Changing the responses of cortical neurons from sub- to suprathreshold using single spikes in vivo.

Action Potential (APs) patterns of sensory cortex neurons encode a variety of stimulus features, but how can a neuron change the feature to which it responds? Here, we show that in vivo a spike-timing-dependent plasticity (STDP) protocol-consisting of pairing a postsynaptic AP with visually driven presynaptic inputs-modifies a neurons' AP-response in a bidirectional way that depends on the relative AP-timing during pairing. Whereas postsynaptic APs repeatedly following presynaptic activation can convert subthreshold into suprathreshold responses, APs repeatedly preceding presynaptic activation reduce AP responses to visual stimulation. These changes were paralleled by restructuring of the neurons response to surround stimulus locations and membrane-potential time-course. Computational simulations could reproduce the observed subthreshold voltage changes only when presynaptic temporal jitter was included. Together this shows that STDP rules can modify output patterns of sensory neurons and the timing of single-APs plays a crucial role in sensory coding and plasticity.DOI:http://dx.doi.org/10.7554/eLife.00012.001.

Using sub-word-level information for confidence estimation with conditional random field models

The task of word-level confidence estimation (CE) for automatic speech recognition (ASR) systems stands to benefit from the combination of suitably defined input features from multiple information sources. However, the information sources of interest may not necessarily operate at the same level of granularity as the underlying ASR system. The research described here builds on previous work on confidence estimation for ASR systems using features extracted from word-level recognition lattices, by incorporating information at the sub-word level. Furthermore, the use of Conditional Random Fields (CRFs) with hidden states is investigated as a technique to combine information for word-level CE. Performance improvements are shown using the sub-word-level information in linear-chain CRFs with appropriately engineered feature functions, as well as when applying the hidden-state CRF model at the word level.

Enhanced infra-red emission from sub-millimeter microelectromechanical systems micro hotplates via inkjet deposited carbon nanoparticles and fullerenes

In this paper, we demonstrate a micro-inkjet printing technique as a reproducible post-process for the deposition of carbon nanoparticles and fullerene adlayers onto fully CMOS compatible micro-electro-mechanical silicon-on-insulator infrared (IR) light sources to enhance their infrared emission. We show experimentally a significant increase in the infrared emission efficiency of the coated emitters. We numerically validate these findings with models suggesting a dominant performance increase for wavelengths <5.5 μm. Here, the bimodal size distribution in the diameter of the carbon nanoparticles, relative to the fullerenes, is an effective mediator towards topologically enhanced emittance of our miniaturised emitters. A 90% improvement in IR emission power density has been shown which we have rationalised with an increase in the mean thickness of the deposited carbon nanoparticle adlayer. © 2013 AIP Publishing LLC.

High contrast holograms using nanotube forest

Nanotube forest behaves as highly absorbent material when they are randomly placed in sub-wavelength scales. Furthermore, it is possible to create diffractive structures when these bulks are patterned in a substrate. Here, we introduce an alternative to fabricate intensity holograms by patterning fringes of nanotube forest on a substrate. The result is an efficient intensity hologram that is not restricted to sub-wavelength patterning. Both the theoretical and experimental analysis was performed with good agreement. The produced holograms show a uniform behaviour throughout the visible spectra. © 2013 AIP Publishing LLC.

Mid-infrared Raman-soliton continuum pumped by a nanotube-mode-locked sub-picosecond Tmdoped MOPFA

We demonstrate a mid-infrared Raman-soliton continuum extending from 1.9 to 3 μm in a highly germanium-doped silica-clad fiber, pumped by a nanotube mode-locked thulium-doped fiber system, delivering 12 kW sub-picosecond pulses at 1.95 μm. This simple and robust source of light covers a portion of the atmospheric transmission window. © 2013 Optical Society of America.

Wavelength tunable graphene modelocked VECSEL

We passively modelock an optically pumped VECSEL by using a single-layer graphene saturable absorber mirror, resulting in pulses as short as 473 fs. A broad wavelength tuning range of 46 nm is achieved with three different VECSEL chips, with a single chip 21 nm are covered. © OSA 2013.

