Symmetric Pumping Research Articles

OSNR enhancement of Rayleigh-assisted Brillouin-Raman fiber laser via double pass configuration.

We propose and demonstrate a 10 GHz spacing multi-wavelength Brillouin-Raman fiber laser (MBRFL) with wide bandwidth and an outstanding optical signal-to-noise ratio (OSNR). This is achieved by utilizing loop mirror at one end of the laser cavity through a symmetrical bi-directional Raman pumping scheme. The setup is arranged in a double pass configuration by employing different lengths of dispersion compensating fibers (DCF). The attainment of MBRFL with outstanding performance necessitates the optimization of Raman pump power, Brillouin pump wavelength, and DCF length. By employing an 11 km DCF, when setting the Brillouin pump wavelength at 1531.4 nm, 504 Stoke lines are produced with a channel spacing of 0.08 nm. All the counted laser lines have less than a 1-dB peak amplitude variation and are spread across a 40.4 nm bandwidth that covers from 1531.4 to 1571.8 nm wavelength. In this case, the Raman pump power is fixed at 900 mW which results in average OSNR and Stokes peak amplitude level of 28 dB and -7 dBm respectively. To date, this is the simplest cavity design with the widest bandwidth and flattest spectrum together with outstanding OSNR attained in 10 GHz spacing multi-wavelength fiber lasers that incorporate a single low-power Raman pump unit.

Bifurcation analysis of complex switching oscillations in a Kerr microring resonator.

Microresonators are micron-scale optical systems that confine light using total internal reflection. These optical systems have gained interest in the past two decades due to their compact sizes, unprecedented measurement capabilities, and widespread applications. The increasingly high finesse (or Q factor) of such resonators means that nonlinear effects are unavoidable even for low power, making them attractive for nonlinear applications, including optical comb generation and second harmonic generation. In addition, light in these nonlinear resonators may exhibit chaotic behavior across wide parameter regions. Hence, it is necessary to understand how, where, and what types of such chaotic dynamics occur before they can be used in practical devices. We study here the underlying mathematical model that describes the interactions between the complex-valued electrical fields of two optical beams in a single-mode resonator with symmetric pumping. Recently, it was shown that this model exhibits a wide range of fascinating behaviors, including bistability, symmetry breaking, chaos, and self-switching oscillations. We employ here a dynamical system approach to perform a comprehensive theoretical study that allows us to identify, delimit, and explain the parameter regions where different behaviors can be observed. Specifically, we present a two-parameter bifurcation diagram that shows how (global) bifurcations organize the observable dynamics. Prominent features are curves of Shilnikov homoclinic bifurcations, which act as gluing bifurcations of pairs of periodic orbits or chaotic attractors, and a Belyakov transition point (where the stability of the homoclinic orbit changes). In this way, we identify and map out distinctive transitions between different kinds of chaotic self-switching behavior in this optical device.

Almost indistinguishable single photons via multiplexing cascaded biphotons with cavity modulation and phase compensation

The cascade-emitted biphotons generated from alkali metal atomic ensembles are an excellent entanglement resource which enables long-distance quantum communication. The communication of quantum information between distant locations can be realized by utilizing the low-loss telecom bandwidth in the upper transition of the cascaded photons in a fiber-based quantum network. Meanwhile, the infrared photon from the lower transition of this highly directional and frequency-correlated biphoton can be created using the four-wave mixing process and can be stored locally as a collective spin wave. Here, we theoretically investigate the frequency entanglement of this biphoton and propose two approaches to remove the two photons' mutual correlations in frequency spaces. The first approach applies an optical cavity which modulates the biphoton spectrum into a more symmetric and narrow spectral function by multiplexing multiple atomic ensembles with phase compensation. The purity of the single photons reaches up to 0.999, and the entanglement entropy $S$ of the biphoton is reduced to 0.006, which is 200 times smaller than the one without multiplexing. The other approach employs a symmetric pumping of the laser fields in two atomic ensembles, which leads to a moderate reduction of $S\ensuremath{\sim}0.3$ when nondiscrimination detection devices are used for both photons. An extremely low frequency entanglement implies an almost indistinguishable single-photon source, which offers a potential resource for photonic quantum emulation and computation.

