Segmented multimode to dual port slot couplers as compact optical sensors with improved sensitivity
TL;DR: In this paper, a segmented silicon based multimode to dual port slot structure on silicon-on-insulator platform is proposed which can be used as a refractive index sensing device.
Abstract: A segmented silicon based multimode to dual port slot structure on silicon-on-insulator platform is proposed which can be used as a refractive-index sensing device. The introduction of segmentation leads to tuning the effective index of the device which results in increasing compactness of the sensing device. Although the structure supporting TM mode is more compact than TE mode, but TE mode is considered here as vertical slots in the output section enhances optical signal in the slots for TE mode only. By considering dual output, the device length is reduced further as dual self-imaging length is less compared to single self-imaging distance for symmetrical multimode section input. The surface sensitivity of the structure has a typical value of∼2249 nm/RIU. Relative sensitivity can be calculated from the ratio of field amplitudes of the arms of the dual output. Matrix method and 2D FDTD is used for the entire analysis.
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TL;DR: New promising sensor designs based on bimodal technology, which promises a significant increase in sensor sensitivity by means of equalizing the group delay of a pair of different optical modes propagating through the waveguide structure are paid.
Abstract: Silicon photonics is the most important technological platform for creating a variety of functional optical elements, including promising types of optical sensors. Moreover, in recent years, 20% of all publications on silicon photonics are devoted to the development of various versions of optical sensors. Their advantage steams from the combination of high technical parameters with the possibility of mass production using CMOS technology of microelectronics and nanophotonics. A brief description of various technological solutions of the last decade that provide progress in the development of optical sensor characteristics is given. Special attention is paid to new promising sensor designs based on bimodal technology, which promises a significant increase in sensor sensitivity by means of equalizing the group delay of a pair of different optical modes propagating through the waveguide structure. The review will be useful for domestic and foreign researchers working in the field of sensor development.
5 citations
TL;DR: In this paper , the precise variation of self-imaging distance with width of a Gaussian input, centrally fed into a symmetric dielectric slab waveguide of width ∼20λ 0.
Abstract: We demonstrate the precise variation of self-imaging distance with width of a Gaussian input, centrally fed into a symmetric dielectric slab waveguide of width ∼20λ0. The width of the Gaussian is varied from the paraxial to completely nonparaxial domain. Unlike the paraxial case, the self-imaging distance is found to depend on the beam width and change with the number of excited modes in the waveguide. These features should be useful in designing devices that exploit self-imaging for improved efficiency, especially in nanophotonic circuits.
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TL;DR: The underlying self-imaging principle in multimode waveguides is described using a guided mode propagation analysis and it is shown that multimode interference couplers offer superior performance, excellent tolerance to polarization and wavelength variations, and relaxed fabrication requirements when compared to alternatives such as directional coupling.
Abstract: This paper presents an overview of integrated optics routing and coupling devices based on multimode interference. The underlying self-imaging principle in multimode waveguides is described using a guided mode propagation analysis. Special issues concerning the design and operation of multimode interference devices are discussed, followed by a survey of reported applications. It is shown that multimode interference couplers offer superior performance, excellent tolerance to polarization and wavelength variations, and relaxed fabrication requirements when compared to alternatives such as directional couplers, adiabatic X- or Y-junctions, and diffractive star couplers. >
2,477 citations
TL;DR: It is shown that by use of a novel waveguide geometry the field can be confined in a 50-nm-wide low-index region with a normalized intensity of 20 microm(-2), approximately 20 times higher than what can be achieved in SiO2 with conventional rectangular waveguides.
