An Optical Modulator in Unmodified, Commercially Available CMOS Technology

Here we present a method and structures for midinfrared, free-space optical communication using unmodified, commercially available complementary metal–oxide–semiconductor integrated circuits. The modulator is based on the free carrier absorption in parasitic PN junction structures under reverse bias. Measured results demonstrate the proof-of-concept with speeds of 100 b/s (1.55- μm wavelength), but at least two orders of magnitude improvement can be achieved. This technology will enable nongalvanic chip-to-chip and chip-to-package communication as an alternative to wire-bonding in applications that benefit from a planar top chip surface, such as chemical sensing lab-on-chip systems as well as general sensors and midinfrared communication.