A Platform for Practical Nanophotonic Systems Nitrides and Oxides for Integrated Plasmonic Devices

The fields of nanophotonics and metamaterials have revolutionized the way we think of optical space (ε,µ), enabling us to engineer the refractive index almost at will, to confine light to the smallest of volumes, as well as to manipulate optical signals with extremely small foot prints and energy requirements. Throughout the past, this field of research has largely been limited to the use of noble metals as plasmonic materials, largely due to the high conductivity (low loss) and wide availability in research institutions. However, the research which follows focuses on the development of two alternative material platforms for nanophotonics: namely the transition metal nitrides and the transparent conducting oxides. Through this research, we have explored the nonlinear optical properties of thin films, demonstrating unique and ultrafast dynamic response, and have designed and realized high performance integrated plasmonic devices. Ultimately, this work aims to demonstrate the impact and potential of alternative plasmonic materials for numerous nanophotonic applications

Simulation of Plasmonic Waveguides Based on Long-Range Surface Plasmon Polaritons

The demand for faster and smaller computing devices is growing larger and larger. In the recent decade, research has proven that plasmonic devices have exciting characteristics and performance for next generation on‑chip structures. However, most of these devices contain noble metals and are not CMOS compatible. This work numerically investigates the performance of plasmonic waveguide designs made of TiN, a CMOS compatible material with optical properties similar to gold. Through our work, we demonstrate that TiN nanophotonic devices can be useful for inter-chip connections. A series of simulations using COMSOL Multiphysics were performed to test the performance of these structures. 2D simulations were completed to gain insights into the relationship between the mode size, propagation length trade-off and how additional parameters such as cladding material, a slight mismatch in refractive index of super and substrate, and the thickness of the metal inside the waveguide, affect performance. We found that waveguides using materials of higher refractive will have better mode confinement, albeit with larger losses. If the same material is used, a slight change of refractive index typically in the range of ±0.01, causes the mode to expand to the side of lower index. Additional 3D simulations for waveguide bends, power splitters, and couplers are still in progress. The data of bend loss, power distribution, and mode shapes will be collected upon completion of the 3-D models. With the simulation data, our group will fabricate these waveguides accordingly and attempt further lab experiments to explore how these structures behave

Ultra-compact modulators based on novel CMOS-compatible plasmonic materials

We propose several planar layouts of ultra-compact plasmonic waveguide modulators that utilize alternative CMOS-compatible materials. The modulation is efficiently achieved by tuning the carrier concentration in a transparent conducting oxide layer, thereby tuning the waveguide either in plasmonic resonance or off-resonance. Resonance significantly increases the absorption coefficient of the plasmonic waveguide, which enables larger modulation depth. We show that an extinction ratio of 86 dB/um can be achieved, allowing for a 3-dB modulation depth in less than one micron at the telecommunication wavelength. Our multilayer structures can potentially be integrated with existing plasmonic and photonic waveguides as well as novel semiconductor-based hybrid photonic/electronic circuits

Fast and slow nonlinearities in Epsilon‐Near‐Zero materials

Novel materials, with enhanced light–matter interaction capabilities, play an essential role in achieving the lofty goals of nonlinear optics. Recently, epsilon‐near‐zero (ENZ) media have emerged as a promising candidate to enable the enhancement of several nonlinear processes including refractive index modulation and harmonic generation. Here, the optical nonlinearity of ENZ media is analyzed to clarify the commonalities with other nonlinear media and its unique properties. Transparent conducting oxides as the family of ENZ media with near‐zero permittivity in the near‐infrared (telecom) band are focused on. The instantaneous and delayed nonlinearities are investigated. By identifying their common origin from the band nonparabolicity, it is shown that their relative strength is entirely determined by a ratio of the energy and momentum relaxation (or dephasing) times. Using this framework, ENZ materials are compared against the many promising nonlinear media that are investigated in literature and show that while ENZ materials do not radically outpace the strength of traditional materials in either the fast or slow nonlinearity, they pack key advantages such as an ideal response time, intrinsic slow light enhancement, and broadband nature in a compact platform making them a valuable tool for ultrafast photonics applications for decades to come

Controlling the plasmonic properties of ultrathin TiN films at the atomic level

By combining first principles theoretical calculations and experimental optical and structural characterization such as spectroscopic ellipsometry, X-ray spectroscopy, and electron microscopy, we study the dielectric permittivity and plasmonic properties of ultrathin TiN films at an atomistic level. Our results indicate a remarkably persistent metallic character of ultrathin TiN films and a progressive red shift of the plasmon energy as the thickness of the film is reduced. The microscopic origin of this trend is interpreted in terms of the characteristic two-band electronic structure of the system. Surface oxidation and substrate strain are also investigated to explain the deviation of the optical properties from the ideal case. This paves the way to the realization of ultrathin TiN films with tailorable and tunable plasmonic properties in the visible range for applications in ultrathin metasurfaces and flexible optoelectronic devices.Comment: 24 pages, 8 Figures, research articl

Gallium-doped Zinc Oxide: Nonlinear Reflection and Transmission Measurements and Modeling in the ENZ Region

Strong nonlinear materials have been sought after for decades for applications in telecommunications, sensing, and quantum optics. Gallium-doped zinc oxide is a II-VI transparent conducting oxide that shows promising nonlinearities similar to indium tin oxide and aluminum-doped zinc oxide for the telecommunications band. Here we explore its nonlinearities in the epsilon near zero (ENZ) region and show n2,eff values on the order of 4.5x10-3 cm2GW-1 for IR pumping on 200-300 nm thin films. Measuring nonlinear changes in transmission and reflection with a white light source probe in the near-IR while exciting in the near-IR provides data in both time and wavelength. Three films varying in thickness, optical loss, and ENZ crossover wavelength are numerically modeled and compared to experimental data showing agreement for both dispersion and temporal relaxation. In addition, we discuss optimal excitation and probing wavelengths occur around ENZ for thick films but are red-shifted for thin films where our model provides an additional degree of freedom to explore. Obtaining accurate nonlinear measurements is a difficult and time-consuming task where our method in this paper provides experimental and modeled data to the community for an ENZ material of interest.Comment: 18 pages, 10 figure

High‐Performance Doped Silver Films: Overcoming Fundamental Material Limits for Nanophotonic Applications

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137336/1/adma201605177-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137336/2/adma201605177_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137336/3/adma201605177.pd