New advanced lighting design and manufacturing process could revolutionize sensing technologies
Engineers from Vanderbilt and Penn State developed a new approach to design and manufacture thin-film infrared light sources with near-arbitrary heat-driven spectral output, along with a machine-learning methodology called reverse design that reduced the optimization time for these devices from weeks or months on a multicore PC to minutes on a consumer desktop PC.
The ability to develop economical, efficient and stylish infrared light sources could revolutionize molecular detection technologies. Additional applications include free space communications, infrared beacons for search and rescue, molecular sensors for monitoring industrial gases, environmental pollutants and toxins.
The research team’s approach, detailed today in Natural materials, uses simple thin-film deposition, one of the most advanced nanofabrication techniques, aided by key advances in materials and machine learning.
Standard thermal emitters, such as incandescent bulbs, generate broadband thermal radiation which limits their use to simple applications. In contrast, lasers and light emitting diodes provide the narrow frequency emission desired for many applications but are generally too inefficient and / or expensive. This directed research towards wavelength-selective thermal emitters to provide the narrow bandwidth of a laser or LED, but with the simple design of a thermal emitter. However, to date, most thermal emitters with user-defined output spectra have required patterned nanostructures fabricated with low throughput and high cost methods.
The research team led by Joshua Caldwell, associate professor of mechanical engineering at Vanderbilt, and Jon-Paul Maria, professor of materials science and engineering at Penn State, set out to address long-standing challenges and create a more efficient process. Their approach takes advantage of the broad spectral tunability of the semiconductor cadmium oxide in concert with a one-dimensional photonic crystal fabricated with alternating layers of dielectrics called a distributed Bragg reflector.
The combination of these multiple layers of materials gives rise to a “Tamm-polariton”, where the emission wavelength of the device is dictated by the interactions between these layers. Until now, these designs have been limited to a single designed wavelength. But creating multiple resonances at multiple frequencies with user-controlled wavelength, linewidth, and intensity is imperative to matching the absorption spectra of most molecules.
Material design was difficult and computationally intensive. Since advanced applications require multi-resonance functionality, the new process had to significantly reduce design time. A typical device, for example, would contain tens to hundreds of configurable parameters, creating high customization requirements requiring unrealistic computation times. For example, in a scenario that independently optimizes nine parameters, sampling 10 points per parameter, the simulations would take 15 days, assuming 100 simulations per second. Yet with more settings, the time increases exponentially – 11 and 12 settings would require three and 31 years, respectively.
To address this challenge, Ph.D. student Mingze He, lead author of the article, proposed an inverse design algorithm that computes an optimized structure in minutes on a mainstream desktop computer. Additionally, this code could provide the ability to match the desired transmit wavelength, linewidth, and amplitude of multiple resonances simultaneously over an arbitrary spectral bandwidth.
Another obstacle was the identification of a semiconductor material that could allow a wide dynamic range of electron densities. For this, the team used a doped semiconductor material, developed by Maria’s research team at Penn State, which enables intentional design of optical properties.
âThis enables the fabrication of advanced mid-infrared light sources at the wafer scale with very low cost and minimal manufacturing steps,â he said.
This experimental section was conducted with collaborators from Penn State while the devices were characterized by He and J. Ryan Nolen, a recent graduate of the Caldwell Group. Together, the two teams successfully demonstrated the ability of reverse-designed infrared light sources.
âCombining the tunability of the cadmium oxide material with the rapid optimization of aperiodic distributed Bragg reflectors offers the possibility of designing infrared light sources with user-defined output spectra. other applications ranging from environmental and remote sensing, spectroscopy and infrared signaling and communications, “says Caldwell.
Significantly, the Caldwell Group opened the Design Algorithm, which can be downloaded from the Natural materials as well as the Caldwell Infrared Nanophotonic Materials and Devices laboratory website.
Their paper, “Deterministic inverse design of Tamm plasmon thermal emitters with multi-resonant control,” was published on October 21.
Design and validation of a world-class multilayer thermal emitter using machine learning
Mingze He et al, Deterministic inverse design of Tamm plasmon thermal emitters with multiresonant control, Natural materials (2021). DOI: 10.1038 / s41563-021-01094-0
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