BACKGROUND:  Silicon has many desirable properties that make it useful for optical and optoelectronic integration. Heretofore, silicon has been employed in passive optoelectronic components such as waveguides. However, silicon is generally perceived to be void of useful nonlinear optical properties needed for active optical functions such as wavelength conversion and amplification. An approach to realizing activation functionalities in silicon is to make use of Raman scattering. Raman scattering bypasses the indirect bandgap and the lack of dipole moment in the material.

INNOVATION:  This innovation permits a silicon Raman laser to produce light in the mid infrared (MIR) portion of the spectrum. This is achieved by incorporating a silicon Raman gain medium in a cascaded cavity configuration. This effects lasing at a high order Raman peak that can readily extend into the MIR spectrum. The cavity can be external (for example using an optical fiber) or internal using micro disk/ring resonators, Fabry Perot cavity or a combination. Such devices would be much smaller than fiber Raman lasers. Silicon Raman lasers is built on a chip scale as opposed to fiber lasers, which are tabletop devices. Also, unlike fiber devices, silicon devices operate in pulsed mode and can operate at room temperature since there are no thermal effects. It provides an inexpensive and compact source of near and mid-IR radiation. This would have application in spectroscopy and sensing. In particular, its unique ability to operate in pulsed mode enables time-resolved spectroscopy. Other applications are in IR counter measures, where a mid-IR source is used to jam heat-seeking missiles, or in laser surgery.

The device has internal electronic modulation capability which facilitates integration with on-chip electronics.

DEVELOPMENT-TO-DATE:  A pulsed Raman laser producing more than 2.5 Watts of pulse power at 1,675 nm with 25 MHz petition rate is demonstrated using a 1.7 cm silicon waveguide as the gain medium. The laser has a threshold at 9W peak pump pulse power and a slope efficiency of 13%. The device operates at room temperature.

ABOUT THE LAB:  This and other developments in optics and electronics can be found at the UCLA Optoelectric Circuits and Systems Laboratory, http://www.ee.ucla.edu/~oecs/.

Reference: UCLA Case No. 2005-171

PCT Publication Number: PCT/US05/036435