Academic literature on the topic 'Micro-résonateurs à mode de galerie'

Understanding the relationship between degassing, crystallization processes and eruption style is a central goal in volcanology, in particular how these processes modulate the magnitude and timing of cyclical Vulcanian explosions in intermediate magmas. To investigate the influence of variations in crystal micro-textures on magma rheology and eruption dynamics, we conducted high-temperature (940°C) uniaxial compression experiments at conditions simulating a shallow volcanic conduit setting on eight samples of high-crystallinity andesite with variable plagioclase microlite populations from the 2004 to 2010 Vulcanian explosions of Galeras volcano, Colombia. Experiments were conducted at different strain rates to measure the rate-dependence of apparent viscosities and assess the dominant deformation processes associated with shear. Variations in plagioclase micro-textures are associated with apparent viscosities spanning over one order of magnitude for a given strain rate. Samples with low numbers of large prismatic microlites behaved consistently with published rheological laws for crystalline dome samples, and displayed extensive micro-cracking. Samples with high numbers of small tabular microlites showed a lower apparent viscosity and were less shear-thinning. The data suggest a spectrum of rheological behavior controlled by concurrent variations in microlite number, size and shape. We use previously published micro-textural data for time-constrained samples to model the apparent viscosity of magma erupted during the 2004–2010 sequence of Vulcanian explosions and compare these results with observed SO2 fluxes. We propose that variations in magma decompression rate, which are known to produce systematic textural differences in the plagioclase microlite cargo, govern differences in magma rheology in the shallow conduit. These rheological differences are likely to affect the rate at which magma densifies as a result of outgassing, leading to magmatic plugs with a range of porosities and permeabilities. The existence of magmatic plugs with variable physical properties has important implications for the development of critical overpressure driving Vulcanian explosions, and thus for hazard assessment during volcanic crises. We suggest a new conceptual model to explain eruption style at andesitic volcanoes based on micro-textural and rheological differences between “plug-forming” and “dome-forming” magma. We advance that existing rheological laws describing the behavior of andesitic magma based on experiments on dome rocks are inappropriate for modeling large Vulcanian explosions (∼106 m3), as the magma involved in these eruptions lacks the characteristics required to form exogenous lava domes.

