Environmental sensing is a topic of increasing interest and has triggered much research towards fully integrated sensor solutions. In this context optical measurement approaches in the infrared can provide intrinsic selectivity and sensitivity for integrated gas sensors. Recently, we proposed the possibility of the incorporation of IR-active plasmonic materials to photonic crystal waveguides, which could allow to increase sensitivities and significantly reduce the size of such sensors. Here, we will first present the overall approach and compare two possible specific realizations.
Dipicolinic acid (DPA), bound to calcium (Ca), is a main component of bacterial endospores. Complexation of DPA with lanthanide ions, particularly Terbium (Tb), allows for rapid detection via monitoring the lanthanide luminescence, with applications spanning from cell imaging to contamination and biohazard detection, to sterilization control. Here we present time-resolved luminescence of the Tb-DPA complex upon UV excitation at 266 nm. Our measurements directly monitor the luminescence dynamics and speak for a rise of the luminescence on the ns time scale, which is orders of magnitude faster than previously reported, and raise questions about the details of the energy transfer process in this complex and the states involved. The results are relevant for the design of more sensitive detection schemes for Tb-DPA fluorescence, as well as for the design of novel Tb-based luminescence probes or novel fluorescence probes working as FRET acceptors of Tb energy.
Automotive LiDAR systems are expected to play a crucial role in the future development of autonomous driving. In the course of the Austrian research project iLIDS4SAM an appropriate LiDAR sensor demonstrator has been designed and developed. Based upon typical requirements for such sensors, e.g. the capability to detect objects of about 10 cm x 13 cm size at a distance of 80 m, a field-of-view of 20° x 90° (V x H) and an image rate of about 17 Hz, a highly innovative 3D laser scanner has been designed which combines state-of-the-art MEMS mirror beam deflection with a rather classical polygon mirror wheel. Integrating a laser diode array of the newest generation, a multipixel APD detector array, waveform digitization as well as online waveform processing, 16 range measurement channels operating simultaneously are realized. The resulting LiDAR sensor offers a range measurement rate of 4.5 million measurements per second, each with the capability to resolve multiple targets. The LiDAR sensor is manufactured as a prototype on the level of an elegant breadboard. This contribution provides insight into the design of the LiDAR sensor and discusses the challenges identified during the design and development phase.
Detecting and classifying particles over a wide range of types and sizes is essential for precise air quality determination. In this study the use of optical waveguide-based particle detection is examined using finite element method (FEM) based simulations. The simulation model assumes a silicon nitride strip waveguide and is built up in 3D using the Comsol Multiphysics platform. The waveguide geometry parameters were varied to identify suitable geometries for single-mode wave guidance of the fundamental quasi-TE and quasi-TM modes. The geometries with their according effective wave indices are reported. Furthermore, the intensity and phase changes of the single-mode wave introduced by the presence of a particle are analyzed und the underlying physical effects are discussed for spherical particles of radii from 50 to 500 nm. The results show non-linear and non-monotonic behavior and give substantial input to understand basic particle interaction with waveguide structures. Furthermore, they provide helpful knowledge for designing waveguide-based particle detectors.
In addition to the two-dimensional intensity distribution in the image plane, light field microscopes capture information about the angle of the incident radiation. This information can be used to extract depth information about the object, calculate all-in-focus images and perform three-dimensional reconstructions from a single exposure. In combination with automated microscopy setups, this makes the technique a promising tool for high-throughput, three-dimensional cell assay evaluation which could substantially improve drug development and screening. To this end, we have developed a novel generalized calibration and three-dimensional reconstruction scheme for a lightfield fluorescence microscope setup. The scheme can handle Keplerian and Galilean light field camera configurations added to infinity corrected microscopes configured to be telecentric as well as non-telecentric or hypercentric. The latter provides a significant advantage over the state of the art as it allows for an application specific optimization of lateral and axial resolution, field-of-view, and depth-of-focus. The reconstruction itself is performed iteratively using an expectation maximization algorithm. Super-resolved reconstructions can be achieved by including experimentally measured pointspread- functions. To reduce the required computational power, sparsity and periodicity of the system matrix relating object space to light field space is exploited. This is particularly challenging for the non-telecentric cases, where the voxel size of the reconstructed object space depends on the axial coordinate. We provide details on the experimental setup and the reconstruction algorithm, and present results on the experimental verification of theoretical performance parameters as well as successful reconstructions of fluorescent beads and three-dimensional cell spheroids.
