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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 14, Iss. 25 — Dec. 11, 2006
  • pp: 12151–12162
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Nanocluster sensitized erbium-doped silicon monoxide waveguides

T. J. Clement, R. G. DeCorby, N. Ponnampalam, T. W. Allen, A. Hryciw, and A. Meldrum  »View Author Affiliations


Optics Express, Vol. 14, Issue 25, pp. 12151-12162 (2006)
http://dx.doi.org/10.1364/OE.14.012151


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Abstract

We describe the fabrication and characterization of micron-scale buried strip waveguides with erbium-doped (~ 1 at. %) silicon monoxide (SiO) cores and SiO2 and polymer claddings. In spite of large core-cladding index offset (Δn~0.4), propagation loss is as low as ~ 1 dB/cm. The crosssection for the 4I13/2 to 4I15/2 erbium transition was estimated as ~10-20 cm2, a factor of 2 to 3 higher than in silica glass. The annealed core material contains a high density of amorphous silicon nanoclusters, which act as efficient broadband sensitizers for erbium. Both a traditional copropagating pump (980 nm wavelength) configuration and a transverse pump (532 nm wavelength, < 10 W/cm2) configuration were tested. In either case, free carrier absorption loss is the dominant pump-induced mechanism and approximately 15–20 % of the erbium population is invertible.

© 2006 Optical Society of America

1. Introduction

There has recently been extensive research [1–9

1. A. J. Kenyon, C. E. Chryssou, C. W. Pitt, T. Shimizu-Iwayama, D. E. Hole, N. Sharma, and C. J. Humphreys, “Luminescence from erbium-doped silicon nanocrystals in silicon: excitation mechanisms,” J. Appl. Phys. 91, 367–374 (2002). [CrossRef]

] on the sensitization of rare-earth ions (especially erbium) by silicon nanoclusters (SiNC). SiNC typically exhibit a strong absorption cross-section for pump light in the visible region, and can efficiently transfer this energy to nearby Er ions [3–5

3. F. Priolo, G. Franzó, D. Pacifici, V. Vinciguerra, F. Iacona, and A. Irrera, “Role of the energy transfer in the optical properties of undoped and Er-doped interacting Si nanocrystals,” J. Appl. Phys. 89, 264–272 (2001). [CrossRef]

]. This has raised hopes for Er doped waveguide amplifiers and lasers in a silicon-compatible material, transversely pumped by broadband sources such as LED arrays [10

10. J. H. Shin, J. Lee, H.-S. Han, J.-H. Jhe, J. S. Chang, S.-Y. Seo, H. Lee, and N. Park, “Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs,” IEEE J. Sel. Top. Quantum Electron 12, 783–796 (2006). [CrossRef]

]. Both crystalline and amorphous SiNC can act as sensitizers, but there is some evidence that small [2

2. M. Fujii, K. Imakita, K. Watanabe, and S. Hayashi, “Coexistance of two different energy transfer processes in SiO2 films containing Si nanocrystals and Er,” J. Appl. Phys. 95, 272–280 (2004). [CrossRef]

, 10

10. J. H. Shin, J. Lee, H.-S. Han, J.-H. Jhe, J. S. Chang, S.-Y. Seo, H. Lee, and N. Park, “Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs,” IEEE J. Sel. Top. Quantum Electron 12, 783–796 (2006). [CrossRef]

] and amorphous [11

11. G. Franzo, S. Boninelli, D. Pacifici, F. Priolo, F. Iacona, and C. Bongiorno, “Sensitizing properties of amorphous Si clusters on the 1.54-µm luminescence of Er in Si-rich SiO2,” Appl. Phys. Lett. 82, 3871–3873 (2003). [CrossRef]

] SiNC are best in terms of maximizing Er luminescence efficiency. Motivated by the latter, we have investigated the properties of relatively low temperature annealed (~500 C) silicon monoxide (SiO) films doped with Er (Er:SiO) [12

12. A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, “Photoluminescence from Erdoped silicon oxide microcavities,” Opt. Mater. 28, 873–878 (2006). [CrossRef]

]. Bulk SiO is believed to be an inherently phase-separated material [13–15

13. A. Hohl, T. Wieder, P. A. van Aken, T. E. Weirich, G. Denninger, M. Vidal, S. Oswald, C. Deneke, J. Mayer, and H. Fuess, “An interface clusters mixture model for the structure of amorphous silicon monoxide (SiO),” J. Non-Crystalline Sol. 320, 255–280 (2003). [CrossRef]

], with nanometer-scale amorphous domains of Si, SiO, and SiO2. Some of us have recently reported [16

16. J. Wang, X. F. Wang, Q. Li, A. Hryciw, and A. Meldrum, “The microstructure of SiO thin films: from nanoclusters to nanocrystals,” Phil. Mag, in press (2006).

] that annealed SiO films contain these same 3 phases, with their relative ratio determined mainly by annealing temperature. The photoluminescence (PL) of Er:SiO films is optimized at an annealing temperature of ~ 500 C [12

12. A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, “Photoluminescence from Erdoped silicon oxide microcavities,” Opt. Mater. 28, 873–878 (2006). [CrossRef]

], and the films contain a high density (~1019 cm-3) of amorphous SiNC with a mean diameter ~ 2.8 nm. As a host material, these films exhibit efficient SiNC-mediated excitation of Er in agreement with similar work by Roberts et al. [17

17. S. W. Roberts, G. J. Parker, and M. Hempstead, “The Photoluminescence of Erbium-doped Silicon Monoxide,” Opt. Mater. 6, 99–102 (1996). [CrossRef]

].

There have been numerous studies concerning PL optimization of Er-SiNC systems (as cited above), but considerable uncertainty remains with respect to the optimization of waveguide devices [18–22

18. H.-S. Han, S.-Y. Seo, J. H. Shin, and N. Park, “Coefficient determination related to optical gain in erbiumdoped silicon-rich silicon oxide waveguide amplifier,” Appl. Phys. Lett. 81, 3720–3722 (2002). [CrossRef]

] based on these materials. Moreover, the underlying material properties that enabled early reports [10

10. J. H. Shin, J. Lee, H.-S. Han, J.-H. Jhe, J. S. Chang, S.-Y. Seo, H. Lee, and N. Park, “Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs,” IEEE J. Sel. Top. Quantum Electron 12, 783–796 (2006). [CrossRef]

, 18

18. H.-S. Han, S.-Y. Seo, J. H. Shin, and N. Park, “Coefficient determination related to optical gain in erbiumdoped silicon-rich silicon oxide waveguide amplifier,” Appl. Phys. Lett. 81, 3720–3722 (2002). [CrossRef]

] of gain in transversely pumped Er:SiNC amplifiers have yet to be fully explained or independently reproduced. Some of the key research questions are summarized as follows:

