This PDF file contains the front matter associated with SPIE Proceedings Volume 12434, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Diffraction gratings are ubiquitous in many optical applications such as sensors, filters, and optical security devices. Capillary force lithography, which utilizes the capillary rise of photopolymer into nanoscale cavities, is a simple and rapid method to construct diffraction gratings without necessitating expensive instruments or complex steps. With the help of spatial light modulators, such as the digital micromirror device, the height of the grating can also be spatially modulated, printing spatially height-modulated gratings. When white light normally impinges on the grating, the light propagates into the grating interferes with light that propagates into air. By varying the height of the grating, the optical path lengths of two lights can be varied, leading to different interference effects and structural coloring. Judicious design of the grating’s parameters and patterning process will even allow encoding of multiple images. In this work, by tuning the height of the grating through the light-controlled capillary force lithography, we demonstrate grating-based structural color printing. This technique is promising for producing the custom patterns for anti-counterfeiting, authentication, and cryptography.

Due to higher integration of optical functionality into compact products like augmented reality into Head-Up-Displays (HUD), there is an increasing demand for very thin and large micro-optical films. Classical production techniques like injection molding are not able to deliver the requested quality or part dimensions. Nano-Imprint-Lithography (NIL) can close this gap and provide very thin and at the same time very large micro-optical products. We will show the general approach and examples for different markets with all necessary steps (origination, tooling and NIL-replication) on substrates from 6” x 6” up to max. size of Gen5-Display-Size (1100 x 1300 mm²).

High-sensitivity accelerometers are key for many applications including ground-based gravitational wave (GW) detectors, in-situ or satellite gravimetry measurements, and inertial navigation systems. We will present our work on the development of optomechanical accelerometers based on the micro-fabrication of mechanical resonators and their integration with laser interferometers to read out their test mass dynamics under the presence of external accelerations. We will discuss the latest developments on compact millimeter-scale resonators made of fused silica and silicon, optimized for frequencies below 1 kHz and exhibiting low mechanical losses. While fused silica has demonstrated high mechanical quality factors at room temperature, silicon devices perform significantly better at very low temperatures, which is particularly relevant for future ground-based gravitational wave detectors where cryogenic environments will be used to improve the sensitivity of the observatories. We will report on our design, modeling, and fabrication process for the silicon-based resonators and present their characterization by means of highly compact fiber-based Fabry-Perot cavities.

We demonstrate a system-level low-power contactless button using MEMS ScAlN-based pyroelectric detector. As pyroelectric detectors can sense instantaneous temperature change, the human finger can act as a thermal source to activate the button. Using our in-house fabricated ScAlN-based pyroelectric detector which does not require any IR source, we package it into a contactless button system designed with electrical read-out circuits and signal processing. This contactless button system could detect the presence of a finger at a center distance measured up to ~4 cm away, ~2 cm radius circle area, suitable for application as contactless elevator button. Our contactless button system using ScAlN-based pyroelectric effect is characterized, tested and compared with a commercial contactless button. The power consumed is measured ~3.5× lower than that of commercial contactless button. The results obtained provide a potential solution towards energy efficient low-power contactless button system.

Recently, two-photon polymerization has been successfully employed to fabricate high-contrast one-dimensional photonic crystals. Using this approach, photonic bandgap reflectivities over 90% have been demonstrated in the infrared spectral range. As a result of this success, modifications to the design are being explored which allow additional tunability of the photonic bandgap. In this paper, a one-dimensional photonic crystal fabricated by two-photon polymerization which has been modified to include mechanical flexures is evaluated. Experimental findings suggest these structures allow mechanically induced spectral shifting of the entire photonic bandgap. These results support the use of one-dimensional photonic crystals fabricated by two-photon polymerization for opto-mechanical applications.

Recent results for flexible manufacturing of fused silica micro-optics using a surface optimization process are presented. Selective laser-induced etching technology (SLE) is used to fabricate highly precise microstructured glass components while thermal annealing is used to smoothen the optical surfaces. An optimization process for SLE printing and thermal annealing is investigated using a response surface methodology. Fabrication parameters such as laser power, writing velocity in the SLE process, as well as annealing temperature and thermal anneal time are varied to minimize the average surface roughness of the glass components. The optimization results show that the average surface roughness of printed glass is reduced from >500nm to ∼ 10nm in an area with a diameter of 250 μm, allowing the process to be used for optical applications.

