Search

For the first time, a CAOS (i.e., Coded Access Optical Sensor) spectrometer is demonstrated. The design implemented uses a reflective diffraction grating and a time-frequency CAOS mode operations Digital Micromirror Device (DMD) in combination with a large area point photo-detector to enable highly programmable linear High Dynamic Range (HDR) spectrometry. Experiments are conducted with a 2850 K color temperature light bulb source and visible band color bandpass and high-pass filters as well as neutral density (ND) attenuation filters. A ~369 nm to ~715 nm input light source spectrum is measured with a designed ~1 nm spectral resolution. Using the optical filters and different CAOS modes, namely, Code Division Multiple Access (CDMA), Frequency Modulation (FM)-CDMA and FM-Time Division Multiple Access (TDMA) modes, measured are improving spectrometer linear dynamic ranges of 28 dB, 50 dB, and 96.2 dB, respectively. Applications for the linear HDR CAOS spectrometer includes materials inspection in biomedicine, foods, forensics, and pharmaceuticals., Comment: 4 pages

Conventional pain assessment methods such as patients’ self-reporting restrict the possibility of easy pain monitoring while pain serves as an important role in clinical practice. Here we report a pain assessment method via 3D face reading camera assisted by dot pattern illumination. The face reading camera module (FRCM) consists of a stereo camera and a dot projector, which allow the quantitative measurement of facial expression changes without human subjective judgement. The rotational offset microlens arrays (roMLAs) in the dot projector form a uniform dense dot pattern on a human face. The dot projection facilitates evaluating three-dimensional change of facial expression by improving 3D reconstruction results of non-textured facial surfaces. In addition, the FRCM provides consistent pain rating from 3D data, regardless of head movement. This pain assessment method can provide a new guideline for precise, real-time, and continuous pain monitoring.

We present the concept and detailed design of a Smart Slit Assembly for next generation spectrometers, and we experimentally demonstrate operation of an individual 221 mu m x 111 mu m smart slit channel employing a MEMS actuated shutter to continuously modulate the intensity of the optical input signal. The MEMS actuated shutter is fabricated in a 211 mu m thick device layer of a Silicon-On-Insulator wafer by Deep Reactive Ion Etching. Electrostatic comb drive actuators allow an absolute displacement of 52 mu m at 74 V, resulting in a continuously tunable shutter efficiency of up to 99.97% at an operating wavelength of 532 nm.

3D imaging of a biological sample provides information about cellular and subcellular structures that are important in cell biology and related diseases. However, most 3D imaging systems, such as confocal and tomographic microscopy systems, are complex and expensive. Here, we developed a quasi-3D imaging tool that is compatible with most conventional microscopes by integrating micromirrors and microchannel structures on coverslips to provide bidirectional imaging. Microfabricated micromirrors had a precisely 45&deg, reflection angle and optically clean reflective surfaces with high reflectance over 95%. The micromirrors were embedded on coverslips that could be assembled as a microchannel structure. We demonstrated that this simple disposable device allows a conventional microscope to perform bidirectional imaging with simple control of a focal plane. Images of microbeads and cells under bright-field and fluorescent microscopy show that the device can provide a quick analysis of 3D information, such as 3D positions and subcellular structures.

The miniaturization of 3D depth camera systems to reduce cost and power consumption is essential for their application in electrical devices that are trending toward smaller sizes (such as smartphones and unmanned aerial systems) and in other applications that cannot be realized via conventional approaches. Currently, equipment exists for a wide range of depth-sensing devices, including stereo vision, structured light, and time-of-flight. This paper reports on a miniaturized 3D depth camera based on a light field camera (LFC) configured with a single aperture and a micro-lens array (MLA). The single aperture and each micro-lens of the MLA serve as multi-camera systems for 3D surface imaging. To overcome the optical alignment challenge in the miniaturized LFC system, the MLA was designed to focus by attaching it to an image sensor. Theoretical analysis of the optical parameters was performed using optical simulation based on Monte Carlo ray tracing to find the valid optical parameters for miniaturized 3D camera systems. Moreover, we demonstrated multi-viewpoint image acquisition via a miniaturized 3D camera module integrated into a smartphone.