Introduction: Socialism – from Eternal Reality to Passing DreamThe Year of Revolutions in 1989 presaged the end of the Cold War. For many people, it must have felt like the end of the Twentieth Century, and the 1990s a period of waiting for the Millennium. However, the 1990s was, in fact, a period of profound transformation in the post-Socialist world.In early representations of Socialism’s end, a dominant narrative was that of collapse. Dramatic events, such as the dismantling of the Berlin Wall in Germany enabled representation of the end as an unexpected moment. Senses of unexpectedness rested on erstwhile perceptions of Socialism as eternal.In contrast, the 1990s came to be a decade of revision in which thinking switched from considering Socialism’s persistence to asking, “why it went wrong?” I explore this question in relation to former-Yugoslavia. In brief, the Socialist Federal Republic of Yugoslavia (SFRY) was replaced through the early 1990s by six independent nation states: Bosnia and Herzegovina, Croatia, Macedonia, Montenegro, Serbia, and Slovenia. Kosovo came much later. In the states that were significantly ethnically mixed, the break-up was accompanied by violence. Bosnia in the 1990s will be remembered for an important contribution to the lexicon of ideas – ethnic cleansing.Revisionist historicising of the former-Yugoslavia in the 1990s was led by the scholarly community. By and large, it discredited the Ancient Ethnic Hatreds (AEH) thesis commonly held by nationalists, simplistic media commentators and many Western politicians. The AEH thesis held that Socialism’s end was a consequence of the up-swelling of primordial (natural) ethnic tensions. Conversely, the scholarly community tended to view Socialism’s failure as an outcome of systemic economic and political deficiencies in the SFRY, and that these deficiencies were also, in fact the root cause of those ethnic tensions. And, it was argued that had such deficiencies been addressed earlier Socialism may have survived and fulfilled its promise of eternity (Verdery).A third significant perspective which emerged through the 1990s was that the collapse of Socialism was an outcome of the up-swelling of, if not primordial ethnic tensions then, at least repressed historical memories of ethnic tensions, especially of the internecine violence engendered locally by Nazi and Italian Fascist forces in WWII. This perspective was particularly en vogue within the unusually rich arts scene in former-Yugoslavia. Its leading exponent was Slovenian avant-garde rock band Laibach.In this article, I consider Laibach’s career and methods. For background the article draws substantially on Alexei Monroe’s excellent biography of Laibach, Interrogation Machine: Laibach and NSK (2005). However, as I indicate below, my interpretation diverges very significantly from Monroe’s. Laibach’s most significant body of work is the cover versions of Western pop songs it recorded in the middle part of its career. Using a technique that has been labelled retroquotation (Monroe), it subtly transforms the lyrical content, and radically transforms the musical arrangement of pop songs, thereby rendering them what might be described as martial anthems. The clearest illustration of the process is Laibach’s version of Opus’s one hit wonder “Live is Life”, which is retitled as “Life is Life” (Laibach 1987).Conventional scholarly interpretations of Laibach’s method (including Monroe’s) present it as entailing the uncovering of repressed forms of individual and collective totalitarian consciousness. I outline these ideas, but supplement them with an alternative interpretation. I argue that in the cover version stage of its career, Laibach switched its attention from seeking to uncover repressed totalitarianism towards uncovering repressed memories of ethnic tension, especially from WWII. Furthermore, I argue that its creative medium of Western pop music is especially important in this regard. On the bases of ethnographic fieldwork conducted in Bosnia (University of Melbourne Human Ethics project 1544213.1), and of a reading of SFRY’s geopolitical history, I demonstrate that for many people, Western popular cultural forms came to represent the quintessence of what it was to be Yugoslav. In this context, Laibach’s retroquotation of Western pop music is akin to a broader cultural practice in the post-SFRY era in which symbols of the West were iconoclastically transformed. Such transformation served to reveal a public secret (Taussig) of repressed historic ethnic enmity within the very heart of things that were regarded as quintessentially and pan-ethnically Yugoslav. And, in so doing, this delegitimised memory of SFRY ever having been a properly functioning entity. In this way, Laibach contributed significantly to a broader process in which perceptions of Socialist Yugoslavia came to be rendered less as a reality with the potential for eternity than a passing dream.What Is Laibach and What Does It Do?Originally of the industrial rock genre, Laibach has evolved through numerous other genres including orchestral rock, choral rock and techno. It is not, however, a rock group in any conventional sense. Laibach is the musical section of a tripartite unit named Neue Slowenische Kunst (NSK) which also encompasses the fine arts collective Irwin and a variety of theatre groups.Laibach was the name by which the Slovenian capital Ljubljana was known under the Austrian Habsburg Empire and then Nazi occupation in WWII. The choice of name hints at a central purpose of Laibach and NSK in general, to explore the relationship between art and ideology, especially under conditions of totalitarianism. In what follows, I describe how Laibach go about doing this.Laibach’s central method is eclecticism, by which symbols of the various ideological regimes that are its and the NSK’s subject matter are intentionally juxtaposed. Eclecticism of this kind was characteristic of the postmodern aesthetics typical of the 1990s. Furthermore, and counterintuitively perhaps, postmodernism was as much a condition of the Socialist East as it was the Capitalist West. As Mikhail N. Epstein argues, “Totalitarianism itself may be viewed as a specific postmodern model that came to replace the modernist ideological stance elaborated in earlier Marxism” (102). However, Western and Eastern postmodernisms were fundamentally different. In particular, while the former was largely playful, ironicising and depoliticised, the latter, which Laibach and NSK may be regarded as being illustrative of, involved placing in opposition to one another competing and antithetical aesthetic, political and social regimes, “without the contradictions being fully resolved” (Monroe 54).The performance of unresolved contradictions in Laibach’s work fulfils three principal functions. It works to (1) reveal hidden underlying connections between competing ideological systems, and between art and power more generally. This is evident in Life is Life. The video combines symbols of Slovenian romantic nationalism (stags and majestic rural landscapes) with Nazism and militarism (uniforms, bodily postures and a martial musical arrangement). Furthermore, it presents images of the graves of victims of internecine violence in WWII. The video is a reminder to Slovenian viewers of a discomforting public secret within their nation’s history. While Germany is commonly viewed as a principal oppressor of Slovenian nationalism, the rural peasantry, who are represented as embodying Slovenian nationalism most, were also the most willing collaborators in imperialist processes of Germanicisation. The second purpose of the performance of unresolved contradictions in Laibach’s work is to (2) engender senses of the alienation, especially as experienced by the subjects of totalitarian regimes. Laibach’s approach in this regard is quite different to that of punk, whose concern with alienation - symbolised by safety pins and chains - was largely celebratory of the alienated condition. Rather, Laibach took a lead from seminal industrial rock bands such as Einstürzende Neubauten and Throbbing Gristle (see, for example, Walls of Sound (Throbbing Gristle 2004)), whose sound one fan accurately describes as akin to, “the creation of the universe by an angry titan/God and a machine apocalypse all rolled into one” (rateyourmusic.com). Certainly, Laibach’s shows can be uncomfortable experiences too, involving not only clashing symbols and images, but also the dissonant sounds of, for example, martial music, feedback, recordings of the political speeches of totalitarian leaders and barking dogs, all played at eardrum-breaking high volumes. The purpose of this is to provide, as Laibach state: “a ritualized demonstration of political force” (NSK, Neue Slowenische Kunst 44). In short, more than simply celebrating the experience of totalitarian alienation, Laibach’s intention is to reproduce that very alienation.More than performatively representing tyranny, and thereby senses of totalitarian alienation, Laibach and NSK set out to embody it themselves. In particular, and contra the forms of liberal humanism that were hegemonic at the peak of their career in the 1990s, their organisation was developed as a model of totalitarian collectivism in which the individual is always subjugated. This is illustrated in the Onanigram (NSK, Neue Slowenische Kunst), which, mimicking the complexities of the SFRY in its most totalitarian dispensation, maps out in labyrinthine detail the institutional structure of NSK. Behaviour is governed by a Constitution that states explicitly that NSK is a group in which, “each individual is subordinated to the whole” (NSK, Neue Slowenische Kunst 273). Lest this collectivism be misconceived as little more than a show, the case of Tomaž Hostnik is instructive. The original lead singer of Laibach, Hostnik committed ritual suicide by hanging himself from a hayrack, a key symbol of Slovenian nationalism. Initially, rather than mourning his loss, the other members of Laibach posthumously disenfranchised him (“threw him out of the band”), presumably for his act of individual will that was collectively unsanctioned.Laibach and the NSK’s collectivism also have spiritual overtones. The Onanigram presents an Immanent Consistent Spirit, a kind of geist that holds the collective together. NSK claim: “Only God can subdue LAIBACH. People and things never can” (NSK, Neue Slowenische Kunst 289). Furthermore, such rhetorical bombast was matched in aspiration. Most famously, in one of the first instances of a micro-nation, NSK went on to establish itself as a global and virtual non-territorial state, replete with a recruitment drive, passports and anthem, written and performed by Laibach of course. Laibach’s CareerLaibach’s career can be divided into three overlapping parts. The first is its career as a political provocateur, beginning from the inception of the band in 1980 and continuing through to the present. The band’s performances have touched the raw nerves of several political actors. As suggested above, Laibach offended Slovenian nationalists. The band offended the SFRY, especially when in its stage backdrop it juxtaposed images of a penis with Marshal Josip Broz “Tito”, founding President of the SFRY. Above all, it offended libertarians who viewed the band’s exploitation of totalitarian aesthetics as a route to evoking repressed totalitarian energies in its audiences.In a sense the libertarians were correct, for Laibach were quite explicit in representing a third function of their performance of unresolved contradictions as being to (3) evoke repressed totalitarian energies. However, as Žižek demonstrates in his essay “Why Are Laibach and NSK Not Fascists”, Laibach’s intent in this regard is counter-totalitarian. Laibach engage in what amounts to a “psychoanalytic cure” for totalitarianism, which consists of four envisaged stages. The consumers of Laibach’s works and performances go through a process of over-identification with totalitarianism, leading through the experience of alienation to, in turn, disidentification and an eventual overcoming of that totalitarian alienation. The Žižekian interpretation of the four stages has, however been subjected to critique, particularly by Deleuzian scholars, and especially for its psychoanalytic emphasis on the transformation of individual (un)consciousness (i.e. the cerebral rather than bodily). Instead, such scholars prefer a schizoanalytic interpretation which presents the cure as, respectively collective (Monroe 45-50) and somatic (Goddard). Laibach’s works and pronouncements display, often awareness of such abstract theoretical ideas. However, they also display attentiveness to the concrete realities of socio-political context. This was reflected especially in the 1990s, when its focus seemed to shift from the matter of totalitarianism to the overriding issue of the day in Laibach’s homeland – ethnic conflict. For example, echoing the discourse of Truth and Reconciliation emanating from post-Apartheid South Africa in the early 1990s, Laibach argued that its work is “based on the premise that traumas affecting the present and the future can be healed only by returning to the initial conflicts” (NSK Padiglione).In the early 1990s era of post-socialist violent ethnic nationalism, statements such as this rendered Laibach a darling of anti-nationalism, both within civil society and in what came to be known pejoratively as the Yugonostagic, i.e. pro-SFRY left. Its darling status was cemented further by actions such as performing a concert to celebrate the end of the Bosnian war in 1996, and because its ideological mask began to slip. Most famously, when asked by a music journalist the standard question of what the band’s main influences were, rather than citing other musicians Laibach stated: “Tito, Tito and Tito.” Herein lies the third phase of Laibach’s career, dating from the mid-1990s to the present, which has been marked by critical recognition and mainstream acceptance, and in contrasting domains. Notably, in 2012 Laibach was invited to perform at the Tate Modern in London. Then, entering the belly of what is arguably the most totalitarian of totalitarian beasts in 2015, it became the first rock band to perform live in North Korea.The middle part in Laibach’s career was between 1987 and 1996. This was when its work consisted mostly of covers of mainstream Western pop songs by, amongst others Opus, Queen, The Rolling Stones, and, in The Final Countdown (1986), Swedish ‘big hair’ rockers. It also covered entire albums, including a version of Andrew Lloyd Webber’s rock opera Jesus Christ Superstar. No doubt mindful of John Lennon’s claim that his band was more popular than the Messiah himself, Laibach covered the Beatles’ final album Let It Be (1970). Highlighting the perilous hidden connections between apparently benign and fascistic forms of sedentarism, lead singer Milan Fras’ snarling delivery of the refrain “Get Back to where you once belong” renders the hit single from that album less a story of homecoming than a sinister warning to immigrants and ethnic others who are out of place.This career middle stage invoked critique. However, commonplace suggestions that Laibach could be characterised as embodying Retromania, a derivative musical trend typical of the 1990s that has been lambasted for its de-politicisation and a musical conservatism enabled by new sampling technologies that afforded a forensic documentary precision that prohibits creative distortion (Reynolds), are misplaced. Several scholars highlight Laibach’s ceaseless attention to musical creativity in the pursuit of political subversiveness. For example, for Monroe, the cover version was a means for Laibach to continue its exploration of the connections between art and ideology, of illuminating the connections between competing ideological systems and of evoking repressed totalitarian energies, only now within Western forms of entertainment in which ideological power structures are less visible than in overt totalitarian propaganda. However, what often seems to escape intellectualist interpretations presented by scholars such as Žižek, Goddard and (albeit to a lesser extent) Monroe is the importance of the concrete specificities of the context that Laibach worked in in the 1990s – i.e. homeland ethno-nationalist politics – and, especially, their medium – i.e. Western pop music.The Meaning and Meaningfulness of Western Popular Culture in Former YugoslaviaThe Laibach covers were merely one of many celebrations of Western popular culture that emerged in pre- and post-socialist Yugoslavia. The most curious of these was the building of statues of icons of screen and stage. These include statues of Tarzan, Bob Marley, Rocky Balboa and, most famously, martial arts cinema legend Bruce Lee in the Bosnian city of Mostar.The pop monuments were often erected as symbols of peace in contexts of ethnic-national violence. Each was an ethnic hybrid. With the exception of original Tarzan Johnny Weismuller — an ethnic-German American immigrant from Serbia — none was remotely connected to the competing ethnic-national groups. Thus, it was surprising when these pop monuments became targets for iconoclasm. This was especially surprising because, in contrast, both the new ethnic-national monuments that were built and the old Socialist pan-Yugoslav monuments that remained in all their concrete and steel obduracy in and through the 1990s were left largely untouched.The work of Simon Harrison may give us some insight into this curious situation. Harrison questions the commonplace assumption that the strength of enmity between ethnic groups is related to their cultural dissimilarity — in short, the bigger the difference the bigger the biffo. By that logic, the new ethnic-national monuments erected in the post-SFRY era ought to have been vandalised. Conversely, however, Harrison argues that enmity may be more an outcome of similarity, at least when that similarity is torn asunder by other kinds of division. This is so because ownership of previously shared and precious symbols of identity appears to be seen as subjected to appropriation by ones’ erstwhile comrades who are newly othered in such moments.This is, indeed, exactly what happened in post-socialist former-Yugoslavia. Yugoslavs were rendered now as ethnic-nationals: Bosniaks (Muslims), Croats and Serbs in the case of Bosnia. In the process, the erection of obviously non-ethnic-national monuments by, now inevitably ethnic-national subjects was perceived widely as appropriation – “the Croats [the monument in Mostar was sculpted by Croatian artist Ivan Fijolić] are stealing our Bruce Lee,” as one of my Bosnian-Serb informants exclaimed angrily.However, this begs the question: Why would symbols of Western popular culture evoke the kinds of emotions that result in iconoclasm more so than other ethnically non-reducible ones such as those of the Partisans that are celebrated in the old Socialist pan-Yugoslav monuments? The answer lies in the geopolitical history of the SFRY. The Yugoslav-Soviet Union split in 1956 forced the SFRY to develop ever-stronger ties with the West. The effects of this became quotidian, especially as people travelled more or less freely across international borders and consumed the products of Western Capitalism. Many of the things they consumed became deeply meaningful. Notably, barely anybody above a certain age does not reminisce fondly about the moment when participation in martial arts became a nationwide craze following the success of Bruce Lee’s films in the golden (1970s-80s) years of Western-bankrolled Yugoslav prosperity.Likewise, almost everyone above a certain age recalls the balmy summer of 1985, whose happy zeitgeist seemed to be summed up perfectly by Austrian band Opus’s song “Live is Life” (1985). This tune became popular in Yugoslavia due to its apparently feelgood message about the joys of attending live rock performances. In a sense, these moments and the consumption of things “Western” in general came to symbolise everything that was good about Yugoslavia and, indeed to define what it was to be Yugoslavs, especially in comparison to their isolated and materially deprived socialist comrades in the Warsaw Pact countries.However, iconoclastic acts are more than mere emotional responses to offensive instances of cultural appropriation. As Michael Taussig describes, iconoclasm reveals the public secrets that the monuments it targets conceal. SFRY’s great public secret, known especially to those people old enough to have experienced the inter-ethnic violence of WWII, was ethnic division and the state’s deceit of the historic normalcy of pan-Yugoslav identification. The secret was maintained by a formal state policy of forgetting. For example, the wording on monuments in sites of inter-ethnic violence in WWII is commonly of the variety: “here lie the victims in Yugoslavia’s struggle against imperialist forces and their internal quislings.” Said quislings were, of course, actually Serbs, Croats, and Muslims (i.e. fellow Yugoslavs), but those ethnic nomenclatures were almost never used.In contrast, in a context where Western popular cultural forms came to define the very essence of what it was to be Yugoslav, the iconoclasm of Western pop monuments, and the retroquotation of Western pop songs revealed the repressed deceit and the public secret of the reality of inter-ethnic tension at the heart of that which was regarded as quintessentially Yugoslav. In this way, the memory of Yugoslavia ever having been a properly functioning entity was delegitimised. Consequently, Laibach and their kind served to render the apparent reality of the Yugoslav ideal as little more than a dream. ReferencesEpstein, Mikhail N. After the Future: The Paradoxes of Postmodernism and Contemporary Russian Culture. Amherst: U of Massachusettes P, 1995.Goddard, Michael. “We Are Time: Laibach/NSK, Retro-Avant-Gardism and Machinic Repetition,” Angelaki: Journal of the Theoretical Humanities 11 (2006): 45-53.Harrison, Simon. “Identity as a Scarce Resource.” Social Anthropology 7 (1999): 239–251.Monroe, Alexei. Interrogation Machine: Laibach and NSK. Cambridge, Mass.: MIT Press, 2005.NSK. Neue Slowenische Kunst. Ljubljana: NSK, 1986.NSK. Padiglione NSK. Ljubljana: Moderna Galerija, 1993.rateyourmusic.com. 2018. 3 Sep. 2018 <https://rateyourmusic.com/artist/throbbing-gristle>.Reynolds, Simon. Retromania: Pop Culture’s Addiction to Its Own Past. London: Faber and Faber, 2011.Taussig, Michael. Defacement: Public Secrecy and the Labor of the Negative. Stanford: Stanford University Press, 1999.Verdery, Katherine. What Was Socialism, and What Comes Next? Princeton, NJ: Princeton University Press.Žižek, Slavoj. “Why Are Laibach and NSK Not Fascists?” 3 Sep. 2018 <www.nskstate.com/appendix/articles/why_are_laibach.php.>

