Ultrafast all optical switching via tunable Fano interference

Tunable Fano and EIT-like resonances based on two cascaded micro-ring resonators

Microring resonators (MRRs) are key building blocks in integrated photonics, but their performances usually suffer from limitations in extinction ratio and slope rate (SR), primarily due to their symmetrical Lorentzian resonance line shape. To overcome these limitations, special transmission spectra (STS), such as Fano resonance and electromagnetically induced transparency (EIT)-like resonance, offer asymmetric line shapes that exhibit a higher extinction ratio (ER) and a steeper SR, thereby enhancing the sensitivity and selectivity of optical switches, filters, and high-sensitivity sensors. However, the current reported works typically achieved only one type of STS and had limited tunability. In this Letter, we experimentally demonstrate a novel, to the best of our knowledge, device using two cascaded MRRs with different quality factors to generate Fano and EIT-like resonances at distinct ports. The ER can reach up to 31.2 dB with a sharp SR of 130.1 dB/ nm, for Fano resonance, and the EIT-like resonance is 12.4 dB. By adjusting the resonator wavelength of the MRRs and the phase shifter, the STS can be working at any desired wavelength. The device is demonstrated on a silicon-on-insulator platform, offering versatile application potential in optical sensors, slow and fast light generation, and microwave photonics.

Beam shifts controlled by orbital angular momentum in a guided-surface plasmon resonance structure with a four-level atomic medium

We proposed a scheme to realize tunable giant Goos-Hänchen (GH) and Imbert Fedorov (IF) shifts of the Laguerre-Gauss (LG) beam on a guided-wave surface plasmon resonance (GWSPR) structure backed by a coherent atomic medium with the spontaneously generated coherence (SGC) effect. The orbital angular momentum carried by the incident LG beam can be applied to enhance and control IF shifts but is not beneficial to GH shifts. However, in the presence of SGC effect in the atomic medium, both GH and IF shifts can be simultaneously enhanced and well controlled. With the SGC effect, the linear absorption of the atomic medium vanishes, while the nonlinear absorption of that can be significantly enhanced and controlled by the trigger field, which contributes to controlling of the beam shifts. In particular, the direction of GH shifts can be switched by the Rabi frequency of the trigger field, which can be interpreted as the result of a competition between the inherent damping and the radiative damping corresponding to the nontrivial change in the loci of the reflection coefficients. This scheme provides an effective method to flexibly control and enhance the beam shifts, so it has potential applications in integrated optics, optical sensors, etc.

Tunable Fano resonance with an ultra-wide free spectral range from a photonic integrated circuit

In this paper, a reconfigurable photonic integrated circuit that can produce various resonances is proposed and demonstrated. Particularly, it can generate a high performance Fano resonance with an ultra-wide free-spectral range. Moreover, the extinction ratio, slope rate, and center wavelength of the Fano resonance are tunable using integrated phase shifters. This work paves the way towards a variety of new applications, including low threshold lasers, low power consumption modulators, and high sensitivity sensors.

Spatially structured multi-wave-mixing induced nonlinear absorption and gain in a semiconductor quantum well

We have studied two-dimensional absorption and gain spectrum in an asymmetric semiconductor triple-coupled-quantum-well (TCQW) nanostructure. Four subband transitions are coupled by using four coherent fields in a close-loop configuration to introduce cross-Kerr effect and four-wave-mixing (FWM) induced nonlinearity in achieving nonlinear absorption and gain profiles. Position-dependent absorption and gain are obtained by applying one, or two coherent fields in a variety of standing wave configurations including superposed field configuration in the standing-wave regime. In addition to the control parameters like Rabi frequency and detuning, the specialty of the model is to employ double-controlled spatial phase-coherence guided by the FWM-induced phase and the phases introduced by the standing wave formation. Our results highlight the high-precision electron localization in spatial domain. The evolution of spatially modulated gain without inversion may be a substitute for obtaining gain from a traditional quantum cascade laser. The importance of the present work is to find its application in designing electro-optic modulators in semiconductor nanostructures in near future.

Dynamically tunable vortex four-wave mixing in a six-level system

We investigate the orbital angular momentum of vortex light in a six-level atomic system with a closed loop. We find that a vortex light field via four-wave mixing (FWM) is sensitive to the relative phase of the driving fields due to forming a closed loop configuration. Thus, it could periodically tune the phase and intensity of the vortex FWM field by adjusting the relative phase of the driving fields. Moreover, the spatial modulation of the vortex FWM phase and intensity also can be achieved by tuning the intensity of the microwave field and detuning of the driving fields.

