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Photonic Structures

The nano-optics section focuses its research on wavelength-scale structures to control photon propagation and the interaction of photons with electronic excitations and spins in semiconductor quantum dots. The principal long term goal is the integration of such functions to achieve the first Semiconductor Integrated Quantum Optical Circuits. Both photonic crystals and ridge waveguide structures are employed to guide and control the photon propagation. Cavities also play a key role, to enable the regime of cavity quantum electrodynamics to be attained.

The research is carried in well equipped laboratories, with a variety of continuous wave and ultrafast lasers, highly stable low optical systems and high resolution spectrometers all available. We are also very well placed by the excellent fabrication facilities which are available in the EPSRC National Centre for III-V Technologies, where we fabricate our structures using high resolution electron beam lithography and reactive ion etching techniques.

The research of this area also has close links to the groups work on quantum dots.

Researchers

Academic Staff: Mark Fox
David Whittaker
Maurice Skolnick
Post-Docs: Maxim Makhonin
Benjamin Royall
PhD Students: Nicholas Wasley
Rikki Coles
James Dixon

Please see below for an overview of some of our recent research highlights

Unpolarized H1 photonic crystal nanocavities fabricated by stretched lattice design

APL 98 041101 (2011)

We investigate the factors that affect the mode splitting in H1 planar photonic crystal cavities and hence demonstrate unpolarized emission with a high quality factor. Finite difference time domain simulations show that systematic errors in the fabrication process such as hole shape and period lift the degeneracy of the orthogonally polarized fundamental modes. By intentionally stretching the photonic crystal lattice in one direction, we show that the wavelength and mode splitting can be tuned to compensate for such fabrication errors. By using this technique, we demonstrate unpolarized emission at 951 nm with a quality factor of ~4500.

Figure1

Figure 1: (a) SEM image of a H1 PhC cavity with zero stretch factor. FDTD simulation results for H1 cavities with (b) stretched lattice design and (c) elliptical holes. In (b) the wavelengths of the Mx and My are shown for e = 1 (filled symbols), e = 0.98 (open symbols), and e = 0.96 (half-filled symbols). FDTD simulations of Q-factor as a function of (d) stretch factor for e = 1 and (e) ellipticity for σ = 1.

Figure2

Figure 2: (a) Mode splitting and (b) Q-factors of the Mx and My modes averaged across four groups of cavities as a function of the stretch factor. The solid line in (a) shows the FDTD simulation results. (c) Polarization dependent μPL spectra of a H1 cavity with σ = 0.998 and mode splitting of ~0.01nm. The inset shows the polar plot of the unpolarized mode.

Control of spontaneous emission from InP single quantum dots in GaInP photonic crystal nanocavities

InP quantum dots embedded in GaInP emit in the red spectral range, which coincides with the maximum efficiency of Si detectors. This makes InP quantum dots an attractive proposition for implementation in optical quantum information processing and free space quantum communication. In this paper we show that L3 PC cavities can be fabricated in GaInP, with Q factors as high as 7,500 and we demonstrate semiconductor quantum dots coupled to photonic crystal cavity modes operating in the visible spectrum. Using time resolved photoluminescence measurements we observe spontaneous emission suppression of the QDs within the photonic bandgap and for a resonantly coupled QD we observe a Purcell enhancement of ~8.

Figure3

Figure 3: (a) Scanning electron microscope image of an L3 photonic crystal. (b) Calculated electric field profile of the L3 fundamental mode. (c) Micro-photoluminescence spectra recorded from a typical GaInP L3 photonic crystal, showing emission from InP QD ensemble (650-685nm) and cavity modes. (d) Fundamental mode emission of cavity with quality factor of ~7,500.

Figure4

Figure 4: a) Photoluminescence spectra of weakly coupled InP QD-cavity system recorded at 10K and 44.5K. (b) Decay transients recorded from the QD at 10K and 44.5K (Δλ=0nm). (d) Measured QD lifetime as a function of QD/cavity detuning.

Splitting and lasing of whispering gallery modes in quantum dot micropillars

Optics Express 18 21 22578

We also work with microcavity pillars and in this work we study the whispering gallery mode (WGM) resonances of GaAs/AlGaAs microcavity pillars containing InAs quantum dots. Figure 3 shows an SEM image of a typical micropillar. High quality factor WGMs are observed from a wide range of pillars with diameters from 1.2 to 50μm. Multimode lasing with sub-milliwatt thresholds and high beta-factors are observed under optical pumping in a 4μm diameter pillar. Figure 4 shows the logarithmic input-output curve for a WGM at 958nm with the onset of lasing observed at a pump power of ~100μW. Mode splitting is observed in WGMs from pillars with diameters of 5μm, 20μm and 50µm and we present a model in which the mode splitting in the larger pillars is caused by resonant scattering from the quantum dots themselves

Figure3

Figure 5: SEM image of a micropillar.

Figure5

Figure 6: Logarithmic input-output curve for the 958nm lasing WGM when pumped at 633 nm.

