A chalcogenide waveguide platform with the combination of GeAsSeTe (IG3)/GeAsSe (IG2) on wet-/dry-etched silicon pedestals is reported. Chalcogenide glasses offer high index contrast and compact footprints, while the post-processing challenges are addressed using Si pedestals. The integration of IG2/IG3 chalcogenides on Si demonstrates ultralow loss of 0.08 ± 0.02 dB/cm at a wavelength of 10 μm. We have measured a thermo-optic coefficient of 1.1x10-4 K-1, which is comparable to Si and GaAs. The combination of simplified fabrication, minimal propagation losses and a strong thermooptic coefficient, positions this waveguide platform as a promising candidate for on-chip tunable long-wave IR spectrometers for practical applications in biomedical diagnostics and environmental sensing.
Molecules have ‘fingerprint’ absorptions in the mid-infrared, enabling their identification via infrared spectroscopy. For applications beyond the lab, such as medical diagnosis, fully integrated mid-infrared spectroscopy on chip would be ideal. Germanium offers low absorption in the mid-IR, making it an ideal candidate for waveguides for mid-IR spectroscopy via the evanescent field. Amorphous germanium could offer a low-cost fabrication route; our work compares methods to deposit amorphous germanium films via RF sputtering, e-beam evaporation and plasma-enhanced chemical vapour deposition (PECVD). In addition to standard germanium waveguides produced by etching a germanium film, an alternative manufacturing method is proposed, where silicon is etched to form pedestals, followed by deposition of amorphous germanium to produce waveguides. Pedestal waveguides offer potential for single-mode operation across a broad wavelength range, making them a strong candidate for spectroscopy applications.
We present continuous wave bi-frequency operation in an optically pumped membrane external-cavity surface-emitting laser (MECSEL). A laser ablation system utilising a digital micromirror device is used to define areas of intra-cavity loss by removing Bragg layers from the surface of the cavity mirror in a crosshair pattern with an undamaged central area. Our MECSEL simultaneously operates on two Hermite-Gaussian spatial modes, the fundamental and a higher order mode, by aligning the laser cavity to be centred on a masked area. We demonstrate bi-frequency operation with a wavelength separation on the order of 5 nm around 1005 nm.
We present coherent laser arrays in a silicon photonics compatible waveguide geometry in optically pumped semiconductor membrane quantum well lasers (MQWLs) on oxidised silicon and silicon carbide substrates. Real and reciprocal space imaging is used to investigate the emission of the laser arrays and mutual coherence is seen to be maintained while operating on single and multiple longitudinal modes in each cavity. Further, we investigate writing laser cavity arrays through micro-structuring of the MQWL and also through the utilisation of a spatial light modulator (SLM) to define areas of gain in the MQWL by shaping the pump beam.
Rifampicin is an antimicrobial drug used to treat tuberculosis. The deterioration of a tuberculosis patient on rifampicin is a serious event with several possible causes. Rapid bedside measurement of rifampicin would enable clinicians to determine if patient deterioration was due to subtherapeutic levels and quickly correct the dosing. It would also support personalised dosing to maximise antimicrobial effectiveness whilst minimising side effects. The optimum therapeutic concentration range is 8 – 24 mg/L. We report ATR-FTIR spectroscopy data for the detection of rifampicin for bedside therapeutic drug monitoring (TDM). We demonstrate a limit of detection of 0.46 mg/L from 20 μL spiked whole blood samples. Using whole blood directly enables bedside measurements because it does not require centrifugation and pipetting to extract plasma, which are generally performed in a central laboratory. The absorption-concentration response had good linearity (R2 = 0.998) up to the highest measured concentration of 100 mg/L. We apply this data to the design of a miniaturised mid-infrared sensor for TDM using silicon photonics. We present an analysis of the optimum interaction length for an evanescent waveguide sensor using the absorption of rifampicin and a numerical model to quantify the contributions of different system and device noise sources. These sensors can be made more sensitive than their benchtop equivalent because of the enhanced evanescent electric field strength and the increased power spectral density of tunable quantum cascade lasers.
