This PDF file contains the front matter associated with SPIE Proceedings Volume 10931, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

This paper presents a new type of piezoelectric quasi-static mirror, which utilizes a three-level-construction comprising a mirror plate (diameter = 0.8 mm), a pillar and four actuators hidden beneath the mirror plate, reducing the chip size to 1.3 mm² . Special folded springs connecting the pillar and actuators are applied to reduce the mechanical non-linearity. Moreover, the newly developed piezoelectric material AlScN delivers large force enabling a mechanical tilting angle of ±12.5° at 150 VDC, as well as benefits like great linearity, repeatability and long-term stability. No angle change larger than 0.02° was observed during 100 on-and-off switching circles with 5 s intervals under 100 VDC. Long-term test over 76 hours under 100 VDC has shown maximum 0.1°shift. More precise measurements are ongoing. Based on the great linearity a simple closed-loop-control has also been developed and more results will be presented in the near future.

In future space missions for Universe and Earth Observation, scientific return could be optimized using MOEMS devices. Large micromirror arrays (MMA) are used for designing new generation of instruments. In Universe Observation, multi-object spectrographs (MOS) are powerful tools for space and ground-based telescopes for the study of the formation and evolution of galaxies. This technique requires a programmable slit mask for astronomical object selection; 2D micromirror arrays are perfectly suited for this task. In Earth Observation, removing dynamically the straylight at the entrance of spectrographs could be obtained by using a Smart Slit, composed of a 1D micro-mirror array as a gating device. We are currently engaged in a European development of micro-mirror arrays, called MIRA, exhibiting remarkable performances in terms of surface quality as well as ability to work at cryogenic temperatures. MMA with 100 × 200 μm² single-crystal silicon micromirrors were successfully designed, fabricated and tested down to 162 K. In order to fill large focal planes (mosaicing of several chips), we are currently developing large micromirror arrays to be integrated with their electronics. 1D and 2D arrays are built on wafer with Through Wafer Vias in order to allow routing of the device on wafer backside, foreseeing integration with dedicated ASICs. The yield of these devices as well as contrast enhancement have been successfully implemented.

Applications like computer generated holography or wavefront shaping call for spatial light modulators (SLMs) with millions of phase-shifting pixels of only a few micrometers size which are precisely addressable in an analogue way at frame rates of many kHz. While liquid crystal on silicon (LCoS) devices are commonly used, they can't offer very high frame rates and their polarization effect is often considered a drawback. On the other hand, MEMS devices with phaseshifting micro mirrors are not readily available but have a high potential to fulfill the requirements. It is quite challenging to reach the desired deflection range with the limited available addressing voltages. For symmetry usually at least two springs are squeezed into the tight space the small pixels offer. This paper presents an innovative way to get a good sensitivity by using a single hinge per pixel that therefore can be made especially weak. It might be astonishing but there actually are various ways to design electrostatic actuators that deliver pure piston movement with only one spring. We discuss the basic concepts of such force-balanced single spring actuators and give a variety of examples and guidelines to tune a basic pixel layout for pure piston motion. Simulations show the tilt-free response and the stability against tilting torques that might be the result of possible imperfections in manufacturing, like lithographical overlay errors or stress gradients. We also show the possibility to dynamically balance the pixel for a pure piston first eigenmode.

In this work we present a deeply-etched MEMS based swept ring laser source with enhanced performance. Performance enhancement is enabled by lensing the single mode (SM) input/output fibers of the MEMS tunable filter. An experimental comparison between the performance using graded-index (GRIN) lensed fibers and cleaved SM fibers in the MEMS-based swept laser system is presented. The GRIN lensed fiber produces a minimum waist radius of about 11.8 μm at 1550 nm, compared to 5 μm for the cleaved fiber. The experimental results show that the insertion loss of the MEMS filter is improved from -11.4 dB to -6.3 dB, while the filter 3-dB linewidth is improved from 9 nm to 5 nm when using the GRIN lensed-fibers. The corresponding threshold current of the swept laser is reduced from 70 mA to 52 mA and the output power is increased by 7.5 dB.

This paper presents a compact handheld gas analyzer, optimized for the multicomponent analysis of hydrocarbon gases, based on a micromachined, tunable Fabry-Pérot filter (μFPF) as a key element. The tuning range from 3.0 μm to 3.7 μm and spectral resolution of 30 to 40 nm (FWHM) cover a region of characteristic absorption of many combustible hydrocarbons and allow an accurate measurement of the concentration of each individual gas. The analyzer functions like a microspectrometer and outperforms the current state of the art for small gas detection handheld devices, using pellistors and NDIR-infrared detectors.