Ces travaux de thèse portent sur la conception, la fabrication et la caractérisation de résonateurs nano-optomécaniques sous forme de disques en arséniure de Gallium (GaAs). Ces disques sont à la fois des résonateurs mécaniques oscillant au GHz, et des résonateurs optiques à mode de galerie à haut facteur de qualité (>10^5). En confinant l'énergie mécanique et optique sur un volume sub-µm^3, ils permettent d'atteindre un couplage optomécanique extrêmement large (g0 >1 MHz). Nous présentons les développements technologiques ayant permis l'intégration de ces résonateurs avec des guides de couplage optique directement sur échantillon semi-conducteur, tout en maintenant des performances à l'état de l'art. Nous discutons les différents mécanismes de couplage optomécanique (pression de radiation, photoélasticité) dans les disques GaAs, ainsi que les sources de dissipation optique et mécanique dans ces résonateurs. Nous présentons également des expériences d'optomécanique à l'air libre et en cryostat à basse température, allant de la mesure du mouvement brownien et l'observation de rétroaction dynamique, jusqu'à des premières tentatives d'approche du régime quantique du mouvement. Enfin, nous présentons un développement nano-optomécanique complémentaire mené sur le matériau nitrure de silicium (SiN), aboutissant à la fabrication de résonateurs à mode de galerie sur puce à haut facteur de qualité. Après l'étude des instabilités optiques et de la dynamique d'auto-pulsation de ces résonateurs, nous présentons des premières signatures de couplage optomécanique dissipatif dans ces systèmes.

