Optical properties of polarization-dependent geometric phase elements with partially polarized light

The behavior of geometric phase elements illuminated with partially polarized monochromatic beams is investigated both theoretically and experimentally. The element discussed in this paper is composed of wave plates with π-retardation and a space-variant orientation angle. We found that a beam emerging from such an element comprises two polarization orders; right-and left-handed circularly polarized states with conjugate geometric phase modification. This phase equals twice the orientation angle of the space-variant wave plate comprising the element. Apart from the two polarization orders, the emerging beam coherence polarization matrix includes a “vectorial interference matrix” which contains information concerning the correlation between the two orthogonal, circularly polarized portions of the incident beam. In this paper we measure this correlation by a simple interference experiment. In addition, we found that the equivalent mutual intensity of the emerging beam is modulated according to the geometric phase induced by the element. Other interesting phenomena concerning propagation will be discussed theoretically and demonstrated experimentally. The experiment made use of a spherical geometric phase element that was realized by use of a space-variant subwavelength grating illuminated with CO₂ laser radiation of 10.6 μm wavelength.     

间插取样光纤光栅多通道滤波器

对间插取样光纤光栅进行了理论分析和数值模拟,并依照理论分析及数值模拟的结果进行了实验研究,采用逐点扫描曝光工艺首次制作出具有10个以上通道数的光纤光栅梳状滤波器。这种方法工艺简单,控制精度要求低,是一种具有良好实用化前景的多通道光纤光栅滤波器制作技术。     

A Compact and Transmissive Device for Dispersion-Compensation of Ultra-short Optical Pulses

We show by computer simulation that a coupled-cavity-type multilayered structure is suitable for the transmissive compensation of group-velocity dispersion for optical pulses of subpicosecond length, and can thus be used to make a simple, compact, and transmissive dispersion-compensation device.     

光致折变布拉格光栅实验研究

本文介绍了 2 48nm、Kr F准分子激光经过石英相位掩膜版的空间调制 ,在载氢增敏处理过的通信光纤与 B/Ge光纤上分别写入光致折变布拉格光栅的实验研究。经实验测定 ,在光栅布拉格波长上 (λH2 =15 46 .45 5 4nm ,λB/Ge=15 45 .15 5 nm) ,两种光栅反射率均大于 99% ,3d B带宽分别为 0 .12 9nm和 0 .182 nm。经比较 ,B/ Ge光纤比氢载光纤具有更好的光敏性和热稳定性     

A combined crossed molecular beam and quasiclassical trajectory study of the Titan-relevant N(2D) + D2O reaction

Following a recent investigation on the N(²D) + H₂O reaction [Homayoon et al., J. Phys. Chem. Lett. 5, 3508 (2014)], we report on an experimental and theoretical study of the isotopologue N(²D) + D₂O reaction. Crossed molecular beam (CMB) experiments were conducted at a collision energy of 10.3 kcal mol^–1. Quasiclassical trajectory calculations were performed on a recent potential energy surface to derive the centre-of-mass functions necessary to simulate the CMB laboratory distributions. Excellent agreement was found. The importance of the channel leading to HON/DON was confirmed. The inclusion of this channel, in addition to that leading to the isomer HNO/DNO, can affect the models considering the coupling between nitrogen and oxygen chemistry in the upper atmosphere of Titan.     

High resolution instrumentation system for fibre-Bragg grating aerospace sensors

A passive technique for high-resolution detection of the wavelength of peak reflection from fibre Bragg grating (FBG) sensors is presented. The approach, based on a de-convolution of the FBG spectrum and the spectrometer resolution, essentially overcomes the low spectral resolution (≈0.1 nm) associated with commercial spectrometers employing CCD detection. The performance of two algorithms, the Centroid Detection algorithm (CDA) and the least squares method (LSQ), are compared. The LSQ algorithm offers resolution enhancement of at least two orders of magnitude and is shown to be independent of the FBG intensity and bandwidth over a broad range.     

Processes limiting the rate of response in photorefractive composites

The processes limiting the rate of response of highly diffractive, reorientationally enhanced photorefractive polymer composite materials are identified from a series of degenerate four wave mixing and Mach–Zehnder interferometric measurements. In the regime of low intensity writing beams charge generation limits the rate of holographic grating formation, but at higher intensities charge transport or reorientation of dye molecules can restrict the rate of grating formation more strongly. A grating risetime of 540 ms is observed in a composite of high dye content with high reorientational mobility of the dye molecules. In this case it is proposed that the charge carrier mobility of the doped poly(N-vinylcarbazole):2,4,7-trinitro-9-fluorenone (PVK:TNF) matrix is the principal limiting factor in grating response rates.     

A Novel Fabrication Technique of Long Period Fiber Gratings

１ＩｎｔｒｏｄｕｃｔｉｏｎＳｉｎｃｅｔｈｅｄｉｓｃｏｖｅｒｙｏｆｐｈｏｔｏｓｅｎｓｉｔｉｖｉｔｙｉｎｇｅｒｍａｎｏｓｉｌｉｃａｔｅｏｐｔｉｃａｌｆｉｂｅｒｓｂｙＨｉｌｅｔａｌ．ｉｎ１９７８［１］，ｓｉｇｎｉｆｉｃａｎｔｐｒｏｇｒｅｓｈａｓｂｅｅｎｍａ...     

A novel high-resolution interference spectrometer

A novel precision wavemeter is presented with a resolution of better than 0·01 nm. A Sagnac interferometer with two diffraction gratings forms the basis of the instrument. Using spatial heterodyning techniques and a CCD camera/frame grabber data acquisition system allows fast computer control and power spectrum analysis. The mode structure and mode hopping characteristics of a typical laser diode were examined as a function of diode injection current.     

Coupling characteristics of laterally coupled gratings with slots

Laterally-coupled ridge-waveguide distributed feedback lasers fabricated without epitaxial regrowth steps have the advantages of process simplification and low cost. We present a laterally coupled grating with slots. The slots etched between the ridge and grating area are designed to suppress the lateral diffusion of carriers and to reduce the influence of the aspect-ratio-dependent-etching effect on the grating morphology in the etching process. Moreover, the grating height in this structure can be decreased to lower the aspect ratio significantly, which is advantageous over the conventional laterally coupled ridge waveguide gratings. The effects of five main structural parameters on the coupling characteristics of gratings are studied by MODE Solutions. It is found that varying the lateral width of the grating can be used as an effective way to tune the coupling strength; narrow slots (100 nm and 300 nm) and wide ridge (2 μm-4 μm) promote the stability of grating coupling coefficient and device performance. It is important to note that the grating bottom should be fabricated precisely. The comparative study of carrier distribution and mode field distribution shows that the introduction of narrow slots can strengthen the competitive advantage and stability of the fundamental mode.