Mid-infrared (MIR) photonics are generating considerable interest because of the potential applications in spectroscopic sensing, thermal imaging, and remote sensing. Silicon photonics is believed to be a promising solution to realize MIR photonic integrated circuits (PICs). The past decade has seen a huge growth in MIR PIC building blocks. However, there is still a need for the development of MIR reconfigurable photonics to enable powerful on-chip optical systems and new functionalities. In this paper, we present an MIR (3.7~4.1 μm wavelength range) MEMS reconfiguration approach using the suspended silicon waveguide platform on the silicon-on-insulator. With the sub-wavelength grating claddings, the photonic waveguide can be well integrated with the MEMS actuator, thus offering low-loss, energy-efficient, and effective reconfiguration. We present a simulation study on the waveguide design and depict the MEMS-integration approach. Moreover, we experimentally report the suspended waveguide with propagation loss (−2.9 dB/cm) and bending loss (−0.076 dB each). The suspended waveguide coupler is experimentally investigated. In addition, we validate the proposed optical MEMS approach using a reconfigurable ring resonator design. In conclusion, we experimentally demonstrate the proposed waveguide platform’s capability for MIR MEMS-reconfigurable photonics, which empowers the MIR on-chip optical systems for various applications.

Ensuring optical transparency over a wide spectral range of a window with a view into the tailpipe of the combustion engine, while it is exposed to the harsh environment of soot-containing exhaust gas, is an essential pre-requisite for introducing optical techniques for long-term monitoring of automotive emissions. Therefore, a regenerable window composed of an optically transparent polysilicon-carbide membrane with a diameter ranging from 100 &micro, m up to 2000 &micro, m has been fabricated in microelectromechanical systems (MEMS) technology. In the first operating mode, window transparency is periodically restored by pulsed heating of the membrane using an integrated resistor for heating to temperatures that result in oxidation of deposited soot (600&ndash, 700 &deg, C). In the second mode, the membrane is kept transparent by repelling soot particles using thermophoresis. The same integrated resistor is used to yield a temperature gradient by continuous moderate-temperature heating. Realized devices have been subjected to laboratory soot exposure experiments. Membrane temperatures exceeding 500 &deg, C have been achieved without damage to the membrane. Moreover, heating of membranes to &Delta, T = 40 &deg, C above gas temperature provides sufficient thermophoretic repulsion to prevent particle deposition and maintain transparency at high soot exposure, while non-heated identical membranes on the same die and at the same exposure are heavily contaminated.

The accurate measurement of oscillation amplitude in high frequency resonant micro-mirrors is critical for the correct operation in high precision applications. This paper proposes a novel technique for measuring the oscillation amplitude using a single photodiode placed in the path of the reflected laser beam. Furthermore, for the first time, a measurement-based comparison for different all-digital fractional-N dividers used for the fine adjustment of the mirror drive frequency is presented. It was found that the dithering method, typically used in instrumentation applications, can be successfully applied for the drive of high performance micro-mirrors whilst requiring minimal circuit complexity., peer-reviewed

Imaging applications based on microlens arrays (MLAs) have a great potential for the depth sensor, wide field-of-view camera and the reconstructed hologram. However, the narrow depth-of-field remains the challenge for accurate, reliable depth estimation. Multifocal microlens array (Mf-MLAs) is perceived as a major breakthrough, but existing fabrication methods are still hindered by the expensive, low-throughput, and dissimilar numerical aperture (NA) of individual lenses due to the multiple steps in the photolithography process. This paper reports the fabrication method of high NA, Mf-MLAs for the extended depth-of-field using single-step photolithography assisted by chemical wet etching. The various lens parameters of Mf-MLAs are manipulated by the multi-sized hole photomask and the wet etch time. Theoretical and experimental results show that the Mf-MLAs have three types of lens with different focal lengths, while maintaining the uniform and high NA irrespective of the lens type. Additionally, we demonstrate the multi-focal plane image acquisition via Mf-MLAs integrated into a microscope.