Semiclassical bifurcations and quantum trajectories: a case study of the open Bose–Hubbard dimer

We consider the open two-site Bose–Hubbard dimer, a well-known quantum mechanical model that has been realised recently for photons in two coupled photonic crystal nanocavities. The system is described by a Lindblad master equation which, for large numbers of photons, gives rise to a limiting semiclassical model in the form of a four-dimensional vector field. From the situation where both sites trap the same amount of photons under symmetric pumping, one encounters a transition that involves symmetry breaking, the creation of periodic oscillations and multistability as the pump strength is increased. We show that the associated one-parameter bifurcation diagram of the semiclassical model captures the essence of statistical properties of computed quantum trajectories as the pump strength is increased. Even for small numbers of photons, the fingerprint of the semiclassical bifurcations can be recognised reliably in observables of quantum trajectories.

Ratchet effect in frequency-modulated waveguide-coupled emitter arrays

We study theoretically the spatial distribution of the polarizations in the array of resonant electromagnetic dipole emitters coupled to a one-dimensional waveguide. The ratchet effect manifests itself in the spatial asymmetry of the distribution of the emitter occupations along the array under symmetrical pumping from both sides. The occupation asymmetry is driven by the periodic modulation in time of the emitter resonance frequencies. We find numerically and analytically the optimal conditions for maximal asymmetry. We also demonstrate that the ratchet effect can be enhanced due to the formation of topological electromagnetic edge states, enabled by the frequency modulation. Our results apply to the classical structures with coupled resonators or arrays of semiconductor quantum wells as well as the quantum setups with waveguide-coupled natural or artificial atoms.

Comparison between Single-Phase Flow Simulation and Multiphase Flow Simulation of Patient-Specific Total Cavopulmonary Connection Structures Assisted by a Rotationally Symmetric Blood Pump

To accurately assess the hemolysis risk of the ventricular assist device, this paper proposed a cell destruction model and the corresponding evaluation parameters based on multiphase flow. The single-phase flow and multiphase flow in two patient-specific total cavopulmonary connection structures assisted by a rotationally symmetric blood pump (pump-TCPC) were simulated. Then, single-phase and multiphase cell destruction models were used to evaluate the hemolysis risk. The results of both cell destruction models indicated that the hemolysis risk in the straight pump-TCPC model was lower than that in the curved pump-TCPC model. However, the average and maximum values of the multiphase flow blood damage index (mBDI) were smaller than those of the single-phase flow blood damage index (BDI), but the average and maximum values of the multiphase flow particle residence time (mPRT) were larger than those of the single-phase flow particle residence time (PRT). This study proved that the multiphase flow method can be used to simulate the mechanical behavior of red blood cells (RBCs) and white blood cells (WBCs) in a complex flow field and the multiphase flow cell destruction model had smaller estimates of the impact shear stress.

Novel Symmetrical Cage Compounds as Inhibitors of the Symmetrical MRP4-Efflux Pump for Anticancer Therapy.

Within the last decades cancer treatment improved by the availability of more specifically acting drugs that address molecular target structures in cancer cells. However, those target-sensitive drugs suffer from ongoing resistances resulting from mutations and moreover they are affected by the cancer phenomenon of multidrug resistance. A multidrug resistant cancer can hardly be treated with the common drugs, so that there have been long efforts to develop drugs to combat that resistance. Transmembrane efflux pumps are the main cause of the multidrug resistance in cancer. Early inhibitors disappointed in cancer treatment without a proof of expression of a respective efflux pump. Recent studies in efflux pump expressing cancer show convincing effects of those inhibitors. Based on the molecular symmetry of the efflux pump multidrug resistant protein (MRP) 4 we synthesized symmetric inhibitors with varied substitution patterns. They were evaluated in a MRP4-overexpressing cancer cell line model to prove structure-dependent effects on the inhibition of the efflux pump activity in an uptake assay of a fluorescent MRP4 substrate. The most active compound was tested to resentisize the MRP4-overexpressing cell line towards a clinically relevant anticancer drug as proof-of-principle to encourage for further preclinical studies.

Analyzing the Impact of Loop Parameter Variations on the Transient Response of Second Order Voltage-Switched CP-PLL

The analysis of the behavior of Charge Pump Phase-Locked Loop (CP-PLL) is a challenging task due to its mixed-signal architecture. Out of its two types, i.e. Current Switched CP-PLL (CSCP-PLL) and Voltage Switched CP-PLL (VSCP-PLL), the prior produces symmetrical pump currents, resulting in an appropriate transient performance to be analyzed. The loop parameters are important to set the gain, target frequency, and assure the stability of the system. The more important is the bandwidth of the loop, which is dependent on the loop filter parameters to perform stable operation and locking time. In this paper, the impact of loop parameter variations on the overall transient behavior of the system is investigated. It has been shown that loop parameters play an important role to ease the design of mixed-signal PLLs.

