a resonance frequency of 270 Hz for the BoPET hinges and a resonance frequency of 10 Hz for the PDMS hinges when the scanning mirror was immersed in water. 3D ultrasound imaging is demonstrated by combining the fast- and slow-scanning together to provide both an augmented field of view (FoV) and high local imaging volume rate.

This paper demonstrates the use of a variable focus MEMS mirror in a frequency-modulated continuous-wave (FMCW) lidar system. The mirror can reveal short range targets that are typically hidden because the lidar was out of focus, and has demonstrated the ability to increase the signal level by over 20 dB for close-range targets. We have also demonstrated the ability to dynamically change the focus of the lidar during each sweep of the galvonometer, thus allowing the resolution of targets at different ranges during each sweep. The electrostatically driven 4 mm diameter mirror has a transition time of less than 1 ms and a focal length that can range from infinity to 56 mm which corresponds to wavefront Zernike fringe defocus coefficient ranging from 0 to 18 μm.

Nowadays, virtual, augmented and mixed reality applications are becoming more and more widespread. With this, the requirements for image quality are getting more demanding, leaving room for improvement of the user experience of the existing systems. While many research groups and companies try to improve on fixed-focus stereo image systems, we propose to make use of real holography as the best possible solution providing all depth cues automatically in a consistent way. Within such holographic display systems, a spatial light modulator (SLM) is re-shaping the incident light generating the desired images. As SLMs with the required properties are not commercially available today, a novel device is being developed within the Horizon 2020 ’REALHOLO’ project funded by the European Union: a MEMS micromirror Array (MMA) with 8 million phase-shifting pixels based on a novel comb drive micro actuator concept. Earlier theoretical work and simulations had showed clear perspectives for a superior performance in comparison to other SLM technologies allowing high frame rates and high precision wave front modulation. By now the first samples of proof-of-concept MMA chips have been fabricated and in this paper we present experimental characterization results: microscope and SEM images, quasi-static response curves measured by white light interferometry (WLI) as well as the dynamic properties like resonance frequency and damping measured by laser doppler vibrometry (LDV). In addition an addressing approach for a minimum mirror settling time is also investigated. We discuss the impact of fabrication tolerances on the overall precision together with the response curve dependency on design parameters and compare the experimental results to simulations.

This paper presents the feasibility of implementing various scan patterns, ranging from quasi-static to resonant driving methods, using newly developed 3D-constructed Al(Sc)N piezoelectric MEMS mirrors. A description of the assembled device and how each driving method was tried and characterized are also provided. According to the quasi-static driving test result, tilting angle of ±10° was achieved by both AlN and AlScN based-MEMS mirrors. For 1D resonant scanning, total optical scan angle (TOSA) of 20° was obtained under the low applied voltage of 1.5 V_pp. Further investigations were conducted on various 2D scan patterns, including Lissajous and circular scans. The characterization results show that Lissajous scan patterns with various field-of-view (FOV) sizes can be realized by adjusting the applied voltage and driving frequencies. In the case of circular scan, a TOSA of 10° was achieved, demonstrating the potential for 360° of omnidirectional scanning using the presented mirror devices. In addition, assessments of the electrical stability of fabricated piezoelectric material under high voltage and the mechanical robustness based on long-term cycling tests were conducted to ensure the reliability of the device. The presented low-power compact Al(Sc)N-based piezoelectric MEMS mirror device possesses a wide range of specifications, affording it the capability for application and customization to meet various purposes, while also holding significant potential for further advancements in its utility.

Recycling is an important issue contributing to economy and ecology. Material sorting is required to discriminate different raw substances. Near infrared spectroscopy is a suitable tool for the analysis of organic matter like plastic waste or textiles. A new design for a miniaturized MEMS based scanning mirror micro spectrometer has been realized for measurements in the 1000 nm to 1900 nm region offering 10 nm resolution. Test measurement in application close use cases have been performed resulting in promising data for different kind of plastic and textile samples.

Photonic MEMS interferometers are proving to be strong candidates for compact miniaturized spectrometers. In this work, a 2 mm x 2 mm MEMS-based Michelson interferometer, composed of a thin beam splitter, one fixed mirror, and one moving mirror, is designed and analyzed using Fourier optics propagation techniques and partial coherent source excitation. The model takes into consideration light divergence effects and beam truncation due to the limited dimensions of the device mirrors and beam splitter. The elementary source model is used to represent a partially coherent light source that is typically used in infrared spectroscopy applications. Flat micromirrors are compared to curved ones to explore the possible performance enhancements of the interferometer yielding an improvement of more than two times in the device optical throughput, which typically limits the performance of MEMS devices when dealing with light bulbs sources.

