Four wave mixing and parametric amplification in Si-nano waveguides using reverse biased pnjunctions

Transcription

1 Four wave mixing and parametric amplification in Si-nano waveguides using reverse biased pnjunctions for carrier removal

2 Acknowledgements A.Gajda 1, G.Winzer 1, L.Zimmermann 2, H.Tian 2, B.Tillack 1,2,T.Richter 3, R. Elschner 3, C.Schubert 3 F. Da Ros 4, D. Vukovic 4, C. Peucheret

3 Joint Lab Silicon Photonics Head: Dr. Lars Zimmermann IC technology Photonics Silicon Photonics Prof. Bernd Tillack Prof.

4 Waveguides for Kerr-related nonlinear signal processing Material Nonlinear coefficient γ [W -1 m -1 ] HNLF 0.02 SiN 1.4 SOH (Silicon-organic-hybrid) 100 D.J. Moss et al.; Nature Photon.,vol.7, pp , August 2013 C. Koos et al.; Nature Photon. Vol. 3, pp , April 2009 c-si-nanowire (crystalline) 300 a-si-nanowire (amorphous) 1200 C. Grillet et. al.; Optics Express, vol. 20,pp

5 c-si for Kerr-related nonlinear signal processing positive High nonlinearity γ ~ 300 W -1 m -1 Low loss down to α ~ 0.3 db/cm 100m HNLF 1cm Si nanowire negative Two photon absorption β TPA ~ cmgw -1 Free carrier absorption due to TPA 4

6 Limitations due to Two-Photon-Absorption For telecom 1.55 µm Absorption α TPA = β TPA P/A eff due to β TPA negligible up to ~ 100 mw pump power Removal of free carriers essential (otherwise only pulsed operation) Maximum nonlinear phase 1.55 µm φ NL = γ P L eff < γ P / α TPA = φ NL,max φ NL,max = A eff γ /β TPA =2π FOM ~ 3 rad allowing for maximum parametric gain ~ 5 db (Δβ=0).15 db (opt. anom. disp.) 5

7 Several optical nonlinear effects in SOI waveguides were observed: Four Wave Mixing (FWM) 1,2,3,4 Self Phase Modulation (SPM) 5 Cross Phase Modulation (XPM) 5 Spontaneous and Stimulated Raman Scattering (SRS) 6,7 Applications utilizing nonlinear effects: Amplification of light Parametric wavelength conversion 1 Y. Kuo et al., Opt. Express 14, W. Mathlouthi et al., Opt. Express 16, M.A.Foster et al., Opt. Express 15, J. R. Ong et al., IEEE PTL. 25, (2013) 5 Q. Lin et al., Opt. Express 15, R. Claps et al., Opt.Express 11, M. Krause et al., Opt. Express.12,

8 Efficient four-wave mixing with CW pump Request: High light confinement Low linear propagation loss Low (anomalous) dispersion of the waveguide Low nonlinear loss: Two photon absorption (TPA) TPA induced free carriers absorption (FCA) Solution: use small waveguides crosssection reduce sidewall roughness use special design of the waveguide pulsed operation go to Mid-Infra-Red (MIR) use p-i-n diode 7

9 Structure geometry 8

10 Electric field distribution Higher slab allowes higher field in the waveguide region A. Gajda et al., Opt. Express, vol. 19, pp , May 2011

11 FCA vs Bias voltage for different slab heights Shallower etch Lower loss A. Gajda et al., Opt. Express, vol. 19, pp , May 2011 Intensity W/cm 2 w i = 1200 nm

12 Carriers screening effect simulation shallower etch depth higher carrier screening threshold A. Gajda et al., Opt. Express, vol. 19, pp , May 2011

13 Photo current due to TPA with reversed pin junction H. Tian et al., JEOS:RP, Aug

14 Estimated FWM conversion gain from simulations α=0.5db/cm and waveguide length L=8cm 13

15 SiO 2 cladding Chromatic Dispersion Si 3 N 4 cladding W W s H Si SiO 2 SiO 2 s H Si Si 3 N 4 SiO 2 actual dispersion ~ ps/nm km 14

