Table of Contents Author Guidelines Submit a Manuscript
Journal of Nanotechnology
Volume 2010 (2010), Article ID 953212, 5 pages
http://dx.doi.org/10.1155/2010/953212
Research Article

Design and Fabrication of 1 2 Nanophotonic Switch

1School of Engineering, Bar-Ilan University, Ramat-Gan 52900, Israel
2Physics Department, Jack and Pearl Resnick Institute of Advanced Technology, Bar-Ilan University, Ramat-Gan 52900, Israel

Received 25 August 2009; Accepted 5 January 2010

Academic Editor: Thomas Thundat

Copyright © 2010 Asaf Shahmoon et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We present the design and the fabrication of a novel nanophotonic switch. The switch is a photonic T-junction in which a gold nano particle is being positioned in the junction using the tip of an atomic force microscope (AFM). The novelty of this switch is related to its ability to control the direction of wave that propagates along a photonic structure. The selectivity of the direction is determined by a gold nanoparticle having dimension of a few tens of nanometer. This particle can be shifted. The shift of the gold nano particle can be achieved by applying voltage or by illuminating it with a light source. The shifts of the particle, inside the air gap, direct the input beam ones to the left output of the junction and once to its right output. Three types of simulations have been done in order to realize the photonic T-junction, and they are as follows: photonic crystal structures, waveguide made out of PMMA, and a silicon waveguide.

1. Introduction

Optical switches have wide usage in optics communication for various purposes including protection of an optical link [1, 2]. Reducing the dimensions of the switch can assist in its integration on a silicon chip together with other electro-optical and microelectronic processing devices that may be positioned on the chip as well. The recent development of nanotechnology fabrication capabilities allows realization of various types of nanophotonic devices on silicon chips [35].

Photonic structures cannot be modified after their fabrication process. Therefore modulators and switches have been developed in order to control propagation of light. Photonic structures such as single mode Y couplers are widely employed as power dividers [6, 7] and combiners in modulators [8], switches [9, 10], and interferometric devices. Several approaches have been proposed in order to control the direction of light. Photonic crystals utilizing liquid crystal orientation that can be changed by adjusting applied field [11] and photonic crystal composed of semiconductor that depends on temperature [12].

Usage of trapped nanoparticle in order to realize a nano photonic modulator has already been demonstrated before [13]. There the position of a nanoparticle that performed the modulation of the output light was controlled using external voltage command. In this paper we present a novel design of a nano photonic switch having a T-junction structure in which there is one input and two outputs. The energy of the input is diverted to one of the outputs by shifting a golden nanoparticle that is positioned in the junction from one side of the junction to the other.

Note that usage of nanoparticle for electro optical applications has already been demonstrated before while the directions and ways of scattering [14, 15] the polarization of the scattered light [16, 17] and its diffraction [18] were characterized.

In Section 2 we present the design and the numerical simulation of the device. Its fabrication is demonstrated in Section 3. The paper is concluded in Section 4.

2. Numerical Simulations

The proposed device has a T-junction shape. In the simulations we used 2D, TE “in plane” mode analysis at a wavelength of 1.55 m. The electromagnetic wave is excited and propagates along the main waveguide until it approaches the 90 degree T-junction. A hole of air gap is being produced at the splitting point. The silicon waveguides consist of a channel waveguide with dimensions of 450 nm width and 250 nm height. Choosing the proper position of a nanoparticle in the junction can change the output channel through which the light output. All simulations in this section were performed using two numerical softwares: R-Soft and Comsol Multiphysics which both solved the Maxwell equations for radiation propagation using Finite-Difference Time-Domain (FDTD) and Finite Elements Method (FEM) approaches, respectively [19].

One way of realizing such a T-junction device is by using photonic crystal structures [20, 21]. In Figure 1(a) one may see a beam splitter having T-junction structure. This is obtained without placing the nanoparticle. When a golden nanoparticle with dimensions of 100 nm is added to the right side of the junction all the light is directed to the left output of the junction as depicted in Figure 1(b). The simulations of Figure 1 were performed using R-Soft.

fig1
Figure 1: Simulations for photonic crystal T-junction. (a) Beam splitting obtained without placing the nanoparticle. (b) Addition of 100 nm particle in the T-junction diverts the light towards the left output channel.

