The index of refraction of waveguide structures can be varied by altering carrier concentration. The waveguides preferably comprise semiconductors like silicon that are substantially optically transmissive at certain wavelengths. Variation of the carrier density in these semiconductors may be effectuated...http://www.google.es/patents/US7203403?utm_source=gb-gplus-sharePatente US7203403 - Modulator based on tunable resonant cavity