The multi-photon induced Fano effect

The ordinary Fano effect occurs in many-electron atoms and requires an autoionizing state. With such a state, photo-ionization may proceed via pathways that interfere, and the characteristic asymmetric resonance structures appear in the continuum. Here we demonstrate that Fano structure may also be induced without need of auto-ionization, by dressing the continuum with an ordinary bound state in any atom by a coupling laser. Using multi-photon processes gives complete, ultra-fast control over the interference. We show that a line-shape index q near unity (maximum asymmetry) may be produced in hydrogenic silicon donors with a relatively weak beam. Since the Fano lineshape has both constructive and destructive interference, the laser control opens the possibility of state-selective detection with enhancement on one side of resonance and invisibility on the other. We discuss a variety of atomic and molecular spectroscopies, and in the case of silicon donors we provide a calculation for a qubit readout application.

Fano resonances occur in many platforms that have auto-ionizing states. Here the authors show that auto-ionizing states are not required for multi-photon Fano resonance in a Si:P system with significant screening by using a pump-probe method.

Optical Boolean chaos

Boolean chaos is widely used in physical systems for its digital-like behavior and complex dynamics. However, electronic logic devices limit the bandwidth of Boolean chaos and its development. Based on an autonomous optical Boolean network, a method of generating optical Boolean chaos with 14 GHz bandwidth is proposed, exploring the physical mechanism of the chaos generated by the system and analyzing the influences of external parameters on the dynamic characteristics of the system. The output status is mainly affected by the detection optical power, carrier recovery time of the semiconductor optical amplifier, and difference between the two self-feedback time delays.

Highly efficient vortex four-wave mixing in asymmetric semiconductor quantum wells

Orbital angular momentum (OAM) is an important property of vortex light, which provides a valuable tool to manipulate the light-matter interaction in the study of classical and quantum optics. Here we propose a scheme to generate vortex light fields via four-wave mixing (FWM) in asymmetric semiconductor quantum wells. By tailoring the probe-field and control-field detunings, we can effectively manipulate the helical phase and intensity of the FWM field. Particularly, when probe field and control field have identical detuning, we find that both the absorption and phase twist of the generated FWM field are significantly suppressed. Consequently, the highly efficient vortex FWM is realized, where the maximum conversion efficiency reaches around 50%. Our study provides a tool to transfer vortex wavefronts from input to output fields in an efficient way, which may find potential applications in solid-state quantum optics and quantum information processing.

Impact of intra- and inter-unit cell symmetry breaking on the optical response of the arrays of nanotrimers

Understanding the impact of geometric changes on the properties of otherwise symmetric nanostructures is of essential importance for nanophotonics. In this Letter, we show that intra- and inter-unit cell symmetry breaking can substantially modify the optical properties of nanotrimers from both the experimental and simulation aspect. Specifically, shifting the location of one nano-dot within the trimer unit cell leads to the formation of magnetic Fano resonances with loop-like polarization patterns that are not present in the symmetric configuration. We further unlock the impact of lattice modification on the optical response of square arrays of trimers with broken three-fold rotation symmetry and with intra-trimer distances as small as 25 nm, showing distinctively different spectral evolutions of the electric and magnetic Fano resonances. The results achieved highlight the symmetry breaking as an essential tool to unlock and strengthen predefined resonances, which can have important applications, particularly in the field of sensing.

Parity-time symmetry in coherent asymmetric double quantum wells

A coherently prepared asymmetric double semiconductor quantum well (QW) is proposed to realize parity-time (PT) symmetry. By appropriately tuning the laser fields and the pertinent QW parameters, PT-symmetric optical potentials are obtained by three different methods. Such a coherent QW system is reconfigurable and controllable, and it can generate new approaches of theoretically and experimentally studying PT-symmetric phenomena.

Asymmetric light diffraction of two-dimensional electromagnetically induced grating with PT symmetry in asymmetric double quantum wells

An asymmetric double semiconductor quantum well is proposed to realize two-dimensional parity-time (PT) symmetry and an electromagnetically induced grating. In such a nontrivial grating with PT symmetry, the incident probe photons can be diffracted to selected angles depending on the spatial relationship of the real and imaginary parts of the refractive index. Such results are due to the interference mechanism between the amplitude and phase of the grating and can be manipulated by the probe detuning, modulation amplitudes of the standing wave fields, and interaction length of the medium. Such a system may lead to new approaches of observing PT-symmetry-related phenomena and has potential applications in photoelectric devices requiring asymmetric light transport using semiconductor quantum wells.

