This PDF file contains the front matter associated with SPIE Proceedings Volume 8554, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

We study the balanced-heterodyne detection of optical squeezing, for which the corresponding spectral density of the photocurrent fluctuations produced at the output of the photo-detector is calculated as the Fourier transform of their autocorrelation function. We show that, for maximal signal-to-noise ratio enhancement by use of squeezed states of light, an optical signal to be measured in this scheme must be carried in the squeezed quadrature of the carrier field. We discuss how this scheme may be exploited in gravitational-wave searching.

We present an unconditionally secure quantum election scheme, which based on a distributed scheme to ensure the privacy of the voters. The voting administrator is made up by two parties who cannot cooperate within a certain period of time, and we use an”identity exchange”scheme to conceal the identity of voters. While the election is completed, nobody except the voter himself can match him with his ballot even if the administrator and the counter collaborate up to do so. The scheme can also work well with noisy and lossy quantum channels.

Electromagnetic waves with polarization modulation are widely utilized in Radar and Lidar, depending on classical mechanics and Shannon information theory. In this paper, a quantum detection system using polarized photons has been studied on theory and experiments based on the laws of quantum electrodynamics. We give emphasis on the limits: standard quantum limit(SQL) and quantum limit (QL) for target detection. Two sets photons of orthogonal 653nm linearly polarized beams: 0°,90°,45° and 135° transmit to the target,and detect the scattered photons 5.7 meters away. Transmitter and Receiver synchronize their clocks to suppress the noise by the time filtering.For some targets, our system can achieve utterly confidential target detection in theory.

Confined indirect excitons in a two-dimensional magnetic lattice are promoted to simulate condensed matter systems. Excitonic particles are magnetically trapped so that a sufficient cooling mechanism can allow the trapped clouds of indirect excitons to experience the Bose-Einstein condensation phase transition. Thus, a long­ range spatial coherence can be resolved causing an inherited phase-locked across all of the coupled sites (single traps). Using an external magnetic bias field a mutual tunneling can adiabatically be exchanged between sites in which case the underline physics of Bose-Hubbard model can be explored such as Mott-insulator and Josephson Effect.

This work deals with the cooling and trapping of single cesium (Cs) atoms in a large-magnetic-gradient magneto-optical trap (MOT) and the confinement of single Cs atoms in a far-off-resonance optical dipole trap (FORT). The experiment setup is based on two large-numerical-aperture lens assemblies which allow us to strongly focus a 1064-nm TEM₀₀-mode Gaussian laser beam to a 1/e² radius of ~ 2.3 μm to form a microscopic FORT for isolating single atom with environment and to efficiently collect the laser-induced-fluorescence photons emitted by single atoms for detecting and recognizing single atom’s internal state. We have tried both of “bottom-up” and “top-down” loading schemes to confine single atoms in the microscopic FORT. In the “bottom-up” scheme, we have successfully prepared single Cs atoms in the MOT and transferred it into FORT with a probability of almost 100%. In the “top-down” scheme, we have achieved ~ 74% of single atom loading probability in the FORT using light-assisted collisions induced by blue detuning laser and with prepared many Cs atoms in the MOT. The relaxation time in hyperfine level of ground state of trapped single Cs atom is measured to be ~5.4 s. To coherently manipulate atomic quantum bits (qubit) encoded in the clock states (m_F = 0 states in F_g = 3 and 4 hyperfine levels) of single Cs atom via the two-photon simulated Raman adiabatic passage (STIRAP), we have prepared two phase-locked laser beams with a frequency difference of ~ 9.192 GHz by optically injecting an 852-nm master laser to lock the +1-order sideband of a 9-GHz current-modulated slave diode laser. The two phase-locked laser beams are used to drive STIRAP process in the Λ-type three-level system consists of Cs |6S_1/2 F_g = 4, m_F = 0> and |6S_1/2 F_g = 3, m_F = 0< long-lived clock states and Cs |6S_1/2 F_e = 4, m_F = +1 > excited state with the single-photon detuning of ~ -20 GHz. Rabi flopping experiments are in progress.

