23 research outputs found
Electro-optic modulation measurement technique and enhancement
No full textMålet med dette Ph.d. projekt var at realisere en optisk kontakt i polet glas SiO2, hvor der skal bruges mindre end 300V til at skifte kontakten. Dette mål blev ikke nået. En forklaring på de høje, men hurtigt aftagende polingresultater publiceret i halvfemserne er fundet eksperimentelt ved undersøgelse af en prøve med revner i topglasset. Ud fra dette konkluderes, at tredjeordensulineariteten (3) af glas er en faktor 10 for lav til at opnå en interessant polet kontakt i SiO2. For at forøge den polinginducerede linearitet skal materialekonstanten (3) forøges. En mulighed, som blev fundet, er at anvende silicium rigt nitrid til kerneglasset, da det er 5 gange mere ulineart end det oprindeligt anvendte materiale Ge:SiON. Der blev udviklet en meget præcis målemetode, som kan bestemme både Efrozen-in, (2), og (3). Metoden kan bruges til måling på alle relevante prøver og usikkerheden af de målte resultater er ~5%. Da fotoniske krystalbølgeledere blev undersøgt, blev der introduceret en ikke-linear koefficient i siliciumet. Dette blev brugt til at lave den første eksperimentelle verifikation, som efterviser at effekten af ikke-lineariteten skalere lineært med gruppeindekset. Til måling af gruppeindekset blev der udviklet en direkte metode baseret på måling af transmissionstiden for en optisk puls. Der blev fundet en verdensrekord for et direkte målt gruppeindeks (ng = 230). Rekorden blev målt for en 20 m symmetrisk W1-bølgeleder. Overførslen af den inducerede ikke-linearitet til en konventionel indeks bølgeleder blev påbegyndt. Når denne koefficient opnås i en sådan bølgeleder vil fremtidige forsøg kunne fastlægge hvor stor den inducerede ikke-lineare koefficient i silicium kan blive. Fremtidige forsøg vil også fastlægge om den inducerede effekt eksisterer for hurtig elektrisk modulation
Quantification of Bimodal Permeability Distributions in Sandstone Using 2D and 3D Imaging Techniques and Computational Analysis
No full textPlanar glass devices for efficient periodic poling
No full textWe demonstrate that frequency-converting devices of high quality can be realised with glass poling. The devices, made with silica-on-silicon technology, are poled with periodic, embedded electrodes, and used for second-harmonic generation. We obtain precise control of the quasi phase-matching wavelength and bandwidth, and a normalised conversion efficiency of 1.4×10-3 %/W/cm2 which, to our knowledge, is the highest obtained so far with periodic glass poling
Glass Waveguides for Periodic Poling
No full textPlanar silica-based waveguide devices have been developed for second-harmonic generation by poling with periodic electrodes. We show that detrimental charge transport can occur along interfaces, but with proper choice of fabrication, high-quality devices are obtained
Poled-glass devices: Influence of surfaces and interfaces
No full textDevices in periodically poled glass must have a large periodic variation of the built-in field. We show that the periodic variation can be severely degraded by charge dynamics taking place at the external (glass–air) interface or at internal (glass–glass) interfaces if the interfaces have imperfections. The problem of the external interface can be solved by poling with periodic electrodes that are buried inside the glass, in many cases improving the poling efficiency dramatically. Internal interfaces can be addressed by the proper choice of waveguide design and processing. Without poling the device, one can reveal the existence of imperfect interfaces by use of electric field induced second-harmonic generation
Banking Regulation and Prompt Corrective Action
No full textWe explore the rationale for regulatory rules that prohibit banks from developing some of their natural activities when their capital level is low, as epitomized by the US Prompt Corrective Action (PCA). This paper is built on two insights. First, in a moral hazard setting, capital requirement regulation may force banks to hold a large fraction of safe assets which, in turn, may lower their incentives to monitor risky assets. Second, agency problems may be more severe in certain asset classes than in others. Taken together, these two ideas explain why, surprisingly, capital regulation, which may cope with risk and adverse selection, is unable to address issues related to moral hazard. Hence, instead of forcing banks to hold a large fraction of safe assets, prohibiting some types of investment and allowing ample scope of investment on others may be the only way to preserve incentives and guarantee funding. In particular, providing incentives to monitor investments in the most opaque asset classes may prove to be excessively costly in terms of the required capital and thus inefficient. We show that the optimal capital regulation consists of a rule that a) allows well capitalized banks to freely invest any amount in any risky asset, b) prohibits banks with intermediate levels of capital to invest in the most opaque risky assets, and c) prohibits undercapitalized banks to invest in any risky asset.banking, prudential regulation, moral hazard
Glass devices for efficient second harmonic generation
No full textWe show here that quasi-phase matched (QPM) planar nonlinear devices of high quality can be fabricated by means of periodic poling of the glass. The devices, used for second-harmonic generation (SHG), have accurately-controlled centre wavelengths, and the normalised conversion efficiencies are approximately one order of magnitude higher than what has previously been reported for periodically poled glass. In conclusion, we have demonstrated that high-quality nonlinear QPM devices can be fabricated in glass-on-silicon. The technology is easily adaptable to any desired wavelength (e.g. 1550 nm) and can be used not only for SHG, but for wavelength conversion processes in general
