For the full implementation of spintronic circuits, it is necessary to transmit spin information from one device to another. Electrons in semiconductors often suffer from high spin relaxation rates, making electrical transport of spin information highly inefficient. Here, we propose optical transport of spin information as an alternative. We demonstrate that the spin information associated with electrons injected from Co2FeSi and Fe layers into the quantum wells of spin light emitting diodes (spin-LEDs) can be transported optically in the form of circularly polarized light and deciphered electrically via the magnetic field dependence of the photocurrent in a distant detector spin-LED.

Ultrafast nonlinear tuning of the reflection properties of AlGaAs photonic crystal waveguides by two-photon absorption

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Abstract:We demonstrate compact tunable phased-array wavelengthdivision multiplexers driven by surface acoustic waves (SAWs) in the low GHz range. The devices comprise two couplers, which respectively split and combine the optical signal, linked by an array of single-mode waveguides (WGs). Two different layouts are presented, in which multi-mode interference couplers or free propagating regions were separately employed as couplers. The multiplexers operate on five equally distributed wavelength channels, with a spectral separation of 2 nm. A standing SAW modulates the refractive index of the arrayed WGs. Each wavelength component periodically switches paths between the output channel previously asigned by the design and the adjacent channels, at a fixed applied acoustic power. The devices were monolithically fabricated on (Al,Ga)As. A good agreement between theory and experiment is achieved.

We have investigated the ambipolar transport of electrons and holes by electrically generated surface acoustic waves (SAWs) on silicon wafers coated with a piezoelectric ZnO film. The transport experiments were carried out by using a focused laser beam to optically excite carriers. The carriers are then captured by the moving SAW piezoelectric field and then transported towards a lateral p-in junction, where they are electrically detected. The piezoelectric modulation modifies the current vs. voltage characteristics of the lateral p-in junction. This behavior is accounted for by a simple model for the change of the junction potential by the SAW fields. We demonstrate that electrons and holes can be acoustically transported over distances approaching 100 lm, the transport efficiency being limited by the low mobility of holes in the material. These results open the way for silicon-based acousto-electric devices using ambipolar transport such as photo-detectors and solar cells. V