  1. For some SiNC sensitized materials [18–19

    18. H.-S. Han, S.-Y. Seo, J. H. Shin, and N. Park, “Coefficient determination related to optical gain in erbiumdoped silicon-rich silicon oxide waveguide amplifier,” Appl. Phys. Lett. 81, 3720–3722 (2002). [CrossRef]

    ], an enhanced cross-section for the 4I13/2 to 4I15/2 Er transition was reported. More recently, no enhancement of this kind was found [20

    20. N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato, “Absorption cross section and signal enhancement in Erdoped Si nanocluster rib-loaded waveguides,” Appl. Phys. Lett. 86, 261103 (2005). [CrossRef]

    , 23

    23. H. Mertens, A. Polman, I. M. P. Aarts, W. M. M. Kessels, and M. C. M. van de Sanden, “Absence of the enhanced intra-4f transition cross section at 1.5 µm of Er3+ in Si-rich SiO2,” Appl. Phys. Lett. 86, 241109 (2005). [CrossRef]

    ]. The required processing conditions and the physical basis for an enhanced cross-section are not fully understood [10

    10. J. H. Shin, J. Lee, H.-S. Han, J.-H. Jhe, J. S. Chang, S.-Y. Seo, H. Lee, and N. Park, “Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs,” IEEE J. Sel. Top. Quantum Electron 12, 783–796 (2006). [CrossRef]

    ].
  2. There is ongoing debate with respect to the optimal densities of Er and SiNC. In particular, the fraction of Er ions that can be non-resonantly pumped via the SiNCs (the so-called excitable fraction) is a subject of much current interest. In several studies spanning a wide range of Er concentration [5–6

    5. P. G. Kik and A. Polman, “Exciton-erbium interactions in Si nanocrystal-doped SiO2,” J. Appl. Phys. 88, 1992–1998 (2000). [CrossRef]

    , 19

    19. P. G. Kik and A. Polman, “Gain limiting processes in Er-doped Si nanocrystals waveguides in SiO2,” J. Appl. Phys. 91, 534–536 (2002). [CrossRef]

    , 24–27

    24. D. Kuritsyn, A. Kozanecki, H. Przybylinska, and W. Jantsch, “Defect-mediated and resonant optical excitation of Er3+ ions in silicon-rich silicon oxide,” Appl. Phys. Lett. 83, 4160–4162 (2003). [CrossRef]

    ], only a few percent of the Er could be non-resonantly pumped. Possible explanations for this limitation include inhomogeneous upconversion (pairinduced quenching) [5–6

    5. P. G. Kik and A. Polman, “Exciton-erbium interactions in Si nanocrystal-doped SiO2,” J. Appl. Phys. 88, 1992–1998 (2000). [CrossRef]

    ], non-linear depopulation mechanisms (Auger deexcitation by SiNC, homogeneous upconversion, excited state absorption, etc.) [4

    4. D. Pacifici, G. Franzo, F. Priolo, F. Iacona, and L. D. Degro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys. Rev. B 67, 245301-1–13 (2003). [CrossRef]

    , 19

    19. P. G. Kik and A. Polman, “Gain limiting processes in Er-doped Si nanocrystals waveguides in SiO2,” J. Appl. Phys. 91, 534–536 (2002). [CrossRef]

    , 27

    27. C. J. Oton, W. H. Loh, and A. J. Kenyon, “Er3+ excited state absorption and the low fraction of nanocluster-excitable Er3+ in SiOx,” Appl. Phys. Lett. 89, 031116 (2006). [CrossRef]

    ], and the short-range nature of the SiNC to Er energy transfer mechanism [26

    26. P. Pellegrino, B. Garrido, J. Arbiol, C. Garcia, Y. Lebour, and J. R. Morante, “Site of Er ions in silica layers codoped with Si nanoclusters and Er,” Appl. Phys. Lett. 88, 121915 (2006). [CrossRef]

    ].
  3. It is well known [4

    4. D. Pacifici, G. Franzo, F. Priolo, F. Iacona, and L. D. Degro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys. Rev. B 67, 245301-1–13 (2003). [CrossRef]

    , 19–21

    19. P. G. Kik and A. Polman, “Gain limiting processes in Er-doped Si nanocrystals waveguides in SiO2,” J. Appl. Phys. 91, 534–536 (2002). [CrossRef]

    ] that carrier-induced absorption (free or confined carrier absorption, FCA or CCA) can be the dominant pump-induced mechanism in SiNC materials. Negation of FCA/CCA effects through semiempirical optimization of the film synthesis procedure, along with optimization of SiNC and Er densities, has been reported [10

    10. J. H. Shin, J. Lee, H.-S. Han, J.-H. Jhe, J. S. Chang, S.-Y. Seo, H. Lee, and N. Park, “Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs,” IEEE J. Sel. Top. Quantum Electron 12, 783–796 (2006). [CrossRef]

    ]. In most Er:SiNC systems [19–21

    19. P. G. Kik and A. Polman, “Gain limiting processes in Er-doped Si nanocrystals waveguides in SiO2,” J. Appl. Phys. 91, 534–536 (2002). [CrossRef]

    ], however, FCA/CCA appears to be a serious impairment.

While silicon monoxide has been proposed as a low-loss guiding medium for the near infrared [17

17. S. W. Roberts, G. J. Parker, and M. Hempstead, “The Photoluminescence of Erbium-doped Silicon Monoxide,” Opt. Mater. 6, 99–102 (1996). [CrossRef]

], to our knowledge this is the first experimental study of SiO waveguides. Using waveguides fabricated in the Er:SiO system (described in the introductory paragraph), we have conducted experiments aimed at assessing the basic properties of SiO as a waveguide core material, as well as addressing the Er:SiNC research questions outlined above.

2. Waveguide fabrication and characterization

The synthesis of Er:SiO films has been described in detail elsewhere [12

12. A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, “Photoluminescence from Erdoped silicon oxide microcavities,” Opt. Mater. 28, 873–878 (2006). [CrossRef]

]. Briefly, thin films were deposited by thermal evaporation of bulk SiO from a baffled box source. Er was incorporated via concurrent electron-beam evaporation of erbium oxide (Er2O3). Deposition of the separate materials was monitored via separate quartz-crystal thickness monitors. The as-deposited films are nearly stoichiometric SiO [16

16. J. Wang, X. F. Wang, Q. Li, A. Hryciw, and A. Meldrum, “The microstructure of SiO thin films: from nanoclusters to nanocrystals,” Phil. Mag, in press (2006).

], and for the present work some films were doped with 1–2 at. % Er as estimated from relative deposition rates.

