This study investigates the thermal optical coefficient (TOC) of Si, SiNx, SiO2, and TiO2, establishing a comprehensive database across temperatures (20°C-80°C) and wavelengths (400nm-1800nm). This dataset informs the design of anti-thermal optical devices. For instance, utilizing TOC disparities at 1550nm, we developed an anti-thermal quarter-wave plate optical mirror with Si and TiO2. This innovative approach harnesses material-specific thermal responses, showcasing potential applications in designing reliable optical platforms. Our research contributes not only to understanding TOC variations but also provides a practical foundation for advancing anti-thermal optical technologies.
In this summary, we report an experimental demonstration of plasma frequency tuning of a multilayer-based ENZ metafilm. The demonstrated ENZ metafilm consists of alternating layers of ITO and SiO2. The optical properties, such as the effective plasma frequency and damping coefficients, of the demonstrated metafilm were controlled by changing the volume fraction of the metal layer. The measured effective permittivity values from an ellipsometry analysis show good agreement with the calculated results using a simple Maxwell-Garnett effective medium theory.
In this summary, we report an experimental demonstration of a low-loss multilayer-based ENZ metafilm. The demonstrated ENZ metafilm consists of alternating layers of Ag and SiN. The optical properties, such as the effective plasma frequency and damping coefficients, of the demonstrated metafilm were controlled by changing the volume fraction of the metal layer. The measured effective permittivity values from an ellipsometry analysis show good agreement with the calculated results using a simple Maxwell-Garnett effective medium theory.
We report our development of Indium tin oxide (ITO) films with thicknesses greater than the typical optical telecommunication wavelength bands (~1550 nm) having epsilon-near-zero (ENZ) property at 1550 nm wavelength for the purpose of providing a new ENZ material platform for building high-contrast metastructure and metasurface devices. The films were grown using a high-power impulse magnetron sputtering (HiPIMS) tool, which allows for more control over film growth. A post-growth thermal annealing allowed the ITO film to reach the ENZ condition at the desirable wavelength. Our goal is to understand how deposition parameters and post deposition annealing conditions affect the film’s optical properties, therefore obtaining a controllable fabrication process for a desired optical property. Using spectroscopic ellipsometry to characterize the films, we show that the thick ITO films grown with HiPIMS exhibit ENZ behavior after post deposition annealing. The regime in which the material exhibits ENZ behavior is shown to be tunable within the wavelength range of 1500-1650 nm by varying the anneal temperature, anneal time, and oxygen exposure during anneal. In comparison with other thick ITO films grown with conventional pulsed DC magnetron sputtering, the optical constants of HiPIMS ITO films are shown to be much more constant with less variation throughout the bulk of the film. This result shows that these ITO films can be used to design a new family of opto-electronic devices that use ENZ ITO as the low-index base for high-contrast metasurface devices and as cladding for waveguides or optical cavities.
We report our in-house R&D efforts of designing and developing key integrated photonic devices and technologies for a chip-scale optical oscillator and/or clock. This would provide precision sources to RF-photonic systems. It could also be the basic building block for a photonic technology to provide positioning, navigation, and timing as well as 5G networks. Recently, optical frequency comb (OFC)-based timing systems have been demonstrated for ultra-precision time transfer. Our goal is to develop a semiconductor-based, integrated photonic chip to reduce the size, weight, and power consumption, and cost of these systems. Our approach is to use a self-referenced interferometric locking circuit to provide short-term stabilization to a micro-resonator-based OFC. For long-term stabilization, we use an epsilon-near-zero (ENZ) metamaterial to design an environment-insensitive cavity/resonator, thereby enabling a chip-scale optical long-holdover clock.
Indium Tin Oxide (ITO) has shown significant potential in becoming a candidate for ε-near-zero (ENZ) metamaterial which can be a host material for EMNZ devices. However, the ENZ ITO material itself has not been thoroughly studied at a device level for several reasons. So far, only relatively thin (hundred nm scale) annealed ITO film has been studied for ENZ purposes. We put an initial effort in characterizing the 2 µm-thick ITO film in respect to its permittivity (ε). The melting point for indium is between 350 C and 400 C, so the annealing temperature falls into this window. A series of 2 µm-thick ITO films were deposited on a 3 µm-thick SiO2 on Si wafer that were annealed at different temperatures and times. These sample were further investigated by a cutting-edge ellipsometry technology. The optical constant depth profile at 1550 nm is measured for various annealing temperature and periods. The results show that both real and imaginary part of permittivity are non-uniform along the growth direction. Under a specific processing window, we are able to achieve a micron-scale of epsilon near-zero ITO film. We also conducted a TEM study to investigate the physical structure of the material. We find the evidence of different partial crystallization across the entire ITO film. The cross-section TEM with low magnification to show entire depth profile of the ITO from the SiO2 interface to the top surface. TEM images show evidence for the different crystal morphology across the ITO film, as the crystal grains varies for different regions of ITO.
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