We present a design approach for compact reconfigurable phased-array wavelength-division multiplexing (WDM) devices with N access waveguides (WGs) based on multimode interference (MMI) couplers. The proposed devices comprise two MMI couplers which are employed as power splitters and combiners, respectively, linked by an array of N single-mode WGs. First, passive devices are explored. Taking advantage of the transfer phases between the access ports of the MMI couplers, we derive very simple phase relations between the arms that provide wavelength dispersion at the output plane of the devices. When the effective refractive index of the WGs is modulated with the proper relative optical phase difference, each wavelength component can switch paths between the preset output channel and the remaining output WGs. Moreover, very simple phase relations between the modulated WGs that enable the reconfiguration of the output channel distribution when the appropriated coupling lengths of the MMI couplers are chosen are also derived. In this way, a very compact expression to calculate the channel assignment of the devices as a function of the applied phase shift is derived for the general case of N access WGs. Finally, the experimental results corresponding to an acoustically driven phased-array WDM device with five access WGs fabricated on (Al,Ga)As are shown.
The control of spin dephasing is an essential requirement for quantum information processing using electron spins in IIIV
semiconductors. GaAs quantum wells grown along the non-conventional  crystallographic direction are
particularly interesting for spintronics due to the long spin lifetimes, which can be electrically controlled. Here, we show
electron spin dynamics in (111) quantum wells by combining spatially-resolved with time-resolved photoluminescence
measurements. The latter allows us to experimentally demonstrate the field induced enhancement of the spin lifetime as
well as the transport of spin over several micrometers along the quantum well plane.
In this paper, photonic devices driven by surface acoustic waves and operating in the GHz frequency range are presented. The devices were designed and fabricated in (Al,Ga)As technology. In contrast to previously realized modulators, where part of the light transmission is lost due to destructive interference, in the present devices light only switches paths, avoiding losses. One of the devices presents two output channels with 180◦-dephasing synchronization. Odd multiples of the fundamental driving frequency are enabled by adjusting the applied acoustic power. A second and more complex photonic integrated device, based on the acoustic modulation of tunable Arrayed Waveguide Gratings, is also proposed.
We propose a novel concept for a semiconductor-based single-photon detector for quantum information processing,
which is capable of discriminating the number of photons in a light pulse. The detector exploits the charge transport by a
surface acoustic wave (SAW) in order to combine a large photon absorption area (thus providing high photon collection
efficiency) with a microscopic charge detection area, where the photo generated charge is detected with resolution at the
single electron level using single electron transistors (SETs). We present preliminary results on acoustic transport
measured in a prototype for the detector as well as on the fabrication of radio-frequency single-electron transistors (RFSETs)
for charge detection. The photon detector is a particular example of acousto-electric nanocircuits that are
expected to be able to control both the spatial and the spin degrees of freedom of single electrons. If realized, these
circuits will contribute substantially to a scalable quantum information technology.
We discuss the formation of a tunable one-dimensional photonic band
gap structure through the modulation of the resonance frequency of
an optical microcavity by a surface acoustic wave (SAW). The
microcavity consists of a λ/2 GaAs layer bounded by
AlAs/GaAs Bragg mirrors. The SAW periodically modulates the optical
thickness of the cavity layer, leading to a light dispersion
relation folded within a mini-Brillouin zone (MBZ) defined by
|kx|≤ π/λSAW (kx denotes the photon wave vector component along the SAW propagation direction x-with-caret). In reflection and diffraction experiments, we observe photon modes bounding the gaps in the center and at the boundary of the MBZ as well as a renormalization of the optical energies. Furthermore, the width of the energy gaps can be tuned by changing the acoustic power densities. The experimental results are in good agreement with a simple model for the dispersion in the presence of SAWs. We show the application of acoustically tunable microcavities in efficient optical on/off switches and modulators as well as a tunable cavity operating at 1.3μm.
We report on the generation of strong surface acoustic wave (SAW) beams on GaAs substrates as well as on their concentration and guiding using acoustic horns and waveguides (WGs). By means of focusing interdigital transducers, we demonstrate the generation of narrow (full width at half maximum of approximately 15 μm), high-frequency (0.5 GHz) SAW beams collimated over distances exceeding 100 μm. The beams can be guided along the surface using narrow (10-μm-wide) WGs of ridge and slot types. The coupling of the SAW into the WGs was achieved using acoustic horns. Coupling power efficiencies of up to 75%, which translates into an eightfold increase of the local acoustic power density within the WG, is demonstrated using slot WGs with a 80-nm-thick aluminum cladding region.