Dr. Chengkuo Lee received his Ph.D. degree in precision engineering from The University of Tokyo, Tokyo, Japan, in 1996. He has co-authored 390+ journal articles and 360+ conference papers. He holds 10 US patents. His google scholar citation is more than 16800+. He is the associate-editor-in-chief of Trans. Nanotechnology (IEEE), and editor-in-chief of Intern. J. Optomechatronics (Taylor & Francis). He is in the Executive Editor Board of J Micromechanics and Microeng. (IOP, UK). He is the Associate editor of J. MEMS (IEEE). He is also the Editor of next journals: Scientific Reports (Springer Nature), Bioelectronic Medicine (BMC, Springer Nature), Internet of Things - Engineering Cyber Physical Human Systems (Elsevier), J. Optical Microsystems (SPIE), Journal of Sensors (Hindawi), Sensors (MDPI), and Micromachines (MDPI). He has chaired many conferences including IEEE NEMS’18, OMN ’16 and ’14, ISMM’14, and Bio4Apps’13 etc. He has been the program chair of OECC 2017. He serves on steering committee and technical program committee for various conferences such as Transducers 2015, IEEE MEMS 2015, IEEE NEMS 2015, IEEE SENSORS 2018, IEEE MEMS 2019, Transducers 2019, IEEE MEMS 2020, and Transducers 2021, etc.
Mid infrared (MIR) that covers 2 µm to 20 µm is an important wavelength range because it overlaps with abundant molecular absorption fingerprints. MIR nanophotonic sensors have great potential for label-free and damage-free spectroscopic sensing in healthcare monitoring, environmental monitoring, and industrial monitoring. Silicon-on-insulator (SOI) is the most common nanophotonic platform and has promoted data communication applications at 1.55 µm. To leverage the mature SOI manufacturing process, we develop the MIR SOI photonic platform working in 3.6 - 4 µm for nitrous oxide (N2O) sensing. However, beyond 4 µm, the buried oxide layer (BOX) starts to absorb. To address this issue, we remove the BOX layer to make the Si waveguide suspended and successfully extend the working wavelength of SOI platform to 6.1 - 7.6 µm. The suspended SOI platform has been demonstrated for volatile organic compound (VOC) sensing at 6.7 µm. On top of the SOI platform, the aluminum nitride-on-insulator (AlNOI) platform is also promising for MIR applications. Because AlN is theoretically transparent in 0.2 µm to 13.6 µm due to its large bandgap of 6.2 eV. In addition, AlN has a satisfactory Pockels coefficient that is highly desired to enable tuning in photonics. Hence, we develop AlNOI photonic platform that works in 3.6 - 4 µm. The tuning capability of AlNOI photonics is also investigated and shows great promise for on-chip modulation. Besides passive photonic waveguides, active nanophotonic components including lasers, photodetectors, and modulators are indispensable components for integrated MIR nanophotonic sensors. However, the conventional on-chip photodetector material, germanium, is transparent in the MIR. And the conventional on-chip modulation mechanism, free carrier dispersion, will cause a high loss in the MIR. Therefore, we develop two-dimensional (2D) material-based active components for the MIR. The 2D black phosphorus (BP)-based on-chip photodetectors and modulators are developed for applications in 3.6 - 4 µm. The graphene-based photodetector is developed for applications in 6.1 - 7.6 µm. Combining the experience gained from the MIR SOI photonics platform development and 2D-material-based active component development, we furthered developed a simple and high-yield transfer printing method to fabricate silicon-on-calcium fluoride (SOCF) waveguide integrated with graphene photodetector. The integrated sensor has been used to detect 0.72% VOC at 6.7 µm.
References:
1. Y. Ma, B. Dong, and C. Lee, Nano Converg. Vol. 7, No.12, pp.1-34 (2020).
2. W. Liu, et al., Nanophotonics, Vol. 10, 1861 (2021).
3. B. Dong, et al., Opt. Lett. Vol. 44, 73 (2018).
4. L. Huang, B. Dong, X. Guo, Y. Chang, N. Chen, X.
Huang, W. Liao, C. Zhu, H. Wang, C. Lee, and K. W. Ang, ACS Nano 13, 913 (2019).
5. Y. Ma, Y. Chang, B. Dong, J. Wei, W. Liu, and C. Lee, ACS Nano, Vol. 15, No.6, p.10084 (2021).
6. J. Wei, C. Xu, B. Dong, C.-W. Qiu, and C. Lee, Nature Photonics, Vol 15, 614 (2021).
7. J. Wei, et al., Nat. Commun, Vol.11, 6404, 2020.
8. J. Wei, et al., J. Appl. Phys., Vol.128, 240901
(2020).
9. Z. Ren, et al., Adv. Optical Mater., Vol. 8, 1900653 (2020).
Acknowledgement: The research grant of NRF-CRP15-2015-02 at the NUS, Singapore.