lOptical coupling structure made by imprinting between single-mode polymer waveguide and embedded VCSEL

Polymer-based integrated optics is attractive for inter-chip optical interconnection applications, for instance, for coupling photonic devices to fibers in high density packaging. In such a hybrid integration scheme, a key challenge is to achieve efficient optical coupling between the photonic chips and waveguides. With the single-mode polymer waveguides, the alignment tolerances become especially critical as compared to the typical accuracies of the patterning processes. We study novel techniques for such coupling requirements. In this paper, we present a waveguide-embedded micro-mirror structure, which can be aligned with high precision, even active alignment method is possible. The structure enables 90 degree bend coupling between a single-mode waveguide and a vertical-emitting/detecting chip, such as, a VCSEL or photodiode, which is embedded under the waveguide layer. Both the mirror structure and low-loss polymer waveguides are fabricated in a process based mainly on the direct-pattern UV nanoimprinting technology and on the use of UV-curable polymeric materials. Fabrication results of the coupling structure with waveguides are presented, and the critical alignment tolerances and manufacturability issues are discussed

Suolan vaikutus selluloosananokiteiden valisiin vuorovaikutuksiin

Improved understanding of the molecular interactions at cellulose-to-solvent interface is important for the design of advanced materials. In this thesis, changes in molecular interactions at cellulose-to-solvent interface with addition of ions (Na, Ca, Cl) are investigated. Different crystal orientations, with different hydrophilicities/hydrophobicities, were modelled and compared to each other. Of particular interest were the molecular interactions which can explain the gelation (increase in viscosity) that has been observed to occur with addition of NaCl to colloidal nanocellulose suspensions. Molecular dynamics simulations were used to examine the effects of salts on cellulose nanocrystal interactions with each other, with the goal of exploring mechanisms that cause attraction between cellulose crystals. Molecular dynamics is very useful in probing molecular interactions that are difficult or impossible to measure in any other way. Steric effects, hydration forces, depletion interactions, and specific ion effects are difficult to model on a macroscopic level but are implicitly included on the molecular level. Differences in hydrophilicity and hydrophobicity of different cellulose surfaces could be clearly seen from the water binding of the surfaces as well as the extent of oriented water. Hydrophobic surfaces showed larger water orientation peaks, consistent with water being more ordered around hydrophobic surfaces. With CaCl2 addition, there was a large increase in the water binding for the slightly hydrophilic (-1-10) and (110) surfaces, while the hydrophobic surfaces showed no such increase. Kirkwood-Buff solution theory was applied to search for attractive depletion forces at nanocellulose interfaces. The results indicate that depletion forces are likely to occur around cellulose strands in solutions containing ions, and that they are likely to contribute to the aggregation and gelation that has been experimentally observed when ions are introduced into nanocellulose aqueous dispersions. Electrostatic screening of repulsive forces from charged defects is another contributing factor in real nanocellulose dispersions which necessarily contain these defects.Uusien selluloosalla vahvistettujen komposiittimateriaalien suunnittelulle on tärkeää ymmärtää paremmin molekyylien väliset vuorovaikutukset selluloosan ja liuottimen rajapinnalla. Tässä diplomityössä tutkitaan selluloosan ja veden rajapinnalla tapahtuvien molekyylien välisten vuorovaikutusten muuttumista, kun veteen lisätään ioneja (Na, Ca, Cl). Eri selluloosakiteen pintojen orientaatioita, joilla on eri hydrofobiset tai hydrofiiliset ominaisuudet, simuloidaan ja niista saatuja tuloksia verrataan. Erityisenä kiinnostuksen kohteena on molekyylien vuorovaikutukset jotka voisivat selittää geeliytymisen (viskositeetin kasvamisen) jota on havaittu tapahtuvan kun suolaa lisätään kolloidisiin nanoselluloosasuspensioihin. Molekyylidynaamisilla simulaatioilla tarkasteltiin suolojen vaikutuksia selluloosananokiteiden välisiin vuorovaikutuksiin, tarkoituksena tutkia mekanismeja jotka aiheuttavat selluloosakiteiden välisiä attraktiivisia vuorovaikutuksia. Molekyylidynamiikka on hyödyllinen tapa tutkia sellaisia molekyylien välisiä vuorovaikutuksia, jotka ovat vaikeita tai mahdottomia tutkia millään muulla keinolla. Steeriset vaikutukset, hydraatiovoimat, depleetiovuorovaikutukset, ja ionien spesifiset ominaisuudet ovat vaikeita mallintaa makroskooppisella tasolla, mutta tulevat implisiittisesti otetuksi huomioon molekyylitason simulaatioissa. Erot selluloosakiteiden hydrofiilisyydessä ja hydrofobisuudessa olivat selvästi nähtävissä selluloosapintojen vedensitomiskyvyssä sekä orientoituneen vesikerroksen paksuudessa. Kuten oli odotettu, veden orientoituminen oli voimakkainta hydrofobisten pintojen lähellä. CaCl2 lisäys aiheutti voimakkaan lisäyksen sitoutuneen veden määrässä lievästi hydrofiilisilla (-1-10) ja (110) pinnoilla, mutta ei hydrofobisilla pinnoilla. Kirkwoodin ja Buffin liuosmallia hyödynnettiin attraktiivisten depleetiovuorovaikutusten tutkimisessa nanoselluloosakiteiden rajapinnoilla. Tulokset kertovat, etta depleetiovuorovaikutuksia todennäköisesti esiintyy nanoselluloosasäikeiden välillä suolaa sisältävissä liuoksissa. Depleetiovoimat vaikuttavat osaltaan aggregoitumiseen ja geeliytymiseen, joita ilmenee, kun suolaa lisätään nanoselluloosan ja veden suspensioihin. Toinen lisääntyneeseen attraktioon vaikuttava tekijä on nanosellulosan pinnalla olevat negatiivisesti varautuneet epäpuhtaudet, joiden välillä vaikuttava repulsiovoima pienenee suolan vaikutuksesta

