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

We present mode conversion between the higher order
${{\bf E}}_{21}^{\boldsymbol{x}}$
and
${{\bf E}}_{12}^{\boldsymbol{x}}$
optical modes in an out-of-plane silicon waveguide exhibiting Berry's phase. Superpositions of the
${{\bf E}}_{21}^{\boldsymbol{x}}$
and
${{\bf E}}_{12}^{\boldsymbol{x}}$
waveguide modes form quasi-Laguerre-Gaussian modes with total angular momentum of
$1\hbar $
per photon for a 720 × 600 nm
²
silicon waveguide core. When the waveguide is deflected out-of-plane by 22.5°, 50% mode conversion occurs from the
${{\bf E}}_{21}^{\boldsymbol{x}}$
mode to the
${{\bf E}}_{12}^{\boldsymbol{x}}$
mode. The concatenation of a quarter wavelength straight section results in an output with
$0.89\hbar $
orbital and
$0.15\hbar $
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.