Norman C. Tien

Linear microvibromotor for positioning optical components

We report an electrostatically driven linear microvibromotor fabricated using surface-micromachining technology. This device is developed for use in actuated micro-optical systems on silicon. Its submicron positioning resolution and a travel range of over 350 /spl mu/m are excellent properties for this application. Vibromotor precision and velocity are characterized, and various drive methods are discussed. A simulation of the vibromotor dynamics is presented to explore optimization and control issues for this device.

Optoelectronic packaging using silicon surface-micromachined alignment mirrors

We describe a batch-assembled optoelectronic packaging technology based on silicon surface-micromachined alignment mirrors and demonstrate that these mechanical structures have the functionality, stability and accuracy required for active semiconductor laser-to-filter (single mode) coupling. In initial experiments, we measure an open-loop position accuracy of 0.2 /spl mu/m, and we achieve repeatable 45% coupling efficiency with good mechanical stability.<<ETX>>

Surface-micromachined mirrors for laser-beam positioning

Abstract Actuated surface-micromachined polysilicon micromirrors for laser-beam positioning have been designed and fabricated. Two types of beam-steering mirrors are discussed which use microhinge technology to achieve the required vertical dimensions and functionality. One mirror, intended for precise beam positioning as needed in optical alignment, is actuated by linear microvibromotors. The other mirror is appropriate for laser-beam scanning and uses electrostatic comb-drive actuators. Four layers of polycrystalline silicon are micromachined to form these devices. Environmental stress testing carried out on the beam-positioning mirror has shown its structure to be relatively insensitive to vibrations below 60 kHz. Further testing has shown negligible changes in mirror position for temperatures varying between 25 and 200°C, and stability under the stress of laser irradiation of 375 mW at 1.06 μm wavelength.

Laser-to-fiber coupling module using a micromachined alignment mirror

We report the fabrication of a laser-to-fiber coupling module that incorporates a movable silicon-micromachined alignment micromirror. The micromirror can position a beam on a fiber within a 0.17 /spl mu/m standard deviation and has a range of motion of more than 200 /spl mu/m. Measurements on the module have shown a reproducible coupling efficiency of 40%. The coupling module provides a means to compensate for placement inaccuracies of passively assembled optical components.

3D MEMS based minimally invasive optical coherence tomography

A 3D optical coherence tomography (OCT) system based on a high-speed micromachined scanning mirror is presented. The sampling resolution of each voxel is 10/spl mu/m/spl times/10/spl mu/m/spl times/10/spl mu/m the optical resolution is 20/spl mu/m/spl times/20/spl mu/m/spl times/10/spl mu/m. In this work test-structures as well as in-vitro and in-vivo biological tissue samples are imaged. Cross-sectional images are collected and displayed in realtime; these images are subsequently combined to reconstruct a 3D image of the sample. Images from the 3D MEMS OCT system have been utilized to clearly identify dysplasia (initial stage of cancer) in hamster cheek pouch tissue by experts in the field, and have shown excellent correlation with histology slides of the same sample.

Precision and performance of polysilicon micromirrors for hybrid integrated optics

We have designed and built integrated, movable micromirrors for on-chip alignment in silicon- optical-bench technology. The mirrors are fabricated using surface micromachining with three polysilicon layers. A polysilicon-hinge technology was used to achieve the required vertical dimensions and functionality for alignment in hybrid photonic integrated circuits. The positioning accuracy of the mirrors is measured to be on the order of 0.2 micrometers . This precision is shown theoretically and experimentally to be sufficient for laser-to-fiber coupling. In the experimental verification, we used external actuators to position the micromirror and obtained 45% coupling efficiency from a semiconductor laser (operating at 1.3 micrometers ) to a standard single-mode optical fiber. The stability and robustness of the micromirrors were demonstrated in shock and vibration tests that showed that the micromirrors will withstand normal handling and operation without the need for welding or gluing. This micromirror technology combines the low-cost advantage of passive alignment and the accuracy of active alignment. In addition to optoelectronic packaging, the micromirrors can be expected to find applications in grating-tuned external-cavity lasers, scanning lasers, and interferometers.

Actuation of polysilicon surface-micromachined mirrors

Two types of polysilicon surface-micromachined actuators designed for moving hinged micromirrors are described. An electrostatic comb-drive actuator comprised of interdigitated capacitors has been used to move a mirror at frequencies of at least a kHz. Impact-actuated linear vibromotors allow mirrors to travel over large (> 100 micrometers ) ranges with submicron positioning.

Impact-actuated linear microvibromotor for micro-optical systems on silicon

Electrostatic actuation has received much attention recently for its potential application in microelectromechanical systems. However, in order to generate the forces needed in many applications, very high voltages (>100 V) are often required. Actuators based on impact have been shown to be a feasible alternative. With impact, a very large force of short duration can be delivered to move a microelement. We describe a surface-micromachined linear-motion microvibromotor to perform this function. The microvibromotor offers: large range of motion, high velocity and precise positioning. Our initial application is to position optical elements, such as mirrors or diffraction gratings, in a micro-optical system on silicon.<<ETX>>

Optical coherence tomography based on high-speed scanning MEMS mirror

An optical coherence tomography (OCT) system based on a high-speed microelectromechanical system (MEMS) mirror is presented. This scanning mirror has high-speed performance because it was actuated by vertical comb drive. The size of mirror was 600 mm x 600 mm and the resonant frequencies were between 3.5 kHz to 8 kHz. In the test of scanner itself, it was operated linearly and scanned up to 30 degree angle. The MEMS mirror also provides 2-axis scanning while occupying a very small volume with extremely low power consumption. In our study, it was integrated with conventional fiber based OCT system. Via 2-axis lateral scanning, combined with an axial scan, a volume (2 mm x 2 mm x 1.4 mm) image of tissue, including a cancerous region, from a hamster cheek pouch was obtained. The axial and lateral resolution of images are 10 mm and about 20 mm respectively.

A MEMS based Optical Coherence Tomography Imaging System and Optical Biopsy Probes for Real-Time, High Resolution In-Vivo and In-Vitro 2-D or 3-D Imaging

A fully-functional, real-time optical coherence tomography (OCT) system based on a high-speed, gimbal-less micromachined scanning mirror is presented. The designed MEMS control architecture allows the MEMS based imaging probes to be connected to a time-domain, a Fourier domain or a spectral domain OCT system. Furthermore, a variety of probes optimized for specific laboratory or clinical applications including various minimally invasive endoscopic, handheld or lab-bench mounted probes may be switched between effortlessly and important driving parameters adjusted in real-time. In addition, artifact free imaging speeds of 33 mus per voxel have been achieved while imaging a 1.4 mmtimes1.4 mmtimes1.4 mm region with 5 mumtimes5 mumtimes5 mum sampling resolution (SD-OCT system)