Optoelectronic and spectral analysis of urine can be performed on site by low-cost portable technology, interfaced to signal processing and machine learning algorithm. These algorithms, trained on a set of previously known diagnostic outputs, can correlate the urine optoelectronic measured parameters with the person’s health status. The proposed solution is the development of an optoelectronic setup, suitable to be embedded in a portable configuration, capable of performing on site and in a short amount of time a urine screening based on a set of techniques of increasing three levels of complexity. The proposed parameters to be measured are dominant color and turbidity (1st level), UV induced fluorescence (2nd level), Raman Spectroscopy (3rd level). The system can be used to perform a set of measurements on a set of urine samples of already known health condition to carry out the training of a machine learning algorithm for assessing the risk of developing Acute Kidney Injury. All the technical information is public open access, available at https://github.com/ISELDEETC/PhotoAKI/tree/main/LUMINA.
It is presented in this work a description of an optomechanical setup to be used for the characterization of planar photonic chips. The system allows the fine tuning of an optical fiber position on an input grating, controlling its XYZ position and its angle of incidence. A similar configuration is used for the output extraction, while a fiber array can be used an alternative to monitor multiple output channels. Such a configuration can be useful for characterization of arrayed sensing devices or Optical Phased Arrays. The system can be used in the visible range and in the IR spectrum as well, provided the input light source is changed. All the setting are controlled manually, and it is prepared to easily perform a sequential analysis of a set of identical circuits, fabricated in a parallel configuration on the same chip. As most of the components are individually and commercially available thought the Thorlabs website, the set up can be easily replicated, so all the system designs are made available in Open Access modality in SolidWorks format. Examples of characterization process and the obtained results are reported to demonstrate the use of the system and to support a tolerance analysis.
Coupling light into or out of a photonic integrated circuit is often accomplished by establishing a vertical link between a single mode optical fibre and a resonant waveguide grating, which is then followed by a tapered and a single mode waveguides. For a chip to fibre coupler, the period of the diffraction grating is often apodized to achieve an optimal beam profile at the input of the optical fibre. The tapered waveguide operates as a spot-size converter, expanding laterally the light beam in the single mode waveguide, to match the profile of the fundamental mode of the resonant waveguide grating. In this work, we propose using subwavelength structures to modulate the refractive index of the tapered waveguide for the lateral expansion of the light beam, when operating at the 1550 nm wavelength. The engineered graded index structure is simulated through adequate numerical methods and its performance is analysed in terms of efficiency and mode profile matching. With our proposed inverted taper waveguide, we were able to obtain an adiabatic power transfer and coupling efficiency with the TE fundamental mode of -0.26 dB and -0.92 dB, respectively. This performance has been achieved in a structure 11.1 μm long and 14.27 μm wide. Furthermore, the obtained fields were fed into a resonant waveguide grating to evaluate the coupling efficiency into the fundamental mode of an optical fibre, resulting in an expected performance decrease of 0.1 dB and ~0.6 dB by comparing respectively with the power transfer and coupling efficiency of the resonant waveguide grating when propagating the calculated TE0 mode.
Photonic systems are gaining an important role in the field of medical diagnosis due to the achievable high sensitivity and selectivity and low cost, enabling the fabrication of disposable point of care diagnosis systems for multiple pathologies. In this work we present the detector subsystem developed for a multi-channel surface plasmon resonance (SPR) based sensor. The core of the system is a multimode interferometer splitter, fabricated in amorphous silicon, followed by multiple sensitive SPR structures with a functionalized gold layer that modulate the transmitted light waves, in the presence of the biomarker, which are then detected by infrared detectors. For this purpose a highly adaptable detection system based on a InGaAs line CCD device was developed. The IR sensor used in the prototype has 128 (50 x 250 μm) pixels but other formats are supported. To adapt to different light guiding structures, the CCD pixels can be combined forming multiple detection channels. Optical sensor configuration and readout operations are performed trough a USB connection using the SCPI standard. The system includes an analog front end with a programmable gain amplifier and offset adjustment followed by a fast analog to digital converter feeding the data to a STM32 family processor. A computer application was also developed for system configuration and signal readout and storage. The testing results from the complete system are presented. Documentation of the developed system is provided for third party use, all the material generated within this work is available online in a repository.