KEYWORDS: Terahertz spectroscopy, Spectroscopy, Data modeling, Artificial neural networks, Refractive index, Data acquisition, Signal to noise ratio, Nondestructive evaluation, Neural networks, Material characterization
Optically pumped waveguide coherent laser arrays are demonstrated in an 1-micron-thick-semiconductor-membrane-InGaAs-quantum-well laser transferred on a silicon carbide heat spreader emitting at 1010 nm. We employ a real and Fourier space imaging setup to study the emission of single and arrays of laser cavities. We are able to create waveguide laser arrays with modal widths of approximately 5-10 μm separated by 5-10 μm which maintain their mutual coherence while operating on either single or multiple longitudinal modes. This laser geometry can be accurately controlled by the laser pump and they offer a new high gain laser platform that permits integration with photonic structures.
Optical spectroscopy offers a potential non-invasive, label free and rapid method to assist clinicians to diagnose diseases for which biomarkers are known. Neonatal respiratory distress syndrome (nRDS) diagnosis in preterm infants is known to be correlated with the lecithin/sphingomyelin ratio (LS ratio) in gastric aspirates, with a ratio less than 2.2 indicating that surfactant replacement therapy is needed. Currently no widespread method exists that can give clinically relevant answers in less than 2 hours from the point of sample collection as it is difficult to identify those who could benefit from prompt surfactant treatment. Various LS ratios were generated using pure dipalmitoylphosphatidylcholine (DPPC) and sphingomyelin (SM) dissolved in dichloromethane and infrared spectra generated using Attenuated Total Reflection (ATR) assisted Fourier Transform InfraRed spectrometry (FTIR). Subsequent analysis obtained the LS ratio using the spectra alone. Further, we demonstrate the application of principal component regression (PCR) and partial least squares (PLS) fits to measured spectra to assist in the determination of the LS ratio using a model trained with multiple runs of the different batches of the same concentration.
We show the characterisation of spectral broadening in the Tantalum Pentoxide waveguide system as a function of pump wavelength, showing spectra for central pump wavelengths of 0.9 to 1.5 um (150 fs, 80 MHz). We have achieved octave spanning spectra with approximately 5 mW of laser power coupled in the waveguide at 1 um pumping wavelength for a linear buried waveguide using a commercial source.
Low-cost, mass-produced biosensing systems needing minimal sample preparation and user intervention are required for many applications, ranging from food safety, water quality and security to personal and preventative medicine and rapid point-of-care diagnostics. Optical techniques have traditionally played a major role in quantitative chemical analysis and remain the mainstay of detection in “lab-on-chip” systems, but the degree of optical functionality integrated within these systems remains limited. Mid-infrared (MIR) absorption spectroscopy at wavelengths between 2.5 µm and 25 µm is widely used for quantitative analysis of biochemical species, as the fundamental vibrations of many biomolecules take place at these frequencies, offering the potential for label-free biosensing through analysis of molecular “fingerprints. However, while telecommunications applications have caused a revolution in photonic materials, devices and integration in the near-infrared, progress in biosensing systems has been hampered by the lack of integrated photonic platforms which can operate over the MIR wavelength region. Improvements in MIR sources and detectors combined with increasing demand for biochemical information to improve understanding of biological systems and to target medical treatment more effectively are driving research into materials and processes for MIR waveguide biosensors. Progress on new materials and approaches for high-sensitivity waveguide evanescent spectroscopies in the MIR which would enable new opportunities for sensitive, selective, label-free biochemical analysis will be described.
Mid-Infrared (Mid-IR) techniques have gained considerable attention because of their inherent molecular selectivity and their potential for rapid label-free detection in applications such as water quality and environmental monitoring, security, food safety, and point-of-care diagnostics. Waveguide evanescent-field-based Mid-IR spectroscopy can detect analytes at very low concentrations using molecular absorption fingerprints, potentially offering high sensitivity and selectivity over a wide range of compounds. Moreover, significant footprint reduction compared to ATR-based FTIR measurements can be achieved with optical waveguide-based Mid-IR sensing through integration of various optoelectronic and microfluidic components realizing fully packaged lab-on-a-chip systems.
Recently we have developed low-loss chalcogenide optical waveguides and demonstrated waveguiding in the mid-wave and long-wave infrared spectral bands. High contrast GeTe4 and ZnSe channel waveguides were fabricated on bulk substrates and on silicon wafers (with suitable optical isolation layers) using lift-off and dry etching techniques after photolithographically patterning the thin films. These waveguides were exhibiting optical losses as low as 0.6 dB/cm in the mid-wave IR band and were validated for the Mid-IR evanescent wave spectroscopy with water and IPA. We have also demonstrated the effectiveness of simple paper-based fluidics with our waveguides.
