Accurate pH monitoring is crucial for many applications, such as, water quality monitoring, blood monitoring, chemical and biological analyses, environmental monitoring and clinical diagnostic. The most common technique for pH measurement is based on the use of conventional glass pH electrodes. Glass electrodes have several limitations, such as mechanical fragility, large size, limited shapes and high cost, making them impractical for implementation as Lab-onchips and pH sensor capsules. Various metal oxides, such as RuO<sub>2</sub>, IrO<sub>2</sub>, TiO<sub>2</sub>, SnO<sub>2</sub>, Ta<sub>2</sub>O<sub>5</sub> and PdO have recently been proposed for the realization of pH sensing electrodes. Specifically, ruthenium oxide exhibits unique properties including thermal stability, excellent corrosion resistance, low hysteresis high sensitivity, and low resistivity. In this paper, we demonstrate the concept of a miniaturized ion selective electrode (ISE) based pH sensor for point-of-care urease monitoring. The sensor comprises a thin film RuO<sub>2</sub> on platinum sensing electrode, deposited using E-beam and R.F. magnetron sputtering, in conjunction with an integrated Ag/AgCl reference electrode. The performance and characterization of the developed pH/urea sensors in terms of sensitivity, resolution, reversibility and hysteresis are investigated. Experimental results show a linear potential-versus-urea-concentration response for urea concentrations in the range 0 - 180 mg/ml. Experimental results demonstrate super-Nernstian slopes in the range of 64.33 mV/pH - 73.83 mV/pH for RF sputtered RuO<sub>2</sub> on platinum sensing electrode using a 80%:20% Ar:O<sub>2</sub> gas ratio. The RuO<sub>2</sub> sensor exhibits stable operation and fast dynamic response, making it attractive for in vivo use, wearable and flexible biomedical sensing applications.
We design, develop and demonstrate the principle of a continuous, non-intrusive, low power microfluidics-based lab-ona- chip (LOC) structure for Circulating Tumor Cell (CTC) separation. Cell separation is achieved through 80 cascaded contraction and expansion microchannels of widths 60 μm and 300 μm, respectively, and depth 60 μm, which enable momentum-change-induced inertial forces to be exerted on the cells, thus routing them to desired destinations. The total length of the developed LOC is 72 mm. The LOC structure is simulated using the COMSOL multiphysics software, which enables the optimization of the dimensions of the various components of the LOC structure, namely the three inlets, three filters, three contraction and expansion microchannel segments and five outlets. Simulation results show that the LOC can isolate CTCs of sizes ranging from 15 to 30 μm with a recovery rate in excess of 90%. Fluorescent microparticles of two different sizes (5 μm and 15 μm), emulating blood and CTC cells, respectively, are used to demonstrate the principle of the developed LOC. A mixture of these microparticles is injected into the primary LOC inlet via an electronically-controlled syringe pump, and the large-size particles are routed to the primary LOC outlet through the contraction and expansion microchannels. Experimental results demonstrate the ability of the developed LOC to isolate particles by size exclusion with an accuracy of 80%. Ongoing research is focusing on the LOC design improvement for better separation efficiency and testing of biological samples for isolation of CTCs.
High-speed card-to-card optical interconnects are highly demanded in high-performance computing and data centers. Compared with other solutions, free-space optical interconnects have the capability of providing both reconfigurability and flexibility. In this paper we propose and experimentally demonstrate a free-space based reconfigurable optical interconnect architecture and it is capable of connecting cards located both inside the same rack as well as in different racks. Results show that 3×10 Gb/s data transmission is achieved with a worst-case receiver sensitivity better than -9.38 dBm.
We report on the observation of an inhomogeneous spin-dependent spatial distribution of heavy-hole excitons
generated by a localized inhomogeneous magnetic weak field. An exciton energy splitting is observed between
the spin-up and spin-down states with an energy gap as a function of the magnetic field.
We propose a simple method to create a local magnetic field minima for the magnetic trapping and confining of
excitons. We observe an enhanced spatially resolved photoluminescence of the optically active heavy-hole excitons
concentrated at the confining region in a multiple quantum wells system. We draw the attention to consider the
proposed trapping mechanism as an approach to reach the Bose-Einstein condensate limit of excitons.
