Integrated all-optical infrared switchable plasmonic quantum cascade laser

We report a type of infrared switchable plasmonic quantum cascade laser, in which far field light in the midwave infrared (MWIR, 6.1 μm) is modulated by a near field interaction of light in the telecommunications wavelength (1.55 μm). To achieve this all-optical switch, we used cross-polarized bowtie antennas and a centrally located germanium nanoslab. The bowtie antenna squeezes the short wavelength light into the gap region, where the germanium is placed. The perturbation of refractive index of the germanium due to the free carrier absorption produced by short wavelength light changes the optical response of the antenna and the entire laser intensity at 6.1 μm significantly. This device shows a viable method to modulate the far field of a laser through a near field interaction.     

Manipulation with molecules

Photonic molecules are mesoscopic hierarchical structures, constructed from ‘monomer’ units with typical dimensions of 1–5 μm, which function as coupled optical resonators. These structures are so named because they confine electromagnetic fields in modes that are closely analogous to bonding and antibonding electronic molecular orbitals in real molecules. Recent experimental advances have shown that photonic molecules can be fabricated in a variety of ways with different functionality. We review here recent work in this newly developing interdisciplinary field that blends chemistry, materials science, and optical physics. Finally, we speculate on possible applications and future research directions.For many years now, researchers in materials and photonics have been keenly interested in the design and fabrication of structures that confine and manipulate electromagnetic fields on length scales comparable to optical wavelengths. The ultimate goal is an all-optical information processing and computation platform using photons in ways analogous to electrons in silicon devices on similar length scales. Specific focus areas such as wafer-scale integration, parallel processing, and frequency management (e.g. add-drop filters), on micron or sub-micron length scales are active areas of photonics research. While a great deal of progress has been made in the burgeoning field of microphotonics, we are still a long way off from realizing important goals such as the optical transistor and all-optical integrated circuits¹.     

High speed all-optical encryption and decryption using quantum dot semiconductor optical amplifiers

A scheme to realize high speed all-optical encryption and decryption using key-stream generators and an XOR gate based on quantum dot semiconductor optical amplifiers (QD-SOAs) was studied. The key used for encryption and decryption is a high speed all-optical pseudorandom bit sequence (PRBS) which is generated by a linear feedback shift register (LFSR) composed of QD-SOA-based logic XOR and AND gates. Two other kinds of more secure key-stream generators, i.e. cascaded design and parallel design, were also designed and investigated. Nonlinear dynamics including carrier heating and spectral hole-burning in the QD-SOA are taken into account together with the rate equations in order to realize all-optical logic operations. Results show that this scheme can realize all-optical encryption and decryption by using key-stream generators at high speed (~250 Gb/s).     

Photocurrent imaging of nanocrystal quantum dots on single-walled carbon nanotube device

Semiconductor nanocrystal quantum dots (NQDs) are considered an attractive candidate for use in optoelectronic applications due to the ease of band gap control provided by varying the particle size. To increase the efficiency of NQDs when practically applied in devices, researchers have introduced the concept of coupling of NQDs to one-dimensional nanostructures such as single-walled carbon nanotubes (SWCNTs), which have a ballistic conducting channel. In the present study, NQDs of CdSe core and CdSe/ZnS are used as light absorbing building blocks. SWCNTs and functionalized NQDs are non-covalently coupled using pyridine molecules in order to maintain their electronic structures. To measure the electrical signals from the device, a NQDs-SWCNT hybrid nanostructure is fabricated as a field-effect transistor (FET) using the dielectrophoresis (DEP) method. A confocal scanning microscope was used to scan the devices using a diffraction-limited laser spot and the photocurrent was recorded as a function of the position of the laser spot. To improve the performance of detecting small electronic signal with high signal-to-noise ratio we used a lock-in technique with an intensity-modulated laser. In this paper, we have demonstrated that detection of local photoconductivity provides an efficient means to resolve electronic structure modulations along NQDs-SWCNT hybrid nanostructures.     

