1,118 research outputs found
Modal coupling in traveling-wave resonators
High-Q traveling-wave-resonators can enter a regime in which even minute scattering amplitudes associated with either bulk or surface imperfections can drive the system into the so-called strong modal coupling regime. Resonators that enter this regime have their coupling properties radically altered and can mimic a narrowband reflector. We experimentally confirm recently predicted deviations from criticality in such strongly coupled systems. Observations of resonators that had Q>10^8 and modal coupling parameters as large as 30 were shown to reflect more than 94% of an incoming optical signal within a narrow bandwidth of 40 MHz
Demonstration of ultra-high-Q small mode volume toroid microcavities on a chip
Optical microcavities confine light spatially and temporally and find
application in a wide range of fundamental and applied studies. In many areas,
the microcavity figure of merit is not only determined by photon lifetime (or
the equivalent quality-factor, Q), but also by simultaneous achievement of
small mode volume V . Here we demonstrate ultra-high Q-factor small mode volume
toroid microcavities on-a-chip, which exhibit a Q/V factor of more than
. These values are the highest reported to date for any
chip-based microcavity. A corresponding Purcell factor in excess of 200 000 and
a cavity finesse of is achieved, demonstrating that toroid
microcavities are promising candidates for studies of the Purcell effect,
cavity QED or biochemical sensingComment: 4 pages, 3 figures, Submitted to Applied Physics Letter
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
Ideality in a fiber-taper-coupled microresonator system for application to cavity quantum electrodynamics
The ability to achieve near lossless coupling between a waveguide and a resonator is fundamental to many quantum-optical studies as well as to practical applications of such structures. The nature of loss at the junction is described by a figure of merit called ideality. It is shown here that under appropriate conditions ideality in excess of 99.97% is possible using fiber-taper coupling to high-Q silica microspheres. To verify this level of coupling, a technique is introduced that can both measure ideality over a range of coupling strengths and provide a practical diagnostic of parasitic coupling within the fiber-taper-waveguide junction
Minimising Bloat Through Development of White Clover (\u3cem\u3eT. Repens\u3c/em\u3e) with High Levels of Condensed Tannins
White clover constitutes a low percentage of the overall sward content in Irish pastureland despite EU directives limiting the use of nitrogenous fertilizers. This is mainly due to the tendency of large amounts of white clover to cause bloat. Bloat is a potentially fatal build up of proteinaceous foam in the guts of ruminants. Some lesser cultivated legumes such as Lotus species contain condensed tannins (CT) that decrease the incidence of bloated animals. The project’s objective is to reduce the risk of bloat by generating white clover cultivars with high CT content. We are investigating whether expression of the ANTHOCYANIN REDUCTASE gene (BAN) in transgenic white clover and Medicago truncatula (model) plants leads to increased CT levels (Xie et al., 2003)
Modal properties of toroidal microcavities
We investigate the resonance structure and modal properties of chip-based toroidal microcavities. The variation of modal volume and radiation quality factor versus the toroidal geometrical aspect ratio is studied
An Emerging Integration of Universal and Culturally Specific Psychologies and its Implications for the Study of Psychopathology
There is an emerging consensus among researchers on the need to integrate universal and culturally specific psychological perspectives. Important tasks in this process have included identifying the appropriate level of generality for putatively universal processes, how to understand culturally different processes in light of shared universal capacities, and the development of transparent scientific means for investigating cultural differences. In this chapter, the authors discuss each of these issues. It appears to be true that many psychological processes appear to reflect culturally-specific instantiations of universal capacities. The authors then consider implications of this emerging integration for psychology, by applying it to the study of psychopathology. They report on formal models that explain why some cultures embrace dysfunction among members. They then use the integrative framework to describe methods for determining whether putative disorders bring universal or contextual life dysfunction, and to clarify etiological models of three disorders. Models of psychopathology can be more informed and precise if they include careful consideration of both universal and cultural influences on behavior. Cultural psychology is not a separate discipline within psychology; rather, it informs, and should be integrated with, the various content domains within the field
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