In addition, we investigate a new family of free-standing Ta2O5 rib waveguides for trace gas detection with evanescent field overlap with the surrounding medium (air) up to about 70%. The waveguides are being fabricated and the fabrication and characterization results will be presented.
This work describes the integration of mid-infrared (MIR) silicon photonics with PDMS microfluidics to perform absorption spectroscopy of IPA-water solutions. The MIR spectral region contains strong absorption bands for many molecules, and photonic devices operating in the MIR can be used in many sensing applications. In this work a preliminary demonstration of a silicon-on-insulator (SOI) device is carried out in which the transmission spectra of different concentrations of water-IPA solutions are measured at wavelengths between 3.725 μm and 3.888 μm. A PDMS microfluidic channel is integrated with the waveguides in order to improve the repeatability of sample handing, reduce reagent volumes and prevent evaporation of the analyte. A microfluidic channel with 3000 x 100 μm cross-section and 30 mm length is bonded to a SOI chip comprising 500 nm thick rib waveguides and a 2 μm thick SiO2top cladding isolating the waveguide mode from the analyte. Trenches were patterned into the SiO2 cladding to create sensing windows of varying lengths (10 μm to 3mm) along different waveguides. The devices were used to detect an expected IPA absorption peak at 3.77 μm, and concentration as low as 3% IPA in water (by volume) was detected. Further work will focus on increasing the sensitivity of the measurement by using increased interaction lengths, reduction of noise and instability, and on the detection of drugs using transmission measurements over a broader wavelength range.
In this paper we present silicon and germanium-based material platforms for the mid-infrared wavelength region and we report several active and passive devices realised in these materials. We particularly focus on devices and circuits for wavelengths longer than 7 micrometers.
Tantalum pentoxide (Ta2O5) is a promising material for mass-producible, multi-functional, integrated photonics circuits on silicon, exhibiting robust electrical, mechanical and thermal properties, as well as good CMOS compatibility. In addition, Ta2O5 has been reported to demonstrate a non-linear response comparable to that of chalcogenide glass, in the region of 3-6 times larger than that of materials such as silica (SiO2) or silicon nitride (Si3N4). In contrast to Si-based dielectrics, it will accept trivalent ytterbium and erbium dopant ions, opening the possibility of on-chip amplification. The high refractive index of Ta2O5 is consistent with small guided mode cross-section area, and allows the construction of micro-ring resonators. Propagation losses as low as 0.2 dB=cm have been reported. In this paper we describe the design of a planar Ta2O5 waveguides optimised for the generation of coherent continuum with near infrared pulse trains at kW peak powers. The Pulse Repetition Frequency (PRF) of the VECSEL can be tuned to a sub-harmonic of the planar micro-ring and the optical pump power applied to the VECSEL can be adjusted so that mode-matching of the VECSEL pulse train with the micro-ring resonator can be achieved. We shall describe the fabrication of Ta2O5 guiding structures, and the characterisation of their nonlinear and other optical properties. Characterisation with conventional lasers will be used to assess the degree of coherent spectral broadening likely to be achievable using these devices when driven by mode-locked VECSELs operating near the current state-of- art for pulse energy and duration.
In this paper we report the physical micromanipulation of standard InP telecommunications laser die in a liquid medium by means of optoelectronic tweezers. Optoelectronic tweezers have been shown to use much less optical power than optical tweezers, they do not require a coherent light source to function and the creation of multiple traps is straightforward. These properties make the technique a very good candidate for the massive parallel micromanipulation of optoelectronic components for assembly on a photonic platform. We discuss the positional and orientation accuracy of the optoelectronic tweezers in relation to the alignment requirements for low-loss coupling between the light sources and the other components in a photonic platform. Our experiments indicate that the accuracy is better than 2 μm and 2° for translations and rotations, respectively.
GeTe4 waveguides were designed and fabricated on silicon substrates with a ZnSe isolation layer. GeTe4 has a refractive index of 3.25 at a wavelength of 9 μm and a lower refractive index isolation layer is needed to realise waveguides on silicon. Numerical modelling was carried out to calculate the thickness of the isolation layer (ZnSe, refractive index ~2.4) required to achieve low loss waveguides. For a loss between 0.1 and 1.0 dB/cm it was found that a ~ 4 μm thick ZnSe film is required at a wavelength of 9 μm. ZnSe thin films were deposited on silicon, GeTe4 waveguides were fabricated by lift-off technique and were characterised for mid-infrared waveguiding.
