Ultrafast all-optical modulation of infrared radiation viametal-semiconductor waveguide structures

摘要

We present a novel optical-optical semiconductor switchingntechnique for application to infrared laser beam modulation andnultrashort infrared laser pulse switching. This method relies on thenultrafast optical excitation, with femtosecond above-bandgap lasernradiation, of an air-filled metal-clad semiconductor waveguide. Guidednelectromagnetic wave analysis combined with time-varying dielectricnproperties of the semiconductor layer are used to investigate thenultrafast switching speed of the structure. The device is capable ofnmodulation at various infrared wavelengths. In particular, weninvestigate intensity modulation of the quasi-TE10 mode forn10.6-Μm laser radiation. At an electron-hole photoinjection densitynof ~1.8×1018 cm-3, an extinction ratio of 83ndB is demonstrated. This ratio is significantly higher than thatnexhibited by current optical-optical semiconductor switches. Potentialnapplications to all-optical Mach-Zehnder metal-clad semiconductornmodulators and self-limiting switches are also discussed