This PDF file contains the front matter associated with SPIE Proceedings Volume 9760, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Micro scanning mirrors that can operate reliably under water is useful in both ultrasound and photoacoustic microscopic imaging, where fast scanning of focused high-frequency ultrasound beams is desired for pixel-by-pixel data acquisition. This paper reports the development of a new micro-fabricated water-immersible scanning mirror with a small form factor. It consists of an optically and acoustically reflective mirror plate, which is supported onto two flexible polymer hinges and driven by an integrated electromagnetic micro-actuator. It can achieve one-axis scanning of ±12.1° at a resonant frequency of 250Hz in air and 210Hz in water, respectively. By optimizing the design and enhancing the fabrication with high-precision optical 3D printing, the overall size of the scanning mirror module is less than 7 mm × 5 mm × 7 mm. The small form factor, large scanning angle, and high resonant frequency of the new water-immersible scanning mirror make it suitable for building compact handheld imaging probes for in-vivo high-speed and wide-field ultrasound and photoacoustic microscopy.

Fast scanning is highly desired for both ultrasound and photoacoustic microscopic imaging. Limited by water environment required for acoustic propagation, traditional mircoelectromechanical system (MEMS) scanning mirrors could not be widely used. In this paper, a new water-immersible scanning mirror microsystem has been designed, fabricated and tested. Polymer hinges were employed to achieve reliable under water performance. Two pairs of high strength neodymium magnet disc and three compact RF choke inductor were used to actuate mirror module. Experimental results show that the fast axis can reach a mechanical scanning angle of ±15° at the resonance frequency of 350 Hz in air, and ±12.5° at the resonance frequency of 240 Hz in water, respectively. The slow axis can reach a mechanical scanning angle of ±15° at the resonance frequency of 20 Hz in air, and ±12.5° at the resonance frequency of 13 Hz in water, respectively. The two scanning axes have very different resonance frequencies, which are suitable for raster scanning.

In this talk, we present the various types of 3D displays, head-mounted projection displays and wearable displays developed in our group using MEMS scanners, compact RGB laser light sources, and spatial light modulators.

Two new technological process flows for the piezoresistive position detection of resonant and quasistatic micro scanning mirrors were developed to increase sensitivities by a factor of 3:6 compared to former sensors, improve signal to noise ratio of the sensor signal and to allow controlled feedback loop operation. The sensor types use differently doped and deposited silicon. One is based on single crystal silicon with a pn-junction to isolate the active sensor area from the device layer silicon, the other one is based on a deposited and structured polysilicon. The sensor characteristics are compared including light, temperature dependence and reliability results.

One- and two-dimensional MEMS scanning mirrors for resonant or quasi-stationary beam deflection are primarily known as tiny micromirror devices with aperture sizes up to a few Millimeters and usually address low power applications in high volume markets, e.g. laser beam scanning pico-projectors or gesture recognition systems. In contrast, recently reported vacuum packaged MEMS scanners feature mirror diameters up to 20 mm and integrated high-reflectivity dielectric coatings. These mirrors enable MEMS based scanning for applications that require large apertures due to optical constraints like 3D sensing or microscopy as well as for high power laser applications like laser phosphor displays, automotive lighting and displays, 3D printing and general laser material processing. This work presents modelling, control design and experimental characterization of gimbal-less MEMS mirrors with large aperture size. As an example a resonant biaxial Quadpod scanner with 7 mm mirror diameter and four integrated PZT (lead zirconate titanate) actuators is analyzed. The finite element method (FEM) model developed and computed in COMSOL Multiphysics is used for calculating the eigenmodes of the mirror as well as for extracting a high order (n < 10000) state space representation of the mirror dynamics with actuation voltages as system inputs and scanner displacement as system output. By applying model order reduction techniques using MATLABR a compact state space system approximation of order n = 6 is computed. Based on this reduced order model feedforward control inputs for different, properly chosen scanner displacement trajectories are derived and tested using the original FEM model as well as the micromirror.