An innovative MEMS design with two movable reflectors is insensitive to acceleration forces. Due to the handheld application, especially the vibration response in the frequency range of 10 to 100 Hz was carefully characterized. An uncooled photodiode is integrated as fast detector, together with a transimpedance amplifier and a sapphire lens for light concentration. The photodiode is working in photovoltaic mode without supply voltage. In comparison to a photoresistor this gives the advantages of less power consumption and compatibility to explosion protection regulations.

A demonstrator was developed by designing a smart sensor module including complex analog and digital signal processing. Integrating this into a commercial, handheld, explosion-proofed Multi-Gas-Detector model results in a robust instrument, which enables field tests under harsh environmental conditions, typical for fire brigade missions. Spectral analysis of combustible gases (methane, ethane, propane and acetylene) is demonstrated with focus on safety-relevant LEL (lower explosion level) detection.

Miniaturized MEMS based spectrometers have attracted interest for mobile high volume applications. Performance parameters like resolution, stability and spectral range gain an increased attention for the comparison of different approaches in addition to the classical characteristics such as size and cost. The necessary resolution must be considered with the requirements of the spectral application in mind. For organic material analysis and similar tasks often resolutions around 10 nm have been regarded to be sufficient. Stability - here predominantly relevant is the wavelength scale - is important for the proper operation of the chemometric evaluation in the NIR range where overtone and combination bands have to be evaluated. Resonant scanner devices offer the opportunity to use simple position readout systems and gather accurate position information by tracking many cycles of the resonant movement.

The deflection of the scanning grating device used in this kind of MEMS based spectrometers becomes a limiting factor for extending the spectral range. By using a plain scanner mirror which illuminates a fixed grating and gathers the reflected radiance simultaneously the spectral range can be doubled applying the same MEMS deflection.

Furthermore, the wider spectral range can be supported by using two or more detectors with different spectral characteristics placed behind two or more separated exit slits. These slits could be integrated into the same MEMS chip like the scanner mirror device.

Several optical designs for miniaturized setups have been compared to find an optimized option which requires affordable optical components only. Here especially the two mirrors in the setup are relevant for a suitable spectrometer performance with acceptable effort. Finally a folded Czerny-Turner type setup has been chosen which can be integrated by the “place and bend” assembly.

A grating-based ultra-compact spectral sensor head was developed to overcome obstacles in characteristics, cost, and size, and it was designed for commercialization in large volume applications. More and more compact spectrometers have been brought to market in recent years—for example, those used for food and beverage quality tests based on measuring sugar content—but their spread is still limited because the conventional types don’t fully fulfill the market requirements. The ultra-compact spectral sensor’s characteristics have been improved while reducing cost and size. Its 20 nm wavelength resolution, equivalent to that of conventional compact spectrometers, was made possible by applying multiplex reflection and small collimation. Using nano-imprint technology, a grating was replicated onto a concave surface inside a compact surface-mount device package. On the opposite side of the concave grating, an entrance slit and a mirror that directs light onto the grating were directly formed on a high-sensitivity CMOS linear image sensor that is sensitive to the 640-1050nm range. The 15μm wide entrance slit was formed on the CMOS silicon chip using MEMS technology, and a short-wavelength cut filter was attached to the entrance window. By reducing the number of components, the structure was simplified. An ultra-compact package measuring 11.7mm × 4mm × 3.05mm and weighing about 0.3g is made possible while maintaining good characteristics and reasonable cost.

Air pollution is used to refer to the release of pollutants into the air, where these pollutants are harmful to the human health and our planet. The main source of these pollutants comes from energy production and consumption that release Volatile Organic Compounds (VOCs) such as BTEX and Aldehydes group. Real time monitoring of these VOCs in factories, stations, homes and in the street is important for analysis of the pollution sources fingerprint and for alerting, when exceeding the harmful limits. In this work we report the use of a MEMS FTIR spectrometer in the mid-infrared for this purpose. The spectrometer works in the wavelength range of 1.6 μm - 4.9 μm with a resolution down to 33 cm^-1. This covers the absorption spectrum of water vapour, BTEX, Aldehydes and CO₂ around 2.65 μm, 3.27 μm, 3.6 μm and 4.3 μm, respectively. The spectra of Toluene with different concentrations are measured, using a multipass gas cell with a physical length of 50 cm and an optical path length of 20 m, showing excellent sensor linearity. The minimum concentration measured is 350 ppb limited by the interference of the side lobes of the strong absorption of water vapour, which can be overcome in the future by humidity compensation. The SNR is measured and found to be 5000:1, corresponding to a detection limit of about 90 ppb. The achieved results open the door for a compact and low-cost solution targeting air pollution monitoring.

