We show that a nonlinear array of coupled waveguides can exhibit discrete self-focusing that in the continuum approximation obeys the so-called nonlinear Schrodinger equation. This process has much in common with the biophysical model of Davydov.

Discrete self-focusing in nonlinear arrays of coupled waveguides.

We present a tutorial review of all-optical switching in fibre and integrated optics waveguides. These switching devices require non-linear refractive index changes in single or coupled waveguides, and involve either the low-power guided modes of the structure or soliton-type waves guided, emitted or captured by waveguides. We discuss the physical principles involved in these all-optical switching schemes, material requirements, recent experiments and limitations. A representative rather than comprehensive list of references is provided.

All-optical waveguide switching

Substrate selection presents particular challenges for the production of high‐quality high‐temperature superconducting (HTS) thin films suitable for applications. Because the substrate is generally a passive component, it is often ignored and assumed to have a negligible effect on the structure residing on top of it. There is also a technological motivation to use substrates that conventional wisdom would argue are unlikely to support high‐quality HTS films. These facts have led to rediscovery of many of the fundamental issues governing the role of the substrate in determining the properties of the thin film(s) it supports. For this reason, the study of issues in substrate selection for HTS materials presents a microcosm for substrate selection more generally. We consider the major issues governing the role of the substrate in HTS thin‐film technology and discuss many of the material classes and specific materials that have been studied for their suitability as substrates for HTS films.

Substrate selection for high‐temperature superconducting thin films

We review the operation of, and materials requirements for, a variety of nonlinear-optics guided-wave devices.

Waveguides and fibers for nonlinear optics

We show that two‐photon absorption can lead to serious deterioration in the all‐optical switching characteristics of nonlinear directional couplers and distributed feedback gratings.

Effect of two‐photon absorption on all‐optical guided‐wave devices

The performance characteristics of an AlGaAs dual waveguide vertical coupler with a nonlinear GaAs/AlGaAs multiquantum well coupling medium are demonstrated. The structure was grown by molecular beam epitaxy and fabricated by optical lithography and ion milling. The nonlinear coupling and modulation behavior is identical to that predicted theoretically. The nonlinear index of refraction and critical input power are estimated to be n2=1.67×10−5 cm2/W and Pc=170 W/cm2, respectively. This device also allows reliable measurement of the nonlinear refractive index for varying quantum well and optical excitation parameters.

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Demonstration of all‐optical modulation in a vertical guided‐wave nonlinear coupler

The performance characteristics of InGaAs/GaAs strained-layer superlattice coplanar ridge-type directional couplers realized by molecular beam epitaxy are reported The measured power transfer characteristics with 115 micron incident photoexcitation demonstrate nonlinear coupling due to absorption associated with the tails of the excitonic resonances in the quantum wells From a theoretical fit of the measured data, the nonlinear refractive index coefficient, n2, of the multiquantum well is found to be 225 x 10 to the -7th sq cm/W This agrees very well with a value of n2 = 19 x 10 to the-7th sq cm/W obtained independently on the same material from interferometric measurents

/pdf/nonlinear-effects-in-coplanar-gaas-ingaas-strained-layer-2a8wf33vh0.pdf

Nonlinear effects in coplanar GaAs/InGaAs strained‐layer superlattice directional couplers

The electro‐optic effect and phase modulation in In0.2 Ga0.8 As/GaAs multiple quantum wells have been experimentally studied for the first time. The experiments were done with 1.06 and 1.15 μm photoexcitation which are, respectively, 25 and 115 meV below the electron–heavy hole excitonic resonance. Strong quadratic electro‐optic effect was observed near the excitonic edge in addition to the linear effect. These are characterized by r63 =−1.85×10−19 m/V and (R33 −R13 )=2.9×10−19 m2 /V2 . In addition, we observe a dispersion in the value of r63 . The relative phase shifts are higher in the strained system at 1.06 μm than in lattice‐matched GaAs/AlGaAs.

/pdf/orientation-dependent-phase-modulation-in-ingaas-gaas-55gfnqxunm.pdf

Orientation‐dependent phase modulation in InGaAs/GaAs multiquantum well waveguides

By depositing a buffer layer of Al2O3 on GaAs, we have been able to laser ablate a superconducting film of Y1Ba2Cu3O7−x overtop. The onset of superconductivity is 92 K and zero resistance is observed at 80 K in a structure with a suitably annealed Al2O3 film which is converted to AlGaO3. Both the Al2O3‐GaAs and the Al2O3‐Y1Ba2Cu3O7−x interfaces are remarkably well preserved with virtually no interdiffusion or interaction. The Al2O3 or homolog AlGaO3 film also prevents decomposition of the GaAs at the deposition temperature of 730 °C.

/pdf/characteristics-of-y-ba-cu-o-superconductor-films-on-gaas-2m4gc787xq.pdf

Characteristics of Y‐Ba‐Cu‐O superconductor films on GaAs with an Al2O3 or AlGaO3 buffer layer

http://deepblue.lib.umich.edu/bitstream/handle/2027.42/28059/0000498.pdf?sequence=1

Yi Chen

Papers

Demonstration of all‐optical modulation in a vertical guided‐wave nonlinear coupler

Nonlinear effects in coplanar GaAs/InGaAs strained‐layer superlattice directional couplers

Orientation‐dependent phase modulation in InGaAs/GaAs multiquantum well waveguides

Characteristics of Y‐Ba‐Cu‐O superconductor films on GaAs with an Al2O3 or AlGaO3 buffer layer

Growth phenomena and characteristics of strained InxGa1-xAs on GaAs