Liu-Gang Si

Carrier-envelope phase-dependent effect of high-order sideband generation in ultrafast driven optomechanical system

We analyze the features of the output field of a generic optomechanical system that is driven by a control field and a nanosecond driven pulse, and find a robust high-order sideband generation in optomechanical systems. The typical spectral structure, plateau and cutoff, confirms the nonperturbative nature of the effect, which is similar to high-order harmonic generation in atoms or molecules. Based on the phenomenon, we show that the carrier-envelope phase of laser pulses that contain huge numbers of cycles can cause profound effects.

Ultraslow temporal vector optical solitons in a cold four-level tripod atomic system

We show the possibility of generating ultraslow temporal vector optical solitons in a cold lifetime-broadened four-level tripod atomic medium under Raman excitation. We demonstrate that the two orthogonally polarized components of the low-intensity signal field can evolve into various distortion-free temporal vector optical solitons, such as bright-bright vector solitons with ultraslow group velocity. These results are produced from the balance of self- and cross-phase modulation effects and dispersion. We also show that Manakov temporal vector solitons may be realized by adjusting the corresponding self- and cross-phase modulation and dispersion effects of our system.

Asymmetric optical transmission in an optomechanical array

Optical cavity combining a mechanical degree of freedom provides a unique platform to implement information transmission and processing via optomechanical effects, and introduces a strong link between nanophotonics and nanomechanics. Here, we study the optical property of a cascaded optomechanical array, which consists of two or more optomechanical systems. We find that the steady states of the optomechanical array have algebraic duality symmetry for the case of two identical optomechanical resonators, which is exactly the embodiment of the spatial symmetry and leads to symmetric optical transmission. Breaking of the algebraic duality symmetry gives rise to different behaviors between the forward and the backward transmission, which can be remarkable under low input power. Our results may have potential application for achieving high precision measurement and on-chip manipulation of light propagation.

Optomechanically induced sum sideband generation

Sum sideband generation in a generic optomechanical system is discussed in the parameter configuration of optomechanically induced transparency. The nonlinear terms of the optomechanical dynamics are taken account and the features of the sum sideband generation are identified based on the analytical treatment. The nonlinear optomechanical interactions between cavity fields and the mechanical oscillation, which emerging as a new frontier in cavity optomechanics, are responsible for the generation of the frequency components at the sum sideband. We analyze in detail the influences of some parameters, including the pump power of the control field and the frequencies of the probe fields, on the sum sideband generation. The results clearly indicate that sum sideband generation can be significantly enhanced via achieving the matching conditions. The effect of sum sideband generation may be accessible in experiments and have potential application for achieving high precision measurement and on-chip manipulation of light propagation.

Tunable slow light in a quadratically coupled optomechanical system

We theoretically investigate the slow light in a quadratically coupled optomechanical system. Different from the linear coupling case, the slow light via quadratic coupling derives from a two-phonon process, and the fluctuation in displacement plays a vital role in nonlinear coherence. The numerical results show that the slow light can be realized in an extensive range of parameters even at high temperature, e.g., 200 K. We also find that the environment temperature which provides almost all of the phonon energy, together with the coupling field power, jointly drive the realization of slow light.

Solitons in optomechanical arrays

We show that optical solitons can be obtained with a one-dimensional optomechanical array that consists of a chain of periodically spaced identical optomechanical systems. Unlike conventional optical solitons, which originate from nonlinear polarization, the optical soliton here stems from a new mechanism, namely, phonon-photon interaction. Under proper conditions, the phonon-photon induced nonlinearity that refers to the optomechanical nonlinearity will exactly compensate the dispersion caused by photon hopping of adjacent optomechanical systems. Moreover, the solitons are capable of exhibiting very low group velocity, depending on the photon hopping rate, which may lead to many important applications, including all-optical switches and on-chip optical architecture. This work may extend the range of optomechanics and nonlinear optics and provide a new field to study soliton theory and develop corresponding applications.

Continuous-variable entanglement in a two-mode four-level single-atom laser

This paper investigate the generation and evolution of continuous-variable entanglement in a two-mode single-atom laser, where the atomic coherence is induced by two classical laser fields (pump and coupling field) driving the corresponding atom transitions. It is found that the intensity of the coupling field can influence effectively the entanglement period of the cavity field. More importantly, our numerical results also show that the intensity and period of entanglement between the two cavity modes as well as the total mean photon number of the cavity field can be increased synchronously by adjusting the corresponding frequency detuning.

Optomechanically induced transparency in the presence of an external time-harmonic-driving force

We propose a potentially valuable scheme to measure the properties of an external time-harmonic-driving force with frequency ω via investigating its interaction with the combination of a pump field and a probe field in a generic optomechanical system. We show that the spectra of both the cavity field and output field in the configuration of optomechanically induced transparency are greatly modified by such an external force, leading to many interesting linear and non-linear effects, such as the asymmetric structure of absorption in the frequency domain and the antisymmetry breaking of dispersion near ω = ωm. Furthermore, we find that our scheme can be used to measure the initial phase of the external force. More importantly, this setup may eliminate the negative impact of thermal noise on the measurement of the weak external force in virtue of the process of interference between the probe field and the external force. Finally, we show that our configuration can be employed to improve the measurement resolution of the radiation force produced by a weak ultrasonic wave.

Optomechanically induced transparency in the mechanical-mode splitting regime

We employ a decoupled Heisenberg-Langevin equation for the observation and physical interpretation of mechanical-mode splitting (MMS) of the movable mirror in a generic optomechanical system. Then we identify some observable and significant features of MMS in a two-mode cavity. That is, the second control field coupled to another optical mode is input to the system to modify the mechanical mode, leading to the suppression of transmission, the appearance of the doublet in the spectrum of the anti-Stokes field, and the emergence of optomechanically induced transparency in corresponding new mechanical modes. Furthermore, we open two transparent windows in virtue of MMS and find the second splitting of the mechanical mode in this two-mode optomechanical system.

Dynamical control of soliton formation and propagation in a Y-type atomic system with dual ladder-type electromagnetically induced transparency

We have investigated the nonlinear interaction between a weak-pulsed probe field and a four-level Y-type atomic system with dual ladder-type electromagnetically induced transparency. Two strong coupling fields induce a quantum destructive interference effect which depletes the population in the two nearly degenerate uppermost levels of the system and dramatically enhances the linear as well as nonlinear dispersion while simultaneously significantly suppressing the probe field absorption. We present the semiclassical quantum analysis of the system. The perturbation method of multiple scales is used to derive a differential envelope equation that describes the propagation of the probe field in the Y-type atomic system. It is then demonstrated that bright and dark optical solitons can be formed in this system.