UV/VIS spectroscopy is a useful and efficient tool for non-destructive remote and real-time monitoring of the maturation of grapes and other agricultural products. For this purpose, we have developed a fully-integrated micro-spectrometer consisting of four LEDs emitting at different wavelengths, which will allow a spectral analysis of the sample under investigation in reflection mode. The positioning of the emitters and photodiodes with respect to each other was optimized using simulations employing a grape model based on the Henyey-Greenstein scattering model, with parameters calculated from reflectance and transmission data of real grapes. The sensor was fabricated on a polyimide stripe on which the optical components were placed and interconnected on one side and an array of electrical contacts on the other side allowed interfacing of the sensor with the driving electronics. With an overall thickness of 11 μm, this sensor stripe can be placed inside a grape bunch and acquire reflectance data continuously in the vineyard during the maturation period.

In this paper, we present a doubly-encoded single-pixel Hadamard transform spectrometer that has its spectral resolution decoupled from its throughput. The proof-of-concept is designed in the 1500 nm to 1600 nm near-infrared (NIR) wavelength range and uses a digital micromirror device (DMD) in conjunction with a fixed mask for encoding. The proposed system can easily be extended to other infrared (IR) wavelengths to achieve maximum throughput and multiplexing advantage.

In the past twenty years optical spectrometers have shrunk dramatically in size, giving us successively laboratoryportable, toaster-sized, instruments; cordless-drill-sized portable instruments for use in the field; and onto spectrometers the size of a computer mouse or deck of cards. The latest development in portable spectroscopy is the availability of very low-cost multispectral sensors, the size of computer chips, leading to the possibility of embedding them into consumer goods, including personal health monitoring, and eventually into medical products. The width of absorption bands in the visible and near-infrared regions for condensed phase samples imply that an instrument with a small number of resolution elements will be able to perform routine analyses, and that spectral range is a more important parameter than spectral resolution. Multispectral sensors can now be incorporated into ‘fitness’ products like smart watches and sports watches, and as photonic miniaturization increases, into ‘wearables’ like smart rings providing the user with health information. Multispectral devices can be produced in volume via semiconductor and optical coating techniques, at very low cost - less than $10 each. Silicon photonics and photonic integrated circuits (PICs), produced en masse using semiconductor manufacturing techniques, are the ideal next step. This paper surveys the field and highlights some ‘smart’ consumer device possibilities from toothbrushes to toilets.

Various compact spectrometer configurations have been proposed to reduce size. But due to the mismatch between the size and the focusing, optical aberration and poor spectral resolution occur. This work reports an aberration correction lens with a transmission grating (ACLG) based compact spectrometer that improves spectral resolution. It is packaged with an assembly of top, bottom parts, and middle ACLG parts, the overall thickness of the spectrometer is 10mm and has an average resolution of 2nm over a wide range of 500 to 1000nm. This compact spectrometer with high performance can serve as a core device of handheld or portable analysis equipment.

Spectral analysis has gained a lot of interest throughout the last decades. Nondestructive and non-contact evaluations can provide multiple information: appearance and composition, but also more complex details, which can be accessed by means of sophisticated methods like fluorescence or Raman scattering. Spectrometers have been widely used for the UV to NIR spectral range. There are applications, where a broad spectral range is beneficial. Typically, the spectral range of a grating based system is limited by higher diffraction orders. Either one decade can be detected or order filters have to be applied to discriminate different orders. A novel concept for a broadband spectrometer is the use of a scanning mirror device to illuminate a fixed grating. Due to the optical path inside, the double wavelength range can be addressed for the identical MEMS deflection. Two or more detectors, each optimized for the relevant spectral range, can be placed in the setup. A first sample of a scanning mirror micro spectrometer (“SMMS”) has been realized and tested successfully. In the NIR spectral range from 1000 nm to 1900 nm a resolution of 10 nm (FWHM) has been achieved. Application examples can be found in the field of agriculture - soil, plant growth and watering, directly leading to food, e.g. ripeness and freshness. Spectrometer with broad spectral range enable simultaneous detection of appearance (color) and composition (NIR); also fungus and aflatoxins can be detected by means of UV to VIS fluorescence. Similar task arise in textile, recycling and other fields where color, composition and conditions are of interest.