Future industrial production will be characterized by the collaborative work of humans and robots, sharing the same factory area (almost) simultaneously. To realize this cooperation in an efficient and safe way, powerful LiDAR systems with a large field of view are essential in order to permanently supervise the human-robot interaction and give instructions for the robotic motion based on the current human behavior. Piezoelectrically driven, resonant MEMS mirrors are often at the heart of such LiDAR systems, due to their high speed, electric power efficiency, and compactness. However, not only the achievable optical field of view, but also the resonant frequencies of the mirror eigenmodes are key parameters that need to be suitable for the specific application scenario and the system components, such as the laser. In this study, we present the FEM-simulation-based development of biaxial MEMS mirrors with 3 mm aperture, specifically optimized for the use in a LiDAR system to monitor and control the human-robot collaboration. The gimbal-less mirrors of Design 1 (and Design 2) exhibit a diminishing coupling between the two resonant modes at 2.4 kHz (2.3 kHz) and 5.6 kHz (5.0 kHz). This enables the individual control of the mirror movement along the two orthogonal axes and a very good light density. The two presented mirrors realize scanned field of views of 60° x 32° and 42° x 42° rectangles, respectively, showing almost no pincushion distortions. Due to the reduced mechanical coupling and mutual influence, the sensing signals possess a high signal-to-noise ratio, enabling the precise determination of the mirror position.

Looseness of belt-pulley which are employed in industrial applications such as compressor and fan is important factor for safe machine operation. In conventional method, current/vibration sensors are attached for regularly inspecting the belt looseness. In contrast, this paper proposes a novel remote sensing method for machine health monitoring, utilizing a biaxial optical system. The bi-axial optical system consists of two groups of reflectors to accommodate stereoscopic images with disparity so that it enables 3D motion measurement with only one image sensor. 3D trajectory of belt can be reconstructed using bi-axial optical system and one image sensor. To improve the 3D accuracy of trajectory, camera calibration algorithms is improved by setting virtual left and right camera parameters to be identical considering the left and right images captured by single image sensor. As a result, 3D accuracy was more improved by 15.75% compared to Zhang’s method. For the actual experiment, four looseness level (normal, slight, moderate, severe damaged) of the belt were monitored. As the looseness level increased, the 3D trajectory of the belt exhibited a curved shape with noticeable quantitative differences. The result shows that the proposed architecture can be utilized to remote machine health monitoring with mobile image sensors.

SF₆ gas sensor is developed to measure SF₆ gas at different concentrations mixed with N2 based on mid-IR absorption of SF₆ at a wavelength of ~10.6 μm. An optical bandpass filter of ~10.6 μm is put in front of a thermal emitter source to allow light of this wavelength to pass through. A CMOS compatible pyroelectric detector is put on the other end of the gas channel to measure the voltage change due to presence of SF₆ gas. Here, we use AlN-based and 12% ScAlN-based pyroelectric detectors respectively. The results show for 100% SF₆ gas sensing, 12% ScAlN-based pyroelectric detector gives ~73% higher response compared to when using AlN-based pyroelectric detector. The voltage drop between reference N₂ gas and different SF₆ gas concentrations is also higher (up to 2x) when using 12% ScAlN-based pyroelectric detector. Based on the measured SF₆ gas responses, we try to estimate the lower limit of detection of our gas sensors when using AlN- and ScAlN- based pyroelectric detectors respectively. Response times taken for both detectors to detect SF₆ concentrations are measured to be ~6.26 s for AlN-based pyroelectric detector and ~1.99 s for 12% ScAlNbased pyroelectric detector. Finally, both pyroelectric detectors’ electrical responses across different frequencies are measured and their 3-dB frequency cutoffs are extracted to be ~13.5 Hz and ~12.6 Hz for AlN- and 12% ScAlN- based pyroelectric detector respectively. The results provide more understanding on characteristics of pyroelectric detectors in SF₆ greenhouse gas sensing based on mid-IR absorption.

Recently, there have been notable advances in nanophotonic structural color generation which enabled various applications in display, anti-counterfeiting, sensors and detectors. However, most advances in this domain have been achieved through the use of high-index materials which require expensive and complex fabrication. In this work, we enable low-index polymer nanostructures to generate structural colors using the multipolar decomposition technique which allows a better understanding and design of the scattering process by identifying the dominant multipole modes from the scattered fields. We set a polymeric (n~1.56) cuboid as the structural color generation platform, examined the contributions of various multipoles from the wave scattered by it, and synthesized the desired color spectrum by adjusting only the height of the cuboid. To validate our findings, we fabricated the designed structural color pixels via light-controlled, low-pressure nanoimprinting and measured the color and spectrum from them. Our experimental results agreed well with the simulation results, providing insights for bringing further advances to structural coloring.

This study focus on the analysis of various plastic samples using the portable MEMS-FTIR spectrometer in both transmission and diffuse reflection modes operating at two resolutions of 10 nm and 16 nm. The analysis focuses on the mid-infrared region spanning from 2000 nm to 4600 nm. Many plastic samples have been differentiated such as Nylon, Polypropylene, Polystyrene, Acrylonitrile butadiene styrene, and colored High-Density Polyethylene. The results shows that transmission module is efficient for clear plastic samples sorting and diffused reflection module is efficient for opaque plastic samples sorting. The findings position the MEMS-FTIR spectrometer as a portable, cost-effective, and accurate solution for plastic analysis tasks, demonstrating versatility and potential advantages over traditional methods in the specified MIR range.