The next step of simulations was to simplify the photonic crystal based T-junction into a regular T-junction waveguide while a narrow slit is positioned in the junction and in which the nanogolden particle ( = 3·107 [S/m]) is placed. In Figure 2(a) one may see the simulation of such a device while the waveguide is made out of PMMA material (refraction index of about 1.6). The readout of the two outputs (the left and the right arms of the T-junction) versus the position of the nanoparticle is seen in Figure 2(b). The size of the particle is 100 nm. The units of the horizontal axis of Figure 2(b) are in microns and thus one may see that shifting the particle a distance of about 400 nm switches the output from the left arm to the right arms of the T-junction device. One may see that extinction ratio of (12 dB) may be obtained in the proposed device. The simulations of Figure 2 were performed using R-Soft.

fig2
Figure 2: Waveguide-based T-junction. (a) Simulations for switching the output channel in a PMMA waveguide. (b) The same simulation as in Figure 2(a) versus the position of the 100 nm particle.

The basic configuration of photonic structures (e.g., modulator, sensor, and logic gate) is already based on silicon waveguide; therefore, in order to adapt the device for silicon a modification to the T-junction is made as depicted in Figure 3. The simulations in this part were carried out using Comsol Multiphysics that solves the second order partial differential wave equation. The wave equation can be described by where is the relative magnetic permeability, is the electric field in the component, is the dielectric coefficient, is the conductivity, is the angular frequency of the propagating light, is the vacuum permittivity, and is the wavenumber.

fig3
Figure 3: Numerical simulation. (a) Refractive index of the simulated device. (b) The power flow distribution along the “Y coupler” without the particle. (c) and (d) The power flow distribution along the “Y coupler” waveguide while the gold nanoparticle ( = 3·107 [S/m]) is placed in the lower and upper part of the air gap, respectively.

The boundary condition at the input of the device was selected in such a way that the Poynting vector is equal to 1. The external boundaries conditions were selected to be scattered (each one of them with a proper direction of scattering), while the internal boundaries conditions were selected to be in “continuity” mode. The “free mesh parameter” function of the Comsol simulator was used to mesh the entire device. We use the subdomain meshing function to mesh each subdomain with the proper mesh size. The mesh parameters of the waveguide region were maximum element size of 30 nm with element growth of 1.2, while in the gold nanoparticle region we choose maximum element size of 1 nm.

Figure 3(a) presents the refractive index of the simulated device. Figure 3(b) present the power flow distribution along the T-junction without the particle. Figures 3(c) and 3(d) presents the power flow distribution along the T-junction waveguide while the gold nanoparticle ( = 3·107 [S/m]) is placed in the lower and upper part of the air gap, respectively. Here one may see that the power flow extinction ratio between the unblocked and the block paths is standing on (12 dB). The power flow distribution pattern at the main waveguide is related to the standing wave that is generated by the backscattering and the reflections. In Figures 3(c) and 3(d), the asymmetric location of the gold nanoparticle inside the air gap causes an asymmetric backscattering which result in an asymmetric shape of the power flow distribution along the main waveguide.

3. Fabrication and Realization

The realization of the proposed devices is presented in Figure 4. Figure 4(a) shows the top view microscope images of the fabricated T-junction. Figure 4(b) shows enlarged image at the splitting point. In order to couple light from a fiber to the proposed waveguide-based device we used tapered fibers having edge with diameter of 3 m.

953212.fig.004
Figure 4: Fabricated “Y coupler.” (a) Top view microscopic image of the overall fabricated device. (b) Enlarged image shows the input waveguide which splits into a pair of waveguides; (c) and (d) show SEM images of the lower and upper encompass areas (shown in Figure 4(b)) that define the coupling of light from fiber to the silicon waveguide and the fabrication of the T-junction itself, respectively. (e) Placing the particle in the slit (the particle is marked with white arrow). Left part is an upper view of the particle and the right part is the 3D mesh.