This paper reports a nanoplasmonic isothermal PCR assay with CRISPR/Cas for real-time SARS-CoV-2 detection. The study utilizes a microchip and a miniaturized hand-held type photothermal PCR system, which comprises a nanoplasmonic photothermal heater and microlens array camera to maintain the temperature and detect fluorescence signal from the chip. CRISPR-based fluorescence signal detection, which proceeds simultaneously with nucleic acid amplification, indicates higher sensitivity and rapid detection. The real-time nanoplasmonic isothermal PCR assay opens a new opportunity for POCT-based CRISPR assay.

This paper reports a plasmon-induced photoacoustic transducer for non-invasive skin tightening using a laser diode and an ultrathin nanoplasmonic optical absorber. The nanoplasmonic absorber consists of three-dimensional Au nanoislands (Au NIs) with high optical absorption and polydimethylsiloxane (PDMS) thin film with high thermal expansion coefficient. The low-cost and compact laser diode (LD) significantly scales down the conventional photoacoustic system based on bulk solid-state lasers and excites the nanoplasmonic absorber with sufficient optical energy to generate MHz-scale ultrasound. This plasmon-induced photoacoustic transducer opens new opportunities for ultrasound in dermatology, extending its application to portable at-home skin-care device.

Analysis of microparticles in liquid samples is important in many settings, such as the analysis of bacteria in biofluids, or microplastics in water. In addition to their specific absorbance peaks, microparticles result in ripples in the ATR spectra measured especially in the shorter wavelength range due to resonance effects. By analyzing these ripples, in addition to the absorbance peaks, the microparticles material and size distribution can be simultaneously identified. We develop a method to extract the size distribution of particles of diameter 6 μm and 10 μm. In addition, we apply the model to ATR spectroscopic measurements of poly(methyl methacrylate) microspheres of different diameters in water to extract their size.

We present a sensor-based, real-time position feedback mechanism for piezoelectric fiber-based optical scanners. In this method, a micro-magnet attached to the tip of the fiber cantilever generates a three-dimensional magnetic field that can be measured by a micro-sized 3D Hall sensor embedded in the cap of the endoscopic probe. A previously recorded mapping between the magnetic field distribution on the sensor and the corresponding spatial location of the magnet, which is invariant with respect to the scanner operation, can then be used at any given time to recall the position of the laser spot on the imaging plane.

Biaxial resonant MEMS-scanners are considered as promising core-device in state-of-the-art imaging and projection systems due to their compactness, the large field-of-view, high speed, and comparably low power consumption. However, the usage in three-dimensional LIDAR modules or projectors for industrial applications is often limited by non-optimal Lissajous-scanning patterns. To achieve dense and spatially uniform Lissajous-trajectories, a suitable frequency ratio of the two oscillation modes is essential. In previous works, the frequency ratio was either maximized or minimized, which often led either to mechanical fragility or undesirable coupling of the two normal modes. For solving the abovementioned problems, a piezoelectrically-driven biaxial MEMS-scanner exhibiting large design flexibility, enabling the individual tailoring of the two orthogonal rotational oscillation-modes and Lissajous-patterns with large fill factor, was developed. This design freedom and decoupling of two axes motions are achieved by a gimbal-less design with individual actuator systems for the two oscillatory axes. Driven by the CMOS-compatible piezoelectric Al(Sc)N, the Q-factor of the resonant mirror with large optical aperture of 5 mm is enhanced by hermetic wafer-level glass-encapsulation. A projection module, which combines the biaxial MEMS-scanner, an RGB-laser-beam combiner, and the electronics for both read-out and control, was developed in the frame of a funded research project (”MEMS-scanner-based laser projection system for maritime augmented reality”). The target of the project was the development of a smart window, in the sense of a MEMS-scanner-based laser projection system for maritime augmented reality, which offers the possibility to fade in safety-relevant information of navigation and ship sensors into the field-of-view of the bridge personnel on the ship’s bridge. Such projector is promising also for further applications in industry, for instance in 3D cameras.