Discovery of Novel Symmetrical 1,4-Dihydropyridines as Inhibitors of Multidrug-Resistant Protein (MRP4) Efflux Pump for Anticancer Therapy.

Despite the development of targeted therapies in cancer, the problem of multidrug resistance (MDR) is still unsolved. Most patients with metastatic cancer die from MDR. Transmembrane efflux pumps as the main cause of MDR have been addressed by developed inhibitors, but early inhibitors of the most prominent and longest known efflux pump P-glycoprotein (P-gp) were disappointing. Those inhibitors have been used without knowledge about the expression of P-gp by the treated tumor. Therefore the use of inhibitors of transmembrane efflux pumps in clinical settings is reconsidered as a promising strategy in the case of the respective efflux pump expression. We discovered novel symmetric inhibitors of the symmetric efflux pump MRP4 encoded by the ABCC4 gene. MRP4 is involved in many kinds of cancer with resistance to anticancer drugs. All compounds showed better activities than the best known MRP4 inhibitor MK571 in an MRP4-overexpressing cell line assay, and the activities could be related to the various substitution patterns of aromatic residues within the symmetric molecular framework. One of the best compounds was demonstrated to overcome the MRP4-mediated resistance in the cell line model to restore the anticancer drug sensitivity as a proof of concept.

Dark Soliton of Polariton Condensates under Nonresonant -Symmetric Pumping**Supported by the National Natural Science Foundation of China under Grant No. 11835011.

A quantum system in complex potentials obeying parity-time () symmetry could exhibit all real spectra, starting out in non-Hermitian quantum mechanics. The key physics behind a -symmetric system consists of the balanced gain and loss of the complex potential. We plan to include the nonequilibrium nature (i.e., the intrinsic kinds of gain and loss of a system) to a -symmetric many-body quantum system, with an emphasis on the combined effects of non-Hermitian due to nonequilibrium nature and symmetry in determining the properties of a system. To this end, we investigate the static and dynamical properties of a dark soliton of a polariton Bose–Einstein condensate under the -symmetric non-resonant pumping by solving the driven-dissipative Gross–Pitaevskii equation both analytically and numerically. We derive the equation of motion for the center of mass of the dark soliton’s center analytically with the help of the Hamiltonian approach. The resulting equation captures how the combination of the open-dissipative character and -symmetry affects the properties of the dark soliton; i.e., the soliton relaxes by blending with the background at a finite time. Further numerical solutions are in excellent agreement with the analytical results.

Polychromatic Cherenkov Radiation Induced Group Velocity Symmetry Breaking in Counterpropagating Dissipative Kerr Solitons.

High-order-dispersion-induced dispersive waves emitted by dissipative Kerr solitons are frequently observed in microresonator frequency comb generation. Also known as soliton Cherenkov radiation, this type of dispersive wave plays a critical role in comb spectrum broadening as well as the formation of soliton bound states. Here, we report the experimental observation of symmetry breaking in the group velocity of counterpropagating solitons in a crystalline microresonator. Induced by the polychromatic Cherenkov radiation, soliton bound states are formed, showing different group velocities with different spatiotemporal separations between constituent solitons. By bidirectionally pumping the microresonator with laser fields of equal power and frequency, we demonstrate the degeneracy lifting of repetition rates of the counterpropagating solitons. Our work not only shines new light on the impact of dispersive waves in nonlinear cavities, but also introduces a novel approach to develop compact dual-comb spectrometers.

Efficient parametric generation in a nonlinear photonic crystal pumped by a dual beam.

We investigate parametric down-conversion in a hexagonally poled nonlinear photonic crystal, pumped by a dual pump with a transverse modulation that matches the periodicity of the χ (2) nonlinear grating. A peculiar feature of this resonant configuration is that the two pumps simultaneously generate photon pairs over an entire branch of modes, via quasi-phase matching with both fundamental vectors of the reciprocal lattice of the nonlinearity. The parametric gain of these modes depends thus coherently on the sum of the two pump amplitudes and can be controlled by varying their relative intensities and phases. We find that a significant enhancement of the source conversion efficiency, comparable to that of one-dimensionally poled crystals, can be achieved by a dual symmetric pump. We also show how the four-mode coupling arising among shared modes at resonance can be tailored by changing the dual pump parameters.