In order to have efficient coupling of light from a fiber (having tapered edge of 3 m) to silicon-based waveguide (having sub micron dimensions) we designed and fabricated a narrow edge to the waveguides [22, 23] as depicted in Figure 4(c) presenting the scanning electron microscope (SEM) image of our fabricated chip.

In Figure 4(d) we present the fabricated T-junction-based switch where an air hole is used instead of the slit. In this hole we will position the nanoparticle. The waveguide is a silicon waveguide fabricated on silicon on insulator (SOI) wafer.

The position of a 100 nm particle in the hole of the T-junction is made using an AFM tip. In the experiment we were able to position the nanoparticle directly into the designated hole by pushing it with the tip of the AFM (using “Nanoman” feature of the AFM). The experimental results presenting the position of the particle are seen in Figure 4(e), where in the left side of the figure we see the upper view of the particle and in the right part of the figure we present the 3D mesh.

The experimental characterization of the proposed device is our next step which will be performed in the near future.

4. Conclusions

In this paper we present a T-junction-based design for a switch in which the output energy is directed to the output channel by shifting a nanoparticle positioned in the T-junction itself. The proposed device was fabricated and a nanoparticle was placed in its allocated proper position using an AFM tip. The anticipated performance of the proposed nano switch was numerically investigated.