To facilitate optimization and interpretation of the transverse pumping experiments described below, the band edge absorption was estimated directly from normal incidence transmittance data [Fig. 1(a)] for SiO films on glass substrates. For an amorphous medium, the optical (Tauc) gap typically corresponds to the point at which the absorption coefficient attains 1000 cm-1 [28

28. J. M. Gonzalez-Leal, R. Prieto-Alcon, J. A. Angel, and E. Marquez, “Optical properties of thermally evaporated amorphous As40S60-xSex films,” J. Non-Crystalline Sol. 315, 124–143 (2003). [CrossRef]

]. For the present material, this occurs at a wavelength of ~575 nm; ie. the Tauc gap is ~2.2 eV. Using the technique developed by Swanepoel [28

28. J. M. Gonzalez-Leal, R. Prieto-Alcon, J. A. Angel, and E. Marquez, “Optical properties of thermally evaporated amorphous As40S60-xSex films,” J. Non-Crystalline Sol. 315, 124–143 (2003). [CrossRef]

], the index of refraction was extracted in the near infrared region [Fig. 1(b)]. Note that the results were almost identical for undoped and Er-doped films. The solid curve is a fit based on the single oscillator Wemple-DiDomenico model [28

28. J. M. Gonzalez-Leal, R. Prieto-Alcon, J. A. Angel, and E. Marquez, “Optical properties of thermally evaporated amorphous As40S60-xSex films,” J. Non-Crystalline Sol. 315, 124–143 (2003). [CrossRef]

], using the values E0=5.4 eV and Ed=14.3 eV for the model parameters. As is typical [28

28. J. M. Gonzalez-Leal, R. Prieto-Alcon, J. A. Angel, and E. Marquez, “Optical properties of thermally evaporated amorphous As40S60-xSex films,” J. Non-Crystalline Sol. 315, 124–143 (2003). [CrossRef]

], E0 is approximately 2.5x the optical gap. The refractive index at 1550 nm (n~1.94) was confirmed using a prism-coupling technique on slab waveguides and is similar to values reported for SiO in the literature [29

29. G. Haas and C. Salzberg, “Optical Properties of Silicon Monoxide in the Wavelength Region from 0.24 to 14.0 Microns,” J. Opt. Soc. Am. 44, 181–187 (1954). [CrossRef]

]. High index contrast waveguides and cavities can thus be realized using SiO as a core material in combination with standard SiO2 and polymer cladding materials.

Fig. 1. (a). Transmittance versus wavelength for an SiO film on glass annealed at 500 C. Inset: Absorption coefficient versus wavelength near the band edge. Periodic oscillation above 500 nm is due to Fabry-Perot interference effects. (b). Refractive index versus wavelength for the same SiO film. The solid curve is a Wemple-DiDomenico fit as described in the text.

Two types of SiO-based waveguides were fabricated. For the first set, the fabrication process was similar to that described in Ref. [30

30. Y. Ago, B. Boulard, M. Couchaud, I. Vasilief, S. Guy, C. Duverger, and B. Jacquier, “Preparation by PVD of Er/Ce-doped PZG fluoride glass channel waveguide for integrated optical amplifiers at 1.5 µm,” Opt. Mater. 28, 195–199 (2006). [CrossRef]

] and the sequence of steps is shown in Fig. 2. Silicon wafers were cleaned in a piranha solution and then placed in a wet thermal oxidation furnace to grow ~ 300 nm of SiO2. CHF3-based reactive ion etching was then used to pattern the SiO2 layer. Using the patterned SiO2 as an etch mask, high aspect ratio ribs were etched into the silicon in an inductively coupled plasma reactive ion etch (ICPRIE) chamber (Oxford Plasmalab 100). A cryogenic etch recipe based on sulfur hexafluoride (SF6) and oxygen (O2) process gases was employed [31

31. M. J. de Boer, J. G. E. Gardeniers, H V. Jansen, E. Smulders, M.-J. Gilde, G. Roelofs, J. N. Sasserath, and M. Elwenspoek, “Guidelines for Etching Silicon MEMS Structures Using Fluorine High-Density Plasmas at Cryogenic Temperatures,” J. Microelectromechanical Sys. 11, 385–401 (2002). [CrossRef]

]. Without removing the SiO2 etch mask, the wafers were again placed in a thermal oxidation furnace to grow a thicker SiO2 layer (~1.4 µm) for undercladding purposes. As shown in Figs. 2(b) and (c), and of key importance for realization of low loss waveguides, the ribs exhibit little roughness after this oxidation step. This was followed by deposition of either SiO or Er:SiO. Owing to the verticality of the rib structures, the evaporated film grows preferentially on the horizontal surfaces atop and between the ribs. A relatively thin and porous film forms on the sides of the ribs. This resulted in isolated regions of dense SiO or Er:SiO (~0.65 µm thick) atop the ribs; each of these regions becomes the core of a rectangular strip waveguide. Cleaved pieces (~2 cm side length) of the wafers were subjected to an optimized annealing process (500°C for 1 hour in a mixed atmosphere of hydrogen and nitrogen [12

12. A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, “Photoluminescence from Erdoped silicon oxide microcavities,” Opt. Mater. 28, 873–878 (2006). [CrossRef]

]), and then a benzocyclobetene (BCB) polymer (Cyclotene, Dow Chemical) upper cladding was spun-cast over the waveguides to improve mechanical durability and to reduce scattering losses. These pieces were further cleaved to produce waveguides of different length (~3–10 mm). The end facet of a completed waveguide is shown in Fig. 2(d). Due to their high core-cladding index contrast, the waveguides are predicted to support multiple propagation modes. However, even the widest guides (~6 µm) exhibited predominately single-mode behavior as described below. We speculate that the higher order modes are greatly attenuated by sidewall scattering and leakage into the silicon rib.

The second set of waveguides was fabricated using a more conventional approach. Briefly, silicon wafers were thermally oxidized to form a SiO2 undercladding (~2 µm thick) and then deposited with ~ 1 µm of Er:SiO and annealed as above. A thin (~20 nm) SU-8 negative photoresist layer was spun-cast, patterned, and developed to form strip-loaded waveguides. Although the SU-8 loading strips are very thin, these guides exhibited twodimensional confinement and single mode behavior (not shown). For both sets of guides, pieces free of upper cladding were kept aside to enable elemental analysis (by electron microprobe analysis) of the Er:SiO layer. Most of the results below pertain to the buried strip waveguides of 6 µm nominal width, which consistently exhibited the lowest overall insertion loss amongst both sets.

Fig. 2. (a)-(d) SEM micrographs showing the sequence of steps in the fabrication of buried strip waveguides (a) End facet view of a tall rib etched in silicon. (b) End facet view of a rib after thermal oxidation. The protrusions near the upper edges of the SiO2 evolve as a result of leaving the SiO2 mask from the silicon etch step. (c) SEM image of the structure in (b), but from a different angle. (d) End facet view of the final waveguide structure, after Er:SiO core and BCB upper cladding deposition.

Fig. 3. (a). Near field profile (as simulated using OptiBPM) of the fundamental TE guided mode for a buried strip waveguide. The geometry of the simulated waveguide is overlaid. (b). The experimental near field mode profile obtained from a buried strip waveguide with nominally the same dimensions as in part (a). A wavelength of 1300 nm was used in both cases.

