Dual Function Ultra-Compact Plasmonic-Assisted Electro-Absorption Modulators and Polarizers on Silicon Waveguide

With photonic circuits continuing to shrink, it is imperative to design on-chip, ultra-compact electro-absorption (EA) modulators without sacrificing other performance parameters. This work describes a new design of a few EA modulators with a minimal footprint because of their high extinction ratio (ER). This is attained by causing significant confinement of light in metal-insulator-metal (MIM) and metal-oxide-semiconductor (MOS) capacitors in the HfO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/ITO/HfO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/Cu stack. Placing the stack horizontally atop the silicon on insulator (SOI) waveguide can yield a very high ER of 85.42 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m, a very tiny 3-dB footprint of 0.0112 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, an insertion loss (IL) of 1.4 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m, energy consumption of 3.4 fJ/bit, and a very high operating speed of 2922.4-974.2 GHz for the TM mode at a wavelength of 1550 nm. The ER for the TE mode is quite low; hence, this modulator also functions as a TE-pass polarizer. A TE modulator & TM-pass polarizer design is also possible, providing outstanding performance (ER of 74.7 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m, 3-dB footprint of 0.0272 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, IL of 0.74 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m, energy consumption of 4.13 fJ/bit, and operating speed of 2407.8-802.6 GHz) for the TE mode when the stack is positioned vertically on both sides of the waveguide. Additionally, the SOI waveguide, which consists of both vertical and horizontal parts of the stack, functions as a polarization-insensitive (PI) modulator. It provides an ER of 59.1 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m (57.02 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m) and an IL of 0.74 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m (0.66 dB/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m) at the 1550 nm wavelength for the TE (TM) polarization, which ensures polarization insensitivity. The 3-dB footprint, energy consumption, and operating speed of the PI modulator are 0.053 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$µ$</tex-math></inline-formula> m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, 16.1 fJ/bit, and 618–206 GHz, respectively. Moreover, these proposed modulators offer an extensive optical bandwidth including, 1310 nm and 1550 nm wavelength, which is advantageous in WDM and communication applications.