A novel CMOS-MEMS staggered vertical comb-based micro scanner using 0.18um 1P6M CMOS foundry process without wafer bonding has been successfully developed. A compact model consisting of both numerical simulations and analytical solutions is used for rapid design optimization. An optimized design with enhanced performance (rotation angle and figure of merit) as well as a critical ratio for improving actuators’ input-output response is proposed. The proposed CMOS-MEMS micro scanner can be very useful for developing next-generation optical MEMS devices.

In this paper, a novel 3D face recognition system utilizing the MEMS-based indirect Time-of-Flight (ToF) region-scanning LiDAR is proposed for long-distance person identification. Specifically, this face recognition system consists of two parts: (1) detection of the targeted face region by IR amplitude image and (2) 3D face recognition with the high-resolution face data of region-scanning. The proposed system is carried out on the self-collected dataset and gets maximum Rank-1 recognition rate of 95% in various distance and illumination conditions. Moreover, the proposed system outperformed the other 3D face recognition system with conventional ToF sensors in the aspect of the Rank-1 recognition rates at long distance of more than 3 meters.

Coherent LiDAR concepts for automotive or unmanned aerial vehicle (UAV) applications are of increasing interest due to their superior performance compared to standard pulse-based systems, especially at longer range. Proposed scanning methods include bulky and slow galvanometer- or polygon scanners that are often impractical for implementation in cars or UAVs. Here, micro-electro-mechanical-system (MEMS) mirrors can be used as an alternative compact scanning device. To merge the advantages of coherent LiDAR technology with the advantages of miniaturized scanning by MEMS mirrors, we present fiber-based frequency modulated continuous wave (FMCW) LiDAR point cloud generation using quasi-static MEMS mirrors. The unique feature of quasi-static MEMS mirrors is their ability to perform a point-to-point scanning and measurement process, while most conventional MEMS mirrors scan the scene continuously. Hence, they enable a compact monostatic system design. We demonstrate the operation of such a system for the first time, to the best of our knowledge. Here, we show the operating principle and design of those quasi-static MEMS mirrors. We also implement and test the generation of the mirror scan pattern using a digital IIR (infinite impulse response) filter method. Lastly, we show the LiDAR point cloud generation in an indoor environment and evaluate the point cloud output for different MEMS mirror sizes, angular resolutions, and ranges.

This paper suggests a MEMS-based indirect time-of-flight (ToF) scanning light detection and ranging (LiDAR) system with parallel-phase demodulation. Based on the parallel-phase demodulation which extremely reduces the integration time maintaining high demodulation contrast, the proposed LiDAR can acquire accurate depth images with mean absolute error (MAE) about 1.5 cm at the distance of 1.85 m using 20 mW laser power. Meanwhile, MAE due to multipath interference (MPI) of the proposed LiDAR originally about 1.5 cm could be further reduced to less than 8 mm using support vector regression (SVR).

The facetVISION array camera architecture allows to reduce the z-height of mobile camera modules to 50% of that of a conventional camera module independent of pixel size and resolution while at the same time providing depth information. It employs folding of the optical path via a mirror bank and segmenting the field of view into different imaging channels using individual inclinations of the mirror facets as well as stitching of the final image by depth-based image rendering. A typical arrangement incorporates four channels in one line with D-cut objectives and about 2:1 aspect ratio image sensors. One pair of cameras captures the upper part of the field of view providing depth there and the second pair accordingly for the lower part of the total field of view. As an option, the mirror bank is rotated, so that the same camera module can be used to capture world-side images as well as selfies sequentially. In demonstrator systems realized by us, we used different combinations of voice coil motors with piezo bending actuators for auto focus and optical image stabilization. Tunable lenses were employed for channel-individual focusing to account for back focal length variations within the array as well as possible changes of the same, especially with respect to temperature. In this paper, we report of the in-detail analysis of the thermal effects within our array camera architecture including tunable lenses. MTF-through-focus curves are captured and evaluated with the camera being exposed to different temperatures and voltage settings for the adaptive lenses.

