MEMS -> D-MEMS yield new flexibility for optical nets

The industry is moving toward optically reconfigurable networks where optical paths, wavelengths and data rates dynamically change to satisfy network system requirements, such as provisioning new wavelengths, balancing data loads and restoring after service malfunctions.

A new class of fiber-optic components is now available to enable dynamically configurable networks. These components switch between optical paths, equalize channel power, manage link dispersion, and optimize amplifier chain performance. D- MEMS (diffractive microelectromechanical systems) technology delivers such dynamic components.

The technology is based on the wave nature of light--interference and diffraction. It enables the fabrication of the D-MEMS actuator, which functions as a voltage-controlled variable-diffraction grating.

The D-MEMS actuator consists of an array of reflective ribbons suspended above a reflective substrate. When the height between the ribbon array and the substrate is one wavelength, the light reflected from these two surfaces is in phase and the device functions as a mirror. A voltage applied between the ribbon array and the substrate creates an electrostatic force. This flexes the ribbon array, therefore decreasing the height and creating a phase difference between the light reflected from the two surfaces.

When the ribbon array is displaced by a quarter wavelength, the light reflected from th e two surfaces is completely out of phase and destructive interference occurs for the nominally reflecting beam. At this point, all of the light is totally diffracted and none is reflected.

D-MEMS actuators are manufactured using standard CMOS processes and materials that take full advantage of established semiconductor foundries with state-of-the-art equipment. This provides manufacturing flexibility and allows for multiple sourcing.

Devices based on D-MEMS have inherent advantages in speed, reliability and power consumption. Since the ribbon array only needs to deflect a few tenths of a micron, the structure can be made very stiff. This stiffness, coupled with low mass, results in a high resonant frequency. This leads to fast response times, typically tens of microseconds.

Noise immunity
An important added advantage of this is immunity to ambient acoustic noise and vibration. Fabricated devices are very reliable since, with these small deflections, the material experie nces negligible fatigue. Devices have been actuated more than 10 billion times with no measurable change in performance.

The D-MEMS grating is effectively a small capacitor in an electrical circuit that has very low power dissipation. Consequently, the device consumes little energy, and does not need to dissipate excess power. This is in contrast to devices using thermal or magnetic actuation mechanisms, which consume considerably more power and may require thermal management.

Lightconnect is currently developing a family of dynamic optical components based on D-MEMS technology. The components demonstrate world-class optical performance and manufacturability and include variable optical attenuators, dynamic gain equalizers, channel equalizers, programmable add/drop multiplexers and high-speed switches. One example is the fast variable optical attenuator (FVOA).