新超导体MgCNi3的虚晶掺杂研究

用全势线性缀加平面波方法,考虑局域自旋密度近似研究虚晶掺杂MgCNi3的超导电性和磁性.计算了自旋极化能带结构、体弹性模量和它对压力的导数、原子磁矩 m 及其变化率.计算结果表明,对于电子掺杂的Mg1-xAlxCNi3(0≤x≤0.5), 超导电性和磁涨落随掺杂量的增加逐渐减小.空穴掺杂的Mg1-xNaxCNi3,在x＝0.12处出现铁磁相变,超导电性消失.在MgCNi3少量空穴掺杂区域(0≤x<0.12),表现为超导与磁涨落共存的不稳定状态.     

Impact of polarization dependent loss on degree of polarization as feedback signal of polarization mode dispersion

Polarization dependent loss (PDL) has been recognized as a critical issue because various inline optical components may have nonnegligible PDL effect that interacts with polarization mode dispersion (PMD).We investigated the impact of PMD-PDL interaction on degree of polarization (DOP), which is the most commonly used feedback signal in PMD compensation. The simulation results of a 40-Gb/s NRZ code optical transmission system show that the maximum PMD increases from approximately 40 ps to more than 45 ps, while minimum DOP declines from approximately 0.6 to approximately 0.2. The interaction of PMD and PDL also induces residual PMD underestimation of 5-8 ps, which causes degradation of PMD compensation performance.     

Study of passive Q-switching for flash-lamp-pumped 1.34-μm Nd:GdVO4 laser

The static laser performance of a-growth Nd:GdVO4 crystal (a-cut, 4 × 4 × 25 (mm)) at 1.34μm pumped by flash-lamp is investigated with different transmissions of output couplers. With the output coupler transmission of T = 30%, the static output energy of 148 mJ is obtained when the pump energy is 35.2 J,and the corresponding electric-optical conversion efficiency is 0.42%. The Q-switched output of lasers with the output wavelength ranging from 1.3 to 1.6 μm can be realized by using Co2+ :LaMgAl11O19 (Co:LMA)as saturable absorber. A flash-lamp-pumped, passively Q-switched Nd:GdVO4 laser with Co:LMA as saturable absorber is demonstrated in plano-concave laser cavity. With the cavity length of 16.3 cm and pump energy of 19.8 J, the single-pulse output energy, pulse width, and peak power are obtained to be 4m J, 80 ns, and 5 × 104 W, respectively.     

Temperature-insensitive fiber Bragg grating dynamic pressure sensing system

Temperature-insensitive dynamic pressure measurement using a single fiber Bragg grating (FBG) based on reflection spectrum bandwidth modulation and optical power detection is proposed. A specifically designed double-hole cantilever beam is used to provide a pressure-induced axial strain gradient along the sensing FBG and is also used to modulate the reflection bandwidth of the grating. The bandwidth modulation is immune to spatially uniform temperature effects, and the pressure can be unambiguously determined by measuring the reflected optical power, avoiding the complex wavelength interrogation system. The system acquisition time is up to 85 Hz for dynamic pressure measurement, and the thermal fluctuation is kept less than 1.2% full-scale for a temperature range of -10 degrees C to 80 degrees C.     

Electrically controlled transfer of spin angular momentum of light in an optically active medium

Spin is an intrinsic property of the photon. A method for using an externally applied dc electric field to manipulate the transfer of spin angular momentum of light in an optically active medium is presented. To discuss this, we first develop a wave coupling theory of the mutual action of natural optical activity and the linear electro-optic effect. Besides being used for analyzing the electrically controlled transfer of spin angular momentum of light, the theory can also be used to describe the propagation of light traveling along an arbitrary direction in any optically active medium with an external dc electric field along an arbitrary direction.     

The influence of subglottal acoustics on laboratory models of phonation

Many previous laboratory investigations of phonation involving physical models, excised larynges, and in vivo canine larynges have failed to fully specify the subglottal system. Many of these same studies have reported a variety of nonlinear phenomena, including bifurcations (e.g., various classes of phonation onset and offset, register changes, frequency jumps), subharmonics, and chaos, and attributed such phenomena to the biomechanical properties of the larynx. However, such nonlinear phenomena may also be indicative of strong coupling between the voice source and the subglottal tract. Consequently, in such studies, it has not been clear whether the underlying mechanisms of such nonlinear phenomena were acoustical, biomechanical, or a coupling of the acoustical and biomechanical systems. Using a physical model of vocal fold vibration, and tracheal tube lengths which have been commonly reported in the literature, it is hypothesized and subsequently shown that such nonlinear phenomena may be replicated solely on the basis of laryngeal interactions with the acoustical resonances of the subglottal system. Recommendations are given for ruling out acoustical resonances as the source of nonlinear phenomena in future laboratory studies of phonation.     

Distributed measurement of birefringence dispersion in polarization-maintaining fibers

A new method to measure the birefringence dispersion in high-birefringence polarization-maintaining fibers is presented using white-light interferometry. By analyzing broadening of low-coherence interferograms obtained in a scanning Michelson interferometer, the birefringence dispersion and its variation along different fiber sections are acquired with high sensitivity and accuracy. Birefringence dispersions of two PANDA fibers at their operation wavelength are measured to be 0.011 ps/(km nm) and 0.018 ps/(km nm), respectively. Distributed measurement capability of the method is also verified experimentally.