Characteristics of tunable wavelength filters based on a-SiC:H multilayered stacked cells are studied both theoretically and experimentally. Curves of gain vs. wavelength illustrate the optical filter characteristics. A capacitive active band-pass filter model supports experimental data. Results show that the use of a double pi’n/pin a-SiC:H heterostructure as active capacitive filters depends on the wavelength and modulated frequency of the trigger light and on the wavelength of the additional optical bias. The devices combine three indispensable functions of transceivers, amplification, detection and wavelength filtering. Experimental and simulated results show the device combines the properties of active short-pass and long-pass filter sections into a capacitive active band-pass filter.

In recent years, lighting solutions have gradually been replaced by more efficient features, taking advantage of Light Emitting Diodes (LEDs) that have progressively conquered the market with increasingly high optical powers, low energy consumption and variable color temperatures. Along with this evolution, Visible Light Communication (VLC) technology has also been developed to use this existing lighting infrastructure and the inherent characteristic of LEDs being easily switched to high frequency to build data transmission systems. The applications of this communication technology using electromagnetic signals in the visible range are currently in a development stage with promising applications in several domains.This paper intends to study an optical communication system based on VLC to establish communication between road infrastructures and. vehicles. For this purpose, four communication channels established through the modulation of white trichromatic LED emitters are used. Detection of the optical signals is performed with a photodiode based on two stacked pin structures made of a-Si:H and a-SiC:H. This device works as an optical filter in the visible spectrum and its spectral sensitivity can be adjusted through stationary optical bias. On-Off-Keying (OOK) modulation is used. The structure of the data blocks to be transmitted was designed to avoid undesirable effects related to ambient light (flickering and/or perceptible variations in color temperature of the white light). The experimental tests of the proposed model were performed using a small-scale prototype. The results show that with the proposed system it is possible to transmit information between road infrastructure and vehicles.  

The concept of connectivity in the dictionary is defined as the ability of a computer or an information system to connect to other devices. This concept is constantly evolving because the devices that require connectivity are becoming increasingly diverse, and information systems are more complex. This increase in connectivity leads to an increase on the amount of transferred information and, consequently, the need for the evolution of telecommunications infrastructure, particularly those that reach our homes, such as passive optical networks. These networks also have their own evolution plan through the standards defined by standardization bodies which have started in the early 2000s with GPON, implemented worldwide today, bringing downstream speeds of 2.5 Gbps and upstream speeds of 1.25 Gbps. Today, we are witnessing the proliferation of technologies that already support 10 Gbps symmetrically, with the first tests of networks capable of delivering 50 Gbps symmetric speeds underway. The evolution of passive optical networks is only possible with the evolution of the optoelectronic components that implement them, and it is in the physical layer that challenges increase with the increase in bandwidth per device or the need for tuneability, as is the case of NG-PON2 standard. In parallel, with the evolution of passive optical networks in recent years, research and industry surrounding photonic integrated circuits have also made significant strides, allowing many of the devices around us to already have simple photonic integrated circuits. In data centers, where the need for bandwidth is much higher, most transceivers are already based on photonic integrated circuits and they bring all the advantages that integration has brought to the electronics domain, such as scalability at production and technological level, price or power consumption. Hence, the hypothesis arises that photonic integrated circuits can be part of the solution for the physical layer of 10 Gbps and beyond passive optical networks. Starting from this point, this thesis begins by presenting the evolution and hardware requirements of passive optical networks, as well as the evolution of photonic integrated circuits and their maturity for this market. This is followed by a theoretical study of the blocks of a transceiver for passive optical networks based on photonic integrated circuits, moving on to its design and testing, presenting experimental results of transceiver prototypes based on photonic integrated circuits. Finally, a techno-economic study and price sensitivity analysis are presented to ensure the feasibility of the proposed solution, along with a discussion of future market possibilities for integrated optical circuits in passive optical networks.

With the advent of Large Language Models (LLMs), developing new computational paradigms is essential to meet ever growing demands for processing power and energy efficiency. Neuromorphic computation, taking inspiration from biological nervous systems, emerges as a promising solution by enabling highly parallel and power-efficient hardware. At the same time, Resonant Tunnelling Diodes (RTDs) have become a key candidate for such hardware due to their unique attributes. RTD scan generate neuron-like spiking signals, posses strong photo detection capabilities suitable for high-frequency optoelectronic systems, and exhibit low power consumption. This dissertation focused on the design, fabrication, and characterization of RTD devices specifically for neuromorphic applications. It begins with analysis of the quantum phenomena that give rise to resonant tunneling in double barrier quantum wells, which produces a macroscopic Negative Differential Resistance (NDR) region. This NDR is responsible for the device’s ability to create high-frequency spikes. To explore how RTDs can interconnect to form hardware neural networks, a dedicated simulator was developed that can model RTD behaviours ranging from individual devices to series and parallel configurations. Experimentally, the work involved fabricating III-V semiconductor devices from a GaAs/AlAs material wafer in a clean room. Several micro fabrication steps were performed, such as photolithography, wet and dry etching, passivation, and metallisation. Process control was achieved using a profilometer and a Scanning Electron Microscope (SEM). Additionally, a thorough electro-optical characterization assessed the photo detection and high-frequency modulation performance of the two fabricated samples, demonstrating strong results such as responsivity values above 1 AW−1 and a large optical modulation bandwidth. In summary, this research advances the understanding of the RTD’s role in neuromorphic computing, successfully outlining their complete fabrication workflow and validating their significant optoelectronic capabilities. This confirms their potential for efficient, brain-inspired hardware.

Ultrathin Cu(In,Ga)Se2 solar cells are a promising way to reduce costs and to increase the electrical performance of thin film solar cells. In this work, we develop an optical lithography process that can produce sub-micrometer contacts in a SiO2 passivation layer at the CIGS rear contact. Furthermore, an optimization of the patterning dimensions reveals constrains over the features sizes. High passivation areas of the rear contact are needed to passivate the CIGS interface so that high performing solar cells can be obtained. However, these dimensions should not be achieved by using long distances between the contacts as they lead to poor electrical performance due to poor carrier extraction. This study expands the choice of passivation materials already known for ultrathin solar cells and its fabrication techniques.