Electromagnetic waves, or light, represent the most important carrier of energy. The ability to engineer the properties of light, through the use of nanophotonic structures, therefore can have profound implications for energy technology. In this talk, we will discuss our efforts in designing nanophotonic structures in the context of energy technology, both for practical applications, as well as for advancing our understanding of fundamental thermodynamic limits of energy harvesting.

Nano-engineering is crucial in realizing compact photonic systems for light routing and conditioning with ever more complex optical functions. It also promises to elevate the precision of experiments in high-precision optical metrology to an unprecedented level, e.g., optical atomic clocks and gravitational wave detectors - the most precise experiments ever developed by humankind. In this contribution, I give an overview of the development and possibilities of nanophotonic devices for applications in precision optical experiments. I explain relevant physical phenomena of light-matter interaction and illustrate the role of material properties in these experiments.

Metal-oxide semiconductors molded into photonic structures are highly promising for photocatalysis, thanks to their unique property of slowing down light, thereby improving light harvesting. However, this ‘slow light’ is limited to specific frequencies in a narrow spectral region. To address this, we fabricated bilayer-bimodal inverse opal (IO) TiO2-BiVO4 photonic structures that generated slow photons at multiple spectral regions. We tuned their frequencies by lattice parameter and light incidence-angle variations and achieved an 8-fold and a 2-fold increase in photocatalytic efficiency compared to non-structured and monolayer counterparts respectively. The strategies presented here can be extended to all solar energy conversion applications.

We show a new approach for achieving precise control over the internal structure of phase-change materials (PCMs) using the glancing angle deposition (GLAD) technique, which offers a foundry-friendly bottom-up growth alternative to commonly used lithography or chemical modification methods that introduce unwanted defects and impurities. We show that by adjusting deposition angle and rotation speed during growth, GLAD can enable a precise and unprecedented engineering of refractive index and extinction coefficient, in both amorphous and crystalline phases of commonly used GeTe and GST PCM films, without the need to alter their chemical composition.

This conference presentation was prepared for SPIE Optics + Photonics, 2023.

A polymer grating that is obliquely deposited with metal as a split nanotube array. A high reflection band is measured when the grating is illuminated with TM polarized light. The FDTD method is adopted to show the localized magnetic field enhancement and demonstrate that there is a phase jump at the reflectance peak wavelength. The equivalent impedance and refractive index are calculated and found to be varied with the morphology of coated metal on the top of each ridge. The anisotropic property on the grating surface is also investigated by analyzing the in-plane iso-frequency curve.

Quantum dots (QDs) are promising color conversion materials for high-end display applications due to their high color purity, tunable bandgap, and high efficiency. However, the color conversion efficiency of QDs is limited by the insufficient absorptance of excitation light. To address this issue, we have realized different structures relying on self-assembled metallic nanostructures and micropores realized by inkjet printing.

This conference presentation was prepared for SPIE Optics + Photonics, 2023.

A basic model of topological insulators, the Su-Schrieffer-Heeger (SSH) model, has been applied in various photonic systems for novel optical effects and related applications. Here, we show that odd-numbered SSH chains may enable extremely broadband waveguide couplers. A special feature of odd-numbered SSH chain is that there is always a zero-energy localized state regardless of its bulk topological invariant value. We utilize this unique feature in adiabatic photonic waveguide systems for spectrally robust optical power dividers or combiners as opposed to the conventional interferometric components such as directional couplers and multimode interference couplers. We demonstrate broadband edge-to-edge and 1N couplers with their power balance persisting over the entire optical telecommunications bands. We provide detailed theory, experimental results, and remaining challenges.

We propose a rigorous algorithm for checking and replacing meta-atoms in the arbitrary metasurface layout, based on any preconditioned element library. To showcase the algorithm performance, we design the small metalens based on arbitrarily shaped nanoparticles with four-fold symmetry. We note that layout and lookup tables can depend on any desired optical parameters provided by the atom, and for each point, the best compatible element will be chosen. This algorithm can help the photonics community to fully exploit the design degree of freedom associated with the generation of arbitrary meta-atom shapes, and to access the new properties of metadevices.

Meta-optics have been built in lab settings for years but not on a commercially viable scale. Using electron beam lithography works well in the lab, but this is not an option for volume manufacturing. Patterning subwavelength meta-atom for visible has been just beyond the capabilities of the high-volume deep UV lithography. Due to this patterning barrier, entry into visible meta-optic volume manufacturing has not yet been possible. Moxtek has overcome this barrier and established a volume process line for visible meta-optics utilizing nanoimprint lithography (NIL). Process stability data to qualify the process line for visible meta-optics, confirms that volume manufacturing of metalenses is possible and the patterning barrier has been removed.

Here, we propose a transparent cooler that incorporates a top PDMS emitter and a bottom semi-transparent reflector. The bottom reflector comprises a Bragg mirror and perforated metallic film with a thickness of 90 microns, reflecting near-infrared Band A and visible, respectively. By adding visible reflection via the metallic mirror area of perforated film, transparency, and reinforced reflection are ensured. Our proposed cooler exhibits significantly improved cooling performance while maintaining visibility.

A simple fabrication technique for simultaneously making a series of large-scale graphene field-effect transistors on Si-substrate with suspended active channel is proposed. This technique is focused on two aspects: 1) preventing the degradation of electrical properties of graphene active channel by defects and chemical residues between graphene and substrate, and 2) proposing simpler fabrication methods of generating many suspended FET devices on a large-scale substrate. To maintain structural integrity of fabricated devices while minimize electrical degradation, we employed a sandwich method, realizing 76% fabrication yield that is higher than other proposed methods of fabricating suspended active channel style FET devices. As our method has a mechanically stable structure, it can be imposed to make electrical devices with various two–dimensional (2D) materials. Our method can also be applied to the engineering of future devices in various applications because a large amount of electrically clean samples can be manufactured at once.

Upconversion material that convert infrared light into visible and ultraviolet photon are capable of a broad range application such as deep tissue bio-imaging, security labelling and anti-counterfeit, etc. Lanthanide-doped sodium yttrium fluoride (NaYF4) upconversion nanoparticles (UCNP) are one of the most efficient UCNPs. However, practical applications of UCNPs are limited owing to their extremely weak and narrow band absorption. Moreover, it is still a great challenge to convert short-wave infrared photon (such as 1550 nm) to visible region since photon should be 3-pumped for visible region emission which hamper itself to a wide variety of applications. To solve this problem, we applied the localized surface plasmon resonance (LSPR) effect of indium tin oxide (ITO) NPs to enhance the 1550 nm absorbance of NaYF4:Er3+ NPs. We have synthesized core-shell NaYF4:Er3+@NaYF4 NPs with particles size distribution of 15 nm via co-precipitation method. Also, We characterized upconversion efficiency of UCNPs with ITO NPs mixture solution with 1550 nm laser (10 mWcm-1).

In this study, a large area optically transparent frequency selecive surface absorber (OTFA) for dual-band millimeter-wave/IR stealth was designed and fabricated. ITO coated PET films were processed by wet etching and laminating with OCA in commercial display production process, 40cm*40cm size OTFA was fabricated. It achieved absorptivity over 95% at 35 GHz and 94 GHz. Also, transmission more than 65% in visible band. ITO pattern at the surface shows average emissivity less than 25%. The study's results suggest that the proposed absorber has significant potential in stealth technology for its large-scale production possibilities, with multispectral stealth performance.