Evanescent field waveguide sensing with subwavelength grating structures in silicon-on-insulator

We explore, to the best of our knowledge, the potential of diffractionless subwavelength grating waveguides for sensing applications. We show that by subwavelength patterning of silicon-wire waveguides the field delocalization can be engineered to increase the sensitivity. Fully vectorial 3D-FDTD simulations confirm the sensitivity enhancement, achieving sensitivities of 0.83 RIU/RIU and 1.5 \ub7 10-3 RIU/nm for bulk and surface sensing, respectively, which compare favorably to state-of-the-art sensing waveguides.Peer reviewed: YesNRC publication: Ye

SWG dispersion engineering for ultra-broadband photonic devices

In most integrated optics platforms device design is restricted to variations in the lateral dimensions, and a small set of etch depths. Sub-wavelength gratings (SWGs) in silicon-on-insulator enable engineering of refractive index in a wide range. SWGs exhibit a pitch smaller than the wavelength of light propagating through them, thereby suppressing diffraction and acting as a homogenous medium with an equivalent refractive index controlled by the duty-cycle. Here, we propose to not only engineer refractive index, but to control SWG dispersion. We use this concept to design ultra-broadband directional couplers (DCs) and multimode interference couplers (MMIs) with a fivefold bandwidth enhancement compared to conventional devices. \ua9 2013 SPIE.Peer reviewed: YesNRC publication: Ye

Subwavelength metastructures for dispersion engineering in planar waveguide devices

High contrast structures with a sub-wavelength pitch, small enough to suppress diffraction, exhibit extraordinary optical properties: depending on the design they may behave as perfect mirrors, anti-reflective interfaces, homogenous materials with controllable refractive index, or strongly dispersive materials. Here we discuss on the design possibilities such structures offer in planar waveguide devices in silicon-on-insulator. We briefly review the application of sub-wavelength structures in a variety of waveguide devices. We then focus on some of the latest advances in the design ultra-compact and ultra-wideband multimode interference couplers based on dispersion engineered sub-wavelength structures.Peer reviewed: YesNRC publication: Ye

An ultra-compact multimode interference coupler with a subwavelength grating slot

Multimode interference couplers (MMIs) are fundamental building blocks in photonic integrated circuits. Here it is experimentally demonstrated, for the first time, a two-fold length reduction in an MMI coupler without any penalty on device performance. The design is based on a slotted 2 7 2 MMI fabricated on a commercial silicon-on-insulator (SOI) substrate. The slot is implemented with a subwavelength grating (SWG) comprising holes fully etched down to the oxide cladding, thereby allowing single etch step fabrication. The device has been designed using an in-house tool based on the Fourier Eigenmode Expansion Method. It has a footprint of only 3.5 \u3bcm x 23 \u3bcm and it exhibits a measured extinction ratio better than 15 dB within the full C-band (1530 nm-1570 nm). SWG engineered slots thus offer excellent perspectives for the practical realization of MMIs couplers with substantially reduced footprint yet with outstanding performance. Multimode interference couplers (MMIs) are fundamental building blocks in photonic integrated circuits. Here it is experimentally demonstrated, for the first time, a two-fold length reduction in an MMI coupler without any penalty on device performance. The design is based on a slotted 2 7 2 MMI fabricated on a commercial silicon-on-insulator (SOI) substrate. The slot is implemented with a subwavelength grating (SWG) comprising holes fully etched down to the oxide cladding, thereby allowing single etch step fabrication. The device has been designed using an in-house tool based on the Fourier Eigenmode Expansion Method. It has a footprint of only 3.5 \u3bcm x 23 \u3bcm and it exhibits a measured extinction ratio better than 15 dB within the full C-band (1530 nm-1570 nm). SWG engineered slots thus offer excellent perspectives for the practical realization of MMIs couplers with substantially reduced footprint yet with outstanding performance. \ua9 2013 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Peer reviewed: YesNRC publication: Ye