Recently, there has been a flurry of research in the field of alternative plasmonic materials, but for telecommunication applications, CMOS compatible materials titanium nitride and doped zinc oxides are among the most promising materials currently available. TiN is a gold-like ceramic with a permittivity cross-over near 500nm. In addition, TiN can attain ultra-thin, ultra-smooth epitaxial films on substrates such as c-sapphire, MgO, and silicon. Partnering TiN with CMOS compatible silicon nitride enables a fully solid state waveguide which is able to achieve a propagation length greater than 1cm for a ~8μm mode size at 1.55μm.
Utilizing doped zinc oxide films as a dynamic material, high performance modulators can also be realized due to the low-loss achieved by the TiN/Si3N4 waveguide. Simply by placing a thin layer of aluminum doped zinc oxide (AZO) on top of the waveguide structure, a modulator with very low insertion loss is achieved. Our recent work has investigated optical tuning of AZO films by the pump-probe method, demonstrating a change in the refractive index of -0.17+0.25i at 1.3μm with an ultrafast response of 1ps. Assuming this change in the refractive index for the AZO film, a modulation of ~0.7dB/μm is possible in the structure with ~0.5dB insertion loss and an operational speed of 1THz. Further optimization of the design is expected to lead to an increased modulation depth without sacrificing insertion loss or speed.
Consequently, nanophotonic technologies are reaching a critical point where many applications including telecom, medicine, and quantum science can see practical systems which provide new functionalities.
Nathaniel Kinsey, Marcello Ferrera, Clayton DeVault, Jongbum Kim, Alexander V. Kildishev, Vladimir M. Shalaev, and Alexandra Boltasseva, "Alternative materials lead to practical nanophotonic components (Presentation Recording)," Proc. SPIE 9546, Active Photonic Materials VII, 95460L (Presented at SPIE Nanoscience + Engineering: August 10, 2015; Published: 5 October 2015); https://doi.org/10.1117/12.2189811.4519370248001.
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