We report on the synthesis of new magneto-optical materials with excellent optical and magneto-optical (MO) properties
for visible-range and near-infrared applications. Bi-substituted composite garnet films fabricated with excess bismuth
oxide content using RF co-sputtering and conventional oven-annealing processes are found to possess simultaneously a
record-high MO quality and strong uniaxial magnetic anisotropy. The films demonstrate nearly-square hysteresis loops
with specific Faraday rotations of up to 10.1 deg/μm at 532 nm and up to 2.6 deg/μm at 635 nm, which are significantly
larger than these measured in garnet films of the same composition prepared without extra bismuth oxide content.
Record-high MO figures of merit are demonstrated in our composite garnet materials due to a significant reduction in
the optical absorption coefficients achieved across the visible spectral range, thus making garnet-oxide composites
highly attractive for use in a range of magneto-optical applications.
We propose a new type of sensors suitable for water quality testing and for monitoring water contamination levels in
domestic, industrial and environmental applications. The proposed sensing scheme uses Fourier transform cavity-enhanced
absorption spectroscopy and novel compact sensing elements based on nanostructured photonic crystal-type
optical coatings enabling the sensitive Fourier-domain processing methodology and maximising the absorption path
length within the measurement system. The measurement scheme is shown to be suitable for the determination of small
changes in the water absorption coefficients at a discrete set of wavelengths in the visible spectral region in response to
small concentrations of pollutants with high sensitivity. The proposed sensors are expected to provide real-time
information on the water contamination levels, as well as potentially the types of substances dissolved.
Magneto-optical imaging is widely used to observe the domain patterns in magnetic materials, visualize defects in
ferromagnetic objects, and measure the spatial distribution of stray magnetic fields. Optimized 1D magneto-photonic
crystals enable a significant increase in the sensitivity of magneto-optical sensors. The properties of such devices based
on the optimized reflection (doubled Faraday rotation) mode and the use of 1D magnetic photonic crystals as sensors are
discussed. Experimental results of the fabrication and characterization of ferrite-garnet layers possessing uniaxial
magnetic anisotropy are shown, and an optimized film structure suitable for magneto-optical imaging is proposed.
A bench prototype photonic-based spectral reflectance sensor architecture for use in selective herbicide spraying systems
performing non-contact spectral reflectance measurements of plants and soil is described and experimental data obtained
with simulated farming vehicle traveling speed of 7 and 22 km/h is presented. The sensor uses a three-wavelength laser
diode module that sequentially emits identically-polarized laser light beams through a common aperture, along one
optical path. Each laser beam enters a multi-spot beam generator which produces up to 14 parallel laser beams over a
210mm span. The intensity of the reflected light from each spot is detected by a high-speed line scan image sensor. Plant
discrimination is based on calculating the slope of the spectral response between the 635nm to 670nm and 670nm to
785nm laser wavelengths. The use of finely spaced and collimated laser beam array, instead of an un-collimated light
source, allows detection of narrow leaved plants with a width as small as 12mm.
In this paper, a reconfigurable photonic bandpass RF filter employing a semiconductor optical amplifier (SOA) and an
Opto-VLSI processor is proposed where a high coherent RF modulated laser carrier is fed into the SOA and through
cross-gain modulation, a low coherence RF-modulated amplified spontaneous emission (ASE) can be generated. By
spectrally slicing the ASE with an optical comb filter, RF-modulated wavebands of different centre wavelengths are
generated. These RF-modulated wavebands are then processed by an Opto-VLSI processor which arbitrarily shapes the
intensity profile of the wavebands. A high-dispersion optical fibre introduces linear true-time delays between the
different wavebands so that after photodetection a photonic bandpass RF filter with multiple taps is realised. The proof-of-
concept of the photonic bandpass filter is experimentally demonstrated, and results show that the filter can operate at
3.6 GHz with more than 25 dB rejection and its working frequency can be tuned by reconfigurable holograms generated
by the Opto-VLSI processor. The filter can work with the laser carrier wavelength in the range of 1523nm to 1566nm
without any optical coherence noises.
