掺E~(3+)石英光纤中频率上转换的实验研究

首次报道了实验研究连续1064nm激光泵浦的掺Er~(3+)石英光纤中频率上转换过程.测量了Er~(3+)/GeO_2/SiO_2和Er~(3+)/Al_2O_3/GeO_2/SiO_2两种光纤发射的可见荧光谱,并用Er~(3+)离子的双光子吸收和受激态吸收过程解释了频率上转换现象.     

掺Er^3＋石英光纤中的共振增强受激四光子混频

首次实验观察到在1064nm激光泵浦下掺Er~(3+)石英光纤中的共振增强受激四光子混频现象和光学自由感应衰减过程.在频域和时域上实验证明了Er~(3+)的~4I_(11/2)激发态能级对受激四光子混频产生的反斯托克斯谱线的增强效应.     

Scattering loss in Nd-doped silica based optical fibers

Rare-earth doped fibers suffer from relatively high attenuation in comparison to conventional communication fibers. In order to improve the properties of such fibers, understanding of the mechanisms involved in scattering effects is of great importance. The effect of Nd-doping, Al-codoping and of the drawing temperature on the scattering effect was investigated for several different optical fibers. To this end a measuring setup was realized which allows absolute measurements of the scattering coefficient at different positions along a fiber. Also separation of total attenuation and scattering effects is possible. The presented results indicate scattering effects as primary source for increased attenuation compared with undoped fibers.     

Scattering loss in Nd-doped silica based optical fibers

Rare-earth doped fibers suffer from relatively high attenuation in comparison to conventional communication fibers. In order to improve the properties of such fibers, understanding of the mechanisms involved in scattering effects is of great importance. The effect of Nd-doping, Al-codoping and of the drawing temperature on the scattering effect was investigated for several different optical fibers. To this end a measuring setup was realized which allows absolute measurements of the scattering coefficient at different positions along a fiber. Also separation of total attenuation and scattering effects is possible. The presented results indicate scattering effects as primary source for increased attenuation compared with undoped fibers.     

Experimental investigation of cutoff phenomena in nonlinear photonic crystal fibers

Modal cutoff is investigated experimentally in a series of high-quality nonlinear photonic crystal fibers. We demonstrate a suitable measurement technique with which to determine the cutoff wavelength and verify the technique by inspecting the near field of the modes that may be excited below and above the cutoff. We observe a double-peak structure in the cutoff spectra, which is attributed to splitting of the higher-order modes. The cutoff is measured for seven different fiber geometries with different pitches and relative hole sizes, and very good agreement with recent theoretical work is found.     

EPR and optical measurements of weakly doped LiNbO3: Er

Optical spectroscopy measurements of the congruent LiNbO₃ (LN) single crystals, weakly doped with Er (0.1–0.3 wt%) and Er (0.3 wt%) and Yb (0.5 wt%), have been carried out. The shape of the optical absorption and additional absorption bands registered after γ-irradiation suggests the presence of Er³⁺ ion pairs. EPR investigations were performed for LN single crystal doped with Er (0.1 wt%). Unusual behaviour of the temperature dependence of the intensity and linewidth of the main EPR line—corresponding to the fine transition of ^evenEr³⁺—ions, is reported. The main EPR line appears to be a superposition of several paramagnetic centres originating from isolated ^evenEr³⁺ ions and ^evenEr³⁺–^evenEr³⁺ pairs of ions. In low temperature region (below 20 K), the main EPR signal is dominated by signals arising from ^evenEr³⁺–^evenEr³⁺ pairs of ions. The inverse intensity of the EPR line at low temperature region fulfils the Curie–Weiss law and enabled to determine the Curie–Weiss constant Θ=1.5±0.5 K. The positive sign of Θ suggests that the ferromagnetic interactions arise in the system of ^evenEr³⁺–^evenEr³⁺ ion pairs in LN. Our results suggest that the distribution of Er ions in congruent LN is not homogeneous and Er impurity ions can form clusters in host lattice even in the case of weak erbium doping.     

