An Examination of the Attitudes towards Immigration across U.S. Demographic Groups

What demographic backgrounds are associated with a person’s attitudes toward immigrants and immigration policies? Applying group threat theory and contact theory, I propose that race, age, education, political views, and religiosity all affect how people view immigration. To test the hypotheses, I analyze data from the 2014 General Social Survey, in which adults living in households in the United States are randomly selected and interviewed. A subset containing 1,022 respondents who answered every question relevant to this study is selected from the 2014 GSS. The univariate analysis shows that most Americans do not agree with the statement that immigrants undermine American culture, and that Americans are divided on whether the number of immigrants should be increased nowadays. The multivariate result indicates that education and political views are the most significant predictors of how one views immigrants and immigration policies, correspondingly, while race, age, and religiosity have no statistically significant relationships with either dependent variable. Statistical findings support the hypothesis that the more liberal a person is, the more likely the person is to agree that immigrants do not undermine American culture and to say that the number of immigrants nowadays should be increased. Contact theory is consistent with the result of this study. However, the findings also demonstrate that immigration is a complicated issue. This study is valuable in understanding the acceptance of immigrants across demographic groups. It also invites additional research on this important topic that will affect the future of th

Semiconductor ring lasers for high speed communications

The work described in this thesis is aimed at exploring the possibility of optically integrating an OTDM transmitter operating at 4X10Gb/s on an appropriate substrate. It has been shown that such an OTDM transmitter system could be integrated on III-V semiconductor quantum well (QW) substrates if the design of the substrate, the choice of fabrication techniques and the design of the devices are carefully considered. Suitable device structures for the three main kinds of devices involved in OTDM transmitters, namely light source, optical multiplexers (couplers) and optical modulators, have been discussed. Significant progress regarding these aspects, both theoretical and experimental, has been achieved. In this work, it has been intended to investigate all the devices from the integration point of view. This has been reflected in many aspects in the device design and fabrication process. Integration has always been a very important factor to consider in the determination of substrate material structure, device configuration, waveguide structure and fabrication techniques. As a result, the devices developed in this project are suitable for the proposed purpose of an integrated OTDM transmitter system. Investigation into integration techniques has also been carried out. The most important was to introduce bandgap difference on a semiconductor QW material. IFVD technique is studied and produced some encouraging results such as the extended cavity SRL, which integrates an active section with a passive MMI coupler. Vertically coupled waveguide structures have also been invstigated in an attempt to produce extended cavity lasers. The design considerations of extended cavity lasers employing this waveguide structure have been discussed

Tailoring Accelerating Beams in Phase Space

An appropriate design of wavefront will enable light fields propagating along arbitrary trajectories thus forming accelerating beams in free space. Previous ways of designing such accelerating beams mainly rely on caustic methods, which start from diffraction integrals and only deal with two-dimensional fields. Here we introduce a new perspective to construct accelerating beams in phase space by designing the corresponding Wigner distribution function (WDF). We find such a WDF-based method is capable of providing both the initial field distribution and the angular spectrum in need by projecting the WDF into the real space and the Fourier space respectively. Moreover, this approach applies to the construction of both two- and three-dimensional fields, greatly generalizing previous caustic methods. It may therefore open up a new route to construct highly-tailored accelerating beams and facilitate applications ranging from particle manipulation and trapping to optical routing as well as material processing.Comment: 8 pages, 6 figure

Spin-orbit interaction of light induced by transverse spin angular momentum engineering

We report the first demonstration of a direct interaction between the extraordinary transverse spin angular momentum in evanescent waves and the intrinsic orbital angular momentum in optical vortex beams. By tapping the evanescent wave of whispering gallery modes in a micro-ring-based optical vortex emitter and engineering the transverse spin state carried therein, a transverse-spin-to-orbital conversion of angular momentum is predicted in the emitted vortex beams. Numerical and experimental investigations are presented for the proof-of-principle demonstration of this unconventional interplay between the spin and orbital angular momenta, which could provide new possibilities and restrictions on the optical angular momentum manipulation techniques on the sub-wavelength scale. This phenomenon further gives rise to an enhanced spin-direction coupling effect in which waveguide or surface modes are unidirectional excited by incident optical vortex, with the directionality jointly controlled by spin-orbit states. Our results enrich the spin-orbit interaction phenomena by identifying a previously unknown pathway between the polarization and spatial degrees of freedom of light, and can enable a variety of functionalities employing spin and orbital angular momenta of light in applications such as communications and quantum information processing

Spiral Transformation for High-Resolution and Efficient Sorting of Optical Vortex Modes

Mode sorting is an essential function for optical multiplexing systems that exploit the orthogonality of the orbital angular momentum mode space. The familiar log-polar optical transformation provides a simple yet efficient approach whose resolution is, however, restricted by a considerable overlap between adjacent modes resulting from the limited excursion of the phase along a complete circle around the optical vortex axis. We propose and experimentally verify a new optical transformation that maps spirals (instead of concentric circles) to parallel lines. As the phase excursion along a spiral in the wave front of an optical vortex is theoretically unlimited, this new optical transformation can separate orbital angular momentum modes with superior resolution while maintaining unity efficiency