Les microrésonateurs à mode de galerie passifs à base de cristal ou de verre fabriqués par la méthode de fusion possèdent un facteur de qualité limité à quelques 10E8. Ceci est généralement dû à la contamination de la surface du résonateur lors de sa fusion. Dans ces travaux, nous proposons de contourner cette limitation en utilisant des microrésonateurs actifs pour compenser les pertes. Afin de caractériser les microrésonateurs actifs de très haut facteur de qualité ainsi obtenu, nous nous appuyons sur la méthode CRDM (Cavity Ring Down Measurement). Cette méthode interférométrique est d'une part bien adaptée à la caractérisation de résonateurs de très haut facteur de qualité et d'autre part elle permet de remonter de manière univoque aux facteurs de qualité intrinsèque Qo et extrinsèque Qe du résonateur. Dans un régime de compensation de pertes, nous avons pu atteindre tous les régimes de couplage et obtenus des facteurs de qualité intrinsèques excédant les 10E10. En régime d'amplification sélective, nous avons démontré expérimentalement que l'on pouvait obtenir des gains élevés allant jusqu'à 33 dB et des retards de groupe excédant 2,3 µs dans ces microrésonateurs actifs. Ces microrésonateurs de très haut facteur de qualité et de très haute finesse peuvent présenter un couplage modal se manifestant par un doublet de résonances. Une confrontation théorie/expérience avec la méthode CRDM permet de mesurer un écart très faible entre les doublets. Par ailleurs, ces microrésonateurs présentant un fort confinement spatial et une forte surtension, sont propices à l'observation d'effets non-linéaires. Une modélisation intégrant l'effet thermique et l'effet Kerr a été réalisée. Une confrontation théorie/expérience nous a permis d'estimer la puissance réellement injectée dans le mode ainsi qu'à estimer le volume du mode.