We present a forward-looking OCT probe featuring a piezoelectric tube actuated resonant fiber scanner providing a fieldof-view of up to 1.8 mm with a lateral resolution of 12 μm. The fully packaged final probe has a total length of 11.3 mm and an outer diameter of 4 mm. The probe is designed to operate in contact mode, and can further be shortened by more than 30%, if configured to operate at a distance from tissue. The scanning fiber bears at its tip a plano-convex imaging lens of 1 mm diameter and 0.6 mm focal length. The two components are assembled via an ultra-high-precision holder, fabricated by a two-photon polymerization based 3D printing tool. This method provides an alignment accuracy better than 1 μm along all axes of the scanning fiber, leading to a good control of both the imaging parameters and the scan pattern around the resonance peak. Furthermore, using a plano-convex lens instead of a GRIN lens provides the same optical functionality within a significantly shorter length and facilitates further miniaturization. Using this probe, we demonstrate 3D OCT measurements of standard calibration targets and in-vivo tissue measurements performed on human skin.

Fiber scanning for forward-view imaging method has been widely used in biomedical imaging. It also attracts great interest in the fields of virtual and augmented reality. In this study, we propose a fiber scanner actuated by a robust Cu/W electrothermal MEMS stage which can be driven quasi-statically. The Cu/W MEMS stage is successfully fabricated after overcoming Cu oxidization. Compared to previous Al/SiO₂ MEMS stages, this new Cu/W MEMS stage, which generates 0.7 mN forces at 1.8 V, offers three times more force. The MEMS stage can travel up to 53 μm at only 1.8 V. A single-mode fiber is assembled on the central platform of the MEMS stage to form a fiber scanner. The travel range can be amplified by four times.

Tunable diode lasers are an important tool for spectroscopy and as laser sources for a wide range of applications. In this paper, an improvement of External Cavity Diode Lasers (ECDLs) is presented. The present generation of ECDLs is designed as a laboratory instrument which is sensitive against ambient disturbance like shock, noise, and temperature fluctuations. In addition, state of the art ECDLs in Littrow and Littman/Metcalf configuration have limitations in terms of tuning range, tuning speed, and size. These technologically disadvantages make it difficult to use ECDLs for various applications. Therefore, we developed a new miniaturized mode-hop free tunable next-generation ECDL design based on a Micro Electro Mechanical System (MEMS) device. It includes the benefits of the current ECDL technology and allows an outstanding improvement in terms of efficiency, stability, repeatability and tuning range. Moreover, the tuning speed is increased into the kHz regime due to the fast nature of the tilting capabilities of the MEMS actuators. The focus will be set on the initial use of this new design in connection with semiconductor laser chips based on GaAs, InP, GaSb and IC. This makes it possible to cover a large area from the near-infrared up to the mid-infrared. Especially the midinfrared contains stronger absorption lines of significant gases, which are of great interest in the field of biomedicine, process control and environmental monitoring. The excellent performance of this innovative ECDL cavity design as well as the low noise promises better possibilities of gas detection for the previously mentioned applications.

We present the design of a non-volatile, bistable silicon photonic MEMS switch. The switch architecture builds on our previously demonstrated silicon photonic MEMS switch unit cell, using vertically movable adiabatic couplers. We here propose to exploit compressive stress in the movable polysilicon waveguides in a controlled manner, to intentionally displace the movable waveguides out of plane upon release. We design the waveguide suspensions to achieve close alignment with the fixed bus waveguide in the ON state, and positioning of the movable waveguide far from the fixed waveguide in the OFF state. Both ON and OFF positions are stable mechanically, without the need for maintaining an actuation voltage. In order to actuate the movable waveguide, we design vertical comb drive actuators that allow to commutate between both stable ON and OFF positions. Finite Element simulations predict electrostatic switch actuation with less than 30 V for compressive stress typically accessible in deposited polysilicon thin films. We validate the bistability mechanism by comparison with a representative experimental demonstrator. The demonstrator consists of a structured 100 nm poly-Si layer, deposited by chemical vapor deposition onto a thermally oxidized (1 μm) silicon wafer, exhibiting a compressive intrinsic stress of 275 MPa. Upon direct writing laser based photolithography, etching and final HF vapor release, the suspended structures bend into either stable position, and we measure a total buckling amplitude of 800 nm, sufficient to entirely de-couple the waveguides optically in the OFF state.

We propose a novel way of mechanical perturbation of photonic crystal cavities for on-chip applications. We utilize the equivalence of the 2D photonic crystals with perfect electric conductor (PEC) boundary conditions to the infinite height 3D counterparts for rod type photonic crystals. Designed structures are sandwiched with PEC boundaries above and below and the perturbation of the cavity structures is demonstrated by changing the height of PEC boundary. Once a defect filled with air is introduced, the metallic boundary conditions is disturbed and the effective mode permittivity changes leading to a tuned optical properties of the structures. Devices utilizing this perturbation are designed for telecom wavelengths and PEC boundaries are replaced by gold plates during implementation. For 10 nm gold plate displacement, two different cavity structures showed a 21.5 nm and 26 nm shift in the resonant wavelength. Optical modulation with a 1.3 MHz maximum modulation frequency with a maximum power consumption of 36.81 nW and impact sensing with 20 μs response time (much faster compared to the commercially available ones) are shown to be possible.

