M. Dinu

Broadband low-dispersion diffraction of femtosecond pulses from photorefractive quantum wells

Photorefractive quantum wells operating by means of the Franz–Keldysh effect were designed to diffract a bandwidth of approximately 8 nm, nearly matching that of 100-fs pulses, with little dispersion in the diffracted pulses. Large diffraction bandwidths are engineered by adjustment of the well width of the quantum wells in a specific nonuniform distribution across the thickness of the device. The causal relationship between the real and the imaginary parts of the refractive index leads to an excitonic spectral phase with linear dependence on wavelength, resulting in almost distortion-free diffraction. These features render photorefractive quantum-well devices suitable candidates for femtosecond pulse-shaping and spectral holography applications, without the previous bandwidth limitations.

ELECTRO-OPTIC AND PHOTOREFRACTIVE PROPERTIES OF LONG-PERIOD FIBONACCI SUPERLATTICES

We have investigated the transverse‐field electroabsorption of long‐period GaAs/AlGaAs Fibonacci superlattices for three different realizations of the Fibonacci sequence and assessed their bandwidth in photorefractive four‐wave mixing experiments. The one‐electron density of states exhibits a wide fractal distribution of quasibands, suggesting the ability to tailor bandwidths for optical applications. Many‐electron effects and the inter‐well coupling shift the excitonic oscillator strength to the low‐energy edge of the spectrum in all cases, producing a diffraction bandwidth that is relatively independent of coupling in both weak‐ and strong‐coupling Fibonacci superlattices.

Photorefractive semiconductor nanostructures

Publisher Summary This chapter provides an introduction to photorefractive semiconductor nanostructures. They are nonlinear optical devices that alter their optical properties in response to time- and space-varying light intensity patterns. They are used to perform dynamic holography under ultra low-light intensities much smaller than those used for traditional nonlinear optical materials. These devices contain nanometer-scale features that enhance their optical properties and alter their electronic transport relative to bulk behavior. They also contain high densities of deep level defects that make the devices semi-insulating. These defects trap and store photogenerated carriers that accumulate into space-charge densities that match the intensity patterns. The trapped charge produces electric fields that modify the optical properties of the nanostructure. The translation of temporally and spatially varying light intensity patterns into physical changes in the optical properties of the material, matching the intensity patterns, is called the photorefractive process. There are several ways that electric fields can be applied to quantum-well structures, and several ways that optical beams can be incident on the devices to write holograms. The various configurations can be summarized by three basic fields and grating geometries. Two of the structures are transmission structures with the optical beams incident on the same face, and one is reflection geometry with the beams incident from opposite faces.

OPTICAL PHASE CONJUGATION IN A MAGNETIC PHOTOREFRACTIVE SEMICONDUCTOR CDMNTE

Magneto-optical phase conjugation was performed in a diluted magnetic photorefractive semiconductor crystal CdMnTe under an applied magnetic field. The magnetic field removes time-reversal symmetry and quenches orthogonal components of the phase-conjugate signal for selected field strengths. The experimental results as functions of magnetic field and incident polarization angle are in good agreement with coupled-mode theory with transmission gratings during magneto-photorefractive mixing.

Chapter 12 – Photorefractive semiconductor nanostructures

Publisher Summary This chapter provides an introduction to photorefractive semiconductor nanostructures. They are nonlinear optical devices that alter their optical properties in response to time- and space-varying light intensity patterns. They are used to perform dynamic holography under ultra low-light intensities much smaller than those used for traditional nonlinear optical materials. These devices contain nanometer-scale features that enhance their optical properties and alter their electronic transport relative to bulk behavior. They also contain high densities of deep level defects that make the devices semi-insulating. These defects trap and store photogenerated carriers that accumulate into space-charge densities that match the intensity patterns. The trapped charge produces electric fields that modify the optical properties of the nanostructure. The translation of temporally and spatially varying light intensity patterns into physical changes in the optical properties of the material, matching the intensity patterns, is called the photorefractive process. There are several ways that electric fields can be applied to quantum-well structures, and several ways that optical beams can be incident on the devices to write holograms. The various configurations can be summarized by three basic fields and grating geometries. Two of the structures are transmission structures with the optical beams incident on the same face, and one is reflection geometry with the beams incident from opposite faces.

Diffraction property of ultrashort laser pulses in photorefractive multiple quantum wells

The diffraction of ultrashort laser pulses from static gratings in photorefractive multiple quantum wells (PRQW) has been investigated for use as a diffractive optical elements in information processing systems with ultrashort laser pulses. The PRQW used in this experiment was specially designed to exhibit broad bandwidth. The desirable spectra of the diffracted pulses from the PRQW was observed experimentally. The bandwidth for one of the PRQW devices was 13 nm.

High-bandwidth diffraction of femtosecond pulses from photorefractive quantum wells

Summary form only given. Photorefractive quantum wells are attractive media for dynamic holography due to their high sensitivities, small saturation intensities, and short response times compared to bulk photorefractives. Such properties are desirable in applications like dynamic femtosecond pulse shaping and spectral holography. However, these devices have suffered from a limited diffractive bandwidth, resulting from the resonant nature of the electro-optic response of multiple quantum wells. The operating bandwidth of a GaAs/AlGaAs photorefractive multiple quantum well device is on the order of 3 nm, in sharp contrast with the 10 nm bandwidth of a 100-fsec pulse. We have overcome the large bandwidth mismatch between femtosecond pulses and photorefractive quantum wells operating via the resonant Franz-Keldysh effect by using density-of-states engineering.

ZnMnSe epilayers with interdigitated contacts for magnetic-field tunable four-wave mixing in the violet spectral region

We have demonstrated and characterized resonant photorefractive four wave mixing in ZnMnSe epilayers under moderate applied voltages using interdigitated electrodes. The giant Zeeman splittings of the excitonic transitions experienced by this material will also make it possible to magnetically tune the wavelength of the photorefractive diffraction.