Low-Loss and Broadband Cantilever Couplers Between Standard Cleaved Fibers and High-Index-Contrast Si$_{3}$N$_{4}$ or Si Waveguides

Abstract

We demonstrate a novel facet coupler for coupling between 10.4- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu$</tex></formula> m mode-diameter cleaved fibers and high-index-contrast Si <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{3}$</tex></formula> N <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{4}$</tex> </formula> or Si waveguides. By creating a cantilevered glass waveguide surrounding an inverse taper and injecting a low-index cladding around the cantilever, we demonstrate coupling loss as low as 0.7 dB/facet to 500 nm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\,\times\,$</tex></formula> 400 nm Si <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$_{3}$</tex></formula> N <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$_{4}$</tex></formula> waveguides, with only 0.2-dB polarization-dependent loss and 0.4-dB wavelength-dependent loss from 1480 to 1580 nm. Coupling loss of 1.5–2.0 dB/facet to 500 nm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\,\times\,$</tex></formula> 220 nm Si waveguides at 1550 nm is also demonstrated.