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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 12 — Jun. 6, 2011
  • pp: 11529–11538
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Reduced propagation loss in silicon strip and slot waveguides coated by atomic layer deposition

T. Alasaarela, D. Korn, L. Alloatti, A. Säynätjoki, A. Tervonen, R. Palmer, J. Leuthold, W. Freude, and S. Honkanen  »View Author Affiliations


Optics Express, Vol. 19, Issue 12, pp. 11529-11538 (2011)
http://dx.doi.org/10.1364/OE.19.011529


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Abstract

When silicon strip and slot waveguides are coated with a 50nm amorphous titanium dioxide (TiO2) film, measured losses at a wavelength of 1.55 μm can be as low as (2 ± 1)dB/cm and (7 ± 2)dB/cm, respectively. We use atomic layer deposition (ALD), estimate the effect of ALD growth on the surface roughness, and discuss the effect on the scattering losses. Because the gap between the rails of a slot waveguide narrows by the TiO2 deposition, the effective slot width can be back-end controlled. This is useful for precise adjustment if the slot is to be filled with, e. g., a nonlinear organic material or with a sensitizer for sensors applications.

© 2011 OSA

1. Introduction

Silicon photonic waveguides have gained a lot of interest over the past years. Mature processes are available for fabricating electronics using the silicon platform, and it is highly promising to exploit the same technology also for photonics at wavelengths near 1.55 μm. We consider two basic waveguide types, namely strip and slot waveguides. Both are high index-contrast structures, where light is confined either in the high-index material of the strip, or in the low-index material that fills the gap of slot waveguides [1

1. V. R. Almeida, Q. Xu, C. A. Barrios, and M. Lipson, “Guiding and confining light in void nanostructure,” Opt. Lett. 29, 1209–1211 (2004). [CrossRef] [PubMed]

, 2

2. Q. Xu, V. R. Almeida, R. R. Panepucci, and M. Lipson, “Experimental demonstration of guiding and confining light in nanometer-size low-refractive-index material,” Opt. Lett. 29, 1626–1628 (2004). [CrossRef] [PubMed]

]. Our strip and slot waveguides were fabricated on silicon-on-insulator (SOI) wafers, where the index contrast between silicon (Si) with a refractive index of n Si = 3.48 and silicon dioxide (SiO2) with n SiO2 = 1.46 amounts to Δn ≈ 2.0. This requires very tight tolerances for the fabrication, and puts stringent conditions for the sidewall roughness of the waveguides. Even with 193nm deep-UV lithography these requirements are hard to meet. For slot waveguides, a well-defined slot width of about 100nm has to be realized in addition. The requirements for an accurate smooth slot are especially high for sensor applications, where the slots are usually filled with air or a watery solution [3

3. C. A. Barrios, K. B. Gylfason, B. Sánchez, A. Griol, H. Sohlström, M. Holgado, and R. Casquel, “Slot-waveguide biochemical sensor,” Opt. Lett. 32, 3080–3082 (2007). [CrossRef] [PubMed]

, 4

4. P. Bienstman, “Label-free biosensing with a slot-waveguide-based ring resonator in silicon on insulator,” IEEE Photon. J. 1, 197–204 (2009). [CrossRef]

]. To solve these problems, we previously suggested using conformal atomic layer deposition (ALD) for coating slot waveguides with amorphous titanium dioxide (TiO2) [5

5. T. Alasaarela, A. Säynätjoki, T. Hakkarainen, and S. Honkanen, “Feature size reduction of silicon slot waveguides by partial filling using atomic layer deposition,” Opt. Eng. 48, 080502 (2009). [CrossRef]

]. We also investigated the waveguiding properties of amorphous ALD-TiO2 slab waveguides, and measured a refractive index of n TiO2 = 2.27 at 1.55 μm [6

6. T. Alasaarela, T. Saastamoinen, J. Hiltunen, A. Saynatjoki, A. Tervonen, P. Stenberg, M. Kuittinen, and S. Honkanen, “Atomic layer deposited titanium dioxide and its application in resonant waveguide grating,” Appl. Opt. 49, 4321–4325 (2010). [CrossRef] [PubMed]

].

