Video-rate volumetric optical coherence tomography (vOCT) is relatively young in the field of OCT imaging but has great potential in biomedical applications. Due to the recent development of the MHz range swept laser sources, vOCT has started to gain attention in the community. Here, we report the first in vivo video-rate volumetric OCT-based microangiography (vOMAG) system by integrating an 18-kHz resonant microelectromechanical system (MEMS) mirror with a 1.6-MHz FDML swept source operating at ∼1.3 μm wavelength. Because the MEMS scanner can offer an effective B-frame rate of 36 kHz, we are able to engineer vOMAG with a video rate up to 25 Hz. This system was utilized for real-time volumetric in vivo visualization of cerebral microvasculature in mice. Moreover, we monitored the blood perfusion dynamics during stimulation within mouse ear in vivo. We also discussed this system’s limitations. Prospective MEMS-enabled OCT probes with a real-time volumetric functional imaging capability can have a significant impact on endoscopic imaging and image-guided surgery applications.
Fraunhofer IPMS developed a new type of small-sized scanning mirror for Laser projection systems in mobile
applications. The device consists of a single crystal mirror plate of 1 mm diameter in a gimbal mounting enabling a bi-resonant
oscillation of both axes at a resonance frequency of about 100 Hz and 27 kHz respectively. The mechanical
scan angle (MSA) achieved is ± 7° for the slow and ± 12° for the fast axis. The mirror angle position and phase can be
read out via two piezo-resistive sensors located at the torsion axes. In order to allow for a minimum device size of the
resonantly driven slow axis the sensor of the inner fast axis was connected by a new kind of thin silicon conductors.
Those are created by means of an etch stop in TMAH etch and kept as thin as possible in order to reduce their
contribution to the mechanical stiffness of the mirror-supporting structures. This new system enables to lead six (or even
more) independent electrical potentials onto the moving parts of the device, whereas the mechanical properties are
mainly determined by only 2 torsion axes. The devices were subsequently characterized and tested. Technology details,
simulation results, pictures of the device and the new conductor structures as well as measurement results are presented.
Magnetically-actuated micromachined scanning mirrors have been developed for pico-projectors using laser beam
scanning (LBS). The human vision system readily detects imperfections in a LBS display, which become objectionable
when scanned beam trajectory errors have amplitudes on the order of only parts per thousand, depending on the human
vision system's sensitivity to the type of error and whether it is static or dynamic. The paper describes the overcoming of
such challenges to achieve a high quality LBS projection.
In this paper, a nonlinear mathematic model for Microvision's MOEMS scanning mirror is presented. The pixel
placement accuracy requirement for scanned laser spot displays translates into a roughly 80dB signal to noise ratio, noise
being a departure from the ideal trajectory. To provide a tool for understanding subtle nonidealities, a detailed nonlinear
mathematical model is derived, using coefficients derived from physics, finite element analysis, and experiments.
Twelve degrees of freedom parameterize the motion of a gimbal plate and a suspended micromirror; a thirteenth is the
device temperature. Illustrations of the application of the model to capture subtleties about the device dynamics and
transfer functions are presented.
The applicability of MOEMS scanning mirrors towards the creation of "flying spot" scanned laser displays is well
established. The extension of this concept towards compact embedded pico-projectors has required an evolution of
scanners and packaging to accommodate the needs of the consumer electronics space. This paper describes the
progression of the biaxial MOEMS scanning mirrors developed by Microvision over recent years. Various aspects of the
individual designs are compared. Early devices used a combination of magnetic quasistatic actuation and resonant
electrostatic operation in an evacuated atmosphere to create a projection engine for retinal scanned displays. Subsequent
designs realized the elimination of both the high voltage electrostatic drive and the vacuum package, and a simplification
of the actuation scheme through proprietary technical advances. Additional advances have doubled the scan angle
capability and greatly miniaturized the MOEMS component while not incurring significant increase in power
consumption, making it an excellent fit for the consumer pico-projector application.
The simplicity of the scanned laser-based pico-projector optical design enables high resolution and a large effective
image size in a thin projection engine, all of which become critical both to the viability of the technology and adoption
by consumers. Microvision's first scanned laser pico-projector is built around a MOEMS scanning mirror capable of
projecting 16:9 aspect ratio, WVGA display within a 6.6 mm high package. Further evolution on this path promises
continued improvement in resolution, size, and power.
Damping is a critical factor affecting the dynamics of resonant scanning micromirrors and the design of their actuator
systems. For any new micromirror design, modeling the damping to sufficient accuracy to predict the performance can
save much effort in testing and redesign. To address this challenge, a simple formula for the air drag on scanning
micromirrors is postulated that contains a drag coefficient, which is treated as a function of the Reynolds number that is
fit to experimental measurements of the damping of two different MEMS scanning mirrors. A formula is found that
describes the drag coefficients for both scanning mirrors for a range of their Reynolds numbers.
This paper describes the design, fabrication, and characterization of the first MEMS scanning mirror with performance
matching the polygon mirrors currently used for high-speed consumer laser printing. It has reflector dimensions of 8mm
X 0.75mm, and achieves 80o total optical scan angle at an oscillation frequency of 5kHz. This performance enables the
placement of approximately 14,000 individually resolvable dots per line at a rate of 10,000 lines per second, a record-setting
speed and resolution combination for a MEMS scanner. The scanning mirror is formed in a simple
microfabrication process by gold reflector deposition and patterning, and through-wafer deep reactive-ion etching. The
scanner is actuated by off-the-shelf piezo-ceramic stacks mounted to the silicon structure in a steel package. Device
characteristics predicted by a mathematical model are compared to measurements.
In 2004, Microvision presented "Scanned Beam Medical Imager" as an introduction to our MEMS-based, full
color scanned beam imaging system. This presentation will provide an update of the technological advancements since
this initial work from 2004. This recent work includes the development of functional prototypes that are much smaller
than previous prototypes using a design architecture that is easily scalable. Performance has been significantly
improved by increasing the optical field of views and video refresh rate. Real-time image processing capabilities have
been developed to enhance the image quality and functionality over a wide range of operating conditions. Actual
images of various objects will be presented.
In this paper we present the analytical and experimental investigation of the air damping of micromachined scanning mirrors with out-of-plane comb drive actuation. A simple, compact model for the damping torque is derived by estimating the orders of magnitude of certain damping contributors. Viscous damping in comb finger gaps is estimated to be the dominant contributor. Because the comb fingers disengage as the scan amplitude increases, the damping coefficient is dependent on the amplitude of angular vibrations. Experimental measurements are presented for a variety of comb-finger geometries. The comb finger length, width, and the gap between comb fingers are varied, and the damping behaviour for single-axis scanning is characterised by measuring the decay rate of free oscillations. The damping is characterised by the exponential decay constant δ, found by fitting to the decaying oscillation amplitude. The predictions of the analytical model are compared to these experimental damping measurements.