Sagnac effect in coupled-resonator slow-light waveguide structures

We study the effect of rotation on the propagation of electromagnetic waves in slow-light waveguide structures consisting of coupled microring resonators. We show that such configurations exhibit a new type of Sagnac effect which can be used for the realization of highly compact integrated rotation sensors and gyroscopes.     

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.     

The Oxidation of Aldehydes to Methyl Esters using Trichloroisocyanuric Acid

Aldehydes are readily oxidized to methyl esters by a solution of methanol, pyridine, and trichloroisocyanuric acid in acetonitrile, acetone, or methylene chloride.     

Thermal analysis of hexadecyltrimethylammonium-montmorillonites

Na-montmorillonite (Na-MONT) was loaded with hexadecyltrimethylammonium cations (HDTMA) by replacing 41 and 90% of the exchangeable Na with HDTMA. The organoclays were labeled OC-41 and OC-90, respectively. Freeze-dried Na-MONT, OC-41, and OC-90 were heated in air at 150, 250, 360, 420, 550, 700, and 900 °C. The thermally treated samples were suspended in water, air-dried, and desiccated over silica during 40 days. All samples were diffracted by X-ray and fitting calculations were performed on each diffractogram. These calculations gave information on basal spacings, relative concentrations, and homogeneity of the different tactoids obtained at each temperature, before and after suspending and desiccating. HDTMA-MONT tactoids with spacing ≥1.41 nm appeared between 25 and 250 °C. OC-41 or OC-90 intercalated monolayers or bilayers of HDTMA, respectively. At 250 °C OC-41 was air-oxidized to a smaller extent than OC-90, resulting in charcoal-MONT tactoids. With further heating the organic matter was gradually oxidized and at 700 °C both clays were collapsed. During the thermo-XRD-analysis of both organoclays three types of charcoal-MONT complexes appeared: (1) LTSC-MONT tactoids with a basal spacing 1.32–1.39 nm, between 250 and 420 °C in both clays; (2) HTSC-α-MONT tactoids with spacing 1.22–1.28 nm, between 360 or 250 and 500 or 550 °C in OC-41 or OC-90, respectively; (3) HTSC-β-MONT with spacing 1.12–1.18 nm, between 360 and 550 °C in both clays, where LTSC and HTSC are low- and high-temperature stable charcoal, respectively. HTSC-β-MONT differs from HTSC-α-MONT by having carbon atoms keying into the ditrigonal holes of the clay-O-planes.     

Spatial modal control of two-dimensional photonic crystal Bragg lasers

We investigate the modal losses and field distributions of different order transverse modes supported by the photonic crystal Bragg structure using a transfer matrix method. We find that only the fundamental transverse mode has a single-lobed near field and far field and there exists a trade-off between ensuring lasing in the fundamental transverse mode and reducing the threshold. Employing these design principles, we experimentally demonstrate a large-area, edge-emitting, and single-mode semiconductor photonic crystal Bragg laser with a single-lobed, diffraction-limited far field under continuous wave condition.     

Thermal analysis of tributylammonium montmorillonite and laponite

Montmorillonite and Laponite loaded with different amounts of tributylammonium cations (TBAH⁺), up to 40 and 30 mmol, respectively, per 100 g clay, were studied by thermo-XRD-analysis. TBAH-smectites heated at 300 and 420°C exhibited basal spacings of 1.30 and 1.24 nm, attributed to smectite tactoids with low- and high-temperature-stable monolayer charcoals, respectively in the interlayers. DTA-EGA and TG of the TBAH-smectites showed four stages of mass loss labeled A, B, C and D. Stage A below 250°C, accompanied by an endothermic DTA peak, resulted from the dehydration of the clay. Mass loss stages B, C and D, at 250–380, 380–605°C and above 605°C, respectively, accompanied by exothermic DTA peaks, were due to three oxidation steps of the organic matter. In mass loss stage B (first oxidation step) mainly organic hydrogen was oxidized to H2O whereas carbon and nitrogen formed low- and high-temperature-stable charcoals. In stages C and D (second and third oxidation steps) low- and high-temperature- stable charcoals were oxidized, respectively. Dehydroxylation of the smectites occurred together with the second and third oxidation steps. Thermal mass loss at each step was calculated from the TG curves showing that in montmorillonite the percentage of high-temperature-stable charcoal from total charcoal decreased with higher TBAH⁺ loadings of the clay whereas in Laponite this percentage increased with higher loadings of the clay.     

Compensation for atmospheric degradation of optical beam transmission by nonlinear optical mixing

The use of nonlinear optical mixing for compensating for atmospheric propagation distortion is considered.     

Beam-quality analysis of surface finish by moiré deflectometry

A novel definition to surface finish based on the increase in the number of transverse modes of radiation due to reflection by a tested surface is proposed. A practical analysis of various surfaces applying a new method, moiré deflectometry, which enables a real-time measurement of surface roughness on shop-floor level, is demonstrated.