Transmission and group delay of microring coupled-resonator optical waveguides

We measured the transmission and group delay of microring coupled-resonator optical waveguides (CROWs). The CROWs consisted of 12 weakly coupled, microring resonators fabricated in optical polymers (PMMA on Cytop). The intrinsic quality factor of the resonators was 18,000 and the interresonator coupling was 1%, resulting in a delay of 110-140 ps and a slowing factor of 23-29 over a 17 GHz bandwidth

Polymer Microring Coupled-Resonator Optical Waveguides

We present measurements of the transmission and dispersion properties of coupled-resonator optical waveguides (CROWs) consisting of weakly coupled polymer microring resonators. The fabrication and the measurement methods of the CROWs are discussed as well. The experimental results agree well with the theoretical loss, waveguide dispersion, group delay, group velocity, and group-velocity dispersion (GVD). The intrinsic quality factors of the microrings were about 1.5 times 10^4 to 1.8 times 10^4, and group delays greater than 100 ps were measured with a GVD between -70 and 100 ps/(nm x resonator). With clear and simple spectral responses and without a need for the tuning of the resonators, the polymer microring CROWs demonstrate the practicability of using a large number of microresonators to control the propagation of optical waves

Atmospheric Deposition of Soluble Organic Nitrogen due to Biomass Burning

Atmospheric deposition of reactive nitrogen (N) species from large fires may contribute to enrichment of nutrients in aquatic ecosystems. Here we use an atmospheric chemistry transport model to investigate the supply of soluble organic nitrogen (ON) from open biomass burning to the ocean. The model results show that the annual deposition rate of soluble ON to the oceans is increased globally by 13% with the increase being particularly notable over the coastal water downwind from the source regions. The estimated deposition of soluble ON due to haze events from the secondary formation is more than half of that from the primary sources. We examine the secondary formation of particulate C-N compounds (e.g., imidazole) from the reactions of glyoxal and methylglyoxal with atmospheric ammonium in wet aerosols and upon cloud evaporation. These ON sources result in a significant contribution to the open ocean, suggesting that atmospheric processing in aqueous phase may have a large effect. We compare the soluble ON concentration in aerosols with and without open biomass burning as a case study in Singapore. The model results demonstrate that the soluble ON concentration in aerosols is episodically enriched during the fire events, compared to the without smoke simulations. However, the model results show that the daily soluble ON concentration can be also enhanced in the without smoke simulations during the same period, compared to the monthly averages. This indicates that care should be taken when using in-situ observations to constrain the soluble ON source strength from biomass burning. More accurate quantification of the soluble ON burdens with no smoke sources is therefore needed to assess the effect of biomass burning on bioavailable ON input to the oceans.Poster abstract A31G-3099 presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec

Atmospheric Chemistry Transport Modeling of Organic Nitrogen Input to the Ocean

Atmospheric deposition of reactive nitrogen (N) species from air pollutants is a significant source of exogenous nitrogen in marine ecosystems. Here we use a process-based chemical transport model to investigate global supply of soluble organic nitrogen (ON) from continental sources to the ocean. The present-day emissions of NO, NH3, and the primary ON are 46, 42, and 11 Tg N/yr. Comparisons of modeled deposition with observations at coastal and marine locations show overall good agreement for inorganic nitrogen and total nitrogen, but significant underestimates for ON when we explicitly calculated volatile ON and particulate ON in the model. The model results suggest that including soluble ON potentially emitted with carbonaceous aerosols and/or transformed from NH4+ on carbonaceous and dust aerosols contributes to a better predictive capability of the deposition rates. The estimated annual total deposition rates of ON to the ocean range from 0.9 to 5.9 Tg N/yr, depending on the solubility at emission and/or the transformation on aerosols. The model results show a clear distinction in the vertical distribution of ON between different sources (i.e., the primary or secondary formation). These results highlight the necessity of improving the process-based quantitative understanding of the solubility of ON in emitted particles and the chemical reactions of inorganic nitrogen species with organics in aerosol and cloud water.Poster abstract B43E-0545 presented at 2013 Fall Meeting, AGU, San Francisco, Calif., 9-13 Dec

Reconciling modeled and observed atmospheric deposition of soluble organic nitrogen at coastal locations

Atmospheric deposition of reactive nitrogen (N) species from air pollutants is a significant source of exogenous nitrogen in marine ecosystems. Here we use an atmospheric chemical transport model to investigate the supply of soluble organic nitrogen (ON) from anthropogenic sources to the ocean. Comparisons of modeled deposition with observations at coastal and marine locations show good overall agreement for inorganic nitrogen and total soluble nitrogen. However, previous modeling approaches result in significant underestimates of the soluble ON deposition if the model only includes the primary soluble ON and the secondary oxidized ON in gases and aerosols. Our model results suggest that including the secondary reduced ON in aerosols as a source of soluble ON contributes to an improved prediction of the deposition rates. The model results show a clear distinction in the vertical distribution of soluble ON in aerosols between different processes from the primary sources and the secondary formation. The model results (excluding the biomass burning and natural emission changes) suggest an increase in soluble ON outflow from atmospheric pollution, in particular from East Asia, to the oceans in the twentieth century. These results highlight the necessity of improving the process-based quantitative understanding of the chemical reactions of inorganic nitrogen species with organics in aerosol and cloud water