Ce mémoire concerne l'étude et la réalisation des résonateurs micro-ondes à quartz à mode de galerie dans la bande K (20-40 GHz). Nous avons évalué expérimentalement les composantes du tenseur permittivité relative et la tangente de perte du quartz en utilisant la technique du résonateur de Courtney. Ces mesures nous ont permis de montrer que la variation de la permittivité avec la température reste peu importante. La sensibilité thermique du résonateur est alors due à la dilatation thermique. La tangente de perte du quartz varie très peu avec la température. Le refroidissement du quartz n'apporte donc qu'un faible gain en terme du coefficient de surtension. Nous avons ensuite réalisé des résonateurs à quartz à mode de galerie fonctionnant à des fréquences de résonances différentes. Des coefficients de surtension de l'ordre de 60 000 à 300K et de 130 000 à 77K ont été obtenus à une fréquence de 16 GHz, et de l'ordre de 30 000 à 300K à une fréquence de 26 GHz. Un modèle basé sur la technique du raccordement modal développée au LPMO nous a permis d'évaluer avec une bonne précision les fréquences de résonance de nos résonateurs. De plus, une technique de sélection modale a été mise au point afin de supprimer les modes parasites autour d'un mode de galerie donné. Le résonateur à 26 GHz a été utilisé pour concevoir un oscillateur en utilisant les technologies disponibles au laboratoire. Le bruit de phase obtenu est de l'ordre de -75dB. Rad2. Hz-1 à 1 kHz de la porteuse. L'utilisation d'un correcteur interférométrique et/ou l'optimisation du circuit d'oscillation peuvent conduire à une nette amélioration de ces performances
This work deals with the study and the realization of Whispering gallery mode quartz resonators in the K-band (20 - 40 GHz). We evaluated experimentally the quartz dielectric properties (permittivity and intrinsic losses) using the Courtney resonator method. These measurements show that the variation of quartz permittivity with temperature is small and then the thermal sensitivity of the resonator is principaly due to thermal dilatation. The quartz loss tangent at low temperature changed very little from their room temperature value at 300K. Thus the cooling of the quartz brings only a weak profit in terms of the quality factor. We also achieved some Whispering Gallery mode quartz resonators working at different resonant frequencies. Experimental quality factors Q around 60 000 at 300K and of 130 000 at 77K have been obtaind at 16 GHz. Moreover, a Q-factor around 30 000 at 300K has been obtained at 26 GHz. A theoretical model, based on a Mode Matching method has been developed at LPMO in order to evaluate with a good precision the resonant frequencies of our resonators. Moreover, the efficiency of the mode selection method has been experimentally demonstrated. The 26 GHz resonator was used in order to design an oscillator. The achieved oscillator presents very good phase noise performances at 300K. These performances can be still improved by optimizing the circuit of oscillation and/or by using an interferometric corrector

Les résonateurs à modes de galerie sont des cavités diélectriques qui supportent des modes à très haut facteur de qualité et à faible volume qui demeurent confinés à l'interface air-diélectrique pour des durées pouvant atteindre voire dépasser la microseconde. L'intérêt de ce fort confinement des modes pour de longues durées est l'accentuation de l'interaction lumière-matière. Par conséquent, de nombreuses interactions non-linéaires telles que l'effet Kerr ou encore l'effet Brillouin à des puissances seuil inversement proportionnelles au carré voire au cube du facteur de qualité du résonateur ont lieu en son sein. Ces propriétés donnent accès à de nombreuses applications dans des domaines divers et variés tels que la spectroscopie, les télécommunications ou encore les micro-ondes. Les travaux de cette thèse ont pour but d'exploiter les non-linéarités Kerr et Brillouin dans les résonateurs à mode galerie à la longueur d'onde de 1550 nm afin de générer des micro-ondes ultra-stables à des fréquences comprises entre 5 et 30 GHz. Le premier chapitre introduit la théorie, la fabrication, le couplage et la caractérisation de résonateurs à des modes de galerie. Le second chapitre concerne la génération de micro-ondes. Nous y présentons nos résultats expérimentaux, la modélisation numérique de peignes de Kerr, ainsi que l'analyse d'instabilités oscillatoires d'origine thermique observées lors de nos travaux expérimentaux, puis nous concluons. Le dernier chapitre traite de l'interaction photons-phonons via le processus de diffusion Brillouin stimulée dans ces mêmes expérimentaux ainsi que le modèle temporel que nous avons développé pour suivre la dynamique de l'onde transmise et de celle rétrodiffusée. Le dernier chapitre conclue nos travaux. Les travaux présentés dans ce manuscrit ont été financé par l'European Research Council dans le cadre du projet NextPhase
Whispering galery mode resonators are dielectric cavities that support modes with ultra-high quality factor and small volume that remain confined in their inner periphery for time duratioons that can be as long as few microseconds. The strong confinement of these modes for such long durations strongly enhances nonlinear effect suchs as Kerr effect or Brillouin effect. These resonators can therefore be used for several applications such as spectroscopy, telecommunications or microwave generation. The objective of this thesis is to use Kerr and Brillouin nonlinearities in these resonators at the laser wavelength of 1550 nm, in order to generate high spectral purity microwave signals with frequencies rangong fros 5 to 30 GHz. The first chapter oh the thesis intriduces the theory, fabrication, coupling and characterisation of whispering gallery mode resonators. The second chapter is about the generation of Kerr optical frequency combs in these resonators and their application to the generation of microwave signals. We present our experimental resuktsdn the numerical modelling of Kerr combs, the analysis of oscillatory instabilities (due to thermal effect) observed during our experiments, and conclue. The third chapter concerns photon-phonon interactions via stimulated Brillouin scattering in these resonators and their application to the generation of microwave signals. We present our experimental results and the temporal model that we developed to track the dynamics of the forward and backscattered fields. The last chapter conclude the thesis. The research presented in this thesis has benne funded by the European Research Council through the project Nextphase

Deux méthodes d'analyses électromagnétiques des Whispering Gallery (W. G) modes des R. D. Sont présentées dans ce mémoire. Une méthode approximative analytique et la méthode des éléments finis permettent de connaître avec précision la fréquence de fonctionnement et la cartographie du champ électromagnétique d'une structure microonde. Ces résultats couplés à une analyse électrique des dispositifs à résonateurs diélectriques ont permis la réalisation de filtres directifs et d'un combineur de puissance utilisant les W. G. Modes des résonateurs diélectriques.

