Microelectromechanical Mirror Research Articles

Modeling of Heat Transfer for a Three-Dimensional Microelectromechanical Mirror Element with Consideration of Its Packaging Features

Modeling of Heat Transfer for a Three-Dimensional Microelectromechanical Mirror Element with Consideration of Its Packaging Features

The Integration of Optical Stimulation in a Mechanically Dynamic Cell Culture Substrate.

A cell culture well with integrated mechanical and optical stimulation is presented. This is achieved by combining dielectric elastomer soft actuators, also known as artificial muscles, and a varifocal micro-electromechanical mirror that couples light from an optical fiber and focuses it onto the transparent cell substrate. The device enables unprecedented control of in vitro cell cultures by allowing the experimenter to tune and synchronize mechanical and optical stimuli, thereby enabling new experimental assays in optogenetics, fluorescent microscopy, or laser stimulation that include dynamic mechanical strain as a controlled input parameter.

Scanning optimization of an electrothermally-actuated MEMS mirror for applications in optical coherence tomography endoscopy

Probe is an important component of the optical coherence tomography (OCT) system. Electrothermally-actuated micro-electromechanical (MEMS) mirrors are especially suitable for OCT endoscopic imaging due to their large scan angle, low driving voltage and high fill factor. However, endoscopic OCT imaging quality would be seriously affected by the nonlinear scanning characteristics of electrothermal MEMS mirrors as well as the distortion due to the need of placing the MEMS mirror on a 45° slope. In this work, an open-loop control method based on the transfer function of the MEMS mirror is proposed to optimize the overall optical trajectory scanned on the sample under a MEMS OCT probe. The transfer function of the electrothermal MEMS mirror is established and the relation between the MEMS mirror’s tilt angle and the final scanning trajectory on the sample is calculated. A PID control model based on the transfer function is developed and employed to generate the driving voltage signals that can be applied to the MEMS mirror for obtaining undistorted scanning trajectories on the sample. Experiments show that the proposed method can correct the scanning nonlinearity and the distortion without adding extra hardware. For instance, the linear scanning ratio is improved from 72% up to 98%; the fan-shaped distortion is reduced by a factor 3–5. This method is also applied to a swept-source OCT system and the image distortions are compensated effectively.

Eighty-Five Percent of Improved Optical Power Delivery to Epiretinal Prostheses Using Rigid Body Compensation Algorithm.

Vision impairment caused by degenerative retinal pathologies such as age-related macular degeneration can be treated using retinal implants. Such devices receive power and data using cables passing through a permanent surgical incision in the eye wall (sclera), which increases the risk to patients and surgical costs. A recently developed retinal implant design eliminates the necessity of the implant cable using a photonic power converter (PPC), which receives optical power and data through the pupil and is directed by an ellipsoidal reflector and micro-electromechanical mirror. We present a misalignment compensation algorithm model that accounts for rigid-body motions of the reflector relative to the eye and applies the correction to the mirror coordinates in the presence of angular misalignment of the reflector. We demonstrate that up to 85% of the nominal optical power can be delivered to the implant with axial reflector misalignments up to 30 deg using the compensation algorithm.

A 1×20 MEMS mirror array with large scan angle and low driving voltage for optical wavelength-selective switches

Wavelength-selective switches (WSSs) are the core devices for reconfigurable optical add-drop multiplexers (ROADMs) that are essential in all-optical networks. WSSs based on microelectromechanical (MEMS) mirror arrays exhibit high potential due to their high switching speed and large port counts, but there still exist challenges to achieve large optical scanning angle at low voltage. This paper presents a 1×20 MEMS mirror array (MMA) design that can scan over 10° in both axes at less than 5 V. The MMA is based on an unique electrothermal bimorph actuator design that can perform 2D scanning and its fill factor reaches 96 %. The 1×20 MMA design has been successfully fabricated using a combined bulk- and surface- micromachining process. The size of each mirror plate is 240 μm by 500 μm. The measured maximum optical scan angles in the x-axis and y-axis are 29.3° and 11.8°, respectively, at 3 V. The measured response time is about 3.7 ms. The thermal crosstalks between adjacent electrothermal actuators are about 10 %. Long-term stability tests show that the angular drifts of the individual mirrors are about 0.002°/h.

Fast Foveating Cameras for Dense Adaptive Resolution.

