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

Abstract

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.

A continuous-wave Raman silicon laser

“…For this waveguide cavity, the total loss of the feedback mirrors (R f ¼ 71% and R b ¼ 90%) at the lasing wavelength is ,2 dB, so a ,1-dB single-pass net gain is needed to reach lasing threshold. From previous measurements 14 , a ,1-dB net c.w. gain is obtained at a pump power of ,400 mW with 25-V reverse bias and ,600 mW with 5-V reverse bias.…”

“…Thus the effective carrier lifetime, representing the lifetime of the free carrier's interaction with the optical mode in the waveguide region, reduces with increased bias voltage. This has been experimentally verified by comparing the measured nonlinear transmission of a silicon waveguide with modelling 9,14 . The measured photocurrent in the reverse-biased p-i-n diode scales with the square of the light power inside the waveguide, indicating that the charge carriers are generated by the TPA process 10 .…”

“…Before performing the lasing experiment, the single-pass c.w. Raman gain of a p-i-n silicon waveguide was measured in a pump-probe experiment 14 , showing a single-pass net gain of .3 dB at a reverse-bias voltage of 25 Vand a pump power of ,700 mW coupled into the waveguide. Figure 2 is a schematic of the Raman laser experiment.…”

“…The lasing threshold is ,280 mW with a 5-V bias and ,180 mW with a 25-V bias. The lower threshold and higher laser output power with higher reverse-bias voltage are expected because the effective carrier lifetime is shorter, resulting in lower nonlinear loss and higher gain 14 . For this waveguide cavity, the total loss of the feedback mirrors (R f ¼ 71% and R b ¼ 90%) at the lasing wavelength is ,2 dB, so a ,1-dB single-pass net gain is needed to reach lasing threshold.…”

Hybrid silicon integration

“…Currently the only silicon based amplifier has been demonstrated using the Raman Amplification [12]. Integration of InP quantum wells with the silicon waveguide allows electrically pumped gain compatible with silicon photonics.…”