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Hybrid opto, electro, and mechanical systems operating at several GHz offer extraordinary opportunities for the coherent control of opto-electronic excitations down to the quantum limit. We introduce here a monolithic platform for GHz semiconductor optomechanics based on electrically excited phonons guided along the spacer of a planar microcavity (MC) embedding quantum well (QW) emitters. The MC spacer bound by cleaved lateral facets acts as an embedded acoustic waveguide (WG) cavity with a high quality factor ($Q\sim10^5$) at frequencies well beyond 6~GHz, along which the acoustic modes live over tens of $\mu$s. The strong acoustic fields and the enhanced optomechanical coupling mediated by electronic resonances induce a huge modulation of the energy (in the meV range) and strength (over 80\%) of the QW photoluminescence (PL), which, in turn, becomes a sensitive local phonon probe. Furthermore, we show the coherent coupling of acoustic modes at different sample depths, thus opening the way for phonon-mediated coherent control and interconnection of three-dimensional epitaxial nanostructures., Comment: 5 Figures

Multimode interference (MMI) devices are key components in modern integrated photonic circuits. Here, we present acoustically tuned optical switches on an (Al,Ga)As platform that enable robust, compact and fast response systems improving on recently demonstrated technology. The device consists of a 2 × 2 MMI device fine-tuned in its center region by a focused surface acoustic wave (SAW) beam working in the low GHz range. In this way, we can tune the refractive index profile over a narrow modulation region and thus control the optical switching behaviour via the applied SAW intensity. Direct tuning of the MMI device avoids losses and phase errors inherent to arrayed waveguide based switches, while also reducing the dimensions of the photonic circuit.

Coherent super-high-frequency (SHF) vibrations provide an excellent tool for the modulation and control of excitations in semiconductors. Here, we investigate the piezoelectric generation and propagation of longitudinal bulk acoustic waves (LBAWs) with frequencies up to 20 GHz in GaAs crystals using bulk acoustic wave resonators (BAWRs) based on piezoelectric thin ZnO films. We show that the electro-acoustic conversion efficiency of the BAWRs depends sensitively on the sputtering conditions of the ZnO films. The BAWRs were then used for the study of the propagation properties of the LBAWs in GaAs in the frequency and temperature ranges from 1 to 20 GHz and 10 and 300 K, respectively, which have so far not been experimentally accessed. We found that the intrinsic acoustic absorption of GaAs in the temperature range from 80 K to 300 K is dominated by scattering with thermal phonons. At lower temperatures, in contrast, the intrinsic acoustic absorption saturates at a frequency-dependent value. Experiments carried out with different propagation lengths indicate that the saturation is associated with losses during reflection at the sample boundaries. We also demonstrate devices with high quality factor fabricated on top of acoustic Bragg-reflectors. The results presented here prove the feasibility of high-quality acoustic resonators embedding GaAs-based nanostructures, thus opening the way for the modulation and control of their properties by electrically excited SHF LBAWs., Comment: Research article

The epitaxial growth of complex heterostructures requires in-situ techniques for detection and control of the growth parameters. In-situ continuous spectral reflectivity measurements are used during molecular beam epitaxial growth to measure the substrate temperature and achieve close growth control on complex structures such as quantum-cascade lasers and microcavities. The corresponding utilized modes of operations are illustrated in detail and are found to enhance the reproducibility and precision of complex growth runs.

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.

We demonstrate compact tunable phased-array wavelength-division 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., The authors thank W. Seidel, and S. Rauwerdink for preparation of the devices. This research has been supported by the international campus of excellence VLC/CAMPUS and by the program INNCIDE from the Spanish Ministry of Economy and Competitiveness (MINECO), through the program "Valoritza i Transfereix" from the Vice-Principal of Research and Scientific Policy of the Universitat de Valencia and through the program INNOVA (grant SP20120860) from the Universitat Politecnica de Valencia. Financial support by the Spanish MINECO Projects TEC2010-21337 and MAT2012-33483 is gratefully acknowledged. A. Crespo-Poveda and B. Gargallo acknowledge financial support through FPI grants BES-2010-036846 and BES-2011-046100, respectively.

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.

Photonic modulators are one of the most important elements of integrated photonics. We have designed, fabricated, and characterized a tunable photonic modulator consisting of two 180 degrees-dephased output waveguide channels, driven by a surface acoustic wave in the GHz frequency range built on (Al,Ga)As. Odd multiples of the fundamental driven frequency are enabled by adjusting the applied acoustic power. A good agreement between theory and experimental results is achieved. The device can be used as a building block for more complex integrated functionalities and can be implemented in several material platforms. (C) 2013 Optical Society of America, We thank J. Pedros for helping with the sample preparation. This work has been supported by the international campus of excellence VLC/CAMPUS and by the program INNCIDE from the Spanish Ministry of Economy and Competitiveness (MINECO), through the program "Valoritza i Transfereix" from the Vice-Principal of Research and Scientific Policy of the Universitat de Valencia and through the program INNOVA (grant SP20120860) from the Universitat Politecnica de Valencia. The authors also acknowledge financial support by the Spanish MINECO Projects TEC2010-21337 and MAT2012-33483. A. Crespo-Poveda and B. Gargallo acknowledge financial support through FPI grants BES-2010-036846 and BES-2011-046100, respectively.

We present a design approach for compact reconfigurable light routers 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. When the effective refractive index of the WGs is modulated with the proper relative optical phase difference, the light can switch paths between the preset output channel and the remaining output WGs. Taking advantage of the transfer phases between the access ports of the MMI couplers, we derive very simple phase relations between the modulated WGs that enable the reconfiguration of the output channel distribution when the appropriate coupling lengths of the MMI couplers are chosen. In this way, very compact expressions for calculating the channel assignment of the devices as a function of the applied phase shift are derived for the general case of N access WGs. Moreover, the situation where the applied phase shift varies sinusoidally, as in acoustically driven devices, is discussed. A transfer matrix formalism is employed to calculate the transmission properties of the routers. In particular, devices with six and seven access WGs are thoroughly described.