Electrically tunable liquid crystal optical microresonators

Because of their small mode volume and high Q-factors, optical microresonators are interesting for applications such as laser sources, active filters and all-optical switches. Especially interesting are tunable resonators, in which the resonance frequency tuning by size, shape, temperature or electric field can be achieved. Here we demonstrate electrically tunable, low-loss whispering-gallery-mode (WGM) resonators made of nematic liquid crystal droplets, embedded in a polymer matrix. The shift in resonant frequencies is achieved via electric field-induced structural distortion of the birefringent liquid crystal resonator medium. Nematic liquid crystal microresonators have a large tuning range of the order of 20nm at 2.6Vνm 1 for a 600nm WGM in 17-νm-diameter droplets and high Q-factors up to 12,000 in 33-νm-diameter droplets. The tunability is approximately two orders of magnitude larger than usually achieved in solid-state microresonators. © 2009 Macmillan Publishers Limited. All rights reserved

Imaging analysis of clock neurons reveals light buffers the wake-promoting effect of dopamine

How animals maintain proper amounts of sleep yet still be flexible to changes in the environmental conditions remains unknown. Here we showed that environmental light suppresses the wake-promoting effects of dopamine in fly brains. A subset of clock neurons, the 10 large lateral-ventral neurons (l-LNvs), are wake-promoting and respond to dopamine, octopamine as well as light. Behavioral and imaging analyses suggested that dopamine is a stronger arousal signal than octopamine. Surprisingly, light exposure not only suppressed the l-LNv responses but also synchronized responses of neighboring l-LNvs. This regulation occured by distinct mechanisms: light-mediated suppression of octopamine responses is regulated by the circadian clock, whereas light regulation of dopamine responses occurs by upregulation of inhibitory dopamine receptors. Plasticity therefore alters the relative importance of diverse cues based on the environmental mix of stimuli. The regulatory mechanisms described here may contribute to the control of sleep stability while still allowing behavioral flexibility