Beam splitter and router via an incoherent pump-assisted electromagnetically induced blazed grating

We propose a scheme for a beam splitter and a beam router via an electromagnetically induced blazed grating in a four-level double-Λ system driven by an intensity-modulated coupling field and an incoherent pump field. The blazed grating relies on the incoherent pump process, which helps in inducing large refractivity with suppressed absorption or even gain. Consequently, the weak probe beam can be effectively deflected with high diffraction efficiency, and, meanwhile, its energy is amplified. When using an intensity mask with two symmetric domains in the coupling field, the presented blazed grating provides the possibility of a symmetric beam splitter. The diffraction efficiency and diffraction order of the gratings are sensitive to the intensity of the coupling field, and, thus, the gratings can function as a tunable asymmetric beam splitter or a beam router, which distributes the probe field into different spatial directions. Therefore, the proposed scheme may have potential applications in optical communication and networking.

Multiple spontaneously generated coherence and phase control of optical bistability and multistability in a tripod four-level atomic medium

Optical bistability (OB) and optical multistability (OM) behaviors induced by multiple spontaneously generated coherence (SGC) are investigated theoretically in a tripod four-level atomic scheme. It is found that OB or OM is sensitive to the SGC effects, and the thresholds of OB can be controlled via changing the strength of multiple SGC or the relative phases of the applied fields. In addition, we can switch OB to OM by adjusting the twofold relative phases of the applied fields or vice versa.

Tunable Fano resonances based on microring resonator with feedback coupled waveguide

We experimentally demonstrate a tunable Fano resonance which originates from the optical interference between two different resonant cavities using silicon micro-ring resonator with feedback coupled waveguide fabricated on silicon-on-insulator (SOI) substrate. The resonance spectrum can be periodically tuned via changing the resonant wavelengths of two resonators through the thermo-optic effect. In addition to this, we can also change the transmission loss of the feedback coupled waveguide (FCW) to tune the resonance spectrum by the injection free carriers to FCW. We also build the theoretical model and we analyze the device performance by using the scattering matrix method. The simulation results are in a good agreement with the experimental results. The measurement maximum extinction ratio of the Fano resonance is as high as 30.8dB. Therefore, the proposed device is a most promising candidate for high on/off ratio optical switching/modulating, high-sensitivity biochemical sensing.

Tunable Fano resonances of a graphene/waveguide hybrid structure at mid-infrared wavelength

A planar graphene/dielectric multilayer structure is investigated, where the graphene surface plasmon polariton and the planar waveguide mode are coupled to realize Fano resonances. Few-layer graphene with high doping levels is used to excite surface plasmons at mid-infrared wavelength. Reflectance of the structure is calculated numerically by transfer-matrix method, and tunable Fano resonances with different line shapes are demonstrated by varying doping levels of graphene. Properties of the Fano resonances are discussed qualitatively by calculating electric field distribution in the structure and quantitatively by utilizing an analytical fitting equation. We also calculate Goos-Hänchen shift of the Fano resonances as an example for potential applications, and find that large Goos-Hänchen shift appears for optimized doping levels of graphene.

Tunneling-induced giant Goos-Hänchen shift in quantum wells

Tunneling-induced quantum interference experienced by an incident probe in the asymmetric double AlGaAs/GaAs quantum well (QW) structure can be modulated by means of an external control light beam and the tunable coupling strengths of resonant tunneling. These phenomena can be exploited to devise a novel intracavity medium to control Goos-Hänchen (GH) shifts of a mid-infrared probe beam incident on a cavity. For a suitably designed QW structure, our results show that maximum negative shift of 2.62 mm and positive shift of 0.56 mm are achievable for GH shifts in the reflected and transmitted light.

Enhanced four-wave mixing efficiency in four-subband semiconductor quantum wells via Fano-type interference

We propose and analyze an efficient way to enhance four-wave mixing (FWM) signals in a four-subband semiconductor quantum well via Fano-type interference. By using Schrödinger-Maxwell formalism, we derive explicitly analytical expressions for the input probe pulse and the generated FWM field in linear regime under the steady-state condition. With the aid of interference between two excited subbands tunneling to the common continuum, the efficiency to generate FWM field is found to be significantly enhanced, up to 35%. More interestingly, a linear growth rate in the FWM efficiency is demonstrated as the strength of Fano-type interference increases in presence of the continuum states, which can be maintained for a certain propagation distance (i.e., 50μm).

