Soliton evolution and control in a two-mode fiber with two-photon absorption

Soliton dynamics are numerically investigated in a two-mode fiber with the two-photon absorption,and the effects of the two-photon absorption on the soliton propagation and interaction are demonstrated in different dispersion regimes.Soliton dynamics depend strictly on the sign and magnitude of the group velocity dispersion(GVD)coefficient of each mode and the strength(coefficient)of the two-photon absorption.The two-photon absorption leads to the soliton collapse,enhances the neighboring soliton interaction in both modes,and increases the energy exchange between the two modes.Finally,an available control is proposed to suppress the effects by the use of the nonlinear gain with filter.

Central distance of interferential mode patterns of elliptical core two-mode fiber

By means of the weakly guiding approximation, the mode spot sizes Wx and Wy of the fundamental mode along the semimajor （x-direction） and semiminor （y-direction） axes of the fiber core in elliptical core two- mode fiber are discussed. The variation of their ratio value Wx/W9 with the operation wavelength A and the length ratio a/b between the semimajor axis and the semiminor axis of the fiber core is analyzed. Based on this analysis, the distribution figures of two-lobe interferential mode patterns are evaluated and simulated quantitatively for different phase difference changes between LP01 and LP~~n modes. The two-lobe interferential mode patterns have the same profile and distribute symmetrically when the phase difference equals ~r/2. Their central distance S becomes larger when W~：/W~ augments gradually. F^rthermore, the equation about the central distance S of the two-lobe interferential mode patterns is given when the operation wavelength varies between 0.65 and 1.31 #m, which is important to applications shuch as sensors and coupling devices between different fibers.

Cylindrical vector beam fiber laser with a symmetric two-mode fiber coupler

We demonstrate a passively mode-locked all-fiber laser generating cylindrical vector beams(CVBs)only using a symmetric two-mode fiber optical coupler(TMF-OC)for both high-order mode excitation and splitting.Theoretical analyses show that for a symmetric TMF-OC with appropriate taper diameter,the second-order mode can be excited and coupled into output tap with high purity due to the effective index difference of different modes.Based on the fabricated TMF-OC,the passively mode-locked fiber laser delivers pulsed CVBs at a center wavelength of 1564.4 nm with 3 d B linewidth of 11.2 nm,pulse duration of 2.552 ps,and repetition rate of3.96 MHz.The purity of both radially and azimuthally polarized beams is estimated to be over 91%.Due to simple fabrication method of the TMF-OC and high purity of the generated CVBs,this mode-locked CVB fiber laser with all-fiber configuration has potential applications in optical trapping,optical communications,material processing,etc.

Modulation instabilities in randomly birefringent two-mode optical fibers

Modulation instabilities in the randomly birefringent two-mode optical fibers （RB-TMFs） are analyzed in detail by accounting the effects of the differential mode group delay （DMGD） and group velocity dispersion （GVD） ratio between the two modes, both of which are absent in the randomly birefringent single-mode optical fibers （RB-SMFs）. New MI characteristics are found in both normal and anomalous dispersion regimes. For the normal dispersion, without DMGD, no MI exists. With DMGD, a completely new MI band is generated as long as the total power is smaller than a critical total power value, named by Per, which increases significantly with the increment of DMGD, and reduces dramatically as GVD ratio and power ratio between the two modes increases. For the anomalous dispersion, there is one MI band without DMGD. In the presence of DMGD, the MI gain is reduced generally. On the other hand, there also exists a critical total power （Per）, which increases （decreases） distinctly with the increment of DMGD （GVD ratio of the two modes） but varies complicatedly with the power ratio between the two modes. Two MI bands are present for total power smaller than Per, and the dominant band can be switched between the low and high frequency bands by adjusting the power ratio between the two modes. The M1 analysis in this paper is verified by numerical simulation.

Generation of nanosecond cylindrical vector beams in two-mode fiber and its applications of stimulated Raman scattering

We present the generation of the nanosecond cylindrical vector beams(CVBs)in a two-mode fiber(TMF)and its applications of stimulated Raman scattering.The nanosecond(1064 nm,10 ns,10 Hz)CVBs have been directly produced with mode conversion efficiency of~18 d B(98.4%)via an acoustically induced fiber grating,and then the stimulated Raman scattering signal is generated based on the transmission of the nanosecond CVBs in a 100-m-long TMF.The transverse mode intensity and polarization distributions of the first-order Stokes shift component(1116.8 nm)are consistent with the nanosecond CVBs pump pulse.

