Research

—Our group focus on experimental and theoretical investigations in optics and optoelectronics and develop state-of-the-art devices with desirable properties for various applications. Our lab is fully equipped with various capabilities, such as spectrometers and spectroscopic imaging setups from visible to THz wavelengths, high power super-continuum sources, fs-laser pump-probe measurement setup, a widely tunable mid-infrared laser,  microscope cryostats (from 10 K-500 K), full-stokes polarimetric imaging setup, single photon auto-correlation measurement setup (in progress), high speed electronic measurements (up to 20 GHz).

We get inspiration from various unique properties achievable by nanostructure engineering as well as emerging materials to develop novel devices with new functionalities or unprecedented performance. More specifically , we have been working on semiconductor heterostructures, optical nanoantennas, plasmonics, graphene and other 2D materials. We identify the practical problems in real applications such as biomedical sensing, infrared imaging, communication, and seek game-changing solutions at the system level.

Here are the areas we have been working on:

1. High performance metamaterials for ultra-compact optoelectronic devices. One  major objective of our research in material engineering is to explore various design concepts to address the major challenges of most state-of-art metasurfaces/metamaterials for real-world device/system applications, i.e., low optical efficiency, insufficient performance and high cost (nanofabrication is time consuming and expensive!). So far, we have demonstrated sub-wavelength thick artificial chiral metamaterials based on double-layer hybrid-metasurfaces with the highest circular polarization selection ratio (>30) and transmission efficiency (up to 90%) [1] for near infrared and visible wavelengths. Plasmonic metamaterials have been generally considered to be very lossy; yet we recently demonstrated a new design strategy for highly efficient plasmonic metamaterials (transmission efficiency >90%), which can be used for polarization control over a broad wavelength range (from 3 to 5 µm) mid-infrared wavelengths [2].

[1] Basiri, X. Chen, J. Bai, P. Amrollahi, et.al., Light: Science & Applications 8, 1-11, 2019. https://www.nature.com/articles/s41377-019-0184-4

[2] Bai, Jing, Yu Yao, “Integrated Plasmonic Flat Optics for Broadband Highly Efficient Stokes Parameter Detection in MIR, 2018 Conference on Lasers and Electro-Optics (CLEO), pp. FM4B-4, 2020

2. Active metasurfaces for high speed/ultrafast light modulation and detection

Low dimensional structures (such as quantum wells, quantum dots), 2D materials and heterostructures have very attractive optoelectronic properties; however, most devices demonstrated suffer from low performance. Integrating them with metasurfaces where their interaction with light can be highly enhanced could lead to promising solutions for optoelectronic devices with high performance and new functionalities. We have demonstrated electrically tunable graphene-plasmonic metasurfaces with nanosecond response time [1] and achieved the first spatial light modulator in the mid-IR wavelength range [2]. We have also been trying to push the limit for ultrafast dynamic control of metasurfaces. Based on a double-enhancement graphene-metasurface design, we have realized optical switching and modulation of infrared light with picosecond response time, low pump power requirement based on a subwavelength-thick (<600 nm in total) structure with < 0.05 mm² [3,4]. Future work include further optimization of the structure designs, gaining more in-depth understanding of the physics and exploring other materials and structures to improve the tuning range and enable capabilities of intensity modulation, phase modulation, etc, with larger dynamic range and smaller insertion loss.

[1]Yao, M. A. Kats, R. Shankar, Y. Song, M. Loncar, J. Kong, and F. Capasso, Nano Letters, 14, 214-219, 2014.

[2]Zeng, Z. Huang, A. Singh, Y. Yao, et. al., Light: Science & Applications vol. 7, 1-8, 2018.

