Progress of HIRFL-CSR Project in 2003

Great progress was achieved in HIRFL-CSR project in the year of 2003. A large number of components has been completed, tested, installed, and commissioned, especially for the HIRFL-upgrade, for the new injection beam line to the CSRm and for the CSRm. The project is now in the transition from the construction to the installation and commissioning phase. Component delivery and installation is proceeding in accordance with schedule. On the average more than 98% of the components have been contracted. More than 350 magnets have been manufactured. The magnets, the power supplies, the vacuum system and the beam detectors for the injection beam line to the CSRm have been installed. All the magnets for the CSRm have been manufactured     

Analysis of Nonlinear Directional Couplers

1 Introduction Since the coupled-mode theory in cylindrical optical-fiber systems was proposed in 1972, the optical coupling between parallel optical waveguides has been a matter of scientific concern. Two-core fiber couplers, especially, have been studied extensively since the success of producing a two-core fiber functioning as a directional coupler in 1980. The wavelength and polarization selectivity of two-core fibers can find many applications. The nonlinear properties of the two-core fiber coupler were also inspected with the realization of an ultrafast all-optical switch.     

Theoretical and experimental researches on C-band three-cavity transit-time effect oscillator

In recent years great progress has been made in the plasma technology, pulsed-power technology, and the PIC simulation tools. At the same time, great efforts have been made in the research of the directed energy weapon. As a result, the technol-ogy of the high power microwave (HPM) has been developing rapidly[1]. Over the past 30 years, dozens of HPM sources have been found, with the maximum peak power reaching 15GW, the maximum energy of the single pulse 600 J, and the frequency stretchi…     

Tunable fiber ring laser employing a Sagnac interferometric filter

Erbium-doped fiber lasers operating in the 1550-nm com-munication window have important applications in wave-length division multiplexing (WDM) communications,true-time-delay (TTD) control of microwave phase-arrayantenna (PAA) systems, and fiber sensors[1-3] .Amongdifferent types of fiber lasers, unidirectional traveling-wave ring laser has the advantages of eliminating backscattering and spatial hole-burning effects, and there-fore has been intensively investigated recently. Opticalfilters…     

Progress in superconducting qubits from the perspective of coherence and readout

Superconducting qubits are Josephson junction-based circuits that exhibit macroscopic quantum behavior and can be manipulated as artificial atoms.Benefiting from the well-developed technology of microfabrication and microwave engineering,superconducting qubits have great advantages in design flexibility,controllability,and scalability.Over the past decade,there has been rapid progress in the field,which greatly improved our understanding of qubit decoherence and circuit optimization.The single-qubit coherence time has been steadily raised to the order of 10 to 100μs,allowing for the demonstration of high-fidelity gate operations and measurement-based feedback control.Here we review recent progress in the coherence and readout of superconducting qubits.     

Numerical Analysis on Transmission Characteristics of a Bragg Grating Assisted Mismatched Fiber Coupler

l IntroductionWavelength-division multiplexing (~) technology is an imPOrtant approach tosatisfy substantial increase of telecommunication network capacity. As one Of keytechnologies used in WDM networks, much progress has been made for wavelengthdivision multipl exing/ demul tip lexing technology thes e years. Based on perfect spectrumcharacteristics of fiber Bragg gratingS and fiber coUPlers, many approaches have beenproPOSed for wavelength-division multiplexing/ de multi pl eXing in a…     

Wide-band double-pass discrete Raman amplifier with reflection of signals and pumps

A wide-band (1530-1610 nm) and high efficient double-pass discrete Raman amplifier is reported. In this Raman amplifier, by using a one-end gilded fiber as the broadband reflector, signals and multi-pump are both reflected to propagate through the gain fiber for a second time. An increase in net gain of more than 150% has been achieved compared with that in the typical co-pumped Raman amplifier. The advantages of this proposed new configuration have been experimentally studied by comparing with the recently existing Raman amplifier configurations.     

Suspended twin-core f iber for optical switching

A kind of novel fiber, comprising two fiber cores which are suspended in air inside the outer cladding via a central thin membrane ,is proposed for optical switching application. When a hydrostatic pressure applied on the optical fiber, the pressure-induced refractive index change of the two fiber cores will contribute to the periodical change of the intensity of guided light in the fiber core. The mode coupling of two cores under different hydrostatic pressure and influences of each structure parameter of the proposed fiber on the switching nressure have been numerically invo.stigated.     

