Nanophotonic structures that can be found in nature, such as wings of Morpho butterfly, nipples on Moth eye, and beetle’s cuticle, are mostly formed on arbitrarily curved surfaces in a large scale. On the other hand, man-made nanophotonic structures including photonic crystals, metamaterials, and plasmonics are still in the laboratory level due to their flat and limited size. Key challenges come from these technology gaps. We develop large-scale, flexible or even stretchable nanophotonic structures that can be conformally wrapped on curvilinear-shaped objects without any significant change in operating characteristics, throughout the use of nanofabrication techniques and integration skills of hard/soft materials. Another interesting point is that artificially controlled bending or stretching of this nanostructure can be also used tunability of optic performance. Compelling applications will include reusable, attachable highly sensitive optics sensors on skin or other soft materials. Integration with micro-optic structure will offer broader functionality.
Figure (left) Antireflective moth eye structure with ideal shape, (center) Bendable antireflective nanostructures, (right) hierarchical micro-/nanostructure on LED surface
 W. I. Nam, Y. J. Yoo and Y. M. Song, Geometrical shape design of nanophotonic surfaces for thin film solar cells, Opt. Express, 24(14), A1033 (2016).
 H. M. Kim, S. H. Kim, G. J. Lee, K. J. Kim and Y. M. Song, Parametric studies on artificial Morpho butterfly wing scales for optical device applications, J. Nanomater., 2015, 451834 (2015).
 Y. M. Song, Y. Jeong, C. I. Yeo, and Y. T. Lee, Enhanced power generation in concentrated photovoltaics using broadband antireflective coverglasses with moth eye structures, Opt. Express 20, A916 (2012).
 Y. M. Song, G. C. Park, S. J. Jang, J. H. Ha, J. S. Yu, and Y. T. Lee, Multifunctional light escaping architecture inspired by compound eye surface structure: From understanding to experimental demonstration, Opt. Express 19, A157 (2011).
 K. Choi, S. H. Park, Y. M. Song, Y. T. Lee, C. J. Hwangbo, H. Yang, and H. S. Lee, Nano-tailoring the surface structure for the monolithic high-performance antireflection polymer film, Adv. Mater. 22, 3713 (2010).
 Y. M. Song, S. J. Jang, J. S. Yu, and Y. T. Lee, Bioinspired parabola subwavelength structures for improved broadband antireflection, Small 6, 984 (2010).
Advanced optoelectronic devices/systems
Insect’s eye camera that we made by mimicking the natural insect’s eye is one of the examples for advanced optoelectronic systems. We will continue similar approaches to develop other interesting optoelectronic devices/systems that show unique characteristics. ‘Beyond biology’ is our vision for designing such systems. Convergence of well-matured optical communication systems and recently developed flexible/stretchable techniques will generate new type of optical communications not only in computer/network systems but also in bio-integrated electronic systems and compact, multi-layered data link systems. We will develop and establish advanced optoelectronic components for this emerging field. Traditional use of optical coupler that contains LEDs and PDs in electronic systems is for isolating the electrical signals. On the other hand, we will translate this configuration to extremely stretchable electronic systems by using directional micro-LEDs and high-sensitive micro-PDs. We will solve problems for this system, some of which are directionality, efficient heat dissipation and packing density.
Figure (left) Insect’s eye cameras with extremely wide field of view, (center) Bendable micro-LED arrays, (right) Bio-degradable transient electronic devices
 Y. M. Song, Y. Xie, V. Malyarchuk, J. Xiao, I. Jung, K.-J. Choi, Z. Liu, H. Park, C. Lu, R.-H. Kim, R. Li, K. B. Crozier, Y. Huang, J. A. Rogers, Digital cameras with designs inspired by the Arthropod eye, Nature 497, 95 (2013).
 R.-H. Kim, S. Kim, Y. M. Song, H. Jung, T.-I. Kim, J. Lee, X. Li, K. D. Choquette, and J. A. Rogers, Flexible vertical light emitting diodes, Small 8, 3123 (2012).
 S.-W. Hwang, H. Tao, D.-H. Kim, H. Cheng, J.-K. Song, E. Rill, M. A. Brenckle, B. Panilaitis, S. M. Won, Y.-S. Kim, Y. M. Song, K. J. Yu, A. Ameen, R. Li, Y. Su, M. Yang, D. L. Kaplan, M. R. Zakin, M. J. Slepian, Y. Huang, F. G. Omenetto, and J. A. Rogers, A physically transient form of silicon electronics, Science 337, 1459 (2012).