This paper presents the application of a real-time closed-loop control for the quasistatic axis of electrostatic micro scanning mirrors. In comparison to resonantly driven mirrors, the quasistatic comb drive allows arbitrary motion profiles with frequencies up to its eigenfrequency. A current mirror setup at Fraunhofer IPMS is manufactured with a staggered vertical comb (SVC) drive and equipped with an integrated piezo-resistive deflection sensor, which can potentially be used as position feedback sensor. The control design is accomplished based on a nonlinear mechatronic system model and the preliminary parameter characterization. In previous papers [1, 2] we have shown that jerk-limited trajectories, calculated offline, provide a suitable method for parametric trajectory design, taking into account physical limitations given by the electrostatic comb and thus decreasing the dynamic requirements. The open-loop control shows in general unfavorable residual eigenfrequency oscillations leading to considerable tracking errors for desired triangle trajectories [3]. With real-time closed-loop control, implemented on a dSPACE system using an optical feedback, we can significantly reduce these errors and stabilize the mirror motion against external disturbances. In this paper we compare linear and different nonlinear closed-loop control strategies as well as two observer variants for state estimation. Finally, we evaluate the simulation and experimental results in terms of steady state accuracy and the concept feasibility for a low-cost realization.

This paper reports on the progress related to a multichannel photonic alignment concept, which aims to achieve submicrometer alignment of the waveguides of two photonic integrated circuits (PICs). The concept consists of two steps: chip-to-chip positioning and fixing provide a coarse alignment after which waveguide-to-waveguide positioning and fixing result in a fine alignment. For the waveguide-to-waveguide alignment, mechanically flexible waveguides are used. Positioning of the waveguides is performed by integrated MEMS actuators. The flexible waveguides and the actuators are both integrated in one of the PICs. This paper reports on the fabrication and the mechanical characterization of the suspended waveguide structures. The flexible waveguide array is created in a PIC which is based on TriPleX technology, i.e. a silicon nitride (Si₃N₄) core encapsulated in a silicon dioxide (SiO₂) cladding. The realized flexible waveguide structures consist of parallel cantilevered waveguide beams and a crossbar that connects the free ends of the waveguide beams. The fabrication of suspended structures consisting of a thick, i.e. 15 µm, TriPleX layer stack is challenged by the compressive mean stress in the SiO₂. We have developed a fabrication method for the reliable release of flexible TriPleX structures, resulting in a 96% yield of cantilever beams. The realized suspended waveguide arrays have a natural out-of-plane deformation, which is studied using white light interferometry. Suspended waveguide beams reveal a downward slope at the base of the beams close to 0:5_. In addition to this slope, the beams have a concave upward profile. The constant curvature over the length of the waveguide beams is measured to range from 0:2 µm to 0:8 µm. The profiles measured over the length of the crossbars do not seem to follow a circular curvature. The variation in deflection within crossbars is measured to be smaller than 0:2 µm.

Photonic crystal split-beam nanocavities allow for ultra-sensitive optomechanical transductions but are degraded due to their relatively low optical quality factors. We report our recent work in designing a new type of one-dimensional photonic crystal split-beam nanocavity optimized for an ultra-high optical quality factor. The design is based on the combination of the deterministic method and hill-climbing algorithm. The latter is the simplest and most straightforward method of the local search algorithm, which provides the local maximum of the chosen quality factors. This split-beam nanocavity is made up of two mechanical uncoupled cantilever beams with Bragg mirrors patterned onto it and separated by a 75 nm air gap. Experimental results emphasize that the quality factor of the second order TE mode can be as high as 19,900. Additionally, one beam of the device is actuated in the lateral direction with the aid of a NEMS actuator and the quality factor maintains quite well even there’s a lateral offset up to 64 nm. We also apply Fano resonance to further increase the Q-factor by constructing two interfering channels. Before tuning, the original Q-factor is 60,000; it’s noteworthy that the topmost Q-factor reaches 67,000 throughout out-of-plane electrostatic force tuning. The dynamic mechanical modes of two devices is analyzed as well. Potentially promising applications, such as ultra-sensitive optomechanical torque sensor, local tuning of fano resonance, all-optical-reconfigurable filters etc, are foreseen.

Many application fields of infrared spectroscopy require small, robust and transportable spectrometers, which are considerable less costly than existing products. Therefore microspectrometer technologies are rapidly emerging and many research groups spend effort on this. Compared to other kinds of devices, micromachined tunable Fabry-Pérot filters are best suited in terms of miniaturization and optical throughput. This paper gives a review of μFP filters for infrared spectroscopy. Different approaches from several groups are compared. Optical performance parameters like wavelength tuning range, spectral resolution and aperture size as well as complexity of fabrication and costs are discussed.