In this paper, we demonstrate to which extent the losses of strip and slot waveguides can be reduced when covering them with a thin TiO2 layer, and in particular we show the first experimental characterization of slot waveguides with ALD controlled slot dimensions. We briefly discuss the influence of surface roughness, and the beneficial effect an ALD-grown layer has on the surface profile. We show how ALD coating with TiO2 makes otherwise non-guiding slot waveguides work properly, and how the mode properties change as a function of coating thickness. The reduced loss and the possibility to control the slot width are of special advantage for nonlinear silicon-organic hybrid (SOH) slot waveguides [7

7. J. Leuthold, W. Freude, J.-M. Brosi, R. Baets, P. Dumon, I. Biaggio, M. L. Scimeca, F. Diederich, B. Frank, and C. Koos, “Silicon organic hybrid technology - a platform for practical nonlinear optics,” Proc. IEEE 97, 1304–1316 (2009). [CrossRef]

, 8

8. C. Koos, P. Vorreau, T. Vallaitis, P. Dumon, W. Bogaerts, R. Baets, B. Esembeson, I. Biaggio, T. Michinobu, F. Diederich, W. Freude, and J. Leuthold, “All-optical high-speed signal processing with silicon-organic hybrid slot waveguides,” Nat. Photonics 3, 216 (2009). [CrossRef]

].

2. Surface roughness and loss

Waveguide losses are mainly due to sidewall surface roughness and to leakage into the substrate, if the optical field is not sufficiently guided. In addition, surface states at the uncovered waveguide boundaries can lead to excess absorption. We believe that absorbing surface states are not prominent in our case, because then the thickness of the TiO2 cover should not influence the loss. However, in Section 5 we show experimentally that a larger cover thickness actually reduces the loss, and this can be explained by the resulting reduction of the surface roughness. Therefore, we concentrate in the following on the influences of waveguide roughness and of leakage into the substrate.

Surface roughness leads to scattering losses, and a detailed theoretical description backed up with experiments has been published for the case of high index-contrast three-dimensional strip waveguides by Poulton et al. [9

9. C. G. Poulton, C. Koos, M. Fujii, A. Pfrang, T. Schimmel, J. Leuthold, and W. Freude, “Radiation modes and roughness loss in high index-contrast waveguides,” IEEE J. Sel. Top. Quantum Electron. 12, 1306–1321 (2006). [CrossRef]

]. Intuitively understandable guidelines were given for fabricating low-loss waveguides.

On the other hand, scattering losses for square Si strip waveguides are found to have a maximum, when the effective index n eff = β/k 0 of the fundamental mode is close to n eff = 1.7 [17

17. F. Grillot, L. Vivien, S. Laval, D. Pascal, and E. Cassan, “Size influence on the propagation loss induced by sidewall roughness in ultrasmall SOI waveguides,” IEEE Photon. Technol. Lett. 16, 1661–1663 (2004). [CrossRef]

]. For n eff < 1.7, the waveguide fields are less confined to the strip, which means that the electric field at the core-cladding boundary (φ(d) in Eq. (1)) and therefore the loss coefficient α become smaller.

3. Atomic layer deposition of TiO2 for reducing surface roughness

Atomic layer deposition (ALD) is a chemical gas phase vapor deposition process. Substrates are placed in a deposition chamber where temperature, pressure and other parameters are appropriately chosen for the process chemistry and the targeted layer properties. Two (or more) chemicals are then supplied sequentially to the inert gas flowing through the deposition chamber to form a single monolayer of material when reacting with each other on the target surface. This monolayer deposition represents one cycle of the process. The number τ = 0, 1, 2, ... of deposition cycles determines the final layer thickness. For deposition of TiO2, we used an ALD process with titanium tetrachloride (TiCl4) and water as precursors. A detailed explanation is found in [6

6. T. Alasaarela, T. Saastamoinen, J. Hiltunen, A. Saynatjoki, A. Tervonen, P. Stenberg, M. Kuittinen, and S. Honkanen, “Atomic layer deposited titanium dioxide and its application in resonant waveguide grating,” Appl. Opt. 49, 4321–4325 (2010). [CrossRef] [PubMed]

].

The conformal change of an initial surface height geometry h(x, 0) due to the cyclic growth of ALD monolayers is described as a function of position x and cycle number τ. Because of the large number of ALD monolayers per final layer, the cycle number τ can be regarded as a continuous “time” variable. We write
h(x,τ)τ=v1+(h(x,τ)x)2.
(2)
The quantity v is the ALD growth rate, and is the resulting thickness of the final layer. For visualizing the ALD growth of materials like amorphous TiO2 or Al2O3, a typical growth rate of v = 0.1nm/cycle was chosen. For the surface to be covered, we assumed an exponentially distributed initial height profile h(x, 0) with an autocorrelation length Lc = 15nm and a root-mean-square (RMS) roughness of σ = 5nm. We solved Eq. (2) with a finite difference scheme.