Nonlinear control of the propagation of optical pulses in doped optical fibers

Results of study of nonlinear processes occurring during the propagation of light pulses in optical fibers doped with atoms of rare-earth elements under conditions of atomic coherence and interference are presented. For a three-level Λ scheme of interaction, the linear (χ⁽¹⁾) and nonlinear (χ⁽³⁾) susceptibilities of such a medium are calculated. It is shown that the coefficients of Kerr nonlinearity and nonlinear absorption can reach extremely large values and can be negative. The competition between linear and nonlinear processes in the Λ scheme allows one to obtain compensation regimes when the coefficients of dispersion or absorption of the optical fiber material vanish. The efficient control of the optical properties of such a system over wide limits proves to be possible owing to variations in the parameters of light pulses at the input of the medium. The necessary conditions for realizing regimes with “slow” light, as well as for self-compression of a probing pulse on ultimately small spatial scales in a doped optical fiber, were obtained.     

掺Er/Er+O的GaN薄膜光学性质的研究

利用Raman散射谱研究了GaN注Er以及Er+O共注样品的振动模，并讨论了共注入O对Er离子发光的影响. 在Raman散射谱中，对于注Er的GaN样品出现了300 cm^-1和670 cm^-1两个新的Raman峰，而对于Er+O共注样品，除了上述两个峰外，在360 cm^-1处出现了另外一个新的峰，其中300 cm^-1峰可以用disorder-activated Raman scattering (DARS)来解释，670 cm^-1峰是由于与N空位相关的缺陷引起的，而360 cm^-1峰是由O注入引起的缺陷络合物产生的. 由于360 cm^-1模的缺陷出现，从而导致Er+O共注入GaN薄膜红外光致发光(PL)强度的下降. 关键词： GaN Er Raman散射 光致发光     

Shallow water rogue wavetrains in nonlinear optical fibers

In addition to deep-water rogue waves which develop from the modulation instability of an optical CW, wave propagation in optical fibers may also produce shallow water rogue waves. These extreme wave events are generated in the modulationally stable normal dispersion regime. A suitable phase or frequency modulation of a CW laser leads to chirp-free and flat-top pulses or flaticons which exhibit a stable self-similar evolution. Upon collision, flaticons at different carrier frequencies, which may also occur in wavelength division multiplexed transmission systems, merge into a single, high-intensity, temporally and spatially localized rogue pulse.     

Dynamics of optical pulses in periodic nonlinear fibers

Dynamics of a two-mode wave packet with strong linear and nonlinear (cross-modulation) coupling is investigated. The effect of the initial conditions of the pulse excitation on its further transformation is considered. The possibility to control the dispersion parameters of the wave packet by varying the initial conditions of its input is pointed out. The effective parameters of the dispersion and nonlinearity that govern the dynamics of an optical pulse in a periodic nonlinear fiber light guide are obtained.     

Propagation of optical pulses in periodic nonlinear fibers

We study the conditions of formation and propagation of soliton pulses in a periodic two-mode nonlinear fiber with allowance for dispersion of the fiber material and intermode dispersion of interacting modes under the condition of their phase synchronism. State University, Ul’yanovsk, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 8, pp. 1032–1042, August, 1998.     

Enhancement of second-order optical susceptibilities of Er doped germanate glasses

During bicolor optical treatment by two coherent laser beams from 25 ps Erbium-glass laser (λ = 1.54 μm), we have established substantial increase of effective optical second-order susceptibility near the critical temperature points corresponding to the glass structural transformation near 435 °C. The increasing Er³⁺ content favors substantial increase of the photoinduced optical second harmonic generation (SHG). This temperature dependence of the second-order optical susceptibilities detected by the SHG correlates well with the differential scanning calorimetric (DSC) measurements. At the same time, the effect exists only in a narrow temperature range (up to 12 °C) . There was not temperature hysteresis. Possible physical mechanisms of the phenomenon observed are discussed.     