We propose criteria and experimental strategies to realise the Einstein-Podolsky-Rosen (EPR) steering nonlocality. One-way steering can be obtained where there is asymmetry of thermal noise on each system. We also present EPR steering inequalities that act as signatures and suggest how to optimise EPR correlations in specific schemes so that the genuine multipartite EPR steering nonlocality (EPR paradox) can also possibly be realised. The results presented here also apply to the spatially separated macroscopic atomic ensembles.

Condensed matter systems are potential candidates to realize the integration of quantum information circuits. Surface phonon polariton (SPhP) is a special propagation mode in condensed matter systems. We present an investigation on the entanglement of SPhP modes. The entangled pairs are generated from entangled photons injected to the system. Quantum performances of entangled SPhPs are investigated by using the interaction Hamiltonian and the perturbation theory. The wave mechanics approach is taken to describe the coupling process as a comparison. Finally, the correlation of system is examined. A whole set of descriptions of SPhP entanglement thus are presented.

Based on the dispersion property of a given photonic crystal fiber (PCF), we study how to directly generate frequency de-correlated photon pairs via pulse pumped spontaneous four wave mixing from both the theoretical and experimental aspects. The numerical investigation shows that to generated the frequency de-correlated photon pairs, the experimental parameters should be properly optimized by balancing the influences of the high order dispersion and the intrinsic sinc oscillation of phase matching function, apart from the satisfaction of specified phase matching condition and the usage of transform limited pump pulses. We also conduct experiment to verify the numerical simulations, and the experimental results qualitatively agree with the calculations. For the filter free case, the experimentally obtained maximum g⁽²⁾ of the individual signal photons is 1.76 ± 0.02. When this kind of photon pairs is used to realize the heralded single photons, the heralding efficiency can reach 86%.

This paper introduces our recent works on quantum light sources based on third-order nonlinear waveguides. Based on the spontaneous four wave mixing (SFWM) effect in optical fibers, we realized high quality correlated photon pair generation. A fiber based heralded single photon source (HSPS) with a preparation efficiency of ~80% under a g²(0) of 0.06 was realized based on it. On the other hand, we demonstrated that the vector scattering processes of the SFWM can be suppressed effectively by the polarization walk off effect in the polarization maintaining fibers (PMFs), by which polarization entangled photon pair generation was realized in a piece of PMF experimentally. We also realized correlated photon pair generation in silicon wire waveguides fabricated by ourselves, demonstrating its low noise performance. These works shows that SFWM in third-order nonlinear waveguides provides a promising way to realize practical quantum light sources compatible with today’s engineering technologies.

Single photon sources (SPSs) play important roles in quantum communication and quantum information processing. Spontaneous four wave mixing (SFWM) in optical fibers provides a promising way to realize practical heralded single photon sources (HSPSs), since it is compatible with current techniques of optical communications. In this paper, two independent HSPSs at 1.5μm band are realized in one polarization maintaining dispersion shifted fiber (PM-DSF) utilizing its large birefringence. When pulsed pump light passes through an optical fiber, two kinds of SFWM will take place simultaneously. One is scalar processes, in which two annihilated pump photons and generated photon pair are all polarized along the same fiber polarization axis. The other is vector processes, in which two annihilated pump photons are polarized along different fiber polarization axes, either for the two photons of the generated pair. In the PM-DSF, the large birefringence generates obvious walk-off effect on the two pump polarization components, which leads to an effective suppression of the vector processes. Hence, by proper pump polarization, correlated photon pairs (CPPs) with different polarization directions can be generated independently by the two scalar processes, which can be used to realize two independent HSPSs. The indistinguishability of the heralded photons generated by the two independent sources is demonstrated by an experiment of Hong-Ou-Mandel (HOM) interference. Using a fiber coupler as the beam splitter, a visibility of HOM dip of 76% is achieved, showing their potential on quantum information.

We investigate the definition of security for encryption scheme in quantum context. We systematically define the indistinguishability and semantic security for quantum public-key and private-key encryption schemes, and for computational security, physical security and information-theoretic security. Based on our definition, we present a necessary and sufficient condition that leads to information-theoretic indistinguishability for quantum encryption scheme. The equivalence between the indistinguishability and semantic security of quantum encryption scheme is also proved.