Controllable optical bistability and Fano line shape in a hybrid optomechanical system assisted by kerr medium: possibility of all optical switching

We theoretically analyse the optical and optomechanical nonlinearity present in a hybrid system consisting of a quantum dot(QD) coupled to an optomechanical cavity in the presence of a nonlinear Kerr medium, and show that this hybrid system can be used as an all optical switch. A high degree of control and tunability via the QD-cavity coupling strength, the Kerr and the optomechanical nonlinearity over the bistable behaviour shown by the mean intracavity optical field and the power transmission of the weak probe field can be achieved.The results obtained in this investigation has the potential to be used for designing efficient all-optical switch and high sensitive sensors for use in Telecom systems.     

All-optical flip-flops based on DFB laser diodes and DFB-arrays

We present numerical and experimental results on a number of different all-optical flip-flops which are based on DFB laser diodes or DFB-arrays. All these flip-flop concepts show potential for fast switching with low switching energy and high extinction ratio. They are moreover very robust in the sense that the switching pulses (and the injected CW beam in some cases) can be of arbitrary wavelength and that the bistability characteristics can be tuned by simple variation of the current injected into the devices. Two different designs for all-optical flip-flop operation will be discussed in detail. The first one is a DFB or DBR laser diode coupled to a semiconductor optical amplifier, in which the bidirectional coupling between laser and amplifier causes the bistability. The second concept is based on bistable behaviour in a single AR-coated DFB laser, with low coupling coefficient and in which a CW signal is injected. These all-optical flip-flops can easily be extended to optically switchable multistate devices with any number of stable states. Such multistate devices are briefly discussed at the end.     

Toward graphene-based quantum interference devices

A new type of quantum interference device based on a graphene nanoring in which all edges are of the same type is studied theoretically. The superposition of the electron wavefunction propagating from the source to the drain along the two arms of the nanoring gives rise to interesting interference effects. We show that a side-gate voltage applied across the ring allows for control of the interference pattern at the drain. The electron current between the two leads can therefore be modulated by the side gate. The latter manifests itself as conductance oscillations as a function of the gate voltage. We study quantum nanorings with two edge types (zigzag or armchair) and argue that the armchair type is more advantageous for applications. We demonstrate finally that our proposed device operates as a quantum interference transistor with high on/off ratio.     

Optical switching and normal mode splitting in hybrid semiconductor microcavity containing quantum well and Kerr medium driven by amplitude-modulated field

ABSTRACT

We theoretically investigate optical bistability/multistability for all optical switching signature in a hybrid semiconductor microcavity system comprising a quantum well and a Kerr nonlinear substrate. The system is essentially two optically coupled microcavities with one of the microcavity being driven by an external amplitude-modulated pump laser. We show that the switching between bistable and multistable behaviour is influenced by the modulated pump laser, Kerr nonlinearity and the optical coupling between the two microcavities. We further investigate the intracavity spectrum of quantum fluctuations which exhibit the well-known normal mode splitting (NMS). The NMS behaviour is also found to be influenced by the system parameters. These results demonstrate that the present hybrid nonlinear system can be used in designing sensitive optical devices.     

DNA-based programming of quantum dot valency, self-assembly and luminescence

The electronic and optical properties of colloidal quantum dots, including the wavelengths of light that they can absorb and emit, depend on the size of the quantum dots. These properties have been exploited in a number of applications including optical detection, solar energy harvesting and biological research. Here, we report the self-assembly of quantum dot complexes using cadmium telluride nanocrystals capped with specific sequences of DNA. Quantum dots with between one and five DNA-based binding sites are synthesized and then used as building blocks to create a variety of rationally designed assemblies, including cross-shaped complexes containing three different types of dots. The structure of the complexes is confirmed with transmission electron microscopy, and photophysical studies are used to quantify energy transfer among the constituent components. Through changes in pH, the conformation of the complexes can also be reversibly switched, turning on and off the transfer of energy between the constituent quantum dots.     