Traditional cameras field of view (FOV) and resolution predetermine computer vision algorithm performance. These trade-offs decide the range and performance in computer vision algorithms. We present a novel foveating camera whose viewpoint is dynamically modulated by a programmable micro-electromechanical (MEMS) mirror, resulting in a natively high-angular resolution wide-FOV camera capable of densely and simultaneously imaging multiple regions of interest in a scene. We present calibrations, novel MEMS control algorithms, a real-time prototype, and comparisons in remote eye-tracking performance against a traditional smartphone, where high-angular resolution and wide-FOV are necessary, but traditionally unavailable.

A Low-Voltage, Low-Current, Digital-Driven MEMS Mirror for Low-Power LiDAR

Microelectromechanical (MEMS) mirrors have provided a fast and compact method to modulate light for mobile-scale projectors, LiDAR, and computational cameras. In this letter, we propose a new MEMS mirror design and its actuation method that is specifically built for low-voltage, low-current, and digital-driven IoT applications. The MEMS mirror specifically designed with direct actuation from the microcontroller was successfully fabricated and characterized. A full low-power LiDAR system based on the fabricated MEMS mirror was demonstrated, which was powered by a 9-V commercial battery.

A Miniature Endoscopic Optical Coherence Tomography Probe Based on C-Lens

We present a novel miniature endoscopic optical coherence tomography (OCT) probe based on an electrothermal microelectromechanical (MEMS) mirror and a C-lens. The MEMS mirror has a relatively large mirror plate of 0.5 mm × 0.5 mm on a small chip size of 1.5 mm × 1.3 mm, leading to the outer diameter of the endoscopic probe down to only 2.5 mm so that the probe is capable of being inserted through the biopsy channel of a conventional endoscope. A long focal length of 12 mm is achieved by properly designing the C-lens. Compared to commonly used GRIN lenses, C-lenses have advantages of much smaller sensitivities of the working distance and spot size to machining variations. The C-lens based probe can scan a large field of view (FOV) of 6 mm × 6 mm at only 5-V drive voltage. A swept source endoscopic OCT system is constructed using this miniature probe. Experiments show that the corresponding lateral and axial resolutions are about 50 and 14 μm, respectively. Various samples including human fingers, onions, and cancerous colon tissue are imaged and the result suggests this large-working-distance, large-FOV endoscopic probe is promising for applications in large tubular organs and large-area lesions.

Circumferential-scanning endoscopic optical coherence tomography probe based on a circular array of six 2-axis MEMS mirrors.

We present a novel circumferential-scan endoscopic optical coherence tomography (OCT) probe by using a circular array of six electrothermal microelectromechanical (MEMS) mirrors and six C-lenses. The MEMS mirrors have a 0.5 mm × 0.5 mm mirror plate and a chip size of 1.5 mm × 1.3 mm. Each MEMS mirror can scan up to 45° at a voltage of less than 12 V. Six of those mirrors have been successfully packaged to a probe head; full circumferential scans have been demonstrated. Furthermore, each scan unit is composed of a MEMS mirror and a C-lens and the six scan units can be designed with different focal lengths to adapt for lesions with uneven surfaces. Configured with a swept source OCT system, this MEMS array-based circumferential scanning probe has been applied to image a swine's small intestine wrapped on a 20 mm-diameter glass tube. The OCT imaging result shows that this new MEMS endoscopic OCT has promising applications in large tubular organs.

Realization of Multicore Fiber Reconfigurable Optical Add–Drop Multiplexer

Space-division multiplexing (SDM) is a calling for devices that fully replace their single-mode fiber counterparts. Fast optical switches represent one such type of key devices. In this letter, we present a free-space optical add-drop multiplexer for multicore fiber (MCF) optical communications. Microelectromechanical mirrors were used as the optical switching element. We first detail the implementation steps leading to the proposed device and then characterize its performance in terms of crosstalk and insertion loss. Overall average crosstalk is around -38 dB, while insertion losses remain large. The device investigated here is another step towards the practical adoption of SDM for optical networks based on MCFs.

Multispecies Heterodyne Phase Sensitive Dispersion Spectroscopy over 80 nm Using a MEMS-VCSEL

Vertical cavity surface emitting lasers fabricated with movable microelectromechanical mirrors can offer continuous single-mode wavelength tuning up to 100 nm with high efficiency and in a very small package. Wide tunability makes these diode lasers ideally suited for multispecies and high-density gas analysis and the first demonstrations of direct absorption spectroscopy and wavelength modulation spectroscopy have already been published. The performance of these systems could nevertheless be enhanced by the use of the new molecular dispersion spectroscopic methods, as heterodyne phase sensitive dispersion spectroscopy. This technique bases its operation on the detection of the profile of the refractive index of the sample under analysis, in contrast to traditional architectures based on the measurement of optical absorption, and this provides noticeable advantages. First, the method is normalization-free, and therefore, the characteristic issue of the nonmonotonic intensity profile during wavelength tuni...