In this paper we present SOI, suspended Si, and Ge-on-Si photonic platforms and devices for the mid-infrared. We demonstrate low loss strip and slot waveguides in SOI and show efficient strip-slot couplers. A Vernier configuration based on racetrack resonators in SOI has been also investigated. Mid-infrared detection using defect engineered silicon waveguides is reported at the wavelength of 2-2.5 μm. In order to extend transparency of Si waveguides, the bottom oxide cladding needs to be removed. We report a novel suspended Si design based on subwavelength structures that is more robust than previously reported suspended designs. We have fabricated record low loss Ge-on-Si waveguides, as well as several other passive devices in this platform. All optical modulation in Ge is also analyzed.
Reduced blood deformability is clinically linked to several diseases. It is important to develop sensitive tools to measure the loss of blood deformability. The evanescent field of an optical waveguide can trap and propel red blood cells along the waveguide. Here we propose to use the evanescent field from a narrow optical waveguide to trap and deform red blood cells. We demonstrate that the intensity gradient of the evanescent field at the edge of narrow waveguides (1-3 μm) can be used to squeeze a blood cell. The RBCs are squeezed to a size comparable to the waveguide width. When the laser is switched on the cell is attracted towards the waveguide and is held in place. Subsequently, the part of the cell not on the waveguide is pulled in across the waveguide. The result is a cell (7-8 μm in diameter) squeezed down to a significantly smaller width (typically 3 μm). The cell regains its original shape when laser is switched-off.
Realization of single-mode waveguides is essential for ultra-sensitive biosensing in the mid-infrared molecular “fingerprint” region for biomedical lab-on-chip applications. High contrast (Δn ≈ 1) germanium telluride (GeTe4) single mode rib waveguides were fabricated on zinc selenide (ZnSe) substrates for evanescent field based sensing to detect analytes at low concentration. Amorphous GeTe4 thin films were deposited by RF-sputtering and were found to transmit over the spectral range from 2μm - 20μm. Photolithography followed by reactive ion etching was carried out to etch the film, forming rib waveguide structures with minimum surface roughness and vertical sidewalls. It was found that films deposited at room temperature have average roughness of about 5nm. Optical constants were determined by IR-VASE ellipsometry.
Thin films of erbium doped tantalum pentoxide were prepared on unheated <100> orientated silicon substrates with a
thermally grown 2 μm thick SiO2 layer using reactive sputtering in an oxygen rich environment for upconversion laser
experiments. Tantalum and Erbium metal targets were co-sputtered using an ion beam assisted reactive process to
produce the high quality amorphous thin film layers. The Erbium dopant concentration was adjusted by varying the
relative deposition rate. Slab waveguide loss before high temperature annealing was measured to be 0.8 dB/cm at 633
nm which reduced to 0.5 dB/cm after annealing at 500 °C. Micron scale waveguides were etched into the deposited thin
film slab waveguides using photolithography and reactive ion etching. Finally a silicon dioxide buffer layer was
deposited on top of the ridge waveguides to help constrict the laser mode and to add a protective layer. 2 cm long
waveguide samples were cleaved and polished to achieve good optical quality end facets for laser experiments.
Upconversion efficiency and laser gain measurements were performed on the final waveguides. Waveguide losses of
6.35 dB/cm were measured for the final ridge waveguides and a coupling efficiency of 48 % was obtained. A positive
net gain of 0.25 dB was measured for upconversion to 551 nm using a pump probe optical setup.
Thin films of two different dielectric materials (Yttrium Oxide and Tantalum Pentoxide) were deposited by reactive
sputtering and reactive evaporation to determine their suitability as a host for a rare earth doped planar waveguide
upconversion laser. The optical properties, structure and crystalline phase of the films were found to be dependent on
the deposition method and process parameters. X-ray diffraction (XRD) analysis on several of the 'as-deposited' thin
films revealed that the films vary from amorphous to highly crystalline depending on material and process parameters.
SEM imaging of the Yttrium Oxide layers revealed a regular column structure confirming their crystalline nature and
SEM imaging of the Tantalum Pentoxide layers revealed a smooth amorphous layer confirming their XRD
diffractrograms. The dielectric thin film layers which allowed guiding in both the visible and infra-red regions of the
spectrum had a more amorphous structure.
