Narrowband Reflection From Weakly Coupled Cladding-Modulated Bragg Gratings

Abstract

A complementary metal-oxide-semiconductor-compatible cladding-modulated grating design with weakly coupled corrugations on long side waveguides is demonstrated on the silicon-on-insulator platform to allow not only a narrowband reflection (Δλ = 0.217 nm) but also an insensitive Bragg wavelength to the grating width change (Δλ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> /ΔW <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 0.0167). Fine-tuning of the reflection bandwidth is also possible by simply adjusting the grating width (Δλ/ΔW <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 0.012). With a 30-nm grating width, as-fabricated cladding-modulated gratings are demonstrated to provide a close-to-unity peak reflectivity, a 0.6 nm reflection bandwidth and a 21.4 dB extinction ratio. The additional propagation loss arising from the introduction of sidewall corrugations is characterized to be only 0.1 dB. Such a superior performance is difficult to be reproduced by simply using stripor slab-type grating counterparts.