Applications of Computational Nanophotonics in Photonic Circuits, Self Assembly, and Solar Energy

Michelle L. Povinelli, Chenxi Lin, Jing Ma, and Camilo A. Mejia University of Southern California, 3737 Watt Way, PHE 614, Los Angeles, CA 90089

Avik Dutt Indian Institute of Technology Kharagpur, Kharagpur, India

Using nanofabrication technologies, it is possible to pattern materials on the scale of the wavelength of light, dramatically altering its propagation. Here we discuss our results in three application areas of nano- and microphotonics. First, we present work that explores how the force of light can be used to move parts of photonic integrated circuits [1]. Photonic integrated circuits use nanofabricated devices to control the flow of light on a chip, much like electrical circuits control the flow of electrons. We have calculated the force of light on movable waveguides, or photonic wires. Given proper designs, we predict that light forces can be used to trigger motion that feeds back to the light signal, changing polarization [2], limiting power flow [3], or giving rise to nonlinear propagation characteristics [4]. These features are expected to contribute new functionalities in on-chip optical signal processing. Second, we discuss the use of light forces to assist and modify self assembly [5]. We calculate the optical forces on particles above photonic crystal slabs using the Maxwell Stress Tensor method in combination with full-vectorial electromagnetic simulations. We show that exciting a guided resonance yields an enhanced attractive force. Lateral forces produce periodic trapping locations dependent on wavelength and polarization. The results suggest that by shining light through a microphotonic template, the formation and reconfiguration of different periodic arrays of nanoparticles can be achieved. We call this process “light-assisted, templated self assembly.” Third, we have studied how nano- and microscale patterning can be used to efficiently absorb light within small volumes. Such “structural absorption engineering” techniques are expected to lead to cheaper, more efficient solar cells. We present results of our electromagnetic calculations on nanowire arrays. We find that optimized nanowire structures have higher broadband absorption than an unpatterned film of the same thickness, even though the volume of absorptive material is lower [6]. We also show that aperiodic nanowire structures can absorb > 100% more light across the solar spectrum than their periodic counterparts. 1. M. L. Povinelli, M. Loncar, M. Ibanescu, E. J. Smythe, S. G. Johnson, F.

Capasso, and J. D. Joannopoulos, "Evanescent-wave bonding between optical waveguides," Optics Letters 30, 3042-3044 (2005).

2. J. Ma and M. L. Povinelli, "Large tuning of birefringence in two strip silicon waveguides via optomechanical motion," Optics Express 17, 17818-17828 (2009).

248

TuH1 (Invited)8:30 AM – 9:00 AM

978-1-4244-8939-8/11/$26.00 ©2011 IEEE

3. J. Ma and M. L. Povinelli, "Effect of periodicity on optical forces between a one-dimensional periodic photonic crystal waveguide and an underlying substrate," Appl. Phys. Lett. 97, 151102 (2010).

4. J. Ma and M. L. Povinelli, "Mechanical Kerr nonlinearities due to bipolar optical forces between deformable silicon waveguides," Optics Express 19, 10102-10110 (2011).

5. C. A. Mejia, A. Dutt, and M. L. Povinelli, "Light-assisted templated self assembly using photonic crystal slabs," Optics Express 19, 11422-11428 (2011).

6. C. Lin and M. L. Povinelli, "Optical absorption enhancement in silicon nanowire arrays with a large lattice constant for photovoltaic applications," Optics Express 17, 19371-19381 (2009).

249