The height profiles h(x) and the RMS roughnesses σ are shown in Fig. 1 for various thicknesses of the deposited layers in steps of 10nm. Each additional 10nm layer makes the surface smoother. The smoothing effect is strongest for the highest spatial frequencies of the initial height profile, while the smoothing for lower spatial frequencies is less effective.

Fig. 1 Simulation of ALD layer growth on a rough surface. The initial surface roughness is exponentially distributed having a correlation length of Lc = 15nm and an effective (RMS) roughness of σ = 5nm. The height profiles h(x) and the RMS roughnesses σ are shown for various thicknesses (0, 10, ..., 50)nm of the deposited layer in steps of 10nm. Each additional 10nm layer makes the surface smoother. The smoothing effect is strongest for the highest spatial frequencies visible in the initial height profile, while the smoothing after applying the first 10nm ALD layer is less effective.

4. Measurements

The loss reduction was demonstrated experimentally with various silicon strip and slot waveguides. The investigated waveguides were fabricated on SOI wafers using the ePIXfab shuttle service [18

18. ePIXfab silicon photonics shuttle service, http://www.epixfab.eu/.

].

The SOI wafers had a device layer thickness of 220nm and a 2 μm thick BOX. Grating couplers were used to couple light in and out of the strip waveguides, which were either directly measured or coupled with appropriate adiabatic, virtually lossless transitions to slot waveguides. The losses from coupling external fibers through grating couplers to the silicon strip waveguides were estimated by comparing transmission through reference waveguides (∼ 450nm wide strip waveguides) to the direct fiber-to-fiber transmission. The losses from grating couplers of chips from the same waveguide fabrication run (but without ALD coating) were determined by separating them from waveguide losses in a cutback measurement. The losses from grating couplers were estimated to be the same for the TiO2 coated chips (2 × 5.5dB), and the actual losses from waveguides were estimated by deducting the reference difference and the grating coupler losses from the measured transmitted power and dividing the result by the waveguide length. For slot waveguides, also the loss from short strip waveguide sections was deducted. The lengths of strip waveguides were 5.5mm and the lengths of slot waveguides were 4mm (+1.9mm strip waveguide feeding sections). For all loss measurements, we excited the quasi-TE fundamental mode at a wavelength of 1.55 μm.

For the investigated strip and slot waveguides we estimated the actual geometry from scanning electron microscope (SEM) images. The strip waveguide widths varied in the range 161 ...450nm. The slot waveguides had rail widths in the range 177...226nm and slot widths of 150...231nm. The SEM image of a slot waveguide cross-section with a designed rail width 260nm and a slot width 140nm is shown in Fig. 2. The actual rail and slot widths measured from the SEM image are 214nm and 191nm, respectively. Not for all the investigated waveguides we could check the geometry with SEM images. The actual dimensional data for the slot waveguides were interpolated with a straight-line fit using the values for rail widths, slot widths, and coating thicknesses, which could be measured from the available SEM images. The estimated dimensional data for the slot waveguides can be found in Table 1. The RMS error in the fitting compared to the dimensions from the SEM images was ±5nm, which is also close to the accuracy of dimensional measurements from the SEM image. The maximum deviation from the dimensions is estimated to be ±9nm.

Fig. 2 SEM image of a slot waveguide cross-section that is ALD-coated with a 30nm thick layer of TiO2.

Table 1. Designed Rail Widths wrd, Designed Slot Widths wsd, Estimated Actual Rail Widths wr, Estimated Actual Slot Widths ws, and the Effective Indices Calculated for the estimated Actual Dimensions with Three Different ALD-TiO2 Thicknesses t

table-icon
View This Table

As a measure of the field confinement, we calculate the effective indices n eff using the film-mode matching (FMM) method [19

19. FIMMWAVE by Photon Design, http://www.photond.com/.

] for all investigated waveguides and layer thicknesses, using the actual waveguide geometry (wr and ws in Table 1) and refractive indices n Si = 3.48, n SiO2 = 1.46, and n TiO2 = 2.27. While neff is a simple and useful indicator for the field confinement, the effective cross-section area A eff [20

20. C. Koos, L. Jacome, C. Poulton, J. Leuthold, and W. Freude, “Nonlinear silicon-on-insulator waveguides for all-optical signal processing,” Opt. Express 15, 5976–5990 (2007). [CrossRef] [PubMed]

, Eq. (1)] would be better suited to estimate the degree of interaction with third-order nonlinear materials in waveguide and cladding.