Optical properties of a laterally confined semiconductor microcavity containing a single quantum well

The semiconductor microcavity with a thin oxide-aperture layer is fabricated, and linear optical transmission spectrum measured for various aperture diameters. First, the observation of bare cavity modes is demonstrated in this microstructure which is capable of confining light field three-dimensionally. Several transverse modes are observed as transmission peaks, which manifests the lateral field confinement achieved well down to 2 μm aperture diameter. And the transmission spectrum of cavity modes coupled to the excitonic resonance is measured for the same microcavity system containing a single quantum well. The result shows that each transverse mode couples to an exciton independently as it approaches the excitonic resonance frequency, giving rise to an anti-crossing behavior between coupled modes.     

Tailorable Dynamics in Nonlinear Optical Metasurfaces

Controlling light with light is essential for all-optical switching, data processing in optical communications and computing. Until now, all-optical control of light has relied almost exclusively on nonlinear optical interactions in materials. Achieving giant nonlinearities under low light intensity is essential for weak-light nonlinear optics. In the past decades, such weak-light nonlinear phenomena have been demonstrated in photorefractive and photochromic materials. However, their bulky size and slow speed have hindered practical applications. Metasurfaces, which enhance light–matter interactions at the nanoscale, provide a new framework with tailorable nonlinearities for weak-light nonlinear dynamics. Current advances in nonlinear metasurfaces are introduced, with a special emphasis on all-optical light controls. The tuning of the nonlinearity values using metasurfaces, including enhancement and sign reversal is presented. The tailoring of the transient behaviors of nonlinearities in metasurfaces to achieve femtosecond switching speed is also discussed. Furthermore, the impact of quantum effects from the metasurface on the nonlinearities is introduced. Finally, an outlook on the future development of this energetic field is offered.     

Optical protocol for quantum state sharing of superposed coherent state

We propose an optical protocol for quantum state sharing of superposed coherent state in terms optical elements. Our protocol can realize a near-complete quantum state sharing of a superposed coherent state with arbitrary coeficients. The realization of this protocol is appealing due to the fact that the quantum state of light is robust against the decoherence and photons are ideal carriers for transmitting quantum information over long distances. This protocol can also be generalized to the multiparty system.     

High Efficiency Light‐Emitting Transistor with Vertical Metal–Oxide Heterostructure

The monolithic integration of light‐emission with a standard logic transistor is a much‐desired multifunctionality. Here, a high‐efficiency light‐emitting transistor (LET) employing an inorganic quantum dots (QDs) emitter and a laser‐annealed vertical metal–oxide heterostructure is reported. The experimental results show that the peak efficiency and luminance of this QDs LET (QLET) are 11% and 8000 cdm^?2, respectively at a monochromatic emitting light wavelength of 585 nm. As far as it is known, these are among the highest values ever achieved for LETs. More importantly, the QLET exhibits an ultrahigh electron mobility of up to 25 cm² V^?1 S^?1, a lower efficiency roll‐off (7% at high 3000 cdm^?2), and excellent stability with long‐duration gate stress switching cycles. Additionally, this approach is compatible with those used in conventional large‐area silicon electronic manufacturing and can enable a scalable and cost‐effective procedure for future integrated versatile displays and lighting applications.     

The effect of barrier width in coupled asymmetric double quantum well structure on passive mode-locking region of existence

Semiconductor two-sectional laser diodes with active region, consisting of two InGaAs quantum wells of different width separated with GaAs barrier are investigated. At barrier thickness of 2 nm quantum wells are coupled and diagonal optical transition originates between them. Peak in absorption spectra of lasing structure related to this diagonal transition is observed. An additional region of passive mode-locking due to this absorption peak takes place at low reverse biases on absorber section.     

