Optical Nonlinear Properties and Carrier Plasma Effect at Low Carrier Density in Silicon Wire Waveguides

Ultrafast dynamics of amplitude and phase in a silicon wire waveguide are measured by a heterodyne pump probe technique at a wavelength of 1.55 μm. We determined the two-photon absorption coefficient and nonlinear refractive index to be β
_TPA
= 0.43 cm/GW and n
₂
= 2.0 × 10
¹⁸
m
²
/W, respectively. A theoretical analysis indicates that the index change due to the carrier plasma effect is linear to the carrier density when it is low as in the case of optical injection.