Direct high-speed modulation of circular polarization (Pc) of coherent light will open the way for new communication technology and offers the possibility to overcome the main bottleneck of the optical telecommunications. Here, by using spin-orbit torque (SOT) with spin Hall effect to control the spin injector magnetization, we report for the first time to achieve electrical control of the circular polarization of light emitted from a quantum dot based light emitting diode (LED) at room temperature [1]. The circular polarization can be modulated between ±25% at 250K and ±16% at 290K after pulsed current switching injector magnetization. A repetition of more than 60 times do not reveal any degradation at the injector/semiconductor interface. Our achievement will directly contribute the implementation of the new optical telecommunication technology with Pc modulation.
[1] P. A. Dainone, et al. “Controlling the helicity of light by electrical magnetization switching”, Nature, to be published.
Optophononic resonators based on GaAs/AlAs multilayer structures can confine near-infrared photons and sub-terahertz phonons. Previous works have studied the generation and detection of coherent acoustic phonons in planar and circular micropillar cavities. However, these structures exhibit only one optical cavity mode, which makes it challenging to reach the efficient generation and sensitive detection simultaneously in a standard pump-probe experiment. Here, we propose the use of elliptical micropillars to reach an improved condition of these two processes. The elliptical cross-section of the microcavity lifts the degeneracy of the fundamental optical modes, related to each of its major and minor axes. By tuning the pump pulses in resonance with one optical mode, the generation efficiency is enhanced by maximizing the electromagnetic field inside the cavity. Meanwhile, the probe pulses at the same wavelength and with orthogonal polarization detects phonons at the slope of the other mode, where it is sensitive to reflectivity changes. We experimentally demonstrated that the phonon amplitude is enhanced by introducing the ellipticity compared to the circular micropillar. This improvement is promising for future developments in constructing efficient phonon transducers.
Nanometer-thick multilayer structures, characterized by contrasts in elastic properties, present promising avenues for engineering and manipulating acoustic phonons at the nanoscale. Semiconductor nano-acoustic cavities, particularly those based on Distributed Bragg Reflectors (DBRs), have demonstrated unique capabilities in simultaneously confining light and acoustic phonons. This dual confinement enhances the generation and detection phononic fields, making these structures attractive for ultra-high-frequency applications and as platforms for simulating solid-state systems. In this study, we further explore the possibilities of hybrid nanostructures that could be both tunable and responsive to ultrafast changes in elastic properties induced by external stimuli such as temperature, humidity, and electrical fields. Building upon our theoretical simulations, our experimental investigation focuses on the dynamics of acoustic phonons spanning the frequency range of 5-500 GHz, utilizing near-infrared pump and probe ultrafast transient reflectivity experiments. The materials under investigation include mesoporous SiO2/TiO2 multilayers with a Nickel transducer, GaAs/AlAs DBR incorporating mesoporous SiO2 as an open cavity layer, YBCO/STO multilayers, and other potential responsive materials. Our long-term objective is to uncover the interplay between these nanostructures and external stimuli through systematic experimentation, shedding light on their tunability and responsiveness. Our experimental findings pave the way for developing nanoacoustic sensing technologies and reconfigurable optoacoustic nanodevices.
To achieve full control over acoustic phonons at ultrahigh frequencies, it is essential to characterize the phonon transport properties. Recent works have shown that surface acoustic waves at gigahertz frequencies can propagate over micrometer distances in different nanostructures such as nanowires, nanogratings, and nanoantennas. Here, we aim at investigating acoustic phonon transport by designing a GaAs/AlAs optophononic waveguide. Along the vertical direction of the waveguide, a Fabry-Perot cavity ensures an efficient confinement of acoustic phonons that has been demonstrated in planar and micropillar structures. In the lateral direction, the interface of air and semiconductor serves as an acoustic mirror to reflect phonons in the waveguide. We perform pump-probe experiments to generate coherent acoustic phonons at one position and detect them remotely on the waveguide. We analyze the signals originated by phonons generated in the pump position reaching the remote probe location, revealing a clear indication of phonon transport at room temperature. Our findings have potential applications in quantum technologies and data processing.
Accessing acoustic phonons at high frequencies in nanostructures becomes more and more essential in nanoelectronics, nano- and opto-mechanics and quantum technologies, as phonons can strongly interact with electrons and photons at the nanoscale. In spontaneous Brillouin scattering processes, the scattered photons energy, direction and polarization are constrained by selection rules for a given input state. These selection rules are usually considered as intrinsic material properties in crystalline solids and the polarization of the scattered photons depends on the polarization of the excitation. In this work, we use elliptical optophononic micropillar resonators to control these optical polarization selection rules. The degeneracy of the optical cavity modes of circular micropillars is lifted due to the elliptical cross-section of the micropillars, leading to two cavity modes orthogonally polarized and split in energy. The optical field polarization state will depend on both orthogonal cavity modes and their associated polarization states. Therefore, an incident laser beam linearly polarized along the diagonal axis of the elliptical pillar undergoes a wavelength dependent polarization rotation. By choosing the polarization and wavelength of the incident laser, we demonstrate that the polarization state of the incident and reflected laser and the Brillouin scattering signal are different. In this way, background-free spontaneous Brillouin scattering spectra can be efficiently measured in a cross-polarization scheme down to 18 GHz. Here, we theoretically and experimentally explore the optimal conditions for the polarization and wavelength of the incident laser, and the ellipticity of the micropillars, to improve the polarization-based filtering applied to Brillouin spectroscopy.
