Sharp resonance of multimode periodic waveguide open resonator defined in SOI Ph.D student: Nikolay Piskunov Supervisor: Henri Benisty Institut d’Optique Graduate School, Laboratoire Charles Fabry, Palaiseau, 91127, France Acknowledgement: IMEC/EpixFab P.Dumon EDOM 2011, March 1

Outline  Broad wg resonators  Theory  critical coupling  Realisation  SoI (EpixFab)   Measurement first results Overall scope : nonlinear optics in structured materials and "on-chip" resonators 2

Resonators & open resonators Fabry-Perot microring(s)/ CROW access/exit guide ~ Gaussian beam Single mode PhC wg...microtores Delicate coupling Broad waveguide resonator H. Benisty, Photon. Nanostruct. Fundam. Applic., 7, 115 (2009). 3

Broad waveguides : minigap clusters Dielectric wgSingle-side corrugated wg Modes interaction Regions: aligned gaps kzkz normalized freq. a/ Brillouin zone edge 4 Free Spectral Range π/a

Critical mode coupling Bunch of modes shaped into very flat bands Light does several local round-trips at each bounce v g ~ 0 far around band edge Large finesse and high Q-factor of resonator,  Fabry-Perot, but opened. 5

h T4 Order m =50 w=5 μm Order m =75 w=7.5 μm a=384 nm h/a= 2.75, 3.00, 3.25, 3.50, 4.00 Realisation on SoI (EpixFab, IMEC) wg width Grating couplers : near-vertical coupling In our case : Lens coupling (50 mm) SoI neff (TE)  2.80 slow light 6 Grating in T6 T8 w W-h Modeling TARGET Grating out Dif. length of device

7 FDTD simulation based on SEM picture Predicted target (triangular shape) Sample best result “bottle shape” Critical Coupling Region Peak Q Results are presented in log scale! Normalized Frequency, a/λ Normalized depth, h/a Region of h/a values in exp. devices PhotonDesign software was used

IN out about 500 µ 30 µm grating coupler OUT grating coupler EpixFab sample (Pieter Dumon, Ghent) 6 mm h/  ~3.00 Device overview

Spectra T(l) acquired by triggered 2D- camera + image analysis Wavelength, nm Y-Pixel number Intensity transmission spectra obtained from Y –  image anlaysis to discard spurious signals from nearby wg's at  y  fieldsimulation 10 µm actual SEM image Tunable laser 2D camera Trig T4 DEVICE Grating out Grating in captSept17_T8_m50_1100uWF_hoa350_18ms_ Y 20 pixels

Analyzing m=50 T4 waveguides x4 x2 h/a=4 h/a=3.5 h/a=3.25 h/a=3 h/a=2.75 Q= 300 Q> Transmission (shifted), arb.un. Single FP Wavelength, nm FSR Theory: λ/m=31 nm (no dispersion) Exp: 25 nm (n group ~1.2 n phase )

x1.5 x2 Analyzing m=50 T8 waveguides h/a=4 h/a=3.5 h/a=3.25 h/a=3 h/a=2.75 Q=750 Q= Triple FP resonator behavior Wavelength, nm Exp. FSR 26 nm Transmission (shifted), arb.un.

Comparison between experimental and calculated results Double FP resonator FSR Calculation was performed using transfer matrices method taking into account wg’s dispersion Width 7.5 nm FSR ~ 15 nm

Nonlinear effects in corrugated waveguides Self-phase modulation (SPM) - process of phase-change of pulse propagating in the medium with nonlinear refractive index Δφ=n 2 ω 0 /c*I 0 *L Δφ>2π Photon energy SignalPumpIdler Optical Parametric Oscillator … & dispersion Even spacing Uneven spacing Q~4000 Finesse f=Q/m=80 Enhancement ~f 2 around I 0 ~10 7 J/cm 2

Conclusion  "Critical coupling" applied to SoI structure  Good in/out coupling maintained at high Q  Periodic waveguide looks like multiple FP  Promising for NLO (SPM&OPO)  Q ~4000 attained (measurements still ongoing) 14

Thank you for attention! 15

Questions x4 x2 16

x4 x2 Questions 17