External Optical Control Research Articles

Multifunctional metasurface for ultrafast all-optical efficient modulation of terahertz wave

Metasurfaces have been widely used to terahertz (THz) modulators due to their unique electromagnetic (EM) modulation properties. However, to realize ultrafast and efficient control of the active metasurfaces remains a critical challenge. Herein, we first demonstrate a multifunctional metasurface modulator based on metal square rings, which have central rotational symmetry with local asymmetry. The former captures more EM energy to achieve strong enhancement of the local EM responses, and the latter generates high quality factor (Q-factor) Fano resonance. By scaling the unit structure, the resonant frequency shifts in an ultra-wideband range of ∼0.29-10 THz, which shows a linear relation between the Q-factor and the scaling factor, and an exponential variation between the full width at half maximum (FWHM) and the scaling factor. The results provide an effective approach to predict the frequency selection characteristics of the modulators in the THz regime. More importantly, by embedding the silicon into the specific position of the metasurface, external optical control results in the unit structure is constructed from meta-atom to molecularization model, the shifting of resonant frequency and the multi-level modulation of amplitude are realized, and the maximum modulation depth (MD) reaches ∼100 %. By systematically studying the dynamics of frequency and amplitude regulation, benefiting from the ultra-short relaxation time of the photo-carriers in silicon bridge, an ultrafast full recovery time of 2000 ps is achieved. Combined with the local field characteristics, the scaled unit structure achieves efficient modulation of the resonant frequency and amplitude under optical pumping, which provides a promising approach for the development of active metasurface modulator suitable for the whole THz band. This work demonstrates the viability of optical control molecularization of specific meta-atoms is applicable to the entire THz band, which has great potential use for future state-of-the-art THz modulators.

Terahertz rectification in ring-shaped quantum barriers

Tunneling is the most fundamental quantum mechanical phenomenon with wide-ranging applications. Matter waves such as electrons in solids can tunnel through a one-dimensional potential barrier, e.g. an insulating layer sandwiched between conductors. A general approach to control tunneling currents is to apply voltage across the barrier. Here, we form closed loops of tunneling barriers exposed to external optical control to manipulate ultrafast tunneling electrons. Eddy currents induced by incoming electromagnetic pulses project upon the ring, spatiotemporally changing the local potential. The total tunneling current which is determined by the sum of contributions from all the parts along the perimeter is critically dependent upon the symmetry of the loop and the polarization of the incident fields, enabling full-wave rectification of terahertz pulses. By introducing global geometry and local operation to current-driven circuitry, our work provides a novel platform for ultrafast optoelectronics, macroscopic quantum phenomena, energy harvesting, and multi-functional quantum devices.

On-chip multi-stage optical delay based on cascaded Brillouin light storage.

Storing and delaying optical signals plays a crucial role in data centers, phased array antennas, communication, and future computing architectures. Here, we show a delay scheme based on cascaded Brillouin light storage that achieves multi-stage delay at arbitrary positions within a photonic integrated circuit. Importantly these multiple resonant transfers between the optical and acoustic domain are controlled solely via external optical control pulses, allowing cascading of the delay without the need of aligning multiple structural resonances along the optical circuit.

Optical thyristor based on GaAs/InGaP materials

The possibility of creating thyristor structures with external optical control by laser radiation with a wavelength of ~800 nm, based on single-crystal wafers of semi-insulating GaAs and layers of InGaP with the lattice parameter compatible with GaAs, is shown.

External Control of Dissipative Coupling in a Heterogeneously Integrated Photonic Crystal—SOI Waveguide Optomechanical System

Cavity optomechanical systems with an enhanced coupling between mechanical motion and electromagnetic radiation have permitted the investigation of many novel physical effects. The optomechanical coupling in the majority of these systems is of dispersive nature: the cavity resonance frequency is modulated by the vibrations of the mechanical oscillator. Dissipative optomechanical interaction, where the photon lifetime in the cavity is modulated by the mechanical motion, has recently attracted considerable interest and opens new avenues in optomechanical control and sensing. In this work we demonstrate an external optical control over the dissipative optomechanical coupling strength mediated by the modulation of the absorption of a quantum dot layer in a hybrid optomechanical system. Such control enhances the capability of tailoring the optomechanical coupling of our platform, which can be used in complement to the previously demonstrated control of the relative (dispersive to dissipative) coupling strength via the geometry of the integrated access waveguide.

Steady-state linear optical properties and Kerr nonlinear optical response of a four-level quantum dot with phonon-assisted transition**Project supported by the National Natural Science Foundation of China (Grant No. 61367003), the Scientific Research Fund of Hunan Provincial Education Department, China (Grant No. 12A140), and the Scientific Research Fund of Guizhou Provincial Education Department, China (Grant Nos. KY[2015]384 and KY[2015]446).

The linear optical properties and Kerr nonlinear optical response in a four-level loop configuration GaAs/AlGaAs semiconductor quantum dot are analytically studied with the phonon-assisted transition (PAT). It is shown that the changes among a single electromagnetically induced transparency (EIT) window, a double EIT window and the amplification of the probe field in the absorption curves can be controlled by varying the strength of PAT κ. Meanwhile, double switching from the anomalous dispersion regime to the normal dispersion regime can likely be achieved by increasing the Rabi energy of the external optical control field. Furthermore, we demonstrate that the group velocity of the probe field can be practically regulated by varying the PAT and the intensity of the optical control field. In the nonlinear case, it is shown that the large SPM and XPM can be achieved as linear absorption vanishes simultaneously, and the PAT can suppress both third-order self-Kerr and the cross-Kerr nonlinear effect of the QD. Our study is much more practical than its atomic counterpart due to its flexible design and the controllable interference strength, and may provide some new possibilities for technological applications.

