Giant Kerr Nonlinearity Research Articles

Large Kerr index with amplification in an open four-level atomic system with twofold lower levels.

This paper presents a new freedom, which is the result of atomic injection and exit rates from a cavity associated with an open system, thus leading to a remarkable giant Kerr nonlinearity with applications in all-optical switching. The influence of atomic injection and exit rate from the cavity on nonlinear susceptibility of an open four-level Λ-type atomic system with twofold lower levels is investigated. It is found that large Kerr nonlinearity accompanied with probe gain can be obtained by adjusting the atomic injection rates and exit rate from the cavity, which is completely different from those presented in previous closed atomic systems. Phase control of Kerr nonlinearity in such an open atomic system is then studied.

Giant Kerr nonlinearity via tunneling induced double dark resonances in triangular quantum dot molecules

A scheme for giant Kerr nonlinearity via tunneling in triangular triple quantum dot molecules is proposed. In such a system, the linear absorption and the Kerr nonlinearity depend critically on the energy splitting of the excited states and the tunneling intensity. With proper parameters, giant Kerr nonlinearity accompanied by vanishing absorption can be realized. The enhancement of Kerr nonlinearity is attributed to the interacting double dark resonances induced by the tunneling between the quantum dots, requiring no extra coupling laser fields.

Giant Kerr nonlinearity and low-power gigahertz solitons via plasmon-induced transparency

We propose a method to enhance Kerr nonlinearity and realize low-power gigahertz solitons via plasmon-induced transparency (PIT) in a new type of metamaterial, which is constructed by an array of unit cell consisting of a cut-wire and a pair of varactor-loaded split-ring resonators. We show that the PIT in such metamaterial can not only mimic the electromagnetically induced transparency in coherent three-level atomic systems, but also exhibit a crossover from PIT to Autler-Townes splitting. We further show that the system suggested here also possess a giant third-order nonlinear susceptibility and may be used to create solitons with extremely low generation power. Our study raises the possibility for obtaining strong nonlinear effect of gigahertz radiation at very low intensity based on room-temperature metamaterials.

Giant Kerr nonlinearity and superluminal and subluminal polaritonic solitons in a Bose-Einstein condensate via superradiant scattering

We propose a setup to generate giant Kerr nonlinearity and polaritonic solitons via matter-wave superradiant scattering. The system we consider is a long cigar-shaped Bose-Einstein condensate (BEC), pumped by a red-detuned laser field with a space-dependent intensity distribution in transverse directions. The pump and the scattered fields propagate along the longitudinal direction. We show that by means of the atom-photon and atom-atom interactions in the system it is possible to produce a giant nonlinear optical effect. We further show that a backward scattering of the laser field from the BEC is favorable for the formation and stable propagation of polaritonic solitons, which are collective nonlinear excitations of the BEC coupled with the scattered laser field. In the case of backward Stokes (anti-Stokes) scattering the system may support robust bright (dark) polaritonic solitons propagating with superluminal (subluminal) velocity.

Large Kerr coefficient via quantum interference induced by incoherent pump field and spontaneous emission

Nonlinear response of a four-level atomic system with two closely lying intermediate levels to the incoherent pump field is investigated. It is shown that without coherent laser control field and just by quantum interference of incoherent pumping field and spontaneous emission, a giant Kerr nonlinearity can be achieved. It is also demonstrated that the enhanced Kerr nonlinearity is located in the reduced absorption region. In addition, the effect of direct and indirect incoherent pump rates on Kerr nonlinearity is then discussed.

Tunneling induced transparency and giant Kerr nonlinearity in multiple quantum dot molecules

The linear absorption and the Kerr nonlinearity of multiple quantum dots molecules controlled by the tunneling rather than the laser fields are investigated. The tunneling between the dots can induce multiple transparency windows. By varying the energy splitting of the excited states and the tunneling intensity, the width of the tunneling induced transparency windows can be narrowed. Within the narrowed transparency windows, the steep dispersion profile of the probe field makes it possible to enhance the Kerr nonlinearity. Therefore more than one probe fields with different frequencies can acquire giant Kerr accompanied by vanishing absorption simultaneously.

Investigation of giant Kerr nonlinearity in quantum cascade lasers using mid-infrared femtosecond pulses

We study the Kerr nonlinearity of quantum cascade lasers (QCLs) by coupling resonant and off-resonant mid-infrared (mid-IR) femtosecond (fs) pulses into an active QCL waveguide. We observe an increase in the spectral width of the transmitted fs pulses as the coupled mid-infrared (mid-IR) pulse power increases. This is explained by the self-phase modulation effect due to the large Kerr nonlinearity of QCL waveguides. We further confirm this effect by observing the intensity dependent far-field profile of the transmitted mid-IR pulses, showing the pulses undergo self-focusing as they propagate through the active QCL due to the intensity dependent refractive index. We experimentally estimate the nonlinear refractive index n2 of a QCL to be ∼8 × 10−9 cm2/W using the far-field beam profile of the transmitted pulses. The finite-difference time-domain simulations of QCL waveguides with Kerr nonlinearity incorporated show similar behavior to the experimental results.