Several conventional methods for measuring propagation loss were considered. However, it was difficult to consistently realize high quality facets by cleaving because of the small chip sizes available (limited by the dimensions of the annealing furnace). As a result, Fabry-Perot and cutback techniques were deemed impractical. Analysis of light scattered from the top of the waveguides was also attempted, but results were not reliable because of the random distribution and size of scattering defects. Thus, an insertion loss method [32

32. G. Tittelbach, B. Richter, and W. Karthe, “Comparison of three transmission methods for integrated optical waveguide propagation loss measurement,” Pure Appl. Opt. 2, 683–700 (1993). [CrossRef]

] was used to approximate propagation losses. Similar to above, output light was collected using an objective lens and delivered to an iris-covered detector or a CCD camera. By measuring the transmitted power with and without the waveguide sample in place, the overall insertion loss of a waveguide was estimated. Index matching fluid was used to minimize reflections, so that most of the loss is attributable to input coupling loss and propagation loss. By simply subtracting the previously determined coupling loss from the overall loss, a first-order estimate of the propagation loss is obtained. To be conservative, we used the theoretically predicted coupling loss (4.4 dB for the 6 µm waveguides) in all calculations. This measurement was performed on dozens of buried strip waveguides, yielding fairly consistent results. Table 1 lists results for 6 of the lowest loss waveguides measured. Because the samples are short and have relatively low loss, there is considerable error (approximately +/- 1 dB/cm [32

32. G. Tittelbach, B. Richter, and W. Karthe, “Comparison of three transmission methods for integrated optical waveguide propagation loss measurement,” Pure Appl. Opt. 2, 683–700 (1993). [CrossRef]

]) inherent to these estimates.

Table 1. Propagation loss at a wavelength of 1300 nm, estimated by subtracting theoretical coupling loss from experimental insertion losses. Results shown are representative of the lowest loss buried strip waveguides measured, with core width 6 µm, and for TE polarized input light. Coupling loss of 4.4 dB was assumed in all cases.

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In general, waveguides that exhibited higher loss also exhibited obvious scattering defects, reflecting the experimental nature of the process. Loss was higher for narrower waveguides, likely due to sidewall scattering. In all cases loss was higher for TM polarized light. This can be attributed to higher leakage into the silicon rib through the relatively thin lower cladding. In fact, the leakage loss contribution was estimated theoretically to be >0.1 dB/cm and >0.3 dB/cm for the TE and TM fundamental modes, respectively. It is expected that further refinement of fabrication processes could result in SiO-based waveguides with even lower losses. These results suggest that SiO is a promising material for high index contrast, low-loss waveguides operating in the near infrared.

3. Spectroscopic analysis

Fig. 4. (a). Transmission scans for strip loaded and buried strip waveguides, corrected for system response and referenced to 1620 nm. (b). The estimated absorption cross-section spectrum for a buried strip guide (6 µm core width), extracted from the data in (a). Also shown is the estimated emission cross-section spectrum, based on experimental photoluminescence data and scaled using the Fuchtbauer-Ladenburg expression.

Table 2. Peak 4I15/2 to 4I13/2 absorption cross-sections estimated for the two different types of waveguides studied. For the buried strip guides, different core widths (4-6 µm) produced slightly different estimates within the range indicated. This might be due in part to the presence of higher order modes in wider guides.

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Waveguide PL spectra were collected for both transverse and co-propagating pump arrangements (see below). The emission cross-section spectrum can be extracted from the PL spectrum using the Fuchtbauer-Ladenberg expression [33

33. E. Desurvire, “Erbium-doped fiber amplifiers: basic physics and characteristics,” in Rare-Earth-Doped Fiber Lasers and Amplifiers, M. J. F. Digonnet, ed., (Marcel Dekker, Inc., New York, 2001).

]:

σ21(λ)=λP48πcn2τradΔλeffIPL(λ),
(1)

4. Optical pumping

As mentioned above, we have previously described [12

12. A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, “Photoluminescence from Erdoped silicon oxide microcavities,” Opt. Mater. 28, 873–878 (2006). [CrossRef]

] non-resonant pumping of Er ions in SiO. To assess the feasibility of Er:SiO for waveguide amplifiers, experiments were conducted using either a transverse or a co-propagating pump beam. The transverse pump source was a frequency-doubled Nd-YAG laser operating at 532 nm, where the SiO films have an absorption length ~ 4 µm. This ensures fairly uniform pumping of the entire depth of the SiO core material. Also, the polymer upper claddings are transparent at 532 nm. The pump laser was focused to a line with 1/e 2 beam widths ~250 µm and ~4 mm, as measured using a beam profiler.

The focused green light was used to pump 4 mm long buried strip waveguides, resulting in reasonably uniform pump intensity along the entire length of the guide. Neutral density filters were placed in the beam line to control the pump intensity. For simplicity, the beam area was defined as the product of the 1/e 2 widths and this area was used in estimating the effective pump intensity. Using the tunable laser described above as a signal probe, transmission scans in the 1520 to 1620 nm range were taken at each of several pump intensities. A schematic of the experimental setup is shown in Fig. 5(a), and a photograph of a waveguide under test is shown in Fig. 5(b). As above, the intrinsic wavelength dependence of the measurement system was taken into account. By collecting luminescence data without the input probe signal, we also verified that amplified spontaneous emission could be neglected in the analysis.

Fig. 5. (a). Schematic of the transverse pumping experiment. PD1 and PD2 are photodetectors, PC is a polarization controller, and WG is the waveguide under test. (b). Photograph of a waveguide under transverse pumping with green light.

SEerb(IP,λ)=T(IP,λ)·T(0,1620)T(0,λ)·T(IP,1620),
(2)

with T(IP,λ) the transmitted power at wavelength λ for pump intensity IP. This assumes negligible Er-induced signal change at 1620 nm and also that the FCA/CCA is wavelength independent. The result is plotted in Fig. 6(b), clearly evoking the shape of the Er emission band shown in Fig. 4(b).

Fig. 6. (a). Transmission scans for a buried strip waveguide under transverse pumping by 532 nm light of varying intensity. (b). The erbium related signal enhancement extracted from the data in (a), as described in the text.

