1. Obtención, caracterización y aplicaciones de dispositivos ópticos basados en nanoestructuras de silicio. PhD Thesis Defense Daniel Navarro Urrios Realisation, characterisation and applications of optical devices based on silicon nanostructures. Dpto. de Física Básica, Universidad de La Laguna

2. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 2/60 Outline General Introduction Amplification studies in planar waveguides based on oxidised porous silicon Form birefringence in Si-Nc planar waveguides Er coupled to Si-Nc optical amplifiers General conclusions

3. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 3/60 Outline General Introduction Amplification studies in planar waveguides based on oxidised porous silicon Form birefringence in Si-Nc planar waveguides Er coupled to Si-Nc optical amplifiers General conclusions

4. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 4/60 General introduction Silicon is the leading material for microelectronics. Huge processing technology (CMOS) infrastructure, process learning and capacity. In photonics it can do also well (waveguides, fast modulators, power splitters and combiners, tuneable optical filters, detectors…) It is the ideal plattform for integrating optical and electrical devices.

5. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 5/60 General introduction However Silicon is NOT an efficient light emitter, internal quantum efficiencies  int ~10 -6 Indirect band-gap Need for an optical amplifier and a signal generator (laser) based on Silicon

6. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 6/60 Different strategies to amplify light based on Silicon materials Dye-doped planar waveguides based on oxidised porous silicon Si-Nc in SiO 2 planar waveguides Er coupled to Si-Nc planar amplifiers

7. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 7/60 Outline General Introduction Amplification studies in planar waveguides based on oxidised porous silicon Form birefringence in Si-Nc planar waveguides Er coupled to Si-Nc optical amplifiers General conclusions

8. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 8/60 Porous silicon formation I HF Si time I Pore dimension 2... 50 nm It is luminiscent (quantum confinement) But hard to realise population inversion Effective refractive index (air + silicon) High absorption in the visible

9. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 9/60 Effect of thermal oxidation Partial oxidation T > 400ºC Natural oxidation Silicon SiO 2 Complete oxidation T > 800ºC Porous silica Densification T > 1000ºC (many hours) Bulk silica Consequences: It becomes transparent for the visible It becomes a passive material Porous structure maintained  good for impregnation We have still control of the refractive index (1.15<n<1.40) Low refractive indices (n  1.15), close to air  good cladding material for building waveguides

10. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 10/60 Planar waveguides Silicon (n=3.5) Core (Porous silicon, less porous, n  1.8) Cladding (Porous silicon, more porous, n  1.35) Core (Porous silica, less porous, n  1.3) Cladding (Porous silica, more porous, n  1.15) Silicon (n=3.5) After oxidation (900ºC, 3h) Cut this way: Cladding (Porous silicon, n  1.35) Silicon (n=3.5) Cladding (Porous silica, n  1.15) Silicon (n=3.5) After oxidation (900ºC, 3h) Core (PMMA-polymethylmethacrylate-,n  1.49) 1)Oxidised porous silicon waveguides 2)Polymeric waveguides with oxidized porous silicon cladding Two types PSW PMW core cladding Si substrate

11. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 11/60 Detector  nm m-line characterisation We can excite each of the modes supported by the planar waveguide Knowledge of the effective refractive indices of the supported modes

12. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 12/60 Nice agreement between experiments and simulations Modelling the waveguides parameters

13. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 13/60 Single-mode waveguides ( =) Single-mode waveguides ( =633nm) Core (500nm) Cladding (5-10  m) Silicon substrate 1) PSW Core (400nm) Cladding (5-10  m) Silicon substrate 2) PMW  TE  50%  TE  70%

14. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 14/60 Dye impregnation (Nile Blue-LC 6900) Chosen because it is quite robust when dried. Impregnation: PSW: 5 min inmersion of the waveguides in ethanol+dye solution PLW: Precursor PMMA solution mixed with the dye Pulsed pump at 532nm

15. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 15/60 Experimental setup Doubled Nd:YAG (532 nm, 5ns pulses) Cylindrical lens To monochromator and PMT Sample Guided PL setup if there is gain, the PL shape should narrow and grow superlinearly with power Spot size: ~3cm  300  m  10 cm lens

16. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 16/60 Guided PL vs Pump Power 1) PSW 2) PMW

17. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 17/60 Variable Stripe Length (VSL) L Amplified Spontaneous Emission (ASE) g depends on power! And passes from negative to positive values by increasing the pump flux

18. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 18/60 Guided PL vs Pump Power 1) PSW 2) PMW Net optical gain has been observed in both cases

19. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 19/60 Further studies on the impregnation of PSW Optical Fiber This signal is not travelling through the waveguide because putting a screen it disappears. Interferences N.A.<0.025 Observation of narrow and linearly polarised spectral peaks

20. 2 1 0 z1z1 z2z2 Incoherent emitters. Each emitter point can interfere only with itself. Collecting the light at 90º

21. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 21/60 z Silicon The first 200-300 nanometers are emitting much stronger

22. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 22/60 Possible explanations Could it be that the pump is being strongly attenuated through the structure? The contrast of the interferences is independent of the pumping wavelength. Also losses would be more than 10 5 cm -1 The concentration of dye in the first hundreds of nanometers is orders of magnitude higher than in the rest of the sample NO Decreasing concentration No dramatic reduction of the contrast

23. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 23/60 In this kind of samples we have observed net gain in the guided configuration. We believe that the main contribution to the gain is due to these first hundreds of nanometers, because we have built micro and macro-cavities and no amplification behaviors with pump power were observed when detecting normal to the sample.

24. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 24/60 Outline General Introduction Amplification studies in planar waveguides based on oxidised porous silicon Form birefringence in Si-Nc planar waveguides Er coupled to Si-Nc optical amplifiers General conclusions

25. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 25/60 Introduction 2 Courtesy of J. Linnros Si nanocrystals usual fabrication techniques

26. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 26/60 Introduction Usual growing techniques : Large size dispersion: Inhomogeneous broadening of the emission band Reduction of the stimulated emission efficiency (not all nanocrystals show optical gain). Courtesy of B. Garrido

27. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 27/60 The studied samples SiO 2 substrate, alternating layers of SiO and SiO 2 are grown by evaporation. After the annealing in N 2 at 1100ºC for 1h monodispersed Si-nanocrystals are formed in a waveguide configuration. Investigation of the waveguiding properties of these samples d SiO (nm)d SiO2 (nm) d SiO /(d SiO +d SiO2 ) Sample D550.50 Sample C450.44 Sample B350.38 Sample A250.29 Optical gain under pulsed pumping has been demonstrated in these samples M. Cazzanelli, D. Navarro-Urrios, et al. Journal of Applied Physics, 96, 3164 (2004).

28. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 28/60 M-line measurements (543nm-633nm) We are able to know the effective index of each mode for each wavelength measured Detector Prism Sample 543nm 633nm

29. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 29/60 Information extracted from m-line, TEM images and mode solver simulations -Thicknesses and number of periods of the SL (TEM images) -Dimension of each period (TEM images) -Effective modal indices (m-line)  Material refractive indices (simulations)

30. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 30/60 Information extracted from m-line, TEM images and mode solver simulations It is impossible to fit the extracted effective indices unless we assume a negative birrefringent structure. The origin of the observed birrefringence is found on the particular structure of the core, i.e., a multilayer periodic structure made of two different kind of layers of different refractive indexes. SiO x SiO 2 Isotropic SL Air “Form Birefringence” Material birefringence= n o >n e

31. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 31/60 Modellization of the structure Theoretical model for a superlattice d SiO2 +d NS =SL period n o and n e :ordinary and extraordinary refractive indices of the equivalent layer N w :number of Si-NC layers in the SL d SiO2 (n SiO2 ) and d NS (n NS ):thicknesses (refractive indexes) of the SiO 2 and nanocrystal single layers of the SL d t : total thickness of the SL n 1,d 1 n 2,d 2............ TE TM nono nene SiO x SiO 2 SL Air d NS, n NS ?

32. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 32/60 Results Unique solution!! 0.63

33. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 33/60 Results Waveguide BWaveguide CWaveguide D 633 nm543 nm633 nm543 nm633 nm543 nm n TE 1.462±0.0011.473±0.0011.476±0.0011.497±0.0011.519±0.0011.553±0.001 n TM 1.456±0.0021.463±0.0011.458±0.0011.471±0.0011.486±0.0011.518±0.001 B 0.006±0.0030.010±0.0020.018±0.0020.026±0.0020.033±0.0020.035±0.002  TE (%) 274244597281  TM (%) 32310355673 n SiOx 1.47551.47901.47551.47901.47551.4790 nono 1.564±0.0031.568±0.0021.600±0.0021.611±0.0021.621±0.0011.643±0.001 nene -1.567±0.0051.581±0.0041.596±0.0021.603±0.0011.624±0.001  (%) --0.5±0.5-1.1±0.3-1.0±0.3-1.1±0.1 d NS -2.2±0.3nm3.1±0.2 nm3.3±0.1nm4.4±0.1 nm Independent calculations …but the same d NS (independent of ) n NS (633nm)= 1.705 n NS (543nm)= 1.735

34. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 34/60 50nm Ion implanted samples with random distributed nanocrystals gave isotropic behavior n o =n e Other studied samples Similar samples growed by sputtering technique showed similar results N. Daldosso et al., Journal of Luminescence, 121, 2, 2006

35. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 35/60 Other studied samples Another type of material birefringence have been also studied Combination of m-line + transmission (linearly polarised light) measurements Reactive Si deposition method + annealing 1100ºC for 1h Vertical structures x y z nono nene  The Si-NC shape would be similar to the ellipsoid of indices

36. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 36/60 Other studied samples Reactive Si deposition method + annealing 1100ºC for 1h Non-perpendicular geometry between the Si beam axis and the substrate nxnx nznz nyny z y x  nene nono x y z We need TEM images for confirmation Transmission measurements M-line measurements

37. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 37/60 Outline General Introduction Amplification studies in planar waveguides based on oxidised porous silicon Form birefringence in Si-Nc planar waveguides Er coupled to Si-Nc optical amplifiers General conclusions

38. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 38/60 We want to improve Erbium (Er 3+ ) Usual EDFAs (Erbium doped Fiber Amplifier) (Erbium doped Fiber Amplifier)  abs  10 -21 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

39. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 39/60 Why Si-Nc? Broad band absorption (UV-VIS) Increment of excitation for Er 3+ :  exc from ~10 -21 (in SiO 2 ) to 10 -16 -10 -18 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

40. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 40/60 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+

41. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 41/60 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 ?

42. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 42/60 The samples Er:Si-nc produced by Reactive Magnetron co-Sputtering and successive annealing to get phase separation and reduction of non radiative defects Dep. conditions Annealing T F. Gourbilleau et al., JAP, 94, 3869 (2003) JAP 95, 3717 (2004). Si-substrate Si-nc doped Er 3+ (1  m) SiO 2 (2÷6  m ) SiO 2 (  m ) 800 nm Annealing time Waveguide sample Anneal ing time (min) Si excess (at. %) Er content (x10 20 cm -3 ) n  B6074±0.11.5450.51 C306-75.4±0.21.5160.48 D106-75.4±0.21.480.28 n increases with annealing time Optical litography and Reactive ion etching

43. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 43/60 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

44. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 44/60 Radiative lifetime determination Also, from Mc Cumber analysis: Local field effects prevail Medium field effects prevail

45. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 45/60 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

46. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 46/60 Total lifetime and cooperative up- conversion  d and C up

47. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 47/60 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 (~10 -21 cm 2 ), for samples B and C, resonant (488 nm) and non-resonant (476 nm) result in the same  exc

48. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 48/60 Excited Er 3+ vs pump flux Photon flux (ph/cm 2 s) …but Simulation Experimental

49. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 49/60 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 is then solved for each R Thus, by integrating over all the shells, we get the temporal dependence of the total excited state population. We have divided discretely the region around the Si-Nc into shells of different probability. The rate equation:

50. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 50/60 Simulations  d =3.8 ms, C up =2x10 -17 cm 3 s -1,  o =3x10 -16 cm 2,  d =5x10 -21 cm 2, R nc =4nm, R o =0.5nm, N NC =1x10 17 cm -3. And this means that only 2-3% of the whole erbium population can be excited trough transfer from Si-Nc. In any case it is about 10-100 excitable Er 3+ per Si-Nc Doing this for each flux we obtain…. Short range interaction

51. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 51/60 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.

52. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 52/60 INPUT OUTPUT PROBE PUMP Signal enhancement (Pump&Probe experimental setup)

53. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 53/60 Signal enhancement probe Signal from sample To detector Si substrate buffer SiO 2 Pump Probe SE>1 SE  1

54. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 54/60 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-60’0.121.25.40.61x10 22 (488nm) C-30’0.651.68.50.765x10 20 (488nm) D-10’0.452.07.50.561x10 21 (532nm)

55. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 55/60 Signal enhancement From maximum gain value: SampleMax N 2 /N Er B-60’11% C-30’9% D-10’7% …but only 1-3% is being excited thorugh transfer from the Si-Nc

56. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 56/60 Conclusions (about oxidised porous silicon waveguides) We have succeed in building two types of dye doped planar waveguides based on oxidised porous silicon (PSW and PMW) We have measured net optical gain around 700nm of about 9cm -1 (PSW) and 13 cm -1 (PMW) With these measurements we have demonstrated the feasibility of using an oxidised porous silicon material both as an embedding medium for other active substances and as an optimum cladding material for growing compact optical amplifiers We have characterised the dye infiltration goodness in the PSW by simulations of the oscillating signal detected travelling parallel to the sample surface. We have concluded that the upper part of the core (~200-300nm) has a much higher dye concentration, and it is indeed providing the measured optical gain.

57. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 57/60 Conclusions (about birefringence in Si-Nc planar waveguides) We have reported for the first time form birefringence phenomena in Si- Nc planar waveguides. In the case of the multilayer structures, we were able to simulate the experimental data with a theoretical model of parallel layers of different refractive indices. With this model, we have been able to evaluate different parameters (n o, n e, n NS ) and to make an upper limit estimation of the nanocrystals diameter (d NS ), which is in good agreement with nominal growing parameters and PL spectra.

58. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 58/60 Conclusions (about Er coupled to Si-Nc optical amplifiers) 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 0.6dB/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

59. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 59/60 Publications In scientific journals: 1.D. Navarro-Urrios, M. Melchiorri, N. Daldosso, L. Pavesi, C. García, P. Pellegrino, B. Garrido, G. Pucker, F. Gourbilleau and R.Rizk, “Optical losses and gain in silicon-rich Silica waveguides containing Er ions”, Journal of Luminescence, 121 249–255 (2006). 2.B. Garrido, C. García, P. Pellegrino, D. Navarro-Urrios, N. Daldosso, L. Pavesi, F. Gourbilleau, R. Rizk, “Distance dependent interaction as the limiting factor for Si nanocluster to Er energy transfer in silica”, Applied Physics Letters, 89, 163103 (2006). 3.C. J. Oton, D. Navarro-Urrios, N. E. Capuj, M. Ghulinyan, L. Pavesi, S. González- Pérez, F. Lahoz, and I. R. Martín, “Optical gain in dye-impregnated oxidized porous silicon waveguides”, Applied Physics Letters, 89, 011107 (2006). 4.N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, C. Sada, F. Gourbilleau and R. Rizk, “Refractive index dependence of the absorption and emission cross sections at 1.54 m m of Er 3+ coupled to Si nanoclusters”, Applied Physics Letters, 88, 161901 (2006). 5.K. Luterová, M. Cazzanelli, J.-P. Likforman, D. Navarro-Urrios, J. Valenta, T. Ostatnický, K. Dohnalová, S. Cheylan, P. Gilliot, B. Hönerlage, L. Pavesi, I. Pelant, “Optical gain in nanocrystalline silicon: comparison of planar waveguide geometry with a non-waveguiding ensemble of nanocrystals”, Optical Materials 27, 750–755 (2005). 6.K. Luterová, D. Navarro-Urrios, M. Cazzanelli, T. Ostatnický, J. Valenta, S. Cheylan, I. Pelant, and L. Pavesi, “Stimulated emission in the active planar optical waveguide made of silicon nanocrystals”, phys. stat. solidi (c), 2, No. 9, 3429-3434 (2005). 7.D. Navarro-Urrios, C. Pérez-Padrón, E. Lorenzo, N. E. Capuj, Z. Gaburro, C. J. Oton and L. Pavesi, “Structural and light-emission modification in chemically post-etched porous silicon”, phys. stat. sol. (a) 202, No. 8, 1518–1523 (2005). 8.E. Lorenzo-Cabrera, C. J. Oton, N. E. Capuj, M. Ghulinyan, D. Navarro-Urrios, Z. Gaburro, L. Pavesi, “Fabrication and optimization of rugate filters based on porous silicon”, phys. stat. sol. (c) 2, No. 9, 3227–3231 (2005). 9.V. Venkatramu, D. Navarro-Urrios, P. Babu, C.K. Jayasankar, V. Lavín, “Fluorescence line narrowing spectral studies of Eu 3+-doped lead borate glass”, Journal of Non- Crystalline Solids 351, 929–935 (2005). 10.E. Lorenzo, C. J. Oton, N. E. Capuj, M. Ghulinyan, D. Navarro-Urrios, Z. Gaburro, L. Pavesi “Porous silicon-based rugate filters”, Applied Optics, 44, 26 (2005). 11.D. Navarro-Urrios, F. Riboli, M. Cazzanelli, A. Chiasera, N. Daldosso, L. Pavesi, C. J. Oton, J. Heitmann, L. X. Yi, R. Scholz and M. Zacharias, “Birefingence characterization of mono-dispersed silicon nanocrystals planar waveguides”Optical Materials 27 (5) pp. 763-768 (2005). 12.N. Daldosso, D. Navarro-Urrios, M. Melchiorri, and L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato, “Absorption cross section and signal enhancement in Er-doped Si-nanocluster rib-loaded waveguides”, Applied Physics Letters, 86, 261103 (2005). 13.M. Cazzanelli, D. Navarro-Urrios, F. Riboli, N. Daldosso, L. Pavesi, J. Heitmann, L.X. Yi, R. Scholz, M. Zacharias, and U. Gösele, “Optical gain in mono-dispersed silicon nanocrystals”, Journal of Applied Physics, 96, 3164 (2004). 14.F. Riboli, D. Navarro-Urrios, A. Chiasera, N. Daldosso, L. Pavesi, C. J. Oton, J. Heitmann, L.X. Yi, R. Scholz and M. Zacharias, “Birefringence in optical waveguides made by silicon nanocrystal superlattices” Applied Physics Letters 85 (7) pp. 1268-1270 (2004). 15.D. Navarro-Urrios, N. Daldosso, L. Pavesi, C. García, P. Pellegrino, B. Garrido, F. Gourbilleau and R. Rizk, “Signal enhancement and limiting factors in waveguides containing Si Nanoclusters and Er 3+ ions”, submitted to Journal of Lightwave Technology. 16.N. Daldosso, D. Navarro-Urrios, M. Melchiorri, C. García, P. Pellegrino, B. Garrido, C. Sada, G. Battaglin, F. Gourbilleau, R. Rizk, L. Pavesi, “Er Coupled Si Nanocluster Waveguide”, to be published in IEEE- Journal of Selected Topics in Quantum Electronics. 17.C. J. Oton, D. Navarro Urrios, M. Ghulinyan, N. E. Capuj, S. González Pérez, F. Lahoz, I. R. Martín and L. Pavesi, “Optical gain in oxidized porous silicon waveguides impregnated with a laser dye”, accepted in Physica Status Solidi. 18.D. Navarro-Urrios, M. Ghulinyan, N. E. Capuj, C. J. Oton, F. Riboli, I. R. Martín and L. Pavesi, “Waveguiding, absorption and emission properties of dye- impregnated oxidized porous silicon”, submitted to Physica Status Solidi. 19.L. Khriachtchev, D. Navarro-Urrios, L. Pavesi, C. J. Oton, N. Capuj and S. Novikov, “Cut-off and m-line spectroscopy of silica layers containing Si nanocrystals: Experimental evidence of optical birefringence”, to be published in Journal of Applied Physics. 20.F. Lahoz, N. E. Capuj, D. Navarro-Urrios, and S. E. Hernández, "Optical amplification in Ho3+ - doped transparent oxyfluoride glass-ceramics at 750nm", submitted to Applied Physics Letters. 21.D. Navarro-Urrios, M. Ghulinyan, P. Bettotti, C. J. Oton, N. E. Capuj, F. Lahoz, I. R. Martin, and L. Pavesi, "Optical gain in dye-doped polymeric slab waveguides on silicon", submitted to Applied Physics Letters. Conference proceedings: 22.C. J. Oton, E. Lorenzo, N. Capuj, F. Lahoz, I. R. Martín, D. Navarro-Urrios, M. Ghulinyan, F. Sbrana, Z. Gaburro, L. Pavesi, “Porous silicon-based Notch filters and waveguides”Proceedings of SPIE, 5840, 434 (2005). 23.Pump-probe experiments on low loss silica waveguides containing Si nanocrystals, D. Navarro-Urrios, N. Daldosso, M. Melchiorri, F. Sbrana, L. Pavesi, C. García, B. Garrido, P. Pellegrino, J.R. Morante, E.Scheid and G. Sarrabayrouse, Mater. Res. Soc. Symp. Proc. Vol. 832, F10.11.1 (2005). 24.Pump-probe experiments on Er coupled Si-nanocrystals rib-loaded waveguides, N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato, Mater. Res. Soc. Symp. Proc. Vol. 832, F11.3.1 (2005). 25.D. Navarro-Urrios, C. Pérez-Padrón, E. Lorenzo, N. E. Capuj, Z. Gaburro, C. J. Oton and L. Pavesi, “Chemical etching effects in porous silicon layers”Proceedings of SPIE, 5118 pp. 109-115 (2003). Contributions to books: 26.“Nanostructured Silicon for Photonics - from Materials to Devices –“, Z. Gaburro, P. Bettotti, N. Daldosso, M. Ghulinyan, D. Navarro-Urrios, M. Melchiorri, F. Riboli, M. Saiani, F. Sbrana and L. Pavesi, Materials Science Foundations, Volume 27 until 28 (2006), ISBN 0-87849-488-x

60. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 60/60 Acknowledgements Finantial Support: European projects SINERGIA and LANCER. Dipartimento di Fisica della Università di Trento Istituto Nazionale per la Fisica della Materia, INFM Integrated Action Spain-Italy, 2004-2006 Special acknoledgements to C. J. Otón, L. Pavesi and N. Daldosso for some slides used in this presentation and to everybody that have collaborated in this research work. Thank you!

61. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 61/60

62. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 62/60

63. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 63/60 Silicon vs. III-V Direct band gap: efficiency –VCSEL 50% –LED 37%, potentially 50% –Tunability400nm -10 μm you choose! –Material and processing expensive –Integration with CMOS devices: costly, low yield, still difficult

64. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 64/60 Oxidised porous silicon waveguides (extra slides)

65. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 65/60 Amplification studies in planar waveguides based on oxidised porous silicon Dye doped oxidized porous silicon waveguides (PSW) Dye doped polymeric waveguides with oxidized porous silicon cladding (PMW)

66. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 66/60 Oxidized porous silicon planar waveguides. 1) Two layers of porous silicon. Core less porous than cladding to achieve light confinement. Different core thicknesses from 500nm to several  m and cladding of several  m. 2) Thermal annealing at 900ºC for 3 hours to completely oxidize the samples and avoid visible light absorption. 3) Impregnation with laser dye dissolved in ethanol. 0 4 8 12 16 (  m) 0 4 8 12 16 (  m) Core CladdingSilicon substrate

67. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 67/60 Detector  nm m-line characterisation After impregnation of the dye

68. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 68/60 core cladding Observation of narrow and linearly polarised spectral peaks N.A.=0.65

69. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 69/60 Also first 300-400nm main emitting region Thicker cladding

70. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 70/60 Decreasing from low to very low pump density powers At low pump power the dye is mainly in the fundamental state. The absorption is maximum and the ray emitted towards the bottom attenuates. No oscillations Oscillations

71. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 71/60 Could it be in the surface? We fit very well the data. Why optical gain. If it is in the surface the overlapping with the confined mode will be very low.

72. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 72/60 Future work SNOM characterization of the profile of dye concentration is in progress. 1D vertical photonic crystals. We have to achieve several microns with high dye concentration if we want to arrive to an eventual microcavity or impregnate a random photonic crystal. We will decrease the porosity of the high index layer although we will loose index contrast.

73. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 73/60 Birefringence extra slides

74. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 74/60 Sample D: The thicknesses of the uncrystallized layers are sufficiently small to neglect its effect on the effective index determination. Procedure (1) The extraordinary and ordinary refractive indexes are univocally extracted from the waveguide simulator software. Using these two values (no and ne) and applying the theoretical formulas we extracted the mean thickness (nanocrystal diameter) and refractive index of the nanocrystal layers (1.705 for the red line, 1.735 for the green one). In order to fit the other samples we will assume that the refractive index of the nanocrystal layers is independent of the sample.

75. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 75/60 Procedure (2) Samples C and B: We worked paralelly with a waveguide simulation software and the theoretical model to extract a unique solution for the parameters of the superlattice compatible with the m-line measurements Sample A: No guided modes were observed Ion implanted samples: No birrefringent behavior was observed, i.e. We can fit the m-line data assuming an isotropic model where n o = n e Check of the model

76. PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 76/60 Gain measurements Sample AWaveguide BWaveguide CWaveguide D g(cm -1 )-26±327±0.222±3-2±0.5 TR-VSL (time resolved variable strip length) measurements High positive optical gain under high pumping energy is observed in waveguides B and C A birefringent structure is not detrimental for the observation of optical gain.