Studies of advanced integrated nano-photonic devices in silicon

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 267-285).Electronic-photonic integrated circuits (EPICs) are a promising technology for overcoming bandwidth and power-consumption bottlenecks of traditional integrated circuits. Silicon is a good candidate for building such devices, due to its high-index contrast and low propagation loss at telecom wavelengths. The current thesis presents recent advances in demonstrating discrete components built in silicon-on-insulator (SOI) platforms, around 1550 nm, that can be used as building blocks for future EPIC systems. The first part of this thesis investigates electro-optic modulators based on one-dimensional photonic crystal microcavities, with femtojoule switching energies, as well as on-chip optical interconnects using the super-collimation effect in two-dimensional photonic crystals, both in hole- and rod-based configurations. The second part focuses on microring-based structures, demonstrating wide thermal tunability and hitless operation of single-ring filters, as well as three more advanced categories of devices suitable for wavelength-division multiplexing (WDM) applications. These are twenty-channel second-order tunable filterbanks (both in dual- and counter-propagating configurations), reconfigurable optical add-drop multiplexers (ROADMs) with telecom-grade specifications, and a dynamical slow light cell for delay lines and optical memory elements. All the devices demonstrated in this thesis can be integrated on the same chip. The small device footprints and the use of the SOI platform are ideal for integration with a standard CMOS process, enabling the fabrication of novel electronic-photonic integrated circuits. These new EPIC systems may one day play an important role in the scaling of current computing systems and taking advantage of the WDM capability to increase operational bandwidth, while keeping the power consumption at low levels.by Marcus Dahlem.Ph.D

Optical studies of super-collimation in photonic crystals

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. [121]-125).Recent developments in material science and engineering have made possible the fabrication of photonic crystals for optical wavelengths. These periodic structures of alternating high-to-low index of refraction materials allow the observation of peculiar effects, in particular, the propagation of optical beams without spatial spreading. This effect, called super-collimation (also known as self-collimation), allows diffraction-free propagation of micron-sized beams over centimeter-scale distances. This linear effect is a natural result of the unique dispersive properties of photonic crystals. In this thesis, these dispersive properties are studied in a two-dimensional photonic crystal slab. Both qualitative and quantitative descriptions are presented. The beam propagation method was used to simulate the evolution of a Gaussian beam inside such structures. The wavelength dependence of the super-collimation effect was studied, and it was observed that the optimum wavelength for this device was around 1500 nm. A precise contact-mode near-field optical microscopy technique was used to obtain high-resolution images of the beam profile at different positions along the photonic crystal, and showed that a 2 [micro]m beam width was conserved over 3 mm. In addition, high-resolution confocal measurements confirmed the size of the beam after 5 mm of propagation.(cont.) The figure of merit associated with the super-collimation effect is defined by the number of diffraction lengths over which the beam stays collimated. The diffraction length is the distance in which a beam will broaden to 2¹ʹ² of its initial width. Previous experimental studies showed figures of merit smaller than 6; the results of this experiment show figures of merit as high as 376, which correspond to more than 14200 lattice constants. Preliminary results were obtained with an 8 mm sample that could achieve a figure of merit of 601.by Marcus Dahlem.S.M

Absence of Structural Impact of Noble Nanoparticles on P3HT: PCBM Blends for Plasmon Enhanced Bulk-Heterojunction Organic Solar Cells Probed by Synchrotron Grazing Incidence X-Ray Diffraction

The incorporation of noble metal nanoparticles, displaying localized surface plasmon resonance, in the active area of donor-acceptor bulk-heterojunction organic photovoltaic devices is an industrially compatible light trapping strategy, able to guarantee better absorption of the incident photons and give an efficiency improvement between 12% and 38%. In the present work, we investigate the effect of Au and Ag nanoparticles blended with P3HT: PCBM on the P3HT crystallization dynamics by synchrotron grazing incidence X-ray diffraction. We conclude that the presence of (1) 80nm Au, (2) mix of 5nm, 50nm, 80nm Au, (3) 40nm Ag, and (4) 10nm, 40nm, 60nm Ag colloidal nanoparticles, at different concentrations below 0.3 wt% in P3HT: PCBM blends, does not affect the behaviour of the blends themselves

