Silicon Photonics for Mid-Infrared Wavelengths

Alexander Spott and Michael Hochberg
Electrical Engineering, University of Washington

(Nanophotonics Lab Website)

Silicon waveguides for Mid-Infrared (MIR) wavelengths have been proposed in a number of theoretical papers, but not demonstrated past 3.5 µm until recently. Using Silicon-on-Sapphire material and direct-write electron beam lithography, the Nanophotonics Lab recently demonstrated working ring resonators at 5.5 µm wavelength. Waveguide losses of 4.0 +/-0.7 dB/cm have been shown, as well as Q-values of 3000. MIR wavelengths have applications in thermal imaging, spectroscopy, and bio-sensing, and ability to fabricate MIR silicon photonics with nanometer precision creates opportunities for new, complex systems at these wavelengths.

Optical micrographs of the primary ring resonator device found to have a Q-factor of 3.0 k, and a group of ring resonators of various dimensions:

Scanning electron micrograph of coupling region of silicon-on-sapphire ring resonator:

A diagram of the test setup including an image of the chip tested.

(a) Transmission spectra for the primary ring reported: tested in a nitrogen-purged environment (top) and tested under normal atmospheric conditions (second). Transmission spectra for a regular waveguide: tested under a nitrogen-purged environment (third) and tested under normal atmospheric conditions (bottom). A Q-factor of 3.0 k and an FSR of 29.7 can be seen.

(b) A plot of transmitted optical power for various devices of a variety of waveguide lengths. The optical power is arbitrarily normalized with the transmission for the shortest device corresponding to 0 dB. A least-squares linear approximation is shown, demonstrating wave- guide losses of 4.0 +/- 0.7 dB/cm.

Applied Physics Letters
97, 213501 (2010) (link)