@ Northeastern University        COE | ECE | MIE
Research Group of Prof. Yongmin Liu
Nano Optics and Plasmonics
Nano optics or nanophotonics explores of the behavior of light at the nanometer scale. Dielectric-based nanophotonics, especially silicon nanophotonics, has manifested a wide range of novel phenomena and applications. However, it still suffers the conventional diffraction limit. Recently, metal-based nano plasmonics has emerged as a new research paradigm in nano optics, which allows us to break the fundamental diffraction limit and confine light into the deep subwavelength scale. Meanwhile, the field intensity can be significantly enhanced due to the strong confinement. We are interested in the nonlinear and quantum optical properties and novel optical devices based on the plasmonic platform.
Nano Materials and Metamaterials
The emerging field of electromagnetic metamaterials offers an entirely new route to design material properties at will. Different from natural materials, the physical properties of metamaterials are not primarily dependent on the chemical constituents, but rather on the internal, specific structures of the building blocks of metamaterials. These building blocks function as artificial "atoms" and "molecules", in analogy to those in natural materials. Through regulated interactions with electromagnetic waves, metamaterials can produce remarkable properties that are difficult or impossible to find in naturally occurring or chemically synthesized materials. We are investigating new optical metamaterials with appropriate architecture design at deep subwavelength scale, and studying the extraordinary wave propagation behavior originating from the negative refractive index, symmetry breaking, anisotropy and chirality of metamaterials.
Nano Devices and Applications
Plasmonics simultaneously combines the fast dynamics of photonic processes and the capability of tight optical confinement well beyond the diffraction limit. It is considered as one of the most candidates for the next generation of ultra-fast and ultra-compact photonic circuits. We have demonstrated important nano optical devices including the plasmonic generator, lens, waveguide bend, etc. In addition, we have been working on other aspects of plasmonics applications ranging from biomedical sensing, near-field microscopy and spectroscopy to energy harvesting. We are also interested in the hybridization of plasmonics and nanoelectronics, which may allow for simultaneous transport of light and electric information, and active control of both of them.
Transformation Optics/Acoustics
Transformation optics has emerged as a new research area, which provides a general methodology and design tool for manipulating electromagnetic waves at will. With transformation optics, researchers have realized a host of striking optical effects and devices, some of which only existed in science fictions and myths (for example, the invisibility cloak). We are designing transformation optical devices at optical frequencies and at the nanoscale, utilizing new electromagnetic theory and modeling software, state-of-the-art fabrication tools as well as greatly improved characterization and analysis techniques. Meanwhile, the geometric transformation approach can be extended to other systems beyond electromagnetic waves, including acoustic waves, liquid flows, surface liquid waves, and even matter waves in quantum mechanics.
Nano Optomechanics
It is known that light can be used to move objects since photons have both linear and angular momentum. The linear momentum carried by photons can induce an optical force on an object, which is used for optical trapping. The angular momentum – in either its spin or orbital form – when altered via the scattering or absorption of light can produce a mechanical torque on an object and thus rotate the object. At the nanoscale, such mechanical forces and torques are unfortunately very small because of the weak interaction between light and matter. We are investigating the next generation of nano optomechanical devices, which can produce significant mechanical forces and torques.
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