Wavelength tunability in whispering gallery mode resonators Gerhard Schunk, Michael Förtsch, Josef Fürst, Dmitry Strekalov, Florian Sedlmeir, Harald Schwefel, Christoph Marquardt and Gerd Leuchs Max Planck Institute for the Science of Light, Institute for Optics, Information and Photonics, University Erlangen-Nuremberg, Erlangen, Germany Summer School on Quantum and Non-Linear Optics 2012

I. Whispering gallery mode (WGM) resonators ACOUSTICS OPTICS ring down timesup to  > 100 s bandwidth  < 10 kHz @ 1.55 m Savchenkov et al., Opt.Express, 15, 6768 (2007)  controllable bandwidth via coupling small mode volume broad transparency window B. Matsko and V. S. Ilchenko, IEEE J. Sel. Topics, vol. 12, no. 1, pp. 3–32 (2006) efficient propagation of acoustic waves

APPLICATIONS IN GENERAL I. Whispering gallery mode (WGM) resonators APPLICATIONS IN GENERAL narrowband photonic cavities (e.g. for filtering) sensors (e.g., bio-sensing, temp., pressure, ...) optical parametric oscillators (OPO) ... APPLICATIONS IN ERLANGEN Terahertz conversion, H. Schwefel group bio-sensing, F. Vollmer group three wave mixing in lithium niobate naturally phase-matched OPO, J. U. Fürst et al., PRL 104, 153901 (2010) and PRL 105, 263904 (2010) single-mode and two-mode squeezing, J. U. Fürst et al., PRL 106, 113901 (2011) single photon source, http://arxiv.org/pdf/1204.3056.pdf, submitted 2012 Optical Resonator Biosensors: Molecular Diagnostic and Nanoparticle Detection on an Integrated Platform (M. Baaske, F. Vollmer), In ChemPhysChem, Wiley Online Library, volume 13, 2012. [bib] [pdf]

I. Whispering gallery mode (WGM) resonators Maxwell equations yield eigenmodes with mode numbers q,l,m P. Debye, Ann. Physik, 30, 57 (1909) [1] spherical harmonics Ylm in angular directions l-m = 0 l-m = 1 l = 10 spherical Bessel functions Jl in radial direction M. Ornigotti, Phys. Rev. A 84, 013828 (2011)

II. Parametric down conversion in WGM resonators energy conservation phase matching one pump photon generates one signal and one idler photon

OVERLAP INTEGRAL II. Parametric down conversion in WGM resonators radial part angular part νs = ls –ms qi qs νi = li –mi Pth = 6.7 µW demonstrated J. U. Fürst et al., PRL 105, 263904 (2010) phase matching depends on spatial overlap fundamental modes (q=1, l-m = 0) overlap best

heralded signal-signal corr. II. Parametric down conversion in WGM resonators SINGLE PHOTON SOURCE VIA SPDC λidler= 1020 nm λsignal = 1120 nm heralded signal-signal corr. http://arxiv.org/pdf/1204.3056.pdf, submitted 2012 signal-idler corr.

III. Setup and experiment 532 nm WGM resonator is a 4.8 % MgO-doped z-cut lithium niobate crystal typ I phase matching (eoo) controlled via bias voltage and temperature no active locking

wavelength tuning over 100 nm and mode-hop free tuning over 150 MHz! III. Setup and experiment first demonstation of tunability of our system: http://arxiv.org/pdf/1204.3056.pdf, submitted 2012 wavelength tuning over 100 nm and mode-hop free tuning over 150 MHz!

TEMPERATURE TUNING IV. Recent results T = 96,8°C λidler= 810 nm WGR λidler= 810 nm 1405 nm 1550 nm OSA measurement

FURTHER TUNING PARAMETERS IV. Recent results FURTHER TUNING PARAMETERS reducing disk size changing Mg concentration demonstration of coupling to a radius = 0.3 mm disk

V. Summary and Outlook SUMMARY PDC in WGM resonators is tunable over more than 300 nm demonstration of PDC up to λsignal=1540 nm and λidler = 812 nm fabrication and coupling to small discs (e.g. r = 0.3 mm) THANK YOU Outlook investigate the whole parameter space of tuning couple this single photon source to other quantum systems (quantum dots, atomic clouds, optomechanical resonators, etc.)