The fraction of inverted Er ions can be estimated as [18

18. H.-S. Han, S.-Y. Seo, J. H. Shin, and N. Park, “Coefficient determination related to optical gain in erbiumdoped silicon-rich silicon oxide waveguide amplifier,” Appl. Phys. Lett. 81, 3720–3722 (2002). [CrossRef]

]

N2Nerb=SEerbpeak2αerbpeak,
(3)

Figure 7(a) shows the relative transmission at the peak and outside of the Er emission band, as a function of pump intensity. While FCA/CCA is reduced and seems to saturate at a lower level for 980 nm pump, it is still the dominant pump-induced mechanism. The photon energy for 980 nm pump is well below the optical bandgap of the host films. However, amorphous materials are characterized by weak absorption extending well below their nominal bandgap [28

28. J. M. Gonzalez-Leal, R. Prieto-Alcon, J. A. Angel, and E. Marquez, “Optical properties of thermally evaporated amorphous As40S60-xSex films,” J. Non-Crystalline Sol. 315, 124–143 (2003). [CrossRef]

]. Charge carriers can thus be generated by pump photons with wavelength extending into the near infrared [17

17. S. W. Roberts, G. J. Parker, and M. Hempstead, “The Photoluminescence of Erbium-doped Silicon Monoxide,” Opt. Mater. 6, 99–102 (1996). [CrossRef]

]. Long transients (seconds to tens of seconds) associated with the FCA/CCA, as reported by others [19

19. P. G. Kik and A. Polman, “Gain limiting processes in Er-doped Si nanocrystals waveguides in SiO2,” J. Appl. Phys. 91, 534–536 (2002). [CrossRef]

, 21

21. M. Forcales, N. J. Smith, and R. G. Elliman, “Pump-probe experiments at 1.54 µm on silicon-rich silicon oxide waveguides,” J. Appl. Phys. 100, 014902 (2006). [CrossRef]

], were also observed here. Another interesting observation was the absence of green emission [6

6. A. Polman and F. C. J. M. van Veggel, “Broadband sensitizers for erbium-doped planar optical amplifiers: review,” J. Opt. Soc. Am. B. 21, 871–892 (2004). [CrossRef]

] under 980 nm pumping, in spite of the fact that significant homogeneous and inhomogeneous upconversion is expected for the Er concentrations studied here (see below). We speculate that this is due to an efficient and non-radiative energy back-transfer from the upper Er levels to the SiNC [34

34. A. J. Kenyon, S. S. Bhamber, and C. W. Pitt, “The infra-red photoresponse of erbium-doped silicon nanocrystals,” Mat. Science. Eng. B 105, 230–235 (2003). [CrossRef]

].

Fig. 7. (a). Relative transmission (relative to the unpumped case) inside and outside the Er emission band, for transverse and co-propagating pump. (b). Erbium inversion versus pump intensity, extracted from the raw data as described in the text.

The inverted fraction of Er is plotted for both pump configurations in Fig. 7(b). There is strong saturation evident in both curves, but especially for the resonant pump. Given the range of 980 nm pump intensity studied, it is evident that even under resonant pumping only ~15–20 % of the Er ions are invertible. This is in contrast to other results (for films with similar Er concentration as studied here) [20

20. N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato, “Absorption cross section and signal enhancement in Erdoped Si nanocluster rib-loaded waveguides,” Appl. Phys. Lett. 86, 261103 (2005). [CrossRef]

, 22

22. N. Daldossoet al., “Refractive index dependence of the absorption and emission cross-sections at 1.54 µm of Er3+ coupled to Si nanoclusters,” Appl. Phys. Lett. 88, 161901 (2006). [CrossRef]

, 26–27

26. P. Pellegrino, B. Garrido, J. Arbiol, C. Garcia, Y. Lebour, and J. R. Morante, “Site of Er ions in silica layers codoped with Si nanoclusters and Er,” Appl. Phys. Lett. 88, 121915 (2006). [CrossRef]

], where ~1–12% of Er ions were excitable via SiNC absorption but ~100% by resonant means. In the present case, the excitable fraction limit (for SiNC-mediated excitation) cannot be entirely attributed to a distance limitation for the SiNC to Er energy transfer [26

26. P. Pellegrino, B. Garrido, J. Arbiol, C. Garcia, Y. Lebour, and J. R. Morante, “Site of Er ions in silica layers codoped with Si nanoclusters and Er,” Appl. Phys. Lett. 88, 121915 (2006). [CrossRef]

]. Nonlinear de-population mechanisms can also limit the Er inversion level; these include Auger de-excitation of Er by energy transfer to excitons in SiNC [5

5. P. G. Kik and A. Polman, “Exciton-erbium interactions in Si nanocrystal-doped SiO2,” J. Appl. Phys. 88, 1992–1998 (2000). [CrossRef]

], homogenous upconversion [4–5

4. D. Pacifici, G. Franzo, F. Priolo, F. Iacona, and L. D. Degro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys. Rev. B 67, 245301-1–13 (2003). [CrossRef]

], and excited state absorption (ESA) [27

27. C. J. Oton, W. H. Loh, and A. J. Kenyon, “Er3+ excited state absorption and the low fraction of nanocluster-excitable Er3+ in SiOx,” Appl. Phys. Lett. 89, 031116 (2006). [CrossRef]

]. For low to moderate pump intensity, a limit of one excited Er ion per SiNC has been associated with both Auger de-excitation and ESA [5

5. P. G. Kik and A. Polman, “Exciton-erbium interactions in Si nanocrystal-doped SiO2,” J. Appl. Phys. 88, 1992–1998 (2000). [CrossRef]

, 27

27. C. J. Oton, W. H. Loh, and A. J. Kenyon, “Er3+ excited state absorption and the low fraction of nanocluster-excitable Er3+ in SiOx,” Appl. Phys. Lett. 89, 031116 (2006). [CrossRef]

]. Again, this is not entirely consistent with the data presented above. However, given the high Er concentrations in our waveguide samples, it is very likely that homogeneous upconversion [4

4. D. Pacifici, G. Franzo, F. Priolo, F. Iacona, and L. D. Degro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys. Rev. B 67, 245301-1–13 (2003). [CrossRef]

] and concentration quenching [4

4. D. Pacifici, G. Franzo, F. Priolo, F. Iacona, and L. D. Degro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys. Rev. B 67, 245301-1–13 (2003). [CrossRef]

, 12

12. A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, “Photoluminescence from Erdoped silicon oxide microcavities,” Opt. Mater. 28, 873–878 (2006). [CrossRef]

] (which increases the non-radiative decay rate of the metastable Er level) contribute to the saturation in Fig. 7(b).