Les microrésonateurs à modes de galerie en matériaux amorphes sont faciles à produire par des techniques de fusion. Leur facteur de qualité est cependant limité à quelques 108 du fait du phénomène de contamination de surface ou d'une absorption résiduelle plus importante que celle des matériaux cristallins. Nous avons développé deux méthodes utilisant des micro-résonateurs actifs, fabriqués par fusion de poudres de verres ZBLALiP dopés Erbium, permettant de dépasser cette limite. Il est tout d'abord possible de compenser les pertes en introduisant du gain optique dans le micro-résonateur. Des facteurs de qualité chargés de 5×109 correspondant à un facteur de qualité intrinsèque de 1010 ont ainsi pu être mesurés. En plus d'une augmentation du facteur de qualité, le gain interne offre un paramètre supplémentaire de contrôle du couplage, cela nous a permis d'obtenir tous les régimes de couplage d'un résonateur à partir du sous couplage jusqu'au régime d'amplification sélective. Nous avons atteint en particulier le régime de transparence, un micro-résonateur dans un tel régime peut trouver des applications comme ligne à retard variable transparente ayant un retard de groupe qui peut être modifié en jouant sur le taux de couplage entre le résonateur et la ligne d'accès. La deuxième méthode consiste à augmenter très fortement la valeur de l'indice de groupe du milieu par des effets de lumière lente. Un indice de groupe d'environ 4×106 a été obtenu via le phénomène d'Oscillations Cohérentes de Populations (OCP) ce qui caractérise un très fort ralentissement de la lumière. Ceci nous a permis d'augmenter, dans une micro-cavité, le temps de stockage des photons de 200 ps à 2,5 ms ce qui correspond à un facteur Q de 3×1012
Glass-based whispering gallery mode (WGM) microresonators are easy to produce by melting techniques. However, they suffer from surface contamination or residual absorption which limits their long term quality factor to only about 108. We show that an optical gain provided by erbium ions can compensate for residual losses. Moreover it is possible to control the coupling regime of an ultrahigh Q-factor microresonator from undercoupling to spectral selective amplification by changing the pumping rate. We demonstrate a critically coupled fluoride glass WGM microresonator with a diameter of 220 μm and a loaded Q-factor of 5,3×109. We also show that by introducing slow-light effects in a monolithic WGM microresonator it is possible to enhance the photon lifetime by several orders of magnitude and circumvent fabrication limitations. We experimentally demonstrate Erbium-doped fluoride glass microresonators with a photon lifetime up to 2,5 ms at room temperature, corresponding to a Q-factor of 3×1012 at 1530 nm, by combining WGM resonance effect and population oscillations

Ces travaux de thèse portent sur l'étude de résonateurs cyclique (à symétrie de révolution) dans lesquels existent des modes confinés de très haute surtension, appelés « modes de galerie ». Dans ces modes, la lumières est guidée dans le diélectrique constituant le résonateur le long d'un cercle équatorial par une succession de réflexion totales internes à l'interface diélectrique/air et les résonances correspondent à une condition de retour en phase. Les résonances sont très fines ce qui permet d'envisager des applications aussi biens passives (filtrage, insertion/extraction) qu'active (laser faible seuil, fonction non-linéaire).
Ce manuscrit de thèse est constitué de deux parties distinctes :
La première partie, qui concerne les fonctions passives à base de micro-résonateur planaire, présente différents outils (numérique et analytique) qui permettent de modéliser le comportement de ces structures et démontre la complémentarité de ces outils.
La deuxième partie concerne les lasers micro-sphériques (dopés Erbium) et plus précisément le problème de l'interaction entre les modes d'une micro-sphère et un miroir métallique.

Ce travail porte sur l'étude expérimentale et théorique des propriétés dispersives de structures photoniques à base de micro‐résonateurs. La caractérisation de la fonction de transfert de résonateurs de facteurs de surtension très élevés (>  108) est difficilement  réalisée à partir des méthodes expérimentales conventionnelles en régime stationnaire.  Nous proposons une méthode hybride spectrale/temporelle associée à un modèle analytique permettant la mesure du facteur de surtension global et  la discrimination, de manière univoque, des facteurs Q0 intrinsèque (résonateur) et Qe extrinsèque (coupleur) du dispositif.   Par cette  simple mesure,  nous déterminons le  régime de couplage et les propriétés dispersives du système sous test.  Cette méthode est appliquée avec succès sur des résonateurs à fibre, des micro‐disques MgF2 et  des microsphères passives et actives.  Dans les résonateurs micro‐sphériques à modes de galerie (haut facteur de qualité et grande finesse : F>105) nous avons notamment étudié leur capacité à réaliser un filtre amplificateur de haute sélectivité(gain supérieur à 20 dB à 1,55 μm et de largeur spectrale de 115 kHz) ainsi que la levée de dégénérescence entre les modes contra‐propagatifs de la cavité.   Ce dernier effet induit par la diffusion Rayleigh se manifeste par un doublet de résonances dont l’écart en fréquence est une signature de l'efficacité de la rétrodiffusion.  Parallèlement, nous proposons différentes architectures à base de cavités couplées dans le but de contrôler la dispersion dans ces systèmes.  Nous avons étudié la transparence induite par couplage de résonateurs dans des structures dites CRIT (équivalent  classique  de  l’EIT) pour la réalisation d’états de lumière lente.  Les limites imposées par les pertes intrinsèques des  résonateurs peuvent être contournées par l’utilisation de résonateurs actifs. Le paramètre  supplémentaire lié au caractère actif des résonateurs offre un potentiel d'application en tant que ligne à retard ajustable tout en conservant une transparence du système d’environ 90% et permet une mise en forme (un contrôle) des différents ordres de dispersion du dispositif.  Nous démontrons également l’augmentation du facteur de qualité par la dispersion induite par couplage de résonateurs actifs.  Ainsi, dans le cas N = 2, nous utilisons un résonateur pour augmenter  artificiellement le chemin optique d’un second jouant le rôle de cavité cible.  Expérimentalement, nous avons obtenu une augmentation du facteur de qualité d’un coefficient 23.  Dans le cas N = 3, l’insertion d’un CRIT actif dans un résonateur sous couplage critique montre que le facteur Q de ce résonateur peut être augmenté et  modulé par le gain dans les résonateurs actifs. Dans le test expérimental effectué sur un système modèle à boucles de fibres optiques dopées Er3+, le facteur Q passe de  4×107 à 2,5×108.  La démonstration expérimentale de ce principe montre la possibilité d’ingénierie du facteur Q par l'utilisation de structures photoniques artificielles actives.