Laplacian Solitons and Symmetry in G_2-geometry

In this paper, it is shown that (with no additional assumptions) on a compact 7-dimensional manifold which admits a $G_2$-structure soliton solutions to the Laplacian flow of R. Bryant can only be shrinking or steady. We also show that the space of symmetries (vector fields that annihilate via the Lie derivative) of a torsion-free $G_2$-structure on a compact 7-manifold is canonically isomorphic to $H^1(M,\mathbb{R})$. Some comparisons with Ricci solitons are also discussed, along with some future directions of exploration

Electrically-pumped, broad-area, single-mode photonic crystal lasers

Planar broad-area single-mode lasers, with modal widths of the order of tens of microns, are technologically important for high-power applications and improved coupling efficiency into optical fibers. They may also find new areas of applications in on-chip integration with devices that are of similar size scales, such as for spectroscopy in microfluidic chambers or optical signal processing with micro-electromechanical systems. An outstanding challenge is that broad-area lasers often require external means of control, such as injection-locking or a frequency/spatial filter to obtain single-mode operation. In this paper, we propose and demonstrate effective index-guided, large-area, edge-emitting photonic crystal lasers driven by pulsed electrical current injection at the optical telecommunication wavelength of 1550nm. By suitable design of the photonic crystal lattice, our lasers operate in a single mode with a 1/e^2 modal width of 25μm and a length of 600μm

Active coupled-resonator optical waveguides. II. Current injection InP-InGaAsP Fabry-Perot resonator arrays

We investigate active, electrically pumped coupled-resonator optical waveguides (CROWs) in the form of InP-InGaAsP Fabry-Perot resonator arrays. We discuss the fabrication of these devices and present measurements of the transmission spectra. The signal-to-noise ratio is found to be a strong function of wavelength and degraded rapidly along the resonator chain away from the input. Our results highlight a number of ingredients toward practical implementations loss-compensated and amplifying CROWs

Two-dimensional Bragg grating lasers defined by electron-beam lithography

Two-dimensional Bragg grating (2DBG) lasers with two quarter-wave slip line defects have been designed and fabricated by electron-beam lithography and reactive ion etching. Unlike conventional two-dimensional photonic crystal defect lasers, which use a large refractive index perturbation to confine light in a plane, the 2DBG structures described here selectively control the longitudinal and transverse wave vector components using a weak index perturbation. Two line defects perpendicular to each other are introduced in the 2DBG to define the optical resonance condition in the longitudinal and transverse directions. In this article, we describe the lithography process used to pattern these devices. The 2DBG lasers were defined using polymethylmethacrylate resist exposed in a Leica Microsystems EBPG 5000+ electron-beam writer at 100 kV. A proximity correction code was used to obtain a uniform pattern distribution over a large area, and a dosage matrix was used to optimize the laser design parameters. Measurements of electrically pumped 2DBG lasers showed modal selection in both the longitudinal and transverse directions due to proper design of the grating and defects, making them promising candidates for single-mode, high power, high efficiency, large-area lasers

Global modeling of SOA: the use of different mechanisms for aqueous-phase formation

There is growing interest in the formation of secondary organic aerosol (SOA) through condensed aqueous-phase reactions. In this study, we use a global model (IMPACT) to investigate the potential formation of SOA in the aqueous phase. We compare results from several multiphase process schemes with detailed aqueous-phase reactions to schemes that use a first-order gas-to-particle formation rate based on uptake coefficients. The predicted net global SOA production rate in cloud water ranges from 13.1 Tg yr-1 to 46.8 Tg yr-1 while that in aerosol water ranges from -0.4 Tg yr-1 to 12.6 Tg yr-1. The predicted global burden of SOA formed in the aqueous phase ranges from 0.09 Tg to 0.51 Tg. A sensitivity test to investigate two representations of cloud water content from two global models shows that increasing cloud water by an average factor of 2.7 can increase the net SOA production rate in cloud water by a factor of 4 at low altitudes (below approximately 900 hPa). We also investigated the importance of including dissolved Fe chemistry in cloud water aqueous reactions. Adding these reactions increases the formation rate of aqueous-phase OH by a factor of 2.6 and decreases the amount of global aqueous SOA formed by 31%. None of the mechanisms discussed here is able to provide a best fit for all observations. Rather, the use of an uptake coefficient method for aerosol water and a multi-phase scheme for cloud water provides the best fit in the Northern Hemisphere and the use of multiphase process scheme for aerosol and cloud water provides the best fit in the tropics. The model with Fe chemistry underpredicts oxalate measurements in all regions. Finally, the comparison of oxygen-to-carbon (O / C) ratios estimated in the model with those estimated from measurements shows that the modeled SOA has a slightly higher O / C ratio than the observed SOA for all cases