When engineering photonic integrated structures, there will be a time that one must consider coupling out the electromagnetic field to an external device. Often, this coupling is made through a single mode optical fibre. Due to the mismatch in mode field diameters between waveguide and fibre modes, the propagating mode inside the dielectric waveguide must undertake a spot-size conversion. It requires to be radially expanded, often laterally by a tapered waveguide and longitudinally through other means, to match the radial profile of the optical fibre mode. Then, the energy must be coupled out of its propagating path into the plane of the optical fibre, through a structure that possesses such functional purpose. In this work, we describe the design steps and optimization of a silicon nitride waveguide/fibre coupler operating in the visible range. To this end, we start by designing an optimized 3D taper waveguide, using Beam Propagation method, that performs as the spot-size converter. Next, through the Eigen Mode Expansion method, a 2D subwavelength grating is designed and optimized regarding substrate leakage and propagating plane energy coupling out, thus vertically validating the energy distribution of the outgoing profile. The required subwavelength grating apodization is accomplished, once more through the Eigen Mode Expansion method, and by carefully engineering a metamaterial that performs accordingly. The obtained diffraction grating is then expanded horizontally to create a 3D structure and laterally validated through Beam Propagation method. Finally, the whole 3D structure is optimized and validated through Finite Differences Time Domain simulations regarding energy profile coupling out, and overlap integral matching is established with the fibre mode profile.
Optical power splitters are widely used in many applications and different typologies have been developed for devices dedicated to this function. Among them, the multimode interference design is especially attractive for its simplicity and performance making it a strong candidate for low-cost applications, such as photonics lab-on-chips for biomedical point of care systems. Within this context, splitting the optical beam equally into multiple channels is of fundamental importance to provide reference arms, parallel sensing of different biomarkers and allowing multiplexed reading schemes. From a theoretical point of view, the multimode structure allows implementation of the power splitting function for an arbitrary number of channels, but in practice its performance is limited by lithographic mask imperfections and waveguide width. In this work we analyze multimode waveguide structures, based on amorphous silicon (a-Si:H) over insulator (SiO2), which can be produced by the PECVD deposition technique. The study compares the performance of several 1 to N designs optimized to provide division of the fundamental quasi-TM mode as a function of input polarization and lithographic roughness. The performance is analyzed in terms of output power uniformity and attenuation and is based on numerical simulations using the Beam Propagation Method and Eigenmode Expansion Propagation Methods.
Combination of carbon-based nanomaterials (CNMs) with AuNPs has been demonstrated to enhance the LSPR response and facilitate the functionalization with specific and selective antibodies. Also, the introduction of CNMs in the plasmonic layer allows tuning of the LSPR central frequency. Joining the double dependence of the LSPR on the MNPs size and the presence of CNMs, it is possible to create a set of plasmonic layers whose LSPR wavelengths are distributed in a spectral range of few tenth of nanometers. This consideration paves the way to an LSPR sensor with an arrayed structure, where each element maximizes its specific LSPR at its own wavelength. Illumination with a broad light source produces a different response in each one of the elements. The working process underlying the sensing operation is that each element of the sensor array acts like a band-stop optical filter for a specific wavelength. The output can be extracted by the application of an image analysis approach to the spatially modulated light crossing the sensor area, based on a color recognition algorithm. A change in the refractive index over the sensor array will shift the rejection band of the sensing elements. An automatized method for color recognition can support the analysis of the refractive index variations yielding the final sensor output. A figure of merit, highlighting the LSPR central wavelength and spectral extension for different LSPR configurations, is also obtained for different sizes of the AuNPs and different flavors of CNMs.
