A cascaded silicon Raman laser

One of the major advantages of Raman lasers is their ability to generate coherent light in wavelength regions that are not easily accessible with other conventional types of lasers(1). Recently, efficient Raman lasing in silicon in the near- infrared region has been demonstrated(2-4), showing great potential for realizing low- cost, compact, room- temperature lasers in the mid- infrared region(5-7). Such lasers are highly desirable for many applications, ranging from trace- gas sensing, environmental monitoring and biomedical analysis, to industrial process control, and free- space communications(8,9). Here we report the first experimental demonstration of cascaded Raman lasing in silicon, opening the path to extending the lasing wavelength from the near- to midinfrared region. Using a 1,550- nm pump source, we achieve stable, continuous- wave, second- order cascaded lasing at 1,848 nm with an output power exceeding 5 mW. The laser operates in single mode, and the laser linewidth is measured to be < 2.5 MHz.