Abstract
In this paper we describe two silicon based optical modulators that have been fabricated as part of two projects in which the Surrey group is involved, the "UK Silicon Photonics project" funded by the UK Engineering and Physical Sciences Research Council (EPSRC), and the European "HELIOS" project funded by the European Union. The modulators exploit the carrier depletion effect in MZI structures, but have different advantages and disadvantages. One has a performance that is close to polarisation independence, whilst the other demonstrates a very high extinction ratio for a 40Gb/s silicon modulator. Both are shown to operate at 40Gb/s. © 2011 SPIE-OSA-IEEE.