Wide-angle structured light with a scanning MEMS mirror in liquid.

Microelectromechanical (MEMS) mirrors have extended vision capabilities onto small, low-power platforms. However, the field-of-view (FOV) of these MEMS mirrors is usually less than 90° and any increase in the MEMS mirror scanning angle has design and fabrication trade-offs in terms of power, size, speed and stability. Therefore, we need techniques to increase the scanning range while still maintaining a small form factor. In this paper we exploit our recent breakthrough that has enabled the immersion of MEMS mirrors in liquid. While allowing the MEMS to move, the liquid additionally provides a "Snell's window" effect and enables an enlarged FOV (≈ 150°). We present an optimized MEMS mirror design and use it to demonstrate applications in extreme wide-angle structured light.

Mitigation of beam fluctuation due to atmospheric turbulence and prediction of control quality using intelligent decision-making tools.

In free-space optical link (FSOL), atmospheric turbulence causes fluctuations in both intensity and phase of the received beam and impairing link performance. The beam motion is one of the main causes for major power loss. This paper presents an investigation on the performance of two types of controller designed for aiming a laser beam to be at a particular spot under dynamic disturbances. The multiple experiment observability nonlinear input-output data mapping is used as the principal components for controllers design. The first design is based on the Taguchi method while the second is artificial neural network method. These controllers process the beam location information from a static linear map of 2D plane: optoelectronic position detector, as observer, and then generate the necessary outputs to steer the beam with a microelectromechanical mirror: fast steering mirror. The beam centroid is computed using monopulse algorithm. Evidence of suitability and effectiveness of the proposed controllers are comprehensively assessed and quantitatively measured in terms of coefficient of correlation, correction speed, control exactness, centroid displacement, and stability of the receiver signal through the experimental results from the FSO link setup established for the horizontal range of 0.5km at an altitude of 15.25m. The test field type is open flat terrain, grass, and few isolated obstacles.

Correction of image distortions in endoscopic optical coherence tomography based on two-axis scanning MEMS mirrors

A two-axis scanning microelectromechanical (MEMS) mirror enables an optical coherence tomography (OCT) system to perform three-dimensional endoscopic imaging due to its fast scan speed and small size. However, the radial scan from the MEMS mirror causes various distortions in OCT images, namely spherical, fan-shaped and keystone distortions. In this paper, a new method is proposed to correct all of three distortions presented in OCT systems based on two-axis MEMS scanning mirrors. The spherical distortion is corrected first by directly manipulating the original spectral interferograms in the phase domain, followed by Fourier transform and three-dimensional geometrical transformation for correcting the other two types of distortions. OCT imaging experiments on a paper with square ink printed arrays and a glass tube filled with milk have been used to validate the proposed method. Distortions in OCT images of flat or curved surfaces can all be effectively removed.

Nonlinear dynamics of a microelectromechanical mirror in an optical resonance cavity

The nonlinear dynamical behavior of a micromechanical resonator acting as one of the mirrors in an optical resonance cavity is investigated. The mechanical motion is coupled to the optical power circulating inside the cavity both directly through the radiation pressure and indirectly through heating that gives rise to a frequency shift in the mechanical resonance and to thermal deformation. The energy stored in the optical cavity is assumed to follow the mirror displacement without any lag. In contrast, a finite thermal relaxation rate introduces retardation effects into the mechanical equation of motion through temperature dependent terms. Using a combined harmonic balance and averaging technique, slow envelope evolution equations are derived. In the limit of small mechanical vibrations, the micromechanical system can be described as a nonlinear Duffing-like oscillator. Coupling to the optical cavity is shown to introduce corrections to the linear dissipation, the nonlinear dissipation and the nonlinear elastic constants of the micromechanical mirror. The magnitude and the sign of these corrections depend on the exact position of the mirror and on the optical power incident on the cavity. In particular, the effective linear dissipation can become negative, causing self-excited mechanical oscillations to occur as a result of either a subcritical or supercritical Hopf bifurcation. The full slow envelope evolution equations are used to derive the amplitudes and the corresponding oscillation frequencies of different limit cycles, and the bifurcation behavior is analyzed in detail. Finally, the theoretical results are compared to numerical simulations using realistic values of various physical parameters, showing a very good correspondence.