Abstract: We present a novel waveguide geometry for enhancing and confining light in a nanometer-wide low-index material. Light enhancement and confinement is caused by large discontinuity of the electric field at highindex-contrast interfaces. We show that by use of such a structure the field can be confined in a 50-nm-wide low-index region with a normalized intensity of 20 mm 22 . This intensity is approximately 20 times higher than what can be achieved in SiO2 with conventional rectangular waveguides. © 2004 Optical Society of America OCIS codes: 030.4070, 130.0130, 130.2790, 230.7370, 230.7380, 230.7390, 230.7400. Recent results in integrated optics have shown the ability to guide, bend, split, and f ilter light on chips by use of optical devices based on high-index-contrast waveguides. 1–5 In all these devices the guiding mechanism is based on total internal ref lection (TIR) in a highindex material (core) surrounded by a low-indexmaterial (cladding); the TIR mechanism can strongly confine light in the high-index material. In recent years a number of structures have been proposed to guide or enhance light in low-index materials, 6–1 1 relying on external ref lections provided by interference effects. Unlike TIR, the external ref lection cannot be perfectly unity; therefore the modes in these structures are inherently leaky modes. In addition, since interference is involved, these structures are strongly wavelength dependent. Here we show that the optical field can be enhanced and conf ined in the low-index material even when light is guided by TIR. For a high-index-contrast interface, Maxwell’s equations state that, to satisfy the continuity of the normal component of electric f lux density D, the corresponding electric field (E-field) must undergo a large discontinuity with much higher amplitude in the low-index side. We show that this discontinuity can be used to strongly enhance and confine light in a nanometer-wide region of low-index material. The proposed structure presents an eigenmode, and it is compatible with highly integrated photonics technology. The principle of operation of the novel structure can be illustrated by analysis of the slab-based structure shown in Fig. 1(a), where a low-index slot is embedded between two high-index slabs (shaded regions). The novel structure is hereafter referred to as a slot waveguide. The slot waveguide eigenmode can be seen as being formed by the interaction between the fundamental eigenmodes of the individual slab waveguides. Rigorously, the analytical solution for the transverse E-field profile Ex of the fundamental TM eigenmode of the slab-based slot waveguide is
1,716 citations
TL;DR: A novel silicon waveguide structure for guiding and confining light in nanometer-wide low-refractive-index material is experimentally demonstrated and it is shown that the structure can be implemented in highly integrated photonics.
Abstract: We experimentally demonstrate a novel silicon waveguide structure for guiding and confining light in nanometer-wide low-refractive-index material. The optical field in the low-index material is enhanced because of the discontinuity of the electric field at high-index-contrast interfaces. We measure a 30% reduction of the effective index of light propagating in the novel structure due to the presence of the nanometer-wide low-index region, evidencing the guiding and confinement of light in the low-index material. We fabricate ring resonators based on the structure and show that the structure can be implemented in highly integrated photonics.
678 citations
TL;DR: A theoretical investigation of silicon-on-insulator nanometer slot waveguides for highly sensitive and compact chemical and biochemical integrated optical sensing is proposed.
Abstract: A theoretical investigation of silicon-on-insulator nanometer slot waveguides for highly sensitive and compact chemical and biochemical integrated optical sensing is proposed. Slot guiding structures enabling high optical confinement in a low-index very small region are demonstrated to be very sensitive to either cover medium refractive index change or deposited receptor layer thickness increase. Modal and confinement properties of slot waveguides have been investigated, considering also the influence of fabrication tolerances. Waveguide sensitivity has been calculated and compared with that exhibited by other silicon nanometer guiding structures, such as rib or wire waveguides, or with experimental values in literature.
357 citations
TL;DR: In this article, a simple matrix method for obtaining propagation characteristics, including losses for various modes of an arbitrarily graded planar waveguide structure which may have media of complex refractive indices, is presented.
Abstract: We present here a simple matrix method for obtaining propagation characteristics, including losses for various modes of an arbitrarily graded planar waveguide structure which may have media of complex refractive indices. We show the applicability of the method for obtaining leakage losses and absorption losses, as well as for calculating beat length in directional couplers. The method involves straightforward 2 × 2 matrix multiplications, and does not require the solutions of any transcendental or differential equations.
244 citations