[3] Basiri, M. Z. Rafique, J. Bai, J. Zuo, S. Choi, Y. Yao, Conference on Lasers and Electro-Optics (CLEO), pp. FTh3Q.2, 2020 (conference abstract and presentation)

[4] Basiri, M. Z. Rafique, Y. Yao, “Ultrafast All-Optical Modulation Based on Active Graphene-metasurfaces”, to be submitted

3. Scale-able manufacturing technology for 2D and 3D optical structures at nanoscale and microscale

The nanophotonic and optoelectronic research involves intense nanofabrication and various characterization methods. Yet, the current processing method based on electron beam lithography is too slow and expensive for device fabrication over millimeter scale or larger. Moreover, we have been constantly exploring new methods for low cost, scalable fabrication of nanostructures and 3D nano/micro-scale structure. We have established collaborations with researchers in biology, chemistry and nanofabrication to develop such efforts specifically for addressing fabrication challenges in nanophotonic structures. We have developed a new technique for 3D printing of thin metal films with smooth surface and high conductivity [1]. We have also explored the feasibility of using DNA origami to couple single emitters (dye molecule or quantum dot) exactly into the hot spot between two coupled plasmonic nanorods with nanometer gap size in between and demonstrated strong coupling effects [2]. This technology is quite promising to realize active plasmonic structures or metasurfaces/metamaterials not possible for current nanofabrication techniques in a much more scalable manner, thanks to the flexibility of DNA origami structure engineering.

[1] Zhao, J. Bai, Y. Yao, and C. Wang. Materials Today, article in press, 2020. https://doi.org/10.1016/j.mattod.2020.03.001

[2] Zhao, X. Chen, A. Basiri, S. Choi, et. al., “DNA Origami-Templated Deterministic Assembly of Single Emitters in Optical Nanocavity Formed by Gold Nanorods”, to be submitted.

4. Optoelectronics and quantum devices based on 2D materials, semiconductor heterostructures 

Mid-infrared optoelectronic devices based on semiconductor nanostructures:  band engineering is a powerful tool to tailoring material properties and enable functionalities which do not exist in bulk semiconductors.  We have been working with semiconductor growth experts closely to investigate novel device applications of semiconductor hetero-structures based on different materials.  More details

Optoelectronics in graphene and 2D materials:  Graphene and TMDCs have very unique optical and electronic properties. We have been exploring the optoelectronic properties of graphene, TMDCs and their heterostructures for advanced optoelectronic devices and quantum devices (single photon emitters, etc, NSF on-going project).

5.  Infrared optoelectronics for molecular sensing and biomedical applications: Highly sensitive molecular sensors are crucial for chemical analysis and biomedical applications. Infrared wavelength regions host the strongest molecular absorption features.  We have carried out collaborative research on molecule sensing and realized highly sensitive detection of fine features in absorption spectra of single layer molecules [1]. We are working in an interdisciplinary research team of nanophotonics, nanomanufacturing, biology and material to address various challenges in realizing label-free, fast and reliable biomolecule sensors. Moreover, in collaboration with experts working on bioengineering applications, we demonstrated a new technology tissue healing and repair based on mid-infrared lasers and hyperspectral imaging [2].

[1] Xiahui Chen, Chu Wang, Yu Yao*, and Chao Wang*,ACS Nano., 11, 8034, 2017. (* corresponding authors)

[2] Ridha, A. Basiri, S. Godeshala, Md Z. Rafique, et. al., “Chromophore-free Sealing and Repair of Soft Tissues using Mid Infrared Light”, submitted.

6. Advanced optoelectronics for ocean and energy applications:

Currently, we have been exploring the application of our full-stokes polarimetric detectors and imaging sensors [1] to underwater applications (DARPA project, on going). In collaboration with solar energy experts, we came up a series of ideas for autonomous field inspection based on polarimetric imaging technology and my group will lead the this effort in building desirable polarimetric imaging systems, exploring proper polarimetry-based inspection protocols and working with them on the field tests (DOE project, on going).

[1] Zuo, J. Bai, S. Choi, A. Basiri, et.al., CMOS integrated full-stokes polarimetric detectors, in preparation