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Multifacet diffractive mirror for optical clock signal distribution

Optical clock signal distribution has widely been discussed to be an attractive way to reduce the clock skew in high speed digital systems. For short interconnection lengths, especially for chip level clock distribution, free space systems using diffractive optical elements (DOEs) have specific advantages. The optoelectronic pathway described in this paper consists of a GaAs laser diode, a microetched silicon mirror, a facetted diffractive element, and silicon photodiodes. The key element of the clock distribution demonstrator is the diffractive element (the mirror), which matches set-up requirements like compactness, an off-axis geometry, and use of an unshaped laser diode beam. The diffractive mirror is computer generated, it is direct E-beam written and its diffraction pattern is dry etched into the surface of a silicon wafer. It is shown that the whole set-up meets the demands of alignment accuracy in an excellent way. This is achieved by the very good imaging characteristic of the DOE and by an alignment technique based on precision mounting of microetched silicon components.