The optical propulsion of mammalian eukaryotic cells along the surface of an integrated channel waveguide is
demonstrated. 10μm diameter polymethylmethacrylate (PMMA) spherical particles and similarly sized mammalian
eukaryotic cells in aqueous medium are deposited in a reservoir over a caesium ion-exchanged channel waveguide. Light
from a fibre laser at 1064nm was coupled into the waveguide, causing the polymer particles or cells to be propelled
along the waveguide at a velocity which is dependent upon the laser power. A theoretical model was used to predict the
propulsion velocity as a function of the refractive index of the particle. The experimental results obtained for the PMMA
particles and the mammalian cells show that for input powers greater than 50mW the propulsion velocity is
approximately that obtained by the theoretical model. For input powers of less than ~50mW neither particles nor cells
were propelled; this is considered to be a result of surface forces (which are not considered in the theoretical model).
The results are discussed in light of the potential application of optical channel waveguides for bioanalytical
applications, namely in the identification and sorting of mammalian cells from mixed populations without the need for
fluorescence or antibody labels.
Novel bottle microresonators fabricated from standard telecommunications optical fiber were recently shown to support
helical whispering gallery modes (WGMs) extending along the bottle length between the bottle necks. Intensity maxima
were observed around the turning points on both sides close to the bottle necks where the WGMs are effectively
reflected. Selective excitation on one side of the bottle microresonator leads to strong power localization at a
symmetrically located turning point for the WGMs and can potentially be exploited to form effective add-drop filters.
Channel dropping characteristics have been studied experimentally for the first time in this novel type of microresonator.
A tapered optical fiber (drawn down to 2-3 microns in diameter with effective index of approximately 1.2) was placed on
one side of the bottle to excite the bottle WGMs. A similar tapered fiber placed symmetrically on the other side of the
bottle acted as a probe to extract the excited modes. We have successfully extracted power from all the resonance
wavelengths using the probe placed at appropriate positions along the bottle, leading to the potential to construct efficient
all fiber add-drop filters.
Design, fabrication and optimization of high refractive index (2.1 @ 1070 nm), sub-micron thickness (200 nm) Tantalum
Pentoxide waveguides is reported. Optimization of fabrication parameters reduces the propagation loss to ~ 1 dB/cm @
1070 nm for Ta2O5 waveguides. Ta2O5 waveguides were found to be stable for high power application with no significant
absorption peaks over a large range of wavelengths (600-1700 nm). Ta2O5 waveguides provide high intensity in the
evanescent field, which is useful for efficient optical propelling of micro-particles. We have employed Ta2O5 waveguide
to propel polystyrene micro-particles with 50 μm/s velocity.
The high-refractive index contrast (▵n ~0.65 as compared to silicon oxide) of Tantalum pentoxide (Ta2O5) waveguide
allows strong confinement of light in waveguides of sub-micron thickness (200 nm). This enhances the intensity in the
evanescent field, which we have employed for efficient propelling of micro-particles. The feasibility of opto-fluidics
sorting of different sized micro-particles based on their varying optical propulsion velocity is suggested. Optical
propulsion of fixed red blood cells (RBC) with velocity higher than previously obtained is also reported. The optical
propulsion velocities of RBC in isotonic solution (0.25 M sucrose) and water have been compared.
Quality-factors of waveguide coupled microsphere resonators of 30 μm diameter are measured. A Teflon buffer layer is
deposited on the waveguide to separate the microsphere from the waveguide and the effect of this separation on the
measured quality-factor is discussed. The whispering-gallery mode propagation along the cavity of the microsphere as
well as the optical path lengths of the modes are determined; the experimental and theoretical data are compared and
discussed. A five-fold increase of the Q-factor was obtained by increasing the sphere-waveguide separation.
In a dielectric waveguide, the optical power is confined mostly in the core of the waveguide, where the refractive index is highest. Outside of the core the field is evanescent, i.e., the field strength decreases exponentially with the distance from the core. This evanescent field can be used to manipulate microparticles. For a particle with index of refraction higher than that of the surrounding medium (water), the optical forces due to the evanescent field act to guide the particle along the waveguide. The use of waveguides to trap particles combines the possibilities of conventional optical tweezers with the techniques employed in integrated optics, and it has the added advantage of integration of several functions on a single chip. We have experimentally observed size-dependent trapping and propulsion at velocities up to 33μm/s of polystyrene spheres, of diameters between 3 and 12μm, and in propulsion of 0.25μm diameter gold spheres at velocities up to 500μm/s. A Y-junction with a multimode input waveguide has been used to sort particles. By moving the input fibre relative to the input waveguide, the light goes into one of the two output branches. We have shown that this principle can be used to sort polystyrene microbeads. Recently we have used counter-propagating waves to move particles in both directions and also to stop a particle at a precise location. Experimental results and simulations for polystyrene microbeads, yeast cells and gold particles are presented.