The ability of a liquid-crystal spatial light modulator (LC-SLM) to generate lens and lens arrays of variable focal lengths
and selectable fields of view (FOV) makes them excellent candidates for many adaptive optics applications including
free-space optical telecommunications, astronomy and retinal imaging. In this paper, we report a range of dynamic lens
and lens array designs and optimization using a LC-SLM as an adaptive Hartmann-Shack wavefront sensor. The
measured wavefront aberration is reconstructed using Zernike polynomials through the application of its conjugated
wavefront onto the LC-SLM to achieve dynamic wavefront detection and correction. Computer algorithms based on
Fourier transformation for lens synthesis have been developed to address the LC-SLM and to generate appropriate phase
holograms that emulate lens and/or lenslet arrays with programmable focal lengths, tilting angles and diameters. The
classic least-square (LS) method is used to determine the Zernike polynomial coefficients for the reconstruction of the
aberrated wavefront. Experimental results demonstrate the dynamic generation of lens arrays of variable focal lengths.
We also experimentally characterize the phase modulation performance and wavefront generation performance of the
LC-SLM through the application of Zernike functions and as diffractive optical elements (DOEs) for dynamic wavefront
This paper presents an integrated MicroPhotonic beamformer that processes RF-modulated optical signals to adaptively
synthesise multiple broadband nulls in smart phased-array antennas. The beamformer is designed to operate at centre
frequency of 5.6 GHz with 1 GHz bandwidth. Designs of the different photonic and RF components are presented.
Simulation results show that a 4-element MicroPhotonic broadband smart antenna beamformer operating in the 5.1-6.1-
GHz range can generate three broadband nulls, with less than 1.121° beam squint.
This paper presents a short-distance reconfigurable high-speed optical interconnects architecture employing a Vertical
Cavity Surface Emitting Laser (VCSEL) array, Opto-very-large-scale-integrated (Opto-VLSI) processors, and a
photodetector (PD) array. The core component of the architecture is the Opto-VLSI processor which can be driven by
digital phase steering and multicasting holograms that reconfigure the optical interconnects between the input and output
ports. The optical interconnects architecture is experimentally demonstrated at 2.5 Gbps using high-speed 1×3 VCSEL
array and 1×3 photoreceiver array in conjunction with two 1×4096 pixel Opto-VLSI processors. The minimisation of the
crosstalk between the output ports is achieved by appropriately aligning the VCSEL and PD elements with respect to the
Opto-VLSI processors and driving the latter with optimal steering phase holograms.
Intracavity-contacted resonant cavity enhanced photodetectors (IC RCEPDs) have been fabricated for monolithic integration with IC VCSELs. A low parasitic capacitance of 0.39 pF and an extrinsic 3-dB bandwidth of 9 GHz are demonstrated by using coplanar metal contacts. Optimization issues on device and epi designs are discussed. The largest frequency saturation photocurrent below which the extrinsic 3-dB bandwidth exceeds 6.5 GHz is 4.2 μA.
In this paper, we propose a time-token multi-Gb/s Wavelength Division Multiplexing Fibre Distributed Data Interface (WDM/FDDI) architecture and examine its throughput efficiency and delay under heavy load for different network configuration using discrete event simulator.
In this paper, we propose and demonstrate a new MicroPhotonic structure for optical packet header recognition based on the integration of an optical cavity, optical components and a photoreceiver array. The structure is inherently immune to optical interference thereby routing an optical header within optical cavities to different photoreceiver elements to generate the autocorrelation function, and hence the recognition, of the header using simple microelectronic circuits. The proof-of-concept is simulated and experimentally demonstrated.
In this paper, a novel reconfigurable 5-tap photonic RF filter based on Opto-VLSI processor is proposed where an Opto-VLSI processor is used in conjunction with a 5-fibre Bragg grating (FBG) array to slice the spectrum of a broad band light source, thus achieving commensurate true-time delays and variable tap weights. The proposed photonic RF filterstructure is experimentally demonstrated by means of several examples which show the capability of the Opto-VLSI processor to synthesise transversal RF filter responses with adaptive weights.