Single photons are essential resource for quantum communication and quantum information processing, which can carry quantum information to distant locations. A promising scheme for single photon generation is the heralded single photon source (HSPS), which is based on the generation of correlated photon pairs (CPPs). Utilizing the quantum correlation property of the CPPs, one photon of the CPP is detected providing an electrical signal to herald the other photon as a single photon output. Recently, 1.5 μm CPP generation through spontaneously four wave-mixing (SFWM) in fiber has focused much attention, which provides a practical way to realize 1.5 μm fiber-based HSPS. The quality of a HSPS is described by the preparation efficiency and g⁽²⁾(0). In the fiber-based HSPS, the preparation efficiency is determined by the loss of the filtering and splitting system and the noise photons generated by spontaneously Raman scattering (SpRS). Considering the impact of the SpRS can be reduced by cooling the fiber and optimizing the frequency detuning of filtering and splitting system, the loss of the filtering and splitting system may give a theoretical up-limit of the preparation efficiency. In this paper, using commercial fiber components, we realize a high quality HSPS based on cooled fiber with a preparation efficiency of 80% under a g⁽²⁾(0) of0.06, showing its great potential in the application of quantum information technology.

We analyze the transition from slow to fast light upon increasing the modulation frequency based on coherent population oscillation in Cascaded Erbium-doped fiber structure. The change from slow to fast light is more obvious in the Cascaded structure. In this structure, the transition bandwidth is lager and the relative delay difference between the maximum fractional advancement and the maximum fractional delay is greater than that in the single-stage fiber.

Similarity of adjacent-frame chaos waveforms from a semiconductor fiber ring laser (SFRL) is investigated numerically in sensing applications. An improved model of a chaos optical fiber fence system based on a SFRL is presented. The optical fiber’s SPM/XPM effects are considered. By this model adjacent-frame similarity’s determinants are studied by comparing their cross-correlation function peaks at different parameters. The relationships between the similarity and the optical fiber’s distributed linear birefringence effect, as well as SPM/XPM effects induced by the nonlinear birefringence are revealed by setting only one effect to work respectively. The characteristics of the chaos waveform with high similarity are researched by the autocorrelation function and power spectrum. The simulation results show that the similarity is more sensitive to the change of azimuth angle than that of the retardation angle of the polarization controller in the ring laser. It has almost no change with the ring length and injection current of semiconductor optical amplifier (SOA). The optical fiber’s distributed linear birefringence and SPM/XPM effects mainly contribute to the formation of polarization chaos light however slightly decrease the similarity. The influence of nonlinear birefringence becomes big and decreases obviously the similarity only at an overlarge SOA current. The chaos waveforms with high similarity have big autocorrelation sub-peaks and the sub-peaks decrease slowly and gradually. Their power spectrums are mixed up with some periodic components. These results are helpful to choose the SFRL’s parameters for the accurate disturbance location in a chaos optical fiber fence system.

In this paper, we reviewed the theoretical and experimental studies on the manipulation of the group delay of light based on the transverse phase modulation effect induced by a Gaussian beam. We introduced the basic theory of slow and fast lights in a thin nonlinear material based on the transverse phase modulation effect. We introduced a simple but effective technique to actively and chromatically control the group velocity of light at arbitrary wavelength, therefore, eliminating the requirements on the optical nonlinearity and the photonic resonance at the signal wavelength. Furthermore, a technique to improve the transverse-modulation-induced relative delay of light in nonlinear media through the combination of an optical nonlinearity and a resonant Fabry-Perot cavity was introduced and theoretically demonstrated in ruby as an example. The introduction of a resonant Fabry-Perot cavity can improve the relative delay by orders of magnitude. The techniques of active chromatic manipulation and resonant improvement of the group delay of light may have potential applications in optical information processing and optical communication network.

We propose optical frequency comb generation in a monolithic micro-ring resonator. Being different from the previously reported nonlinear optical frequency combs, our scheme is based on more efficient quadratic frequency conversion rather than the third-order nonlinearity. To overcome the phase mismatch, a partly poled nonlinear ring is employed. Cascading second harmonic generation and parametric down conversion processes thus are realized through quasi-phase matching (QPM). Coupling equations are used to describe the related nonlinear interactions among different whispering-gallery modes, showing some interesting characteristics that are different from conventional QPM technology.

