Raman scattering in hydrogenated amorphous silicon waveguides at telecommunication wavelengths

Raman scattering in crystalline Si waveguides has been in much attention since the measurements of spontaneous and stimulated Raman scattering at telecommunication wavelengths. Various applications such as a Raman laser and a Raman amplifier have been studied. On the other hand, optical waveguides using hydrogenated-amorphous Si (a-Si:H) have also been researched The advantages are low-temperature film deposition for three-dimensional photonic circuits and a highlyreliable fabrication process using CMOS electronics facilities. The a-Si:H is an advantageous nonlinear material due to its expected lower nonlinear absorption resulting from the larger electronic bandgap compared with crystalline Si, and large nonlinear figure of merit in an a-Si:H wire waveguide have been achieved In this talk, we introduce the first observation of Raman emission in a 13-mm-long a-Si:H wire waveguide at telecommunication wavelength of 1550 nm. The a-Si:H wire waveguide has a low propagation loss of 2 dB/cm and ultra-fast carrier decay time of less than 100 fs. Using a continuous wave pump laser at 1443.4 nm, we observe backward spontaneous Raman scattering at a peak wavelength of 1550.1±0.25 nm. The Raman frequency shift is 477±1 cm⁻¹, which agrees with a value obtained from a commonly used a-Si:H film. We estimate Raman gain coefficient from the measured Raman spectrum and discuss the possibility of Raman amplification.