Electromagnetically induced grating in the microwave-driven four-level atomic systems

A new scheme to investigate an electromagnetically induced grating in an N-type configuration in the presence of a strong-standing coupling field, additional coherent fields, and microwave driven fields is presented. By considering the coherent population trapping (CPT) condition in a four-level microwave driven N-type atomic system, a novel nonlinear optical storage is obtained via linear absorption vanishing and giant Kerr nonlinearity during light propagation. It is revealed that nonlinear properties in this atomic medium are maximum in the CPT condition, and these nonlinear properties could be affected and modulated by means of a microwave driven field. In this condition high-phase modulated diffraction efficiency is attained. The diffraction pattern is sensitive to variables of the phase and amplitude of microwave field. Consequently one can control the efficiency of different orders of grating more conveniently. The first-order diffraction efficiency of the grating, about 45%, can be obtained by choosing optimum values for the phase and amplitude of the microwave field. It is shown that the phase and modulation grating could be controlled effectively by atomic field-radiation parameters such as the interaction length L of atomic samples and applied field detunings. It has been noted that a novel fast communication device could be obtained at the zero absorption point and on the superluminal light level.

Enhanced Kerr nonlinearity with nonlinear amplification based biexciton coherence

In this paper, the theoretical investigation of giant Kerr nonlinearity based on biexciton coherence in GsAs multiple quantum wells with 17.5 nm GaAs wells and 15nm Al0.3Ga0.7 barriers is presented. The destructive quantum interference in this configuration is set up by two continuous wave control fields that couple to a biexciton state. It is shown that nonlinear susceptibilities of two weak probe and signal fields can be controlled by exciton spin relaxation and biexciton coherence which resulted from many-particle Coulomb interactions in semiconductors. It is found that the exciton spin relaxation can enhance the Kerr coefficient in the absence of probe absorption. We hope that our proposed method could be helpful for the next generation of all-optical systems based on quantum coherence and interference in semiconductor nanostructures.

Switching feature of EIT-based slow light giant phase-sensitive Kerr nonlinearity in a semiconductor quantum well

A four level inverted Y-type quantum well semiconductor is proposed based on phase-sensitive Kerr nonlinearity with a closed-loop configuration. It is found that as the Rabi-frequency of coupling field increases, the maximal Kerr nonlinearity intensifies and at the same time the probe linear and nonlinear absorption decreases at Telecom wavelength λ=1550nm. The impact of an incoherent pumping field as well as the relative phase of the applied fields on nonlinear optical properties of the QW medium is then discussed. The temporal behavior of the Kerr nonlinearity and the required switching time for switching the nonlinear dispersion are also discussed. The results may be useful for understanding the switching feature of EIT-based slow light Kerr nonlinearity enhancement systems and have potential application in optical information processing and transmission.

Giant Kerr nonlinearity induced by tunneling in triple quantum dot molecules

A scheme for giant enhancement of the Kerr nonlinearity in linear triple quantum dot molecules is proposed. In such a system, the tunneling-induced transparency window obtained in double quantum dot molecules splits into two windows, due to the coupling with the third quantum dot. And most important, the Kerr nonlinearity can be enhanced by several orders of magnitude, compared with that generated in double quantum dot molecules. With proper detuning of the tunneling, giant Kerr nonlinearity accompanied by vanishing absorption can be realized, which opens the possibility to enhance self-phase modulation in tunneling controllable semiconductor nanostructures under conditions of low light levels. Quantitative analysis shows that the giant Kerr nonlinearity is attributed to the interacting double dark resonances induced by the tunneling between the triple quantum dots, therefore no extra laser fields are required.

Impact of exciton spin relaxation (ESR) on Kerr nonlinearity in a quantum well nanostructure

In this paper, phase control of Kerr nonlinearity in a GsAs multiple quantum wells (MQWs) with 17.5nm GaAs wells and 15nm Al0.3Ga0.7 barriers is studied. The role of exciton spin relaxation and biexciton binding energy as well as Rabi frequencies of applied fields on phase control of Kerr nonlinearity and nonlinear absorption is also discussed. It is found that exciton spin relaxation (spin decoherence) and biexciton binding energy which resulted from many-particle interaction in semiconductors have essential roles in producing giant Kerr nonlinearity with nonlinear amplification for some values of relative phase between applied fields. Our study provides a suitable treatment for the next generation of all-optical systems in semiconductor nanostructures. Moreover, we hope that our theoretical work may be helpful for the future experimental works based on many-particle interaction in the semiconductors.

