Efficient optical coupling between a polymeric waveguide and an ultrafast silicon MSM photodiode

One task of the integration of optoelectronic functions with silicon devices is the construction of an optical waveguide on Si and the optical coupling of this waveguide to a silicon photodetector. We have fabricated polymeric strip waveguides on Si and demonstrate a very efficient design for the optical coupling between the polymeric waveguide and an ultrafast Si-based metal-semiconductor-metal (MSM) mesa-type photodetector. This detector uses high-quality epitaxial Si as the sensitive layer, which is sandwiched between two metallic contacts. If these MSM detectors are excited by a vertically incident free beam of λ=840 nm and pulses of 100-fs full-width at half-maximum (FWHM), they respond with electrical pulses of 3, 5-ps length (FWHM, T=300 K)