Power beaming and DARPA’s persistent optical wireless energy relay (POWER) programWinsor, Robert; Jaffe, Paul
doi: 10.1117/12.3050148pmid: N/A
Energy is a fundamental currency in the battlespace. It is required to cause and transport military effects. Recognizing energy as a key aspect of warfare provides a new optimization surface to balance energy generation, storage, and distribution to more effectively achieve military objectives. In this way, generating and delivering military effects can be seen as an interconnected web of energy transactions. Dominating the energy web to more rapidly and reliably move energy through the battlespace and deliver military effects is the essence of warfare. DARPA perceives an opportunity to disrupt distribution by leveraging power beaming for near-instantaneous energy transport in a resilient, multi-path network. The DARPA POWER (Persistent Optical Wireless Energy Relay) program is a meaningful step toward building a new, more resilient energy distribution network.
Toward a laser-based power delivery for space applications: preliminary qualification of radiation sensitivityMauro, Anna; Bellone, Aurora; Olivero, Massimo; Blanc, Wilfried; Benabdesselam, Mourad; Mady, Frank; Vallan, Alberto; Perrone, Guido
doi: 10.1117/12.3044227pmid: N/A
Establishing permanent bases on the Moon will require to develop wireless power transmission systems using high-power fiber lasers to support lunar missions where solar or nuclear energy is insufficient. Key challenges include minimizing weight, managing extreme temperatures, and mitigating ionizing radiation’s effects. This study investigates the sensitivity to X-rays of commercial rare-earth doped optical fibers for high-power lasers in accelerated tests. Different approaches are considered and compared, such as monitoring power degradation and fiber temperature changes, variation of the Rayleigh scattering signatures, and modifications of the spectral response of a fiber Bragg grating inscribed in a small section of the active fiber.
1.1eV GaInAs cell development for dual-use solar and 1070nm laser power convertersMeeker, D. T. T.; Geisz, J. F.; VanSant, K. T.; Collins, S.; Friedman, D. J.; France, R. M.
doi: 10.1117/12.3042339pmid: N/A
Dual-use photovoltaic cells can receive solar and laser power simultaneously to generate current, an application relevant to space and terrestrial industries. This study investigates two concepts of solar cells optimized for dual-use 1070 nm laser and solar power conversion, a single-junction and triple-junction cell. The cell designs are based upon the 3- junction inverted metamorphic solar cell, previously shown highly efficient for solar conversion. Because it is closely bandgap-tuned for a 1070 nm laser, the 1 eV bottom junction is incorporated into each of the two designs, making its development key to the success of both concepts. However, each design requires some modification for efficient dual use. The single-junction device requires optimization to reduce short wavelength absorption of the broad solar spectrum. In both devices, the graded buffer layers in the GaInAs cell affect the cell’s performance by reducing threading dislocations in the active junction. However, the buffer in the three-junction device also acts as a lateral transport layer and so affects the fill factor depending on its sheet resistance. By varying the buffer thickness, we demonstrate a direct relationship between buffer thickness and sheet resistance reduction, while considering implications to open-circuit voltages. We also performed resistance modeling to determine the optimal grid spacing and thickness of the grid fingers to minimize losses due to sheet resistance and grid shading. Efficiency data for a one junction GaInAs cell demonstrates a laser conversion efficiency of 38% at 1070 nm wavelength without an anti-reflection coating.
15 years of laser power beaming demonstrationsNugent, Tom; Bashford, David; Bashford, Thomas; Sayles, Thomas J.; Kirby, Mitchell A.
doi: 10.1117/12.3043841pmid: N/A
PowerLight Technologies (PLT) has designed, built, tested, and demonstrated more than 20 power-by-light systems for both Free Space Power (FSP) and Power over Fiber (PoF) between 2007 and 2024 (demonstrations prior to 2018 were performed under the company’s original name, LaserMotive). Embracing a wide scope of applications, PLT’s projects span across ground-to-ground, ground-to-air, ground-to-water, and water-to-water scenarios, showcasing versatility of the technology. A profound commitment to safety remains at the core of each project. Through numerous innovative transmitter (TX) and receiver (RX) packaging designs, the various projects demonstrate compact configurations and operational relevance in their respective areas. A wide range of energy transmission capabilities, scalable from 10 to 1,000 watts (with potential for higher outputs), has been demonstrated by PLT. The team has showcased kilometer-scale distance coverage, efficiently delivering power over distances ranging from 1.5 to 1,000 meters, while ongoing developments suggest designs capable of spanning several kilometers. Systems with demonstrated performance firsts across many metrics, including delivered electric power levels up to 1 kilowatt, ranges up to 1 kilometer, receiver specific power ratios up to 800 watts/kilogram, safety D3 times as low as 1 millisecond, and other metrics, are presented.