Superluminal surface polaritonic solitons at weak light level via coherent population oscillation

We investigate the possibility of generating nonlinear surface polaritons at the interface between a negative-index metamaterial and a dielectric doped with two-level quantum emitters by means of coherent population oscillation (CPO) working at room temperature. Based on the CPO and the strong confinement of the optical field near the interface, we find that the system can possess a giant Kerr nonlinearity. We demonstrate that it is possible to obtain a type of surface polaritonic solitons which is not only robust during propagation but also has ultraweak generation power and superluminal propagating velocity.

Enormous enhancements of the Kerr nonlinearity at C-band telecommunication wavelength in an Er3+-doped YAG crystal

A novel solid configuration is proposed to achieve a giant Kerr nonlinearity with reduced absorption under conditions of slow light levels. It is shown that an enhanced Kerr nonlinearity accompanied with negligible absorption can be obtained just through the proper tuning of intensity of coherent driving field at C-band telecommunication wavelength which is practical for communication applications. Moreover, the impact of incoherent pump field as well as frequency detuning of coherent field on manipulating the linear and nonlinear optical properties of the yttrium–aluminum-garnet (YAG) crystal medium is discussed. The presented results may be of interest to researchers in the field of all-optical signal processing and solid-state quantum information science.

Large Kerr nonlinearity in a crystal of molecular magnets system

A novel scheme is proposed to investigate the possible giant Kerr nonlinearity in a crystal of molecular magnets. The crystal is subjected to one dc magnetic field and two probe and coupling ac magnetic fields. By studying the steady-state behavior of the medium, we show that an enhanced Kerr nonlinearity with negligible absorption can be achieved under condition of slow light levels, just by properly adjusting the coupling field. Also, the transient evolution of nonlinear dispersion is proposed. It is found that the frequency detunings of probe and coupling fields, as well as the intensity of coupling field, lead to the large Kerr nonlinearity. Our results can be used as a guideline for optimizing and controlling the switching process in the crystal of molecular magnets, which is much more practical than that in the atomic system because of its flexible design and the long relaxation times.

Kerr nonlinearity and EIT in a double Lambda type atomic system

The giant Kerr nonlinearity in a four-level double Lambda type atomic system is theoretically predicted. We find that an enhanced Kerr nonlinearity can be achieved just by the intensity of coupling filed that lies within the transparency window. It is also shown that the giant Kerr nonlinearity with reduced absorption can be achieved by the quantum interference mechanisms.

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.

Some optical properties of four-level media via coherent and incoherent pumping fields

The optical properties of a four-level atomic system via coherent and incoherent pumping fields are investigated. The giant Kerr nonlinearity with reduced linear and nonlinear absorption, which has a major role in decreasing the threshold of optical bistability (OB), can be obtained with subluminal light propagation via adjusting the intensities of coupling fields. An incoherent pumping field is noticed to be an extra parameter to reduce the threshold of OB and multistability, and it can be used as an effective parameter in producing lasing with or without population inversion. In this model, optical multistability is achieved simply by tuning the intensity of coupling laser fields. Furthermore, it is shown that the subluminal and the superluminal light propagation can be obtained by appropriate values of the incoherent pumping rate.

All-optical switching in a photonic crystal with a defect containing anN-type four-level atomic system

We study the transmission spectra of a one-dimensional photonic crystal with a defect containing a four-level atomic medium that exhibits a greatly enhanced third-order susceptibility while having a vanishing linear susceptibility dependent on the electromagnetically induced transparency. Two ways of controlling the transmission of a photonic crystal are discussed: via absorption, i.e., nonlinear (two-photon) absorption of the probe field enhanced by constructive quantum interference, and via dispersion, which comes down to shifting the resonance frequency of the defect mode for the probe field by varying the refractive index based on the giant Kerr nonlinearity (cross-phase modulation). We demonstrate that such systems enable nonlinear all-optical switching at ultralow intensities of the coupling and switching laser fields.

Giant Kerr nonlinearity induced by interacting quantum coherences from decays and incoherent pumping

A scheme for generating the giant enhancement of the Kerr nonlinearity in a four-level system with the quantum coherences from the decays and the incoherent pumping is proposed. Compared with that generated in a general four-level system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. By using the numerical results, we show that the remarkable enhancement should be attributed to the interaction of the quantum coherences from the decays and the incoherent pumping.