Signal enhancement and limiting factors in waveguides containing Si nanoclusters and Er 3+ ions D. Navarro Urrios, N. Daldosso, L. Ferraioli, F. Gourbilleau, R. Rizk, P. Pellegrino, B. Garrido and L. Pavesi

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas2/20 Introduction to the system under study. Characterisation and modelling of the studied samples. Signal enhancement setup and measurements. Conclusions Outline

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas3/20 We want to improve Erbium (Er 3+ ) Usual EDFAs (Erbium doped Fiber Amplifier) (Erbium doped Fiber Amplifier) abs cm 2 abs cm 2 Expensive pumping source (resonant, intense and coupled) by using Si substrate buffer SiO 2EDWA (Erbium doped Waveguide Amplifier) By taking advantage of the coupling between Si-nc and Er 3+ ions between Si-nc and Er 3+ ions Introduction x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas4/20 Why Si-nc? Broad band absorption (UV-VIS) Increment of excitation for Er 3+ : exc from ~ (in SiO 2 ) to cm 2 (with Si-nc) Fast (~ 1 s) and efficient (~55%) energy transfer from Si-nc to Er 3+ Possibility of electrical pumping Higher index contrast for light confinement CMOS compatibility

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas5/20 Excitons: Steady state: N exc 4 I 15/2 4 I 13/2 4 I 11/2, 4 I 9/2 Er 3+ Introduction N exc : density of excitons N NC : total density of Si-nc NC : absorption cross section : intrinsic lifetime of the exciton k t : average coupling rate C ind : percentage of Er 3+ coupled to Si-nc Exciton generation and strong Auger Intrinsic recombination Transfer to Er 3+

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas6/20 Absorption and stimulated emission term Important for pump and probe measurements N exc N1N1 N2N2 Er 3+ Excitation term De-excitation mechanisms Introduction abs, em, exc, d, C up ?

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas7/20 Dep. conditions Annealing T The samples Er:Si-nc produced by Reactive Magnetron co-Sputtering and successive annealing to get phase separation and reduction of non radiative defects Si-substrate Si-nc doped Er 3+ (1 m) SiO 2 (2÷6 m ) SiO 2 ( m ) 800 nm Annealing time Waveguide Sample Annealing time (min) Si excess (at. %) Er content (x10 20 cm -3 ) n A24073 ± B6074± C ± D ± n increases with annealing time Optical litography and Reactive ion etching F. Gourbilleau et al., JAP, 94, 3869 (2003) JAP 95, 3717 (2004). N Si-nc 1x10 17 cm -3

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas8/20 Determination of abs and em Mc Cumber relation: From transmission measurements abs and em abs and em similar to that of Er 3+ in SiO 2 5dB/cm Decreasing with annealing time

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas9/20 Total lifetime and cooperative up-conversion Quantitative measurements of the photon flux emitted from the samples. It is so possible to correlate the number of emitted photons with N 2

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas10/20 Total lifetime and cooperative up-conversion d and C up Decreases with annealing time Increases with annealing time

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas11/20 Excitation cross section at low pump power exc …but seems to be flux dependent, the slope is changing with increasing pump flux exc is orders of magnitude higher than that of Er 3+ in pure silica (~ cm 2 ), for samples B and C, resonant (488 nm) and non-resonant (476 nm) result in the same exc

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas12/20 Excited erbium population vs photon flux Population inversion

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas13/20 Modelling Model for exc Er 3+ ions near the Si-nc are efficiently coupled to them, whereas Er 3+ ions far away behave more and more as Er 3+ in SiO 2 that can be excited only directly. We consider that the first Er to be excited and therefore the strongest coupled would be the closest to the Si-nc The coupling diminishes with the distance R nc RoRo

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas14/20 Simulations d =3.8 ms, C up =2x cm 3 s -1, o =3x cm 2, d =5x cm 2, R nc =4nm, R o =0.5nm, N NC =1x10 17 cm -3. Doing this for each flux we obtain…. Short range interaction And this means that only 2-3% of the whole erbium population can be excited trough transfer from Si-nc. The rest can only be excited directly because simply it is too far In any case it is about excitable Er 3+ per Si-nc

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas15/20 INPUT OUTPUT PROBE PUMP Signal enhancement (Pump&Probe experimental setup)

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas16/20 Signal enhancement probe Signal from sample To detector Si substrate buffer SiO 2 Pump Probe SE>1 SE 1 Internal gain = g

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas17/20 Signal enhancement SampleMax SE (dB/cm) Propagation Losses (dB/cm) Absorption Losses (dB/cm) Max internal gain (CA corrected) (dB/cm) needed (ph/cm 2 s) B x10 22 (488nm) C x10 20 (488nm) D x10 21 (532nm)

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas18/20 Signal enhancement From maximum gain value: SampleMax N 2 /N Er B-6011% C-309% D-107% …but only 2-3% is being excited thorugh transfer from the Si-nc

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas19/20 Conclusions We have measured and quantified reliable values for: Absorption and emission cross sections Total lifetimes and cooperative up-conversion coefficients Effective excitation cross sections at low pump power Indirectly excitable Er 3+ population through Si-nc energy transfer (2-3% of the Er 3+ concentration) Using a pump and probe technique we have demonstrated values of internal gains of around 0.7dB/cm We still have to optimize the Si-nc:Er 3+ ratio and the characteristics of the Si-nc in order to excite the whole Er population through indirect energy transfer

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas20/20 THANK YOU!

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas21/20

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas22/20

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas23/20 As much Er 3+ as possible (avoiding up-conversion phenomena, N Er 4-5 x cm -3 ) Enough Si-nc to excite all the Er 3+ ions Good modal confinement Low waveguide losses (not that due to absorption of Er 3+ ) Gain favouring Gain limiting Up-conversion (shifts the pump threshold for population inversion towards higher pump energies) Excited state absorption Non radiative de-excitation (Auger de-excitation with a nearby exciton) Carrier absorption in Si-nc (decreases the signal and blocks the transfer to Er ions)

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas24/20 Propagation losses at 1600nm Losses at 1600 nm are essentially propagation losses of the rib loaded waveguide

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas25/20 Radiative lifetime determination Also, from Mc Cumber analysis: Local field effects prevail Medium field effects prevail

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas26/20 Excited Er 3+ vs pump flux Photon flux (ph/cm 2 s) …but Simulation Experimental

D. Navarro-Urrios, Microtechnologies for the New Millenium 2007, 2-4 May, Maspalomas27/20 Around 96% of the total volume of the sample is occupied by Er 3+ that are only excitable through direct photon excitation, because simply they are too far from a Si-nc.