Authors:	X. Nie, N. Turk, Y. Li, Z. Liu, R. Baets
Title:	High extinction ratio on-chip pump-rejection filter based on cascaded grating-assisted contra-directional couplers in silicon nitride rib waveguides
Format:	International Journal
Publication date:	4/2019
Journal/Conference/Book:	Optics Letters
Volume(Issue):	44(9) p.2310-2313
DOI:	10.1364/OL.44.002310
Citations:	30 (Dimensions.ai - last update: 21/4/2024) 7 (OpenCitations - last update: 19/4/2024) Look up on Google Scholar
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Abstract

We present an on-chip filter that is based on the grating-assisted contra-directional coupler (GACDC) implemented on a silicon nitride rib waveguide platform. This filter enjoys the benefit of an unlimited free spectral range (FSR) on the red side of the stop/passband. Unlike a Bragg reflector, the GACDC filter has the advantage of coupling the rejected light contra-directionally into a bus waveguide, instead of reflecting it back to the input. This property makes it an add/drop filter suitable for pump rejection and allows effective cascading to provide an even higher extinction ratio compared to the single-stage version. In this Letter, we experimentally demonstrate that a 16-stage cascaded GACDC filter can provide a stop band with a bandwidth smaller than 3 nm and an extinction ratio as high as 68.5 dB.