All entries for chih-hung hsieh

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Design and Fabrication of Dielectric Nanostructured Bending Adapter for Optical Frequencies

• Authors: C.-H. Hsieh, H. Xu, Y. Lu, H. Gao, B. Zhang, H. Sun, G. Barbastathis.
• Sponsorship: Singapore-MIT Alliance for Research and Technology – Independent Research Group: Center for Environmental Sensing and Modeling, Air Force Office of Scientific Research MURI, Institute for Soldier Nanotechnologies

Transformation optics has inspired numerous conceptual devices since the first theoretical model of invisibility cloaks^[1],^[2]. However, the transition of these concepts into industrial applications is now widely acknowledged as a challenging bottleneck. A practical design strategy that can be adopted by industrial engineers is thus desirable at this stage. Here we propose an integrated design strategy imposing practical constraints on the area-preserving affine coordinate transformation as a general practical method to solve the problem of nonmagnetism. Practical concerns related to fabrication such as anisotropy degree and bending angles serve as additional constraints to the transformation. More details about the derivation and simulation can be found in^[3]. In Figure 1, we simulate the light propagating in the waveguide with or without bending adapter using finite difference time domain (FDTD) software. Obviously, the field distribution of the propagating light makes a 60° turn by the proposed bending adapter compared to a reference. In addition, Figure 2 shows the fabrication results of the bending adapter using electron beam lithography and reactive ion etching (RIE)^[4]. Ongoing work will focus on characterizing the adapter’s performance based on a near-field scanning optical microscope. In conclusion, we not only illustrate how to apply this practical strategy to the design of a two-dimensional electromagnetic waveguide bending adapter, but also fabricate the device for the verification. Our study is a significant step toward practical use of ideal transformation optics devices that can be implemented with natural dielectric materials.



Figure 1: FDTD simulations of the proposed bending adapter are compared to the reference without nanograting at the adapter region. Both 2D (infinite thickness at the direction perpendicular to the paper) and 3D (finite-height structure) cases agree with that the light is turned by 60° using the bending adapter.



Figure 2: Bending adapter consist of a 140-nm period nanograting (50% duty cycle) rotated 2.69° with respect to the horizon. The coupling grating deflects the light into a slab waveguide, and an impedance matching layer for reducing reflection at the boundary between the bending adapter and slab waveguide is created by a group of α-Si nanorods.




1. J. B. Pendry, D. Schurig, and D. R. Smith, “Controlling electro- magnetic fields,” Science 312, pp. 1780–1782, June 2006. [↩]
2. U. Leonhardt, “Optical conformal mapping,” Science 312, pp. 1777–1780, June 2006. [↩]
3. H. Xu, B. Zhang, T. Yu, G. Barbastathis, and H. Sun, “Dielectric waveguide bending adapter with ideal transmission: practical design strategy of area-preserving affine transformation optics,” Journal of the Optical Society of America B 29, pp. 1287-1290, May 2012. [↩]
4. Y. Lu, H. Xu, H. Gao, C. Hsieh, B. Zhang, H. Sun, and G. Barbastathis, “Design and fabrication of dielectric nanostructured bending adaptor for optical frequencies,” International Conference at Optical MEMS and Nanophotonics (OMN), 2012, pp. 172-173 [↩]