In light-field microscopy, a single point emitter gives rise to a complex diffraction pattern, which varies with the position of the emitter in object space. In order to use deconvolution-based wave-optical reconstruction schemes for light-field imaging systems, established methods rely on theoretical estimation of such diffraction patterns. In this paper we propose a novel method for direct experimental estimation of the light-field point spread function. Our approach relies on a modified reversed micro-Hartmann test to acquire a composite light-field point spread function of several thousand point emitters in the object plane simultaneously. By using fiducial markers and a custom image processing algorithm we separate the contributions of individual point emitters directly in raw light-field images and allow the construction of the forward imaging process without any prior assumption about the optical system required. The constructed forward imaging model can finally be applied in the 3D-deconvolution based wave-optical reconstruction scheme.
Laser-induced breakdown spectroscopy (LIBS) technology holds the potential for onsite real-time measurements of steel products. However, for a mobile and robust LIBS measurement system, an adequate small and ruggedized laser source is a key requirement. In this contribution, we present tests with our compact high-power laser source, which, initially, was developed for ignition applications. The CTR HiPoLas® laser is a robust diode pumped solid-state laser with a passive Q-switch with dimensions of less than 10 cm3. The laser generates 2.5-ns pulses with 30 mJ at a maximum continuous repetition rate of about 30 Hz. Feasibility of LIBS experiments with the laser source was experimentally verified with steel samples. The results show that the laser with its current optical output parameters is very well-suited for LIBS measurements. We believe that the miniaturized laser presented here will enable very compact and robust portable high-performance LIBS systems.
LIBS-technology holds the potential for on-site real-time measurements of steel products. However for a mobile and
robust LIBS measurement system, an adequate small and ruggedized laser source is a key-requirement. In this
contribution, we present tests with our novel compact high power laser source, which, initially, was developed for
ignition applications. The CTR HiPoLas® laser is a robust diode pumped solid state laser with a passive Q-switch with
dimensions of less than 10 cm³. The laser generates 2.5 ns-pulses with 30 mJ at a maximum continuous repetition rate of
about 30 Hz. Feasibility of LIBS experiments with the laser source was experimentally verified with steel samples. The
results show that the laser with its current optical output parameters is very well suited for LIBS measurements. We
believe that the miniaturized laser presented here will enable very compact and robust portable high-performance LIBS
systems.
A light field camera acquires the intensity and direction of rays from a scene providing a 4D representation L(x,y,u,v) called the light field. The acquired light field allows to virtually change view point and selectively re-focus regions algorithmically, an important feature for many applications in imaging and microscopy. The combination with hyperspectral imaging provides the additional advantage that small objects (beads, cells, nuclei) can be categorised using their spectroscopic signatures. Using an inverse fluorescence microscope, a LCTF tuneable filter and a light field setup as a test-bed, fluorescence-marked beads have been imaged and reconstructed into a 4D hyper-spectral image cube LHSI(x,y,z,λ). The results demonstrate the advantages of the approach for fluorescence microscopy providing extended depth of focus (DoF) and the fidelity of hyper-spectral imaging.
Many applications of MOEMS microscanners rely on accurate position feedback. For MOEMS devices which do not
have intrinsic on-chip feedback, position information can be provided with optical methods, most simply by using a
reflection from the backside of a MOEMS scanner. By measuring the intensity distribution of the reflected beam across a
quadrant diode, one can precisely detect the mirror’s deflection angles. Previously, we have presented a position sensing
device, applicable to arbitrary trajectories, which is based on the measurement of the position of the reflected laser beam
with a quadrant diode. In this work, we present a novel setup, which comprises the optical position feedback
functionality integrated into the device package itself. The new device’s System-in-Package (SiP) design is based on a
flip-folded 2.5D PCB layout and fully assembled as small as 9.2×7×4 mm³ in total. The device consists of four layers,
which supply the MOEMS mirror, a spacer to provide the required optical path length, the quadrant photo-diode and a
laser diode to serve as the light source. In addition to describing the mechanical setup of the novel device, we will
present first experimental results and optical simulation studies. Accurate position feedback is the basis for closed-loop
control of the MOEMS devices, which is crucial for some applications as image projection for example. Position
feedback and the possibility of closed-loop control will significantly improve the performance of these devices.