A 2D pixelated optical beam scanner controlled by the laser wavelength

We present a chip-based optical beam scanner based on a dispersive optical phased array (OPA) that illuminates the far field with a pixelated pattern. To scale up theOPAto a large number of antennas, we break it up intomanageable blocks with acceptable losses. The 2D wavelength scanning within a block is handled by dispersive delay lines. Between blocks, there are no delay lines, and theOPAwill only have constructive interference for a discrete set of wavelengths. This results in the far-field illumination of a pixelated pattern along both x and y directions. The sidelobes and the power in the main lobe can be controlled by the power distribution of the individual OPA antennas

Targeted delivery of functionalized PLGA nanoparticles to macrophages by complexation with the yeast Saccharomyces cerevisiae

Nanoparticles (NPs) are able to deliver a variety of substances into eukaryotic cells. However, their usage is often hampered by a lack of specificity, leading to the undesired uptake of NPs by virtually all cell types. In contrast to this, yeast is known to be specifically taken up into immune cells after entering the body. Therefore, we investigated the interaction of biodegradable surface-modified poly(lactic-co-glycolic acid) (PLGA) particles with yeast cells to overcome the unspecificity of the particulate carriers. Cells of different Saccharomyces cerevisiae strains were characterized regarding their interaction with PLGA-NPs under isotonic and hypotonic conditions. The particles were shown to efficiently interact with yeast cells leading to stable NP/yeast-complexes allowing to associate or even internalize compounds. Notably, applying those complexes to a coculture model of HeLa cells and macrophages, the macrophages were specifically targeted. This novel nano-in-micro carrier system suggests itself as a promising tool for the delivery of biologically active agents into phagocytic cells combining specificity and efficiency

Toll-Like Receptor 2 Release by Macrophages: An Anti-inflammatory Program Induced by Glucocorticoids and Lipopolysaccharide

Glucocorticoids (GCs) are widely prescribed therapeutics for the treatment of inflammatory diseases, and endogenous GCs play a key role in immune regulation. Toll-like receptors (TLRs) enable innate immune cells, such as macrophages, to recognize a wide variety of microbial ligands, thereby promoting inflammation. The interaction of GCs with macrophages in the immunosuppressive resolution phase upon prolonged TLR activation is widely unknown. Treatment of human alveolar macrophages (AMs) with the synthetic GC dexamethasone (Dex) did not alter the expression of TLRs -1, -4, and -6. In contrast, TLR2 was upregulated in a GC receptor-dependent manner, as shown by Western blot and qPCR. Furthermore, long-term lipopolysaccharide (LPS) exposure mimicking immunosuppression in the resolution phase of inflammation synergistically increased Dex-mediated TLR2 upregulation. Analyses of publicly available datasets suggested that TLR2 is induced during the resolution phase of inflammatory diseases, i.e., under conditions associated with high endogenous GC production. TLR2 induction did not enhance TLR2 signaling, as indicated by reduced cytokine production after treatment with TLR2 ligands in Dex- and/or LPS-primed AMs. Thus, we hypothesized that the upregulated membrane-bound TLR2 might serve as a precursor for soluble TLR2 (sTLR2), known to antagonize TLR2-dependent cell actions. Supernatants of LPS/Dex-primed macrophages contained sTLR2, as demonstrated by Western blot analysis. Activation of metalloproteinases resulted in enhanced sTLR2 shedding. Additionally, we detected full-length TLR2 and assumed that this might be due to the production of TLR2-containing extracellular vesicles (EVs). EVs from macrophage supernatants were isolated by sequential centrifugation. Both untreated and LPS/Dex-treated cells produced vesicles of various sizes and shapes, as shown by cryo-transmission electron microscopy. These vesicles were identified as the source of full-length TLR2 in macrophage supernatants by Western blot and mass spectrometry. Flow cytometric analysis indicated that TLR2-containing EVs were able to bind the TLR2 ligand Pam3CSK4. In addition, the presence of EVs reduced inflammatory responses in Pam3CSK4-treated endothelial cells and HEK Dual reporter cells, demonstrating that TLR2-EVs can act as decoy receptors. In summary, our data show that sTLR2 and full-length TLR2 are released by macrophages under anti-inflammatory conditions, which may contribute to GC-induced immunosuppression