 Y. Zhang , S. Wang , X. Li , J.A. Fan , S. Xu , Y. M. Song , K.J Choi , W.H Yeo W.S. Lee , S.N. Nazaar , B. Lu , L. Yin , K.C. Hwang , John A. Rogers , Y.G. Huang , Experimental and Theoretical Studies of Serpentine Microstructures Bonded To Prestrained Elastomers for Stretchable Electronics, Adv. Funct. Mater. 24, 2028 (2014).
Next-generation optical healthcare systems
As one of the efforts for system level devices, we will focus on new opportunities for next-generation optical healthcare systems. Health monitoring devices that mount on the human skin are of great interest in clinical health care, due to their capabilities in noninvasive, physiological diagnostics. Intrinsic optical signals (IOSs) from human body based on diffuse optical tomography provide versatile information, such as brain function, blood oxygen saturation, and cancer detection. However, currently available techniques have some limitations, i.e., large, heavy and uncomfortable tool kits and unstable signals that arise from the unfavorable nature of the skin/device interface. Recently developed skin-like electronics technology that is intimately contacted to skin can be directly applied to this IOS system to solve abovementioned problems, but there are still challenges including development of power delivery systems for stable LED/PD operations and efficiency improvement of ultra-compact, light-weight LEDs/PDs. We will develop optic/electronic/wireless components separately and will conduct systematic studies on stable operations for integrated forms of these components.
Figure (left) Image of a device laminated on the skin of the forehead, with an operating μ-ILED, (center) Multiplexed force touch sensor array integrated with the QLED, (right) Integrated system wirelessly powered with RF scavenging.
 K. I. Jang, H. U. Chung, S. Xu, C. H. Lee, H. Luan, J. Jeong, H. Cheng, G. T. Kim, S. Y. Han, J. W. Lee, J. Kim, M. Cho, F. Miao, Y. Yang, H. N. Jung, M. Flavin, H. Liu, G. W. Kong, K. J. Yu, S. I. Rhee, J. Chung, B. Kim, J. W. Kwak, M. H. Yun, J. Y. Kim, Y. M. Song, U. Paik, Y. Zhang, Y. Huang, J. A. Rogers, Soft network composite materials with deterministic and bio-inspired designs, Nat. Commun. 6, 6556.(2015).
 K.I. Jang, S.Y. Han, S. Xu, K.E. Mathewson, Y.H. Zhang, J.W. Jeong, G.T. Kim, R.C. Webb, J.W. Lee, T.J. Dawidczyk, R.H. Kim, Y. M. Song, W.H. Yeo, S. Kim, H. Cheng, S.I. Rhee, J.H. Chung, B.G. Kim, H.U. Chung, D.J. Lee, Y.Y. Yang, M.G. Cho, J.G. Gaspar, R. Carbonari, M. Fabiani, G. Gratton, Y.G. Huang, J.A. Rogers, Rugged and breathable forms of stretchable electronics with adherent composite substrates for transcutaneous monitoring, Nat. Commun. 5, 4779 (2014).
 Y. Hattori, L. Falgout, W. Lee, S.Y. Jung, E. Poon, J.W. Lee, I. Na, A. Geisler, D. Sadhwani, Y. Zhang, Y. Su, X. Wang, Z. Liu, J. Xia, H. Cheng, R.C. Webb, A.P. Bonifas, P. Won, J.W. Jeong, K.I. Jang, Y. M. Song, B. Nardone, M. Nodzenski, J.A. Fan, Y. Huang, D.P. West, A.S. Paller, M. Alam, W.H. Yeo, J.A. Rogers, Multifunctional Skin-Like Electronics for Quantitative, Clinical Monitoring of Cutaneous Wound Healing, Adv. Healthc. Mater. 10.1002/adhm.201400073 (2014).
 T.-I. Kim, J. G. McCall, Y. H. Jung, X. Huang, E. R. Siuda, Y. Li, Y. M. Song, H. A. Pao, C. Lu, S. D. Lee, I. S. Song, G. C. Shin, M. P. Tan, Y. Huang, J. A. Rogers, Injectable, cellular-scale optoelectronics with applications for wireless optogenetics, Science 340, 211 (2013).