Recently developed tunable MEMS Fabry- Perot interferometers based on Ag thin-film mirrors[1] have enabled building highly miniaturized spectral imagers covering almost the complete VNIR wavelength range. The level of miniaturization required by modern smartphone industry has created extremely compact, high performance electronics and camera technologies and by utilizing these technologies together with the novel MEMS FPI’s, it is possible to create extremely compact spectral imagers while still achieving good performance. This paper presents a spectral imager design that can be fit inside an envelope of 1 cubic inch (25.4 × 25.4 × 25.4 mm³ ) and it will be capable of recording images at freely selectable wavelengths within the range of ca. 650 nm - 950 nm. The imager field of view is ca. 12.5° × 10° and the image size is 640 × 512 pixels. Nominally the imager will be focused from ca. 0.5 m to infinity, but with additional optics it is possible to use the imager as a microscope. The compact size of the imager allows the easy integration to almost any available platform, including small drones, nanosatellites or planetary rovers, where small size is essential. It is also possible to integrate the imager to handheld devices, so the potential field of applications will be extensive.

Real-time sensing of 3D geometric information is essential for autonomous vehicles and robots for detection of obstacles and environment. In most case of autonomously maneuvering robots, the relative motion of 3D sensor and the target object is involved so that accurate 3D geometry, as well as the relative velocity, need to be acquired for safe operation. In this paper, a small form-factor scanner-based 3D sensing system and operating architecture, so-called homodyne mixing method and its experimental verification are presented. Special attention is put on the accuracy improvement with small size realization under relative motion between sensor and objects in the application to autonomous working robots operating under various working environment. In the homodyne mixing method, as the working principle, phase delay induced by the time-of-flight of the amplitude-modulated light wave flying between camera and object is indirectly measured.¹ The homodyne mixing method has less computational and hardware complexity than other 3D sensing methods and it is robust to external light and has advantages in miniaturization. However, the homodyne mixing method is sensitive to the relative movement between the sensor and targeting object because it uses continuously modulated light wave. In this paper, an improved light processing methodology is established to tackle this weakness in a moving situation. The presented light processing methodology is robust to the relative movement and has the advantage to control the measurement precision of 3D depth information through variable scanning FOV (Field of View). As the application of suggesting a 3D sensing device and system to recognition in the robot system, we propose a geometry recognition method that extracts typical geometric features of objects from point-cloud data obtained from the 3D sensor. The result shows that the recognition of the geometry of an object is quick and accurate more than previous recognition technology using only an RGB color image.² By combining the sensor system and object geometry recognition method, we can provide the solution of the 3D object recognition system for autonomous robot operating in an undetermined environment. The experimental verification is presented for the evaluation of the 3D sensing system.

Eyes of insects in the nature have been evolved in assorted structures according to the place of residence, hours of living, or the way of perception. The structure of the insect eye not only has different composition that dissolve the incoming light according to its direction of origin, i.e., an apposition and a superposition eyes, but also has a wide field-of-view (FOV), a high spatial resolution, and a sensitivity. Conventional artificial compound eye cameras have limited features that only focus on one of the characteristics of the insect eye, such as lens diameter and lens barrel length. We report an optically adjustable ultrathin arrayed camera, which adjusts the FOV, lens diameter and focal length independently. The ultrathin arrayed camera consists of UV-curable resin based microlens array on CMOS image sensor and each lens is surrounded by a liquid-filled blocking layer to reduce optical cross-talks between neighboring lenses. Fabrication of the arrayed lens includes photolithography process of Au/Cr metal pattern on frontside and Cr pattern on backside of borosilicate glass. Each of the lenses are replicated from microhole arrays fabricated by isotropic wet etching of the borosilicate glass with HF (49%) etchant. The arrayed camera has adjustable lens diameter and curvature by etching time control and SU-8 post thickness control during photolithography. Fingerprint image was successfully obtained by an image processing from individual optical channels. This ultrathin arrayed camera will suggest a new approach to the development of light-filled camera and compact ultrathin camera in the medical, industrial, or military fields.

We report on a concept of a benchtop microscope for routine applications. This concept system transfers key features of a high-end laser scanning microscope to a dedicated confocal fluorescence imaging system with appropriate footprint and reduced systems complexity. The optical beam path is specifically designed for the purposes of confocal imaging leading to a short beam path length that fulfills the footprint requirements. The system allows an optical 3D scanning through the sample of up to 100 depths of focus without moving the sample. The scanning unit consists of a 2D MEMS scanning mirror spanning and a deformable mirror forming 3 virtual scanning axes. For a compact integration of the detection beam path, a confocal detector with an actuated MEMS pinhole was developed to adjust the optical sectioning. The selected light sources are directly modulated lasers operating at wavelengths that are frequently used for fluorescence imaging in life science applications. To provide a simple interface to almost any user’s hardware such as laptops or tablets, the systems architecture for real time control and data acquisition is based on a FPGA.