Ultrafast all-optical switching in AlGaAs photonic crystal waveguide interferometers

Appl. Phys. Lett. 95, 141108

In this work we used photonic crystals integrated into AlGaAs Mach-Zehnder interferometers (Fig. 5) to demonstrate ultrafast switching. By optically exciting electrons and holes in one arm of the interferometer, a non-linearity can be induced and switching times as short as 3ps are achieved by surface recombination at the air holes in the photonic crystal (Fig. 6). The fast recombination times and high nonlinearities of the AlGaAs material make this design suitable for high speed all-optical switching applications.

Figure6

Figure 7: Schematic of the Mach-Zehnder interferometer switch. (b) Scanning electron micrograph (SEM) of the W3 PhC waveguides.

Figure7

Figure 8: Time dependence of the nonlinear transmission spectra for (a) the ridge waveguide reference sample and (b) the three different types of PhC design. (c) Switching times of the three different types of PhC and the unpatterned ridge waveguide reference sample. (d) Power dependence of the transmission change.

Copyright (2009) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in (Appl. Phys. Lett. 95, 141108 )

References

  1. Control of spontaneous emission from InP single quantum dots in GaInP photonic crystal nanocavities
    I. J. Luxmoore, E. Daghigh Ahmadi, N. A. Wasley, A. M. Fox, A. I. Tartakovskii, A. B. Krysa, and M. S. Skolnick
    Applied Physics Letters 97 18 181104 (2010) http://link.aip.org/link/?APL/97/181104
  2. Splitting and lasing of whispering gallery modes in quantum dot micropillars
    B.D. Jones, M. Oxborrow, V.N. Astratov, M. Hopkinson, A. Tahraoui, M.S. Skolnick, and A.M. Fox
    Optics Express 18 21 22578 (2010) http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-21-22578
  3. Ultrafast all-optical switching in AlGaAs photonic crystal waveguide interferometers
    D. Szymanski, B. D. Jones, M. S. Skolnick, A. M. Fox, D. O'Brien, T. F. Krauss, and J. S. Roberts
    Applied Physics Letters 95 14 141108 (2009) http://link.aip.org/link/?APL/95/141108
  4. High Q Modes in Elliptical Microcavity Pillars
    D. M. Whittaker, P. S. S. GuimarĂ£es, D. Sanvitto, H. Vinck, S. Lam, A. Daraei, J. A. Timpson, A. M. Fox, M. S. Skolnick, Y. -L. D. Ho, J. G. Rarity, M. Hopkinson, and A. Tahraoui
    Applied Physics Letters 90 161105 (2007)
  5. Control of Polarization and Mode Mapping of Small Volume High Q Micropillars
    A. Daraei, D. Sanvitto, J. A. Timpson, A. M. Fox, D. M. Whittaker, and M. S. Skolnick, P. S. S. Guimaraes, H. Vinck, A. Tahraoui, P. W. Fry, S. L. Liew, and M. Hopkinson
    Journal of Applied Physics 102 043105 (2007)
  6. Whispering Gallery Resonances in Semiconductor Micropillars
    V. N. Astratov, S. Yang, S. Lam, B. D. Jones, D. Sanvitto, D. M. Whittaker, A. M. Fox, M. S. Skolnick, A. Tahraoui, P. W. Fry, M. Hopkinson
    Applied Physics Letters 91 071115 (2007)
  7. Mode structure of the L3 photonic crystal cavity
    A. R. A. Chalcraft, S. Lam, D. O'Brien, T. F. Krauss, M. Sahin, D. Szymanski, D. Sanvitto, R. Oulton, M. S. Skolnick, A. M. Fox, D. M. Whittaker, H.-Y. Liu, and M. Hopkinson
    Applied Physics Letters 90 241117 (2007) http://link.aip.org/link/?APL/90/241117
  8. Polarized Quantum Dot Emission from Photonic Crystal Nanocavities studied under Mode Resonant Excitation
    R. Oulton, B. D. Jones, S. Lam, A. R. A. Chalcraft, D. Szymanski, D. O'Brien, T. F. Krauss, D. Sanvitto, A. M. Fox, D. M. Whittaker, M. Hopkinson, M. S. Skolnick
    Optics Express 15 17221 (2007)
  9. Enhanced all optical tuning of leaky eigenmodes in photonic crystal waveguides
    A D Bristow, D Kundys, A Z Garcia-Deniz, J P Wells, A M Fox, M S Skolnick and D M Whittaker
    Optics Letters 31 2284 (2006)
  10. Control of the nonlinear carrier response time of AlGaAs photonic crystal waveguides by sample design
    P Murzyn, AZ Garcia-Deniz, DO Kundys, AM Fox, JPR Wells, DM Whittaker, MS Skolnick, TF Krauss and JS Roberts
    Applied Physics Letters 88 141104 (2006)
  11. Control of polarized single quantum dot emission in high quality factor microcavity pillars
    A. Daraei, A. Tahraoui, D. Sanvitto, J. A. Timpson, P. W. Fry, M. Hopkinson, P. S. S. Guimaraes, H. Vinck, D. M. Whittaker, M. S. Skolnick, and A. M. Fox
    Applied Physics Letters 88 051113 (2006)
  12. Observation of ultrahigh quality factor in a semiconductor microcavity
    D. Sanvitto, A. Daraei, T. A. Tahraoui, M. Hopkinson, P. W. Fry, D. M. Whittaker and M. S. Skolnick
    Applied Physics Letters 86 191109 (2005)
Last updated Thursday, 3rd January 2013