Tuning a racetrack ring resonator by an integrated dielectric MEMS cantilever

The principle, fabrication and characterization of a dielectric MEMS cantilever located a few 100 nm above a racetrack ring resonator are presented. After fabrication of the resonators on silicon-on-insulator (SOI) wafers in a foundry process, the cantilevers were integrated by surface micromachining techniques. Off-state deflections of the cantilevers have been optimized to appropriately position them near the evanescent field of the resonator. Using electrostatic actuation, moving the cantilevers into this evanescent field, the propagation properties of the ring waveguide are modulated. We demonstrate 122 pm tuning of the resonance wavelength of the optical ring resonator (in the optical C-band) without change of the optical quality factor, on application of 9 V to a 40 µm long cantilever. This compact integrated device can be used for tuning/switching a specific wavelength, with very little energy for operation and negligible cross talk with surrounding device

Micro bimorph cantilever switches for tuning integrated optical systems

We propose to use a self aligning technology (Figure 1) to integrate micro bimorph cantilevers with tips with respect to e.g. the holes in a photonic band gap (PBG) microresonator coupling section in order to perturb its evanescent field [1]. Using a simplified process, we first fabricated bimorph cantilevers on top of silicon, by surface micromachining techniques in which the upper electrode is a thin layer of Chromium on the top of a thick layer of dielectric material which is Silicon Rich Nitride (SiN). The resonance frequencies and pull in voltages of these electrostatically actuated bimorph cantilevers with off-state deflection [2] are analysed and it is found that the higher resonance frequencies come at the price of larger switching voltages (Figure 2-3). This allows for fabrication of relative stiff cantilevers with resonance frequencies in the MHz range to interact with the evanescent field of PBG crystals in which the mechanical elements start to play a role typically with a distance <400 nanometers. We have also fabricated bimorph cantilevers without tips, integrated on top of various optical systems like ring resonators, photonic crystals and planar waveguides. Analytical and numerical models are developed to predict the resonance frequencies and the pull-in voltages of these switches, including the effect of undercut and validated it with experimental data. We have observed selective wavelength on/off switching by perturbing the near band edge resonance of a waveguide grating with a 20 μm wide silicon nitride AFM cantilever, without using its tip area (Figure 4). The observed mechanical perturbation allows 15 dB on/off switching of a specific wavelength and a wavelength tuning of approximately 60 pm. In conclusion, here we describe the technology for fabricating integrated bimorph switches, the optimization studies of the cantilever designs and measurements of mechano-optical interactions using an AFM based cantilever. These optical switches have potential application in the field of elecommunication networks

Antarctic ice sheet and oceanographic response to eccentricity forcing during the early Miocene

Stable isotope records of benthic foraminifera from ODP Site 1264 in the southeastern Atlantic Ocean are presented which resolve the latest Oligocene to early Miocene (~24–19 Ma) climate changes at high temporal resolution (&lt;3 kyr). Using an inverse modelling technique, we decomposed the oxygen isotope record into temperature and ice volume and found that the Antarctic ice sheet expanded episodically during the declining phase of the long-term (~400 kyr) eccentricity cycle and subsequent low short-term (~100 kyr) eccentricity cycle. The largest glaciations are separated by multiple long-term eccentricity cycles, indicating the involvement of a non-linear response mechanism. Our modelling results suggest that during the largest (Mi-1) event, Antarctic ice sheet volume expanded up to its present-day configuration. In addition, we found that distinct ~100 kyr variability occurs during the termination phases of the major Antarctic glaciations, suggesting that climate and ice-sheet response was more susceptible to short-term eccentricity forcing at these times. During two of these termination-phases, ?18O bottom water gradients in the Atlantic ceased to exist, indicating a direct link between global climate, enhanced ice-sheet instability and major oceanographic reorganisations

Mechanical tuning of optical race-track ring resonators

This paper presents the fabrication and mechanical characterization of electrostatically actuated micro bimorphs integrated with race-track ring resonators, for optical tuning applications. The bimorphs, having an upward deflection in the off-state, are integrated by surface micromachining techniques with race-track ring resonators fabricated on Silicon On Insulator (SOI) wafers. Using electrostatic actuation, these bimorphs are pulled into the evanescent field of the ring resonator thereby modulating the propagation properties. Pull-in voltages of the bimorphs have been measured statically and the effect of electrostatic spring softening (ESS) on the resonance frequency has been measured dynamically. The resonance wavelength of the optical ring resonator could be tuned by 50 pm by applying an 8.5 V DC voltage to a 40 μm long bimorph, bringing it into close proximity of the ring resonator waveguide. To the best of our knowledge, this is the first experimental demonstration of tuning of race track ring resonators by integrated, electrostatically actuated bimorphs.\ud \u

Variations in DNA methylation of interferon gamma and programmed death 1 in allograft rejection after kidney transplantation

Background: The role of DNA methylation in the regulation of the anti-donor-directed immune response after organ transplantation is unknown. Here, we studied the methylation of two mediators of the immune response: the pro-inflammatory cytokine interferon γ (IFNγ) and the inhibitory receptor programmed death 1 (PD1) in naïve and memory CD8+ T cell subsets in kidney transplant recipients receiving immunosuppressive medication. Both recipients experiencing an episode of acute allograft rejection (rejectors) as well as recipients without rejection (non-rejectors) were included. Results: CpGs in the promoter regions of both IFNγ and PD1 were significantly (p < 0.001) higher methylated in the naïve CD8+ T cells compared to the memory T cell subsets. The methylation status of both IFNγ and PD1 inversely c

Pharmacokinetics and pharmacodynamics of topotecan administered daily for 5 days every 3 weeks

Topotecan is a novel semisynthetic derivative of the anticancer agent camptothecin and inhibits the intranuclear enzyme topoisomerase I. The lactone structure of topotecan, which is in equilibrium with the inactive ringopened hydroxy acid, is essential for this activity. The open form predominates at physiological pH. We performed a pharmacokinetic, study as part of a phase I study in patients with various types of soli