Nonlinear carrier dynamics in a quantum dash optical amplifier

Results of experimental pump-probe spectroscopy of a quantum dash optical amplifier biased at transparency are presented. Using strong pump pulses we observe a competition between free carrier absorption and two-photon induced stimulated emission that can have drastic effects on the transmission dynamics. Thus, both enhancement as well as suppression of the transmission can be observed even when the amplifier is biased at transparency. A simple theoretical model taking into account two-photon absorption and free carrier absorption is presented that shows good agreement with the measurements

Slow-light enhanced gain in active photonic crystal waveguides

Slow light is a fascinating physical effect, raising fundamental questions related to our understanding of light-matter interactions as well as offering new possibilities for photonic devices. From the first demonstrations of slow light propagation in ultra-cold atomic gasses, solid-state Ruby and photonic crystal structures, focus has shifted to applications, with slow light offering the ability to enhance and control light-matter interactions. The demonstration of tuneable delay lines, enhanced nonlinearities and spontaneous emission, enlarged spectral sensitivity and increased phase shifts illustrate the possibilities enabled by slow light propagation, with microwave photonics emerging as one of the promising applications. Here, we demonstrate that slow light can be used to control and increase the gain coefficient of an active semiconductor waveguide. The effect was theoretically predicted but not yet experimentally demonstrated. These results show a route towards realizing ultra-compact optical amplifiers for linear and nonlinear applications in integrated photonics and prompts further research into the rich physics of such structures

SOX11 expression correlates to promoter methylation and regulates tumor growth in hematopoietic malignancies

<p>Abstract</p> <p>Background</p> <p>The transcription factor SOX11 plays an important role in embryonic development of the central nervous system (CNS) and is expressed in the adult immature neuron but is normally not expressed in any other adult tissue. It has recently been reported to be implicated in various malignant neoplasms, including several lymphoproliferative diseases, by its specific expression and in some cases correlation to prognosis. SOX11 has been shown to prevent gliomagenesis <it>in vivo </it>but the causes and consequences of aberrant expression of <it>SOX11 </it>outside the CNS remain unexplained.</p> <p>Results</p> <p>We now show the first function of <it>SOX11 </it>in lymphoproliferative diseases, by demonstrating <it>in vitro </it>its direct involvement in growth regulation, as assessed by siRNA-mediated silencing and ectopic overexpression in hematopoietic malignancies. Gene Chip analysis identified cell cycle regulatory pathways, including Rb-E2F, to be associated with SOX11-induced growth reduction. Furthermore, promoter analysis revealed that <it>SOX11 </it>is silenced through DNA methylation in B cell lymphomas, suggesting that its regulation is epigenetically controlled.</p> <p>Conclusions</p> <p>The data show that SOX11 is not a bystander but an active and central regulator of cellular growth, as both siRNA-mediated knock-down and ectopic overexpression of <it>SOX11 </it>resulted in altered proliferation. Thus, these data demonstrate a tumor suppressor function for <it>SOX11 </it>in hematopoietic malignancies and revealed a potential epigenetic regulation of this developmentally involved gene.</p