8/23/2007

The name "silicon evanescent laser" is misleading since the silicon isn't emitting any Light

Researchers at UC Santa Barbara (UCSB) have built the world's first mode-locked silicon evanescent laser.
According to TFA, the stimulated emission of light actually takes place in an indium phosphide (InP) laser diode. The laser diode is bonded to a silicon waveguide, which acts like a miniature optical fiber to guide the laser light around the chip. The "evanescence" is because the laser light is evanescently coupled from the laser diode into the waveguide. A proper description of evanescent coupling requires a pretty sophisticated understanding of electromagnetism, but the short version is that if you shine a laser beam parallel and adjacent (within a few microns) of a waveguide or optical fiber, some of the laser light will hop over and start propagating down the waveguide or fiber. In particular, by placing the actual laser parallel to and near a carefully-designed waveguide, you can have almost all of the laser light emitted into the waveguide, even though the constituent atoms of the waveguide are not emitting any light at all! For this reason, I think the name "silicon evanescent laser" is misleading since the silicon isn't emitting any Light.

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