Since the curves for resonant and non-resonant pump seem to converge to a similar saturation level, it appears that ~80% of the Er ions are non-invertible (unbleachable). Wojdak et al. [25

25. M. Wojdak, M. Klik, M. Forcales, O. B. Gusev, T. Gregorkiewicz, D. Pacifici, G. Franzo, F. Priolo, and F. Iacona, “Sensitization of Er luminescence by Si nanoclusters,” Phys. Rev. B. 69, 233315 (2004). [CrossRef]

] reported similar behavior for films with similar Er concentration; 70% of their Er ions were unbleachable by any means. Perhaps the simplest possible explanation for this behavior is the well-known pair-induced quenching (PIQ) (also called inhomogeneous upconversion) mechanism [35

35. R. S. Quimby, W. J. Miniscalco, and B. Thompson, “Clustering in erbium-doped silica glass fibers analyzed using 980 nm excited-state absorption,” J. Appl. Phys. 76, 4472–4478 (1994). [CrossRef]

]. In PIQ, paired (or clustered in general) Er ions are active in the sense that they contribute to the usual absorption features. However, they are noninvertible due to rapid ion-ion interactions within the clusters [36

36. E. Maurice, G. Monnom, B. Dussardier, and D. B. Ostrowsky, “Clustering-induced nonsaturable absorption phenomenon in heavily erbium-doped silica fibers,” Opt. Lett. 76, 2487–2489 (1995). [CrossRef]

]. The onset of significant clustering in pure SiO2 occurs for Nerb~1018 cm-3 [35

35. R. S. Quimby, W. J. Miniscalco, and B. Thompson, “Clustering in erbium-doped silica glass fibers analyzed using 980 nm excited-state absorption,” J. Appl. Phys. 76, 4472–4478 (1994). [CrossRef]

], well below the Er concentrations studied here. Given that Er is generally thought to reside preferentially within the SiO2 regions of Er:SiNC systems [4

4. D. Pacifici, G. Franzo, F. Priolo, F. Iacona, and L. D. Degro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys. Rev. B 67, 245301-1–13 (2003). [CrossRef]

, 10

10. J. H. Shin, J. Lee, H.-S. Han, J.-H. Jhe, J. S. Chang, S.-Y. Seo, H. Lee, and N. Park, “Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs,” IEEE J. Sel. Top. Quantum Electron 12, 783–796 (2006). [CrossRef]

, 26

26. P. Pellegrino, B. Garrido, J. Arbiol, C. Garcia, Y. Lebour, and J. R. Morante, “Site of Er ions in silica layers codoped with Si nanoclusters and Er,” Appl. Phys. Lett. 88, 121915 (2006). [CrossRef]

], it is somewhat surprising that PIQ is rarely cited [5

5. P. G. Kik and A. Polman, “Exciton-erbium interactions in Si nanocrystal-doped SiO2,” J. Appl. Phys. 88, 1992–1998 (2000). [CrossRef]

] as an explanation for the excitable fraction limit. Further, the solubility of Er in Si is even lower than that in SiO2 [8

8. V. Yu. Timoshenko, M. G. Lisachenko, O. A. Shalygina, B. V. Kamenev, D. M. Zhigunov, S. A. Teterukov, and P. K. Kashkarov, “Comparative study of photoluminescence of undoped and erbiumdoped size-controlled nanocrystalline Si/SiO2 multilayered structures,” J. Appl. Phys. 96, 2254–2260 (2004). [CrossRef]

]. However, it should be noted that Pellegrino et al. [26

26. P. Pellegrino, B. Garrido, J. Arbiol, C. Garcia, Y. Lebour, and J. R. Morante, “Site of Er ions in silica layers codoped with Si nanoclusters and Er,” Appl. Phys. Lett. 88, 121915 (2006). [CrossRef]

] saw no evidence of Er clustering in Er:SiNC films annealed at temperatures less than 850 C. Within the framework of a simplified two-level model for the Er ion [3

3. F. Priolo, G. Franzó, D. Pacifici, V. Vinciguerra, F. Iacona, and A. Irrera, “Role of the energy transfer in the optical properties of undoped and Er-doped interacting Si nanocrystals,” J. Appl. Phys. 89, 264–272 (2001). [CrossRef]

], the inversion level in the presence of clustering can be approximated as [35

35. R. S. Quimby, W. J. Miniscalco, and B. Thompson, “Clustering in erbium-doped silica glass fibers analyzed using 980 nm excited-state absorption,” J. Appl. Phys. 76, 4472–4478 (1994). [CrossRef]

]

N2Nerb=(1k)σeffϕPτ211+σeffϕPτ21
(4)

where k is the fraction of clustered (unbleachable) Er ions, σeff is the effective excitation crosssection, ϕP is the pump flux, and τ21 is the lifetime of the metastable Er level. Thus, we can define a characteristic saturation flux: ϕps=1/effτ21). Assuming direct resonant excitation of Er ions in the 980 nm pump case, and using σeff~10-20 cm2 (ie. similar to the values in Table 2) and τ21~1 ms (see the discussion in Section 3 and in Ref. [12

12. A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, “Photoluminescence from Erdoped silicon oxide microcavities,” Opt. Mater. 28, 873–878 (2006). [CrossRef]

]), we estimate a saturation pump intensity IPS~2×104 W/cm2. This is in reasonable agreement with the curve in Fig. 7(b). However, there is likely some indirect excitation of Er via SiNC (given the CCA/FCA observed for 980 nm pump), which will increase σeff. For the 532 nm transverse pump case, using σeff~10-15 cm2 [5

5. P. G. Kik and A. Polman, “Exciton-erbium interactions in Si nanocrystal-doped SiO2,” J. Appl. Phys. 88, 1992–1998 (2000). [CrossRef]

, 12

12. A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, “Photoluminescence from Erdoped silicon oxide microcavities,” Opt. Mater. 28, 873–878 (2006). [CrossRef]

] and the same value for τ21 produces IPS~0.4 W/cm2, also in reasonable agreement with the data. Note that the 532 nm pump is quasi-resonant with Er absorption lines, causing some direct excitation. However, given typical cross-sections for Er ions in insulating hosts (<10-20 cm2) and the maximum photon flux in our transverse pumping experiment (~1019 cm-2), the fraction of directly excited Er ions can be neglected.

The data in Fig. 7 clearly confirm the 3–5 orders of magnitude increase in excitation crosssection widely reported for Er:SiNC systems [1–9

1. A. J. Kenyon, C. E. Chryssou, C. W. Pitt, T. Shimizu-Iwayama, D. E. Hole, N. Sharma, and C. J. Humphreys, “Luminescence from erbium-doped silicon nanocrystals in silicon: excitation mechanisms,” J. Appl. Phys. 91, 367–374 (2002). [CrossRef]

]. Compared to Er:SiNC systems with lower silicon content [20

20. N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato, “Absorption cross section and signal enhancement in Erdoped Si nanocluster rib-loaded waveguides,” Appl. Phys. Lett. 86, 261103 (2005). [CrossRef]

, 25

25. M. Wojdak, M. Klik, M. Forcales, O. B. Gusev, T. Gregorkiewicz, D. Pacifici, G. Franzo, F. Priolo, and F. Iacona, “Sensitization of Er luminescence by Si nanoclusters,” Phys. Rev. B. 69, 233315 (2004). [CrossRef]

], the Er:SiO films enable a higher excitable fraction of Er and the Er inversion saturates for considerably lower pump intensity. In fact, significant Er inversion is exhibited at pump intensities within the range of high power LEDs [10

10. J. H. Shin, J. Lee, H.-S. Han, J.-H. Jhe, J. S. Chang, S.-Y. Seo, H. Lee, and N. Park, “Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs,” IEEE J. Sel. Top. Quantum Electron 12, 783–796 (2006). [CrossRef]

]. However, the onset of CCA/FCA in the present films occurs at pump intensity similar to that in reference [21

21. M. Forcales, N. J. Smith, and R. G. Elliman, “Pump-probe experiments at 1.54 µm on silicon-rich silicon oxide waveguides,” J. Appl. Phys. 100, 014902 (2006). [CrossRef]

] and much lower than that in Ref. [20

20. N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato, “Absorption cross section and signal enhancement in Erdoped Si nanocluster rib-loaded waveguides,” Appl. Phys. Lett. 86, 261103 (2005). [CrossRef]

].