Three-dimensional imaging solutions provide depth perception that cannot be achieved with traditional two-dimensional systems. A 3D optical inspection system can be implemented using structured light as 3D sensing technology. In this paper, we show that structured light can be projected onto the measured object by means of an innovative scanning microsystem that employs a single-axis torsional MEMS mirror for fast steering a near infra-red laser beam on a diffractive silicon microstructure. As a proof of principle of the functionality of the designed microsystem, the generated line patterns are shone on 3D objects and deformation of the projected lines is detected with a CMOS camera. From line deformation, the object depth is calculated and found in accordance to the geometrical size. The developed miniaturized solution overcomes typical drawbacks of other scanning technologies such as large size and heavy weight.

This paper presents three novel techniques for the measurement of capacitance variation in high-frequency operation of angular comb-drive structures, with applications including optical projection micro-mirrors. The first technique uses a lock-in amplifier in order to measure the impedance of the comb structure by superimposing a test signal having a frequency that is at least one order of magnitude higher than the micro-mirror resonant frequency. The second measurement setup uses a digitizing oscilloscope to measure the capacitance from the instantaneous voltage and current in the comb structure. The third setup consists of a micro probe controlled by a high-resolution positioner in order to tilt the mirror to a desired angle. This allows for static capacitance measurement at different mirror deflection using a high precision LCR meter. The measurement results from the different setups were found to be in agreement with each other. The results were further verified against analytical and numerical modelling., peer-reviewed

This work reports the design and opto-mechanical characterization of high velocity comb-drive actuators producing in-plane motion and fabricated using the technology of deep reactive ion etching (DRIE) of silicon-on-insulator (SOI) substrate. The actuators drive vertical mirrors acting on optical beams propagating in-plane with respect to the substrate. The actuator-mirror device is a fabrication on an SOI wafer with 80 μm etching depth, surface roughness of about 15 nm peak to valley and etching verticality that is better than 0.1 degree. The travel range of the actuators is extracted using an optical method based on optical cavity response and accounting for the diffraction effect. One design achieves a travel range of approximately 9.1 µm at a resonance frequency of approximately 26.1 kHz, while the second design achieves about 2 µm at 93.5 kHz. The two specific designs reported achieve peak velocities of about 1.48 and 1.18 m/s, respectively, which is the highest product of the travel range and frequency for an in-plane microelectromechanical system (MEMS) motion under atmospheric pressure, to the best of the authors’ knowledge. The first design possesses high spring linearity over its travel range with about 350 ppm change in the resonance frequency, while the second design achieves higher resonance frequency on the expense of linearity. The theoretical predications and the experimental results show good agreement.

Optofluidics is a rapidly growing versatile branch of adaptive optics including a wide variety of applications such as tunable beam shaping tools, mirrors, apertures, and lenses. In this review, we focus on recent developments in optofluidic lenses, which arguably forms the most important part of optofluidics devices. We report first on a number of general characteristics and characterization methods for optofluidics lenses and their optical performance, including aberrations and their description in terms of Zernike polynomials. Subsequently, we discuss examples of actuation methods separately for spherical optofluidic lenses and for more recent tunable aspherical lenses. Advantages and disadvantages of various actuation schemes are presented, focusing in particular on electrowetting-driven lenses and pressure-driven liquid lenses that are covered by elastomeric sheets. We discuss in particular the opportunities for detailed aberration control by using either finely controlled electric fields or specifically designed elastomeric lenses.

A silicon micromirror driven by a single S-shaped piezoelectric actuator has been demonstrated for 2-D scanning mirror applications. A large mirror (1.65 mm x 2 mm) and an S-shaped PZT actuator are formed after the fabrication process. Three modes of operation are investigated: bending, torsional and mixed. The resonant frequencies obtained for bending and torsional modes are 27 Hz and 70 Hz respectively. The maximum measured optical deflection angles obtained at 1 Vpp are ±7.26° and ±1.18° respectively for bending and torsional modes. Various 2-D Lissajous patterns are demonstrated by superimposing two ac sinusoidal electrical signals of different frequencies (27 Hz and 70 Hz) into one signal to be used to actuate the mirror.

A silicon micromirror driven by a piezoelectric Pb(Zr,Ti)O 3 beam actuator has been demonstrated for two-dimensional scanning mirror applications. The mirror is micromachined from the device layer of an SOI wafer, while the piezoelectric beam actuator contains multilayers of Pt/Ti/PZT/Pt/Ti/SiO 2 /Si which is deposited and released from a SOI wafer. A 1x10 PZT arrayed actuator are separately arranged in parallel on a Si beam. Bending mode is measured at 34Hz as while the torsional mode is measured at 197Hz. We demonstrated 2-D raster scanning patterns by applying AC bias of 34Hz on half of the 10 actuators and 197Hz on the other half actuators.

