SI-BASED SURFACE-RELIEF POLYGONAL GRATINGS FOR 1-TO-MANY WAFER-SCALE OPTICAL CLOCK SIGNAL DISTRIBUTION

In contrast to volume holographic material where 1-to-many fanouts are realized using multiplexed volume holograms, we report in this paper the first Si-based surface-relief polygonal gratings aiming at optical clock signal distribution application. Surface-relief gratings with 1 -mu m period (0.5 mu m feature size) were fabricated using reactive io n beam etching (RIE), Both hexagonal and square gratings were demonstr ated for 1-to-4 and 1-to-6 fanouts, Surface-normal input and output co upling schemes were carried out with an combined coupling efficiency o f 65%, Employment of substrate modes in silicon greatly releases the r equired grating spacing for the demonstrated two-way surface-normal co upling, 7.5 GHz 1-to-4 clock signal distribution operating at 1.3 mu m was demonstrated with a signal-to-noise ratio as high as 60 dB, The i ntensity fluctuation among fanout beams was measured to be within 1dB, Generalization of 1-to-many fanout can be realized by implementing a polygonal grating with an equivalent number of facets.