We present our latest work and investigation of exceptional point in plasmonic nanostructures. We show that the non-Hermitian singularity can be effectively deployed in small scale sensors and pave the path for engineering metamaterials with novel properties.
We proposed and experimentally demonstrated a new method to engineer ultra-high efficiency and linear polarization achromatic meta-lens from visible to telecommunication wavelength: 660 nm to 1200 nm with 90 % efficiency. Our proposed method is a promising approach for broadband structured interfaces. This new design surpasses the current state of the art of metalens which is mainly focus on circular polarization with limited bandwidth and efficiency.
We have demonstrated the first plasmonic exceptional points (EPs) at subwavelength scale. The plasmonic EPs are based on the hybridization of detuned resonances in multilayered plasmonic crystals to reach a critical complex coupling rate between nanoantennas arrays, and, exhibit the dispersion of exceptional points around the non-Hermitian singularity and enhanced nanosensing was observed. The ability to drive plasmons to EPs lays the foundation to explore topological physics at small scales and to novel sensors and optoelectronic devices based on topological polaritonic effects
Small semiconductor lasers have attracted a wide interest in academia owing to their potential as highly integrated components in photonic circuits. Particularly, microdisk lasers exploiting whispering gallery modes have been regarded as a good candidate because of ultrasmall modal volume and low threshold property. To exploit large index difference between gain and surrounding medium, microdisk resonators with an underlying post using undercut etching have been proposed and widely investigated in many previous studies. However, it has been challenging in microdisk laser to operate single mode due to the large number of exsiting whispering gallery modes. Here, we propose and demonstrate a novel subwavelength scale microdisk laser. InGaAsP multi-quantum wells microdisk is self-suspended in air by connecting bridges. The behavior of TE-like whispering gallery modes, which belong to most dominant class of mode in thin disk configuration, is both numerically and experimentally investigated. We highlight that bridge does not only provide mechanical stability, but the number of bridges can be an important factor to improve or suppress wave confinement of whispering gallery modes by protecting or breaking spatial symmetry of mode. Moreover, a suitable choice of bridges increases quality factor by up to 79% comparing to the microdisk resonator without bridges. Using this scheme, we numerically and experimentally investigate mode selectivity and further demonstrate single mode microdisk lasers operating at near-infrared telecommunication wavelength.
Topological insulator is a material in which helical conducting states exist on the surface of the bulk insulator. These states can transport electrons or photons at the boundary without any back scattering, even in presence of obstacles enabling to make topological cavities with arbitrary geometries that light can propagate in one direction. Here, we present the demonstration of the first experimental non-reciprocal topological laser that operates at telecommunication wavelengths. The unidirectional stimulated emission from edge states is coupled to a selected waveguide output port with an isolation ratio of 11 dB. Topological cavities are made of hybrid photonic crystals (i.e., two different photonic crystals) with distinct topological phase invariants, which are bonded on a magnetic material of yttrium iron garnet to break the time-reversal symmetry. Our experimental demonstration, paves the way to develop complex nonreciprocal topological devices of arbitrary geometries for integrated and robust generation and transport of light in classical and quantum regimes.
Topological insulator is a material in which helical conducting states exist on the surface of the bulk insulator. These states can transport electrons or photons at the boundary without any back scattering, even in presence of obstacles enabling to make topological cavities with arbitrary geometries that light can propagate in one direction. Here, we present the demonstration of the first experimental non-reciprocal topological laser that operates at telecommunication wavelengths. The unidirectional stimulated emission from edge states is coupled to a selected waveguide output port with an isolation ratio of 11 dB. Topological cavities are made of hybrid photonic crystals (i.e., two different photonic crystals) with distinct topological phase invariants, which are bonded on a magnetic material of yttrium iron garnet to break the time-reversal symmetry. Our experimental demonstration, paves the way to develop complex nonreciprocal topological devices of arbitrary geometries for integrated and robust generation and transport of light in classical and quantum regimes.
We present progress on the experimental observation of exceptional points (EPs) in passive plasmonic nanostructures. The system has EPs which are degeneracies in open wave systems where at least two energy levels and their corresponding eigenstates coalesce. They manifest themselves by the simultaneous degeneracy of both resonant frequencies and its linewidths. We consider a plasmonic system based on a multilayer plasmonic structure with structural offset [1, 2]. The realization of an EP via hybridized modes requires the control of at least two physical parameters. The two parameters used for the above system to reach an EP are the shift between bars and the periodicity.
We demonstrate a simple and efficient technique that allows for a complete characterization of silica-based tapered optical fibers with sub-wavelength diameters ranging from 0.5 μm to 1.2 μm. The technique is based on Brillouin reflectometry using a single-ended heterodyne detection. It has a high precision sensitivity down to 1% owing to the strong dependence of the Brillouin spectrum on the taper diameter. We further investigate the tensile strain dependence of the Brillouin spectrum for an optical microfiber up to 5% of elongation. The results show strong dependences of several Brillouin resonances with different strain coefficients ranging from 290 MHz/% to 410 MHz/% with a specific nonlinear deviation at high strain. Those results therefore show that optical micro and nanofibers could find potential application for sensitive strain optical sensing.
Fabrication and characterization of submicron optical waveguides is one of the major challenges in modern photonics, as they find many applications from optical sensors to plasmonic devices. Here we report on a novel technique that allows for a complete and precise characterization of silica optical nanofibers. Our method relies on the Brillouin backscattering spectrum analysis that directly depends on the waveguide geometry. Our method was applied to several fiber tapers with diameter ranging from 500 nm to 3 μm. Results were compared to scanning electron microscopy (SEM) images and numerical simulations with very good agreement and similar sensitivity.
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