Optical fibers guide light between separate locations and enable new types of fluorescence imaging. Fiber-optic fluorescence imaging systems include portable handheld microscopes, flexible endoscopes well suited for imaging within hollow tissue cavities and microendoscopes that allow minimally invasive high-resolution imaging deep within tissue. A challenge in the creation of such devices is the design and integration of miniaturized optical and mechanical components. Until recently, fiber-based fluorescence imaging was mainly limited to epifluorescence and scanning confocal modalities. Two new classes of photonic crystal fiber facilitate ultrashort pulse delivery for fiber-optic two-photon fluorescence imaging. An upcoming generation of fluorescence imaging devices will be based on microfabricated device components.

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Fiber-optic fluorescence imaging.

A Miniature Head-Mounted Two-Photon Microscope: High-Resolution Brain Imaging in Freely Moving Animals

A novel microelectromechanical systems (MEMS) actuation technique is developed for retinal scanning display and imaging applications allowing effective drive of a two-axes scanning mirror to wide angles at high frequency. Modeling of the device in mechanical and electrical domains, as well as the experimental characterization is described. Full optical scan angles of 65deg and 53deg are achieved for slow (60 Hz sawtooth) and fast (21.3 kHz sinusoid) scan directions, respectively. In combination with a mirror size of 1.5 mm, a resulting thetasopt D product of 79.5 degmiddotmm for fast axis is obtained. This two-dimensional (2-D) magnetic actuation technique delivers sufficient torque to allow non-resonant operation as low as dc in the slow-scan axis while at the same time allowing one-atmosphere operation even at fast-scan axis frequencies large enough to support SXGA (1280 times 1024) resolution scanned beam displays

Two-axis electromagnetic microscanner for high resolution displays

“Structured”, “Textured” or “Engineered” Surfaces

Laser scanners have been an integral part of MEMS research for more than three decades. During the last decade, miniaturized projection displays and various medical-imaging applications became the main driver for progress in MEMS laser scanners. Portable and truly miniaturized projectors became possible with the availability of red, green, and blue diode lasers during the past few years. Inherent traits of the laser scanning technology, such as the very large color gamut, scalability to higher resolutions within the same footprint, and capability of producing an always-in-focus image render it a very viable competitor in mobile projection. Here, we review the requirements on MEMS laser scanners for the demanding display applications, performance levels of the best scanners in the published literature, and the advantages and disadvantages of electrostatic, electromagnetic, piezoelectric, and mechanically coupled actuation principles. Resonant high-frequency scanners, low-frequency linear scanners, and 2-D scanners are included in this review.

/pdf/mems-laser-scanners-a-review-3umum14m4r.pdf

MEMS Laser Scanners: A Review

This paper reports on design, fabrication and characterization of high-Q MEMS resonators to be used in optical applications like laser displays and LIDAR range sensors. Stacked vertical comb drives for electrostatic actuation of single-axis scanners and biaxial MEMS mirrors were realized in a dual layer polysilicon SOI process. High Q-factors up to 145,000 have been achieved applying wafer level vacuum packaging technology including deposition of titanium thin film getters. The effective reduction of gas damping allows the MEMS actuator to achieve large amplitudes at high oscillation frequencies while driving voltage and power consumption can be minimized. Exemplarily shown is a micro scanner that achieves a total optical scan angle of 86 degrees at a resonant frequency of 30.8 kHz, which fulfills the requirements for HD720 resolution. Furthermore, results of a new wafer based glass-forming technology for fabrication of three dimensionally shaped glass lids with tilted optical windows are presented.

https://www.mdpi.com/2072-666X/3/2/509/pdf

High-Q MEMS Resonators for Laser Beam Scanning Displays

A compact two-mirror microscanner has been fabricated to build the central part of a miniaturized confocal laser scanning microscope. This microscope shall be mounted at the tip of an endoscope to provide high resolution imaging for medical diagnostics. In order to achieve a resolution of 500 X 500 image elements large scan angles and also large mirror dimensions have to be realized within a spatially strong limited housing. While bulk silicon technology on the one hand enables fabrication of micromirrors with nearly ideal elastical behavior, those actuators on the other hand often are too fragile for a lot of applications. This paper describes the design, fabrication and assembling of electrostatically driven torsional micromirrors that meet the requirements of fast two-dimensional scanning with high angular precision over large scan angles, compact design and also high shock resistance. This is achieved with the combination of bulk silicon technology with metal surface micromachining. Besides medical diagnostics these microscanners can be used in a wider range of applications such as displays, two-dimensional barcode scanning, multiplexing of fiber optics, etc.

