KEYWORDS: Free space optics, Modulation, Data modeling, Data transmission, Telecommunications, Atmospheric modeling, Signal attenuation, Systems modeling, Optical transmission, Fiber optic gyroscopes
The emerging technology of power-by-light enables power and data delivery over a single Free Space Optical (FSO) link for electrically isolated, interference-free remote operation. Telecom wavelength bands (λ ≈ 1550 nm) are well known for applications in data communication over optical fiber and overlap atmospheric transparency windows, extending the reach of FSO power and data systems through the air. This creates the opportunity to directionally deliver significant power (above 1mW) and high speed data wirelessly over long distances. FSO channels can experience turbulence and weather conditions that affect data and power transmission. Hence, they should be modeled and verified against measurements under varied atmospheric conditions. This will help improve model precision and robustness in predicting FSO channel performance. Accurate modeling of data transmission in FSO channels is urgently required to support the design of wireless optical communication systems for remote areas to which fiber deployment is difficult or uneconomic and instead long-range data communications between ground stations and High-Altitude Platform Systems (HAPS) may be employed. We have modelled an FSO channel transmitting data and power at 1550 and 1520 nm respectively under various meteorological conditions. The system model was developed in the commercially available OptiSystem software for modeling signals transmission. Different weather conditions translate directly to different FSO channel signal attenuations, impacting both data and power transmission. We also explore the impact of different modulation schemes such as Quadratic Amplitude Modulation (QAM), Pulse Amplitude Modulation (PAM), and Quadratic Phase Shift Keying (QPSK) on the bit error rate of the transmitted data thereby achieving the optimal required hardware design parameters. We found that QPSK is predicted to have the longest viable FSO range across all weather conditions and that power cannot be transmitted past 1 km in foggy weather.
Photonic power converters (PPCs) are photovoltaic cells that convert monochromatic light into electric power. The impact of luminescent coupling (LC) on InGaAs-based PPCs is studied. Multi-junction PPCs are simulated using an experimentally validated drift-diffusion model, and the contribution of LC is quantified. Up to 85% of the photons emitted across the InGaAs layers are re-absorbed in the dual-junction device considered. This number increases to 96% when a back reflector is included due to improved light management. Interference effects produced by multiple reflections are examined as a function of the emission angle.
The standard method to measure subcell external quantum efficiency (EQE) for multi-junction photovoltaics (MJPV) uses light biasing to bring each subcell into current limitation. This method is suitable when each subcell absorbs in a different wavelength range. However, isolating individual subcells via light biasing is difficult for semitransparent subcells with overlapping absorptance, as in MJPV designed for monochromatic irradiance in power-by-light systems. For these cells, the standard measurement approach falls short. Here, we present an alternative technique that incorporates a negative bias voltage to overcome this limitation. We demonstrate subcell EQE measurements in MJPV devices with up to six GaAs subcells.
We have developed a machine learning empowered computational framework to facilitate design space exploration for optoelectronic devices. In this work, we apply dimensionality reduction and clustering machine learning algorithms to identify optimal ten-junction C-band photonic power converter (PPC) designs. We outline our framework, design optimization procedure, calibrated optoelectronic model, and experimental calibration devices. We report on top performing device designs for on-substrate and flat back-reflector architectures. We comment on the design sensitivity for these PPCs and on the applicability of dimensionality reduction and clustering algorithms to assist in optoelectronic device design.
KEYWORDS: Solar cells, Photovoltaics, Solar energy, Silicon, Perovskite, Manufacturing, Sustainability, Dye sensitized solar cells, Design, Energy efficiency
This report provides a snapshot of emerging photovoltaic (PV) technologies. It consists of concise contributions from experts in a wide range of fields including silicon, thin film, III-V, perovskite, organic, and dye-sensitized PVs. Strategies for exceeding the detailed balance limit and for light managing are presented, followed by a section detailing key applications and commercialization pathways. A section on sustainability then discusses the need for minimization of the environmental footprint in PV manufacturing and recycling. The report concludes with a perspective based on broad survey questions presented to the contributing authors regarding the needs and future evolution of PV.
Photonic power converters designed to operate in the telecommunications O-band were measured under non-uniform 1319 nm laser illumination. Two device architectures were studied, based on lattice-matched InGaAsP on an InP substrate and lattice-mismatched InGaAs grown on GaAs using a metamorphic buffer. The maximum measured efficiencies were 52.9% and 48.8% for the lattice-matched and -mismatched designs respectively. Both 5.4-mm2 devices were insensitive to the incident laser spot size for input powers of < 250 mW and exhibited better performance for larger spot sizes with more uniform illumination profiles at higher powers.
Photonic power converters (PPCs) are one of the main components of optical power transmission systems, generating electrical power via the photovoltaic effect. We simulate ultrathin PPCs designed for operating at the telecommunication wavelength of 1310 nm with 9 and 12 times thinner absorbing layers using cubic and pyramidal nanostructured back reflectors (BRs), respectively. While increasing efficiency by 13% (rel.) over conventional PPCs, results also show superior light trapping for pyramidal BR with twice the absorption of a simple double pass absorber layer of the same thickness and higher short-circuit current for pillar BR reaching 94% of an ideal Lambertian surface.
KEYWORDS: Silicon, Germanium, Interfaces, Multijunction solar cells, Photovoltaics, Electrochemical etching, Transmission electron microscopy, Chemical mechanical planarization, Solar cells
III-V solar cell cost reduction and direct III-V/Si integration can both be realized by depositing a thin layer of high-quality Ge on relatively low-cost Si substrates. However, direct epitaxial growth of Ge on Si substrates is difficult due to the 4% lattice mismatch between the film and the substrate. Threading dislocations (TDs) introduced within the Ge layer have a detrimental effect on device performances. The goal of this research is to address the perennial need to minimize the defect density of Ge epilayers grown on a Si substrate. We seek to accommodate the effects of the lattice mismatch by introducing a porous Si interface layer to intercept dislocations and prevent them from reaching the active layers of the device. The porous Si layer is formed through dislocation-selective electrochemical deep etching and thermal annealing. The porous layer created beneath the top Ge layer can both act as dislocation traps and as a soft compliant substrate, which displays high flexibility. Transmission electron microscopy (TEM) analysis of the Ge/porous Si interface shows that the lattice mismatch strain of the Ge films was almost relaxed. The surface roughness of this modified Ge/Si substrate has been reduced using chemical mechanical polishing (CMP) process to fulfil the requirements for epitaxy of III-V alloys. Finally, we present simulation results exploring the effect of threading dislocations on device performance.
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