Profound developments of miniaturized spectrometry systems enable new breakthrough applications such as online monitoring systems for specific molecules by Surface Enhanced Raman Spectroscopy (SERS). The spectrometry system is based on SERS active surfaces in-situ generating nanoparticles and miniaturized detectors with tunable Fabry-Pérot- Interferometers (FPI) with very sharp transmission peaks and a FWHM bandwidth below 2 nm. The key part of this online monitoring system is a tunable FPI, which is fabricated with MEMS technology. This contribution presents a 7.5 x 7.5 mm² chip size FPI, consisting of a moveable reflector on a 210 nm thin and up to 5.5 mm in diameter Si3N4 membrane on a silicon carrier, and a fixed reflector on glass. The optical resonator with an aperture of 2 mm diameter is designed for the central wavelength of 570 nm and realized by adhesive SU-8 bonding of the silicon on glass substrate. The moveable Si3N4 membrane is fabricated by combined wet and dry etching of silicon. The dielectric (HL)4 Si3N4/ SiO2 reflector stack with a reflectance of 93 % is deposited by PE-CVD on the LP-CVD-Si3N4 and structured by dry etching on the membrane and the glass. The measured peak transmittance is between 52 % and 74 % with a FWHM bandwidth between 1.3 nm and 2.0 nm. It was shown, that the FPIs are tunable over the spectral range from 555 nm to 585 nm which is relevant for this SERS application with a tuning voltage of 25 V.

In this work we report a novel optical MEMS deeply-etched mirror with metallic coating and vertical slot, where the later allows reflection and transmission by the micromirror. The micromirror as well as fiber grooves are fabricated using deep reactive ion etching technology, where the optical axis is in-plane and the components are self-aligned. The etching depth is 150 μm chosen to improve the micromirror optical throughput. The vertical optical structure is Al metal coated using the shadow mask technique. A fiber-coupled Fabry-Pérot filter is successfully realized using the fabricated structure. Experimental measurements were obtained based on a dielectric-coated optical fiber inserted into a fiber groove facing the slotted micromirror. A versatile performance in terms of the free spectral range and 3-dB bandwidth is achieved.

In this work we report, for the first time to the best of our knowledge, a bulk-micromachined wideband MEMS-based spectrometer covering both the NIR and the MIR ranges and working from 1200 nm to 4800 nm. The core engine of the spectrometer is a scanning Michelson interferometer micro-fabricated using deep reactive ion etching (DRIE) technology. The spectrum is obtained using the Fourier Transform techniques that allows covering a very wide spectral range limited by the detector responsivity. The moving mirror of the interferometer is driven by a relatively large stroke electrostatic comb-drive actuator. Zirconium fluoride (ZrF₄) multimode optical fibers are used to connect light between the white light source and the interferometer input, as well as the interferometer output to a PbSe photoconductive detector. The recorded signal-to-noise ratio is 25 dB at the wavelength of 3350 nm. The spectrometer is successfully used in measuring the absorption spectra of methylene chloride, quartz glass and polystyrene film. The presented solution provides a low cost method for producing miniaturized spectrometers in the near-/mid-infrared.

In this work, we present a novel architecture for Fourier transform spectrometers based on cascaded low-finesse FP interferometers. One of the interferometers has fixed path length while the second is a scanning one using a relatively large stroke electrostatic comb-drive actuator. The fixed interferometer results in a spectrum modulation and, hence, a shifted version of the interferogram away from the point of the zero spacing between the two mirrors. The shifted interferogram can then be used with the Fourier transform algorithm to obtain the spectrum of the measured light. This cascaded FP configuration results in a simple arrangement of mirrors on a line, which makes it much tolerant to misalignment errors. The proposed configuration is implemented using the MEMS DRIE technology on an SOI wafer with a simple MEMS process flow without metallization or dielectric coating of the vertical optical surface. The fabricated compact structure is measured with both a laser source with narrow spectrum at 1550 nm and a wide spectrum source composed of an SLED and the ASE of a semiconductor optical amplifier source. The obtained results validate the concept of the new configuration.