5. Experimental results

At a wavelength of 1.55 μm, we measured the total loss resulting from leakage into the silicon substrate and from roughness-induced scattering for a number of differently dimensioned strip (Fig. 3) and slot waveguides (Fig. 4). Figure 3a shows the strip waveguide losses as a function of initial Si strip width, at various ALD growth thicknesses. As the loss reduction due to the ALD cover can largely be due to the increase of waveguide dimensions for a particular initial strip width, it is better to plot the loss as a function of effective index values n eff calculated for each waveguide structure, as is done in Fig. 3b for strip waveguides, and also for slot waveguides in Fig. 4. Strip and slot waveguides behave in a surprisingly similar manner. The loss decays quickly with increasing n eff, starting at the BOX refractive index, below which no light is guided at all. With increasing n eff the mode experiences a better guiding, and leakage loss reduces. However, because the field φ(d) at the core-cladding boundary increases, roughness-induced scattering losses gain weight, so that a shallow minimum appears at n eff ≈ 1.6. For n eff ≈ 1.8, a more or less pronounced loss maximum is found. This is connected to the maximum roughness loss reported in [9

9. C. G. Poulton, C. Koos, M. Fujii, A. Pfrang, T. Schimmel, J. Leuthold, and W. Freude, “Radiation modes and roughness loss in high index-contrast waveguides,” IEEE J. Sel. Top. Quantum Electron. 12, 1306–1321 (2006). [CrossRef]

, Fig. 5, Eq. (40), (41)], but here it is also influenced by leakage losses. With increasing n eff, i. e., for an increased propagation constant β chosen by a broader silicon strip (assuming the strip height remains constant because of technological constraints), the roughness losses become less and less important [9

9. C. G. Poulton, C. Koos, M. Fujii, A. Pfrang, T. Schimmel, J. Leuthold, and W. Freude, “Radiation modes and roughness loss in high index-contrast waveguides,” IEEE J. Sel. Top. Quantum Electron. 12, 1306–1321 (2006). [CrossRef]

]. The maximum n eff is set by the requirement that the waveguide should remain singlemoded.

Fig. 3 Strip waveguides with various dimensions. Measured propagation losses as a function of (a) initial strip width, and (b) quasi-TE modal effective index n eff = β/k 0. Parameter: TiO2 cover height 0 ... 50nm.
Fig. 4 Slot waveguides with various dimensions, which can be found in Table 1 with the respective waveguide numbers. Measured slot waveguide propagation losses as a function of quasi-TE modal effective index n eff = β/k 0 for a) all measured slot waveguides, b) only waveguides 1...5, and c) only waveguides 21...25. Waveguide numbers are growing from higher to lower effective indices in each plot. Parameters: Waveguide numbers (only a)), TiO2 cover height t = 20 ... 50nm.
Fig. 5 Measured propagation loss of slot waveguides with n eff > 1.55 (no leakage loss) as a function of the remaining air slot width after coating. The thicker coating gives a stronger loss reduction, especially for the narrow air gaps. Parameters: Slot waveguide numbers (see Table 1), TiO2 cover height t = 30 ... 50nm.

For the strip waveguides, Fig. 3(b) shows that the largest reduction of losses from 11dB/cm of an uncoated one to 5.7dB/cm of a waveguide covered with 50nm of TiO2 is reached when n eff ≈ 1.65. The details of observed loss reduction features cannot be easily explained from basic modefield simulations, and describing them may require rigorous scattering models with accurate information on surface roughness properties. The smallest loss of 2dB/cm was found for the broadest strip (450nm, n eff = 2.45). In this case, a 50nm thick TiO2 cover did not improve the loss any further. We estimate an uncertainty of ±1dB/cm for the measurements, based on the variation of transmission values caused in a large part by the uncertainties in the measurement setup.

For slot waveguides, the measured losses as a function of n eff are shown in Fig. 4. With a 50nm thick TiO2 cover, minimum losses of 7dB/cm, with an estimated uncertainty of ±2dB/cm (also largely due to the uncertainty of the measurement setup), were reached for n eff = 1.69 (wr = 207nm, ws = 230nm).

To illustrate the measurement accuracy, we compared five slot waveguides (waveguides 5, 10, 15, 20, and 25) with similar dimensions as given above and found the loss values (71, 74, 79, 65, 67)dB/cm without any cover (on average ( 716+8) dB/cm). With a 50nm thick TiO2 cover, we measured losses of (10, 9, 9, 8, 7) dB/cm (on average ( 92+1) dB/cm). For another set of five slot waveguides with similar dimensions (waveguides 2, 7, 12, 17, and 22) we measured the loss values (81, 78, 87, 83, 91)dB/cm without cover (on average (84 ± 7)dB/cm). With a 50nm thick TiO2 cover we found (12, 12, 13, 15, 15) dB/cm (on average (13.5 ± 1.5)dB/cm).