One of the important challenges for widespread application of MOEMS devices is to provide a modular interface for easy handling and accurate driving of the MOEMS elements, in order to enable seamless integration in larger spectroscopic system solutions. In this contribution we present in much detail the optical design of MOEMS driver modules comprising optical position sensing together with driver electronics, which can actively control different electrostatically driven MOEMS. Furthermore we will present concepts for compact spectroscopic devices, based on different MOEMS scanner modules with lD and 2D optical elements.
KEYWORDS: Microelectromechanical systems, Spectrometers, Mirrors, Signal to noise ratio, Sensors, FT-IR spectroscopy, Spectral resolution, Near infrared, Packaging, System integration
With a trend towards the use of spectroscopic systems in various fields of science and industry, there is an increasing
demand for compact spectrometers. For UV/VIS to the shortwave near-infrared spectral range, compact hand-held
polychromator type devices are widely used and have replaced larger conventional instruments in many applications.
Still, for longer wavelengths this type of compact spectrometers is lacking suitable and affordable detector arrays. In
perennial development Carinthian Tech Research AG together with the Fraunhofer Institute for Photonic Microsystems
endeavor to close this gap by developing spectrometer systems based on photonic MEMS. Here, we review on two
different spectrometer developments, a scanning grating spectrometer working in the NIR and a FT-spectrometer
accessing the mid-IR range up to 14 μm. Both systems are using photonic MEMS devices actuated by in-plane comb
drive structures. This principle allows for high mechanical amplitudes at low driving voltages but results in gratings
respectively mirrors oscillating harmonically. Both systems feature special MEMS structures as well as aspects in terms
of system integration which shall tease out the best possible overall performance on the basis of this technology.
However, the advantages of MEMS as enabling technology for high scanning speed, miniaturization, energy efficiency,
etc. are pointed out. Whereas the scanning grating spectrometer has already evolved to a product for the point of sale
analysis of traditional Chinese medicine products, the purpose of the FT-spectrometer as presented is to demonstrate
what is achievable in terms of performance. Current developments topics address MEMS packaging issues towards long
term stability, further miniaturization and usability.
One key challenge in the field of microfluidics and lab-on-a-chip experiments for biological or chemical applications is the remote manipulation of fluids, droplets and particles. These can be volume elements of reactants, particles coated with markers, cells or many others. Light-driven microfluidics is one way of accomplishing this challenge. In our work, we manipulated micrometre sized polystyrene beads in a microfluidic environment by inducing thermal flows. Therefore, the beads were held statically in an unstructured microfluidic chamber, containing a dyed watery solution. Inside this chamber, the beads were moved along arbitrary trajectories on a micrometre scale. The experiments were performed, using a MOEMS (micro-opto-electro-mechanical-systems)-based laser scanner with a variable focal length. This scanner system is integrated in a compact device, which is flexibly applicable to various microscope setups. The device utilizes a novel approach for varying the focal length, using an electrically tunable lens. A quasi statically driven MOEMS mirror is used for beam steering.
The combination of a tunable lens and a dual axis micromirror makes the device very compact and robust and is
capable of positioning the laser focus at any arbitrary location within a three dimensional working space. Hence, the developed device constitutes a valuable extension to manually executed microfluidic lab-on-chip experiments.
Recently, we have realized a new position sensing device for MOEMS mirrors applicable to arbitrary trajectories, which
is based on the measurement of a reflected light beam with a quadrant diode. In this work we present the characteristics of this device, showing first experimental results obtained with a test set-up, but also theoretical considerations and
optical ray-tracing simulations.