An updated Programmable Light System (PLS) is demonstrated using a MEMS Mirror Module (MMM), allowing users to program the brightness and shape of a projected white light in a variety of dynamic solid-state lighting applications, e.g. in automotive dynamic headlights. The MMM is a new module which consists of a fast beam steering MEMS mirror with high optical laser power handling and a smart MEMS Driver with real time monitoring of the MEMS mirror for better system safety and mirror control. The PLS consists of the MMM, a multi-Watt 445-450nm laser source with beam shaping optics, a phosphor target, and projection optics to project a white light within the field of view of up to 60°. Devices such as the 1.2mm diameter A3I12.2 and 2.0mm diameter A7M20.1 aluminum coated mirror have been tested at >8W of CW power before seeing any damage to the device. The A7M20.1 MEMS mirror has been extensively tested (>100 hours) with 4W of CW power at room temperature with no physical damage. Same 4W operation, has also been successfully tested at elevated environmental temperature of 100°C during extended tests.

PLS prototypes to date utilize only ~1W-2W laser diode sources, as limited by power of available laser diodes. The extended tests and thermal studies of the MMM however show that operation at up to 100°C with e.g. 4W CW power could be safely run for at least 10000 hours, even with MEMS mirrors with a simple aluminum coating (no protection or enhancement layers).

This paper reports a new micromachined two-axis water-immersible micro scanning mirror using BoPET (biaxiallyoriented polyethylene terephthalate) hinges. A new fabrication process based on lithography, wafer-bonding, and reactive ion etching on a hybrid silicon-polymer substrate was developed to enable high-resolution patterning, miniaturization and also batch fabrication capability. For demonstration, a prototype scanning mirror was designed, fabricated and tested. Its overall size was reduced to 5×5×5 mm³, which is comparable to that of a typical siliconbased micro scanning mirror. The testing results show good raster scanning performance. This approach could enable the miniaturization and batch fabrication of water-immersible scanning mirrors for different scanning optical and acoustic imaging applications in liquid environments.

Optical cavities have many applications in optical telecommunications and sensing. The microcavities enabled by MEMS technology are able to achieve ultra-compact devices for different functionalities including filtering, refractometry, spectroscopy, biomedical optics and atomic studies. For most of these applications, the cavity has to be large enough for the insertion of the sample under test while still providing adequate quality factor over a wide spectral range. In this work we present an optical microcavity with improved optical performance using novel curved slotted micromirrors. The slotted mirrors enable an ultra-wide spectral range extending from the visible range to theinfrared range. The curved slotted mirrors, rather than the flat ones, improve the optical performance in terms of the side mode suppression ratio and3-dB spectral width. The microcavity is fabricated using deep reactive ion etching on silicon wafer with 140 µm etching depth optionally followed by metal sputtering on the mirrors sidewall to improve its reflectivity. The spacing between the two slotted mirrors is 140 µm enabling micro-fluidic tubes or fluid samples to be inserted in the cavity. The performance of the optical resonator is experimentally verified in the infrared region around 1550 nm wavelength. The curved mirrors improved the rejection ratio to about 20 dB compared to the about 3 dB for the flat mirrors, while the quality factor is close to 1000. The shift in the response of the resonator acting as a refractometer is measured due to the insertion of toluene in the micro tube. The presented structure opens the door for biological analysis on chip over wide spectral range.

As it is well-known, the laser radiation, propagated through different mediums, is affected by wavefront distortions and thus the quality of the radiation is significantly decreased. To compensate for the wavefront aberrations adaptive optics means are used. We developed miniature bimorph mirror with 37 electrodes. To manufacture this type of mirrors two technologies were used. Those are laser engraving technology for drawing electrode grid on the piezoceramic disc, and ultrasonic welding technology to connect wires to the control electrodes. Main parameters of such a deformable mirror were investigated and presented in this paper.

Miniaturized spectrometry systems are achievable e.g. by the use of MEMS based tunable Fabry-Pérot Interferometers (FPI) as wavelength selective filter elements. Main part of a FPI is the reflector which is usually realized as a stack of alternating dielectric layers with high and low refractive index. To achieve high reflectance layer stacks with larger number of layers and/or layers with a higher refractive index contrast are needed. Both have to be integrated within the manufacturing processes chain which in practice proves to be a difficult process.

We present a FPI with a (TiO₂/SiO₂)³ reflector stack with a reflectance of 97 % and TiO₂ as high refractive index layer for the use in the VIS-range of 555 nm to 585 nm. Main achievements of TiO₂ instead of Si₃N₄ are a higher reflectance and a minimized reflector complexity. Furthermore, we introduce a dry etch process which is compatible and integrated in the manufacturing process chain of the MEMS FPI.

