Dependence of Arc Plasma Dispersion Capability on its Temperature

The relationship between the dispersion capability and the temperature of argon arc plasma at 1 atm is deduced in view of the plasma＇s refractive index equation. The results indicate that argon arc plasma has a normal dispersion and its dispersion capability is nonlinear to the plasma＇s temperature in a wide range of temperature and wavelength region. According to the results of numerical calculation, the preferred optical methods are believed to be suitable for the diagnosis of argon arc plasma in different temperature regions.     

Broadband dispersion compensating fiber using index-guiding photonic crystal fiber with defected core

We present a novel broadband dispersion compensating photonic crystal fiber with defected core in this paper. The small central defect of air hole can flexibly control the chromatic dispersion properties of this kind of photonic crystal fiber. This kind of fiber has broadband large negative chromatic dispersion, and the chromatic dispersion coefficient varies from -440 to -480 ps/（nm.km） in the measured wavelength range of 1500 - 1625 nm. The calculated chromatic dispersion curve is well matched to the measured chromatic dispersion coefficient in the range of 1500 - 1625 nm. The proposed photonic crystal fiber can be used to design the dispersion compensating fiber in the desired wavelength range by adjusting its structural parameters.     

Guided modes in the chiral negative refractive index fiber

The novel characteristics of guided modes in the chiral negative refractive index fiber are investigated theoretically in this letter.We derive the characteristic equation of guided modes.Based on two types of chiral metamaterial parameters,we present the dispersion curves,energy flux,and power of guided modes.Some abnormal features,such as the existence of surface mode and dispersion curves with different shapes,intersection of dispersion curves of different guided modes,negative energy flux in the achiral cladding,and zero power at some normalized frequencies,are found in the chiral negative refractive index fiber.     

Broadband dispersion compensating fiber using index-guiding photonic crystal fiber with defected core

We present a novel broadband dispersion compensating photonic crystal fiber with defected core in this paper.The small central defect of air hole can flexibly control the chromatic dispersion properties of this kind of photonic crystal fiber.This kind of fiber has broadband large negative chromatic dispersion,and the chromatic dispersion coefficient varies from-440 to-480 ps/(nm·km)in the measured wavelength range of 1500-1625 nm.The calculated chromatic dispersion curve is well matched to the measured chromatic dispersion coefficient in the range of 1500-1625 nm.The proposed photonic crystal fiber can be used to design the dispersion compensating fiber in the desired wavelength range by adjusting its structural parameters.     

Design and optimization of weakly-coupled few-mode fiber with low nonlinearity

By investigating the influence of the difference of refractive index between core and cladding(nco-ncl),normalized frequency(V)and core radius(α)on both the intramodal and intermodal nonlinear coefficients(NCs)respectively,we design a novel weakly-coupled four-mode fiber with low nonlinearity.In general,under the premise of ensuring the low NCs between two non-degenerate modes,this design can reduce the intermodal NCs(0.5 W-1·km-1)between two degenerate modes and optimizes the parameters of differential group delays(DGDs)and chromatic dispersion.The optimized few mode fiber(FMF)is eligible for transmission and mode de-multiplexing in the receiver.     

Effect of Fe concentration on the nonlinear refraction and reverse saturable absorption in ferroelectric X-cut LiNbO_3 crystal

In this Letter, the effects of the iron(Fe) dopant concentration on the nonlinear optical properties of iron-doped ferroelectric X-cut Li Nb O3 crystals plates are studied by using the Z-scan technique with a cw laser at the wavelength of 532 nm. The amount of iron in the compound is varied from 0 to 0.15 mol%. Measurements of nonlinear refractive index n2 and the nonlinear absorption coefficient β are determined. The sign of the nonlinear refractive index is found to be negative and the magnitude is on the order of 10-8cm2∕W. This nonlinear effect increases as the concentration increases from 0 to 0.15 mol%. A good linear relationship is obtained between nonlinear refractive index, nonlinear absorption coefficient, and concentration.     

Distributed optical fiber surface plasmon resonance sensors

The relationships of the resonant wavelength of optical fiber surface plasmon resonance (SPR) sensors to the modulation layer refractive index, thickness and the refractive index of the bulk medium are obtained by using theoretical calculation model of optical fiber SPR sensors under certain conditions, which indicates that resonant wavelength of the sensors is approximately linear with modulation layer thickness. Based on the linear relationship, multiple SPR sensors with different resonant wavelengths can be fabricated in a single optical fiber named as distributed optical fiber surface plasmon resonance sensors (DOFSPRSs). Experimental results are presented, showing that it is practical to fabricate more than one SPR sensors in a single optical fiber.     

Distributed optical fiber surface plasmon resonance sensors

The relationships of the resonant wavelength of optical fiber surface plasmon resonance (SPR) sensors to the modulation layer refractive index, thickness and the refractive index of the bulk medium are obtained by using theoretical calculation model of optical fiber SPR sensors under certain conditions, which indicates that resonant wavelength of the sensors is approximately linear with modulation layer thickness. Based on the linear relationship, multiple SPR sensors with different resonant wavelengths can be fabricated in a single optical fiber named as distributed optical fiber surface plasmon resonance sensors (DOFSPRSs).Experimental results are presented, showing that it is practical to fabricate more than one SPR sensors in a single optical fiber.     