This paper presents near- and mid- infrared (NIR-MIR) wavelength range optical MEMS Fabry-Perot interferometers (FPIs) developed for automotive and multi-gas sensing applications. MEMS FPI platform for NIR-range consist of LPCVD (low-pressure chemical vapour) deposited polySi-SiN λ/4-thin film Bragg reflectors, with the air gap formed by sacrificial SiO2 etching in HF vapour. Characterization results for the NIR MFPI devices for λ = 1.5 – 2.0 μm show resolution of 15 nm at the optimization wavelength of 1750 nm. We also present a MIR-range MEMS FPI for λ = 2.5 – 3.5 μm, which utilizes silicon and air in within the Bragg reflector structure to provide a high contrast for improved resolution. Characterization results show a FWHM (Full Width Half Maximum) of 20 nm in comparison to the 50 nm resolution provided by earlier MEMS FPIs realized for hydrocarbon sensing with conventional CVD-thin film materials. The improved resolution and the extended operation region shows potential to enable simultaneous sensing of CO2 and multiple hydrocarbons.

In this contribution, a microoptical imaging system is demonstrated that is inspired by the insect compound eye. The array camera module achieves HD resolution with a z-height of 2.0 mm, which is about 50% compared to traditional cameras with comparable parameters. The FOV is segmented by multiple optical channels imaging in parallel. The partial images are stitched together to form a final image of the whole FOV by image processing software. The system is able to acquire depth maps along with the 2D video and it includes light field imaging features such as software refocusing. The microlens arrays are realized by microoptical technologies on wafer-level which are suitable for a potential fabrication in high volume.

In this study, a MEMS sensing device, which is applicable to point-of-care testing (POCT), is developed by integrating an optical manipulation and detection technique. The diffusion coefficient is a parameter, which is sensitive to the size, the construction and the interaction of the sample, thus, the measurement of the diffusion coefficient of the bio-sample, such as proteins, is useful for the clinical diagnosis to detect interactions and conformational changes with high sensitivity. Several diffusion sensing methods have been developed, however, the technique applicable to POCT is not established because of the difficulties due to the requirement of the measurement in a short time and a small sensing device. In this study, in order to realize a high-speed detection (ms ~ s) with small sample volume (~ μl) and small apparatus (tens of cm) without particular preparations, the micro optical diffusion sensor utilizing laser-induced dielectrophoresis (LIDEP), which is a manipulation technique based on optoelectronic tweezers, is developed. The microscale concentration distribution is formed in the microchannel by LIDEP and act as the transient diffraction grating, then, the diffusion phenomenon is optically observed. For these techniques, a photoconductive layer is essential and a hydrogenated amorphous silicon (a-Si:H) deposited by a plasma-enhanced chemical vapor deposition is generally utilized as the layer. In this study, the a-Si:H is deposited using a reactive RF magnetron sputtering method under several conditions, while changing the source gas compositions. The sensing device is fabricated with proposed a-Si:H, and the feasibility study for bio-sample measurement is conducted.

This work presents an integrated closed-loop driving circuit for previously reported PZT resonant micro-mirrors, which is based on embedded capacitive position sensors for minimizing the system footprint. Signals with a high SNR of 84 dB were measured, when the mechanical scan angle of the micro-mirror was 2◦, so that high controlling resolution of 14 bit for the complete motion range of the mirror is enabled. The total power consumption of the closed-loop system is only 0.86mW. Measurement results of the closed-loop driven micromirror system are presented, demonstrating its competitiveness due to the great reliability, high precision and low-power consumption. Additionally, the implementation and performance of a self-resonant loop is discussed. Finally, the fabrication, temperature dependency and performance of embedded capacitive position sensors for single and dual axis PZT resonant micro-mirrors is evaluated and presented.

The vast majority of cameras and imaging sensors relies on the identical single aperture optics principle with the human eye as natural antetype. Multi-aperture approaches – in natural systems so called compound eyes and in technology often referred to as array-cameras have advantages in terms of miniaturization, simplicity of the optics and additional features such as depth information and refocusing enabled by the computational manipulation of the system´s raw image data. The proposed imaging principle is based on a multitude of imaging channels transmitting different parts of the entire field of view. Adapted image processing algorithms are employed for the generation of the overall image by the stitching of the images of the different channels. The restriction of the individual channel´s field of view leads to a less complex optical system targeting reduced fabrication cost. Due to a novel, linear morphology of the array camera setup, depth mapping with improved resolution can be achieved. We introduce a novel concept for miniaturized array-cameras with several mega pixel resolution targeting high volume applications in mobile and automotive imaging with improved depth mapping and explain design and fabrication aspects.

