This study addresses the challenges and research gaps in traffic monitoring and control, as well as traffic simulation, by proposing an integrated approach that utilizes Visible Light Communication (VLC) to optimize traffic signals and vehicle trajectory at urban intersections. The feasibility of implementing Vehicle-to-Vehicle (V2V) VLC in adaptive traffic control systems is examined through experimental results. Environmental conditions and their impact on real-world implementation are discussed. The system utilizes modulated light to transmit information between connected vehicles (CVs) and infrastructure, such as street lamps and traffic signals. Cooperative CVs exchange position and speed information via V2V communication within the control zone, enabling flexibility and adaptation to different traffic movements during signal phases. A Reinforcement Learning, coupled with the Simulation of Urban Mobility (SUMO) agent-based simulator, is employed to find the best policies to control traffic lights. The simulation scenario was adapted from a real-world environment in Lisbon, and it considers the presence of roads that impact the traffic flow at two connected intersections. A deep reinforcement learning algorithm dynamically control traffic flows by minimizing bottlenecks during rush hour through V2V and Vehicle-to-Infrastructure (V2I) communications. Queue/request/response interactions are facilitated using VLC mechanisms and relative pose concepts. The system is integrated into an edge-cloud architecture, enabling daily analysis of collected information in upper layers for a fast and adaptive response to local traffic conditions. Comparative analysis reveals the benefits of the proposed approach in terms of throughput, delay, and vehicle stops, uncovering optimal patterns for signals and trajectory optimization. Separate training and test sets allow monitoring and evaluating our model.
This paper presents a method for supporting wayfinding in crowded buildings using Visible Light Communication (VLC). Luminaires are repurposed to transmit encoded messages, providing location-based information to users. Tetra chromatic LEDs and OOK modulation efficiently transmit data, while error detection techniques ensure reliable transmission. Users carry receivers that interpret the light signals and perform localization calculations. Wayfinding algorithms guide users with turn-by-turn directions, landmarks, and alerts. The system integrates VLC into an edge/fog architecture, utilizing existing lighting infrastructure for efficient data processing and communication. It enables indoor navigation without GPS, demonstrating self-localization and optimizing routes. This method enhances accessibility and convenience in unfamiliar buildings.
Power splitting is usually accomplished in photonic integrated circuits through multimode interference devices. A compact form of such structures is the multimode interference reflector, which enables efficient light manipulation and wavelength selection. Being able to precisely tune the output characteristics of multimode interference reflectors is of paramount importance for various applications in communication systems and signal processing. Conventional methods for output tuning often rely on complex design iterations and simulations, hindering their scalability and adaptability. This research explores a novel approach to tune multimode interference reflectors using deep neural networks. By leveraging the learning capabilities of neural networks, a framework to accurately model the intricate relationships between the input parameters and the output responses of multimode interference reflector devices is being explored. A representation of a matrix of inference reflectors is considered. Then, a dataset is generated from rigorous simulations to train a neural network to predict the multimode interference reflector configuration under diverse operating conditions. A Generative Adversarial Network (GAN) is being optimized to tune the reflection characteristics of multimode interference reflectors to meet desired specifications, such as signal routing requirements and power division ratio at the output. The proposed method will significantly reduce the design cycle time, offering a substantial advantage in rapid prototyping and deployment of multimode interference reflector based photonic circuits, and showcases the potential of using neural networks for tuning these devices, presenting a transformative and data-driven approach to optimize the performance of photonic integrated circuits.
An increasing number of integrated photonic solutions find applications in the fields of biomedicine, manufacture, quantum computation and telecommunications. Size mismatch between optical fibers, light sources, photodetectors and photonic waveguides is usually significant, typically with the former having cross-sections on the orders of hundreds of micrometers or more and the latter a few micrometers or hundreds of nanometers. Efficiency in coupling light to and from photonic integrated circuits is an extremely important parameter since it influences device’s performance, affecting signal-to-noise ratio. Several approaches exist for light coupling, such as off-plane coupling with the assistance of grating couplers, on-plane/edge coupling with or without the assistance of tapers and adiabatic coupling. In this study we focus on grating couplers designed in amorphous silicon-on-insulator (SOI) platforms. Grating couplers are compact, can be tested at wafer-level, and do not require application specific fiber terminations, such as lenses and/or tapers. Two approaches in the optimization of grating couplers were explored, one based on a lithographic mask defined by the superposition of two different grating patterns, with different periods, having an offset to provide a random distribution of grating elements, and a technique based on the quadratic variation of the refractive index of the grating structure along its length. Results were obtained from 2D-FDTD simulations. Coupling efficiencies for the quasi-TE mode over -13 dB and -3 dB were obtained for the random and quadratic variations of the effective refractive index at a wavelength of 1550 nm, without bottom reflectors.
