Wibool Piyawattanametha

Two-axis MEMS Scanning Catheter for Ultrahigh Resolution Three-dimensional and En Face Imaging

Ultrahigh resolution two and three-dimensional optical coherence tomography (OCT) imaging was performed using a miniaturized, two-axis scanning catheter based upon microelectromechanical systems (MEMS) mirror technology. The catheter incorporated a custom-designed and fabricated, 1-mm diameter MEMS mirror driven by angular vertical comb (AVC) actuators on both an inner mirror axis and an outer, orthogonal gimbal axis. Using a differential drive scheme, a linearized position response over +/- 6 degrees mechanical angle was achieved. The flexible, fiber-optic catheter device measured < 5 mm in outer diameter with a rigid length of ~ 2.5 cm at the distal end. In vivo and ex vivo images are presented with < 4 microm axial and ~ 12 microm transverse resolution in tissue.

Surface- and bulk- micromachined two-dimensional scanner driven by angular vertical comb actuators

In this paper, we present the design, fabrication, and measurements of a two-dimensional (2-D) optical scanner with electrostatic angular vertical comb (AVC) actuators. The scanner is realized by combining a foundry-based surface-micromachining process (Multi-User MEMS Processes-MUMPs) with a three-mask deep-reactive ion-etching (DRIE) postfabrication process. The surface-micromachining provides versatile mechanical design and electrical interconnect while the bulk micromachining offers high-aspect ratio structures leading to flat mirrors and high-force, large-displacement actuators. The scanner achieves dc mechanical scanning ranges of /spl plusmn/6.2/spl deg/ (at 55 Vdc) and /spl plusmn/4.1/spl deg/ (at 50 Vdc) for the inner and outer gimbals, respectively. The resonant frequencies are 315 and 144 Hz for the inner and the outer axes, respectively. The 1-mm-diameter mirror has a radius of curvature of over 50 cm. [1454].

Angular vertical comb-driven tunable capacitor with high-tuning capabilities

This paper reports on a novel tunable capacitor with electrostatic angular vertical comb-drive (AVC) actuators. The AVC tunable capacitor creates a large offset in comb fingers through a small rotation angle-an advantage not found in conventional lateral comb-drive devices. High capacitance and large continuous tuning ratio is achieved in a compact device area. The largest tuning varactor demonstrates capacitance values between 0.27-8.6 pF-a tuning ratio of more than 31:1, the highest ever reported. The maximum quality factor Q is 273 at 1 GHz near the minimum capacitance value.

Surface-micromachined confocal scanning optical microscope

Summary form only given.The confocal scanning microscope (CSM) can create high-resolution three-dimensional (3D) images of thick and light-scattering objects from successive acquisition of 2D images through its optical sectioning property. This capability allows us to develop a micro-optical-endoscope for high-quality in vivo imaging of living tissue. The microelectromechanical system (MEMS) approach has shown great promise to produce miniaturized CSMs by batch fabrication. We propose a novel surface micromachined 2D scanner to extend the performance of CSMs. This microscope is called surface-micromachined confocal scanning optical microscope (CSOM).

A 2D scanner by surface and bulk micromachined vertical comb actuators

We present the design, fabrication, and demonstration of a fully decoupled 2D gimbal scanner with angular vertical comb (AVC) actuators. The device is realized by combining a foundry surface-micromachining process (MUMPs) with a 3-mask deep-reactive-ion- etching (DRIE) post process. Surface-micromachining provides versatile mechanical design and electrical interconnect while bulk micromachining offers flat micromirrors and high-force actuators. The scanner achieves DC mechanical scanning ranges of /spl plusmn/6.2/spl deg/ (at 55 Vdc) and /spl plusmn/4.1/spl deg/ (at 50 Vdc) for the inner and outer gimbals, respectively. The 1-mm mirror has a radius of curvature of 40 cm.

Scanning micromirrors: An overview

An overview of the current state of the art in scanning micromirror technology for switching, imaging, and beam steering applications is presented. The requirements that drive the design and fabrication technology are covered. Electrostatic, electromagnetic, and magnetic actuation techniques are discussed as well as the motivation toward combdrive configurations from parallel plate configurations for large diameter (mm range) scanners. Suitability of surface micromachining, bulk micromachining, and silicon on insulator (SOI) micromachining technology is presented in the context of the length scale and performance for given scanner applications.

A surface and bulk micromachined angular vertical combdrive for scanning micromirrors

We present a high performance scanning micromirror with angular vertical comb actuators realized by combining MUMPs with a 3-mask deep-reactive-ion-etching post process. A DC scan angle of /spl plusmn/4/spl deg/ (mechanical) is achieved at 40 V.

A MEMS Non-interferometric Differential Confocal Scanning Optical Microscope

This paper describes a novel microelectromechanical system (MEMS) non-interferometric differential confocal scanning optical microscope. It consists of a single mode fiber aperture, a 450×450 µm2 2-D scanner, and a 1.8-mm-diameter graded index objective lens. We have acheived a lateral resolution of 1.6 µm and a field of view of 60×60 µm2. A depth resolution of 0.6 µm is achieved in differential mode. The MEMS confocal microscpe is very compact and suitable for endoscopic imaging applications.

Ultrahigh resolution OCT imaging with a two-dimensional MEMS scanning endoscope

This paper reports preliminary results from the development and application of a two-dimensional MEMS endoscopic scanner for OCT imaging. A 1 mm diameter mirror provides high aperture over large scan angle and can scan at rates of hundreds of Hz in both axes. The mirror is integrated with focusing optics and a fiber-optic collimator into a package of ~5 mm diameter. Using a broadband femtosecond laser light source, ultrahigh axial image resolution of < 5 um in tissue is achieved at 1.06 um center wavelength. Ultrahigh resolution cross-sectional and three-dimensional OCT imaging is demonstrated with the endoscope with ~12 um transverse resolution and < 5 um axial resolution.

High-Resolution 3D OCT Imaging with a MEMS Scanning Endoscope

Three-dimensional imaging is achieved by optical coherence tomography (OCT) integrated with a two-axis MEMS scanner to enable noninvasive volume imaging of biological tissues. The longitudinal scan is obtained by optical coherence interferometry. The transverse scan is obtained by tilting the two-axis MEMS mirror to scan the optical beam across the target. High-resolution OCT imaging has enabled in vivo observation of tissue architectural layers and differentiation of normal from tumor lesions within the human gastrointestinal tract. MEMS scanner based catheters with distal beam scanning can image with higher speed, precision, and repeatability than conventional linear scanning catheters. In this work, a 1-mm diameter MEMS scanning mirror with collimator and focusing optics is integrated into a compact 5-mm diameter package that is compatible with limited space in the endoscope. A large fill factor mirror provides high aperture over large scan angle and frequencies of hundreds of Hz in both axes. Using a broadband femtosecond laser light source, high axial image resolution of ~5 um is achieved at 1.06 um wavelength. Transverse resolution of ~ 12-um is demonstrated for cross-sectional image with the endoscope.