Single photon scattering in a pair of coupled-resonator waveguides coupled to a quantum emitter

We theoretically investigate the single photon scattering in a pair of coupled-resonator waveguides coupled to a two-level quantum emitter. It reveals that the incident photon transporting probabilities can be controlled by adjusting the coupling strength between the two-level system and the coupled-resonator waveguide. Two optical nano-devices, quantum optical switch and beam splitter are proposed. In addition, the influence of the dissipation of the two-level system on the photon transporting properties is also analyzed.     

Semiconductor quantum templates: bottom-up design of optical devices and photonic circuits using sub-nanoscale high monolayer features and quantum optics

We propose an alternative bottom-up technique for designing, fabricating and monolithically integrating optical components, including functional distributed feedback lasers, modulators, waveguides, etc in a single semiconductor wafer without any need for etching or post-processing epitaxial growth. The proposed technique is based on the formation of semiconductor quantum templates at the well/barrier interfaces of quantum well structures. Such templates are responsible for changing the thickness of a quantum well in designated regions by adding one extra monolayer of the well material in those regions during the growth process. We show that, using a control laser field, these templates or sub-nanoscale high monolayer features allow us to spatially control the formation of electromagnetically induced transparency, gain without inversion, and coherent enhancement/suppression of the refractive index along the plane of the quantum well. We demonstrate that this can lead to bottom-up design capabilities for functional optical devices and their monolithic integration using a single epitaxial growth process.     

Controllable nonlinear effects in a hybrid optomechanical semiconductor microcavity containing a quantum dot and Kerr medium

We theoretically investigate the nonlinear effects in a hybrid quantum optomechanical system consisting of two optically coupled semiconductor microcavities containing a quantum dot and a Kerr nonlinear substrate.The steady-state behaviour of the mean intracavity optical field demonstrates that the system can be used as an all optical switch. We further investigate the spectrum of small fluctuations in the mechanical displacement of the movable distributed Bragg reflectors and observe that normal mode splitting takes place for high Kerr nonlinearity and pump power. In addition, we have shown that steady state of the system exhibits two possible bipartite entanglements by proper tuning of the system parameters. The entanglement results suggest that the proposed system has the potential to be used in quantum communication platform. Our work demonstrates that the Kerr-nonlinearity can effectively control the optical properties of the hybrid system, which can be used to design efficient optical devices.     

Analysis of quantum noise in a singly resonant nondegenerate optical parametric oscillator

We have analyzed the evolution of quantum operators in a three-wave mixing process by using the nonlinear polarization driven wave equations and linearization of the quantum operators. We have theoretically shown that a nondegenerate optical parametric amplifier can generate amplitude-squeezed light when operated in the backconversion regime. Furthermore, a nondegenerate optical parametric oscillator, where only the signal wave is resonant, is proved to generate amplitude-squeezed light when the pump intensity is above the value at which 100% photon conversion efficiency is achieved. The calculated limit for amplitude-squeezing in this case is 3 d B.     

Optical bistability and multistability driven by external magnetic field in a dielectric slab doped with nanodiamond nitrogen vacancy centres

Abstract

The theoretical investigation of controlling the optical bistability (OB) and optical multistability (OM) in a dielectric medium doped with nanodiamond nitrogen vacancy centres under optical excitation are reported. The shape of the OB curve from dielectric slab can be tuned by changing the external magnetic field and polarization of the control beam. The effect of the intensity of the control laser field and the frequency detuning of probe laser field on the OB and OM behaviour are also discussed in this paper. The results obtained can be used for realizing an all-optical bistable switching or development of nanoelectronic devices.     

The quantum interference effect transistor

We give a detailed discussion of the quantum interference effect transistor (QuIET), a proposed device which exploits the interference between electron paths through aromatic molecules to modulate the current flow. In the off state, perfect destructive interference stemming from the molecular symmetry blocks the current, while in the on state, the current is allowed to flow by locally introducing either decoherence or elastic scattering. Details of a model calculation demonstrating the efficacy of the QuIET are presented, and various fabrication scenarios are proposed, including the possibility of using conducting polymers to connect the QuIET with multiple leads.