Reduction of mobile mechanical parts in Optical Phased Arrays and the overall miniaturization of the system can be claimed to improve robustness to harsh environment condition and reduction of the overall power consumption. An optical phased array configuration built on structure developed in a silicon photonic integrated circuit technology, may be able provide a solution to fit these requirements. Nevertheless, there is some drawback and some fabrication complexity that can be limiting the direct application for automotive solution in a low-cost configuration. In this work, it is presented the design and the simulation of an amorphous silicon phased array working at a wavelength of 1550 nm. Potential and limitation of this approach will be outlined.
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.
Sensors based on the Local Surface plasmon Resonance (LSPR) are attractive due to their simple structure and good sensitivity, but the expensive optoelectronic part of the device is limiting the practical applications. There is a need for new strategies to bring the excellent detection properties of LSPR sensors to the playground of low-cost devices and materials. In this work, it is proposed a novel approach to the output extraction of from LSPR sensor whose sensing element is composed by metal nanoparticles (MNPs). Illuminated with an incident broad light source, the sensor produces a spectral transmission output where the MNPs act like a band-stop optical filter for a specific wavelength. An alteration of the refractive index in the surrounding medium corresponds directly to a shift of the filtering rejection band, which corresponds to a slight change in the colour of the light transmitted by the sensor elements. This colour change can be captured by a CMOS photo-camera, used as an image sensor. It is proposed in this paper an approach based on an automatized image processing algorithm for colour change detection, yielding to a system capable of detecting refractive index variations, avoiding the use of expensive spectrometers. The algorithm comprises three stages: (1) Region of interest detection: images are first cropped using the Otsu threshold binary image to remove the uninteresting areas in the image. (2) Image segmentation: using the watershed algorithm, the sensor elements (sample) area is detected automatically in the cropped image. The segmentation is done using the gradient image, where the watershed markers are the regions of low gradient and barriers are the areas of high values inside the image. (3) The resulted sample region is then processed to find its average or dominant LAB colour and then compare it to its corresponding sample image immersed in different mediums using the colour difference measurement CIEDE2000.
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.
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.
This work reports the optimisation of a plasmonic waveguide sensor based on amorphous silicon compounds (a-SiC:H, a-SiN:H or a-SiCN:H) using the FDTD method and modal decomposition. The sensor consists of an array of parallel surface plasmon interferometers with different propagation lengths, each one comprising a thin layer of metal embedded into an amorphous silicon waveguide. In order to reduce the complexity and hardware, we have proposed a structure consisting of an array of parallel surface plasmon interferometers with different propagation lengths, such that at the end of the plasmonic structure the modes can interfere constructively or destructively depending on the refractive index of the sampling medium and the propagation length. The variation of the output intensity at the end of each waveguide element provides a convenient interrogation scheme. In this work we analyse different solutions for splitting the input fundamental mode into the different parallel waveguides, including multi-mode interference structures and directional coupler splitters. By exploring amorphous silicon compounds that can be deposited by Pressure Enhanced Chemical Vapor Deposition (PECVD) at low temperatures, we aim to achieve a low-cost process that is compatible with back-end CMOS processing and wavelengths in the visible to near infrared range.
Lithographic technology has been one of the main upholders to Moore's law in the semiconductor industry for the last decades. The underlying reason that enabled the evolution in semiconductor industry has been a steady silicon wafer printing cost, while being able to dramatically increase the number of nodes that can be printed per chip. Key developments in lithography such as wavelength decreasing, together with performance increase in lens and imaging technology, should be accounted for almost all the reduction of cost per function in integrated circuits technology. In this work, we will be presenting the simulation of two mitigation techniques for the impact of defects introduced by manufacturing processes. Namely, the lithographic mask limited resolution on the geometry of the representative device. These perturbations are a consequence of the lithographic mask limited resolution on the geometry of the representative device. For this purpose, the Beam Propagation and Finite Differences Time Domain methods will be used to simulate a multimode interference structure based on silicon nitride. The structure will be affected by previously mentioned perturbations and we expect results revealing a strong dependence between mask resolution, and imbalance and power loss. Two strategies will be followed concerning the mitigation of power loss and imbalance introduced by the limited resolution of lithographic mask: - Access waveguides tapering; - Adjustable power splitting ratios through the electro-optic effect. Through both strategies we aim to achieve an improvement on device’s performance but, in the latter are expected finer tuning capabilities, being enabled by dynamic compensation of power loss and imbalance when in a closed loop control architecture.