The fabrication of optical waveguides using MEMS technology usually leads to scallops on the waveguide sidewalls, causing scattering loss due to the resulting surface roughness. Since these waveguides are usually wide and multimode, we extend the model based on perturbation theory developed by Dietrich Marcuse to the case of multimode slab waveguides. We compare the resulting model to the use of the Generalized Harvey-Shack scattering model and the ray picture to model the scattering loss. The comparison is performed for a waveguide width between 20 μm and 500 μm, and length ranging from 1 mm to 5 mm.

Understanding the dynamic behavior of photopolymers in nanoscale environment is essential to improving MEMS/NEMS device fabrication technologies. Here, we unveil the highly nonlinear behaviors of photopolymers exhibited during the process of light-controlled, low-pressure nanoimprinting. Such peculiarities can complicate the relation between the UV-dose and the height of the nanoimprinted feature, degrading the accuracy of the height control. To address the issue, we establish a theoretical process model and used the control of the nanoimprinting height for structural coloring applications. Our findings will broadly benefit nanotechnology and nanoscience.

Highly reflective micromirrors have been in high demand in recent decades. This is due to their usage in many systems, such as optical scanners, lab-on-chip spectrometers, and microfabricated structures for gas sensing applications. In these applications, highly reflective micromirrors have been used extensively. Deeply etched vertical micromirrors that have high reflectivity are used in these structures. Upon fabrication using deep-reactive-ion-etching (DRIE) technology, they are coated with metallic layers using the Magnetron Ion Sputtering process. In this article, we investigate the effects of the metallization process of fabricated vertical micromirrors. We derive a model to study the effects of the non-idealities caused by the process, such as the structure’s porosity and the metal layer thickness variation, on the reflective performance of the metalized surface. This is investigated using a Gaussian beam source – which is analogous to a single-mode fiber input. The vertical micromirror investigated is composed of a silicon substrate of 1 mm thickness and an aluminum metal layer of thickness that varies from 74 to 82 nm in the vertical direction, which represents a reflection coefficient magnitude that varies from about 89% at minimum metal thickness to about 95% at maximum thickness. The reflected beam is studied in terms of power, skewness and kurtosis.

This paper presents the design, fabrication, and testing of a silicon-on-insulator wafer (SOI) based electrothermally actuated MEMS mirror for a micro-endoscope. Finite element analysis (FEA) was conducted using CoventorWare to optimize the design parameters. A fabrication process flow was developed and the process steps were optimized based on the design. The micromirror was fabricated and tested. The results demonstrate the successful design and fabrication of a micromirror suitable for a micro-endoscope application.

A compact imaging Köhler homogenizer with adjustable flattop size was implemented for a DLP engine. It is composed of pulsed UV LED, collimator aspheric lens, double-sided micro-lens array (MLA) with 34×15 micro-lenses and 0.8mmx1.76mm pitch size, and condenser lens. The homogenizer is dedicated for DMD chip of size 1920×1080 pixels (4K resolution) for 3D printer application. The produced flattop at the DMD has 98% measured uniformity and 85% optical efficiency. The calculated Fresnel number was greater than 60, indicating that our MLA has low diffraction effects. A low-cost RTIR prism was proposed using a wedge and a right-angle prism. Compared to conventional RTIR, the structure characterized by low cost and simplicity in assembly.

Miniaturized vectorial beam steering mirrors are required in numerous applications like (i) LIDAR, (ii) diagnostic imaging or (iii) miniaturized therapeutic laser systems. In this article we present a new type of electrostatically driven vectorial (2D quasi-static) MEMS scanning mirror with monolithic integrated position sensors. The vectorial MEMS scanner was specially optimized for the requirements of a compact therapeutic photocoagulation laser system for the treatment of retinal eye diseases. This requires a highly miniaturized MEMS scanning system for fast and precise vectorial beam positioning of the treatment laser with a positioning time of ≤ 5 ms. The quasi-static 2D drive of the presented 2D MEMS scanning mirror is based on electrostatic vertical comb actuators in combination with a noncardanic suspension of the 2.2 mm circular mirror plate. To measure and control the actual beam position piezoresistive position sensors are monolithically integrated into the MEMS design. The MEMS scanner was designed for a quasistatic (mechanical) 2D tilt angle of ± 2 ° for both scan axes each in two frequency variants with 714 Hz and 1 kHz at 70 V and 130 V drive voltage, respectively. For high laser powers of > 1.5 W (average power) at 519 nm wavelength, highly reflective optical coatings based on a symmetric HRC design of enhanced (hybrid) Al with R ≥ 98 % are used.