We present the numerical simulations of soliton spectral tunneling (SST) effect in multi-cladding single mode fibers with three zero-dispersion wavelengths. Fiber geometries with appropriate refractive index difference and fiber radius are selected to generate this unique dispersion property. The mechanism of multi-cladding fibers exhibiting multi zerodispersion wavelengths is discussed. Simulation results clearly show SST effect in the proposed multi-cladding fiber. The dependence of the output SST frequency on fiber geometry is investigated numerically and analytically. The detailed studies present the phase-matching condition of dispersive pulses in different engineered dispersion curves of multi-cladding fibers. The soliton numbers of input pulse show a significant role on the threshold length of SST effect.

We investigate the features of the self-deflection of the screening-photorefractive spatial soliton and the influence of first-order and higher-order space charge field on the propagation characteristics by considering the diffusion effect, The results show that the center of the optical beam moves on a parabolic trajectory; As to the highter-order space charge field, the self-bending process is further enhanced by a factor that varies cubically with the applied field. The numerical study shows that the bending distance of the soliton beam center increase, reaching its maximum value at the characteristic temperature. Numerical investigations show that the in-phase interaction will result in the separation of two solitons from each other, As for the anti-phase interaction side, two solitons separated each other and delect simultaneously to the same side.

In this study, Au colloidal nanoparticle is performed by laser ablation method. The linear and nonlinear absorption of the laser dye Rhodamine B dissolved in DI water with and without the presence of Au nanoparticles were investigated. The emission spectra of the samples were studied. Results show the red shift of the fluorescence emission in the case of dye with the presence of Au nanoparticles. The measurement of nonlinear absorption in Au, Au/Rhodamine B and Rhodamine B solutions were carried out using the standard Z-scan technique. Our measurements indicate positive signs for the nonlinear optical absorption coefficients of the samples.

We demonstrated an efficient way for generating a mid-infrared source at 3.16 μm by coherent coincidence downconversion. The signal light at 1.04 μm was frequency downconverted by the synchronized pump pulses at 1.55 μm with a conversion efficiency of 65%.

Transverse localization of light in one-dimensional waveguide arrays with width disorder has been studied in both linear and nonlinear regimes. Defect mode is generated in the bandgap of the disordered waveguide array when introducing refractive index modulation into a single waveguide, and its localization strength depends on the width disorder level of the waveguide array. The evolution of the nonlinear disordered modes with either the self-focusing or the self-defocusing optical nonlinearities has been studied. The results show that the nonlinear disordered modes may be delocalized significantly due to the resonant interaction with the nearby eigen modes in the width-disordered waveguide array.

Four-wave mixing (FWM) has been extensively explored in optical fibers and more recently in on-chip silicon-oninsulator (SOI) waveguides. A phase-matched FWM with a pair of degenerate pump photons generating and amplifying signal and idler photons is referred as modulational instability (MI). Following theory of FWM in waveguide arrays, we utilize evanescent couplings between neighboring waveguides to control the phase-matching condition in FWM. In experiments, a set of single-channel SOI nanowaveguides with the waveguide width decreasing from 380nm to 340nm demonstrate that changing the waveguide group velocity dispersion (GVD) at the pump wavelength from being anomalous to being normal makes MI gain gradually disappear. We also perform the same experiment with an array of two 380nm-wide SOI waveguide, and demonstrate that for the large separation of 900nm and 800nm, MI gain is present as for the single waveguide; while for the small separation of 400nm, the MI gain disappears. This transformation of phase-matching in FWM is attributed to the fact that the coupling induced dispersion changes the net GVD of the symmetric supermode from being anomalous for large separation to being normal for small separation. Our observation illustrates that the coupling-induced GVD can compete and exceed in value the GVD of a single SOI nanowaveguide. This creates a new previously unexplored degree of freedom to control FWM on chips.

Stemming from the pursuit of a simple system to produce squeezed state for long distance continuous variable quantum communication, we present an all-fibre source of pulsed twin beams at 1550 nm band by using a high gain fiber optical parametric amplifier. The noise of intensity difference of the twin beams is below the shot noise limit by 3.1 dB (10.4 dB after correction for losses).