KEYWORDS: Mirrors, Sensors, Light sources, Microopto electromechanical systems, Light, Signal detection, Optical sensing, Ray tracing, Signal to noise ratio, Microelectromechanical systems
A tilt mirror’s deflection angle tracking setup is examined from a theoretical point of view. The proposed setup is based
on a simple optical approach and easily scalable. Thus, the principle is especially of interest for small and fast oscillating
MEMS/MOEMS based tilt mirrors. An experimentally established optical scheme is used as a starting point for accurate
and fast mirror angle-position detection. This approach uses an additional layer, positioned under the MOEMS mirror's
backside, consisting of a light source in the center and two photodetectors positioned symmetrical around the center. The
mirror’s back surface is illuminated by the light source and the intensity change due to mirror tilting is tracked via the
photodiodes. The challenge of this method is to get a linear relation between the measured intensity and the current
mirror tilt angle even for larger angles. State-of-the-art MOEMS mirrors achieve angles up to ±30°, which exceeds the
linear angle approximations. The use of an LED, small laser diode or VCSEL as a lightsource is appropriate due to their
small size and inexpensive price. Those light sources typically emit light with a Gaussian intensity distribution. This
makes an analytical prediction of the expected detector signal quite complicated. In this publication an analytical
simulation model is developed to evaluate the influence of the main parameters for this optical mirror tilt-sensor design.
An easy and fast to calculate value directly linked to the mirror’s tilt-angle is the “relative differential intensity” (RDI =
(I1 − I2) / (I1 + I2)). Evaluation of its slope and nonlinear error highlights dependencies between the identified parameters
for best SNR and linearity. Also the energy amount covering the detector area is taken into account. Design optimizing
rules are proposed and discussed based on theoretical considerations.
In this paper we present a driver for accurate positioning of certain electrostatically driven micro-opto-electromechanical system (MOEMS) based scanner mirrors. The driver unit can control up to six quasi-static mirror axes using closed loop control. The electronics are described in this contribution together with different closed-loop control algorithms, which were implemented for fast and accurate positioning. Results from closed loop operation are compared to the characteristics of the devices when driven in open loop mode. Settlings times and operating bandwidth can be improved by a factor of up 40.
Recently, we have developed compact modules comprising optical position sensing, and driver electronics, with closed
loop control, which can measure the trajectory of resonantly driven 2D-micro-scanner mirrors. In this contribution we
present the optical design of the position sensing unit and highlight various critical aspects. Basically position encoding
is obtained using trigger signals generated when a fast photodiode is hit by a laser beam reflected from the backside of
the mirror. This approach can also be used in the case of 2D-mirrors. In our device the backside of the mirror is hit by
two crossed orthogonal laser beams, whose reflections pass cylindrical mirrors in order to suppress the orthogonal
dimension. Mirror deflection around one axis is compensated at the plane of the detection diodes while deflection around
the other axis leads to a linear displacement of the beam. The optical design of the unit has to provide the optimal
compromise between the requirements for small size and simplicity on the one hand and optical accuracy on the other.
Martin De Biasio, Thomas Arnold, Gerald McGunnigle, Raimund Leitner, Andreas Tortschanoff, Nina Fietz, Lars Weitkämper, Dirk Balthasar, Volker Rehrmann
A Raman mapping system for detecting and discriminating minerals such as dolomite, marble, calcite and pyrite
is demonstrated. The system is built from components that are suitable for industrial conditions. Together
with a signal processing and a classier the system was shown to be capable of discriminating between several
important classes of mineral. The technique is a potential alternative to sensing methods currently used for
mineral sorting.
We present a CTIS system that uses an optimized diffractive optical element (DOE) to project the spectral and
spatial information simultaneously onto a CCD. We compare the DOE with and older approach based on glass
gratings and found that the DOE gave an improved spectral response. We argue that a DOE is the most effective
approach for CTIS.