A miniature methane sensor composed of a long ultra-low loss waveguide and a micro-ring resonator filter is proposed with high sensitivity and good selectivity. This sensor takes advantage of the evanescent field to implement methane concentration detection at a near infrared band (1650 nm). In the sensor, two waveguides, a strip waveguide and a slot waveguide, are specially designed and discussed based on three common semiconductor materials, including silica, silicon nitride, and silicon. Through simulations and numerical calculations, we determine that for the strip waveguide, the optimal evanescent field ratio (EFR) is approximately 39.8%, while the resolution is 32.1 ppb using a 15-cm waveguide length. For the slot waveguide, the optimal EFR is approximately 61.6%, and the resolution is 20.8 ppb with a 15-cm waveguide length.

We have fabricated and characterized a Fully Programmable Micro-Diffraction Grating (FPMDG) with 64 silicon micro-mirrors for spectral shaping in the visible and near-infrared wavelength range. The FPMDG arrays of 50μm and 80μm wide and 700μm long silicon micro-mirrors have been fabricated in a process based on anodic bonding of an 8μm-SOI wafer and a borosilicate glass wafer. The detrimental bending of the micro-mirrors during electrostatic actuation has been minimized through separation of the mechanical and optical sections of the device. Flexures incorporating serpentine structures have been used to reduce the actuation dependence on length and thickness. Independent addressing of the micro-mirrors with negligible cross-talk and with bending of the micro-mirrors smaller than 0.14μm over 700μm have been demonstrated.

The Grating Light Valve (GLV) is a microelectromechanical reflection grating. It operates on the principle of controlled diffraction of incident light due to electrostatic deflection of microbeams, thus producing bright and dark pixels in a display system. This unique approach offers significant advantages compared to other display systems in terms of speed, high optical efficiency, accuracy and ease of manufacturing. At the same time monolithic integration of MEMS on top of CMOS is getting more popular because CMOS-integrated MEMS exhibit less parasitics and have a reduced assembly and packaging cost over hybrid approaches. The relatively low deposition temperature (~450^oC) of poly-SiGe compared to poly-Si (~800^oC) makes poly-SiGe suitable for back end processing. Hence, in this work we report the fabrication and functioning of CVD poly-SiGe GLVs in terms of their response to the amplitude and frequency of the applied actuation voltage.

International audience; We propose an original approach of a miniature scanning confocal microscope that uses two electrostatic scanners with microoptical lenses. For this chip-scale microscope, we demonstrated the use of optical feedback of VCSEL's laser as an active detection. The z-axis scanner will provide a vertical motion of the first microlens in the range of 100 ¿m, controlling the focal length of the objective. Raster scanning (30 ¿m in both directions) of a specimen by the focused illumination spot will be implemented by actuating of second microlens by x-y-axis scanner.

International audience; We demonstrated active Q-switching of an erbium-doped fibre laser using a deformable metallic micro-mirror. The electrostatically actuated micro-mirror acts as one of the laser cavity reflectors and, at the same time, as a switching/modulator element. When actuated, its shape changes from planar to a concave curvature, allowing control of the Q-factor of the laser cavity. The mirror/switching element is small, compact, highly reflective and achromatic, with a great integration potential. The laser system operates at frequencies between 20 and 120 kHz and generates short pulses (FWHM down to 300 ns) and high peak powers, up to 160 times greater than the continuous emission.