Design and optimization of with low weakly-coupled few-mode fiber nonlinearity

By investigating the influence of the difference of refractive index between core and cladding （nco - ncl）, normalized frequency （V） and core radius （α） on both the intramodal and intermodal nonlinear coefficients （NCs） respectively, we design a novel weakly-coupled four-mode fiber with low nonlinearity. In general, under the premise of ensuring the low NCs between two non-degenerate modes, this design can reduce the intermodal NCs （〈 0.5 W-l·km^-1） between two degenerate modes and optimizes the parameters of differential group delays （DGDs） and chromatic dispersion. The optimized few mode fiber （FMF） is eligible for transmission and mode de-multiplexing in the receiver.     

Periodic solitons in dispersion decreasing fibers with a cosine profile

Periodic solitons are studied in dispersion decreasing fibers with a cosine profile. The variable-coefficient nonlinear Schr¨odinger equation, which can be used to describe the propagation of solitons, is investigated analytically. Analytic soliton solutions for this equation are derived with the Hirota’s bilinear method. Using the soliton solutions, we obtain periodic solitons, and analyze the soliton characteristics. Influences of physical parameters on periodic solitons are discussed. The presented results can be used in optical communication systems and fiber lasers.     

Orientation-enhanced nonlinear optical properties and phase-conjugate reflective system of a novel Azobenzene doped polymer film

This paper reports that the nonlinear refractive index of a novel organic optical storage film doped azo-diphenylamine polymer is measured by using the $Z$-scan technique. The nonlinear refractive index up to $3.7\times 10 ^{ - 6 }$~cm$^{2}$/W induced by thermo-optical effect is obtained. It indicates that the sample has excellent optical nonlinear properties. The physical mechanism of the great nonlinear optical effect is analysed and the optical conjugate characteristic is also discussed with degenerate four-wave-mixing. The phase conjugate wave diffracted from the formative refractive index grating in the sample is acquired and its equivalent reflectivity reaches about 22{\%}. On this basis, the reflective wave phase-conjugated mirror system was designed, and the image aberration experienced in propagation in the storage experiment is corrected by using the system.     

A study of multi-trapping of tapered-tip single fiber optical tweezers

We develop a pair of tapered-tip single fiber optical tweezers, and study its multi-trapping characteristic. The finite difference time domain method is employed to simulate the trapping force characteristic of this pair of single fiber optical tweezers, and the results show that the number of trapped particles depends on the refractive index and the size of the particles. The trapping force of this pair of tapered-tip single fiber optical tweezers is calibrated by the experimental method, and the experimental results are consistent with the theoretical calculation results. The multi-trapping capability realized by the tapered-tip single fiber optical tweezers will be practical and useful for applications in biomedical research fields.     

Research on WDM optical fiber transmission system based on fiber Raman amplifier

After wavelength division multiplexing (WDM) optical fiber transmission system based on fiber Raman amplifier (FRA) is investigated in detail, the influence of the collocation of dispersion compensation fiber (DCF), the dispersion coefficient, dispersion slope (DS), effective core area, nonlinear index, length of FRA, launch power and the bandwidth of Bessel filter on bit error rate (BER) is deduced. The influence of Rayleigh backscattering noise on optical signal noise ratio (OSNR) is also investigated, which affects the performance of long haul transmission badly. The result indicates that the broadband long haul transmission can be realized through the reasonable design of the fiber. The result is useful to the optimal design of the WDM optical fiber transmission system based on FRA.     

Nonlinear optical characterization of phosphate glasses based on ZnO using the Z-scan technique

The nonlinear optical properties of a phosphate vitreous system [(ZnO)_x-(MgO)_30-x-(P₂ O₅)₇₀], where x=8, 10, 15, 18, and 20 mol% synthesized through the melt-quenching technique have been investigated by using the Z-scan technique. In the experiment, a continuous-wave laser with a wavelength of 405 nm was utilized to determine the sign and value of the nonlinear refractive (NLR) index and the absorption coefficient with closed and opened apertures of the Z-scan setup. The NLR index was found to increase with the ZnO concentration in the glass samples by an order of 10^-10 cm²·W^-1. The real and imaginary parts of the third-order nonlinear susceptibility were calculated by referring to the NLR index (n₂) and absorption coefficient (β) of the samples. The value of the third-order nonlinear susceptibility was presented by nonlinear refractive or absorptive behavior of phosphate glasses for proper utilization in nonlinear optical devices. Based on the measurement, the positive sign of the NLR index shows a self-focusing phenomenon. The figures of merit for each sample were calculated to judge the potential of phosphate glasses for application in optical switching.     