Optical microsphere resonators, with their exceptionally low optical losses and high Q-factors, are attracting a lot of interest in integrated optics and related fields. Not being accessible by free-space beams, whispering gallery modes (WGM) of a microsphere resonator require near-field coupler devices. Efficient evanescent coupling has been demonstrated previously by using thin tapered fibres, fibre half-block couplers, angle-polished fibres and bulk prisms. In this work, we demonstrate WGM excitation in microspheres, from 8 to 15 μm in diameter, by using an integrated optics channel waveguide. Light from a tunable laser was coupled into a single mode K+ ion-exchanged channel waveguide formed in BK7 glass substrate. Dry borosilicate glass microspheres were dispersed on the substrate surface. Polystyrene microspheres were suspended in electrolyte water solution and confined in a closed cell on top of the waveguide. The light was coupled to the particles sitting on the waveguide surface. The scattered light was observed through the microscope. As the laser wavelength was tuned, the observed images were recorded with a CCD camera. WGM excitation was observed through the increased scattered light intensity at certain wavelengths. In the case of glass microspheres and a Ti:Sapphire tunable laser, the obtained resonance quality (Q-) factors were about 400. The resonances observed in polystyrene microspheres using a tunable diode laser had lower Q-factors and were deteriorating with decreasing particle size.
In this paper, we present both a theoretical evaluation and the fabrication of a novel polymerase chain reaction (PCR) microdevice. This microdevice contains elements for both thermal cycling and fluorescence detection. The proposed device is composed of a reaction chamber with integrated temperature sensor, heaters, p-n diode and optical filter. The advantage of combining these in a single structure is that real time detection of DNA amplification will be possible using a small volume of the PCR solution. The photodiode is covered by a thin film optical filter in order to block out the light which is used to excite the fluorophore dyes. CdS is used for the first time for such a filter and the complete micro-fabrication process is described.
Ultra-high bandwidth continua generated by ultrashort fs pulses have
been attracting enormous interest for applications such as general
spectroscopy, Optical Coherence Tomography and metrology. Dispersion
engineering is one of the key aspects of optimised continuum generation in optical waveguides. However in addition, the dispersion
of the pump pulse can be continuously adapted to control bandwidth and spectral characteristics of the generated continua. In this work we report on a systematic investigation of how 2nd, and 3rd order dispersion affects the continuum generated in strongly nonlinear planar waveguides. A ~30 fs Ti:Sapphire tuned to 800 nm was used as a pump source delivering ~3 nJ pulses. The chirp of the pulses was controlled completely-arbitrarily by an acousto-optic programmable dispersive filter (Dazzler). The power launched into the structures was kept constant to compare the generated continua as the pulse dispersion is varied. High refractive index tantalum pentoxide (Ta2O5) waveguides grown by standard silicon processing techniques were used. The devices investigated were specially designed tapered ridges with ~5 mm2 input modal volume and zero group velocity dispersion
at ~l - 3.7 mm. Self-phase modulation, which is responsible for
the spectral broadening of the continua, is tracked by finely tuning the both 2nd and 3rd order dispersions. The nonlinear propagation is dramatically influenced by the simultaneous presence of these dispersive effects resulting in a change of bandwidth and spectral shape. Pulse widths of up to Dl > 100 nm for launched powers as low as 300 pJ. Spectral peak intensity can also be systematically modulated by simply scanning the 2nd and 3rd order dispersion around their relative zeros. Specific combinations of high order dispersion contribution are currently targeted as a route to control and optimise the continua bandwidths and to control dispersion lengths in specifically engineered waveguides.
