Photorefractive Multiple Quantum Wells

Publications


D. D. Nolte, D. H. Olson, G. E. Doran, W. H. Knox, and A. M. Glass
   "Resonant photodiffractive effect in semi-insulating multiple quantum wells"
   J. Opt. Soc. Am. B 7, 2217 (1990).


Abstract
We use semi-insulating multiple quantum wells to combine the holographic
properties of the photorefractive effect with the large resonant optical
nonlinearities of quantum-confined excitons.  GaAs-AlGaAs multiple-quantum-
well structures are made semi-insulating by proton implantation.  The implant
damage produces defects that are available to trap and store charge during 
transient holographic recording by means of coherent excitation.  The 
advantages of charge storage and resonant optical nonlinearity combine to
produce new optical devices with large sensitivities.  The potential us of 
these devices for image processing is demonstrated by using the Franz-Keldysh
effect in four-wave mixing at wavelengths near 830 nm.



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Q. N. Wang, D. D. Nolte and M. R. Melloch
   "Two-Wave Mixing in Photorefractive AlGaAs/GaAs Quantum Wells"
    Appl. Phys. Lett. 59, 256-258 (1991).



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Q. Wang, R. M. Brubaker, M. R. Melloch, and D. D. Nolte
   "Photorefractive quantum wells: transverse Franz-Keldysh geometry"
   J. Opt. Soc. Am. B 9, 1626 (1992).


Abstract
The photorefractive properties of semi-insulating AlGaAs-GaAs multiple 
quantum wells are described for the transverse Franz-Keldysh geometry with
the electric field in the plane of the quantum wells.  Combining the strong
electroabsorption of quantum-confined excitons with the high resistivity of
semi-insulating quantum wells yields large nonlinear optical sensitivities.
The photorefractive quantum wells have effective nonlinear optical 
sensitivities of n2=10^3 cm^2/W and alpha2/alpha0 = 10^4 cm^2/W for applied
fields of 10 kV/cm.  Photorefractive gains approaching 1000 cm^-1 have been
observed in two-wave mixing under dc electric fields and stationary fringes.
The transverse Franz-Keldysh geometry retains the general transport properties
and behaviour of conventional bulk photorefractive materials.  The resonant
excitation of free electrons and holes in the quantum wells leads to novel
behavior associated with electron-hole competition.  We demonstrate that
under resonant excitation of electrons and holes the device resolution is
fundamentally limited by diffusion lengths but is insensitive to long drift
lengths.



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R. M. Brubaker, Q. N. Wang, E. S. Harmon, M. R. Melloch, and D. D. Nolte
   "Steady-state four-wave mixing in photorefractive quantum wells with
       femtosecond pulses"
   J. Opt. Soc. Am. B 11, 1038 (1994).