A continuous-wave Raman silicon laser.

Achieving optical gain and/or lasing in silicon has been one of the most challenging goals in silicon-based photonics 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 silicon. However, because of the nonlinear optical loss associated with two-photon absorption (TPA)-induced free carrier absorption (FCA), until now lasing has been limited to pulsed operation. 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.

An all-silicon Raman laser.

The possibility of light generation and/or amplification in silicon has attracted a great deal of attention for silicon-based optoelectronic applications owing to the potential for forming inexpensive, monolithic integrated optical components. Because of its indirect bandgap, bulk silicon shows very inefficient band-to-band radiative electron-hole recombination. Light emission in silicon has thus focused on the use of silicon engineered materials such as nanocrystals, Si/SiO2 superlattices, erbium-doped silicon-rich oxides, surface-textured bulk silicon and Si/SiGe quantum cascade structures. Stimulated Raman scattering (SRS) has recently been demonstrated as a mechanism to generate optical gain in planar silicon waveguide structures. In fact, net optical gain in the range 2-11 dB due to SRS has been reported in centimetre-sized silicon waveguides using pulsed pumping. Recently, a lasing experiment involving silicon as the gain medium by way of SRS was reported, where the ring laser cavity was formed by an 8-m-long optical fibre. Here we report the experimental demonstration of Raman lasing in a compact, all-silicon, waveguide cavity on a single silicon chip. This demonstration represents an important step towards producing practical continuous-wave optical amplifiers and lasers that could be integrated with other optoelectronic components onto CMOS-compatible silicon chips.

Net continuous wave optical gain in a low loss silicon-on-insulator waveguide by stimulated Raman scattering.

We observe for the first time net continuous wave optical gain in a low loss silicon-on-insulator waveguide based on stimulated Raman scattering. We show that nonlinear optical loss due to two-photon absorption induced free carrier absorption can be significantly reduced by introducing a reverse biased p-i-n diode in the waveguide. For a 4.8 cm long waveguide with an effective core area of ~1.6 microm2, we obtain a net CW Raman gain of > 3dB with a pump power of ~700mW inside the waveguide.

Lossless optical modulation in a silicon waveguide using stimulated Raman scattering.

In this paper we describe a new modulation scheme using stimulated Raman scattering in conjunction with a reverse biased p-i-n diode embedded in a silicon waveguide. We show optical modulation of a weak probe beam by modulating the reverse bias voltage of the silicon waveguide excited by a strong pump beam. The probe beam modulation is due to the two-photon absorption-induced carrier density modulation in the waveguide. By tuning the probe wavelength to the Stokes wavelength, we demonstrate for the first time a lossless optical modulator in silicon with modulation speeds up to 80-MHz.

Net optical gain in a low loss silicon-on-insulator waveguide by stimulated Raman scattering.

We observe for the first time net optical gain in a low loss silicon waveguide in silicon-on-insulator (SOI) based on stimulated Raman scattering with a pulsed pump laser at 1.545 microm. We show that pulsed pumping with a pulse width narrower than the carrier recombination lifetime in SOI significantly reduces the free carrier generation rate due to two-photon absorption (TPA) in silicon. For a 4.8 cm long waveguide with an effective core area of ~1.57 microm2, we obtained a net gain of 2 dB with a pump pulse width of ~17 ns and a peak pump power of ~470 mW inside the waveguide.