Since the zeroth-order Bessel and Airy function are invariant propagation modes in free space, they can be potentially used not only in time but also in space. Different from nonlinear solitary wave, Airy-Bessel configuration wave packets with particle-like nature are a kind of stable linear wave packets without spatio-temporal spread during propagation in free space because it combine spatial Bessel beams with temporal Airy pulses. In the paper, by studying spatially induced group velocity dispersion effect during propagation of ultrashort pulsed Bessel beams, we find that Gaussian- Bessel wave packets can evolve as Airy-Bessel in given propagation conditions. The research results are expected to open up one new channel to generate stable linear localized wave packets.

Analytic expression of the ionization probability about 3+1 resonance enhanced multi-photon ionization (REMPI) process is deduced with the theory of rate equation, which implies the interaction of photon and material. Based on the expressions, the influence of laser intensity, laser pulse duration and spontaneous radiation lifetime on the ionization probability is analyzed theoretically. It is found that the ionization probability increases with laser intensity and laser pulse duration until gets to saturation. After that, the ionization probability will oscillate around the saturation value if laser intensity increases further. The amplitude of oscillation increases with laser intensity at first, and then it will decrease even get to zero after a maximum peak comes out. We attribute the appearance of the oscillation to the phenomena of quantum coherence caused by the splitting of energy level in strong laser field. As to the fact that the ionization probability becomes to zero with the increase of laser intensity, it indicates that laser intensity is strong enough so as to make the neutral particles getting to the region of ionization suppression. It is also found that the variation of ionization probability with spontaneous radiation lifetime is far smaller than the one with ionization rate. So the influence of the spontaneous radiation lifetime on ionization probability could be ignored.

For the first time, the SHG efficiency of RBBF crystal in type-I and type-II phase matching has been simulated. RBBF crystal is pumped by the fundamental radiation of a Q-switched Nd:YAG laser with the wavelength of 1064nm and the shape of plane wave or Gaussian beam. When the pumped radiation is of plane wave, the conversion efficiency of RBBF in type-I and type-II could be as high as 100% and 78%. When the pumped radiation is of Gaussian beam, the conversion efficiency shows a monotonically increasing trend in the type-I phase matching, and in the type-II phase matching the conversion efficiency varies periodically.

Base on three wave coupled equations and energy conservation law, the frequency doubling properties of CsBe₂BO₃F₂ (CBBF) are analyzed theoretically at the first time. The phase matching angle, effective nonlinear coefficient, walk-off angle and permitted parameters are simulated in type I and type II phase matching. The difference of the CBBF optical properties between type-I and type-II are elucidated.: a wider phase matching range, a larger effective NLO coefficient and a smaller walk-off angle in range of 693.9~2730 nm in type-I were obtained. The properties of CBBF have been compared with the KBe2BO₃F₂ (KBBF) crystal. The larger lowest wavelength limit, smaller walk-off angles, a broader permitted angle and a larger peak value of the permitted wavelength of CBBF were proved.

We study the evolutions of spatiotemporal chaos for the photorefractive ring oscillator. As the system parameters are changed, we obtain different patterns such as the frozen random state, the pattern selection state, the defect chaotic diffusion state and fully developed turbulence state in the one- dimensional map lattice system. We can observe symmetry breaking from four corners and the boundaries and finally lead to spatiotemporal chaos in the two-dimensional map lattices system. Then we demonstrate that the global and local constant bias can suppress spatiotemporal chaos in photorefractive ring oscillator by varying the bias strength. Only if we choose suitable bias strength, spatiotemporal chaos in photorefractive ring oscillator system can be controlled into stable periodic states.

The chaotic dynamic characteristic in Bose-Einstein Condensate (BEC) system of a 1D tilted optical superlattice potential with attractive interaction is investigated in this paper. The spatial evolution of chaos was shown numerically by resolving Gross-Pitaevskii (G-P) equation for the system with the fourth Runge-Kutta(RK) algorithm. Numerical analysis reveals that as the tilt or the amplitude of the optical superlattice potential is increased the chaos in the BEC system increases. These elements make the chaotic system more unstable and the phase-space orbit becomes more chaotic. The chaotic system can be effectively controlled to a stable periodic orbit through adjusting the amplitude of the optical superlattice potential and initial condition. Controlling chaos can also be realized by spatial constant bias in the BEC system of a 1D tilted optical superlattice potential with attractive interaction. Phase orbits are suppressed gradually then the chaotic states of the BEC system are converted into period one through quais-period.

