Low-Cost Micromechanically Tunable Optical Devices: Strained Resonator Engineering, Technological Implementation and Characterization

The rapid growth of the optical communication branches and the enormous demand for more bandwidth require novel networks such as dense wavelength division multiplexing (DWDM). These networks enable higher bitrate transmission using the existing optical fibers. Micromechanically tunable optical microcavity devices like VCSELs, Fabry-Pérot filters and photodetectors are core components of these novel DWDM systems. Several air-gap based tunable devices were successfully implemented in the last years. Even though these concepts are very promising, two main disadvantages are still remaining. On the one hand, the high fabrication and integration cost and on the other hand the undesired adverse buckling of the suspended membranes. This thesis addresses these two problems and consists of two main parts: • PECVD dielectric material investigation and stress control resulting in membranes shape engineering. • Implementation and characterization of novel tunable optical devices with tailored shapes of the suspended membranes. For this purposes, low-cost PECVD technology is investigated and developed in detail. The macro- and microstress of silicon nitride and silicon dioxide are controlled over a wide range. Furthermore, the effect of stress on the optical and mechanical properties of the suspended membranes and on the microcavities is evaluated. Various membrane shapes (concave, convex and planar) with several radii of curvature are fabricated. Using this resonator shape engineering, microcavity devices such as non tunable and tunable Fabry-Pérot filters, VCSELs and PIN photodetectors are succesfully implemented. The fabricated Fabry-Pérot filters cover a spectral range of over 200nm and show resonance linewidths down to 1.5nm. By varying the stress distribution across the vertical direction within a DBR, the shape and the radius of curvature of the top membrane are explicitely tailored. By adjusting the incoming light beam waist to the curvature, the fundamental resonant mode is supported and the higher order ones are suppressed. For instance, a tunable VCSEL with 26 nm tuning range, 400µW maximal output power, 47nm free spectral range and over 57dB side mode suppresion ratio (SMSR) is demonstrated. Other technologies, such as introducing light emitting organic materials in microcavities are also investigated.

A Language for Interactive Cooperative Agents

Cooperative behaviour of agents within highly dynamic and nondeterministic domains is an active field of research. In particular establishing highly responsive teamwork, where agents are able to react on dynamic changes in the environment while facing unreliable communication and sensory noise, is an open problem. Moreover, modelling such responsive, cooperative behaviour is difficult. In this work, we specify a novel model for cooperative behaviour geared towards highly dynamic domains. In our approach, agents estimate each other’s decision and correct these estimations once they receive contradictory information. We aim at a comprehensive approach for agent teamwork featuring intuitive modelling capabilities for multi-agent activities, abstractions over activities and agents, and a clear operational semantic for the new model. This work encompasses a complete specification of the new language, ALICA.

Verbal proficiency as fitness indicator: Experimental and comparative research on the evolutionary psychology of language and verbal displays