The measurement of relevant process emissions is a challenging task, especially when access for measurement technology is limited. One example is the optical combustion chamber monitoring of internal combustion engines. The access is limited and spatial resolution for observation is limited by the possible use of optical elements in the combustion chamber. So far, data acquisition has been realized with the aid of spark plugs with integrated connections to an optical sensor. This optical spark plug has the function of a spark plug and simultaneously enables the detection of light in the engine. The optical spark plug is positioned in the center of the combustion chamber which allows for a symmetrical design for a 360° field of view. Our approach is to build an alternative fiber-based light sensor without the function of a spark plug, because if no ignition unit is installed, there is more space for additional optical elements for higher optical spatial resolution than conventional light sensors with ignition function. The main challenge is the miniaturization of the optical and mechanical set up. Due to the fixed position of the spark plug and the limited access to the combustion chamber, the light sensor must be inserted at an angle into the combustion chamber at a different location, so, the optical system must be asymmetric. This paper presents the results of the design and fabrication of a combustion chamber light sensor with respect to the optical and mechanical challenge of spatially resolved detection of light pulses in a combustion chamber of an engine under an oblique access to the combustion chamber.

This paper presents a novel readout for a μ-Coriolis mass flow sensor based on a differential optical reflective method, using a vertical-cavity surface-emitting laser (VCSEL) and two photodiodes (PD). The new readout detects change in applied mass flow rate by measuring the phase shift between the two photodiode signals. Such a setup offers a non-contact and robust sensing method. Measurements are presented for mass flow of DI-water up to 10 gram/hour resulting in a phase shift of 8.7 degrees.

MEMS (micro electro mechanical system) based piston mirror arrays are key elements for real time computer generated holograms (CGH) in visualisation technologies like virtual, augmented and mixed reality (VR/AR/MR). The EU funded Project REALHOLO is developing a spatial light modulator (SLM) that is based on comb drive MEMS actuators that can fulfil the tight requirements of the optical and mechanical performance and the high level of integration. A previous design already outlined perspectives for a superior performance in comparison to other approaches for high frequency and high precision wave front modulation, but has restrictions due to the resolution and feature size of the i-line lithography system used for manufacturing. This paper discusses the optimisation of the design applying an advanced manufacturing process using DUV lithography that allows smaller features and therefore offers additional design options. By introducing an improved comb drive geometry the electrostatic force was significantly increased, which allowed the optimisation of other geometries, like horizontal and vertical gaps and additional shielding structures, for an even more linear actuator response and reduced crosstalk. The electrostatic and structural FEM simulations will show the significant improvements in overall performance, compared to the previous iteration and other types of SLMs. The improved actuator can potentially extend the field of application from the desired automotive driver assistance holographic 3D display to head mounted displays for VR, AR and MR applications as well as other technologies like material processing.

The package of a Micro-Opto-Electro-Mechanical System (MOEMS), a Micro Mirror Array (MMA) based Spatial Light Modulator (SLM), has to stay stable over the full operation temperature range and throughout SLM lifetime in spite of the inevitably different coefficients of thermal expansion (CTE) of the various materials involved. Additionally, in our case the window not only protects the MMA from mechanical damage and corrosion but also serves an optical function as part of a beam combiner. Within the European Union funded Project REALHOLO we are therefore developing a packaging concept that accomplishes the desired optical functionality while meeting the challenge of precise alignment of the window relative to the micro mirrors in lateral direction, which is the motivating factor behind the FEM simulations presented here. The objective of this research is to stabilize the package when subjected to temperature changes by simulating its thermomechanical behaviour with Ansys Workbench^TM. A heatsink, a silicon crystal-based MEMS chip, and a window are glued together to form the package. Materials used for window and heatsink components, respectively, are chosen for a best possible CTE match. The significant parameters to be considered for package optimization are the misalignment between window and chip, the stress induced in the package, especially the glue, and the global deformation of the MMA surface. This paper discusses the challenges and possible solution based on a series of simulation findings.