References

  1. Z. Zalevsky, D. Mendlovic, E. Marom et al., “Ultrafast all-optical switching,” Journal of Optical Networking, vol. 1, no. 5, pp. 170–183, 2002. View at Google Scholar · View at Scopus
  2. R. Appelman and Z. Zalevsky, “All-optical switching technologies for protection applications,” IEEE Communications Magazine, vol. 42, no. 11, pp. S35–S40, 2004. View at Publisher · View at Google Scholar · View at Scopus
  3. P. Dainesi, A. Küng, M. Chabloz et al., “CMOS compatible fully integrated Mach-Zehnder interferometer in SOI technology,” IEEE Photonics Technology Letters, vol. 12, no. 6, pp. 660–662, 2000. View at Publisher · View at Google Scholar · View at Scopus
  4. A. Liu, R. Jones, L. Liao et al., “A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor,” Nature, vol. 427, no. 6975, pp. 615–618, 2004. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  5. Q. Xu, S. Manipatruni, B. Schmidt, J. Shakya, and M. Lipson, “12.5 Gbit/s carrier-injection-based silicon micro-ring silicon modulators,” Optics Express, vol. 15, no. 2, pp. 430–436, 2007. View at Google Scholar · View at Scopus
  6. Y. Sugimoto, N. Ikeda, N. Carlsson, K. Asakawa, N. Kawai, and K. Inoue, “Light-propagation characteristics of Y-branch defect waveguides in AlGaAs-based air-bridge-type two-dimensional photonic crystal slabs,” Optics Letters, vol. 27, no. 6, pp. 388–390, 2002. View at Google Scholar · View at Scopus
  7. A. Klekamp, P. Kersten, and W. Rehm, “An improved single-mode Y-branch design for cascaded 1:2 splitters,” Journal of Lightwave Technology, vol. 14, no. 12, pp. 2684–2686, 1996. View at Google Scholar · View at Scopus
  8. Q. Xu, B. Schmidt, S. Pradhan, and M. Lipson, “Micrometre-scale silicon electro-optic modulator,” Nature, vol. 435, no. 7040, pp. 325–327, 2005. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  9. A. Sharkawy, S. Shi, D. Prather, and R. Soref, “Electro-optical switching using coupled photonic crystal waveguides,” Optics Express, vol. 10, no. 20, pp. 1048–1059, 2002. View at Google Scholar
  10. F. Sun, J. Yu, and S. Chen, “A 2×2 optical switch based on plasma dispersion effect in silicon-on-insulator,” Optics Communications, vol. 262, no. 2, pp. 164–169, 2006. View at Publisher · View at Google Scholar · View at Scopus
  11. H. Takeda and K. Yoshino, “Tunable light propagation in Y-shaped waveguides in two-dimensional photonic crystals utilizing liquid crystals as linear defects,” Physical Review B, vol. 67, no. 7, pp. 731061–731064, 2003. View at Google Scholar · View at Scopus
  12. H. Takeda and K. Yoshino, “Tunable light propagation in Y-shaped waveguides in two-dimensional photonic crystals composed of semiconductors depending on temperature,” Optics Communications, vol. 219, no. 1–6, pp. 177–182, 2003. View at Publisher · View at Google Scholar · View at Scopus
  13. O. Limon, L. Businaro, A. Gerardino, L. Bitton, A. Frydman, and Z. Zalevsky, “Fabrication of electro optical nano modulator on silicon chip,” Microelectronic Engineering, vol. 86, no. 4–6, pp. 1099–1102, 2009. View at Publisher · View at Google Scholar · View at Scopus
  14. B. M. Nebeker, G. W. Starr, and E. D. Hirleman, “Light scattering from patterned surfaces and particles on surfaces,” in Optical Characterization Techniques for High-Performance Microelectronic Device Manufacturing II, vol. 2638 of Proceedings of SPIE, pp. 274–284, Austin, Tex, USA, 1995. View at Publisher · View at Google Scholar · View at Scopus
  15. M. I. Mishchenko and L. D. Travis, “Light scattering by size/shape distributions of non-spherical particles of size comparable to a wavelength,” in Atmospheric Propagation and Remote Sensing, vol. 1968 of Proceedings of SPIE, pp. 118–129, September 1993.
  16. L. Sung, G. W. Mulholland, and T. A. Germer, “Polarization of light scattered by particles on silicon wafers,” in Surface Characterization for Computer Disk, Wafers, and Flat Panel Displays, vol. 3619 of Proceedings of SPIE, pp. 80–89, San Jose, Calif, USA, 1999. View at Scopus
  17. J. H. Kim, S. H. Ehrman, G. W. Mulholland, and T. A. Germer, “Polarized light scattering from metallic particles on silicon wafers,” in Optical Metrology Roadmap for the Semiconductor, Optical, and Data Storage Industries II, vol. 4449 of Proceedings of SPIE, pp. 281–290, San Jose, Calif, USA, 2001. View at Publisher · View at Google Scholar · View at Scopus
  18. J. Vargas-Ubera, D. Gale, and J. Felix-Aguilar, “The range of validity of the Fraunhofer approximation in the estimation of particle size distributions from light diffraction,” in 4th Iberoamerican Meeting on Optics and 7th Latin American Meeting on Optics, Lasers, and Their Applications, vol. 4419 of Proceedings of SPIE, pp. 435–438, Tandil, Argentina, September 2001. View at Publisher · View at Google Scholar · View at Scopus
  19. http://www.rsoftdesign.com/aboutUs.php/.
  20. T. T. Alkeskjold, J. Lægsgaard, A. Bjarklev et al., “All-optical modulation in dye-doped nematic liquid crystal photonic bandgap fibers,” Optics Express, vol. 12, no. 24, pp. 5857–5871, 2004. View at Publisher · View at Google Scholar · View at Scopus
  21. M. F. Yanik, S. Fan, M. Soljacic, and J. D. Joannopoulos, “All-optical transistor action with bistable switching in a photonic crystal cross-waveguide geometry,” Optics Letters, vol. 28, no. 24, pp. 2506–2508, 2003. View at Google Scholar · View at Scopus
  22. P. E. Barclay, K. Srinivasan, and O. Painter, “Design of photonic crystal waveguides for evanescent coupling to optical fiber tapers and integration with high-Q cavities,” Journal of the Optical Society of America B, vol. 20, no. 11, pp. 2274–2284, 2003. View at Google Scholar · View at Scopus
  23. P. E. Barclay, K. Srinivasan, M. Borselli, and O. Painter, “Efficient input and output fiber coupling to a photonic crystal waveguide,” Optics Letters, vol. 29, no. 7, pp. 697–699, 2004. View at Publisher · View at Google Scholar · View at Scopus