Coupled spherical cavities
This project was initiated in 2003 in attempt to develop Coupled Resonator Optical Waveguides (CROWs) [1] formed by spherical dielectric cavities with sizes in 2-30 mm range. We experimentally studied optical transport due to coupling between WGMs in disordered chains of polystyrene microspheres [2] and theoretically investigated WGM transport in microcylinder CROWs [3]. Most recently we observed novel types of optical modes and new mechanisms of optical transport in such structures. These include experimental observation of nanojet-induced modes [4] theoretically predicted [5] by Z. Chen et al., observation of quasi-WGMs and Fano resonances in size-mismatched bispheres [6,7] and observation of percolation of WGMs [8] in 3D lattices of coupled spherical cavities. In this project we develop theory and technology of such circuits of microspheres as well as new device concepts of lasers, tunable optical delay lines, microspectrometers and sensors based on coupled microspheres. This research is funded by ARO and NSF.
References
[1] A. Yariv, Y.Xu, R.K. Lee, and A. Scherer, “Coupled-resonator optical waveguide: A proposal and analysis”, Opt. Lett. 24, 711-713 (1999).
[2] V.N. Astratov, J.P. Franchak, and S.P. Ashili, “Optical coupling and transport phenomena in chains of spherical dielectric microresonators with size disorder”, Appl. Phys. Lett. 85, 5508-5510 (2004).
[3] S. Deng, W. Cai, and V. N. Astratov, “Numerical study of light propagation via whispering gallery modes in microcylinder coupled resonator optical waveguides”, Opt. Express 12, 6468-6480 (2004).
[4] A.M. Kapitonov and V.N. Astratov, “Observation of nanojet-inducing modes with small propagation losses in chains of coupled spherical cavities”, Opt. Lett. 32, 409-411 (2007).
[5] Z. Chen, A. Taflove, and V. Backman, “Highly efficient optical coupling and transport phenomena in chains of dielectric microspheres”, Opt. Lett. 31, 389-391 (2006).
[6] A. V. Kanaev, V. N. Astratov, and W. Cai, “Optical coupling at a distance between detuned spherical cavities”, Appl. Phys. Lett. 88, 111111 (2006).
[7] S.P. Ashili, V.N. Astratov, and E.C.H. Sykes, “The effects of inter-cavity separation on optical coupling in dielectric bispheres”, Opt. Express 14, 9460-9466 (2006).
[8] V.N. Astratov and S.P. Ashili, “Percolation of light in 3D lattices of spherical cavities with coupled whispering gallery modes”, to be submitted to Appl. Phys. Lett. (2007).
Pillar microcavities
In 2006 jointly with our long standing collaborator, Low Dimensional Structures and Devices (LDSD) group from the University of Sheffield, UK, we observed WGMs in AlAs/GaAs pillar microcavities [1]. These modes are interesting due to their high Q-factors (up to 20000) and small modal volumes ~0.1 mm3 allowing efficient coupling with single near-surface quantum dots in micropillars. These investigations of coherent light-matter coupling through a single mode of high-Q microcavity have become an important area of fundamental studies in quantum cavity electrodynamics with potential applications [2] in quantum information processing and in developing single photon sources. Some advantages of WGMs in comparison with previously studied “photonic dot” states [3-5] in micropillars will be used in our future work to achieve strong coupling between individual photonic and electronic states.
Reference
[1] V.N. Astratov, S. Yang, S. Lam, D. Sanvitto, A. Tahraoui, D.M. Whittaker, A.M. Fox, and M.S. Skolnick, “Observation of whispering gallery resonances in circular and elliptical semiconductor pillar microcavities”, to be submitted to Appl. Phys. Lett.. (2007).
[2] J.M. Gerard and B. Gayral, “InAs quantum dots: artificial atoms for solid-state cavity-quantum electrodynamics”, Physica E 9, 131-139 (2001).
[3] J.M. Gerard, D. Barrier, J.Y. Marzin, R. Kuszelewicz, L. Manin, E. Costard, V. Thierry-Mieg, and T. Rivera, “Quantum boxes as active probes for photonic microstructures: The pillar microcavity case”, Appl. Phys. Lett. 69, 449-451 (1996).
[4] J.P. Reithmaier, M. Röhner, H. Zull, F. Schäfer, A. Forchel, P.A. Knipp, and T.L. Reinecke, “Size dependence of confined optical modes in photonic quantum dots”, Phys. Rev. Lett. 78, 378-381 (1997).
[5] D. Sanvitto, A. Daraei, A. Tahraoui, M. Hopkinson, P.W. Fry, D.M. Whittaker and M.S. Skolnick, “Observation of ultrahigh quality factor in a semiconductor microcavity”, Appl. Phys. Lett. 86, 191109 (2005).
Polycrystalline opals
In 1995 a group from Ioffe Institute, St.-Petersburg, Russia, launched synthetic opals [1] as novel 3D photonic crystals for visible light. This work stimulated world-wide interest in inverted and functional opals for years to come. For photonic crystal applications the presence of domains in self-assembled opals is usually considered as a disadvantage. However the scattering properties of polycrystalline opals are rather interesting [2] and can be used in a completely different application connected with developing spatio-spectral diversity filters [3] for multimode spectroscopy. In this project jointly with DISP group from Duke University and with a group from JINR in Russia we study scattering properties of opals with artificially enhanced polycrystallinity for applications in mitimode spectrometers.
References
[1] V.N. Astratov, V.N. Bogomolov, A.A. Kaplyanskii, A.V. Prokofiev, L.A. Samoilovich, S.M. Samoilovich, and Y.A. Vlasov, “Optical spectroscopy of opal matrices with CdS embedded in its pores: quantum confinement and photonic band gap effects”, Nuovo Cimento 17, 1349-1354 (1995).
[2] V.N. Astratov, A.M. Adawi, S. Fricker, M.S. Skolnick, D.M. Whittaker, and P.N. Pusey, “Interplay of order and disorder in the optical properties of opal photonic crystals”, Phys. Rev. B 66, 165215 (2002).
[3] Z. Xu, Z. Wang, M.E. Sullivan, D.J. Brady, S.H. Foulger, and A. Adibi, “Multimodal multiplex spectroscopy using photonic crystals”, Opt. Express 11, 2126-2133 (2003).