16 Fabrication Used technology : BiCMOS (IHP Frankfurt (Oder)) 8 SOI wafers, 220 nm top Si layer and 2 μm buried oxide (BOX) Linear loss lower than 1 db/cm for waveguides with 50 nm slab and p-i-n diode Doping level in p and n regions of cm nm p i n 1,2 um Andrzej Gajda 15

17 Four Wave Mixing measurement setup 16

18 Conversion efficiency two definitions Signal input to Idler output ratio η = P P idler signal ( L) ( ) (*) 0 used in theoretical investigation (*) includes the gain-loss properties of waveguide Signal output to Idler output ratio η = P P idler signal ( L) ( ) (**) L used in experimental work (**) easy to measure (using Optical Spectrum Analyzer) (**) Y. Kuo et al. Opt. Express 14, (2006) (*) J. R. Ong et al., IEEE PTL. 25, (2013) 17

19 Waveguides without p-i-n Pump wavelength λ pump = nm Signal wavelength λ signal = nm Maximum efficiency -23 P pump = 26 dbm Waveguide lengths L = 1cm and L = 4 cm A. Gajda et al., Opt. Express, vol. 20, pp , June

20 FWM in p-i-n diode assisted waveguide Pump wavelength λ pump = nm Signal wavelength λ signal = nm Conversion efficiency η max ~-2 P pump = 26 dbm Waveguide length L = 4 cm A. Gajda et al., Opt. Express, vol. 20, pp , June

21 Wavelength conversion vs. detuning for different pump wavelengths -0.7 db this work -4.4 db Ong et.al., UC San Diego db Malouthi et. al., Intel db Kuo et. al., Intel 2006 Waveguide length L = 4 cm Bias voltage: U bias = 20 V Pump power P pump = 26 dbm Maximum efficiency η max (λ pump =1542nm, Δλ=3nm)=-0.7 db A. Gajda et al., Opt. Express, vol. 20, pp , June

22 Bit Error Rate (BER) Measurement setup 40 Gb/s NRZ OOK DC BIAS SIGNAL nm MZM PC DUT OBPF PRE AMPLIFIED RECEIVER PUMP nm EDFA OBPF PC Pump power in the waveguide : 20 dbm Signal power in the waveguide :0 dbm 21

23 FWM Conversion spectrum & Bit Error Rate Bias [V] CE [db] No junction Power [dbm] Input 20V bias 0V bias w/o junction -4.6 db -9.5 db Wavelength [nm] A. Gajda et al., Group IV Photonics

24 Measured bandwidth of FWM 3 db bandwidth of 10 nm Estimated dispersion of the waveguide D = ps/nmkm η 0L contains incoupling loss of 4 db per coupler Conversion Efficiency [db] η 0L sim η 0L meas η LL sim η LL meas Signal wavelength [nm] A. Gajda et al., Group IV Photonics

25 Bit-Error Rate measurement Back to back Idler 0V bias Idler 20V bias w/o junction -log(ber) B2B Signal, 20V bias Idler, 20V bias Idler, 0V bias P rec [dbm] The power penalty of 0.2 db for idler in the 20V bias case A. Gajda et al., Group IV Photonics

26 Phase sensitive amplification set up Power [dbm] CW Wavelength [nm] DC BIAS PM OPTICAL PROCESSOR EDFA PC Si WAVEGUIDE OSA F. Da Ros et al., ECOC

27 Phase sensitive amplification Results Power [dbm] a) Input Output max Output min Wavelength [nm] 15.5 db Phase Sensitive Gain [db] cm w/ junction cm w/ junction cm w/ junction 4 cm w/o junction b) Input Signal Phase [deg] Spectra at the input and output for maximum and minimum gain (4 cm waveguide) Phase-sensitive gain versus signal phase (45 mw pump power per pump) F. Da Ros et al., ECOC

28 Conclusions Si-nanowires with reverse biased pin-junction suitable for FWM and parametric amplification despite TPA Wavelength conversion efficiencies up to 0.7 db Phase sensitive gain with ER=15 db Pump powers in the order of 100 mw are sufficient Further improvements expected with suitable dispersion tailoring This work was co-funded by the German Research Foundation (DFG) in the framework of SFB