Microelectromechanical system (MEMS)-based thermal emitter is a key component in an optical sensor to provide broadband emission at mid-infrared wavelengths, where a lot of molecules have their unique absorption profile. However, the thermal emission from a MEMS emitter is typically fixed at a specific spatial coordinate. In this work, a MEMS thermal emitter with piezoelectric actuation to realize active tuning is demonstrated. Thermal emission comes from a doped silicon layer acting as a resistive heater. Piezoelectric actuation is enabled by an aluminum nitride layer on a designed cantilever. The devices are fabricated on a complementary metal-oxide semiconductor (CMOS)-compatible process line. The fabricated thermal emitter at the tip of the cantilever generates broadband MIR thermal emission with spectrum peaked around 10 μm wavelength, and piezoelectric actuation with a displacement of more than 20 μm. The work paves the way towards self-adaptable MEMS directional emitter for various applications including chemical/gas sensing.

High resolution spectroscopy via tunable lasers usually requires CW operation with mode-hop-free wavelength tuning. To suppress mode hopping by laser resonator-length tuning, Fraunhofer IPMS developed a novel electrostatic non-resonant translational micromirror. The combination of this device with a MOEMS grating within an external-cavity MIR QCL results in a miniaturized module that meets the requirements of high-resolution spectroscopy. The translational micromirror features a 5-mm aperture, an arbitrary actuator stroke of up to 120 µm and multiple independent electrostatic actuators to compensate for tip or tilt up to 350 µrad. We compare characterization and FEA simulation data, demonstrating the unique characteristics and the operational capability for a variety of applications.

Miniaturized vectorial beam steering mirrors are required in numerous applications like (i) LIDAR, (ii) diagnostic imaging or (iii) miniaturized therapeutic laser systems. To increase simultaneously static tilt angle (≥ ±5°) and mirror aperture (≥ 3mm) electro-dynamic driven MEMS vector scanners, actuated by moving magnet drives, were developed. Here, Fraunhofer IPMS uses a hybrid MEMS concept combining its experience in the fabrication of monolithic silicon 2D MEMS scanning mirrors with existing know-how in MEMS micro-assembly technologies. Two designs of electro-magnetic driven vectorial 2D MEMS scanners are presented, (i) a non-gimbaled 2D vector scanner with 8 mm mirror aperture and ≥ ±2° quasi-static tilt angle and (ii) a 2D vector scanner with gimble suspended moving magnet drive. The gimbaled electro-magnetic MEMS scanner has a 5 mm large aperture and enables large quasi-static tilt angles of ±13° on both scan axis. Eigenfrequencies are 142 Hz (X) and 124 Hz (Y) allowing non-resonant vectorial scanning with speeds up to 100…400°/s. A step response time < 10 ms is achieved in closed loop control for both axes. This hybrid electro-magnetic MEMS approach significantly expands the parameter space of the previous monolithic electro-static scanners.

A translatory MOEMS actuator is presented, which enables a precise out-of-plane translatory oscillation of a 5mm mirror with 700 μm large stroke at 267Hz, when driven at 4V in parametric resonance. Due to significant gas damping operation in vacuum is needed. The minimum requirements on vacuum pressure (pmax ≥ 3.21 Pa, Q ≥ 1177) were determined experimentally. Therefore, the MOEMS are permanently encapsulated by means of a wafer-level-vacuum package. The hermetic sealing of MEMS WLVP (stack of 4 wafer 6”) was realized by glass-frit bonding (i) to be compatible to MEMS process AME75 and (ii) to avoid any (vertical) TWI. The ductile glass frit bond layer allows hermetic sealing also on non-ideal wafer topologies with height differences of several 100 nm. But high process temperatures of 435°C are required. Despite the high process temperatures (430°C needed for glass frit bonding) a sufficient static mirror planarity of ≤ λ/10 was achieved. The paper will discuss details of VWLP development and MEMS system integration. The longterm stability of 0.1 Pa inner vacuum pressure was successfully tested to be < 10a using a Ne fine leakage test. For system integration into a miniaturized FT-NIR spectrometer selected MEMS with minimal tilt were used. The NIR-FTS achieved a spectral resolution of 8.3 cm^-1 and SNR ≤ 8000 (with co-adding of 1000 spectra). The new translatory MEMS are very promising for compact FTS. The versatility and ruggedness of a MOEMS-FTS makes it ideal for process control in harsh environments (e.g. surveillance of fast chemical reactions).