Mixing light in plasmonic circuits for all optical modulation and switching Tim Davis†‡, Daniel Gomez†‡ and Fatima Eftekhari‡ †CSIRO Manufacturing Flagship, Private Bag 10, Clayton South, Victoria, Australia 3169 ‡Melbourne Centre for Nanofabrication, ANFF, 151 Wellington Road, Clayton, Victoria, Australia 3168 CSIRO MANUFACTURING FLAGSHIP LSPs as optical circuits Incident light field Light incident on a metal nanoparticle excites coherent oscillations of the electric charge at the metal surface – this is a localised surface plasmon (LSP) Circuit – a closed path around which flows electrical current For LSPs it is the displacement current which flows More complex circuits are made by coupling LSPs. These can be used to mix optical signals together Electric charge excitation Coupling of plasmonic particles Plasmon hybridization Fano resonances Dark modes Induced transparency … Isolated particles Plasmon coupling alters the excitations of the particles Davis et al. PRB (79), 155423 (2009) Davis et al. Nano Letters (10) 2618 (2010) Plasmonic circuits for mixing optical signals Input optical signals Inputs via free‐space coupling, dielectric or metal waveguides, optical antennas … Processed optical signal Plasmon coupling leading to filtering and mixing Davis et al. PRB (79), 155423 (2009) Davis et al. Nano Letters (10) 2618 (2010) Eftekhari et al. Optics Letters (39) 2994 (2014) Plasmonic difference circuit 200 nm Output Plasmonic circuit (Wheatstone bridge) 20 nm Input 1 + Nanoscale metal rods + + + - - Output related to differences at the inputs Davis et al: J. Appl. Phys. (106), 043502 (2009); Eftekhari et al. Optics Letters (39) 2994 (2014) Input 2 All‐optical modulation Output related to phase difference of input Input generating phase difference at output “Control” beam “Signal” beam “Signal” beam The “control” beam is used to modulate the Modulate the interference of light at the “inputs” “signal” beam by driving the “output” All‐optical modulation 100% modulation “control” beam “signal” beam • • Incidence angle 25 degrees to surface normal 680 nm light For 100% modulation only 8% of the control beam is mixed with the signal beam! Davis, Gómez, Eftekhari, Optics Letters (39), 4938‐4941 (2014) All‐optical modulation Modulation depends on: 1) the amplitude ratio C/S 2) the relative phase 3) Incidence angle Theory All‐optical switch Plasmonic switching effect by interference ‐ all‐optical control of the blaze of the grating polariser Diffraction grating of optical circuits Davis et al, Optics Letters (39), 4938‐4941 (2014) Summary • Discussed the idea of localised surface plasmons as forming part of optical circuits • Used an electrical systems analogy to describe coupled LSPs • Demonstrated a plasmonic circuit that detects optical phase differences • Showed an array of plasmonic circuits that mix optical signals together to induce modulation by interference • Demonstrated all‐optical switching or a diffraction grating with an optically controlled blaze Acknowledgements Fatima Eftekhari Daniel Gomez CSIRO AMTCP CSIRO Office of the Chief Executive Melbourne Centre for Nanofabrication Australian National Fabrication Facility Thank you Manufacturing Flagship Dr. Tim Davis t +61 3 9545 2881 e [email protected] w www.csiro.au MANUFACTURING FLAGSHIP CSIRO Nanophysics Team