Standard FT-IR spectrometers are large, usually static, and expensive and require operation by qualified personnel. The
presented development involves achievements in MEMS technologies and electronics design to address size, speed and
power requirements and develop a fully integrated miniaturized FT-IR spectrometer. A suitably matched interaction of
multiple new components - source, interferometer, detector and control and data processing - develops unique MEMS
based spectrometers capable of reliable operation and finally results in compact, robust and economical analyzers. The
presented system now aims at a high performance level to measure in the range between 5000-750 cm-1 at a spectral
resolution better than 10 cm-1. The Michelson interferometer design and the desired performance put several demands on
the MOEMS device. Amongst these, a mirror travel of ± 500 μm and a minimal dynamic deformation of < λ/10 peak-to
peak in combination with a large mirror aperture of 5 mm were the most challenging goals. However, a signal-to-noise
ratio of 1000 is required to qualify a FT-IR system as a sensor for industrial applications e.g. process control. The
purpose of the system, presented in this work, is to proof that this is feasible on the basis of MEMS technology and it is
demonstrated that most of these specifications could be already met.
For MOEMS devices which do not have intrinsic on-chip feedback, position information can be provided with optical
methods, most simply by using a reflection from the backside of a MOEMS scanner. Measurement of timing signals
using fast differential photodiodes can be used for resonant scanner mirrors performing sinusoidal motion with large
amplitude. While this approach provides excellent accuracy it cannot be directly extended to arbitrary trajectories or
static deflection angles. Another approach is based on the measurement of the position of the reflected laser beam with a
quadrant diode. In this work, we present position sensing devices based on either principle and compare both approaches
showing first experimental results from the implemented devices
KEYWORDS: Mirrors, Microopto electromechanical systems, Control systems, Scanners, Analog electronics, Microcontrollers, Microelectromechanical systems, Digital signal processing, Actuators, Amplifiers
In this paper we present closed-loop control for accurate positioning of micro optical mechanical system (MOEMS)
based scanner mirrors. An analog and a microcontroller based implementation of the control loop have been
implemented and are presented in this paper. In particular, the measured results are compared to the characteristics of the
devices when driven in open loop mode. Settlings times and operating bandwidth can be improved by a factor of 10
compared to open loop operation. Digital implementations have advantages in terms of flexibility, but show limitations
for fast signals due to time discretization.
We have developed compact devices to control electrostatically driven resonant micromirrors with one and two axes. For stable oscillation with large amplitude, operation close to resonance must be ensured under varying environmental conditions. Our devices feature optical position sensing and driver electronics with closed loop control. In this contribution, we present in much detail the novel two-dimensional device and highlight specific aspects of this system.
We show results on the progress in the development of MOEMS based FT spectrometers dedicated to operate in the mid-IR. Recent research is performed within an EC-FP7 project with the goal to show the feasibility of miniaturized high
performance infrared spectroscopic chemical analyzers. Exploiting the high analyte selectivity of the mid-IR paired with
the inherent sensitivity of an FT-IR spectrometer, such devices could be used in a wide range of applications, from air
monitoring over in-line real-time process control to security monitoring. For practical applicability in these fields,
appropriate detection limits and spectral quality standards have to be met. The presented system aims at a performance to
measure in the range between 4000-700 cm-1 at a spectral resolution better than 10 cm-1, which would clearly outmatch
previous MOEMS based spectrometer approaches. A further technological advantage is the rapid-scan capability. The
MOEMS devices oscillate at 500 Hz. A spectrometer based on this device can acquire 1,000 scans per second in
forward-backward mode. The interplay of all these components with the challenges in system integration will be
described in detail and experimental results will be shown, presenting a significant step forward in smart spectroscopic
sensors, microsystems technology and vibrational spectroscopy instrumentation.
Spectral imaging measures data that is spatially and spectrally resolved: that is at each point in the image
the spectrum is measured. Classical spectral imaging requires that the sample is scanned either spatially or
spectrally. The main drawback of the classical approaches is that they are sequential. This paper presents a
computed tomographic imaging spectrometer (CTIS) that can image two spatial and one spectral dimension in
one camera frame. Unlike hyper-spectral imaging techniques which provide full spatial and spectral resolution,
with the proposed technique there is a tradeoff between spatial and spectral resolution. The proposed CTIS
system uses two crossed glass gratings that project the spectral and spatial image information to a 2D CCD
camera array. The current system is designed for microscopic applications in pathology and cell imaging as well
as macroscopic material analysis.