Theoretical and experimental analysis of bidirectionally pumped 1.3 μm Pr3+-doped ASE source

We have analyzed the characteristics of 1.3 μm praseodymium (Pr3+) doped bidirectionally pumped double pass (BIP-DP) configuration amplified spontaneous emission (ASE) source theoretically and experimentally. The source’s simulation model was established and corresponding simulated results were given. The effects of pump ratio, Pr3+-doped fiber (PDF) length, total pump power and source’s optical losses were researched. The output power of BIP-DP ASE source is mainly affected by the total pump power, PDF length and source’s optical losses, while it has little relationship with the pump ratio. The BIP-DP ASE source operating at the symmetric bi-directional pump condition was constructed experimentally. The acquired output power of more than 5 mW has been obtained experimentally, which was with the quasi-gaussian output spectrum, and its 3 dB bandwidth is ~ 20 nm.

Observation of a local maximum in the stationary turbulent spectrum of capillary waves on the surface of liquid hydrogen

The results of experimental studies of wave turbulence in a system of capillary waves formed on the surface of liquid hydrogen at a temperature of 15 K in a cylindrical cell with monochromatic radially symmetric pumping are presented. The local maximum formation with a decrease in the pumping amplitude was observed for the first time in the high-frequency region of the inertial range of the stationary turbulent spectrum at the direct cascade edge. The occurrence of a local maximum can be associated with a significant manifestation of viscous damping in the high-frequency region of the spectrum.

Phase Frequency Detector and Charge Pump for Low Jitter PLL Applications

In this paper a new technique is presented to improve the jitter performance of conventional phase frequency detectors by completely removing the unnecessary one-shot pulse. This technique uses a variable pulse-height circuit to control the unnecessary one-shot pulse height. In addition, a novel charge-pump circuit with perfect current-matching characteristics is used to improve the output jitter performance of conventional charge pumps. This circuit is composed of a pair of symmetrical pump circuits to obtain a good current matching. As a result, the proposed charge-pump circuit has perfect current-matching characteristics, wide output range, no glitch output current, and no jump output voltage. In order to verify such operation, circuit simulation is performed using 0.18 μm CMOS process parameters.

Alternating electric field-induced ion current rectification and electroosmotic pump in ultranarrow charged carbon nanocones.

Pumping fluid in ultranarrow (sub-2 nm) synthetic channels, analogous to protein channels, has widespread applications in nanofluidic devices, molecular separation, and related fields. In this work, molecular dynamics simulations were performed to study a symmetrical sinusoidal electric field-induced electroosmotic pump in ultranarrow charged carbon nanocone (CNC) channels. The results show that the CNC channels could rectify the ion current because of the different ion flow rates in the positive and negative half circles of the sinusoidal electric field. Electroosmotic flow (EOF) rectification yielded by the ion current rectification is also revealed, and net water flow from the base to the tip of the CNC channels is observed. The simulations also show that the preferential ion current conduction direction in the ultranarrow CNC channels (from base to tip) is opposite to that in conical nanochannels with tip diameters larger than 5 nm (from tip to base). However, the preferential EOF direction is the same as that of large conical nanochannels (from base to tip). We also investigated the influences of ion concentration and the amplitudes and periods of the sinusoidal electric field on the EOF pump. The results show that high ion concentration, large amplitudes, and long periods are desired for high EOF pumping efficiency. Finally, through comparison with a constant electric field and a pressure-induced water pump, we prove that the EOF pump under an alternating electric field has a higher pump efficiency. The approach outlined in this work provides a general scheme for pumping fluid in ultranarrow charged conical nanochannels.

Parity solitons in nonresonantly driven-dissipative condensate channels

We study analytically and numerically the condensation of a driven-dissipative exciton-polariton system using symmetric nonresonant pumping geometries. We show that the lowest condensation threshold solution carries a definite parity as a consequence of the symmetric excitation profile. At higher pump intensities competition between the two parities can result in critical quenching of one and saturation of the other. Using long pump channels, we show that the competition of the condensate parities gives rise to a different type of topologically stable defect propagating indefinitely along the condensate. The defects display repulsive interactions and are characterized by a sustained wavepacket carrying a pair of opposite parity domain walls in the condensate channel.