Surface plasmon resonance sensors have emerged has one of the most suitable approaches for biosensing. A common approach consists of exciting the plasmons at the interface between a functionalized metal film and a sample medium containing the analyte. The propagation of the surface plasmon is highly dependent on changes of the refractive index of the surrounding environment thus providing a mechanism for sensing. The typical interrogation schemes are based on scanning over the wavelength or the incident angle to search for the resonance condition. These solutions require additional motor-driven rotation stages, prisms or other bulky components, introducing complexity which prevents the fabrication of fully on-chip devices. This work reports a simulation study of an amorphous silicon waveguide structure consisting of an array of parallel surface plasmon interferometers with different propagation lengths, each one comprising a thin layer of gold embedded into a-Si:H waveguide. The surface plasmon modes at the end of the plasmonic structure can interfere constructively or destructively depending on the refractive index of the analyte and the interferometer’s length. The variation of the output intensity at the end of each element of the array provides a convenient interrogation scheme that is suitable for on-chip integration. In this paper we investigate this setup and analyze the output power at the end of the array as a function of the refractive index of the sampling medium. The setup is simulated and characterized by the eigenmode expansion method.
Surface Plasmon Resonance occurs when a polarized electromagnetic field strikes a metallic surface at the separation interface between metal and an insulator. This phenomenon is characterized by the conduction electrons resonant oscillation at the interface, resulting on propagating plasmon waves on the metallic surface. Since this wave is generated at the boundary between the metallic surface and the external medium, these structures are highly sensitive to alterations on the surrounding environment, namely the refractive index, and may be used in sensing structures. The large majority of these devices use noble metals, namely gold or silver, as the active material. 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. However, their high cost is a limiting factor if the intended target is large scale manufacturing. In this work, we performed Finite Differences Time Domain simulations on a Surface Plasmon Resonance based sensing structure, considering cost-effective materials such as aluminium for the active metal and hydrogenated amorphous silicon for the waveguide supporting elements, and verified that these structures are able to detect refractive index variations of the surrounding environment at the 1550 μm operating wavelength. This sensing architecture has also been modelled with dispersive materials, losses included, to reflect as much as possible physical reality, revealing good performance capabilities when compared to similar noble metals based devices.
In this paper we present a simulation study that intends to characterize the influence of defects introduced by manufacturing processes on the geometry of a semiconductor structure suitable to be used as a multimode interference (MMI) 3 dB power splitter. Consequently, these defects will represent refractive index fluctuations which, on their turn, will drastically affect the propagation conditions within the structure. Our simulations were conducted on a software platform that implements both Beam Propagation and FDTD numerical methods. This work supports the development of a biomedical plasmonic sensor, which is based on the coupling between the propagating modes in a dielectric waveguide and the surface plasmon mode that is generated on an overlaid metallic thin film, and where the output readout is achieved through an a-Si:H photodiode. By using a multimode interference 1×2 power splitter, this sensor device can utilize the non-sensing arm as a reference one, greatly facilitating its calibration and enhanced performance. Amorphous silicon can be deposited by PECVD processes at temperatures lower than 300°C, an attractive characteristic which makes it back-end compatible to CMOS fabrication processes. As the spectral sensitivity of amorphous silicon is restricted to the visible range, this sensing device should be operating on a wavelength not higher than 700 nm, thus a- SiNx has been the material hereby proposed for both waveguides and MMI power splitter.
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.
In the past several decades, the Finite-Difference Time-Domain (FDTD) method has become one of the most powerful numerical techniques in solving the Maxwell’s curl equations and has been widely applied to solve complex optical and photonic problems. This method divides space and time into a regular grid and simulates the time evolution of Maxwell’s equations. This paper reports some results, obtained by a set of FDTD simulations, about the characteristics of amorphous silicon waveguides embedded in a SiO2 cladding. Light absorption dependence on the material properties and waveguide curvature radius are analysed for wavelengths in the infrared spectrum. Wavelength transmission efficiency is determined analysing the decay of the light power along the waveguides and the obtained results show that total losses should remain within acceptable limits when considering curvature radius as small as 3 μm at its most.
In this work we correlate the dimension of the waveguide with small variations of the refractive index of the material
used for the waveguide core. We calculate the effective modal refractive index for different dimensions of the waveguide
and with slightly variation of the refractive index of the core material. These results are used as an input for a set of
Finite Difference Time Domain simulation, directed to study the characteristics of amorphous silicon waveguides
embedded in a SiO2 cladding. The study considers simple linear waveguides with rectangular section for studying the
modal attenuation expected at different wavelengths. Transmission efficiency is determined analyzing the decay of the
light power along the waveguides. As far as near infrared wavelengths are considered, a-Si:H shows a behavior highly
dependent on the light wavelength and its extinction coefficient rapidly increases as operating frequency goes into visible
spectrum range. The simulation results show that amorphous silicon can be considered a good candidate for waveguide
material core whenever the waveguide length is as short as a few centimeters. The maximum transmission length is
highly affected by the a-Si:H defect density, the mid-gap density of states and by the waveguide section area. The
simulation results address a minimum requirement of 300nm×400nm waveguide section in order to keep attenuation
below 1 dB cm-1.
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