(1) For the fundamental investigation on broadband slow light plasmonic/metamaterials, we designed an adiabatically graded metallic grating structure to support surface plasmon modes. Because of the nonuniform geometric feature, the localized optical properties of the grating are adiabatically changed. When we couple the white light into the structure, SPP modes at different frequencies will be slowed down simultaneously, which is a kind of broadband slow light system working in room temperature.
Consider that the resonance frequency (or cutoff frequency) at different positions along the structure are different, the SPP modes at different frequency will be "trapped" at different positions, which is so called trapped rainbow effect. We demonstrated this concept in THz domain in 2008, in telecom and visible domain in 2009 and published two PRL papers. Recently, we experimentally demonstrated the effect in visible domain, which was published by PNAS on March 29, 2011. Currently, we are developing applications based on this intriguing effect for novel detector, energy harvesting materials with enhanced light-matter interactions.
(2) For the biosensor work, we focused on developing sensitive, low cost and portable sensor device for label-free biosensing. Recently, we are working on developing a hybrid plasmonic interferometer sensor integrated with laser diode and photodetector on a single chip. If successful, the sensor system will get rid of bulky external optics, which is so called optics free plasmonic biosensor chip. Importantly, the sensitivity and figure of merit of the sensor performance is comparable with conventional surface plasmon resonance sensing system.
(3) For the plasmonic enhanced thin-film PV work, we are trying to boost the power conversion efficiency for OPV devices using plasmonic nanostructures. The fundamental investigation on broadband slow light for black material discussed in topic (1) is also useful for this investigation. We are pursuing broadband, polarization and angle insensitive nanostructures to trap sun light in the thin-film OPV layers. The metallic nano-plasmonic structure can also function as electrode for OPV devices, with promising enhancement potential for OPV devices.
(4) We also have interests in designing ultra-compact THz/mid IR polarizer converter based on plasmonic/metamaterial subwavelength patterns which can convert a linear polarized THz/mid-IR radiation by 90 degree with a very high efficiency. Based on this design, left/right-circular polarized light can also be produced which is still under investigation.