MEMS (micro electro-mechanical systems) are often expected to take a development as microelectronics did in the last 35 years. Several devices are already established in mass markets like acceleration sensors, gyros, pressure sensors, ink jet heads and the DLP micromirror array. On the other hand many companies have stopped their business after the telecom bubble. Others are struggling. Many dreams based on MEMS-devices that were not at all mature and could not be manufactured in high numbers. When a commercial product is the goal, several questions must be answered already in concept phase. The specifications must clearly reflect the requirements of the application. Performance and price must be competitive to any other technology. The relation between fabrication process and design is strong and mutual. The process must create all features of the device and the design must consider the limitations of the process. Only if the design is tolerant against all process variations reproducible performance can be achieved. And only if the design is robust in all process steps the devices can survive. Regarding the time and cost frame it is always preferable to change the layout rather than the process. This article looks at MEMS technology and identifies what has been adopted from CMOS, what is desirable to adopt and what needs new solutions. Examples are given in the fields of design, modeling layout, process, test, and packaging., NA

The measurement of shearing force is increasingly important in the detection of slipping and the measurement of friction. In this paper, we propose a promising shearing force measurement device that is 16.3 mm × 2.9 mm × 6.0 mm, using an integrated micro displacement sensor and a trapezoidal external metallic frame. The optoelectronic subsection of the sensor is 6.5 mm × 6.5 mm, and is 1.6 mm thick. This subsection is used to measure the tilt angle of a mirror on the ceiling of the frame caused by the shearing force applied to the upper surface of the frame. We have been able to successfully obtain a linear output change for a single axis shearing force, and determined that the measurement sensitivity differs largely due to the material and shape of the frame. Therefore, if these factors are known this device can be embedded in various applications.

A silicon micromirror (5 mm×5 mm) with gold coating, actuated by piezoelectric Pb(Zr,Ti)O3 cantilever beams, has been demonstrated for variable optical attenuator (VOA) applications. The device is micromachined from a SOI substrate of 5 μm thick Si device layer, with multilayers of Pt/Ti/PZT/Pt/Ti being deposited for use as electrodes. The PZT thin film is deposited by solgel technique and the microstructures are later released from the backside to form a 1×10 array of PZT cantilever arranged in parallel. A piezoelectric constant value of 116 pm V −1 was estimated and an attenuation of 40 dB was reached when a DC driving voltage of 1V was applied to the top electrodes of all the ten cantilevers while the bottom electrodes are grounded.

We show the first results of a linear 100-micromirror array capable of modulating the phase and amplitude of the spectral components of femtosecond lasers. Using MEMS-based reflective systems has the advantage of utilizing coatings tailored to the laser wavelength range. The innovative features of our device include a novel rotational, vertical comb-drive actuator and an X-shaped, laterally reinforced spring that prevents lateral snap-in while providing flexibility in the two degrees of freedom of each mirror, namely piston and tilt. The packaging utilizes high-density fine-pitch wire-bonding for on-chip and chip-to-PCB connectivity. For the first deployment, UV-shaped pulses will be produced to coherently control the dynamics of biomolecules.

The advent of cell phone cameras extensively pushed market needs for micro lenses and supported developments like the Wafer-Level-Camera Technology [1]. Different optical applications and patterning methods for micro lenses require different sets of materials. Micro ink-jet printing (micro IJP) is an alternative and innovative direct patterning method for the manufacture of micro optical systems. We demonstrate the development of two material compositions - an epoxy resin and a sol-gel based material which are used as inks with physical parameters adapted to the patterning technique so that stable and reproducible drops in both continuous and drop-on-demand (DoD) mode can be generated. The manufacturing of micro lenses, the lens characterization, their geometry and their optical properties are presented. (C) 2010 Elsevier B.V. All rights reserved.

After microelectromechanical systems (MEMS) devices have been well established, components of higher complexity are now developed. Particularly, the combination with optical components has been very successful and have led to optical MEMS. The technology of choice for us is the silicon-on-insulator (SOI) technology, which has also been successfully used by other groups. The applications presented here give an overview over what is possible with this technology. In particular, we demonstrate four completely different devices: (a) a 2 /spl times/ 2 optical cross connector (OXC)with an insertion loss of about 0.4 dB at a switching time of 500 /spl mu/s and its extension to a 4 /spl times/ 4 OXC, (b) a variable optical attenuators (VOA), which has an attenuation range of more than 50 dB (c) a Fourier transform spectrometer (FTS) with a spectral resolution of 6 nm in the visible, and (d) an accelerometer with optical readout that achieves a linear dynamic range of 40 dB over /spl plusmn/6 g. Except for the FTS, all the applications utilized optical fibers, which are held and self-aligned within the MEMS component by U-grooves and small leaf springs. All devices show high reliability and a very low power consumption.