We have developed compact devices comprising optical position sensing and driver electronics with closed loop control,
capable of driving resonant 1D- and 2D-MOEMS scanner mirrors. Position encoding is realized by measuring a laser
beam reflected from the backside of the mirror. In the 2D-device we use cylindrical mirrors in order to suppress the
deflection of the orthogonal dimension. This reduces the problem to the control of two independent 1D-oscillations and
allows accurate position sensing. The phase between the oscillations of the two orthogonal axes is actively controlled to
achieve a stable Lissajous figure. In this contribution we also demonstrate that this approach is scalable for
synchronization of separate MEMS mirrors.
Resonantly driven oscillating MOEMS mirrors have many applications in the fields of optics, telecommunication and
spectroscopy. Assuring stable resonant oscillation with well controlled amplitude under varying environmental
conditions is a complex task, which can impede or retard incorporation of such MOEMS mirrors in large systems. For
this we have developed compact modules comprising optical position sensing and driver electronics with closed loop
control, which can ensure stable resonant operation of 1D and 2D micro-mirrors. In this contribution we present in much
detail the position encoding and feedback scheme, and show very first experimental results with the novel 2D device.
With MEMS, it became possible to build pocket-sized spectrometers for various spectral ranges, including the near-IR or mid-IR. These systems are highly rugged and can measure spectral changes at ms time resolution or co-add several hundreds of scans to one spectrum achieving adequate signal-to-noise ratios. Two spectrometer systems a scanning grating based spectrometer and a FT-IR spectrometer both based on a micromechanical scanning mirror technology are presented. Furthermore, the focus of this work is on the development of an analyzer for dissolved CO2 showing the methodology and also first implementation steps towards a sensor solution. CO2(aq) calibration samples were prepared by different NaHCO3 concentrations in solution. Spectra and calibration data acquired with both MEMS based spectrometer prototypes are presented.
Resonantly driven oscillating MOEMS mirrors are used in various fields in optics, telecommunications and
spectroscopy. One of the important challenges in this context is to assure stable resonant oscillation with well controlled
amplitude under varying environmental conditions. For this reason, we developed a compact device comprising a
resonant MOEMS micro-mirror, optical position sensing, and driver electronics, with closed loop control, which ensures
operation close to the mirror resonance. In this contribution we present this device and show experimental results with a
23 kHz MOEMS mirror, which demonstrate its capabilities and limitations.
We present a new method for detecting the accurate position of micro-electro-opto-mechanical system (MOEMS)
devices, thus enabling the implementation of closed-loop controls. The ensuing control mechanism allows building
robust MOEMS-based Fourier-transform infrared (FTIR) spectrometers with large mechanical amplitudes and thus good
spectral resolutions. The MOEMS mirror device, a rectangular 1.65 mm² metalized plate mirror suspended on bearing
springs and driven by comb-structured electrodes, is driven by a rectangular signal with a duty cycle of 50% and high
voltage levels up to 140 V at a frequency near twice its mechanical resonance frequency. Out-of-plane mirror
displacements of up to ±100 μm have thus been achieved. To handle the high bandwidth of the sinusoidal mirror position
reference signal, which is generated by a laser reference interferometer, an analog position detection circuit is necessary.
This dedicated circuit demodulates the reference signal and generates a highly accurate control signal returning the zerocrossing
position of the mirror. This permits the implementation of a closed-loop control, which ensures optimally stable
MOEMS mirror movement and maximal mechanical amplitude, even under varying environmental conditions. While
this solution has been developed for a specific MOEMS device, the principle is widely applicable to related components.
We present an improved FTIR spectrometer using a novel MOEMS actuator and discuss in detail the properties of the
MOEMS component and the resulting FT-IR sensor device. Spectral resolution and the spectral range allow making use
of the inherent multi-analyte detection capabilities giving the spectroscopy platform an advantage over singlewavelength
IR sensors. With its further miniaturization potential due to its MOEMS core, this compact, energy efficient
and robust spectrometer can thus act as transducer for portable and ultra-lightweight spectroscopic IR sensors, e.g. all
purpose hazardous vapor sensors, sensors for spaceborne and Micro-UAV based IR analysis, and many more.
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