A method is presented for the covalent attachment of oligonucleotides to silicon (100) surfaces patterned with micron-scale features. UV light exposure of hydrogen-terminated silicon (100) coated with alkenes functionalized with N-hydroxysuccinimide ester groups results in Si-C bonded monolayers. The N-hydroxysuccinimide ester surfaces act as a template for the subsequent covalent attachment of DNA oligonucleotides. In order to create patterns of surface attached DNA oligonucleotides with high density, the surface attachment chemistry has been investigated and optimised. Micron-scale patterning of surfaces was achieved by exposure with UV laser light via a mask. DNA oligonucleotide patterns, with feature sizes of several microns, were reliably produced over large areas. The patterned surfaces were characterised with scanning electron microscopy, epifluorescence microscopy and ellipsometry. Hybridisation with fluorescent label- and gold nanoparticle-conjugates of the complementary oligonucleotide is achieved. The methods offer reliable approaches for the creation of micron-scale motifs of DNA on surfaces.
A 32-analyte integrated optical immunofluorescence multisensor system has been realized and tested for the first time. The sensor system is based upon bio/immuno-chemistry at the waveguide surface and fluoroimmunoassay in the evanescent fields of the optcal waeguides, to enable rapid, simultaneous and high-sensitivity fluorescence detection of up to 32 pollutants in water, and automatic regeneration for immediate reuse. The system has been demonstrated for estrone and a detection limit of 13 ng/L has been achieved.
We present simultaneous electrochemical and waveguide surface plasmon resonance measurements demonstrating the electrochemically controlled desorption of a thiol monolayer from a gold electrode. Self-assembled thiol layers are used in biosensors to enable the attachment of lipids to the sensor. This work demonstrates the potential for development of the device for biological sensing applications. Simultaneous SPR electrochemical measurements are made during the thiol desorption and these results are discussed and compared to the results of a numerical simulation.
Planar optical waveguides may be used for the sensitive real-time interrogation of the optical properties of very thin films attached at surfaces, and microfabrication allows the definition of integrated optical circuits, including electrodes, for sensor arrays. Sensing techniques based upon thin-film absorption and refractive index changes are presented, including electrochemically-controlled surface reactions, and present work on fluoroimmunosensor arrays and instrumentation are discussed. In particular, integrated optical immunoprobes for environmental analysis are described.
We have developed, modeled and optimized optical transducers for total internal reflection fluorescence (TIRF). The transducers are part of a compact and rugged immuno-analytical instrument designed for simultaneous detection of up to six analytes in aquatic samples (e.g. atrazine and 2,4-D). Binding inhibition assays, using Cy5.5 labeled antibodies to detect the target analytes, have been carried out. Calibration curves with mid-points of tests below 1 (mu) g/1 and detection limits below 0.1 (mu) g/1 have been achieved. As transducer either ion exchanged integrated optical channel waveguides or planar multimode slab waveguides have been employed. The transducer performance was significantly enhanced by incorporating thin high index films at the waveguide surface and by applying high refractive index solutions in the superstrate. Peak signal enhancement factors of more than ten have been observed and an increase in signal to noise ratio by a factor of more than four have been achieved. Strong polarization dependent effects on the enhancement by high index films have been found both theoretically and experimentally.
Integrated optical transducers for the detection of chemical and biochemical species and for optical measurements on bulk media are the subject of intense research effort. While many such sensors have been demonstrated in research laboratories worldwide, commercial exploitation of integrated optical sensors has proceeded slowly. Progress towards incorporating multiple-output sensors, based around the use of integrated optical Mach-Zehnder interferometers, into a robust and inexpensive instrument is described in this paper. A 1D CCD array is used to acquire the multiple outputs, resulting in ready alignment and a flexible approach to device reconfiguration and offering particular promise for application to multianalyte transducers where several signals must be interrogated simultaneously. The sensitivity and low noise demonstrated by the detection system is expected to allow the use of cheap, stable, LED light sources in practical systems.
A regenerable channel waveguide fluorescence sensor for environmental monitoring is reported. The sensor has been characterized as a detector of the pesticide 2,4 dichlorophenoxyacetic acid. A binding inhibition assay, using fluorescent Cy5.5 dye-labeled antibodies, was monitored at the modified surface of the glass waveguide to detect the target analyte. Three calibration curves were determined and averaged. The averaged calibration curve has a mid-point of 0.68 ppb and a calculated detection limit of 0.28 ppb. Incorporation of a 20 nm thick tantalum pentoxide film at the waveguide surface enhanced the peak fluorescence signal by a factor of approximately 6 compared with an uncoated sensor.
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