Daniel Hill

High efficiency silicon nitride surface grating couplers

High efficiency surface grating couplers for silicon nitride waveguides have been designed, fabricated, and characterized. Coupling efficiencies exceeding 60 % are reported at a wavelength of 1.31 mum, as well as angular and wavelength -3 dB tolerances of 4 degrees and 50 nm, respectively. When the wavelength is increased from 1310 nm to 1450 nm the coupling efficiency progressively decreases but remains above 20 % at 1450 nm. The influence of the duty ratio of the grating has also been investigated: maximum coupling efficiency was obtained at 50 % duty ratio.

Vertical multiple-slot waveguide ring resonators in silicon nitride

This article describes the first demonstration of ring resonators based on vertical multiple-slot silicon nitride waveguides. The design, fabrication and measurement of multiple-slot waveguide ring resonators with several coupling distances and ring radii (70 microm, 90 microm and 110 microm) have been carried out for TE and TM polarizations at the wavelength of 1.3 microm. Quality factors of 6,100 and 16,000 have been achieved for TE and TM polarization, respectively.

Light coupling and distribution for Si3N4∕SiO2 integrated multichannel single-mode sensing system

We present an efficient and highly alignment-tolerant light coupling and distribution system for a multichannel Si3N4/SiO2 single-mode photonics sensing chip. The design of the input and output couplers and the distribution splitters is discussed. Examples of multichannel data obtained with the system are given.

A high efficiency silicon nitride grating coupler

The experimental demonstration of a high efficiency silicon nitride grating coupler is reported for wavelengths from lambda = 1.25 to 1.45 mum for TE polarization. At the resonant angle, a coupling efficiency higher than 60% has been measured.

Real-time label-free biosensing with integrated planar waveguide ring resonators

We review the use of planar integrated optical waveguide ring resonators for label free bio-sensing and present recent results from two European biosensor collaborations: SABIO and InTopSens. Planar waveguide ring resonators are attractive for label-free biosensing due to their small footprint, high Q-factors, and compatibility with on-chip optics and microfluidics. This enables integrated sensor arrays for compact labs-on-chip. One application of label-free sensor arrays is for point-of-care medical diagnostics. Bringing such powerful tools to the single medical practitioner is an important step towards personalized medicine, but requires addressing a number of issues: improving limit of detection, managing the influence of temperature, parallelization of the measurement for higher throughput and on-chip referencing, efficient light-coupling strategies to simplify alignment, and packaging of the optical chip and integration with microfluidics. From the SABIO project we report refractive index measurement and label-free biosensing in an 8-channel slotwaveguide ring resonator sensor array, within a compact cartridge with integrated microfluidics. The sensors show a volume sensing detection limit of 5 x 10-6 RIU and a surface sensing detection limit of 0.9 pg/mm2. From the InTopSens project we report early results on silicon-on-insulator racetrack resonators.

Bowtie plasmonic nanoantenna arrays for polarimetric optical biosensing

We report on the first polarimetric plasmonic biosensor based on arrays of bowtie nanoantennas. Using the Finite Element Method (FEM) the phase retardation between the components of light polarized parallel and perpendicular to the axis of the nanoantennas is studied. After optimizing them for high volumetric sensitivity at a wavelength of 780 nm, sensitivities ~5 rad/RIU are obtained, corresponding to a detection limit ~10-7 RIU when using the polarimetric readout platform. Surface sensitivity values resulted from studies of phase retardation changes from a coverage of bioreceptors and analytes.

MOS based nanocapacitor using C-AFM

This report details the attempts made to realise nanocapacitors for nanoscale MOS based integrated circuits by AFM anodic oxidation, and therefore isolation, of nano-sized squares of poly-silicon, titanium and aluminium on Si/SiO2. Conductive AFM (C-AFM) was used to perform topographical and electrical characterisation. The experiments were performed with contact mode C-AFM, in ambient air, using Pt-Ir, Co-Cr and Ti coated (20nm) n-type silicon cantilevers. Each sample consisted of a 3-5nm thick conductor deposited on 6nm of SiO2, which was thermally grown on Phosphorus doped (1019 cm-3) n-type Si(100) substrates. Standard cleaning and passivation processes were used. Poly-silicon was immediately found to be too rough to oxidise. Initial current-voltage measurements inside of the titanium-oxide squares suggest initial isolation followed by degradation through Fowler-Nordheim tunnelling. Measurement inconsistencies seen suggest charge storage on the surface or tip with the barrier height of the native titanium oxide thought to be responsible. Al has a thicker natural oxide. To overcome this we designed a series of structures consisting of a Ti finger on SiO2, that is connected to a Ti bond pad, allowing direct probing by a semiconductor parameter analyser. AFM anodic oxidation was performed upon these Ti fingers to reduce their in-plane dimensions towards the nanoscale. To confirm the existence of a nanocapacitor topographical and electrical measurements were then done on and around them.