Transient and nonlinear analysis of slow-light pulse propagation in an optical fiber via stimulated Brillouin scattering

We investigate slow-light pulse propagation in an optical fiber via transient stimulated Brillouin scattering. Space-time evolution of a generating slow-light pulse is numerically calculated by solving three-wave coupled-mode equations between a pump beam, an acoustic wave, and a counterpropagating signal pulse. Our mathematical treatments are applicable to both narrowband and broadband pump cases. We show that the time delay of 85% pulse width can be obtained for a signal pulse of the order of subnanosecond pulse width by using a broadband pump, while the signal pulse is broadened only by 40% of the input signal pulse. The physical origin of the pulse broadening and distortion is explained in terms of the temporal decay of the induced acoustic field. (C) 2009 Optical Society of America

Reducing group-velocity-dispersion-dependent broadening of stimulated Brillouin scattering slow light in an optical fiber by use of a single pump laser

We propose a method of effectively extending the stimulated Brillouin scattering (SBS) gain bandwidth in a single-mode optical fiber to reduce group-velocity-dispersion (GVD)-dependent pulse spread of SBS slow light. This can be done by overlapping doublet SBS gain spectra synthesized from a single pump laser. Numerical calculations are performed to verify our proposed method. We find that there exists the optimum spectral separation between two center frequencies of the doublet SBS gain spectrum with respect to the inherent spectral width of the pump laser, which makes it possible to effectively reduce the signal pulse broadening due to GVD. We show that the maximum time delay of the amplified signal pulse can be approximately two times longer than that by a previously reported method using a single broadband pump laser. (c) 2008 Optical Society of America.

Zero-broadening SBS slow light propagation in an optical fiber using two broadband pump beams

A new method of tailoring stimulated Brillouin scattering (SBS) gain spectrum for slow light propagation is proposed by use of two Gaussian-shaped broadband pump beams with different powers and spectral widths. The central frequency interval between the two pump beams are carefully set to be two inherent Brillouin frequency shift, ensuring that the gain spectrum of one pump has the same central frequency with the loss spectrum of the other one. Different gain profiles are obtained and analyzed. Among them a special gain profile is found that ensures a zero-broadening of the signal pulse independent of the Brillouin gain. This is owing to the compensation between the positive gain-dependent broadening and the negative GVD (group velocity dispersion) dependent broadening. The relationship of two pump beams is also found for constructing such a gain profile. It provides us a new idea of managing the broadening of SBS-based slow pulse by artificially constructing and optimizing the profile of gain spectrum. (c) 2008 Optical Society of America.

SBS-based slow light in optical fibers: optimum design considerations for undistorted slow-light signal propagation in steady-state and transient regimes

SPIE

Distortion management of SBS slow light in a single-mode optical fiber by optimization of broadband SBS gain spectrum

SPIE

Flat Surface Plasmon Polariton Bands in Bragg Grating Waveguide for Slow Light

The formations of the surface plasmonpolariton (SPP) bands in metal/air/metal (MAM) sub-wavelength plasmonic grating waveguide (PGW) are proposed. The band gaps originating from the highly localized resonances inside the grooves can be simply estimated from the round trip phase condition. Due to the overlap of the localized SPPs between the neighboring grooves, a Bloch mode forms in the bandgap and can be engineered to build a very flat dispersion for slow light. A chirped PGW with groove depth varying is also demonstrated to trap light, which is validated by finite-difference time-domain (FDTD) simulations with both continuous and pulse excitations.