Electrostatically driven micromirrors for a miniaturized confocal laser scanning microscope

Scanning laser projection using resonant actuated MEMS scanning mirrors is expected to overcome the current
limitation of small display size of mobile devices like cell phones, digital cameras and PDAs. Recent progress in the
development of compact modulated RGB laser sources enables to set up very small laser projection systems that become
attractive not only for consumer products but also for automotive applications like head-up and dash-board displays.
Within the last years continuous progress was made in increasing MEMS scanner performance. However, only little is
reported on how mass-produceability of these devices and stable functionality even under harsh environmental
conditions can be guaranteed. Automotive application requires stable MEMS scanner operation over a wide temperature
range from -40° to +85°Celsius. Therefore, hermetic packaging of electrostatically actuated MEMS scanning mirrors
becomes essential to protect the sensitive device against particle contamination and condensing moisture. This paper
reports on design, fabrication and test of a resonant actuated two-dimensional micro scanning mirror that is hermetically
sealed on wafer level. With resonant frequencies of 30kHz and 1kHz, an achievable Theta-D-product of 13mm.deg and
low dynamic deformation <20nm RMS it targets Lissajous projection with SVGA-resolution. Inevitable reflexes at the
vacuum package surface can be seperated from the projection field by permanent inclination of the micromirror.

Wafer-level vacuum packaged resonant micro-scanning mirrors for compact laser projection displays

A resonant biaxial comb-actuated 7mm-MEMS scanning mirror with tripod-suspension is developed to provide omnidirectional scanning in an automotive time-of-flight LIDAR sensor application. Wafer level vacuum packaging technology is applied to enable circular scanning at 550Hz at large tilt angle.

Biaxial resonant 7mm-MEMS mirror for automotive LIDAR application

Low-cost automotive laser scanners for environmental perception are needed to enable the integration of advanced driver assistant systems into all automotive vehicle segments, which is a key to reduce the number of traffic accidents on roads. Within the scope of the European-funded project MiniFaros, partners from five different countries have been cooperating in developing a small-sized low-cost time-of-flight-based range sensor. An omnidirectional 360-deg laser scanning concept has been developed based on the combination of an omnidirectional lens and a biaxial large aperture MEMS mirror. The concept, design, fabrication, and first measurement results of a resonant biaxial 7-mm gimbal-less MEMS mirror that is electrostatically actuated by stacked vertical comb drives is described. Identical resonant frequencies of the two orthogonal axes are necessary to enable the required circle scanning capability. A tripod suspension was chosen, since it minimizes the frequency splitting of the two resonant axes. Low-mirror curvature is achieved by a thickness of the mirror of more than 500 μm. Hermetic wafer-level vacuum packaging of such large mirrors based on multiple wafer bonding has been developed to enable a large mechanical tilt angle of ±6.5  deg in each axis. Due to the large targeted tilt angle of ±15  deg and because of the MEMS mirror actuator having a diameter of 10 mm, a cavity depth of about 1.6 mm has been realized.

Ulrich Hofmann

Papers

High-Q MEMS Resonators for Laser Beam Scanning Displays

Electrostatically driven micromirrors for a miniaturized confocal laser scanning microscope

Wafer-level vacuum packaged resonant micro-scanning mirrors for compact laser projection displays

Biaxial resonant 7mm-MEMS mirror for automotive LIDAR application

Resonant biaxial 7-mm MEMS mirror for omnidirectional scanning