Higher Order Mode Conversion From Berry's Phase in Silicon Optical Waveguides

• Main Authors: Ryan J. Patton, Ronald M. Reano
• Format: Article
• Language: English
• Published: IEEE 2021-01-01
• Series: IEEE Photonics Journal
• Subjects: Berry's phase; integrated optics; mode converters; optical orbital angular momentum (OAM); optical waveguides; silicon photonics
• Online Access: https://ieeexplore.ieee.org/document/9511833/

We present mode conversion between the higher order <inline-formula><tex-math notation="LaTeX">${{\bf E}}_{21}^{\boldsymbol{x}}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">${{\bf E}}_{12}^{\boldsymbol{x}}$</tex-math></inline-formula> optical modes in an out-of-plane silicon waveguide exhibiting Berry&#x0027;s phase. Superpositions of the <inline-formula><tex-math notation="LaTeX">${{\bf E}}_{21}^{\boldsymbol{x}}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">${{\bf E}}_{12}^{\boldsymbol{x}}$</tex-math></inline-formula> waveguide modes form quasi-Laguerre-Gaussian modes with total angular momentum of <inline-formula><tex-math notation="LaTeX">$1\hbar $</tex-math></inline-formula> per photon for a 720 &#x00D7; 600 nm² silicon waveguide core. When the waveguide is deflected out-of-plane by 22.5&#x00B0;, 50&#x0025; mode conversion occurs from the <inline-formula><tex-math notation="LaTeX">${{\bf E}}_{21}^{\boldsymbol{x}}$</tex-math></inline-formula> mode to the <inline-formula><tex-math notation="LaTeX">${{\bf E}}_{12}^{\boldsymbol{x}}$</tex-math></inline-formula> mode. The concatenation of a quarter wavelength straight section results in an output with <inline-formula><tex-math notation="LaTeX">$0.89\hbar $</tex-math></inline-formula> orbital and <inline-formula><tex-math notation="LaTeX">$0.15\hbar $</tex-math></inline-formula> spin angular momentum per photon. Orbital angular momentum generation in a waveguide platform provides a route for on-chip applications that utilize the angular momentum of light for sensing, optical manipulation, non-linear optics, and communications.