Characterization of high power, kilometer-scale power over fiber cablingKirby, Mitchell A.; Sayles, Thomas J.; Smith, Mathew; Weinthal, Warren; Valencia, Christopher; Nugent, Tom
doi: 10.1117/12.3043825pmid: N/A
Long-distance optical power beaming can deliver kilowatts of power over kilometers distances, addressing the need for flexible power distribution in wireless mobile networks, autonomous systems, Internet of Things (IoT) devices, and edge computing applications. This technology includes both Free Space Power (FSP) and Power over Fiber (PoF). PoF systems convert electric power from an existing source into high-intensity light using a laser transmitter, which then transmits this light through optical fiber cables to a receiver system. The receiver converts the light back into electricity using photovoltaic materials. Key components of this technology are laser transmitters, photovoltaic receivers, and multimode fiber optic cabling. Herein we describe initial tests performed to assess the suitability of 105 m core, 125 m cladding multi-mode fiber optic cables for optical power delivery in PoF. Characterizing point defects, localized losses, and bulk losses can be used to better understand techniques for the successful deployment of PoF systems, whereas signal quality effects, like dispersion, are less significant. Initial measurements of meter- and kilometer-scale PoF cables at optical power levels up to 200 watts are presented and discussed.
InGaN photovoltaic laser power converters for atmospheric and submarine optical wireless power transfersSanmartín, Pablo; Almonacid, Florencia; García-Loureiro, Antonio; Fernández, Eduardo F.
doi: 10.1117/12.3040547pmid: N/A
Optical Wireless Power Transfer (OWPT) has surfaced as a transformative technology among long-range wireless power transmission options, capable of delivering kilowatts of power across kilometric distances. By eliminating physical connections, OWPT enables energy supply in harsh environments such as the deep ocean, outer space, or remote terrestrial locations with complicated access. However, the main challenge hindering its widespread adoption is the reduced system efficiency, particularly at high-power densities ( 100Wcm-2 ), where the efficiency of Photovoltaic Laser Power Converters (PVLPC) experiences significant degradation. To address this limitation, there is an urgent need for PVLPCs that can efficiently withstand intense monochromatic irradiances. Previous theoretical studies have identified InGaN as a promising material for improving state-of-the-art performance due to its tunable wide bandgap, which can be optimized for the specific transmission medium, and reduce series resistance losses. This work investigates the impact of the energy gap on efficiency across varying light intensities and its effect on overall system performance in both air and underwater environments. The results indicate that efficiencies as high as 76.5% can be achieved at 95Wcm-2 , and over 71% at 1000 Wcm-2 , for the highest energy gap alloy, In0.1Ga0.9N. Furthermore, system efficiencies of 69.7% are estimated for 10 km atmospheric transfers, and 52.6 and 36.9% for 20 and 40 m underwater transmissions, respectively. This work highlights the potential of InGaN-based PVLPCs to advance OWPT to new performance thresholds.
Long-duration operation of 100W power over fiber unitSayles, Thomas J.; Bashford, Thomas; Saelzer, Max; Smith, Mathew; Johnson, Isaac; Kirby, Mitchell A.; Nugent, Tom
doi: 10.1117/12.3043817pmid: N/A
Power over Fiber (PoF) is getting closer to commercialization for telecommunications and other industries, including for “high” power (meaning output more than 10W electrical). Beyond demonstrating basic performance metrics, hardware needs to be tested under a variety of conditions to ensure it can operate as expected before it can be sold and deployed. To that end, PowerLight has been operating Power over Fiber units for extended durations. This paper reports on a PoF unit that remained operational for 12 months nearly continually, powering multiple devices in the 10 W to 100 W electric power range. The system involves a temperature-controlled laser transmitter system that provides continuous optical power out in a thermally stable condition. The system features a fiber-coupled laser(s) with 20m of optical fiber connected to a receiver unit that performs the optical to electrical conversion. The system was rated and tested to deliver more than 150W of continuous electrical power out. The long-term operation powered three devices that consumed an average of ~70 W and was witnessed by numerous visitors to PowerLight Technologies’ (PLT’s) facilities. In addition to power delivery, a data-exfiltration system was integrated to log run-time statistics such as power delivery and component temperature. It describes the PoF system and highlights progress toward field-ready systems capable of providing continuous power to distributed assets.
Power over fiber for undersea applicationsKirby, Mitchell A.; Sayles, Thomas J.; Johnson, Isaac; Smith, Mathew; Valencia, Christopher; Weinthal, Warren; Nugent, Tom
doi: 10.1117/12.3043798pmid: N/A
This study presents a water-tight laser-based Power over Fiber (PoF) system designed to deliver electrical power to underwater sensors located hundreds of meters away. The optical Power Distribution System (PDS) employs two near-infrared (NIR) laser diodes coupled with telecom-grade fiber optic cables, delivering up to 3 watts of electrical power each to two separate receiver systems that use photovoltaic (PV) cells for optical-to-electrical conversion. The system achieves a 10-15% end-to-end efficiency. The laser transmitter housing, receiver housing, fiber-optic cable, and connectors are rated for depths up to 200 meters and have been tested up to 140 meters. The optical PDS has logged over 5,700 hours of continuous operation in a test tank at room temperature, demonstrating thermal and electrical stability. PoF solutions for undersea applications could significantly enhance power delivery by reducing common issues associated with copper cables, providing neutrally buoyant tethering options, and potentially enabling innovative methods for distributing electricity in underwater environments.