5. Summary and conclusions

Acknowledgments

This work was supported by the Natural Sciences and Engineering Research Council of Canada and TRLabs. We would like to thank George Braybrook for the SEM images. Devices were fabricated at the Nanofab of the University of Alberta.

References and links

1.

A. J. Kenyon, C. E. Chryssou, C. W. Pitt, T. Shimizu-Iwayama, D. E. Hole, N. Sharma, and C. J. Humphreys, “Luminescence from erbium-doped silicon nanocrystals in silicon: excitation mechanisms,” J. Appl. Phys. 91, 367–374 (2002). [CrossRef]

2.

M. Fujii, K. Imakita, K. Watanabe, and S. Hayashi, “Coexistance of two different energy transfer processes in SiO2 films containing Si nanocrystals and Er,” J. Appl. Phys. 95, 272–280 (2004). [CrossRef]

3.

F. Priolo, G. Franzó, D. Pacifici, V. Vinciguerra, F. Iacona, and A. Irrera, “Role of the energy transfer in the optical properties of undoped and Er-doped interacting Si nanocrystals,” J. Appl. Phys. 89, 264–272 (2001). [CrossRef]

4.

D. Pacifici, G. Franzo, F. Priolo, F. Iacona, and L. D. Degro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys. Rev. B 67, 245301-1–13 (2003). [CrossRef]

5.

P. G. Kik and A. Polman, “Exciton-erbium interactions in Si nanocrystal-doped SiO2,” J. Appl. Phys. 88, 1992–1998 (2000). [CrossRef]

6.

A. Polman and F. C. J. M. van Veggel, “Broadband sensitizers for erbium-doped planar optical amplifiers: review,” J. Opt. Soc. Am. B. 21, 871–892 (2004). [CrossRef]

7.

F. Gourbilleau, M. Levalois, C. Dufour, J. Vicens, and R. Rizk, “Optimized conditions for an enhanced coupling rate between Er ions and Si nanoclusters for an improved 1.54-µm emission,” J. Appl. Phys. 95, 3717–3722 (2004). [CrossRef]

8.

V. Yu. Timoshenko, M. G. Lisachenko, O. A. Shalygina, B. V. Kamenev, D. M. Zhigunov, S. A. Teterukov, and P. K. Kashkarov, “Comparative study of photoluminescence of undoped and erbiumdoped size-controlled nanocrystalline Si/SiO2 multilayered structures,” J. Appl. Phys. 96, 2254–2260 (2004). [CrossRef]

9.

C.-C. Kao, et al., “Correlation between Si-related and erbium photoluminescence bands and determination of erbium effective excitation cross-section in SiO2 films,” J. Appl. Phys. 98, 013544 (2005). [CrossRef]

10.

J. H. Shin, J. Lee, H.-S. Han, J.-H. Jhe, J. S. Chang, S.-Y. Seo, H. Lee, and N. Park, “Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs,” IEEE J. Sel. Top. Quantum Electron 12, 783–796 (2006). [CrossRef]

11.

G. Franzo, S. Boninelli, D. Pacifici, F. Priolo, F. Iacona, and C. Bongiorno, “Sensitizing properties of amorphous Si clusters on the 1.54-µm luminescence of Er in Si-rich SiO2,” Appl. Phys. Lett. 82, 3871–3873 (2003). [CrossRef]

12.

A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, “Photoluminescence from Erdoped silicon oxide microcavities,” Opt. Mater. 28, 873–878 (2006). [CrossRef]

13.

A. Hohl, T. Wieder, P. A. van Aken, T. E. Weirich, G. Denninger, M. Vidal, S. Oswald, C. Deneke, J. Mayer, and H. Fuess, “An interface clusters mixture model for the structure of amorphous silicon monoxide (SiO),” J. Non-Crystalline Sol. 320, 255–280 (2003). [CrossRef]

14.

K. Schulmeister and W. Mader, “TEM investigation on the structure of amorphous silicon monoxide,” J. Non-Crystalline Sol. 320, 143–150 (2003). [CrossRef]

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B. Friede and M. Jansen, “Some comments on so-called ‘silicon monoxide’,” J. Non-Crystalline Sol. 206, 202–203 (1996). [CrossRef]

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J. Wang, X. F. Wang, Q. Li, A. Hryciw, and A. Meldrum, “The microstructure of SiO thin films: from nanoclusters to nanocrystals,” Phil. Mag, in press (2006).

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S. W. Roberts, G. J. Parker, and M. Hempstead, “The Photoluminescence of Erbium-doped Silicon Monoxide,” Opt. Mater. 6, 99–102 (1996). [CrossRef]

18.

H.-S. Han, S.-Y. Seo, J. H. Shin, and N. Park, “Coefficient determination related to optical gain in erbiumdoped silicon-rich silicon oxide waveguide amplifier,” Appl. Phys. Lett. 81, 3720–3722 (2002). [CrossRef]

19.

P. G. Kik and A. Polman, “Gain limiting processes in Er-doped Si nanocrystals waveguides in SiO2,” J. Appl. Phys. 91, 534–536 (2002). [CrossRef]

20.

N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato, “Absorption cross section and signal enhancement in Erdoped Si nanocluster rib-loaded waveguides,” Appl. Phys. Lett. 86, 261103 (2005). [CrossRef]

21.

M. Forcales, N. J. Smith, and R. G. Elliman, “Pump-probe experiments at 1.54 µm on silicon-rich silicon oxide waveguides,” J. Appl. Phys. 100, 014902 (2006). [CrossRef]

22.

N. Daldossoet al., “Refractive index dependence of the absorption and emission cross-sections at 1.54 µm of Er3+ coupled to Si nanoclusters,” Appl. Phys. Lett. 88, 161901 (2006). [CrossRef]

23.

H. Mertens, A. Polman, I. M. P. Aarts, W. M. M. Kessels, and M. C. M. van de Sanden, “Absence of the enhanced intra-4f transition cross section at 1.5 µm of Er3+ in Si-rich SiO2,” Appl. Phys. Lett. 86, 241109 (2005). [CrossRef]

24.

D. Kuritsyn, A. Kozanecki, H. Przybylinska, and W. Jantsch, “Defect-mediated and resonant optical excitation of Er3+ ions in silicon-rich silicon oxide,” Appl. Phys. Lett. 83, 4160–4162 (2003). [CrossRef]

25.

