Subwavelength-grating contradirectional couplers for large stopband filters

Abstract

Manipulating the coupling coefficient at subwavelength scales provides an additional degree of freedom in designing integrated Bragg gratings. We demonstrate asymmetric contradirectional couplers (contra-DCs) using sidewall-corrugated subwavelength grating (SWG) waveguides for broadband add-drop Bragg filters. We show that a SWG can effectively increase the overlap of coupled modes and thus the photonic band gap. The measured spectra show good agreement with the prediction of photonic band structure simulations. A record bandwidth of 4.07 THz (33.4 nm) has been achieved experimentally. A four-port Bragg resonating filter made of a phase-shifted Bragg grating SWG contra-DC is also demonstrated for narrow-band (near 100 GHz) filtering. All these devices are achieved on the 220-nm silicon-on-insulator platform with a compact length of less than 150 μm. These large stopband filters may find important applications such as band splitting, reconfigurable channel band switching, bandwidth-tunable filtering, and dispersion engineering.

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“…Recently, Charron et al demonstrated an SWG waveguidebased contra-DC design that supports ultrabroadband operation [38]. The SWG waveguide consists of alternating subwavelength elements that are laterally displaced.…”

On‐Chip Metamaterial Enabled Wavelength (De)Multiplexer

“…[6] Recently, Bragg grating filters have also been actively demonstrated for onchip WDM systems. The designs of Bragg grating filter are largely grouped into two main categories, grating assisted contradirectional couplers (GACDCs), [7][8][9] and multimode waveguide Bragg grating (MBG), [10][11][12] depending on whether the mode coupling operation occurs in the two separate waveguides or the same one. These filters have competitive performances with the merits of box-like spectral responses, low ILs, flexible bandwidths, and large FSRs.…”

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“…This ease of integration fueled a large research interest and a widespread application in integrated optics. Since their first demonstration [6][7][8], a large number of devices with improved performance have been proposed, including edge couplers [9,10], surface gratings [11,12], resonators [13], filters [14], surface emitting lasers [15], directional couplers [16,17], polarization splitters, [18,19], and multi-mode interference (MMIs) couplers [20]. The use of a graded index SWG metamaterial has also been recently proposed in a III-V platform to reduce facet reflectivity [21].…”