肥料氮在土壤-作物系统中的转化与释放规律

本文以公主岭市长期定位监测基地的黑土为研究对象，通过15N同位素标记盆栽试验，系统研究了化肥及其配施玉米秸秆处理土壤不同形态氮库的容量特性、释放规律及其对作物的持续供氮能力。结果表明： 标记化肥氮施入土壤，连续三个生长季主要以有机氮的形式残留于土壤中，其次是固定态铵，无机氮最小。新形成土壤有机氮和“新固定”的固定态铵活性较高，极易释放供作物吸收利用，连续三季作物土壤固定态铵的净释放率最高，氨基酸氮次之，有机氮最低。与土壤有机氮库相比，土壤无机氮库中标记肥料氮的残留率较低，高量氮肥处理残留率高于低量氮肥处理，与单施化肥相比，化肥配施玉米秸秆降低了标记肥料氮在土壤无机氮库中的残留，说明高量氮肥的施用会增加其在无机氮库中的残留，化肥与有机物料配合施用能够促进无机氮肥向土壤有机氮的转化，从而避免无机氮大量积累而造成氮素损失。 标记氮肥在土壤中的残留率随作物生长季的增加而降低，经过连续三季作物的吸收利用，其在土壤中的残留率平均为15.8%；而作物对标记肥料氮的利用率和标记肥料氮的损失率随着作物生长季的增加而增加，至第三季作物成熟期，作物对标记肥料氮的利用率平均为61.1%，标记肥料氮的损失率平均为23.1%。在单施化肥处理中，高量氮肥的施用降低了标记肥料氮在土壤中的残留率，增加了氮素损失率；与单施化肥处理相比，化肥配施玉米秸秆能明显增加标记肥料氮在土壤和作物中的回收率，降低氮素损失率，从而说明通过施入有机物料玉米秸秆合理调节土壤中C源和N素营养的施用比例可以达到增加氮肥在土壤中的残留率，提高氮肥利用率的目的。

自交联材料在肥料养分控释上的应用研究

目前在包膜控释肥料方面的研究热点是采用树脂型包膜材料制备包膜肥料，并且取得了一定的成绩，控释效果比较良好，但由于树脂材料需用大量有机溶剂，给生产成本和工艺都带来了新的问题。本试验针对此问题，选用水性聚氨酯（PU）和水性丙烯酸（PA）作为包膜材料，应用旋转包膜工艺和流化床包膜工艺制备包膜肥料，采用水培法、淋溶法、土培法、电镜观察等方法对其进行释放性能评价，最终确定水性聚氨酯和水性丙烯酸在肥料中应用的效果。结果表明： 以旋转包膜工艺、用水性聚氨酯（PU）为膜材料制备的9种包膜肥料，并做了封闭处理，通过扫描电镜观察都形成了致密连续的控释膜，经评价都具有一定的控释效果，其中CRF-6（水性聚氨酯用量6%，封闭剂用量3%）、CRF-9（水性聚氨酯用量9%，封闭剂用量3%）两种包膜肥料控释性能较优，水培条件下其氮素初期溶出率分别为29.11%和19.48%，钾素初期溶出率分别为33.15%和24.93%。各种评价方法结果表明：同一材料不同包膜量控释效果比较：6%用量优于9%用量，优于3%用量。封闭剂用量在2%时效果相对较好。 以流化床包膜工艺、用水性聚氨酯（PU）和水性丙烯酸（PA）为膜材料制备的15种包膜肥料，经检测FCRF-9（PA:PU=1:2，9%）、FCRF-11（PA:PU=1:1，6%）和FCRF-12（PA:PU=1:1，9%）这3种肥料控释效果最为突出，在水培条件下其氮素初期溶出率分别为12.58%、15.62%和16.02%。材料组合以水性聚氨酯（PU）和水性丙烯酸（PA）以1：2复合包膜最理想。对于同一包膜材料不同用量控释效果顺序：9%用量优于6%用量，优于3%用量。与普通肥料肥料相比，包膜肥料吸湿率大幅下降。 旋转包膜工艺与流化床包膜工艺比较表明：在低用量时，水性包膜材料在流化床包膜工艺与旋转包膜工艺制备肥料控释性能没有差异；在高用量时，流化床包膜工艺比旋转包膜工艺更适合应用于水性高分子材料肥料包膜。