Polarization switchable diffraction based on subwavelength plasmonic nanoantennas.

We prove theoretically and experimentally the concept of polarization holography by producing visible diffraction through radiation emitted by plasmonic nanoantennas. We show a methodology to selectively activate the nanoantenna emission by controlling the orientation of the electric field of a beam. Additionally, we demonstrate that it is possible to superpose two independent transverse nanoantennas in the same plane without producing interference in their radiated field. Hence, we introduce an alternative view to the traditional concept of holography where fringes (or diffractive units) are band-limited to half the wavelength.

Origin of transient crosstalk and its reduction in phase-only LCOS wavelength selective switches

The transient crosstalk in a phase-only liquid crystal on silicon (LCOS) based wavelength selective switch using a Fourier transform setup was investigated. Its origin was identified using an in situ test procedure and found to be related to the transient phase patterns displayed by the LCOS device during the switching. Two different methods were proposed to reduce the transient crosstalk without the need to modify the optics or electronics in use. Experimental results show both methods are able to reduce the worst-case transient crosstalk by at least 5 dB. © 1983-2013 IEEE.

Demonstration of multi-casting in a 1 × 9 LCOS wavelength selective switch

A multi-functional 1 × 9 wavelength selective switch based on liquid crystal on silicon (LCOS) spatial light modulator technology and anamorphic optics was tested at a channel spacing of 100 and 200 GHz, including dynamic data measurements on both single beam deflection and multi-casting to two ports. The multi-casting holograms were optimized using a modified Gerchberg-Saxton routine to design the core hologram, followed by a simulated annealing routine to reduce crosstalk at non-switched ports. The effect of clamping the magnitude of phase changes between neighboring pixels during optimization was investigated, with experimental results for multi-casting to two ports resulting in a signal insertion loss of-7.6 dB normalized to single port deflection, a uniformity of ±0.6%, and a worst case crosstalk of-19.4 dB, which can all be improved further by using a better anti-reflection coating on the LCOS SLM coverplate and other measures. © 2013 IEEE.

Modeling sub-threshold current-voltage characteristics in thin film transistors

In this paper, we present a physically-based compact model for the sub-threshold behavior in a TFT with an amorphous semiconductor channel. Both drift and diffusion current components are considered and combined using an harmonic average. Here, the diffusion component describes the exponential current behavior due to interfacial deep states, while the drift component is associated with presence of localized deep states formed by dangling bonds broken from weak bonds in the bulk and follows a power law. The proposed model yields good agreement with measured results. © 2013 IEEE.

Ultrathin silicon nitride microring resonator for biophotonic applications at 970 nm wavelength

We experimentally demonstrate a high-Q ultrathin silicon nitride microring resonator operating at wavelength of 970 nm that is favorable for large variety of biophotonic applications. Implementation of thin device layer of 200 nm allows enhanced interaction between the optical mode and environment, while still maintaining high quality factor of resonator. In addition, we show the importance of spectral window around 970 nm to improve device sensing capability. © 2010 American Institute of Physics.

Quantum key distribution for 10 Gb/s dense wavelength division multiplexing networks

We demonstrate quantum key distribution (QKD) with bidirectional 10 Gb/s classical data channels in a single fiber using dense wavelength division multiplexing. Record secure key rates of 2.38 Mbps and fiber distances up to 70km are achieved. Data channels are simultaneously monitored for error-free operation. The robustness of QKD is further demonstrated with a secure key rate of 445 kbps over 25km, obtained in the presence of data lasers launching conventional 0 dBm power. We discuss the fundamental limit for the QKD performance in the multiplexing environment. © 2014 AIP Publishing LLC.

Sub-100fs pulse generation from a fiber oscillator mode-locked by nanotubes

We report an ultrafast fiber laser based on carbon nanotube saturable absorber. 84 fs pulses are generated directly from the fiber oscillator with 61.2 nm spectral width. © 2011 Optical Society of America.