Modulation instability induced by cross-phase modulation with the fourth-order dispersion in dispersion-decreasing fiber

The modulation instability (MI) induced by cross-phase modulation (XPM) in dispersion-decreasing fiber (DDF), whose dispersion decreases along the direction of propagation, is solved and analyzed by the perturbation method for the extended nonlinear Schr¨odinger equation, considering the higher-order dispersion. The change of the gain spectra with incident power and dispersion decaying factor are also given respectively. Due to the fourth-order dispersion, XPM occurs at two gain spectral regions in both the normal and the anomalous dispersion regimes of DDF. The two gain spectral regions in the anomalous dispersion regime are larger than those in the normal dispersion regime. Moreover, the gain spectrum of the second region in the anomalous dispersion regime is near zero compared with that in the normal dispersion regime, indicating that XPM can be easily produced in the anomalous dispersion regime. The spectral width increases with the increase of the incident optical power and the dispersion decaying factor.     

Linear and Nonlinear Intersubband Optical Absorptions and Refractive Index Changes in InGaN Strained Single Quantum Wells： Strong Built-in Electric Field Effects

Considering the strong built-in electric field （BEF） effects due to the spontaneous and piezoelectric polarizations, the intersubband optical absorptions and refractive index changes for an InxGa1-xN/AlyGa1-yN strained single quantum well are studied theoretically within the framework of the density matrix method and effective-mass approximation. The linear, third-order nonlinear and total absorption coefficients and refractive index changes are calculated as a function of the incident optical intensity and photon energy. Our results show that both the incident optical intensity and the strong BEF have great influence on the total absorptions and refractive index cllanges. The results are significant for designing some important photodetectors and the photonic crystal devices with adjustable photonic band structures.     

Experimental study of nonlinear switching characteristics of conventional 2×2 fused tapered couplers

The nonlinear switching characteristics of fused fiber directional couplers were studied experimentally. By using femtosecond laser pulses with pulse width of 100 fs and wavelength of about 1550 nm from a system of Ti:sapphire laser and optical parametric amplifier (OPA), the nonlinear switching properties of a null coupler and a 100% coupler were measured. The experimental results were coincident with the simulations based on nonlinear propagation equations in fiber by using super-mode theory. Nonlinear loss in fiber was also measured to get the injected power at the coupler. After deducting the nonlinear loss and input efficiency, the nonlinear switching critical peak powers for a 100% and a null fused couplers were calculated to be 9410 and 9440 W, respectively. The nonlinear loss parameter PN in an expression of αNL=αP/PN was obtained to be PN = 0.23 W.     

Soliton guidance and nonlinear coupling for polarized vector spiraling elliptic Hermite–Gaussian beams in nonlocal nonlinear media

We investigate the incoherent beams with two orthogonal polarizations in nonlocal nonlinear media, one of which is a fundamental Gaussian beam and the other is spiraling elliptic Hermite–Gaussian beam carrying the orbital angular momentum(OAM).Using the variational approach, we obtain the critical power and the critical OAM required for the vector spiraling elliptic Hermite–Gaussian solitons.In the strong nonlocality region, two components of the vector beam contribute to the nonlinear refractive index in a linear manner by the sum of their respective power.The nonlinear refractive index exhibits a circularly symmetrical profile in despite of the elliptic shapes for spiraling Hermite–Gaussian beams.We find that in the strong nonlocality region, the critical power and the rotational velocity are the same regardless of the relative ratio of the constituent powers.The nonlinear refractive index loses its circular symmetry in weak nonlocality region, and the nonlinear coupling effect is observed.Due to the radiation of the OAM, the damping of the rotation is predicted, and can be suppressed by decreasing the proportion of the spiraling elliptic component of the vector beam.     

Study of mode propagation with 632.8-nm laser in tapered fiber

The material dispersion of a tapered fiber is described by Sellmeier＇s equation. The dependence of refractive index on wavelength and doping concentration is discussed. A He-Ne laser with the output wavelength of 632.8 nm is used in the experiment. When the cutoff frequency of the fiber is less than the laser frequency, the guiding modes of a singl~-mode fiber （at 1550 am） are investigated. The results show that the original single-mode fiber becomes a multi-mode waveguide. The propagation and mode coupling of the light in the taper region are analyzed. By controlling the taper end size of the fiber, the unique tapered fiber can convert a multi-mode beam into a single-mode one.     

Exact chirped multi-soliton solutions of the nonlinear Schr(o|¨)dinger equation with varying coefficients

In this letter, exact chirped multi-soliton solutions of the nonlinear Schrodinger (NLS) equation with varying coefficients are found. The explicit chirped one- and two-soliton solutions are generated. As an example, an exponential distributed control system is considered, and some main features of solutions are shown. The results reveal that chirped soliton can all be nonlinearly compressed cleanly and efficiently in an optical fiber with no loss or gain, with the loss, or with the gain. Furthermore, under the same initial condition, compression of optical soliton in the optical fiber with the loss is the most dramatic. Also, under nonintegrable condition and finite initial perturbations, the evolution of chirped soliton has been demonstrated by simulating numerically.