Nyuk Yoong Voo

Pump-noise-induced linewidth contributions in distributed feedback fiber lasers

We investigate experimentally and theoretically the linewidth of an Er-Yb-doped distributed feedback fiber laser. We find that two noise sources are mainly responsible for the observed behavior, fundamental thermal noise at low pump power levels and temperature fluctuations induced by pump intensity noise at higher powers. Potential techniques to overcome these limitations are discussed.

Anomalous linewidth behavior in short-cavity single-frequency fiber lasers

An experimental investigation of the anomalous linewidth behavior in a distributed feedback fiber laser is presented. It is found that not only does the linewidth deviate from the Schawlow-Townes linewidth formula by increasing with pump and laser power, but it also varies significantly with the pumping configuration. These observations have potentially important implications for the design and operation of such fiber lasers.

DFT/TDDFT and Experimental Studies of Natural Pigments Extracted from Black Tea Waste for DSSC Application

We report results of combined experimental and theoretical studies of black tea waste extract (BTE) as a potential sensitizer for TiO2-dye-sensitized solar cells (DSSCs). UV-vis absorption data revealed that BTE contains theaflavin. DSSC sensitized with pigment complexes of BTE showed a photon-energy conversion efficiency of %, while a significant increase (%) is observed when pH of the pigment solution was lowered. The HOMO and LUMO energy levels were calculated using experimental data of UV-vis absorption and cyclic voltammetry. These calculations revealed a reduction of the band gap by 0.17 eV and more negativity of HOMO level of acidified pigment, compared to that of original pigment. Combined effect of these developments caused the enhanced efficiency of DSSC. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) computational calculations were carried out to study the four theaflavin analogues which are responsible for the dark colour of BTE. According to the calculations, two theaflavin analogues, theaflavin and theaflavin digallate, are the most probable sensitizers in this dye-sensitized solar cell system.

Tunable silver-shell dielectric core nano-beads array for thin-film solar cell application

The absorbance spectra of thin-film solar cells (TFSCs) can be enhanced by constructing the tunable periodic Ag-shell nano-bead (PASNB) arrays in the active material. In this paper, we investigated a plasmonic thin-film solar cell (TFSC) which composed of the arrays of PASNB deposited onto a crystalline silicon layer. By performing three-dimensional finite element method, we demonstrate that near field coupling among the PASNB arrays results in SPR modes with enhanced absorbance and field intensity. The proposed structure can significantly enhance the plasmonic activity in a wide range of incident light and enlarge working wavelength of absorbance in the range of near-UV, visible and near-infrared. We show that the sensitivity of the PASNB arrays reveals a linear relationship with the thickness of Ag-shell nano-bead (ASNB) for both the anti-bonding and bonding modes in the absorbance spectra. The broadband of absorbance spectra could be expanded as a wide range by varying the thickness of ASNB while the particle size is kept constant. Simulation results suggest this alternative scheme to the design and improvements on plasmonic enhanced TFSCs can be extended to other nanophotonic applications.

Linewidth and phase noise characteristics of DFB fibre lasers

The anomalous linewidth behavior in a DFB fiber laser is investigated. It is shown that not only does the linewidth deviate drastically from the Schawlow-Townes linewidth formula by increasing with pump and laser power, but it also varies significantly with the pumping configuration used. These results have potentially important implications for the design and operation of such fiber lasers.

The general synthesis of complex analogue filters

General methods for the synthesis of complex analogue filters are developed for implementation by active-RC, gm-C, switched-capacitor (SC) and switched-current (SI) techniques. These have been incorporated into the filter design software XFILTER.

Constrained tâtonnement for fast and incentive compatible distributed demand management in smart grids

Growing fuel costs, environmental awareness, government directives, an aggressive push to deploy Electric Vehicles (EVs) (a single EV consumes the equivalent of 3 to 10 homes) have led to a severe strain on a grid already on the brink. Maintaining the stability of the grid requires automatic agent based control of these loads and rapid coordination between them. In the literature, a number of iterative pricing, signaling and tâtonnement (or bargaining) approaches have been proposed to allow smart homes, storage devices and the autonomous agents that control them to be responsive to the state of the grid in a distributed manner. These existing approaches are not scalable due to slow convergence and moreover the approaches are not incentive compatible. In this paper, we present a tâtonnement framework for resource allocation among intelligent agents in the smart grid, that non-trivially generalizes past work in this area. Our approach based on the work in server load balancing involves communicating carefully chosen, centrally verifiable constraints on the set of actions available to agents and cost functions, leading to distributed, incentive compatible protocols that converge in a constant number of iterations, independent of the number of users. These protocols can work on the top of prior approaches and result in a substantial speed-up, while ensuring that it is in the best interests of the agents to be truthful. We demonstrate this theoretically and through extensive simulations for three important scenarios that have been discussed in the literature. We extend the techniques to account for capacity limits in each time slot, the EV charging problem and the distributed storage control problem. We establish the generality and usefulness of this technique and making the case that it should be incorporated into future smart grid protocols.

Multiple phase-shift all-fibre DFB lasers

A double (2 times pi/2) phase-shifted Er/Yb fibre DFB laser shows a 50% reduction of the shift in lasing wavelength and a 10% reduction of the linewidth, compared to standard single phase-shifted fibre DFB designs

Dominant causes of linewidth in DFB fiber lasers

We present experimental arid theoretical results on the linewidth of an Er-Yb doped DFB fiber laser. Recently observed dependencies on pump configuration and power are explained by pump noise induced temperature fluctuations.

An amplitude-modulated spectrally optimised Er3+ fibre ASE source for use with optical fiber sensors: an example optimised for acetylene gas sensing

We describe a compact, pulsed, broadband source for sensing using ASE from Er3+ doped fibre driven by an amplitudemodulated pump. Quiescent pumping halved rise time. The spectrum could be tailored with reflective fibre filters, eg. for C2H2 gas detection.