The emerging dual-focus lenses are drawing increasing attention recently due to their wide applications in both academia and industries, including laser cutting systems, microscopy systems, and interferometer-based surface profilers. In this paper, a miniature electrically tunable rotary dual-focus lens is developed. Such a lens consists of two optical elements, each having an optical flat surface and one freeform surface. The two freeform surfaces are initialized with the governing equation Ar²θ (A is the constant to be determined, r and θ denote the radii and angles in the polar coordinate system) and then optimized by ray tracing technique with additional Zernike polynomial terms for aberration correction. The freeform surfaces are achieved by a single-point diamond turning technique and then a PDMS-based replication process is utilized to materialize the final lens elements. To drive the two coaxial elements to rotate independently, two MEMS thermal rotary actuators are developed and fabricated by a standard MUMPs process. The experimental results show that the MEMS thermal actuator provides a maximum rotation angle of about 8.2 degrees with an input DC voltage of 6.5 V, leading to a wide tuning range for both the two focal lengths of the lens. Specifically, one focal length can be tuned from about 30 mm to 20 mm while the other one can be adjusted from about 30 mm to 60 mm.

Designing a miniaturized and efficient optical filter which can be actively tuned is a modern engineering challenge. This paper propose a design of a device with a nano scale size for active tuning the resonance frequency of a metal-insulator-metal plasmonics optical filter. The design is based on controlling the relative position between two stubs in metal-Insulator-metal plasmonics waveguide using NEMS technology. The mechanical design parameter is chosen carefully to be compatible with modern fabrication technology and a reasonable fabrication process of the device is proposed. The analysis of the mechanical and optical design is done and shows a promising performance. For the chosen mechanical design parameters, the optical resonance wavelength can be tuned from 1.45μm to 1.65μm using 7VDC actuation voltage.

We investigate the transition of optical regimes of miniaturized optical systems using two canonical examples, where the refraction of light limits the system performance. A ball-lens and a solid immersion lens (SIL) are considered, whose refractive responses can be intuitively described by ray optics when the system size is relatively large. For miniaturized systems, the optical response differs from that of conventional large systems. Since such new responses occur when the refractive response of light start to disappear, this boundary is called the refraction limit. Our intension is to bring insights into new phenomena beyond such a boundary.. First, the refraction limit of the ball-lens is identified with three different criteria: the focal length, the spot size, and the amount of depolarization. The light confinement effect of nanoscale SILs, which have an intentionally deformed shape, demonstrates the diminishing effect of the refractive response of light. Likewise, beyond the refraction limit of the miniaturized systems, the signature of refractive degradations vanishes, and the shape errors of elements become negligible.

The paper presents the design and fabrication of an optically pumped 1550nm tunable MEMS VCSEL with an enclosed MEMS. The MEMS is defined in SOI and the active material, an InP wafer with quantum wells are bonded to the SOI and the last mirror is made from the deposition of dielectric materials. The design brings in flexibility to fabricate MEMS VCSELs over a wider range of wavelengths. The paper discusses results from the simulations and bonding results from fabrication. The device will push the boundaries for wavelength sweep speed and bandwidth.

Electrowetting lens is a promising technique for non-mechanical vari-focal lens, because of fast response time, wide expressible diopter, and etc. Although electrowetting related papers are actively published, no one did not clearly define the relationship among electrowetting parameters, especially in AC driven case. Analysis for AC voltage driving is needed because AC electrowetting has many advantages like low hysteresis and short settling time. In this experiment we confirmed that the response time depends on aperture size and applied voltage. Response time measurement for lens aperture of 200-1000um and applied voltage of 0-70V with 1kHz frequency was conducted. Experimental data was compared with simulation result by COMSOL Multiphysics program with the same condition, and they correspond with each other well. As voltage increases, the overshoot height becomes higher, so it has longer oscillation and settling time. On the other hand if aperture size decreases, the surface tension of lens wall could be delivered effectively to the center region of meniscus, so it has less oscillation and shorter settling time. The result was that in 500um aperture no more than 30V should be applied to ensure 1ms response time. In 200um aperture, the voltage limit is disappeared.