Four wave mixing and parametric amplification in Si-nano waveguides using reverse biased pnjunctions for carrier removal E-Mail: petermann@tu-berlin.de
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 4 2 3 4 1 1
Joint Lab Silicon Photonics Head: Dr. Lars Zimmermann IC technology Photonics Silicon Photonics Prof. Bernd Tillack Prof.
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. 597-607, August 2013 C. Koos et al.; Nature Photon. Vol. 3, pp. 216 219, April 2009 c-si-nanowire (crystalline) 300 a-si-nanowire (amorphous) 1200 C. Grillet et. al.; Optics Express, vol. 20,pp. 22609-22615. 2012 3
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 ~ 0.5 1 cmgw -1 Free carrier absorption due to TPA 4
Limitations due to Two-Photon-Absorption For telecom wavelengths @ 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 shift @ 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
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, 2006 2 W. Mathlouthi et al., Opt. Express 16, 2008 3 M.A.Foster et al., Opt. Express 15, 2007 4 J. R. Ong et al., IEEE PTL. 25, 1699-1701 (2013) 5 Q. Lin et al., Opt. Express 15, 2007 6 R. Claps et al., Opt.Express 11, 2003 7 M. Krause et al., Opt. Express.12, 2004 6
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
Structure geometry 8
Electric field distribution Higher slab allowes higher field in the waveguide region A. Gajda et al., Opt. Express, vol. 19, pp. 9915 9922, May 2011
FCA vs Bias voltage for different slab heights Shallower etch Lower loss A. Gajda et al., Opt. Express, vol. 19, pp. 9915 9922, May 2011 Intensity 1.65 10 8 W/cm 2 w i = 1200 nm
Carriers screening effect simulation shallower etch depth higher carrier screening threshold A. Gajda et al., Opt. Express, vol. 19, pp. 9915 9922, May 2011
Photo current due to TPA with reversed pin junction H. Tian et al., JEOS:RP, Aug. 2012 12
Estimated FWM conversion gain from simulations α=0.5db/cm and waveguide length L=8cm 13
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 ~ - 2000 ps/nm km 14
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 10 17 cm -3 500 nm p i n 1,2 um Andrzej Gajda 15
Four Wave Mixing measurement setup 16
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, 11721-11726 (2006) (*) J. R. Ong et al., IEEE PTL. 25, 1699-1701 (2013) 17
Waveguides without p-i-n Pump wavelength λ pump = 1552.5 nm Signal wavelength λ signal = 1550.0 nm Maximum efficiency -23 db @ P pump = 26 dbm Waveguide lengths L = 1cm and L = 4 cm A. Gajda et al., Opt. Express, vol. 20, pp. 13100 13107, June 2012 18
FWM in p-i-n diode assisted waveguide Pump wavelength λ pump = 1552.5 nm Signal wavelength λ signal = 1550.0 nm Conversion efficiency η max ~-2 db @ P pump = 26 dbm Waveguide length L = 4 cm A. Gajda et al., Opt. Express, vol. 20, pp. 13100 13107, June 2012 19
Wavelength conversion vs. detuning for different pump wavelengths -0.7 db this work -4.4 db Ong et.al., UC San Diego 2013-5.5 db Malouthi et. al., Intel 2008-8.5 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. 13100 13107, June 2012 20
Bit Error Rate (BER) Measurement setup 40 Gb/s NRZ OOK DC BIAS SIGNAL 1550.5 nm MZM PC DUT OBPF PRE AMPLIFIED RECEIVER PUMP 1552.0 nm EDFA OBPF PC Pump power in the waveguide : 20 dbm Signal power in the waveguide :0 dbm 21
FWM Conversion spectrum & Bit Error Rate Bias [V] CE [db] No junction - 26.9 0-9.5 20-4.6 Power [dbm] 20 0-20 -40 Input 20V bias 0V bias w/o junction -4.6 db -9.5 db -60 1549 1550 1551 1552 1553 1554 1555 Wavelength [nm] A. Gajda et al., Group IV Photonics 2013 22
Measured bandwidth of FWM 3 db bandwidth of 10 nm Estimated dispersion of the waveguide D = -2450 ps/nmkm η 0L contains incoupling loss of 4 db per coupler Conversion Efficiency [db] 0-10 -20-30 -40 η 0L sim η 0L meas η LL sim η LL meas 1540 1545 1550 1555 1560 1565 Signal wavelength [nm] A. Gajda et al., Group IV Photonics 2013 23
Bit-Error Rate measurement Back to back Idler 0V bias Idler 20V bias w/o junction -log(ber) -4-5 -6-7 B2B Signal, 20V bias Idler, 20V bias Idler, 0V bias -8-9 -32-30 -28-26 -24-22 -20-18 P rec [dbm] The power penalty of 0.2 db for idler in the 20V bias case A. Gajda et al., Group IV Photonics 2013 24
Phase sensitive amplification set up Power [dbm] 0-10 -20-30 -40 CW -50 1547.8 1548.8 1549.8 1550.8 1551.8 Wavelength [nm] DC BIAS PM OPTICAL PROCESSOR EDFA PC Si WAVEGUIDE OSA F. Da Ros et al., ECOC 2013 25
Phase sensitive amplification Results Power [dbm] 10 0-10 -20-30 -40-50 a) Input Output max Output min -60 1549.35 1549.6 1549.85 1550.1 1550.35 1550.6 1550.85 Wavelength [nm] 15.5 db Phase Sensitive Gain [db] -10-12 -14-16 -18-20 -22-24 4 cm w/ junction -26 2 cm w/ junction -28 1 cm w/ junction 4 cm w/o junction b) -30 0 45 90 135 180 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 2013 26
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 SFB787. 27