Ces travaux de recherches s’inscrivent dans le cadre de l’utilisation de résonateurs cryogéniques à fort coefficient de surtension pour le filtrage hyperfréquence et pour la métrologie du temps et des fréquences. Les procédés cryogéniques permettent d’une part l’utilisation de matériaux supraconducteurs, et d’autre part de profiter des caractéristiques avantageuses des matériaux diélectriques à basse température. Dans le premier chapitre, un protocole novateur a été élaboré afin de caractériser des filtres planaires supraconducteurs en bande C. Dans le chapitre 2, des prototypes fonctionnels ont permis de caractériser les différentes solutions passives permettant d’accéder au filtre via une fibre optique afin de réduire le poids et le volume des équipements adjacents. Dans le dernier chapitre, des résonateurs saphir cryogéniques ont été dimensionnés afin de créer les conditions nécessaires à la création d’une oscillation de type MASER
These research works have been done in order to use high-Q cryogenic resonators for HF filters and time and frequency metrology. Cryogenic process allows using superconducting materials and advantages of low–temperature dielectric materials. The first chapter describes a new setup to test C-band planar superconducting filters. The second one presents prototypes using optoelectronic devices to decrease the weight and the volume of equipments connected to the previous filter. In the last chapter, cryogenic sapphire resonators have been designed to allow necessary conditions for a MASER effect

Nous présentons dans ce mémoire de thèse des travaux qui portent sur l'étude de micro résonateurs à modes de galerie et en anneau couplés dans le but d'applications aux fonctions optiques de traitement du signal.
Dans une première partie nous présentons un modèle matriciel pour décrire la propagation de la lumière dans des structures à anneaux couplés. L'utilisation de ce modèle se résume pour des structures dont on connaît les coefficients de couplage entre les guides.
Dans le cas de résonateurs constitués d'un milieu qui ne présente pas d'effets non-linéaires nous avons montré que les structures à anneaux couples permettent de réaliser la synthèse de filtres optiques.
Si les résonateurs sont le siège d'une non linéarité dispersive d'ordre 3 nous avons deux cas possibles en fonction du type d'excitation. Hors résonance nous avons montré que nous pouvons obtenir potentiellement des dispositifs /N+1/ stables en utilisant un système formé de /N/ anneaux couplés, ainsi que la tristabilité dans un seul anneau en utilisant un signal de commande. A résonance nous avons montré que l'on peut obtenir la fonction de remise en forme du signal pour des débits de 40 Gb/s.
La deuxième partie porte sur les travaux réalisés sur l'oscillateur optoélectronique. Dans le schéma classique d'un tel oscillateur la fonction de retard optique est obtenue en utilisant une ligne à fibre optique de longueur proportionnelle au retard nécessaire. Nous voulons remplacer cette ligne avec une ligne à retard à base de microrésonateurs. Nous présentons des procédés de fabrication de résonateurs sphériques et diverses méthodes de mesure de leurs facteurs de qualité, proportionnel au retard induit.

Micro- and nanolectromechanical systems (MEMS/NEMS) incorporating two-dimensional structural elements such as plates attracted significant interest in recent years. In this work, we explore implementation of a model based on Berger’s approximation, which significantly simplifies the formulation of a curved plate and describes it by a single governing equation. The solution of this equation is based on the Galerkin decomposition with buckling modes of an initially flat plate used as the base functions. To track the unstable branches of the equilibrium curve, a continuous method based on the Riks algorithm is implemented. The validation of the models is conducted for two loading cases, “mechanical” deflection-independent load, and electrostatic displacement-dependent load. In the case of an initially flat plate, results provided by the reduced order (RO) Galerkin models were compared to results available in the literature. In the case of a curved plate undergoing “mechanical” loading, results of a direct finite elements (FE) analysis, as well as of a finite differences (FD) analysis, were used as a reference. We show that the DOF Berger RO model can be conveniently used for analysis of plates with small curvature, as it provides satisfactory accuracy. Further more, a single DOF model can be used for the development of a bistability criterion.

Curved beams subjected to transverse force may exhibit a latching phenomena, namely remain in their buckled configuration under zero force such that an opposite force is required for their release. In this study, we investigate the latching in bistable electrostatically actuated prestressed curved beams. The analysis is based on a reduced order (RO) model resulting from the Galerkin decomposition with buckling modes of a straight beam as base functions. Criteria for the existence of latching are derived in terms of the beam geometric parameters and the axial load. Two conditions are formulated: A necessary criterion establishes the appearance of latching on the symmetric response curve and a sufficient condition which assures the existence of latching in the presence of bifurcations. A comparison between the model results and those obtained by numerical analysis shows good agreement up to a certain elevation. It is noted that as the latching is not affected by the nonlinear electrostatic load, the obtained criteria stand for all types of loading.

The axisymmetric snap-through of an initially curved circular micro plate, subjected to a transversal distributed electrostatic force is studied. The analysis is based on a reduced order (RO) model resulting from the Galerkin decomposition, with buckling modes of a flat plate used as the base functions. In order to check the validity of the RO model, the corresponding problem for a displacement-independent (“mechanical”) load is solved, and a comparison between the RO model and those obtained using finite elements (FE) analysis is carried out. It is shown, that the two are in good agreement, indicating that the RO model can be used for a plate undergoing electrostatic loading. However, the study shows that at least three degrees of freedom (DOF) are required for an accurate prediction of the equilibrium path and bistability. The coupled electromechanical analysis shows that due to the nonlinearity of the electrostatic load, the snap-through occurs at a lower displacement than in the case of the “mechanical” load. Moreover, the study concludes that actuation of plates of realistic dimensions can be achieved by reasonably low voltages.