In this contribution we report on a low cost plasmonic electrode for light-sensing applications. The electrode combines a conducting nonstoichiometric indium oxide (InOx) layer with an ultrathin (~5 nm) discontinuous Au layer. The InOx and Au layers were deposited on glass substrates by plasma enhanced reactive thermal evaporation and thermal evaporation, respectively. Several device configurations with one or two Au layer(s) sandwiched between InOx layers were fabricated and characterized. The morphological and structural properties of both Au and InOx layers were analyzed using AFM and XRD techniques. In particular, the effect of thermal annealing (673 K, 15 min) on the surface morphology of Au layers grown on bare glass and InOx-coated substrate was investigated. It has been also found that the oxide film grown above an underlying nanostructured Au layer is amorphous, while a reference InOx film on glass is nanocrystalline with a smooth surface. The electrical properties of InOx grown on the Au surface are worsened due to Au-induced structural disorder. The observed difference in transmission spectra of the glass/InOx/Au and glass/Au/InOx structures indicates the difference in the morphology of the metal layer. Thus, the optical and morphological properties of the InOx electrode can be varied in a wide range by incorporating several Au layers.
In this work we present a simulation study about the characteristics of a semiconductor structure suitable to be used as a guided wave optical biosensor, based on Surface Plasmonic Resonance effects (SPR). The proposed structure is a planar metal-dielectric waveguide where the sensor operation is based on the coupling between the fundamental propagation TM mode and the surface plasmon excited at the outer boundary of the metal, which interfaces the sample medium. Gold and aluminum are the metals considered for the plasmonic coating, amorphous silicon and others PECVD materials are considered for the waveguide structure. The results are based on modal analysis of the waveguide and plasmonic modes. The results obtained point out the possibility of generating SPPs in the near infrared range by including a functionalized cover of reduced graphene oxide (rGO) over the metal layer.
The large majority of surface plasmon resonance (SPR)-based devices use noble metals, namely gold or silver, in their manufacturing process. These metals present low resistivity, which leads to low optical losses in the visible and near-infrared spectrum ranges. Gold shows high environmental stability, which is essential for long-term operation, and the lower stability of silver can be overcome through the deposition of an alumina layer, for instance. However, their high cost is a limiting factor if the intended target is large-scale manufacturing. This work considers a cost-effective approach through the selection of aluminum as the plasmonic material and hydrogenated amorphous silicon instead of its crystalline counterpart. This SPR structure relies on Fano resonance to improve its response to refractive index deviations of the surrounding environment. Fano resonance is highly sensitive to slight changes of the medium, hence the reason we incorporated this interference phenomenon in the proposed sensing structure. We report the results obtained when conducting finite-difference time-domain algorithm-based simulations on this metal–dielectric–metal structure when the active metal is aluminum, gold, and silver. Then, we evaluate their sensitivity, detection accuracy, and resolution. The obtained results for our proposed sensing structure show good linearity and similar parameter performance as the ones obtained when using gold or silver as plasmonic materials.
The large majority of surface plasmon resonance based devices use noble metals, namely gold or silver, in their manufacturing process. These metals present low resistivity, which leads to low optical losses in the visible and near infrared spectrum ranges. Gold shows high environmental stability, which is essential for long-term operation, and silver’s lower stability can be overcome through the deposition of an alumina layer, for instance. However, their high cost is a limiting factor if the intended target is large scale manufacturing.
In this work, it is considered a cost-effective approach through the selection of aluminum as the plasmonic material and hydrogenated amorphous silicon instead of its crystalline counterpart. This surface plasmon resonance device relies on Fano resonance to improve its response to refractive index deviations of the surrounding environment. Fano resonance is highly sensitive to slight changes of the medium, hence the reason we incorporated this interference phenomenon in the proposed device.
We report the results obtained when conducting Finite-Difference Time Domain algorithm based simulations on this metal-dielectric-metal structure when the active metal is aluminum, gold and silver. Then, we evaluate their sensitivity, detection accuracy and resolution, and the obtained results for our proposed device show good linearity and similar parameter performance as the ones obtained when using gold or silver as plasmonic materials.
Localized surface plasmons (LSP) can be excited in metal nanoparticles (NP) by UV, visible or NIR light and are described as coherent oscillation of conduction electrons. Taking advantage of the tunable optical properties of NPs, we propose the realization of a plasmonic structure, based on the LSP interaction of NP with an embedding matrix of amorphous silicon. This study is directed to define the characteristics of NP and substrate necessary to the development of a LSP proteomics sensor that, once provided immobilized antibodies on its surface, will screen the concentration of selected antigens through the determination of LSPR spectra and peaks of light absorption. Metals of interest for NP composition are: Aluminium and Gold. Recent advances in nanoparticle production techniques allow almost full control over shapes and size, permitting full control over their optical and plasmonic properties and, above all, over their responsive spectra. Analytical solution is only possible for simple NP geometries, therefore our analysis, is realized recurring to computer simulation using the Discrete Dipole Approximation method (DDA). In this work we use the free software DDSCAT to study the optical properties of metal nanoparticles embedded in an amorphous silicon matrix, as a function of size, shape, aspect-ratio and metal type. Experimental measurements realized with arrays of metal nanoparticles are compared with the simulations.
