Anisotropic nonlinear response of silicon

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Anisotropic nonlinear response of silicon in the
near-infrared region
Jidong Zhang1, Qiang Lin2,, Giovanni Piredda2,
Robert W. Boyd2, Govind P. Agrawal2, and
Philippe M. Fauchet1,2
1. Department of ECE, University of Rochester,
Rochester, NY 2. Institute of Optics, University
of Rochester, Rochester, NY
Present position California Institute of
Technology
This work is supported in part by AFOSR
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Outline

• Motivation
• Experiments
• Results and Analysis
• Conclusion

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Motivation nonlinear silicon photonics
Nonlinear Si photonics

• Fast almost instantaneous nonlinear process
• Compact and low power Sis large nonlinearity (
  gt 10,000X silica fiber)
• Integratable system-on-chip

Rong et. al. Nature Photonics 1, p.232,
(2007) Claps et. al. Opt. Express 11, p.731,
(2003) Foster et. al. Nature 441, p.960,
(2006) Dulkeith et. al. Opt. Express 14, p.5524,
(2006) Lin et. al. Opt. Express 14, p.4786, (2006)
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Motivation symmetry and polarization
For TM mode
0 0 1
For TE mode
Even if the WG is designed to have a polarization
independent linear response, its nonlinearities
still show anisotropy
Reed et al. IEEE J. Sel. Top. Quant. Electron.
12, 1335 (2006) Raghunathan et. al. J. Lightwave
Technol. 23, 2094 (2005)
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Motivation problems and solutions

• Problems
• Previous results are obtained through indirect
  measurements
• -- Measurements based on 3rd harmonic
  generation are affected by dispersive
  nonlinearities
• -- Measurements based on TPA current depend on
  unknown relation between photocurrent and
  nonlinear optical absorption
• Previous results focus more on opaque region ( ?
  1.1 µm)

• Our goals
• Provide a direct measurement of the polarization
  dependence of nonlinearity
• Characterize the nonlinearity anisotropy over a
  broad spectrum range
• Offer more reliable proof of the anisotropic
  nonlinear response of Si

Moss et. al. Opt. Lett. 14, 57 (1989) Wang et.
al. Phys. Rev. Lett. 57, 1647 (1986) Burns et.
al., Phys. Rev. B 4, 3437 (1971) Wynne, Phys.
Rev. 178, 1295 (1969). Lin et. al. Opt. Express
14, 4786 (2006) Salem et. al. Opt. Lett. 29, 1524
(2004) Kagawa et. al. Jap. J. Appl. Phys. 46, 664
(2007)
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Experiments setup
Open aperture
Close aperture
Valley/peak position, amplitude
Polarization dependence of ßT
Polarization dependence of n2
Dip position, depth
Sheik-Bahae et. al. IEEE J. Quant. Electron. 26,
760 (1990). DeSalvo et. al. Opt. Lett. 18, 194
(1993).
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Experiments results

• Period ? lattice symmetry
• Amplitude ? polarization dependence of n2 and ßT

n2 and ßT show similar anisotropy
Ratio constant for the wavelengths measured (1.2
to 2.4 µm)
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Experiments discussions

• Our results are consistent with previous THG
  measurements that shows anisotropic nonlinearity
• Compared with THG results, our measurements show
  that the anisotropy in Sis transparent band is
  not dispersive
• Our result differs from APDs photo current
  measurement results

Moss et. al. Opt. Lett. 14, 57 (1989) Salem et.
al. Opt. Lett. 29, 1524 (2004)
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Conclusions

• We provide the first direct characterization of
  the polarization dependence of Sis ?(3) over a
  broad spectral range between 1.2 µm and 2.4 µm
• We measure the magnitude of anisotropy
  ?(3)1111/ ?(3)1122 2.36
• Our results offer direct proof of Sis
  anisotropic nonlinear response

Next talk on the dispersion of Sis
nonlinearities will be given at 445pm in this
room
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Thank you!
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z-scan traces
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Experiments setup
(1-1-0) Si wafer
(1-0-0) Si wafer
Optical Kerr effect
Intensity
Self-focusing
Z position