We present an experiment where a reconfigurable photonic processor fabricated in glass by femtosecond laser micromachining is used for the generation of four-photons GHZ entangled states, with high efficiency and fidelity. The chip is used in synergy with a bright and quasi-deterministic source of single photons based on semiconductor quantum dot. The very efficient interfacing of these two platforms is ensured by the excellent connectivity between glass photonic circuits and standard optical fibers. In addition, in order to benchmark the quality of the generated states, this processor is used to implement a quantum secret sharing protocol on chip.
THz coherent acoustic phonons on a scale of sub-picoseconds in temporal-periodicities and nanometers in wavelengths are promising in various fields such as nanometrology/nanoimaging, THz devices and heat management. By merging advanced ultrafast laser spectroscopy and sophisticated nanotechnologies, the excitation and detection of bulk coherent acoustic phonons in the THz regime have been accomplished. Nevertheless, coherent surface acoustic waves (SAWs) realized by metallic gratings deposited on a substrate, are still below 100 GHz. In this report, we take advantage of the cleaved superlattice (SL) surface with immediately reachable nanometer periodicity and atomic-level interface quality to monitor SAWs by femtosecond lasers. Rayleigh SAWs above 100 GHz and bulk surface skimming acoustic waves up to 1THz, with deeply sub-optical-wavelength periodicities, are observed on cleaved Al0.3Ga0.7As/GaAs SLs and cleaved In0.2Ga0.8N/GaN SLs, respectively. The observations open a path towards THz opto-acoustic/acousto-optic transducers.
Semiconductor quantum dots have emerged as excellent artificial atoms to both generate and manipulate quantum light. When embedded in cavities, they can generate single photons and entangled photons with unparalleled efficiency and high quantum purity. In this talk, I will discuss how such devices can be used to generate strings of many entangled photons. The method, leveraging the spin-selective optical transition in a charged quantum dot, leads to the generation of indistinguishable photons in linear cluster states or GHZ states at high rates, realizing an important milestone for scaling-up optical quantum technologies.
Integrated quantum photonics is a key tool towards large scale quantum technologies. In this work we present an AlGaAs-based photonic circuit for on-chip generation and manipulation of broadband polarization-entangled photon pairs. The quantum state is generated by Type-II spontaneous parametric down conversion in AlGaAs Bragg reflection waveguides at telecom wavelengths and room temperature. Polarization entangled photons are manipulated over a frequency band of around 50 nm by an integrated polarizing beam splitter. We demonstrate Hong-Ou-Mandel visibility of 80% for a quantum device where the photon pairs generation and manipulation are implemented in a single chip.
In-rich InGaN/GaN nanowires (NWs) are key optoelectronic materials, which can close the green gap of the light emitting diodes and can be used in efficient high-bandgap solar cells for integration in tandem devices. Realization of these devices requires as a first step the optimization of the NW structure and their electrical parameters. Electron Beam Induced Current (EBIC) microscopy is well suited to probe nanoscale devices with a high resolution and to extract the material parameters.
Here, we analyze the electrical properties of axial GaN and InGaN/GaN n-p and p-n junction NWs using EBIC microscopy. III-N NWs were grown on Si(111) substrates by molecular beam epitaxy using Mg as a p-dopant and Si as an n-dopant. The growth conditions were adjusted to optimize the doping order with an abrupt axial junction without a parasitic radial overgrowth. From the EBIC analysis of the GaN p-n junctions, the doping level and the minorities carrier diffusion lengths were extracted. Next, a p-GaN/i-InGaN/n-GaN junction containing an In-rich InGaN segment [1] was grown yielding a flat and strong EBIC signal in the InGaN NW portion. NW arrays were then contacted and their behavior under visible light was analyzed.
[1] Morassi et al., Cryst. Growth Des., 2545, 18 2018
“Photonics Multiannual Strategic Roadmap 2014-2020” mentions flexible electronics, light sources, displays, sensors and solar cells as key emerging technologies with a high expected growth of the market share. Technologies based on organic semiconductors still suffer from a short lifetime and low efficacy as compared to their inorganic counterparts. To make a flexible device from inorganic semiconductors one should shrink the size of the active elements and to integrate them on mechanically-flexible substrates. This can be achieved using control-by-design nanowires.
In this work, we address the growth of nitride nanowires on novel substrates and the fabrication and characterization of flexible devices based on nitride nanowires. First, we will discuss the epitaxy of GaN nanowires on graphene-on-SiO2 substrates. We show that without any catalyst or intermediate layer, the nanowires grow on graphene with an excellent selectivity compared to the uncovered SiO2 surface. Taking advantage of this selectivity, we demonstrate that organized arrays of nanowires can be synthesized by structuring the graphene layer. Next, we will discuss the approach for nanowire lift-off, transfer into polymer-embedded membranes and flexible contacting. The realization and characterization of flexible light sources, photodetectors and piezogenerators will be presented.
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