Summary: Recent research on the evolution of language and verbal displays (e.g., Miller, 1999, 2000a, 2000b, 2002) indicated that language is not only the result of natural selection but serves as a sexually-selected fitness indicator that is an adaptation showing an individual’s suitability as a reproductive mate. Thus, language could be placed within the framework of concepts such as the handicap principle (Zahavi, 1975). There are several reasons for this position: Many linguistic traits are highly heritable (Stromswold, 2001, 2005), while naturally-selected traits are only marginally heritable (Miller, 2000a); men are more prone to verbal displays than women, who in turn judge the displays (Dunbar, 1996; Locke & Bogin, 2006; Lange, in press; Miller, 2000a; Rosenberg & Tunney, 2008); verbal proficiency universally raises especially male status (Brown, 1991); many linguistic features are handicaps (Miller, 2000a) in the Zahavian sense; most literature is produced by men at reproduction-relevant age (Miller, 1999). However, neither an experimental study investigating the causal relation between verbal proficiency and attractiveness, nor a study showing a correlation between markers of literary and mating success existed. In the current studies, it was aimed to fill these gaps. In the first one, I conducted a laboratory experiment. Videos in which an actor and an actress performed verbal self-presentations were the stimuli for counter-sex participants. Content was always alike, but the videos differed on three levels of verbal proficiency. Predictions were, among others, that (1) verbal proficiency increases mate value, but that (2) this applies more to male than to female mate value due to assumed past sex-different selection pressures causing women to be very demanding in mate choice (Trivers, 1972). After running a two-factorial analysis of variance with the variables sex and verbal proficiency as factors, the first hypothesis was supported with high effect size. For the second hypothesis, there was only a trend going in the predicted direction. Furthermore, it became evident that verbal proficiency affects long-term more than short-term mate value. In the second study, verbal proficiency as a menstrual cycle-dependent mate choice criterion was investigated. Basically the same materials as in the former study were used with only marginal changes in the used questionnaire. The hypothesis was that fertile women rate high verbal proficiency in men higher than non-fertile women because of verbal proficiency being a potential indicator of “good genes”. However, no significant result could be obtained in support of the hypothesis in the current study. In the third study, the hypotheses were: (1) most literature is produced by men at reproduction-relevant age. (2) The more works of high literary quality a male writer produces, the more mates and children he has. (3) Lyricists have higher mating success than non-lyric writers because of poetic language being a larger handicap than other forms of language. (4) Writing literature increases a man’s status insofar that his offspring shows a significantly higher male-to-female sex ratio than in the general population, as the Trivers-Willard hypothesis (Trivers & Willard, 1973) applied to literature predicts. In order to test these hypotheses, two famous literary canons were chosen. Extensive biographical research was conducted on the writers’ mating successes. The first hypothesis was confirmed; the second one, controlling for life age, only for number of mates but not entirely regarding number of children. The latter finding was discussed with respect to, among others, the availability of effective contraception especially in the 20th century. The third hypothesis was not satisfactorily supported. The fourth hypothesis was partially supported. For the 20th century part of the German list, the secondary sex ratio differed with high statistical significance from the ratio assumed to be valid for a general population.