Temperature-insensitive sensor for glucose brix measurement based on compact spindle-shaped structure with two-mode fiber

A temperature-insensitive sensor for glucose brix measurement based on compact spindle-shaped structure with two-mode fiber(TMF) is proposed. Due to the bending of optical fiber caused by flame baking, some of the light energy transmitted in the core leaks into the cladding area as an evanescent wave, which excites the higher-order cladding mode of the sensor. The experimental results show that when the length of TMF is 3 cm and the bending diameter is 4 mm, the maximum glucose brix sensitivity of the sensor is 0.368 nm/% from 0 to 21%. The sensor is insensitive to temperature from 10 °C to 50 °C, which can avoid the problem of temperature cross-sensitivity. A compact spindle-shaped sensor is a potential effective sensor with a simple structure, easy fabrication and low cost. The sensor can be used to detect glucose content in areas such as crops quality assessment and the research of pharmacy and bioengineering.

Monolithic all-fiber mid-infrared supercontinuum source based on a step-index two-mode As2S3 fiber

We demonstrate efficient supercontinuum generation extending into mid-infrared spectral range by pumping a twomode As2S3 fiber in the normal dispersion regime. The As2S3 fiber is fusion spliced to the pigtail of a near-infrared supercontinuum pump source with ultra-low splicing loss of 0.125 dB, which enables a monolithic all-fiber mid-infrared supercontinuum source. By two-mode excitation and mixed-mode cascaded stimulated Raman scattering, a supercontinuum spanning from 1.8 μm to 4.2 μm is obtained. Over 70% of the supercontinuum power is converted to wavelengths beyond2.4 μm. This is the first experimental report with respect to the multimode mid-infrared supercontinuum generation in a step-index two-mode chalcogenide fiber.

Improvement on refractive index sensing by exploiting the tapered two-mode fibers

The spectral characteristics and sensitivities of a tapered two-mode fiber sandwiched between two single-mode fibers are systematically investigated. Theoretical calculations reveal that a dispersion turning point(DTP)appears when the group effective refractive index(RI) difference between the fundamental mode and the higher-order mode equals zero;as a result, ultrahigh RI sensitivities can be achieved. Furthermore, the location of the DTP is strongly dependent on the tapering condition. Then, we experimentally demonstrate high sensitivities of the RI sensor with the waist diameter of 4 μm by means of immersing it in a flow cell filled with glycerol solution. In further tracking of the resonant wavelength shift around the DTP, it is found that the proposed RI sensor exhibits a sensitivity of 1.81 × 104 nm/RIU and a limit of detection down up to 3.29 × 10-5 RIU in a liquid glycerol solution.

“Zero‑Strain” NiNb_(2)O_(6) Fibers for All‑Climate Lithium Storage

Niobates are promising all-climate Li^(+)-storage anode material due to their fast charge transport,large specific capacities,and resistance to electrolyte reaction.However,their moderate unit-cellvolume expansion(generally 5%–10%)during Li^(+)storage causes unsatisfactory long-term cyclability.Here,“zero-strain”NiNb_(2)O_(6) fibers are explored as a new anode material with comprehensively good electrochemical properties.During Li^(+)storage,the expansion of electrochemical inactive NiO_(6) octahedra almost fully offsets the shrinkage of active NbO_(6) octahedra through reversible O movement.Such superior volume-accommodation capability of the NiO_(6) layers guarantees the“zero-strain”behavior of NiNb_(2)O_(6) in a broad temperature range(0.53%//0.51%//0.74%at 25//−10//60℃),leading to the excellent cyclability of the NiNb_(2)O_(6) fibers(92.8%//99.2%//91.1%capacity retention after 1000//2000//1000 cycles at 10C and 25//−10//60℃).This NiNb_(2)O_(6) material further exhibits a large reversible capacity(300//184//318 mAh g−1 at 0.1C and 25//−10//60℃)and outstanding rate performance(10 to 0.5C capacity percentage of 64.3%//50.0%//65.4%at 25//−10//60℃).Therefore,the NiNb_(2)O_(6) fibers are especially suitable for large-capacity,fast-charging,long-life,and all-climate lithium-ion batteries.

Nonclassical properties in the resonant interaction of a three level ∧-type atom with two-mode field in coherent state

In this paper, we study the nonclassical properties of the electromagnetic field resulting from the interaction of a three-level ∧-type atom with a two-mode field initially in the coherent state, such as squeezing properties and sub-Poisson statistics. We show that the squeezing can be enhanced by selective atomic measurement.

Nonclasssical Properties in Two-Mode Fields Resonantly Interacting with a Three-Level -Type Atom

Some noclassical properties in electromagnetic field are investigated for the interaction of two-modes initially taken in coherent-state representation with the three-level -type atom, such as squeezing properties and violation of the Cauchy-Schwartz inequality. The enhancement of field squeezing is found by selective atomic measurement. The Cauchy-Schwartz inequality is violated by the application of the classical field followed by detection in excited state.

