Strip-slot waveguide mode converters for TE₀ have been widely investigated. Here we demonstrate a polarization-insensitive converter numerically and experimentally. The polarization-insensitive performance is achieved by matching the optical field distribution of the 2-fold image of the Multimode Interference (MMI) and the TE₀ (TM₀) mode of a slot waveguide. The working principle for this MMI-based mode converter is thoroughly analyzed with the quantitatively evaluated optical field overlap ratio that is theoretically derived from the orthonormal relation of eigenmodes. Based on the analysis, the MMI-based polarization-insensitive converters are then simulated and fabricated. The simulation and measurement results indicate that the proposed scheme is a robust design since it is not only polarization-insensitive but also wavelength-insensitive and fabrication-tolerant. Moreover, the mode converter is as small as 1.22 μm × 4 μm while the measured conversion efficiencies are 95.9% for TE₀ and 96.6% for TM₀. All these excellent properties make the proposed mode converter an ideal solution for coupling light between strip and slot waveguides when both TE and TM polarizations are considered.

Addendum: "Large room-temperature quantum linear magnetoresistance in multilayered epitaxial graphene: Evidence for two-dimensional magnetotransport" [Appl.We propose and demonstrate gold nanoparticle decorated graphene as an ideal system for studying carrier inhomogeneity induced magnetoresistance. Large linear magnetoresistance has been realized in the system and the magnitude can be tuned by a gate. By detailed study, we provide an empirical expression, which reveals the dependence of the magnetoresistance on density fluctuations and mobility. The induced magnetoresistance is temperature independent and can be strongly enhanced by the high mobility of graphene, hence offers potential for magnetic sensor applications. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4897277]Graphene, being only one atom thick, represents a perfect two dimensional electron gas (2DEG) material. Unlike most of conventional 2DEG systems, e.g., semiconductor heterostructures, where electron gas is buried in bulk materials, graphene is completely exposed to environment. This provides direct access to its electron gas. For instance, the surface morphology can be imaged in atomic resolution, while the charge carrier distribution can be mapped out at the same time. 1 The band structure can also be engineered by simple surface functionalization. 2 Recently, there has been increasing interest in using absorption of metal adatoms to modify the interactions between different degrees of freedom in graphene, such as the spin-orbit interaction 3-6 and electron-phonon interaction. 7-9 As predicted by theories, some salient condensed matter phenomena, such as topological insulators, 3,5,10 ferromagnetic order, 11,12 and superconductivity 7,9 can be realized in graphene by this means. Experimental confirmation of the predictions will offer a unique opportunity to study these phenomena, owing to the great tunability of graphene. Such an advantage has been nicely demonstrated in a recent experiment, 13,14 where the superconducting transition of a graphene/superconductor islands hybrid has been studied. In that system, the coupling between superconducting islands can be conveniently tuned via carrier density in graphene by a back gate.In this work, we propose to use graphene to study the linear magnetoresistance (LMR) induced by carrier inhomogeneity. LMR has attracted lots of attention, partially due to its application in magnetic field sensors. It has been seen in various systems, for instance, Bismuth, 15 graphite, 16 Indium antimonide, 17 LaSb 2 , 18 InAs, 19 multilayer epitaxial graphene, 20 and Bi 2 Te 3 . 10,21 However, the mechanism can be very different. It is well known that the specific topology of the Fermi surface, i.e., an open orbit, can lead to LMR. 22 Beside this classical effect, when the carrier is of low density and small effective mass, the quantum limit, in which all carriers lie in the lowest Landau level, can be reached. It has been proposed that LMR can arise in such condition, called quantum LMR. 16,23 In the pas...

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