Manufacturing of the 7.5 mm x 7.5 mm chip size FPI is done on 6" wafers consisting of a moveable reflector on a 210 nm thin and 5 mm in diameter LP-Si₃N₄ membrane and a fixed reflector with an aperture of 2 mm in diameter. The measured peak transmittance is between 28 % and 37 % with a FWHM bandwidth between 1.5 nm and 1.8 nm. It could be shown that the FPIs are tunable over the spectral range from 555 nm to 585 nm with a maximum control voltage of 45 V using the 18th interference order.

The place and bend assembly can be used for the integration of optical systems. Miniaturized setups can be realized using well-established 2D pick and place tools for the component assembly. Afterwards the 3D body and the optical path inside - even complex off-axis designs - can be realized by bending the substrate along preprocessed bending lines in the substrates.

The combination of mechanical and optical properties of the substrate material are highly important for the integration and the intended operation. The bending process must not affect the shape of the substrate itself in an undesired way. The optical properties are relevant for the accurate operation. In turn the body parts must be sufficiently nontransparent in the entire range, stray light from surface scattering should be low and fluorescence must be absent.

The mechanical and optical properties of materials for 3D printed substrates have been investigated. 3D printing offers favorable options for development, prototyping and small to medium volume production. 3D printing is characterized by low initial cost, availability and material selection. Several options for 3D printed material have been considered and investigated. Besides the material properties also the overall accuracy resulting from different process option for 3D printing are relevant for the future applications.

Perforated periodic nanostructures (i.e. nanohole arrays) have become of great alternatives for transmissive structural coloration due to high transmission efficiency and high sensitivity upon incident angles. However, structural colors of conventional periodic nanostructures inevitably exhibit a substantial color-crosstalk due to the multiple resonances. Our previous work (M.-S. Ahn et al., nanoscale) had already reported that the complementary plasmonic structures (CPS) effectively attenuate the high-order resonances, and thus improve color-purity in the range from VIS (red) to NIR. In this work, we successfully demonstrated transmissive structural coloration with high color-purity in fully visible ranges by using inverted CPS (iCPS) of aluminum (Al) nanoholes and nanodisks. Unlike previous Ag CPS, the Al iCPS features inverted configuration of suspended nanoholes and buried nanodisks by high refractive index (polyurethane acrylate; PUA) substrate, which blue-shifts the resonances of Al nanoholes and redshifts the extinction dip of Al nanodisks. As a result, carefully engineered extinction dip effectively suppresses the first-order resonance of Al nanoholes, and thus iCPS exhibit a pure visible-coloration with a single resonance, depending on the incident angles. iCPS were nanofabricated by UV nanoimprinting lithography (UV-NIL) and thermal evaporation of aluminum, which enables uniform nanopattering with inch scale. Polyurethane acrylate (PUA) was used for a substrate due to its high refractive index and UV-curable property. After the replication of nanohole patterns into PUA, aluminum was evaporated on PUA nanohole substrate. Then the Al nanoholes are formed on top surface of PUA and Al nanodisks are buried in PUA nanohole. Structural coloration of iCPS provides a new direction for a tunable optical filter that highly requires tunability and selectivity.

In this paper, we demonstrate a compact Silicon photonics-based on-chip integrated interference vibrometer. Unlike conventional readout methods, the demonstrated system is alignment-free and offers multiplex sensing. The intensity that is modulated by the cantilever motion by a photodetector. We present the static and dynamic response of the cantilever by electrostatic excitation validated using ac commercial Laser-Doppler-Vibrometer. We also present a detailed simulation, optimisation and sensitivity analysis of the proposed on-chip vibrometer. Furthermore, the tunability of the sensor to achieve maximum sensitivity is demonstrated.

Photoacoustic (PA) spectroscopy is among the most sensitive techniques used to monitor chemical emission or detect gas traces. In the mid-infrared, where most of gases of interest have their strongest absorption lines, this technique takes advantage of the high optical power and room temperature operation of quantum cascade lasers (QCL). We have recently demonstrated that centimeter-size PA cells can compete, with bulky commercial systems for gas sensing without any compromises on performances. We demonstrate a new step towards cost reduction, extreme integration, and mass deployment of such PA sensors with a miniaturized silicon PA-cell fabricated on standard CMOS tools. The design, fabrication and characterizations of this new sub-centimeter PA cell built on a silicon platform are presented. First, the component has been designed using a detailed physical model, accounting for viscous and thermal losses, and metamodel-based optimization techniques. Second, it has been fabricated on our 200 mm CMOS pilot line. Several wafers have been released and diced. Single chips have then been assembled with commercial capacitive microphones and finally characterized on our reference gas bench. The photoacoustic simulations and the acoustics experiments are in a good agreement. The tiny PA cell exhibits a sensitivity down to the ppm level for CO₂ at 2300 cm^-1, as well as for CH₄ at 3057 cm^-1 even in a gas flow. Taking advantage of the integration of QCLs on Si and photonic circuitry, the silicon PA cell concept is currently being extended towards a fully integrated multigas detector.

