Ultra-high-Q toroid microcavities on a chip

We demonstrate microfabrication of ultra-high-Q microcavities on a chip, exhibiting a novel toroid-shaped geometry. The cavities possess Q-factors in excess of 100 million which constitutes an improvement close to 4 orders-of-magnitude in Q compared to previous work [B. Gayral, et al., 1999]

Fabrication and coupling to planar high-Q silica disk microcavities

Using standard lithographic techniques, we demonstrate fabrication of silica disk microcavities, which exhibit whispering-gallery-type modes having quality factors (Q) in excess of 1 million. Efficient coupling (high extinction at critical coupling and low, nonresonant insertion loss) to and from the disk structure is achieved by the use of tapered optical fibers. The observed high Q is attributed to the wedged-shaped edge of the disk microcavity, which is believed to isolate modes from the disk perimeter and thereby reduce scattering loss. The mode spectrum is measured and the influence of planar confinement on the mode structure is investigated. We analyze the use of these resonators for very low loss devices, such as add/drop filters

Ultralow-threshold microcavity Raman laser on a microelectronic chip

Using ultrahigh-Q toroid microcavities on a chip, we demonstrate a monolithic microcavity Raman laser. Cavity photon lifetimes in excess of 100 ns combined with mode volumes typically of less than 1000 µm^3 significantly reduce the threshold for stimulated Raman scattering. In conjunction with the high ideality of a tapered optical fiber coupling junction, stimulated Raman lasing is observed at an ultralow threshold (as low as 74 µW of fiber-launched power at 1550 nm) with high efficiency (up to 45% at the critical coupling point) in good agreement with theoretical modeling. Equally important, the wafer-scale nature of these devices should permit integration with other photonic, mechanical, or electrical functionality on a chip

Ultra-high-Q microcavity operation in H2O and D2O

Optical microcavities provide a possible method for boosting the detection sensitivity of biomolecules. Silica-based microcavities are important because they are readily functionalized, which enables unlabeled detection. While silica resonators have been characterized in air, nearly all molecular detections are performed in solution. Therefore, it is important to determine their performance limits in an aqueous environment. In this letter, planar microtoroid resonators are used to measure the relationship between quality factor and toroid diameter at wavelengths ranging from visible to near-IR in both H2O and D2O, and results are then compared to predictions of a numerical model. Quality factors (Q) in excess of 10^8, a factor of 100 higher than previous measurements in an aqueous environment, are observed in both H2O and D2O

Study of the 12C+12C fusion reactions near the Gamow energy

The fusion reactions 12C(12C,a)20Ne and 12C(12C,p)23Na have been studied from E = 2.10 to 4.75 MeV by gamma-ray spectroscopy using a C target with ultra-low hydrogen contamination. The deduced astrophysical S(E)* factor exhibits new resonances at E <= 3.0 MeV, in particular a strong resonance at E = 2.14 MeV, which lies at the high-energy tail of the Gamow peak. The resonance increases the present non-resonant reaction rate of the alpha channel by a factor of 5 near T = 8x10^8 K. Due to the resonance structure, extrapolation to the Gamow energy E_G = 1.5 MeV is quite uncertain. An experimental approach based on an underground accelerator placed in a salt mine in combination with a high efficiency detection setup could provide data over the full E_G energy range.Comment: 4 Pages, 4 figures, accepted for publication in Phys. Rev. Let

Evaluation of NSCAT scatterometer winds using equatorial Pacific buoy observations

As part of the calibration/validation effort for NASA's Scatterometer (NSCAT) we compare the satellite data to winds measured at the sea surface with an array of buoys moored in the equatorial Pacific Ocean. The NSCAT data record runs from September, 1996 through the end of June, 1997. The raw NSCAT data, radar backscatter, is converted to wind vectors at 10 meters above the surface assuming a neutrally stratified atmosphere, using the NSCAT-1 and NSCAT-2 model functions. The surface winds were measured directly by the TAO (Tropical Atmosphere Ocean) buoy array which spans the width of the equatorial Pacific within about 8° of the equator. The buoy program and data archive are maintained by the Pacific Marine Environmental Laboratory, at the National Oceanic and Atmospheric Administration, in collaboration with institutions in Japan, France and Taiwan. We also use data from two buoys maintained by the Woods Hole Oceanographic Institution located along 125°W. Since the buoy winds are measured at various heights above the surface, they are adjusted for both height and atmospheric surface layer stratification before comparisons are made to the NSCAT data. Co-location requirements include measurements within 100 km and 60 minutes of each other. There was a total of 5580 comparisons for the NSCAT-1 model function and 6364 comparisons for the NSCAT-2 model function. The NSCAT wind speeds, using the NSCAT-1 model function, are lower than the buoy wind speeds by about 0.54 ms-1 and have a 9.8° directional bias. The NSCAT-2 winds speeds were lower than the TAO buoy winds by only 0.08 ms-1, but still have the same 9.8° directional bias. The wind retrieval algorithm selects the vector closest to the buoy approximately 88% of the time. However, in the relatively low wind speed regime of the TAO array, approximately 4% of the wind vectors are more than 120° from the buoy wind.Funding was provided by the National Aeronautics and Space Administration under Contract No. 957652

Evaluation of critical congenital heart defects screening using pulse oximetry in the neonatal intensive care unit.

ObjectiveTo evaluate the implementation of early screening for critical congenital heart defects (CCHDs) in the neonatal intensive care unit (NICU) and potential exclusion of sub-populations from universal screening.Study designProspective evaluation of CCHD screening at multiple time intervals was conducted in 21 NICUs across five states (n=4556 infants).ResultsOf the 4120 infants with complete screens, 92% did not have prenatal CHD diagnosis or echocardiography before screening, 72% were not receiving oxygen at 24 to 48 h and 56% were born ⩾2500 g. Thirty-seven infants failed screening (0.9%); none with an unsuspected CCHD. False positive rates were low for infants not receiving oxygen (0.5%) and those screened after weaning (0.6%), yet higher among infants born at &lt;28 weeks (3.8%). Unnecessary echocardiograms were minimal (0.2%).ConclusionGiven the majority of NICU infants were ⩾2500 g, not on oxygen and not preidentified for CCHD, systematic screening at 24 to 48 h may be of benefit for early detection of CCHD with minimal burden

Nonlinear transmission through a tapered fiber in rubidium vapor

Sub-wavelength diameter tapered optical fibers surrounded by rubidium vapor can undergo a substantial decrease in transmission at high atomic densities due to the accumulation of rubidium atoms on the surface of the fiber. Here we demonstrate the ability to control these changes in transmission using light guided within the taper. We observe transmission through a tapered fiber that is a nonlinear function of the incident power. This effect can also allow a strong control beam to change the transmission of a weak probe beam.Comment: 10 pages, 4 figure