Picosecond pulse generation in a hybrid Q-switched laser source by using a microelectromechanical mirror

We present a novel Q-switched laser source using a micro-optical-electromechanical mirror (MOEM) designed for short pulse emission. It is based on a hybrid configuration including a passively Q-switched microchip laser coupled to a fiber cavity closed by a cantilever type MOEM acting as an active modulator. This specially designed mirror with a single reflecting gold membrane is switched by low bias voltage ~50 V (peak to peak). This device emits pulses at tunable repetition rates up to 1.6 kHz, with ~564 ps duration and 3.4 kW peak power, which constitutes the shortest pulse duration ever reported with MOEMs based pulsed lasers.

Observer-Based Intensity-Feedback Control for Laser Beam Pointing and Tracking

This paper presents an investigation of the control problem of aiming a laser beam under dynamic disturbances, using light intensity for feedback only. The idea is to steer the beam with a biaxial microelectromechanical mirror, which is driven by a control signal generated by processing the beam intensity sensed by a single photodiode. Since the pointing location of the beam is assumed to be unavailable for real-time control, a static nonlinear mapping from the 2-D beam location to the photodiode sensor measurement output is estimated with the use of the least-squares algorithm, treating data from a biaxial optical position sensor as inputs to the static mapping. This formulation results in a nonlinear Wiener-Hammerstein system composed of a linear subsystem connected in series to a nonlinear static output mapping. Conceptually, the controller design problem is addressed with the integration of an observer and a pair of linear time-invariant single-input/single-output controllers into one system. This approach motivates two research questions that are considered independently in this paper. The first is about the multiple-experiment observability of the considered nonlinear optical system. The second is about the search of an heuristic method, based on the extended Kalman filter (EKF) algorithm, for estimating the state of the linear subsystem, necessary for implementing the proposed control approach. Here, we present a compelling answer for the first question and we propose a methodology to tackle the second. It is important to state that the problem considered in this article is very challenging, because the nonlinear static output map of the system is not one-to-one. In order to address this issue, we introduce the idea of integrating stable output disturbance models into the design of the proposed EKF-based observer. This is the main contribution of the paper, which could have an impact in the way other nonlinear control problems are addressed in the future. Evidence of the suitability of the proposed method is provided through experimental results from a case relevant to free-space optics for communications and directed energy applications.

Compact adaptive optics system for multiphoton fundus imaging

A compact adaptive optics system was developed and integrated into the system for multiphoton laser scanning ophthalmoscopy. Defocus, astigmatism, trefoil, and coma are compensated via a combination of telescope and rotating pairs of phase plates. The spherical aberration as well as all dynamic aberrations are corrected by an active micro-electromechanical (MEMS) mirror. Wavefront measurement is conducted by fast SHS and pyramid sensor devices. The MEMS-mirror based adaptive optics system was validated in a study on 60 eyes of 30 subjects.The adaptive-optical multiphoton ophthalmoscope is aimed at detecting the early onset of retinal diseases such as e.g. age-related macula degeneration.

Adaptive flat multiresolution multiplexed computational imaging architecture utilizing micromirror arrays to steer subimager fields of view

A thin, agile multiresolution, computational imaging sensor architecture, termed PANOPTES (processing arrays of Nyguist-limited observations to produce a thin electro-optic sensor), which utilizes arrays of microelectromechanical mirrors to adaptively redirect the fields of view of multiple low-resolution subimagers, is described. An information theory-based algorithm adapts the system and restores the image. The modulation transfer function (MTF) effects of utilizing micromirror arrays to steering imaging systems are analyzed, and computational methods for combining data collected from systems with differing MTFs are presented.

Novel active Q-switched fiber laser based on electrostatically actuated micro-mirror system

<p style="padding:2px; border: 0.05em solid; margin: 2px">It has come to the attention of the Optical Society of America that this article should not have been submitted owing to its substantial replication, without appropriate attribution, of significant elements found in the following previously published material: A. Crunteanu, D. Bouyge, D. Sabourdy, P. Blondy, V. Couderc, L. Grossard, P. H. Ploger and A. Barthelemy, "Deformable micro-electromechanical mirror integration in a fibre laser Q-switched system," J. Opt. A: Pure Appl. Opt. 8 S347-S351 (2006).</p>In this paper, active Q-switching of a double clad codoped erbium-Ytterbium fiber laser using a deformable metallic micro-mirror system is demonstrated. The electrostatically actuated micro-mirror acts both as the end laser cavity reflector and as 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 200 kHz and generates short pulses (FWHM down to 300 ns) and high peak powers.