Reconfigurable multi-channel optical filters are presented in this paper. The operation principle of the reconfigurable filter is based on the dynamic beam steering capacity of Opto-VLSI processor in conjunction with a high dispersion free space grating. The dispersion grating separates the input signal spectrum while the Opto-VLSI processor is driven by optimised phase holograms to dynamically select the wavelengths to be coupled into the output port. Experimental results show that up to 8 bands can be synthesised, with a wavelength tuning span of 10 nm and a 3dB bandwidth less than 0.5nm.
213nm Solid-state laser technology provides an alternative method to replace toxic excimer laser in LASIK system. In this paper, we report a compact fifth harmonic generation system to generate high pulse energy 213nm laser from Q-switched Nd:YAG laser for LASIK application based on three stages harmonic generation procedures. A novel crystal housing was specifically designed to hold the three crystals with each crystal has independent, precise angular adjustment structure and automatic tuning control. The crystal temperature is well maintained at ~130°C to improve harmonic generation stability and crystal operation lifetime. An output pulse energy 35mJ is obtained at 213nm, corresponding to total conversion efficiency ~10% from 1064nm pump laser. In system verification tests, the 213nm output power drops less than 5% after 5 millions pulse shots and no significant damage appears in the crystals.
In this paper, a MicroPhotonic-based high-Q tunable RF filter architecture is proposed. The architecture uses a Vertical Cavity Surface Emitting Laser (VCSEL) array, a 2D ultra-wideband photo-receiver array and a multi-cavity optical substrate to generate a large number of optical true-time delays thus achieving arbitrary, high-resolution RF filter transfer characteristics. By tuning the responses of the different optical cavities, adaptive high-Q RF filter characteristics can be realized over a wide RF frequency range. Proof-of-concept experimental results demonstrate the adaptability of the MicroPhotonic-based RF filter.
In this paper we present and demonstrate a dynamic lens and lens array generation method with programmable focal length based on an Opto-VLSI processor. The Opto-VLSI is driven by computer generated algorithm to generate a discrete Fresnel lens phase hologram. By optimizing the phase hologram, lenses and lens arrays of different focal lengths ranging from 300mm to infinity can be realized. The optical axis of each lens element can be independently addressed to simultaneously focus and steer an optical beam within an angular range of ±0.5°.
In 1959, the physicist Richard Feynman advised his colleagues that "there's plenty of room at the bottom." He envisioned a discipline devoted to manipulating smaller and smaller units of matter. "I am not afraid," he wrote, "to consider the final question as to whether, ultimately -- in the great future -- we can arrange the atoms the way we want, the way very atoms, all the way down." However, in early 1980's the doom and gloom of silicon MOS transistors was foreshadowed and scaling of the humble MOS transistors beyond 140 nm appeared as the impossible dream. Manipulation of material science, the emergence of low-K material and copper technology together with new techniques in lithography and processing have paved the way for revised predication that has foreshadowed the feature sizes in the order of 20 nm - 30 nm will occur somewhere between 2012 and 2016. Coupled with these developments, nanochemists have began to probe into matter and now Nanochemistry is beginning to shape the future of new materials and better understand the unique properties of assemblies of atoms and molecules on a scale that range between that of individual building blocks and the bulk material, thus confirming Feynman's vision. At this level quantum effects can be significant and innovative ways of carrying out chemical reactions become possible.
A novel tunable optical filter structure based on an Opto-VLSI processor is proposed in this paper. The architecture is capable of dynamically tuning multiple pass-bands through reconfiguration of the size and shape of holographic diffractive gratings generated by the Opto-VLSI processor. Results for an experimental 3-passband tunable filter are presented confirming over 25dB of dynamic range and passband bandwidth of 2 nm.
MicroPhotonic broadband RF signal processors utilize the capability of photons to perform true-time delay processing at very low loss that is unattainable by conventional electronic methods. In this paper, we present a novel MicroPhotonic interference mitigation filter architecture that utilises a CMOS Si photoreceiver/VCSEL array in conjunction with a true-time-delay multi-cavity optical substrate to realise an adaptive transversal RF processor with arbitrary response. Results show that the proposed MicroPhotonic structure can synthesize adaptive interference mitigation with a shape factor (ratio of the -40<i>dB</i> bandwidth to the -3<i>dB</i> bandwidth) as low as 2 and passband ripples less than 0.25<i>dB</i>.