High-frequency electro-optic measurement of strained silicon racetrack resonators

Area of Science:

• Optoelectronics
• Materials Science
• Nonlinear Optics

Background:

• Strained silicon waveguides exhibit electro-optic effects attributed to induced nonlinear susceptibility (χ(2)).
• Understanding the mechanisms behind these effects is crucial for high-speed optical modulation.

Purpose of the Study:

• To investigate the high-frequency electro-optic response of strained silicon racetrack resonators.
• To differentiate between induced nonlinear effects and plasma carrier dispersion in strained silicon.

Main Methods:

• High-frequency measurements were performed on strained silicon racetrack resonators with controlled mechanical strain.
• Optical modulation was analyzed as a function of applied voltage frequency and strain levels.

Main Results:

• Optical modulation vanished at high frequencies, irrespective of applied strain, indicating a mechanism faster than carrier lifetime.
• DC modulation showed minimal dependence on strain.
• Plasma carrier dispersion was identified as the dominant mechanism responsible for the observed electro-optic effect.

Conclusions:

• The electro-optic effect in strained silicon is primarily due to plasma carrier dispersion, not a static induced χ(2) nonlinearity.
• An upper limit for the high-speed effective nonlinear optical coefficient (χeff,zzz(2)) was determined to be (8±3) pm/V at -0.5 GPa stress.
• This upper limit is significantly lower than previously reported values from static measurements, impacting device design for high-speed applications.