The Fabry-Perot interferometers (FPI) are essential components of many hyperspectral imagers (HSI). While the Piezo-FPI (PFPI) are still very relevant in low volume, high performance applications, the tunable MOEMS FPI (MFPI) technology enables volume-scalable manufacturing, thus having potential to be a major game changer with the advantages of low costs and miniaturization. However, before a FPI can be utilized, it must be integrated with matching optical assembly, driving electronics and imaging sensor. Most importantly, the whole HSI system must be calibrated to account for wide variety of unwanted physical and environmental effects, that significantly influence quality of hyperspectral data. Another challenge of hyperspectral imaging is the applicability of produced raw data. Typically it is relatively low and an application specific software is necessary to turn data into meaningful information. A versatile analysis tools can help to breach the gap between raw hyperspectral data and the user application. This paper presents a novel HSI hardware platform that is compatible with both MFPI and PFPI technologies. With an MFPI installed, the new imager can have operating range of λ = 600 - 1000 nm with FWHM of 15 - 25 nm and tuning speed of < 2 ms. Similar to previous imager in Ref. 1, the new integrated HSI system is well suited for mobile and cloud based applications due to its small dimensions and connectivity options. In addition to new hardware platform, a new hyperspectral imaging analysis software was developed. The new software used in conjunction with the HSI provides a platform for spectral data acquisition and a versatile analysis tool for a processing raw data into more meaningful information.

More and more small spectrometers have been brought to market in recent years. Compactness is certainly a necessary feature for spectrometers used in the field, but keeping the detection capability sufficiently high is also key to fulfilling application requirements. Using MOEMS technologies, we developed an FTIR engine for field use that is both compact and has good detection capability. The FTIR engine measures 59mm x 28mm x 35mm and weighs about 130g. Although compact, it has a signal-to-noise ratio (SNR) higher than 40 dB, a light efficiency higher than 15%, and sensitivity from 4000 to 8500 cm^-1. This new FTIR engine has a φ3mm MEMS movable mirror formed on a Si wafer surface to enhance light utilization. The MEMS actuator is driven with an amplitude of 125 micrometers orthogonal to the surface. A fixed mirror was formed on the 4.4mm thick compensating plate through metal deposition. A miniature MEMS mirror device measuring 21mm x 14mm x 4.8mm was fabricated, which integrates the movable mirror and fixed mirror by direct bonding. A 4.4mm thick trapezoidal prism beam splitter was placed on the MEMS device, and it combines two light arms reflected in the same direction to obtain interferograms with an InGaAs PIN photodiode. In addition, a VCSEL was integrated in the housing of the FTIR engine to monitor the driving mirror position.

Novel concepts of on-chip Fourier transform spectrometers is proposed. The principal element in the spectrometer is semiconductor waveguide directional couplers. The optical path difference can be tuned by varying the coupling length or influencing the propagation mode of the directional coupler. Solutions of both these two methods are proposed, and the theories are verified by spectra recovering. They function well around 1.5 μm wavelength. Further enhancement can be achieved by cascading more stages of directional couplers or extending the coupling length. This design meets the requirement of small size, weight and power and may be useful in future on-chip spectroscopic sensors.

Infrared portable spectral sensors are greatly required for rapid and simultaneous analysis of material composition; triggering new applications in the domain of on-site spectroscopy. At the same time, miniaturization of Fourier transform infrared (FTIR) spectrometers based on the silicon technology has been proven to be one of the most promising approaches for wide spectral range applications. In this work, we present a fiber-free MEMS FTIR spectrometer working in the wavelength range of 1.8 μm to 6.8 μm (5500-1470 cm^-1). The spectrometer is based on the use of a monolithically integrated scanning Michelson interferometer, assembled with external reflecting micro-optical part, which is responsible for light coupling to and from the MEMS chip. The measured signal-to-noise ratio of the spectrometer is larger than 5000:1 with a spectral resolution of 66 cm^-1. The experimental results of measuring the transmission of a polystyrene reference calibration film show four absorption peaks in the Mid Infra-Red (MIR) range at 3.27, 3.5, 5.15, 6.24 μm in close agreement with theoretical predictions.

The “MEMS-in-the-lens” active lens for a laser scanning microscope comprises a high numerical aperture front element, a 3D+ MOEMS beam scanner and a collimating back lens. The scanner utilizes a silicon gimbal with SU-8 polymer flexures and deformable membrane mirror. The mirror aperture is 4 mm in diameter, and is capable of 9 μm deflection for focus control, with four annular electrodes to allow tuning of primary and secondary spherical aberration. The gimbal supports tip/tilt actuation up to ±3° for lateral beam scanning. We show confocal imaging using a benchtop mockup of the active lens, illustrating the potential for this approach to support 3D microscopy for optical biopsy applications.