Design, fabrication and characterisation of nano-imprinted single mode waveguide structures for intra-chip optical communications

In the Information and Communications Technology (ICT) sector, the demands on bandwidth continually grow due to increased microprocessor performance and the need to access ever increasing amounts of stored data. The introduction of optical data transmission (e.g. glass fiber) to replace electronic transmission (e.g. copper wire) has alleviated the bandwidth issue for communications over distances greater than 10 meters, however, the need has arisen for optical data transfer over shorter distances such as those found inside computers. A possible solution for this is the use of low-cost single mode polymer based optical waveguides fabricated by direct patterning Nanoimprint Lithography (NIL). NIL has emerged as a scalable manufacturing technology capable of producing features down to the hundred nanometer scale with the potential for large scale (roll-to-roll) manufacturing. In this paper, we present results on the modeling, fabrication and characterization of single mode waveguides and optical components in low-loss ORMOCER™ materials. Single mode waveguides with a mode field diameter of 7 μm and passive structures such as bends, directional couplers and multi-mode interferometers (MMIs) suitable for use in 1550 nm optical interconnects were fabricated using wafer scale NIL processes. Process issues arising from the nano-imprint technique such as residual layers and angled sidewalls are modeled and investigated for excess loss and higher order mode excitation. Conclusions are drawn on the applicability of nano-imprinting to the fabrication of circuits for intrachip/ board-level optical interconnect. cop. 2015 SPIE

Multi-level single mode 2D polymer waveguide optical interconnects using nano-imprint lithography

Single and multi-layer passive optical interconnects using single mode polymer waveguides are demonstrated using UV nano-imprint lithography. The fabrication tolerances associated with imprint lithography are investigated and we show a way to experimentally quantify a small variation in index contrast between core and cladding of fabricated devices. 1x2 splitting devices based on directional couplers and multimode interference interferometers are demonstrated to have less than 0.45 dB insertion loss with 0.02 ± 0.01 dB power imbalance between the outputs. We demonstrate an 'optical via' with an insertion loss less than 0.45 dB to transfer light from one optical signal plane to another. A 1x4 two-dimensional optical port is experimentally demonstrated to spatially split the input power with an insertion loss of 1.2 dB. © 2015 Optical Society of America

Scalable electro-photonic integration concept based on polymer waveguides

A novel method for fabricating a single mode optical interconnection platform is presented. The method comprises the miniaturized assembly of optoelectronic single dies, the scalable fabrication of polymer single mode waveguides and the coupling to glass fiber arrays providing the I/O's. The low cost approach for the polymer waveguide fabrication is based on the nano-imprinting of a spincoated waveguide core layer. The assembly of VCSELs and photodiodes is performed before waveguide layers are applied. By embedding these components in deep reactive ion etched pockets in the silicon substrate, the planarity of the substrate for subsequent layer processing is guaranteed and the thermal path of chip-to-substrate is minimized. Optical coupling of the embedded devices to the nano-imprinted waveguides is performed by laser ablating 45 degree trenches which act as optical mirror for 90 degree deviation of the light from VCSEL to waveguide. Laser ablation is also implemented for removing parts of the polymer stack in order to mount a custom fabricated connector containing glass fiber arrays. A demonstration device was built to show the proof of principle of the novel fabrication, packaging and optical coupling principles as described above, combined with a set of sub-demonstrators showing the functionality of the different techniques separately. The paper represents a significant part of the electro-photonic integration accomplishments in the European 7th Framework project "Firefly" and not only discusses the development of the different assembly processes described above, but the efforts on the complete integration of all process approaches into the single device demonstrator

Extracellular vesicles and high‐density lipoproteins : Exercise and oestrogen‐responsive small RNA carriers

Decreased systemic oestrogen levels (i.e., menopause) affect metabolic health. However, the detailed mechanisms underlying this process remain unclear. Both oestrogens and exercise have been shown to improve metabolic health, which may be partly mediated by circulating microRNA (c-miR) signalling. In recent years, extracellular vesicles (EV) have increased interest in the field of tissue crosstalk. However, in many studies on EV-carried miRs, the co-isolation of high-density lipoprotein (HDL) particles with EVs has not been considered, potentially affecting the results. Here, we demonstrate that EV and HDL particles have distinct small RNA (sRNA) content, including both host and nonhost sRNAs. Exercise caused an acute increase in relative miR abundancy in EVs, whereas in HDL particles, it caused an increase in transfer RNA-derived sRNA. Furthermore, we demonstrate that oestrogen-based hormonal therapy (HT) allows the acute exercise-induced miR-response to occur in both EV and HDL particles in postmenopausal women, while the response was absent in nonusers.peerReviewe