C. Randy Giles

Lucent Microstar micromirror array technology for large optical crossconnects

Electrostatically actuated, 500micrometers diameter, Si surface micromachined 2-axis tilting micromirrors were designed and fabricated in a 2 structural + 1 interconnect layer polysilicon process. The mirrors are capable of large, continuous, controlled, DC tilt in any direction at moderate actuation voltages. The lowest-mode resonance frequency is sufficiently high to decouple from the ambient vibration noise and allow setting times of less than a few milliseconds. The Au- coated reflectors, suspended in gimbal mounts via torsional springs and bearings, are tilted by applying voltage to four electrically independent sets of fixed electrodes on the substrate. The electrodes and the springs are designed to optimize actuation voltages, resonance frequencies and the deflection range. To achieve the range, the mounts are lifted and fixed fifty microns above the substrate surface during the release process by a self-assembly mechanism powered by tailored residual stress in a separate metalization layer. Square arrays with 1 mm pitch containing independently addressable identical 16, 64 and 256 mirrors were fabricated and hermetically packaged. Based on these devices, fully functional, bitrate and wavelength independent, single stage, low insertion loss, single mode fiber optical crossconnect system are built.

The Little Machines That are Making it Big

Microelectromechanical systems are currently used in a variety of applications, including triggering airbags and measuring the Casimir force. In the future, they may revolutionize the way we think about machines.

Optical MEMS devices for telecom systems

As telecom networks increase in complexity there is a need for systems capable of manage numerous optical signals. Many of the channel-manipulation functions can be done more effectively in the optical domain. MEMS devices are especially well suited for this functions since they can offer large number of degrees of freedom in a limited space, thus providing high levels of optical integration. We have designed, fabricated and tested optical MEMS devices at the core of Optical Cross Connects, WDM spectrum equalizers and Optical Add-Drop multiplexors based on different fabrication technologies such as polySi surface micromachining, single crystal SOI and combination of both. We show specific examples of these devices, discussing design trade-offs, fabrication requirements and optical performance in each case.

MEMS/MOEMS for lightwave networks: Can little machines make it big?

Silicon micromechanics is an emerging field which is beginning to impact almost every area of science and technology. In areas as diverse as the chemical, automotive, aeronautical, cellular and optical communications industries, Silicon micromachines are becoming the solution of choice for many problems. In this paper we will describe what they are, how they are builit and show how they have the potential to revolutionize lightwave systems. Devices such as optical switches, variable attenuators, active equalizers, add/drop multiplexers, optical crossconnects, gain tilt equalizers, data transmitters and many others are beginning to find ubiquitous application in advanced lightwave systems. We will show examples of these devices and describe some of the challenges in attacking the billions of dollars in addressable markets for this technology. 1. What is a MEMS Device? MEMS research is an outgrowth of the vast capabilities developed by the semiconductor industry, including deposition, etching, and lithography, as well as an array of chemical processes such as anisotropic and highly selective etches having different etch rates for different crystallographic orientations and materials. These processes, which were originally developed to build microelectronic devices, are also capable of building micromechanical devices—structures capable of motion on a microscopic scale. MEMS devices are built in much the same way as a silicon integrated circuit (see the figure, upper left hand side). Various films such as polysilicon, silicon nitride, silicon dioxide, and gold are deposited and patterned to produce complicated, multilayer three-dimensional structures. However, the major difference is a release step at the end. In a MEMS device, some of the layer materials are removed using a selective etch, leaving a device with moveable elements. MEMS devices offer a number of advantages to designers. They are made using integrated circuit (IC) batch-processing techniques, so although fabrication may consist of a complicated, multistep process, the devices are economical to produce because many are made simultaneously. In addition, designers and *For more information please contact David Bishop, djblucent.com Also published in Proceedings of SPIE Volumes 4174, 4176, 4177, 4178, 4179, and 4180. In Materials and Device Characterization in Micromachining Ill, YuIi Vladimirsky, Philip J. Coane, Editors, Proceedings of SPIE Vol. 4175 (2000) • 0277-786X!OO/

