Novel all-optical cross-connect switch uses fewer mirrors

Valerie C. Coffey

In today`s WDM networks, information is converted from light into an electronic signal to be routed to the next circuit pathway and converted back into light as it travels to the next network destination. In an all-optical network, the electronics are removed from the equation, eliminating the need to convert the signals, and improving network performance.

A collaboration of scientists at C Speed Corp. (Santa Clara, CA), Stanford University (Stanford, CA), and the University of California (Davis, CA) have described a new configuration of all-optical cross-connect (OXC) switches that may provide an alternative to costly optical-to-electronic and electronic-to-optical conversion. An OXC switch architecture called the confocal switch uses 2N mirrors instead of N2 mirrors to achieve full cross-connect functionality (N being the number of input and output fibers). The low mirror count leads to better fabrication yield and favorable scaling to high numbers of fiber ports, while low crosstalk and insertion loss are maintained.

This free-space optical fiber cross-connect uses a pair of micromirror arrays to redirect optical beams from an input-fiber array to an output array. Each mirror`s rotational axes lie at its center, and the mirror centers are collinear in both arrays. Mirror size is proportional to the optical beam radius at the mirror, and spacing between adjacent mirrors is proportional to the size of the optical beam waist. The optical beam waist is centrally located between the mirror arrays to create a symmetric switch that minimizes mirror size and switching time. This confocal switch architecture is well suited for simultaneous wavelength switching of multiple wavelength channels. The micromirrors, which are 300 µm in diameter and 1.5-µm thick, are fabricated using three-polysilicon-layer processing, released in hydrofluoric acid, and dried in supercritical carbon dioxide. The mirrors, fabricated flat on the surface of the chip, are assembled with microprobes and metallized with 50 nm of aluminum to enhance reflectivity. In a design that allows rotation about two perpendicular axes, mirrors as large as 600 µm in diameter could address 322 = 1024 ports, which shows that confocal switches have the potential for scaling to high port counts. For details, contact Paul Hagelin at

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