A novel chaotic synchronization configuration is proposed. This system is constructed on the basis of unidirectionally coupled VCSELs and signal transmission in fiber. The transmitter VCSEL is subject to an isotropic optical feedback, the receiver VCSEL is subject to an orthogonal optical injection from the transmitter VCSEL, the chaotic signal transmission in fiber channel is adopted, also message encoding and decoding of the chaotic system have been investigated. The results show that, during to the fiber nonlinear and chromatic dispersion, the amplitude characteristics of chaotic signal are distorted partially and the system synchronization quality will be impaired, but message can be hidden efficiently in the chaotic signal during the fiber transmission with additive chaos modulation (ACM). Better decoding performance is achieved by choosing appropriate matched parameters.

We study numerically the dynamics of a beam in a focusing photorefractive nonlinear optical lattice with a longitudinal potential barrier. Such kind of lattice with the refractive index modulation in both transverse and longitudinal directions can be realized by induced optically in photorefractive crystals. Different soliton states are found with different position of the input pulse, which exhibits compression or splitting during transmission. The results also indicate that the intensity of a beam and the transverse modulation frequency of lattice can affect apparently the ability of tunneling. For the same lattice depth, the smaller the transverse frequency of the lattice is and the higher peak intensity the soliton possesses, the easier the soliton tunnels through. However, when we increase the frequency of optical lattice, the optical beam can successfully pass through the barrier for the relatively small value of lattice depth as well. Otherwise, the beam splits into some filaments when the lattice depth is large enough. In addition, we find that beam can exhibit the behavior of oscillation during transmission and the oscillation frequency of spatial soliton is influenced by the biased field.

Ghost imaging (correlated imaging) has been extensively investigated in recent years, both theoretically and experimentally. By using the second-order or high-order coherence properties of light field and the correlation measurement, ghost imaging was realized with quantum entangled light, pseudo-thermal light and even true thermal light. In this work, basing on the theory of statistical optics, we model the dynamic process of thermal variation, and obtain the ghost interference and ghost imaging by means of simulated calculation. In the later experiment, a pseudo-thermal source is firstly prepared by using a laser beam to pass through a rotating ground glass plate, and the parameters of the pseudo-thermal source are obtained via Hanbury-Brown-Twiss (HBT) experiment. With the pseudo-thermal light, we perform ghost interference. The experimental results demonstrate the accordance of numerical prediction. And our conclusion shows that the quality of ghost interference is influenced by the size of the pinhole in the reference path, the little pinhole due to a higher quality of ghost interference.

The effect of pump focusing on the performance of ghost imaging is studied experimentally on an entangled source. Theoretical results show that the correlation properties of the entangled photon source are destroyed when the conversion crystal is pumped by a focused laser beam. The experiment is performed on a compact entangled source produced by type-II non-collinear degenerate SPDC, and the results demonstrate that the “walk off” effects almost have no effect on the image, while the pump focusing greatly degrades the visibility of the image. However, a sharp image could be reproduced in the configuration first proposed in Ref. [8] for the case with pump focusing.

We report experimental investigations of two kinds of high-contrast optical filters by utilizing a laser-pumped atomic vapor and properly-designed Fabry-Perot bulk etalon, which are based on the demand of the detection of quantum correlated Stokes and anti-Stokes photon pairs in a Λ-type three-level atomic ensemble, respectively. Laser-pumped cesium (Cs) atomic filter achieves typical peak transmission ~ 74.3% and the distinction ratio between excitation channel and 9.19GHz- frequency-detuned signal channel is ~ 26.7 dB at 47.15°C. The transmission peak can be tuned within the range of Doppler line-width of Cs D₂ line. The temperature-stabilized narrow-band etalon filter with dozens of GHz resonant transmission tunability is realized with typical peak transmission of ~ 91.7% and the distinction ratio between pump and signal channel of ~27.5 dB. These techniques are useful for atom-photon interaction experiments, especially for Stokes and anti-Stokes photon pairs generation experiments based on collective Raman excitation of Cs atomic ensemble.