Design for reliability of MEMS/MOEMS for lightwave telecommunications

1 5.00 2 manufacturers can exploit the extensive capabilities of the IC fabrication industry and can profitably use previous-generation equipment. In an era in which an IC factory costs a billion dollars and is obsolete in less than five years, the ability to reuse the equipment for a new class of cutting edge products is very appealing. IC fabrication techniques also allow designers to integrate micromechanical, analog, and digital microelectronic devices on the same chip, producing multifunctional integrated systems. Contrary to intuition, MEMS devices have proven to be robust and long-lived, especially ones whose parts flex without microscopic wear points. Research in this area has been extremely active over the last decade, producing microscopic versions of most macro-machines. In particular, many of us believe that the size scale at which these machines work well make them a particularly good match to optics problems where the devices, structures and relevant wavelengths range in size from one to several hundred microns. 2. Where in a Lightwave Network will they be Applied? Work at Bell Labs in Optical MEMS has focused on a number of devices such as optical modulators, variable attenuators, switches, add/drop multiplexers, active equalizers and optical crossconnects. Shown in the figure (upper right hand side) is an overview of places in lightwave networks where we see application for MEMS components. Each red dot is a place where MEMS can be the solution of choice. Clearly, there exist many opportunities[References I -4]. In the figure, LHS center, is a micrograph of our 1x2 MEMS optical switch. The mirror is connected to a see-saw and either reflects the light from the optical fiber on the left to the fiber at right angles to it or moves out of the way to allow the light to go straight into the other fiber. In the figure, RHS center, is a micromirror for use in a variable attenuator. Light from a fiber at right angles to the mirror gets reflected to an output fiber and the coupling between the two can be adjusted by applying a voltage to the electrode to the left of the large mirror. In the figure on the lower LHS is an array of micromirrors for use in an add/drop multiplexer. In operation, each wavelength of light in an optical fiber gets spatially demultiplexed by a grating and lands on its own mirror to be correctly routed to either the output port or the drop port. Finally, shown on the lower RHS is a two axis micromirror for use in a lxN optical switch. The mirror is doubly gimbaled so that light can be routed in two directions to allow complex switching functions to be accomplished. Clearly, the possibilities for novel optical devices and functions are endless. Summary Although no MEMS device has yet been deployed in an active lightwave network, the wealth of new capabilities presented by MEMS optical devices places them as certain candidates for imminent commercial success. The optical MEMS industry is estimated to become a multi-billion dollar business in five years. Many companies, including Lucent Technologies, identify MEMS as

Scalable micro mechanical optical crossconnects

Optical Micro-Electro-Mechanical Systems (Optical MEMS, or MOEMS) comprise a disruptive technology whose application to telecommunications networks is transforming the horizon for lightwave systems. The influences of materials systems, processing subtleties, and reliability requirements on design flexibility, functionality and commercialization of MOEMS are complex. A tight inter-dependent feedback loop between Component/ Subsystem/ System Design, Fabrication, Packaging, Manufacturing and Reliability is described as a strategy for building reliability into emerging MOEMS products while accelerating their development into commercial offerings.

Article comprising a light-actuated micromechanical photonic switch

Optical crossconnect switches with large port counts are the key components for the management of upcoming optical networks. Most technologies proposed for optical switches are essentially planar in geometry, which leads to switch dimensions scaling with the square of the port number. Planar technologies will not scale beyond 64 X 64 ports. To achieve larger (256 X 256, 1296 X 1296) switches, a three dimensional switch geometry is required. Micro electro-mechanical systems (MEMS) are the key technology to implement array of small two tilt axis beam steering mirrors. The presented systems consist of 2D arrays of MEMS mirrors and 2D fiber arrays each with a collimating microlens array. A cross connect path consist of light leaving one fiber and being collimated and projected onto a MEMS micro-mirror by a microlens. The first micro-mirror tilts so as to direct the beam onto a second micro-mirror, and the second micro-mirror tilts so as to direct the light towards a microlens where it is coupled into the output fiber. In this configuration the length of the switch scales linearly with number of ports, and the maximum port number is determined by used the micro mirror technology. Two switches are presented: the first with 256 port and a mean insertion loss of 7 dB and the second with 1296 ports and an insertion loss of 5.1 dB. Both switch show a crosstalk smaller than -50 dB. The optical performance has been verified with input optical signals ranging from 40 DWDM 40 Gb/s and 320 Gb/s TDM data. On the switch with 1296 ports a potential aggregate switch capacity of 2.08 Petabit/s has been demonstrated.