Combined thermionic emission and tunneling of hot electrons (thermo-tunneling) has emerged as a potential new solidstate cooling technology. Practical implementation of thermo-tunneling, however, requires the formation of a nanometer-sized gap spanning macroscopically significant surfaces. Thermo-tunneling is a term used to describe combined emission of hot electrons (thermionic emission) and tunneling of electrons through a narrow potential barrier between two surfaces (field emission). Thermo-tunneling of hot electrons across a few-nanometer gap has application to vacuum electronics, flat panel displays, and holds great potential in thermo-electric cooling and energy generation. Development of new thermo-tunneling applications requires creation of a stable nanometer gap between two surfaces. This presentation is focused on our effort to investigate the stability of the the thin flexible structure under electrostatic and lorenz forces opposing each other. In this presentation, we report the result of numerical simulation with some mathematical simplifications. The mathematical model used for the numerical simulation is well studied in the literature. Using forth-order partial differential beam equation, we studied the steady state solutions of the thermo-tunneling beam model using Galerkin method. Essential output parameters of the model include a central contact area measured by its length (delta) and the thermo-tunneling current. Both parameters are determined as a function of the externally applied external potential and magnetic field. Numerical solutions of the model show two possible operating modes: (1) symmetric deformation with negligibly small current; and (2) asymmetric mode where the B-field controls the current and contact area. Under practical values for the externally applied magnetic and electric fields, it has been shown that the second mode is only possible for electrode with very low work functions, e.g. below 0.5 eV. Therefore, novel materials such as Diamond-like carbon films are likely to be essential in thermo-tunneling applications.

Developing a transient fully-meshed model of coupled-domain microsystems is of paramount importance not only for accurate simulation and design but also for creating more accurate low-order or macro dynamic models. So in this paper, a complete nonlinear finite element model for coupled-domain MEMS devices considering electrostatic and squeeze film effects is presented. For this purpose, we use the Galerkin weighted-residual technique for developing the finite element model that capture the original microsystem's nonlinear behaviors, such as the structural dynamics, the squeeze-film damping, the electrostatic actuation and the geometric nonlinearity caused by inherent residual stresses. In addition, using the Newmark's nonlinear solution, technique, the extracted dynamic equilibrium equations are discretised and simulated. The system dynamic behavior is successfully modeled by using the developed nonlinear finite element model and finally some simulated results of electrostatic microactuator behaviors are verified with experimental findings and are in very good agreement.

A micro-macro simulation algorithm for the calculation of polymeric flow is developed and implemented. The algorithm couples standard finite element techniques to compute velocity and pressure fields with stochastic simulation techniques to compute polymer stress from simulated polymer dynamics. The polymer stress is computed using a microscopic-based rheological model which combines aspects of network and reptation theory with aspects of continuum mechanics. The model dynamics include two Gaussian stochastic processes each of which is destroyed and regenerated according to a survival time randomly generated from the material’s relaxation spectrum. The Eulerian form of the evolution equations for the polymer configurations are spatially discretized using the discontinuous Galerkin method. The algorithm is tested on benchmark contraction domains for a polyisobutylene (PIB) solution. In particular, the flow in the abrupt die entry domain is simulated and the simulation results are compared with experimental data. The results exhibit the correct qualitative behavior of the polymer and agree well with the experimental data.

This paper deals with the voltage response of electrostatically actuated NEMS resonators at superharmonic resonance. In this work a comparison between Boundary Value Problem (BVP) model, and Reduced Order Model (ROM) is conducted for this type of resonance. BVP model is developed from the partial differential equation by replacing the time derivatives with finite differences. So, the partial differential equation is replaced by a sequence of boundary value problems, one for each step in time. Matlab’s function bvp4c is used to numerically integrate the BVPs. ROMs are based on Galerkin procedure and use the mode shapes of the resonator as a basis of functions. Therefore, the partial differential equation is replaced by a system of differential equations in time. The number of the equations in the system is equal to the number of mode shapes (or modes of vibration) used in the ROM. One mode of vibration ROM is solved using the method of multiple scales. Two modes of vibration ROM is numerically integrated using Matlab’s function ode15s in order to obtain time responses, and a continuation and bifurcation analysis is conducted using AUTO 07P. The effects of different nonlinearities in the system on the voltage response are reported. This work shows that BVP model is a valid method to predict the voltage response of a micro/nano cantilevers.

The asymmetric buckling of a shallow initially curved stress-free micro beam subjected to distributed nonlinear deflection-dependent electrostatic force is studied. The analysis is based on a two degrees of freedom reduced order (RO) model, resulting from the Galerkin decomposition with linear undamped eigen-modes of a straight beam used as the base functions. Simple approximate expressions are derived defining the geometric parameters of beams for which an asymmetric response bifurcates from the symmetric one. The necessary criterion establishes the conditions for the appearance of bifurcation points on the unstable branch of the symmetric response curve; the sufficient criterion assures a realistic asymmetric buckling bifurcating from the stable branches of the curve. It is shown that while the symmetry breaking conditions are affected by the nonlinearity of the electrostatic force, its influence is less pronounced than in the case of the symmetric snap-through criterion. A comparison between the RO model results and those obtained by direct numerical analysis shows good agreement between the two and indicates that the obtained criteria can be used to predict non-symmetric buckling in electrostatically actuated bistable micro beams.

The differential equation governing the motion of an electrically excited capacitive microcantilever beam is a nonlinear PDE [1]. Accurate analysis about its motion is of great importance in MEMS' dynamical response. In this paper first the nonlinear 4th order 2 point boundary value problem (ODE) governing the static deflection of the system is solved using three methods. 1. The nonlinear part is linearized and its exact solution is obtained. 2. For low applied DC voltages (not near pull-in) the solutin is found using the direct straight forward perturbation analysis. 3. Numerical computer solutions which are used for the previous solution's verifications. The next parts are devoted to the dynamic solution. The nonlinear time variant 4th order PDE governing the dynamic deflection of an electrically excited microbeam is scrutinized. First using the Galerkin Method the mode shapes and the first three mode temporal equations of the linearized equation are found. Considering no damping, using the perturbations method the temporal equations are solved in three states: far from resonance, near 1:1 resonance and near 1:2 resonance. Finally the damped equation is solved using the aforementioned method. In the literature no closed form solution for this problem is presented.

Micro and nano devices incorporating bi-stable structural elements such as micro beams are designed to exploit the fact that the latter possess two stable configurations at the same actuation force. Generally, the transition of a micro beam from one table state to another, namely the snap-through which is essentially dynamic phenomenon, can be initiated by either static or dynamic activations. In this work, results of theoretical and numerical investigations of the transient dynamics of a pre-stressed initially curved double clamped micro beams actuated by a time dependent electrostatic load are presented. We show by means of a reduced order model of a shallow beam, derived using the Galerkin procedure, that the beam may exhibit various types of responses. For certain beam characteristics, the second stable state is inaccessible under a static loading but is attainable only by means of a specially tailored dynamic actuation. This gives way to the possibility of trapping the dynamically bi-stable beam at a stable configuration which is close to the electrode by applying special loading sequences.