Controllable double tunneling induced transparency and solitons formation in a quantum dot molecule

We consider the coupling effect between interdot tunneling coupling and external optical control field to study the linear optical property and the formation of temporal optical solitons in a quantum dot molecules system, analytically. The results show that the double tunneling induced transparency (TIT) windows are appeared in the absorption curve of probe field because of the formation of dynamic Stark splitting and quantum destructive interference effect from the two upper levels. Interestingly, the width of the TIT window becomes wider with the increasing intensity of the optical control field. We also find that the Kerr nonlinear effect of the probe field can be modulated effectively through coherent control both the control field and the interdot tunneling coupling in this system. Meanwhile, we demonstrate that the formation of dark or bright solitons can be practical regulated by varying the intensity of the optical control field.

Behaviour and external optical control of surface charges in a coplanar barrier discharge analysed from transverse and longitudinal electric field measurement

A transverse electric field in addition to a longitudinal electric field on the dielectric barrier in a coplanar barrier discharge is measured by a technique of laser polarization analysis using an electro-optic crystal. Spatial and temporal behaviour of charges on the surface is studied with these experimental results. Furthermore, it is demonstrated that the accumulated charges on the coplanar barrier are modulated by external irradiation of pulsed laser and the discharge is controlled with this surface charge modulation.

Eleven-wavelength switchable fiber ring laser with a dispersion compensation fiber and a delayed interferometer

We demonstrate a fiber ring laser with a dispersion compensation fiber (DCF) and a delayed interferometer (DI) with temperature control, which is able to switch eleven wavelengths one by one. In ring cavity, DCF supplies different effective cavity lengths for different wavelengths, DI generates a wavelength comb corresponding to the ITU grid, a flat-gain erbium-doped fiber amplifier (EDFA) provides uniform gain for each lasting wavelength, and a semiconductor optical amplifier (SOA) not only acts as active modulator, but also alleviates homogeneous broadening effect of EDFA. Stable pulse trains with a pulsewidth about 40 ps at 10 GHz have been obtained by injecting external optical control signals into the laser. Wavelength switching process among eleven wavelengths is achieved by merely tuning an intracavity optical delay line.

Experimental demonstration of frequency-agile terahertz metamaterials

Metamaterials exhibit numerous novel effects1,2,3,4,5 and operate over a large portion of the electromagnetic spectrum6,7,8,9,10. Metamaterial devices based on these effects include gradient-index lenses11,12, modulators for terahertz radiation13,14,15 and compact waveguides16. The resonant nature of metamaterials results in frequency dispersion and narrow bandwidth operation where the centre frequency is fixed by the geometry and dimensions of the elements comprising the metamaterial composite. The creation of frequency-agile metamaterials would extend the spectral range over which devices function and, further, enable the manufacture of new devices such as dynamically tunable notch filters. Here, we demonstrate such frequency-agile metamaterials operating in the far-infrared by incorporating semiconductors in critical regions of metallic split-ring resonators. For this first-generation device, external optical control results in tuning of the metamaterial resonance frequency by ∼20%. Our approach is integrable with current semiconductor technologies and can be implemented in other regions of the electromagnetic spectrum. Metamaterials that possess frequency tunability enable new device functions. By external optical control through the incorporation of semiconductors in metallic split-ring resonators, the researchers provide an elegant solution to frequency-agile terahertz metamaterials.

Photochemical Single-Molecule Affinity Switch

Manipulation and control at the molecular level is a prerequisite for future nanomachines and nanodevices. In order to build a bistable molecular affinity switch, we have synthesized a supramolecular guest−host system whose binding affinity can externally be controlled and repetitively switched by UV light or heating. This photochemical macrocycle, which incorporates a supramolecular resorc[4]arene receptor cavity and two photodimerizable anthracene moieties, has been investigated by single-molecule force spectroscopy under external optical control which proved the repetitive and selective activation and deactivation at the level of individual molecular complexes. This synthetic photochemical single-molecule reaction acts as an intermolecular switch and can be affinity-tuned under external control, which allows new concepts for directed molecular assembly and motional functionalities at the nanoscale in the future.

All-optical Lyot-filter-assisted flip-flop operation using a semiconductor optical amplifier

All-optical flip-flop operation using external optical control is demonstrated in a single semiconductor optical amplifier (SOA)-based fiber ring laser with an intracavity Lyot filter. Its operation is based on the principle of cross-gain saturation in the SOA. A unique feature of this flip-flop is its ability to be set and reset at multiple wavelength pairs of an auxiliary continuous wave control light that is injected into the fiber ring cavity; this, together with the wide wavelength tunability of the Lyot filter makes the flip-flop potentially useful in wavelength-division multiplexing applications. Bistable output at 1571 nm with a contrast ratio of 20 dB between the two output power states of the flip-flop using -3 dBm power of the external optical control is demonstrated