Abstract
The plasma dispersion effect and free-carrier absorption are widely used to change refractive index and absorption coefficient in Si-based optical modulators. However, the weak free-carrier effects in Si cause low modulation efficiency, resulting in large device footprint and power consumption. Here, we theoretically and experimentally investigate the enhancement of the free-carrier effects by strain-induced mass modulation in silicon-germanium (SiGe). The application of compressive strain to SiGe reduces the conductivity effective mass of holes, resulting in the enhanced free-carrier effects. Thus, the strained SiGe-based optical modulator exhibits more than twice modulation efficiency as large as that of the Si modulator. To the best of our knowledge, this is the first demonstration of the enhanced free-carrier effects in strained SiGe at the near-infrared telecommunication wavelength. The strain-induced enhancement technology for the free-carrier effects is expected to boost modulation efficiency of the most Si-based optical modulators thanks to high complementary metal-oxide-semiconductor (CMOS) compatibility.
Highlights
The plasma dispersion effect and free-carrier absorption are widely used to change refractive index and absorption coefficient in Si-based optical modulators
Mach-Zehnder interferometer (MZI) optical modulator, in which the refractive index of the phase shifters are modulated by carrier depletion, is one of the most promising modulators in terms of modulation speed and optical bandwidth
To supplement the weak plasma dispersion effect and free-carrier absorption in Si, the introduction of ring resonators instead of MZIs2,11, and slow-light structures using photonic crystals[12,13] have been investigated, while the optical bandwidth has been reduced in such structures
Summary
Younghyun Kim[1], Mitsuru Takenaka[1], Takenori Osada[2], Masahiko Hata2 & Shinichi Takagi[1]. We report the enhancement of the plasma dispersion effect and free-carrier absorption by strain-induced mass modulation in a Si/strained SiGe/Si double-heterostructure waveguide with a lateral pin junction for carrier injection in the near-infrared wavelength range from 1.3 to 1.6 mm, which is the most important range of wavelengths for optical fiber communication. We have demonstrated that the strain-induced enhancement of the plasma dispersion effect and free-carrier absorption in biaxial compressive strained SiGe is effective for boosting the modulation efficiency of Si-based optical modulators. The optical attenuation of the SiGe-based in-line intensity optical modulator is more than twice as large as that of the Si modulator This is the first demonstration of enhanced free-carrier absorption in SiGe through strain-induced mass modulation for the telecommunication wavelength range from 1.3 to 1.6 mm. The strain-induced enhancement of the plasma dispersion effect and free-carrier absorption is one of the most promising technologies for boosting the performance of Si-based optical modulators
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