S.S. Lee

Micromachined free-space integrated micro-optics

Abstract The surface-micromachining technique has been employed to fabricate novel three-dimensional micro-optical elements for free-space integrated optics. The optical axes of these optical elements are parallel to the substrate, which enables the entire free-space optical system to be integrated on a single substrate. Microscale Fresnel lenses, mirrors, beam splitters, gratings, and precision optical mounts have been successfully fabricated and characterized. In addition, micropositioners such as rotary stages and linear translational stages are monolithically integrated with the optical components using the same surface-micromachining process to provide on-chip optical alignment or optomechanical switching. Self-aligned hybrid integration with semiconductor edge-emitting lasers and vertical cavity surface-emitting lasers are also demonstrated for the first time. This new free-space micro-optical bench (FSMOB) technology could significantly reduce the size, weight, and cost of most optical systems, and could have a significant impact on optical switching, optical sensing and optical data-storage systems as well as on the packaging of optoelectronic components.

Design and nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch

In this paper, we demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in an optical cross-connect. We show switching times of less than 10 ms and optical power stability of better than 0.2 dB. The mirrors, made from 10-/spl mu/m-thick single-crystal silicon and with a radius of 400-450 /spl mu/m, are able to tilt to 8/spl deg/ corresponding to 80% of touchdown angle. This is achieved using a nonlinear closed-loop control algorithm, which also results in a maximum actuation voltage of 85 V, and a pointing accuracy of less than 150 /spl mu/rad. This paper will describe the MEMS mirror and actuator design, modeling, servo design, and measurement results.

Surface‐micromachined free‐space micro‐optical systems containing three‐dimensional microgratings

Free‐space micro‐optical systems on a chip containing three‐dimensional microgratings have been demonstrated using surface‐micromachining technique. The micrograting is integrated with a rotary stage, a collimating micro‐Fresnel lens, and an edge‐emitting laser held by three‐dimensional alignment structures on a single Si substrate. Diffraction patterns for various grating rotation angles are observed. Another optical interconnect module consisting of three cascaded microgratings is also demonstrated. The micrograting is a basic building block for many micro‐optical systems and is very attractive for applications in microspectrometers, free‐space optical interconnect, optoelectronic packaging, and wavelength‐division multiplexed integrated micro‐optical systems.

Realization of novel monolithic free-space optical disk pickup heads by surface micromachining

A novel monolithic free-space optical disk pickup head has been fabricated by micromachined micro-optical bench technology. The pickup head contains a self-aligned semiconductor edge-emitting laser, a collimating lens, a beam splitter, two focusing lenses, and two 45 degrees mirrors. All optical components are built monolithically on Si substrates. The 45 degrees mirror directs the optical output beam in the surface-normal direction. This novel design could signif icantly reduce the size and the weight of the optical pickup head as well as the cost of the assembly processes. The weight reduction could also greatly increase the data access rate.

Free-Space Integrated Optics Realized by Surface-Micromachining

A surface-micromachined free-space micro-optical bench (FS-MOB) technology has been proposed to monolithically integrate micro-optical elements, optomechanical structures, micropositioners, and microactuators on the same substrate. Novel three-dimensional micro-optical elements have been fabricated by surface-micromachining techniques. The optical axes of these optical elements are parallel to the substrate, which enables the entire free-space optical system to be integrated on a single substrate. Mocro-scale Fresnel lenses, refractive microlenses, mirrors, beam-splitters, gratings, and precision optical mounts have been successfully fabricated and characterized. Integration of micro-optical elements with translation or rotation stages provides on chip optical alignment or optomechanical switching. This new free-space micro-optical bench technology could significantly reduce the size, weight, an cost of most optical systems, and could have a significant impact on optical switching, optical sensing and optical data storage systems as well as packaging of optoelectronic components.

Micromachined integrated optics for free-space interconnections

A novel surface micro-machined micro-optical bench (MOB) has been demonstrated. Free-space micro-optics such as micro-Fresnel lenses, rotatable mirrors, beam-splitters and gratings are implemented on a single Si chip using IC-like microfabrication processes. Self-aligned hybrid integration with semiconductor lasers are also demonstrated for the first time. The MOB technology realizes a microoptical system on a single Si chip and has significant impact on free-space integrated optics, optical switching, optical data storage, and optoelectronic packaging. free-space. Using this new technique, threedimensional micro-optical components can be fabricated integrally on a single Si chip. The Si substrate serves as a “micro-optical bench (MOB)” on which micro-lenses, mirrors, gratings and other optical components are pre-aligned in the mask layout stage using computer-aided design and then constructed by microfabrication. Additional fine adjustment can be achieved by the on-chip micro-actuators and micropositioners such as rotational and translational stages. With hybrid integration of active optical devices, a complete optical system can be constructed on the MOB, as illustrated in Fig. 1.

Modular MEMS-based optical cross-connect with large port-count

We describe and demonstrate a modular microelectromechanical systems (MEMS)-based optical cross-connect (OXC) architecture. The OXC port count increases modularly by adding new optical modules, and a maximum cross-connectivity of /spl sim/ 350 /spl times/ 350 can be achieved in the current design. Each optical module has 16 ports with closed-loop servo-controlled MEMS mirrors. Using a prototype OXC system, mounted in a standard telecommunications equipment bay comprising optical modules, folding mirrors, and other optical elements, we demonstrate switching times of less than 10 ms, excellent optical power stability of less than /spl plusmn/ 0.15-dB variation, and immunity to stochastic vibrations. An automatic power peak-up process is performed when the power falls below 0.5-dB off the maximum coupled power for any connection.

Surface-micromachined micro-XYZ stages for free-space microoptical bench

Micro-XYZ stages have been monolithically integrated with microactuators and out-of-plane microoptical elements, all fabricated by the same surface-micromachined process, on Si free-space microoptical bench. Optical beam adjustment with three degrees of freedom has been realized without angular squinting. A positioning accuracy of 11 nm has been achieved by the integrated scratch drive actuators, with the travel distance larger than 30 /spl mu/m in each direction.

Electrostatic actuation of three-dimensional MEMS mirrors using sidewall electrodes

We propose and demonstrate electrostatic sidewall-electrodes actuation of three-dimensional (3-D) microelectromechanical systems (MEMS) gimbal mirrors. The linearity of the mirror angle dependence on actuation voltage is improved with the sidewall-electrodes actuation. In addition, the undesired spring-softening effect commonly found in electrostatic actuation, where the mirror resonance frequency decreases with increased tilt angle, is significantly reduced. Sidewall actuation enables superior performance of 3-D MEMS mirrors including large pull-in angles, reduced actuation voltages, improved device reliability, and fast switching times.

Tunable three-dimensional solid Fabry-Perot etalons fabricated by surface-micromachining

We report on novel tunable three-dimensional solid Fabry-Perot etalons fabricated by the surface-micromachining technique. The Fabry-Perot etalon is monolithically integrated with an on-chip rotation stage for angle tuning. A wavelength tuning range of 45 nm has been achieved at 1.3 /spl mu/m wavelength for a rotation angle of 70/spl deg/. The optical properties of the polysilicon materials have also been characterized using the etalon as testing vehicles.