Based on a Λ-type three-level system consists of cesium (Cs) 6S_1/2 (Fg = 3) and 6S1/2 (Fg = 4) long-lived ground states and 6P_3/2 (Fe = 4) excited state, we have experimentally measured and theoretically analyzed the characters of coherent population trapping (CPT) resonances in Cs vapor cells with different partial pressure of neon (Ne) as buffer gas around room temperature. The impact of some experimental parameters, such as the relative intensity ratio between two phase-locked laser beams, the laser intensity, with or without buffer gas and the partial pressure of Ne, the temperature and the longitudinal magnetic field, on the CPT resonance was studied in details. With the optimized parameters, we got typical CPT signal with the full-width half-maximum (FWHM) linewidth as narrow as ~ 181 Hz in a Cs vapor cell filled with 30 Torr of Ne as buffer gas.

Based on the four-wave mixing mechanism and fanning effect, the threshold coupling constant for mutually pumped phase conjugator (MPPC) with one interaction region and two interaction regions is studied in theory. The relation of the the threshold coupling strength for MPPC and the fanning intensity is studied. Due to the more efficient fanning, preset grating in MPPC has the ability to reduce threshold coupling constant and improve output efficiency. These characteristics predicted by theory have been used to explain the previous experiment phenomenon. The dependence of threshold coupling constants for MPPC on the amplitude ratio of incident pump beams is presented. The threshold coupling constant for one-interaction-region MPPC is lower than that for two-interaction-regions MPPC.

We numerically study the nonlinear switching characteristics of optical transmission through optimized fiber Bragg grating with a π phase shift. The nonlinear coupled-mode equations were solved numerically based on the time-dependent transfer-matrix method. The result shows that the π phase shift grating is superior to the uniform grating in the enhancement, corresponding to the local intensity of the light inside the grating. It shows that the use of π phase shift gratings reduces effectively the switching threshold, but the on-off contrast is generally declined which can be generally improved through the introduction of tapered parameters. In addition, the narrowed transmitted pulse for positive-tapered nonlinear Bragg grating is a Bragg soliton owing to the balance of anomalous group velocity dispersion and self-phase modulation (SPM). It can be found that the tapered nonlinear Bragg grating with a π phase shift is more preferable for achieving the larger on-off contrast.

The probe absorption spectrum of the Λ-three-level system driven by bichromatic coupling field and weak probe field is investigated. We obtain the probe absorption spectra for different frequency detunings of coupling field by solving the density matrix equation and numerical analysis. Three electromagnetically induced absorption (EIA) peaks are simultaneously observed in the absorption profile of probe field. We report the dependence of position and relative intensity of EIA on the frequency detuning of the bichromatic coupling field. The results show that central EIA always appears at the resonant frequency of probe field, with the constant intensity. The position of the secondary EIA vary with the frequency detuning of coupled field, and the intensity of the absorption peaks decrease with the increasing detuning.

We study the quantum interference in three-photon resonant nondegenerate six-wave mixing (NSWM) in a five-level system in which the middle level of six-wave mixing and other level are coupled by a strong laser field. The coupling field-dependence of the NSWM signal intensity and the spectrum of the NSWM with a coupling field are discussed. We find that in the presence of a strong coupling field, the three-photon resonant NSWM spectrum exhibits Autler-Townes splitting, which reflects the levels of the dressed states. It also leads to either suppression or enhancement of the NSWM signal.

Both electromagnetically induced absorption (EIA) and transparency (EIT) can be obtained in a modified quasi-lambda four level system consisting of an optical-radio two-photon coupling field and a probing field. A physical account of EIA and EIT is given in terms of a transient state picture in this paper. It can be seen that the optical coupling field in this quasi-lambda four level system has a crucial effect on the forming of EIA and EIT. An EIA is observed under a resonant optical coupling and it evolves into an EIT when there is a detuning.

Recently, specialty fibers with various functional material doping have attracted significant attention. In this paper, we fabricated Nb-doped silica fiber and measured its resonant optical nonlinearity with long-period fiber gratings (LPFG) interferometer. The Nb-doped fiber was made with a combined MCVD and ALD technology. Then, we fabricated a pair of LPFGs and cascaded them as a Mach-Zehnder interferometer (MZI).By measuring the wavelength shifts of the interference fringe with the 532nm laser pump power, the resonant nonlinear refractive index of Nb-doped silica fiber around 1537 nm was estimated to be 8.12×10^-16m²/W.