Wall Conditioning Operation on the HL-2A Tokamak and Conceptual Design for the Device Modification

During the 2006 experiment campaign of HL-2A, about 2000 shots have been implemented, the plasma current of 433 kA and 3.0 s duration have been obtained. The wall conditioning methods such as glow discharge cleating （GDC） , siliconization and Ti sublimation were applied. The experiment results of wall conditioning research will be introduced in this report. At the same time, the conceptual design of modification of HL-2A tokamak has obtained great progress, two modification schemes have been obtained, and the conceptual design results will be presented.     

Statistical potentials for 3D structure evaluation:From proteins to RNAs

Structure evaluation is critical to in silico 3-dimensional structure predictions for biomacromolecules such as proteins and RNAs.For proteins,structure evaluation has been paid attention over three decades along with protein folding problem,and statistical potentials have been shown to be effective and efficient in protein structure prediction and evaluation.In recent two decades,RNA folding problem has attracted much attention and several statistical potentials have been developed for RNA structure evaluation,partially with the aid of the progress in protein structure prediction.In this review,we will firstly give a brief overview on the existing statistical potentials for protein structure evaluation.Afterwards,we will introduce the recently developed statistical potentials for RNA structure evaluation.Finally,we will emphasize the perspective on developing new statistical potentials for RNAs in the near future.     

Strain Sensor Using Optical Fiber Unsymmetrical F-P Cavity and the Characteristic Analysis

1 IntroductionSuper-accuracy measurements are increasingly needed with rapid development ofscience and technology. In all kinds of measurements, the optical fiber sensors have. many advantages such as inherent immunity to electronical disturbances, high isolationand can be used in explosive and combutive circuxnstances. OPtical fiber sensors can bedivided into two general classes, interferometric devices and intensity-based devices. In' recent years, great effort has been devoted to the devef…     

A new demodulation technique for optical fiber interferometric sensors with[3×3]directional couplers

Optical fiber interferometric sensors based on[3×3]couplers have been used in many fields.A new technique is proposed to demodulate output signals of this kind of sensors.The technique recovers the signal of interest by fitting coefficients of elliptic(Lissajous)curves between each fiber pair.Different from other approaches,this technique eliminates the dependence on the idealization of[3×3]coupler,provides enhanced tolerance to the variance of photoelectric converters.and is anti-polarization in a certain extent. The main algorithm has been successfully demonstrated both by numerical simulation and experimental result.     

Rare-earth ions-doped mid-infrared(2.7–3 μm) bulk lasers:a review [Invited]

Mid-infrared (MIR) laser sources operating in the 2.7–3μm spectral region have attracted extensive attention for many applications due to the unique features of locating at the atmospheric transparency window,corresponding to the"characteristic fingerprint"spectra of several gas molecules,and strong absorption of water.Over the past two decades,significant developments have been achieved in 2.7–3μm MIR lasers benefiting from the sustainable innovations in laser technology and the great progress in material science.Here,we mainly summarize and review the recent progress of MIR bulk laser sources based on the rare-earth ions-doped crystals in the 2.7–3μm spectral region,including Er~(3+)-,Ho~(3+)-,and Dy~(3+)-doped crystalline lasers.The outlooks and challenges for future development of rare-earth-doped MIR bulk lasers are also discussed.     

A new phase-shifted long-period fiber grating for simultaneous measurement of torsion and temperature

A novel phase-shifted long-period fiber grating(PS-LPFG)for the simultaneous measurement of torsion and temperature is described and experimentally demonstrated.The PS-LPFG is fabricated by inserting a pretwisted structure into the long-period fiber grating(LPFG)written in single-mode fiber(SMF).Experimental results show that the torsion sensitivities of the two dips are?0.114 nm/(rad/m)and?0.069 nm/(rad/m)in the clockwise direction,and?0.087 nm/(rad/m)and?0.048 nm/(rad/m)in the counterclockwise direction,respectively.The temperature sensitivities of the two dips are 0.057 nm/℃ and 0.051 nm/℃,respectively.The two dips of the PS-LPFG exhibit different responses to torsion and temperature.Simultaneous measurement of torsion and temperature can be implemented using a sensor.The feasibility and stabilization of simultaneous torsion and temperature measurement have been confirmed,and hence this novel PS-LPFG demonstrates potential for fiber sensing and engineering applications.     