Stability Consideration of the Voltage Switched Charge-pump Phase Locked Loop using Linear Approach

The aim of this study to provide possible criteria to consider the stability of Voltage Switched Charge-Pump Pump Phase Locked Loop (VSCP-PLL). Stability of the conventional CP-PLL architecture is often determined by Gardner's stability plane, when PLL system is locked and near the fixed point. In the latest work it has been shown that, this stability criterion is not conservative enough when considering initial condition far from the fixed point. However, Gardner's criterion is based on the PLL operating with a Current Switched Charge Pump (CSCP), which provides an ideal pump current during switching states. Nevertheless, a Voltage Switched Charge Pump (VSCP) is often used in many commercially available CP-PLL circuits (like 4046 family). The VSCP offers design simplicity but generates a peculiar effect related to the non-constant current flowing through the electrical load of Loop Filter (LF) w. r. t. operating point (average input voltage) of the Voltage Controlled Oscillator (VCO). This non-linearity may complicate the PLL characteristics making it difficult to analyze the stability of the system, since there is no any particular criterion developed to study the stability of a VSCP-PLL. In this study, a procedure is proposed for PLL designers to apply similar Gardner's stability criterion developed for the CSCPPLL to a VSCP-PLL. The stability simulations are performed using an efficient discrete time Event-Driven (ED) model. The stability condition is observed for the initial operating conditions far from the fixed point by simulating the transient domain of the VSCP-PLL in the Gardner’s plane considering symmetrical and asymmetrical pump current.

Fundamentals of Highly Non-Degenerate Cascaded Four-Wave Mixing

By crossing two intense ultrashort laser pulses with different colors in a transparent medium, like a simple piece of glass, a fan of multicolored broadband light pulses can be simultaneously generated. These newly generated pulses are emitted in several well-defined directions and can cover a broad spectral range, from the infrared to the ultraviolet and beyond. This beautiful phenomenon, first observed and described 15 years ago, is due to highly-nondegenerate cascaded four-wave mixing (cascaded FWM, or CFWM). Here, we present a review of our work on the generation and measurement of multicolored light pulses based on third-order nonlinearities in transparent solids, from the discovery and first demonstration of highly-nondegenerate CFWM, to the coherent synthesis of single-cycle pulses by superposition of the multicolored light pulses produced by CFWM. We will also present the development and main results of a dedicated 2.5-D nonlinear propagation model, i.e., with propagation occurring along a two-dimensional plane while assuming cylindrically symmetric pump beam profiles, capable of adequately describing noncollinear FWM and CFWM processes. A new method for the generation of femtosecond pulses in the deep-ultraviolet (DUV) based on FWM and CFWM will also be described. These experimental and theoretical results show that highly-nondegenerate third-order nonlinear optical processes are formally well understood and provide broader bandwidths than other nonlinear optical processes for the generation of ultrashort light pulses with wavelengths extending from the near-infrared to the deep-ultraviolet, which have many applications in science and technology.

Evaluation of 100G DP-QPSK long-haul transmission performance using second order co-pumped Raman laser based amplification.

We present, for the first time, a detailed investigation of the impact of second order co-propagating Raman pumping on long-haul 100G WDM DP-QPSK coherent transmission of up to 7082 km using Raman fibre laser based configurations. Signal power and noise distributions along the fibre for each pumping scheme were characterised both numerically and experimentally. Based on these pumping schemes, the Q factor penalties versus co-pump power ratios were experimentally measured and quantified. A significant Q factor penalty of up to 4.15 dB was observed after 1666 km using symmetric bidirectional pumping, compared with counter-pumping only. Our results show that whilst using co-pumping minimises the intra-cavity signal power variation and amplification noise, the Q factor penalty with co-pumping was too great for any advantage to be seen. The relative intensity noise (RIN) characteristics of the induced fibre laser and the output signal, and the intra-cavity RF spectra of the fibre laser are also presented. We attribute the Q factor degradation to RIN induced penalty due to RIN being transferred from the first order fibre laser and second order co-pump to the signal. More importantly, there were two different fibre lasing regimes contributing to the amplification. It was random distributed feedback lasing when using counter-pumping only and conventional Fabry-Perot cavity lasing when using all bidirectional pumping schemes. This also results in significantly different performances due to different laser cavity lengths for these two classes of laser.