M. Wojdak, M. Klik, M. Forcales, O. B. Gusev, T. Gregorkiewicz, D. Pacifici, G. Franzo, F. Priolo, and F. Iacona, “Sensitization of Er luminescence by Si nanoclusters,” Phys. Rev. B. 69, 233315 (2004). [CrossRef]

26.

P. Pellegrino, B. Garrido, J. Arbiol, C. Garcia, Y. Lebour, and J. R. Morante, “Site of Er ions in silica layers codoped with Si nanoclusters and Er,” Appl. Phys. Lett. 88, 121915 (2006). [CrossRef]

27.

C. J. Oton, W. H. Loh, and A. J. Kenyon, “Er3+ excited state absorption and the low fraction of nanocluster-excitable Er3+ in SiOx,” Appl. Phys. Lett. 89, 031116 (2006). [CrossRef]

28.

J. M. Gonzalez-Leal, R. Prieto-Alcon, J. A. Angel, and E. Marquez, “Optical properties of thermally evaporated amorphous As40S60-xSex films,” J. Non-Crystalline Sol. 315, 124–143 (2003). [CrossRef]

29.

G. Haas and C. Salzberg, “Optical Properties of Silicon Monoxide in the Wavelength Region from 0.24 to 14.0 Microns,” J. Opt. Soc. Am. 44, 181–187 (1954). [CrossRef]

30.

Y. Ago, B. Boulard, M. Couchaud, I. Vasilief, S. Guy, C. Duverger, and B. Jacquier, “Preparation by PVD of Er/Ce-doped PZG fluoride glass channel waveguide for integrated optical amplifiers at 1.5 µm,” Opt. Mater. 28, 195–199 (2006). [CrossRef]

31.

M. J. de Boer, J. G. E. Gardeniers, H V. Jansen, E. Smulders, M.-J. Gilde, G. Roelofs, J. N. Sasserath, and M. Elwenspoek, “Guidelines for Etching Silicon MEMS Structures Using Fluorine High-Density Plasmas at Cryogenic Temperatures,” J. Microelectromechanical Sys. 11, 385–401 (2002). [CrossRef]

32.

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33.

E. Desurvire, “Erbium-doped fiber amplifiers: basic physics and characteristics,” in Rare-Earth-Doped Fiber Lasers and Amplifiers, M. J. F. Digonnet, ed., (Marcel Dekker, Inc., New York, 2001).

34.

A. J. Kenyon, S. S. Bhamber, and C. W. Pitt, “The infra-red photoresponse of erbium-doped silicon nanocrystals,” Mat. Science. Eng. B 105, 230–235 (2003). [CrossRef]

35.

R. S. Quimby, W. J. Miniscalco, and B. Thompson, “Clustering in erbium-doped silica glass fibers analyzed using 980 nm excited-state absorption,” J. Appl. Phys. 76, 4472–4478 (1994). [CrossRef]

36.

E. Maurice, G. Monnom, B. Dussardier, and D. B. Ostrowsky, “Clustering-induced nonsaturable absorption phenomenon in heavily erbium-doped silica fibers,” Opt. Lett. 76, 2487–2489 (1995). [CrossRef]

OCIS Codes
(130.3120) Integrated optics : Integrated optics devices
(160.2750) Materials : Glass and other amorphous materials

ToC Category:
Integrated Optics

History
Original Manuscript: October 12, 2006
Revised Manuscript: November 30, 2006
Manuscript Accepted: December 2, 2006
Published: December 11, 2006

Citation
T. J. Clement, R. G. DeCorby, N. Ponnampalam, T. W. Allen, A. Hryciw, and A. Meldrum, "Nanocluster sensitized erbium-doped silicon monoxide waveguides," Opt. Express 14, 12151-12162 (2006)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-25-12151


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References

  1. A. J. Kenyon, C. E. Chryssou, C. W. Pitt, T. Shimizu-Iwayama, D. E. Hole, N. Sharma and C. J. Humphreys, "Luminescence from erbium-doped silicon nanocrystals in silicon: excitation mechanisms," J. Appl. Phys. 91, 367-374 (2002). [CrossRef]
  2. M. Fujii, K. Imakita, K. Watanabe, and S. Hayashi, "Coexistance of two different energy transfer processes in SiO2 films containing Si nanocrystals and Er," J. Appl. Phys. 95, 272-280 (2004). [CrossRef]
  3. F. Priolo, G. Franzò, D. Pacifici, V. Vinciguerra, F. Iacona, and A. Irrera, "Role of the energy transfer in the optical properties of undoped and Er-doped interacting Si nanocrystals," J. Appl. Phys. 89, 264-272 (2001). [CrossRef]
  4. D. Pacifici, G. Franzo, F. Priolo, F. Iacona, and L. D. Degro, "Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification," Phys. Rev. B  67, 245301-1-13 (2003). [CrossRef]
  5. P. G. Kik and A. Polman, "Exciton-erbium interactions in Si nanocrystal-doped SiO2," J. Appl. Phys. 88, 1992-1998 (2000). [CrossRef]
  6. A. Polman, and F. C. J. M. van Veggel, "Broadband sensitizers for erbium-doped planar optical amplifiers: review," J. Opt. Soc. Am. B. 21, 871-892 (2004). [CrossRef]
  7. F. Gourbilleau, M. Levalois, C. Dufour, J. Vicens, and R. Rizk, "Optimized conditions for an enhanced coupling rate between Er ions and Si nanoclusters for an improved 1.54-μm emission," J. Appl. Phys. 95, 3717-3722 (2004). [CrossRef]
  8. V. Yu. Timoshenko, M. G. Lisachenko, O. A. Shalygina, B. V. Kamenev, D. M. Zhigunov, S. A. Teterukov, and P. K. Kashkarov, "Comparative study of photoluminescence of undoped and erbium-doped size-controlled nanocrystalline Si/SiO2 multilayered structures," J. Appl. Phys. 96, 2254-2260 (2004). [CrossRef]
  9. C.-C. Kao,  et al., "Correlation between Si-related and erbium photoluminescence bands and determination of erbium effective excitation cross-section in SiO2 films," J. Appl. Phys. 98, 013544 (2005). [CrossRef]
  10. J. H. Shin, J. Lee, H.-S. Han, J.-H. Jhe, J. S. Chang, S.-Y. Seo, H. Lee, and N. Park, "Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs," IEEE J. Sel. Top. Quantum Electron 12, 783-796 (2006). [CrossRef]
  11. G. Franzo, S. Boninelli, D. Pacifici, F. Priolo, F. Iacona, and C. Bongiorno, "Sensitizing properties of amorphous Si clusters on the 1.54-μm luminescence of Er in Si-rich SiO2," Appl. Phys. Lett. 82, 3871-3873 (2003). [CrossRef]
  12. A. Hryciw, C. Blois, A. Meldrum, T. Clement, R. DeCorby, and Q. Li, "Photoluminescence from Er-doped silicon oxide microcavities," Opt. Mater. 28, 873-878 (2006). [CrossRef]
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