Hybrid quantum-well system for wavelength-channel selection

We consider a hybrid quantum-well structure consisting of regions whose properties alternate between active Raman gain and electromagnetically induced transparency. We present both analytical and numerical results that indicate a large light beam defection using spatially inhomogeneous pump and control lasers. We show well-isolated on-chip wavelength selection or channeling capabilities without light field attenuation or distortion, demonstrating the advantages of the system for possible important applications in integrated circuits for optical telecommunications.

Electromagnetically induced grating based on the giant Kerr nonlinearity controlled by spontaneously generated coherence

We propose a scheme for realizing electromagnetically induced grating via the giant Kerr nonlinearity in a coherently driven four-level system with spontaneously generated coherence. In the presence of spontaneously generated coherence, Kerr nonlinearity can be enhanced with vanishing linear absorption. Thus, with a standing-wave coupling field, one can achieve a pure absorption grating, which leads the probe field to gather the zero-order direction when the detuning of the coupling field is on resonance. Moreover, we can obtain a pure phase grating, which diffracts a weak probe light into the first-order direction and the second-order direction when the detuning of the coupling field is off resonance.

Electromagnetically induced grating in asymmetric quantum wells via Fano interference

We propose a scheme for obtaining an electromagnetically induced grating in an asymmetric semiconductor quantum well (QW) structure via Fano interference. In our structure, owing to Fano interference, the diffraction intensity of the grating, especially the first-order diffraction, can be significantly enhanced. The diffraction efficiency of the grating can be controlled efficiently by tuning the control field intensity, the interaction length, the coupling strength of tunneling, etc. This investigation may be used to develop novel photonic devices in semiconductor QW systems.

Strongly interacting photons in asymmetric quantum well via resonant tunneling

We propose an asymmetric quantum well structure to realize strong interaction between two slow optical pulses. The essential idea is the combination of the advantages of inverted-Y type scheme and resonant tunneling. We analytically demonstrate that giant cross-Kerr nonlinearity can be achieved with vanishing absorptions. Owing to resonant tunneling, the contributions of the probe and signal cross-Kerr nonlinearities to total nonlinear phase shift vary from destructive to constrictive, leading to nonlinear phase shift on order of π at low light level. In this structure, the scheme is inherent symmetric for the probe and signal pulses. Consequently, the condition of group velocity matching can be fulfilled with appropriate initial electron distribution.

Giant kerr nonlinearity, controlled entangled photons and polarization phase gates in coupled quantum-well structures

We study linear and nonlinear propagations of probe and signal pulses in a multiple quantum-well structure with a four-level, double Λ-type configuration. We show that slow, mutually matched group velocities and giant Kerr nonlinearity of the probe and the signal pulses may be achieved with nearly vanishing optical absorption. Based on these properties we demonstrate that two-qubit quantum polarization phase gates can be constructed and highly entangled photon pairs may be produced. In addition, we show that coupled slow-light soliton pairs with very low generation power can be realized in the system.

Dynamically induced double photonic bandgaps in the presence of spontaneously generated coherence

We study a four-level double-Lambda system with spontaneously generated coherence driven by a standing-wave coupling field. It is found that two well-developed photonic bandgaps with reflectivities of about 90% can be generated on the probe resonance in the presence of maximal spontaneously generated coherence. The induced double photonic bandgaps become, however, severely malformed when spontaneously generated coherence vanishes. Dynamic control of the double photonic bandgaps may be exploited to achieve a novel two-port double-channel routing scheme for weak light signals in quantum networks.

Dual-channel all-optical wavelength conversion switching by four-wave mixing

We report an experimental demonstration of dual-channel all-optical wavelength conversion switching in hot Rb vapor. In a four-level atomic system, a coupling field and a pump field interact with both (87)Rb and (85)Rb isotopes simultaneously and facilitate the generation of two nonlinear signals when the probe field is applied to the corresponding transition. Each nonlinear signal is switched on and off separately by the pump field at different frequencies based on four-wave mixing and isotope shifts.

Carrier-envelope-phase dependent coherence in double quantum wells

By analyzing the interaction of a few-cycle laser pulse within an asymmetric semiconductor double quantum well structure, we show that the transient coherence thus produced is strongly dependent on the carrier-envelope-phase (CEP) and significantly enhanced due to the Fano-type interference. A method to determine the CEP is proposed by directly mapping the CEP dependent coherence to the quantum beat signals.