The Role of Epistemic Monitoring in Language Comprehension

In der psycholinguistischen Forschung ist die Annahme weitverbreitet, dass die Bewertung von Informationen hinsichtlich ihres Wahrheitsgehaltes oder ihrer Plausibilität (epistemische Validierung; Richter, Schroeder & Wöhrmann, 2009) ein strategischer, optionaler und dem Verstehen nachgeschalteter Prozess ist (z.B. Gilbert, 1991; Gilbert, Krull & Malone, 1990; Gilbert, Tafarodi & Malone, 1993; Herbert & Kübler, 2011). Eine zunehmende Anzahl an Studien stellt dieses Zwei-Stufen-Modell von Verstehen und Validieren jedoch direkt oder indirekt in Frage. Insbesondere Befunde zu Stroop-artigen Stimulus-Antwort-Kompatibilitätseffekten, die auftreten, wenn positive und negative Antworten orthogonal zum aufgaben-irrelevanten Wahrheitsgehalt von Sätzen abgegeben werden müssen (z.B. eine positive Antwort nach dem Lesen eines falschen Satzes oder eine negative Antwort nach dem Lesen eines wahren Satzes; epistemischer Stroop-Effekt, Richter et al., 2009), sprechen dafür, dass Leser/innen schon beim Verstehen eine nicht-strategische Überprüfung der Validität von Informationen vornehmen. Ausgehend von diesen Befunden war das Ziel dieser Dissertation eine weiterführende Überprüfung der Annahme, dass Verstehen einen nicht-strategischen, routinisierten, wissensbasierten Validierungsprozesses (epistemisches Monitoring; Richter et al., 2009) beinhaltet. Zu diesem Zweck wurden drei empirische Studien mit unterschiedlichen Schwerpunkten durchgeführt. Studie 1 diente der Untersuchung der Fragestellung, ob sich Belege für epistemisches Monitoring auch bei Informationen finden lassen, die nicht eindeutig wahr oder falsch, sondern lediglich mehr oder weniger plausibel sind. Mithilfe des epistemischen Stroop-Paradigmas von Richter et al. (2009) konnte ein Kompatibilitätseffekt von aufgaben-irrelevanter Plausibilität auf die Latenzen positiver und negativer Antworten in zwei unterschiedlichen experimentellen Aufgaben nachgewiesen werden, welcher dafür spricht, dass epistemisches Monitoring auch graduelle Unterschiede in der Übereinstimmung von Informationen mit dem Weltwissen berücksichtigt. Darüber hinaus belegen die Ergebnisse, dass der epistemische Stroop-Effekt tatsächlich auf Plausibilität und nicht etwa auf der unterschiedlichen Vorhersagbarkeit von plausiblen und unplausiblen Informationen beruht. Das Ziel von Studie 2 war die Prüfung der Hypothese, dass epistemisches Monitoring keinen evaluativen Mindset erfordert. Im Gegensatz zu den Befunden anderer Autoren (Wiswede, Koranyi, Müller, Langner, & Rothermund, 2013) zeigte sich in dieser Studie ein Kompatibilitätseffekt des aufgaben-irrelevanten Wahrheitsgehaltes auf die Antwortlatenzen in einer vollständig nicht-evaluativen Aufgabe. Die Ergebnisse legen nahe, dass epistemisches Monitoring nicht von einem evaluativen Mindset, möglicherweise aber von der Tiefe der Verarbeitung abhängig ist. Studie 3 beleuchtete das Verhältnis von Verstehen und Validieren anhand einer Untersuchung der Online-Effekte von Plausibilität und Vorhersagbarkeit auf Augenbewegungen beim Lesen kurzer Texte. Zusätzlich wurde die potentielle Modulierung dieser Effeke durch epistemische Marker, die die Sicherheit von Informationen anzeigen (z.B. sicherlich oder vielleicht), untersucht. Entsprechend der Annahme eines schnellen und nicht-strategischen epistemischen Monitoring-Prozesses zeigten sich interaktive Effekte von Plausibilität und dem Vorhandensein epistemischer Marker auf Indikatoren früher Verstehensprozesse. Dies spricht dafür, dass die kommunizierte Sicherheit von Informationen durch den Monitoring-Prozess berücksichtigt wird. Insgesamt sprechen die Befunde gegen eine Konzeptualisierung von Verstehen und Validieren als nicht-überlappenden Stufen der Informationsverarbeitung. Vielmehr scheint eine Bewertung des Wahrheitsgehalts oder der Plausibilität basierend auf dem Weltwissen – zumindest in gewissem Ausmaß – eine obligatorische und nicht-strategische Komponente des Sprachverstehens zu sein. Die Bedeutung der Befunde für aktuelle Modelle des Sprachverstehens und Empfehlungen für die weiterführende Forschung zum Vehältnis von Verstehen und Validieren werden aufgezeigt.

Optimization in the Technological Steps for the Fabrication of Large Area Micromirror Arrays

Micromirror arrays are a very strong candidate for future energy saving applications. Within this work, the fabrication process for these micromirror arrays has been optimized and some steps for the large area fabrication of micromirror modules were performed. At first the surface roughness of the insulation layer of silicon dioxide (SiO2) was investigated. This SiO2 thin layer was deposited on three different type of substrates i.e. silicon, glass and Polyethylene Naphthalate (PEN) substrates. The deposition techniques which has been used are Plasma Enhanced Chemical Vapor Deposition (PECVD), Physical Vapor Deposition (PVD) and Ion Beam Sputter Deposition (IBSD). The thickness of the SiO2 thin layer was kept constant at 150nm for each deposition process. The surface roughness was measured by Stylus Profilometry and Atomic Force Microscopy (AFM). It was found that the layer which was deposited by IBSD has got the minimum surface roughness value and the layer which was deposited by PECVD process has the highest surface roughness value. During the same investigation, the substrate temperature of PECVD was varied from 80° C to 300° C with the step size of 40° C and it was found that the surface roughness keeps on increasing as the substrate holder temperature increases in the PECVD process. A new insulation layer system was proposed to minimize the dielectric breakdown effect in insulation layer for micromirror arrays. The conventional bilayer system was replaced by five layer system but the total thickness of insulation layer remains the same. It was found that during the actuation of micromirror arrays structure, the dielectric breakdown effect was reduced considerably as compared to the bilayer system. In the second step the fabrication process of the micromirror arrays was successfully adapted and transferred from glass substrates to the flexible PEN substrates by optimizing the conventional process recipe. In the last section, a large module of micromirror arrays was fabricated by electrically interconnecting four 10cm×10cm micromirror modules on a glass pane having dimensions of 21cm×21cm.