42 research outputs found
Compact spectrometer based on disordered multi-mode interferometer
We demonstrate a compact (40 m 260 m) spectrometer
based on multimode interference aided by scattering of light from random
SiO-filled hole arrays on a silicon-on-insulator platform. We characterize
the performance of the spectrometer for wavelengths around 1310 nm, and report
that the spectrometer can reconstruct a broadband 67 nm source, as well
as Lorentzian probes of 1 nm bandwidth. This compact nanometer level
resolution spectrometer can be fabricated at a low cost for lab-on-a-chip
sensing and imaging applications.Comment: 11 pages, 6 figure
Graphene oxide integrated silicon photonics for detection of vapour phase volatile organic compounds
From Springer Nature via Jisc Publications RouterHistory: received 2020-01-07, accepted 2020-05-17, registration 2020-05-20, pub-electronic 2020-06-12, online 2020-06-12, collection 2020-12Publication status: PublishedAbstract: The optical response of a graphene oxide integrated silicon micro-ring resonator (GOMRR) to a range of vapour phase Volatile Organic Compounds (VOCs) is reported. The response of the GOMRR to all but one (hexane) of the VOCs tested is significantly higher than that of the uncoated (control) silicon MRR, for the same vapour flow rate. An iterative Finite Difference Eigenmode (FDE) simulation reveals that the sensitivity of the GO integrated device (in terms of RIU/nm) is enhanced by a factor of ~2, which is coupled with a lower limit of detection. Critically, the simulations reveal that the strength of the optical response is determined by molecular specific changes in the local refractive index probed by the evanescent field of the guided optical mode in the device. Analytical modelling of the experimental data, based on Hill-Langmuir adsorption characteristics, suggests that these changes in the local refractive index are determined by the degree of molecular cooperativity, which is enhanced for molecules with a polarity that is high, relative to their kinetic diameter. We believe this reflects a molecular dependent capillary condensation within the graphene oxide interlayers, which, when combined with highly sensitive optical detection, provides a potential route for discriminating between different vapour phase VOCs
IndiumâDoped Silicon for Solar CellsâLightâInduced Degradation and DeepâLevel Traps
From Wiley via Jisc Publications RouterHistory: received 2021-02-28, rev-recd 2021-06-11, pub-electronic 2021-07-21Article version: VoRPublication status: PublishedFunder: EPSRC (UK); Grant(s): EP/TO25131/1Funder: Department of Science and Technology (DOST), Government of the PhlippinesFunder: Fundação para a CiĂȘncia e a Tecnologia; Id: http://dx.doi.org/10.13039/100008382; Grant(s): UIDB/50025/2020, UIDP/50025/2020Indiumâdoped silicon is considered a possible pâtype material for solar cells to avoid lightâinduced degradation (LID), which occurs in cells made from boronâdoped Czochralski (Cz) silicon. Herein, the defect reactions associated with indiumârelated LID are examined and a deep donor is detected, which is attributed to a negativeâU defect believed to be InsO2. In the presence of minority carriers or above bandgap light, the deep donor transforms to a shallow acceptor. An analogous transformation in boronâdoped material is related to the BsO2 defect that is a precursor of the center responsible for BO LID. The electronic properties of InsO2 are determined and compared to those of the BsO2 defect. Structures of the BsO2 and InsO2 defects in different charges states are found using firstâprinciples modeling. The results of the modeling can explain both the similarities and the differences between the BsO2 and InsO2 properties
Modeling the Non-Hermitian Infinity-Loop Micro-Resonator over a Free Spectral Range Reveals the Characteristics for Operation at an Exceptional Point
We develop a 4 Ă 4-matrix model based on temporal coupled mode theory (TCMT) to elucidate the intricate energy exchange within a non-Hermitian, resonant photonic structure, based on the recently described infinity-loop micro-resonator (ILMR). We consider the structure to consist of four coupled resonant modes, with clockwise and counterclockwise propagating optical fields, the interplay between which gives rise to a rich spectral form with both overlapping and non-overlapping resonances within a single free spectral range (FSR). Our model clarifies the precise conditions for exceptional points (EPs) in this system by examining neighboring resonances over the device free spectral range (FSR). We find that the system is robust to the conditions for observing an EP, despite the presence of non-zero coupling of signals, or crosstalk, between the resonant modes
Rate equation modelling of erbium luminescence dynamics in erbium-doped silicon-rich-silicon-oxide
AbstractErbium doped silicon-rich silica offers broad band and very efficient excitation of erbium photoluminescence (PL) due to a sensitization effect attributed to silicon nanocrystals (Si-nc), which grow during thermal treatment. PL decay lifetime measurements of sensitised Er3+ ions are usually reported to be stretched or multi exponential, very different to those that are directly excited, which usually show a single exponential decay component.In this paper, we report on SiO2 thin films doped with Si-nc's and erbium. Time resolved PL measurements reveal two distinct 1.54ÎŒm Er decay components; a fast microsecond component, and a relatively long lifetime component (10ms). We also study the structural properties of these samples through TEM measurements, and reveal the formation of Er clusters. We propose that these Er clusters are responsible for the fast ÎŒs decay component, and we develop rate equation models that reproduce the experimental transient observations, and can explain some of the reported transient behaviour in previously published literature