Metamaterials have the potential to revolutionize optical components and devices. Though first designed and demonstrated at microwave frequencies, metamaterials have since been scaled to operate at nearly all frequencies over the electromagnetic spectrum. Metamaterials have now been demonstrated with unique properties at terahertz (THz), infrared (IR) and visible wavelengths. No matter what bandwidth range is targeted, metamaterials expand the palette of available electromagnetic material properties, providing a greater range of freedom for the design of novel optical devices. Material properties such as negative refractive index or optical magnetism are relatively new areas of exploration, with their potential only just beginning to be unlocked at visible wavelengths. More recently, the emergence of transformation optical materials (see Transformation Optics and Cloaking) has provided even further motivation for the development of optical metamaterials.
One of the core research thrusts of CMIP has been the development of design and fabrication methods for high frequency metamaterials. Taking advantage of the extensive micro- and nano-fabrication capabilities available in the Shared Materials and Instrumentation Facility (SMiF) at Duke, a team of CMIP researchers are engaged in producing functional optical metamaterial and plasmonic structures for a variety of applications, from millimeter wave imaging to optical modulation and switching. The fabrication of optical metamaterials is led by Dr. Nan Jokerst, who serves as director of the SMiF. Dr. Jokerst and her group bring extensive experience in the fabrication of photonic and opto-electronic circuits, enabling CMIP to insert novel metamaterial and plasmonic components with more conventional technologies. The hybridization of advanced metamaterial concepts with integrated optics and the associated mature, powerful and efficient lithographic techniques is one of the key strengths of CMIP.
Dr. Jokerst and other CMIP researchers make use of a variety of state-of-the-art lithographic patterning techniques to create functional optical metamaterials and integrated plasmonics. Many samples are fabricated on low-cost, spin-coated polymers such as polyimide or benzocyclobutene (BCB), as well as dielectric substrates such as silicon dioxide and silicon nitride. All steps of the processing can be performed in the SMiF, allowing for a rapid cycle time between the design of a structure and its confirmation. Samples designed for millimeter wave through near-IR wavelengths can be fabricated using photolithography, while samples designed for visible wavelengths can be fabricated via direct-write electron beam lithography. Both of these capabilities are within the SMiF.
Dr. Jokerst's group brings particular expertise in methods of heterogeneous integration, through which metamaterial and plasmonic elements can be combined with chip-scale integrated photonic systems. Thin film heterogeneous integration is a class of fabrication processes that integrates dissimilar materials into a single system without limitations for lattice matching conditions, and fewer limitations for coefficient of thermal expansion mismatch between materials than in traditionally integrated (e.g. bump bonded) systems. The use of heretogeneous integration is of particular value in developing hybrid metamaterials in which active, tunable or nonlinear materials are combined with metamaterial or plasmonic structures to create dynamically controllable or loss-compensated composites.