Sean R. Samuelson

A Large Piston Displacement MEMS Mirror With Electrothermal Ladder Actuator Arrays for Ultra-Low Tilt Applications

A large displacement piston motion micromirror is designed, fabricated, and tested with device features tuned to applications requiring ultralow tilt. The fabricated MEMS mirror is based on electrothermal actuation and has a footprint of 1.9 mm × 1.9 mm with a mirror aperture of 1 mm. The application optimized device holds key features of ultralow maximum tilt of 0.25 ° and a strongly linear motion of 90 μm achievable at only 1.2 V. This device is further characterized in an interferometric system to determine the piston mode and the accurate piston displacement as a function of voltage, power, and frequency.

Handheld miniature probe integrating diffuse optical tomography with photoacoustic imaging through a MEMS scanning mirror.

We describe a novel dual-modality imaging approach that integrates diffuse optical tomography (DOT) and photoacoustic imaging (PAI) through a miniaturized handheld probe based on microelectromechanical systems (MEMS) scanning mirror. We validate this dual-modal DOT/PAI approach using extensive phantom experiments, and demonstrate its application for tumor imaging using tumor-bearing mice systematically injected with targeted contrast agents.

A 2.8-mm Imaging Probe Based On a High-Fill-Factor MEMS Mirror and Wire-Bonding-Free Packaging for Endoscopic Optical Coherence Tomography

This paper reports a miniature optical coherence tomography (OCT) probe and high-resolution 3D OCT imaging results obtained with this probe. The probe is only 2.8-mm in diameter, enabled by a unique high-fill-factor electrothermal MEMS mirror with hidden actuators and a novel wire-bonding-free (WBF) packaging technique. The MEMS mirror has a large mirror aperture of 1 mm with a chip size of only 1.55×1.7×0.5 mm3. The fabricated device achieves large 2-D scan optical angles up to 46° at only 4.8 V. High-resolution 3D OCT imaging results are also demonstrated using this assembled probe.

Endoscopic swept-source optical coherence tomography based on a two-axis microelectromechanical system mirror

Abstract. A microelectromechanical system (MEMS) mirror based endoscopic swept-source optical coherence tomography (SS-OCT) system that can perform three-dimensional (3-D) imaging at high speed is reported. The key component enabling 3-D endoscopic imaging is a two-axis MEMS scanning mirror which has a 0.8×0.8  mm2 mirror plate and a 1.6×1.4  mm2 device footprint. The diameter of the endoscopic probe is only 3.5 mm. The imaging rate of the SS-OCT system is 50  frames/s. OCT images of both human suspicious oral leukoplakia tissue and normal buccal mucosa were taken in vivo and compared. The OCT imaging result agrees well with the histopathological analysis.

High-Fill-Factor Micromirror Array With Hidden Bimorph Actuators and Tip–Tilt-Piston Capability

This paper presents the design, fabrication, packaging, and characterization of a novel high-fill-factor micromirror array (MMA) actuated by electrothermal bimorphs. In this paper, 4 × 4 MMA devices with an 88% area fill factor at normal incidence, 1.5 mm × 1.5 mm subaperture size, and single-crystal-silicon-supported mirror plates have been fabricated based on a single silicon-on-insulator wafer, without additional bonding/transfer processes. The bimorph actuators are hidden underneath the mirror plates, which are also protected by silicon walls. The MMA devices can directly be surface mounted onto driving circuit chips or printed circuit boards after fabrication. The subapertures can generate large tip-tilt-piston scanning and can individually be addressed. Static characterizations of the packaged devices show that each subaperture can achieve a piston stroke of ~310 μm and optical deflection angles greater than ±25° in both the x- and y-axes, all at 8-V dc. The preliminary laser-steering optical-phased-array capability of the obtained MMA device has also experimentally been demonstrated. This paper is based on the conference proceedings presented at the 23rd IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2010), Hong Kong.

A Miniature Fourier Transform Spectrometer by a Large-Vertical-Displacement Microelectromechanical Mirror

A microelectromechanichal system (MEMS) mirror based miniature Fourier transform spectrometer is reported. A spectral resolution of 19.2 cm-1has been achieved with a 261 ?m physical scan range generated by the large-vertical-displacement MEMS mirror.

Miniaturizing Fourier Transform Spectrometer With an Electrothermal Micromirror

An amplitude-division Fourier transform spectroscopy system has been constructed. The system design hinges on an electrothermally actuated micromirror with large piston motion. The micromirror is composed of electrothermal mesh actuators and can generate up to 95 μm usable linear optical path difference of the system at only 0.8 Vdc. A custom electrical system is developed to control the micromirror and data processing is implemented to extract the spectrum from interferograms. The system can achieve a spectral resolution of 5 nm at 532 nm.

A mirror-tilt-insensitive Fourier transform spectrometer based on a large vertical displacement micromirror with dual reflective surface

We report a miniature mirror-tilt-insensitive (MTI) Fourier transform spectrometer. A large-vertical-displacement (LVD) MEMS mirror is used to generate large scan range for high spectral resolution. The LVD MEMS mirror is also reflective on both surfaces. The maximum tilting angle of the MEMS mirror is 1.7° for its entire 1-mm scan range. The combination of a corner-cube retroreflector and dual-reflective MEMS mirror has been used to compensate the mirror tilting successfully and resulted in high spectral resolution of 8.1 cm−1.

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.

Probe alignment and design issues of microelectromechanical system based optical coherence tomography endoscopic imaging

Endoscopic optical coherence tomography (OCT) imaging has been demonstrated using microelectromechanical system (MEMS) technology by several research groups. The focus of this work is to study how the OCT imaging performance is affected by the radius of curvature of MEMS mirrors as well as the optical alignment accuracy inside small imaging probes. The goal of this study is to provide guidance for assembly tolerance and design optimization of OCT endoscopic probes. Gaussian beam propagation is used for theoretical analysis which is confirmed by optical simulation and verified experimentally with a time-domain OCT system as well. It has been found that the OCT imaging is very sensitive to the distance from the fiber end to the gradient-index (GRIN) lens, which needs to be controlled within 0.1 mm to achieve working distance (WD) longer than 3.5 mm and lateral resolution around 25 μm. The impact on image quality of the MEMS mirror is negligible if the radius of curvature of the mirror surface is greater than 200 mm. In addition, we studied the astigmatism introduced by cylindrical plastic tubing; the maximum astigmatism ratio is 1.1 when the WD is around 2.5 mm.