The mechanism of breakdown in laminar-turbulent transition of a supersonic boundary layer on a flat plate-temporal mode

Recently, more and more attentions have been paid to the transition and turbulence of compressible flows, especially supersonic flows, but progress is very slow. In general, attentions were paid to the evolution of disturbances in laminar flow region, and the mechanism of breakdown process in laminar-turbulent transition remains unclear. The conventional idea of what leads to laminar-turbulent transition is that the transi-tion starts from the amplification of disturbances, and when the distur…     

Yb~(3+)-doped double-clad fiber laser with all fiber cavity

A novel all fiber cavity Yb~(3+)-doped double-clad fiber laser (DCFL) based on two double-clad fiber (DCF) Bragg grating is presented. The fiber Bragg gratings (FBGs) as the input and output mirrors have been formed in Yb~(3+)-doped DCF with the phase-mask method, and their reflectivities are 99% and 22%, respectively. When the input pump power is 417 mW, the maximum output power is 144 mW with linewidth <0.1 nm at the wavelength of 1.057 μm, over 40-dB signal-to-noise ratio (SNR), and 50.8% slope efficiency.     

Pulse generation of erbium-doped fiber laser based on liquid-exfoliated FePS_3

As a preferable material in the field of photo-detection and catalysis, the characteristics of FePS_3 in broad wavelength range have been proven by many experimental studies. However, FePS_3 has not been used as a saturable absorber(SA)in fiber lasers yet. We propose and demonstrate the generation of a single wavelength and dual-wavelength based on an Er-doped fiber laser(EDFL) at 1.5 μm by using an innovative FePS_3 saturable absorber for the first time. The result shows that a stable passively Q-switched pulse can be generated, which demonstrates that the new two-dimensional(2D) material FePS_3 served as SA provides a valid method to realize passively Q-switched laser. In addition, we achieve the output of the dual-wavelength pulse by properly rotating the polarization controller. To the best of our knowledge, the dual-wavelength pulse EDFL could be applied in biomedicine, spectroscopy, and sensing research.     

RNA structure prediction:Progress and perspective

Many recent exciting discoveries have revealed the versatility of RNAs and their importance in a variety of cellular functions which are strongly coupled to RNA structures. To understand the functions of RNAs, some structure prediction models have been developed in recent years. In this review, the progress in computational models for RNA structure prediction is introduced and the distinguishing features of many outstanding algorithms are discussed, emphasizing threedimensional(3D) structure prediction. A promising coarse-grained model for predicting RNA 3D structure, stability and salt effect is also introduced briefly. Finally, we discuss the major challenges in the RNA 3D structure modeling.     

Experimental demonstration of single-mode fiber coupling using adaptive fiber couplerExperimental demonstration of single-mode fiber coupling using adaptive fiber couplerExperimental demonstration of single-mode fiber coupling using adaptive fiber couplerExperimental demonstration of single-mode fiber coupling using adaptive fiber coupler

Coupling plane wave into a single-mode fiber （SMF） with high and steady coupling efficiency is crucial for fiber- based free-space laser systems, where random angular jitters are the main influencing factors of fiber coupling. In this paper, we verified a new adaptive-optic device named adaptive fiber coupler （AFC） which could compensate angular jitters and improve the SMF coupling efficiency in some degree. Experiments of SMF coupling under the angular jitter situation using AFC have been achieved. Stochastic parallel gradient descent （SPGD） algorithm is employed as the control strategy, of which the iteration rate is 625 Hz. In closed loop, the coupling efficiency keeps above 65% when angular errors are below 80/3tad. The compensation bandwidth is 35 Hz at sine-jitter of 15 ~rad amplitude with average coupling efficiency of above 60%. Also, experiments with simulated turbulence have been studied. The average coupling efficiency increases from 31.97% in open loop to 61.33% in closed loop, and mean square error （MSE） of coupling efficiency drops from 7.43% to 1.75%.