Sharp resonance of multimode periodic waveguide open resonator defined in SOI

1. 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, 07-08 March

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

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

4. Broad waveguides : minigap clusters Dielectric wg Single-side corrugated wg Modes interaction Regions: aligned gaps 0.5 Free Spectral Range normalized freq. a/l Brillouin zone edge 0 0 π/a 0 1 kz

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

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

7. FDTD simulation based on SEM picture 5 4.5 Peak Q Region of h/a values in exp. devices Normalized depth, h/a 4 Predicted target (triangular shape) CriticalCoupling Region Sample best result “bottle shape” 2 PhotonDesign software was used Normalized Frequency, a/λ Results are presented in log scale!

8. captSept17_T8_m50_1100uWF_hoa350_18ms_ 45 50 field simulation 55 60 1520 1530 1540 1550 1560 1570 1580 0.2 0.15 0.1 0.05 0 -0.05 1520 1530 1540 1550 1560 1570 1580 Spectra T(l) acquired by triggered 2D-camera + image analysis 20 pixels Y-Pixel number Grating in actual SEM image T4 DEVICE Intensity Tunable 10 µm laser Grating out Trig 2D camera 1520 1580 Wavelength, nm transmission spectra obtained from Y – l image anlaysis to discard spurious signals from nearby wg's at ±Dy. Y

9. 3 2.5 2 1.5 1 x2 0.5 x4 0 1520 1530 1540 1550 1560 1570 1580 Analyzing m=50 T4 waveguides Single FP Transmission (shifted), arb.un. FSR h/a=4 Q= 300 Theory: λ/m=31 nm (no dispersion) Exp: 25 nm (ngroup ~1.2 nphase) h/a=3.5 h/a=3.25 h/a=3 Q>1000 h/a=2.75 Wavelength, nm

10. 3.5 2.5 2 1.5 1 x1.5 0.5 x2 0 1520 1530 1540 1550 1560 1570 1580 Analyzing m=50 T8 waveguides Transmission (shifted), arb.un. Triple FP resonator behavior Q=750 h/a=4 Exp. FSR 26 nm h/a=3.5 h/a=3.25 h/a=3 Q=4000 h/a=2.75 Wavelength, nm

11. Comparison between experimental and calculatedresults Double FP resonator FSR FSR + + + - Width 7.5 nm FSR ~ 15 nm Calculation was performed using transfer matrices method taking into account wg’s dispersion

12. Nonlinear effects in corrugated waveguides Self-phase modulation (SPM)- process of phase-change of pulse propagating in the medium with nonlinear refractive index Δφ=n2ω0/c*I0*L Δφ>2π Enhancement ~f2 around 65000 I0 ~107 J/cm2 Q~4000 Finesse f=Q/m=80 Optical Parametric Oscillator … & dispersion Signal Pump Idler Even spacing Uneven spacing Photon energy

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

14. Thank youfor attention!

15. 3 2.5 2 1.5 1 x2 0.5 x4 0 1520 1530 1540 1550 1560 1570 1580 Questions

16. 3 2.5 2 1.5 1 x2 0.5 x4 0 1520 1530 1540 1550 1560 1570 1580 Questions