A scheme for approximate conditional teleportation of entangled two-mode cavity state without Bell state measurement

An alternative scheme to approximately conditionally teleport entangled two-mode cavity state without Bell state measurement in cavity QED is proposed. The scheme is based on the resonant interaction of a ladder-type three-level atom with two bimodal cavities. The entangled cavity state is reconstructed with only one atom interacting with the two cavities successively.

Phenomenon of Resonance in a Two-Mode Laser with an Input Additive Signal

Exact formulas for the power spectrum and signal-to-noise ratio (SNR) with periodic additive signal arecalculated in the linear system.Then the phenomenon of resonance is studied in detail.We show that resonancepeak and suppressed valley exist in the curves of the SNR versus the coefficient of self-saturation, the net gain and thecross-coupling coefficient of the laser system.

Entropy squeezing for a two-level atom in two-mode Raman coupled model with intrinsic decoherence

In this paper, we investigate the entropy squeezing for a two-level atom interacting with two quantized fields through Raman coupling. We obtain the dynamical evolution of the total system under the influence of intrinsic decoherence when the two quantized fields are prepared in a two-mode squeezing vacuum state initially. The effects of the field squeezing factor, the two-level atomic transition frequency, the second field frequency and the intrinsic decoherence on the entropy squeezing are discussed. Without intrinsic decoherence, the increase of field squeezing factor can break the entropy squeezing. The two-level atomic transition frequency changes only the period of oscillation but not the strength of entropy squeezing. The influence of the second field frequency is complicated. With the intrinsic decoherence taken into consideration, the results show that the stronger the intrinsic decoherence is, the more quickly the entropy squeezing will disappear. The increase of the atomic transition frequency can hasten the disappearance of entropy squeezing.

Two-mode intelligent coordinating control of position for the welding positioner

A new intelligent control method for welding positioner is proposed. Applying an improved fuzzy controller and a variable PID controller, a two-mode intelligent coordinating controller ( TMICC ) is designed on basis of fuzzy logic and rules. The simulation and experimental results show that this control system can obtain better dynamic and static characteristics.

Generation and Properties of Two-Mode Circular States

Two-mode circular states,which are superposition states from some two-mode coherent states,are studiedtheoretically.It is shown that under certain conditions two-mode circular states may exhibit nonclassical effects,suchas sub-Poissonian statistics and intermode correlation.We propose schemes to generate two-mode circular states by theinteraction of a trapped ion with traveling wave lasers.

Teleportation of Two-Mode Quantum State of Continuous Variables

Using two Einstein-Podolsky Rosen pair eigenstates |η) as quantum channels, we study the teleportationof two-mode quantum state of continuous variables.

Preparation and control of entangled states in the two-mode coherent fields interacting with a moving atom via two-photon process

We investigate the preparation and the control of entangled states in a system with the two-mode coherent fields interacting with a moving two-level atom via the two-photon transition. We discuss entanglement properties between the two-mode coherent fields and a moving two-level atom by using the quantum reduced entropy, and those between the two-mode coherent fields by using the quantum relative entropy. In addition, we examine the influences of the atomic motion and field-mode structure parameter p on the quantum entanglement of the system. Our results show that the period and the duration of the prepared maximal atom-field entangled states and the frequency of maximal two-mode field entangled states can be controlled, and that a sustained entangled state of the two-mode field, which is independent of atomic motion and the evolution time, can be obtained, by choosing appropriately the parameters of atomic motion, field-mode structure, initial state and interaction time of the system.

One- and Two-Mode Combination Squeezing Operator for Two Harmonic Oscillators with Coordinate-Momentum Coupling

By virtue of the technique of integration within an ordered product of operators, we derive the normal ordering expansion of a one- and two-mode combination squeezing operator for two harmonic oscillators with coordinate- momentum coupling. It turns out that this squeezing operator just diagonalizes the Hamiltonian H=p^21/2m1＋m1ω^21x^21/2＋p^222m2＋m2ω^22x^22/2-λx2p1 so its ground state is a one- and two-mode combination squeezed state. Quantum fluctuation in the ground state is calculated.

Two-Mode Converters at 1.3μm Based on Multimode Interference Couplers on InP Substrates

Two-mode converters at 1.3μm, aiming at applications in mode-division multiplexing in Ethernet systems, are proposed and experimentally demonstrated. Based on multimode interference couplers, the two-mode converters with 50% and 66% mode conversion efficiencies are designed and fabricated on InP substrates. AIode conver- sion from the fundamental mode （TEo） to the first order mode （TE1） is successfully demonstrated within the wavelength range of 1280-1320nm. The 1.3-μm mode converters should be important devices in mode-division multiplexing systems in Ethernet systems.