Oversized waveguides and resonators for millimeter waves

If real monolithic systems^* turn out to be impractical at millimeter-wave frequencies, oversized waveguides and resonators are useful alternatives in component and system design. Low losses, high Q factors, and inexpensive manufacturing are their advantages. Starting with an explanation of the term oversized, the loss reductions, Q factors, inherently oversized guides, such as the H-guide and its modifications, excitation of higher-order modes, laterally oversized H-guides, and the effects of coupling are described. A brief consideration of applications concludes the presentation.     

Weakly coupled bound states in quantum waveguides

We study the eigenvalue spectrum of Dirichlet Laplacians which model quantum waveguides associated with tubular regions outside of a
bounded domain. Intuitively, our principal new result in two dimensions asserts that any domain obtained by adding an arbitrarily small ``bump' to the tube (i.e., , open and connected, outside a bounded region) produces at least one positive eigenvalue below the essential spectrum of the Dirichlet Laplacian . For sufficiently small ( abbreviating Lebesgue measure), we prove uniqueness of the ground state of and derive the ``weak coupling' result using a Birman-Schwinger-type analysis. As a corollary of these results we obtain the following surprising fact: Starting from the tube with Dirichlet boundary conditions at , replace the Dirichlet condition by a Neumann boundary condition on an arbitrarily small segment , , of . If denotes the resulting Laplace operator in , then has a discrete eigenvalue in no matter how small is.

     

Anhydrous Sol-Gel Synthesis of Titania-Doped Siloxane Polymer for Integrated Optics

Sol-gel synthesis of organic-inorganic hybrid materials for planar waveguides and devices has received growing interest due to its low-cost processing and good suitability for doping. Titania is an important optical dopant, but homogeneous incorporation of titania in silica is difficult to be achieved by the conventional sol-gel process (aqueous system) because of the significant difference between the hydrolysis rates of the precursors. In this paper, we report an anhydrous sol-gel process for synthesising titania-doped siloxane polymers. The process consists of a hydrolysis of 3-methacryloxypropyltrimethoxysilane (MPS) with boric acid under anhydrous conditions, and a condensation with dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPhDMS) and titanium ethoxide (TET). Optical characterisations for the produced titania-doped polymer were performed, and results showed that TET doping is useful for reducing the OH concentration of the synthesised polymer and is also effective for improving the optical quality of spin coatings. DMDMS and DPhDMS are favourable in reducing the birefringence and in increasing the thermostability of the material, and the methacryl groups of MPS are UV-polymerizable, which is useful for low cost fabrication of waveguides by photolithographic process. The results of ellipsometry scanning measurements show that titania is homogeneously incorporated in the hybrid matrix, suggesting that the anhydrous sol-gel process is useful for preparation of UV-sensitive titania-doped siloxane polymers for optical applications.     

Control of Semiconductor Particle Size in Sol-Gel Thin Films

Thin silica and silica-titania films containing CdS and PbS quantum size particles were obtained by separate preparation of the matrix and the colloidal sols and successive mixing. Sulfide particles were obtained by reaction of metal acetates with thioacetamide and control of particle size was achieved by surface capping agents. Powders and thin films deposited on soda-lime slides were prepared and characterized by XRD. Absorption spectra were recorded on films. The nonlinear refractive index was measured by anm-line technique on a CdS-doped sample. The nonlinear effect was found to be reversible and an ₂ value of −3 10⁻⁹ cm²/kW was measured.     

Fabrication of optical waveguide devices using gas‐assisted UV micro/nanoimprinting with soft mold

Wavelength limitation and diffraction of light are the bottlenecks encountered in the production of structures by conventional lithography. Nano‐imprinting has been a potential process for mass production of nanometer structures at low cost. This paper reports an innovative process to replicate the ridge‐shaped microstructures on the silicon mold onto the photoresist using gas‐assisted pressing mechanism and soft mold. The microstructures on the silicon mold are replicated unto PC films. The soft mold is obtained by casting the PDMS with the PC film as templates, PDMS mold and UV‐curable photoresist are brought into contact, and are pressurized by gas and cured by UV‐light at the same time. After curing, structures for optical wave guilding can be obtained, In this process, through the control of gas pressure, the residual layer of the ridge‐shaped component for light guilding can eliminated. Etching is no longer needed to get rid of the residual layer. This process is effective for mass production for replication of microstructures at low cost. Copyright © 2007 John Wiley & Sons, Ltd.     

微乳液聚合

介绍了微乳化工艺和助乳化剂对单体液滴大小、乳化剂的吸附、乳液稳定性、聚合动力学和乳胶粒子大小及分布的影响,并讨论了单体亚微液滴成核机理。     

Scalar analysis of arbitrarily shaped optical waveguides by full guided mode expansion method and optimized sine method

This paper shows that the full guided mode expansion method and the optimized sine method, with a rather rigorous procedure of determing the dimensions of reference waveguides, provide simple, fast and accurate way for the scalar analysis of arbitrarily shaped optical waveguides. Use of a smaller matrix results in good agreement with previous works.     

On propagation through long step tapers

In integrated optics, tapered waveguides usually possess step changes in waveguide width or other dimensions, due to lithographic limitations. We present a theoretical asymptotic analysis of the effect of these steps when compared with the ideal smooth taper. We present some figures for the size of the effect, conclude that the effect is significant in certain situation and that making the taper too long will reduce its performance, or in the worst instance cause the taper to function as badly as a butt join.     

Potassium Titanyl Phosphate and Its Isomorphs: Growth,Properties, and Applications

Potassium titanyl phosphate (KTP) and its isomorphs have received enormous attention in the last 2 decades. In particular, KTP assumes importance due to its large nonlinear optic and electrooptic coefficients together with the broad thermal and angular acceptance for second harmonic generation. This article provides an overview of the material aspects, structural, physical, and chemical properties and device feasibility of the KTP family of crystals. Some of the current areas of research and development along with their significance in understanding the physical properties as well as device applications are addressed. Optical waveguide fabrication processes and characteristics with their relevance to the present-day technology are highlighted. Studies performed so far have enabled us to understand the fundamental aspects of these materials and what needs to be pursued vigorously is the exploitation of their device applications to the maximum extent.     

A study of negative index grating growth in germanosilicate planar waveguides

Negative index grating growth in germanosilicate planar waveguides fabricated by hollow cathode(HC)-PECVD are characterised in detail. Differences in index modulation growth, both in terms of the grating strength and the rate of negative index change as a function of fluence, are observed. On the other hand, the average index change of the two polarisation states shows the same rate of growth revealing that grating growth is dependent on more than on index change triggered by simple isotropic uv-defect interactions.