Sharp resonance of multimode periodic waveguide open resonator defined in SOI

Ph.D student: Nikolay PiskunovSupervisor: Henri Benisty

Institut d’Optique Graduate School, Laboratoire Charles Fabry, Palaiseau, 91127, France

Acknowledgement: IMEC/EpixFab P.Dumon

EDOM 2011, 07-08 March1

Outline

Broad wg resonators

Theory critical coupling

Realisation SoI (EpixFab)

Measurement first results

Overall scope : nonlinear optics instructured materials and "on-chip" resonators

2

Resonators & open resonators

Fabry-Perot

microring(s)/CROW

access/exit guide

~ Gaussian beam

Single mode PhCwg

...microtores

Delicate coupling

Broad waveguide resonator

H. Benisty, Photon. Nanostruct. Fundam. Applic., 7, 115 (2009).3

Broad waveguides : minigap clustersDielectric wg Single-side corrugated wg

Modes interactionRegions: aligned gaps

kz

nor

mal

ized

fre

q. a

/

Brillouin zone edge

4

FreeSpectralRange

00 1

0.5

0 π/a

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.

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 couplingIn our case : Lens coupling (50 mm)

SoI neff (TE) 2.80

slowlight

6

Gratin

g i

n

T6 T8

w

W-h

Modeling TARGET

Gratin

g o

ut

Dif. length of device

wnm 24

7

FDTD simulation based on SEM picture

Predicted target(triangular shape)

Sample best result “bottle shape”

CriticalCouplingRegion

Results are presented in log scale!Normalized Frequency, a/λ

5

4.5

4

2

Region of h/a values in exp. devices

PhotonDesign software was used

Spectra T(l) acquired by triggered 2D-camera + image analysis

Wavelength, nm

transmission spectra obtainedfrom Y – image anlaysisto discard spurioussignals from nearby wg's at y

field simulation

10 µm

actual SEM image

Tunablelaser

2D cameraTrig

T4 DEVICE

Grating out

Grating in

captSept17_T8_m50_1100uWF_hoa350_18ms_

1520 1530 1540 1550 1560 1570 1580

45

50

55

60

1520 1530 1540 1550 1560 1570 1580-0.05

0

0.05

0.1

0.15

0.2

9

Y

20 pixels

1520 1580

Analyzing m=50 T4 waveguides

1520 1530 1540 1550 1560 1570 15800

0.5

1

1.5

2

2.5

3

x4

x2

h/a=4

h/a=3.5

h/a=3.25

h/a=3

h/a=2.75

Q= 300

Q>1000

10

Single FP

Wavelength, nm

FSRTheory: λ/m=31 nm(no dispersion)Exp: 25 nm(ngroup ~1.2 nphase)

1520 1530 1540 1550 1560 1570 15800

0.5

1

1.5

2

2.5

3.5

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=4000

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Triple FP resonator behavior

Wavelength, nm

Exp. FSR 26 nm

Comparison between experimental and calculated results

12

++

+-

Double FP resonator

1520 1530 1540 1550 1560 1570 1580

0,0

0,1

0,2

0,3

0,4

Tra

nsm

issi

on, ar

b.u

n.

Wavelength, nm

m75 T6 h/a=3.25 calculation

FSR FSR

Calculation was performed using transfer matrices method taking into account wg’s dispersion

Width 7.5 nmFSR ~ 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=n2ω0/c*I0*L

Δφ>2π

Photon energy

Signal Pump Idler

Optical Parametric Oscillator … & dispersion

Even spacing

Uneven spacing

Q~4000Finesse f=Q/m=80

Enhancement ~f2 around 65000I0 ~107 J/cm2

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 youfor attention!

15

Questions

1520 1530 1540 1550 1560 1570 15800

0.5

1

1.5

2

2.5

3

x4

x2

16

15201530154015501560157015800

0.5

1

1.5

2

2.5

3

x4

x2

Questions

17