Silicon carbide (SiC), which is the leading representative of the third-generation of semiconductors, possesses many excellent physical properties. However, its advantages also incur difficulties in processing, which calls for special processing techniques, such as femtosecond laser machining. In addition, SiC has shown unprecedented potential for optoelectronic applications. Knowledge of the nonlinear absorption coefficient and the nonlinear refractive index coefficient of SiC is required in both of the fields. In this work, the nonlinear absorption coefficient and the nonlinear refractive index coefficient of semi-insulating (SI) 6H-SiC and SI 4H-SiC, the most pervasive SiC polytypes, are measured in an extensive spectral range from 400 nm to 1000 nm with the Z-scan technique. Besides, the spectral dependence of the nonlinear optical properties is analyzed, facilitated by linear absorption spectrum. Especially, two-photon absorption (2PA) and three-photon absorption (3PA) coefficients of SI 6H-SiC and SI 4H-SiC are characterized in the respective spectral ranges. From the characterization of SiC, we can observe self-focusing phenomenon for nonlinear refraction. In the end, we unravel the potential of SiC for ultrafast all-optical switching based on the measured nonlinear optical properties.
Silicon
carbide (SiC) is one of the most promising wide-band gap
semiconductors for future technological applications, with the potential
for high-temperature and low-loss photonic devices. In this study,
we investigated the ultrafast visible light all-optical switching
in 6H-SiC, in which nondegenerate two-photon absorption appeared to
be dominant. Using an 820 nm femtosecond laser beam as the modulation
source, differential transmission on the order of 10% was achieved
across the visible spectrum from 420 to 720 nm with the highest modulation
depth reaching 27%. The dependence of the optical switching performance
on wavelength, fluence, and polarization has been illustrated and
analyzed in details. Our results provide an in-depth guideline for
exploring SiC, of which the nonlinear optical properties could help
to realize ultrafast all-optical switching devices in the visible
regime.
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