We propose the development and realization of a plasmonic structure based on the LSP interaction of metal nanoparticles with an embedding matrix of amorphous silicon. This structure need to be usable as the basis for a sensor device applied in biomedical applications, after proper functionalization with selective antibodies. The final sensor structure needs to be low cost, compact and disposable. The study reported in this paper aims to analyze different materials for nanoparticles and embedding medium composition. Metals of interest for nanoparticles composition are Aluminum, Gold and Alumina. As a preliminary approach to this device, we study in this work the optical properties of metal nanoparticles embedded in an amorphous silicon matrix, as a function of size, aspect-ratio and metal type. Following an analysis based on the exact solution of the Mie theory, experimental measurements realized with arrays of metal nanoparticles are compared with the simulations.
Active-matrix organic light-emitting diodes (AMOLEDs) are ideal for future TV applications due to their ability to faithfully reproduce real images. However, pixel luminance can be affected by instability of driver TFTs and aging effect in OLEDs. This paper reports on a pixel driver utilizing a metal-insulator-semiconductor (MIS) sensor for luminance control of the OLED element. In the proposed pixel architecture for bottom-emission AMOLEDs, the embedded MIS sensor shares the same layer stack with back-channel etched a Si:H TFTs to maintain the fabrication simplicity. The pixel design for a large-area HD display is presented. The external electronics performs image processing to modify incoming video using correction parameters for each pixel in the backplane, and also sensor data processing to update the correction parameters. The luminance adjusting algorithm is based on realistic models for pixel circuit elements to predict the relation between the programming voltage and OLED luminance. SPICE modeling of the sensing part of the backplane is performed to demonstrate its feasibility. Details on the pixel circuit functionality including the sensing and programming operations are also discussed.
The device under study is an a-SiC:H/a-Si:H pinpin photodiodes produced by PECVD (Plasma Enhanced Chemical Vapour Deposition) and has a structure that consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructure with low conductivity doped layers. This device structure has been demonstrated useful in optical communications that use the WDM technique to encode multiple signals in the visible light range. We present in this work experimental results about C-V measurements of the device under complex conditions of illumination. Also it is presented an analysis based on the transient response of the device when illuminated by a pulsed light, with and without optical bias superposition. Rising and decaying times of the collected photocurrent will be outlined under the different conditions. A simulation study outlines the role played by each pin substructure on the response speed and gives some hint on the possible optimization of this device.
We present a new near-infrared photodetectors fabricated based on Hg3In2Te6 semiconductor compound. This ternary compound is a direct-gap n-type semiconductor with the band gap of 0.74 eV and carrier concentration about 1013 cm-3 at room temperature. Surface-barrier structures a transparent conducting metal oxide electrode-interfacial chemical grown oxide-semiconductor substrate with an active area from 3 to 50 mm2 have been fabricated by chemical oxidation of Hg3In2Te6 surface for the potential barrier's formation. The composition of oxide layer (40% In2O3, 50% TeO2, and 10% HgO) was determined using XPS analysis. Tin-doped indium oxide (ITO) film (as transparent conducting electrode) was deposited over this layer by magnetron RF sputtering technique. The devices are very sensitive to light with the wavelength from 0.4 to 1.7 micrometer. A self-calibrated photodetectors, which permit 100% external quantum efficiency (within error not exceeding 2%) at wavelengths of 1.3 and 1.5 micrometer, have been developed. The photodetectors fabricated on thin Hg3In2Te6 substrates have a low producing price and can be fabricated with a large photosensitive area. Photodetectors with an active area of 3 mm2 exhibit the rise and fall times from 2 to 4 ns under 1.3 micrometer pulse irradiation. Both basic material aspects and devices fabrication technique is detailed discussed.
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