Radiation-induced nonlinear optical response of quartz fibers

The intensity of radiation-induced luminescence and transient optical losses in KU-1 (Russia) and K-3 (Japan) quartz glass optical tibers irradiated in a fast pulsed fission reactor (a pulse duration of 80 μs and a neutron flux up to 7 × 10¹⁶ cm^–2 s^–2) has been measured in the visible range. The intensity of the fast luminescence component nonlinearly depends on the neutron flux. The luminescence intensity and the transient optical losses depend on the probe light intensity. Suppression of radiation-induced luminescence is observed at wavelengths that are longer or shorter than the probe light wavelength. Light probing leads to an increase in transient optical losses and a more rapid recovery of transparency. A model of two photon fluxes is proposed to analyze the relationship of the effects of suppression of radiation-induced luminescence and the increase in optical losses upon light probing. The effect of suppression of radiation-induced luminescence can be used to control the optical properties of fibers in radiation fields.     

Measurement of nonlinear properties and optical limiting ability of Rhodamine6G doped silica and polymeric samples

The third order nonlinear optical properties of Rhodamine6G (Rh6G) doped silica and polymeric samples have been investigated using single beam z-scan technique under excitation by the second harmonic of Nd:YAG laser beam (532 nm). The nonlinear refractive index, nonlinear absorption coefficient, real and imaginary parts of third order nonlinear susceptibility in the samples of silica and poly-methylmethacrylate (PMMA) matrices are measured. Thermal contribution to the nonlinear refractive index in case of undoped silica samples has been calculated in order to have better accuracy of the material response contribution to third order nonlinearity. The comparative study of the optical limiting performance of Rh6G doped silica and polymeric samples show that Rh6G doped silica is relatively superior for optical limiting applications.     

The optical properties of trivalent rare earth ions (Er3+) doped borotellurite glass

Erbium doped borotellurite glass has been fabricated by using conventional melting method. The density and molar volume have been calculated and analyzed while their optical properties were studied by measuring the optical absorption and luminescence spectra at room temperature. From the XRD results, since the patterns do not exhibit any diffraction line thus it confirms their amorphous nature. It is found that the density of the glass samples increased and the molar volume decreased with respect to Er ions content. Meanwhile, the upconversion emissions centered at 487, 523, 558, 642, 695 and 782 nm have been observed under the 650 nm excitation in the ⁴ F _9/2 level. Some other results will be analysed and discussed in details.     

Phase-matching condition between acoustic and optical waves in doped fibers

A new technique, recently proposed [1] for achieving phase-matching in Brillouin scattering in a dielectric fiber doped by three-level Λ-type ions, can lead to a dramatic increase of efficiency of ponderomotive nonlinear interaction between electromagnetic waves and holds promise for applications in quantum optics. In this paper, we investigate possibilities to establish phase-matching condition for acoustic modes in confined geometries that exhibit nonzero cutoff frequencies.     

Upconversion mechanisms and thermal effects of Er3+ in Er3+ doped yttria nanocrystals

Efficient Er³⁺:Y₂O₃ phosphor is synthesized by the sol–gel method. Rate equations for Er³⁺ energy level populations are used to investigate pump power and temperature dependences of upconversion intensity as well as the fluorescence decay profiles. Excited state absorption cross section of Er^{3+ 4}I_13/2 of 6.8×10^?27 m² and cross relaxation rate of 6200 s^?1 are determined from comparison between theoretical predictions and experimental data. In addition, it is found that effect of temperature on the phonon-assistant absorption cannot be neglected. This work provides references for the prediction of the upconversion behavior in Er³⁺ singly doped matrix.     

非线性单模光纤中源啁啾孤子相互作用

本文采用分步傅氏变换法对非线性单模光纤中源啁啾孤子相互作用进行了详细的数值研究.所得结果揭示了先源啁啾对孤子相互作用影响的本质,为设计光源啁啾情况下的孤子传转系统提供了依据.     

Optical properties of high-delta air silica microstructure optical fibers

We analyze the waveguide properties of microstructure optical fibers consisting of a silica core surrounded by a single ring of large air holes. Although the fibers can support numerous transverse spatial modes, coupling between these modes even in the presence of large perturbations is prevented for small core dimensions, owing to a large wave-vector mismatch between the lowest-order modes. The result is an optical fiber that can appear single mode with propagation properties that can be achieved only in multimode waveguides.