Nature 498, 470–474 (2013)

In 2005, researchers at Intel realized a continuous-wave all-silicon Raman laser based on stimulated Raman scattering in a rib waveguide structure. However, its practicality was limited by its millimetre-scale size and its milliwatt-scale lasing threshold. Now, Yasushi Takahashi and colleagues in Japan have demonstrated a laser based on the same principle, but whose size is of the order of micrometres and whose lasing threshold is just 1 μW. The key to these improvements was the use of a miniature photonic-crystal cavity (with a cavity size of less than 10 μm) that has a large quality factor and a small modal volume. Varying the air-hole radius of the cavity with nanometre precision made it possible to tune the frequency spacing between the even nanocavity modes so as to match the silicon Raman shift of 15.6 THz. The result was the efficient generation of Raman scattered light and enhanced Raman gain. The researchers anticipate that their design strategy could lead to a variety of Raman amplification devices based on photonic-crystal cavities and waveguides.