A continuous-wave Raman silicon laser

Last month, Intel researchers reported a notable advance in optoelectronics (Nature 433, 292–294; 2005). They had produced an all-silicon laser on a single chip, making silicon, the foundation of modern microelectronics, a real prospect for optical applications. Now Intel's labs report the first experimental demonstration of a continuous wave laser in a silicon waveguide cavity on a single chip. This is another step towards silicon-based optoelectronic circuits for applications in communications and computing. Achieving optical gain and/or lasing in silicon has been one of the most challenging goals in silicon-based photonics1,2,3 because bulk silicon is an indirect bandgap semiconductor and therefore has a very low light emission efficiency. Recently, stimulated Raman scattering has been used to demonstrate light amplification and lasing in silicon4,5,6,7,8,9. However, because of the nonlinear optical loss associated with two-photon absorption (TPA)-induced free carrier absorption (FCA)10,11,12, until now lasing has been limited to pulsed operation8,9. Here we demonstrate a continuous-wave silicon Raman laser. Specifically, we show that TPA-induced FCA in silicon can be significantly reduced by introducing a reverse-biased p-i-n diode embedded in a silicon waveguide. The laser cavity is formed by coating the facets of the silicon waveguide with multilayer dielectric films. We have demonstrated stable single mode laser output with side-mode suppression of over 55 dB and linewidth of less than 80 MHz. The lasing threshold depends on the p-i-n reverse bias voltage and the laser wavelength can be tuned by adjusting the wavelength of the pump laser. The demonstration of a continuous-wave silicon laser represents a significant milestone for silicon-based optoelectronic devices.