Photoacoustic endoscopy (PAE) is an exciting new tool specifically for many endoscopic diagnosis. We present a miniature all-optical probe that enables forward-view PAE without using a scanner. The probe utilizes an imaging fiber bundle and a gradient-index (GRIN) objective lens for delivery, focusing, and scanning of excitation laser pulses. Due to the fixed spatial relationship between the entrance and the output of the imaging fiber bundle, the laser scanning can be implemented on the proximal end face, and coherently transferred to the distal end face. The output light from the imaging fiber bundle is then focused by the GRIN objective lens, which results in an enlarged field of view (FOV) and working distance. For acoustic detection, a fiber-optic Fabry-Perot sensor is integrated to detect the generated acoustic waves from a wide field. The outer diameter of the PAE probe is 2.4 mm. The forward-view endoscopic imaging is presented to show the imaging capability of the PAE probe. The results show that our PAE probe is capable of forward-view photoacoustic imaging with high resolution (7.8−10.4 μm) and wide FOV (>3.5 mm).

Three-dimensional (3D) endoscopes provide depth information and help determining the surgical sites more accurately. Among the conventional 3D endoscopic techniques, efforts on implementation of structured illumination method into 3D imaging system was actively made due to the potential of light environmental robustness and miniaturization. However, structured illumination methods are suffering from the low resolution, which is affected by the light patterns density and uniformity with minimized projector. In this work, we demonstrate switchable pattern projector module using rotational offsets of double microlens arrays (MLAs) for 3D endoscopic imaging with structured illumination method. The pattern projector module includes diffractive optical element part of double MLAs with rotational offsets for double diffraction pattern generation and the switchable light source part of fiber bundle comprised of the GRIN fiber for collimating laser at the center and other surrounding fibers for white-light illumination. The double MLAs was fabricated using double-sided photolithography on 4-inch borosilicate wafer, thermal reflow with hydrophobic nano film, and parylene-c coating. The period, curvature and rotational offset angle of double MLAs were determined to have high density and uniformity of the projected dot array patterns. The calculated disparity map of non-textured 3D object showed increase on resolution and robustness on surrounding light environment compared to the disparity map with stereoscopic imaging method. The 3D imaging system using the projector module can provide depth information with miniaturized system and lead to various applications for medical imaging as well as other imaging applications in industrial and military fields.

To improve the feasibility of endoscopic inspection processes we developed a system that provides online information about position, orientation and viewing direction of endoscopes, to support the analysis of endoscopic images and to ease the operational handling of the equipment. The setup is based on an industrial endoscope consisting of a camera, various MEMS and multimodal data fusion. The software contains algorithms for feature and geometric structure recognition as well as Kalman filters. To track the distal end of the endoscope and to generate 3D point cloud data in real time the optical and photometrical characteristics of the system are registered and the movement of the endoscope is reconstructed by using image processing techniques.

To achieve optical biopsy for gastro-intestinal (GI) endosopy with the use of nonlinear optical (NLO) endomicroscopes, integration of NLO technology with the design of a conventional flexible GI endoscope is necessary. One key challenge has been to design an NLO distal tip which can be compatible with flexible GI endoscopy retroflexion curvature radius as small as 20 mm to provide bending angle up to 210 degrees; the state-of-the-art NLO miniaturized design still consists of a long rigid “needle” shape probe at the distal end that can be damaged during the retroflex procedure when passing through the instrument channel of a flexible GI endoscope for in vivo imaging. To circumvent this design challenge, authors present a line scan multiphoton endomicroscope utilizing a novel simplified microelectromechanical systems (MEMS) scanner. This unique MEMS scanner consists of a customized single-axis dichroic MEMS scanner (SADMS) and vibrates at the back focal point of a customized micro-objective lens. This work demonstrates the new NLO scanner design can be compatible with conventional flexible GI endoscope to offer in situ functional microscopic imaging capability.

Accurate modeling of MOEMS mirrors is crucial for their design and fabrication, as well as for proper control within its target applications. This paper proposes a novel identification method using a generalized nonlinear SDOF model of an electrostatically actuated 1D resonant MOEMS mirror solely based on measured scanning trajectories and the current generated by the movement of the comb-drive electrodes. The nonlinear stiffness and damping are identified from a decay measurement while the comb-drive torque and the rotor inertia are derived from an actuated decay measurement, where a constant voltage is applied. The simulation with the identified parameters closely matches the measured frequency response including bifurcations and hysteresis. Furthermore a period-based modified index of agreement is proposed for nonlinear systems showing values of over 0.995 at each period along the decay.