To better examine the dependency of losses on the slot width, we plot the loss of slot waveguides with effective indices n eff > 1.55 as a function of the air slot width remaining after coating (Fig. 5). For the chosen n eff range, substrate leakage is not significant anymore, and the losses are larger for narrower slots. Due to a more effective surface smoothening, a thicker coating with a height of 50nm leads to lower losses, especially for narrow air slots.

6. Conclusions

Losses in silicon strip and slot waveguides can be reduced with a TiO2 cover grown by atomic layer deposition (ALD). For waveguides with low effective refractive index n eff, i. e., with a relatively small field confinement, the measured losses stem mostly from leakage through the 2 μm buried oxide into the silicon substrate. For a better field confinement (larger n eff), scattering from the rough waveguide sidewalls dominates the loss. We found that a 50 nm thick TiO2 cover reduces the loss of a 230nm wide strip waveguide from > 50dB/cm to 5.7dB/cm, or from 11dB/cm to 5.7dB/cm when compared to a 320nm wide uncoated waveguide with similar n eff of ~ 1.65. For 450nm wide strip waveguides the loss is as small as (2 ± 1)dB/cm. The loss of slot waveguides reduces from 71dB/cm to (7 ± 2)dB/cm.

As a further advantage, the waveguiding properties for strip waveguides and the slot width for slot waveguides can be adjusted in a back-end process. For slot waveguides this is especially convenient, if a sensor sensitizer or a nonlinear material is used to fill a precisely controlled slot.

Acknowledgments

We acknowledge support by the Academy of Finland (grant 128826 and 134087 for A. S.) and by the Finnish Funding Agency for Technology and Innovation (TEKES). T. A. acknowledges support from Graduate School of Modern Optics and Photonics, Emil Aaltonen Foundation, and from Walter Ahlström Foundation. This work was further supported by the German Research Foundation (DFG) through DFG Center for Functional Nanostructures (CFN), Karlsruhe School of Optics & Photonics (KSOP), and through the Initiative of Excellence, all at Karlsruhe Institute of Technology (KIT), by the European projects EURO-FOS (grant 224402) and SOFI (grant 248609), and by the German Ministry of Education and Research in the framework of the joint project MISTRAL (BMBF grant 01BL0804). We are grateful for technological support by the European Network of Excellence ePIXnet (now ePIXfab, silicon photonics platform of IMEC and CEA-LETI).

References and links

1.

V. R. Almeida, Q. Xu, C. A. Barrios, and M. Lipson, “Guiding and confining light in void nanostructure,” Opt. Lett. 29, 1209–1211 (2004). [CrossRef] [PubMed]

2.

Q. Xu, V. R. Almeida, R. R. Panepucci, and M. Lipson, “Experimental demonstration of guiding and confining light in nanometer-size low-refractive-index material,” Opt. Lett. 29, 1626–1628 (2004). [CrossRef] [PubMed]

3.

C. A. Barrios, K. B. Gylfason, B. Sánchez, A. Griol, H. Sohlström, M. Holgado, and R. Casquel, “Slot-waveguide biochemical sensor,” Opt. Lett. 32, 3080–3082 (2007). [CrossRef] [PubMed]

4.

P. Bienstman, “Label-free biosensing with a slot-waveguide-based ring resonator in silicon on insulator,” IEEE Photon. J. 1, 197–204 (2009). [CrossRef]

5.

T. Alasaarela, A. Säynätjoki, T. Hakkarainen, and S. Honkanen, “Feature size reduction of silicon slot waveguides by partial filling using atomic layer deposition,” Opt. Eng. 48, 080502 (2009). [CrossRef]

6.

T. Alasaarela, T. Saastamoinen, J. Hiltunen, A. Saynatjoki, A. Tervonen, P. Stenberg, M. Kuittinen, and S. Honkanen, “Atomic layer deposited titanium dioxide and its application in resonant waveguide grating,” Appl. Opt. 49, 4321–4325 (2010). [CrossRef] [PubMed]

7.

J. Leuthold, W. Freude, J.-M. Brosi, R. Baets, P. Dumon, I. Biaggio, M. L. Scimeca, F. Diederich, B. Frank, and C. Koos, “Silicon organic hybrid technology - a platform for practical nonlinear optics,” Proc. IEEE 97, 1304–1316 (2009). [CrossRef]

8.

C. Koos, P. Vorreau, T. Vallaitis, P. Dumon, W. Bogaerts, R. Baets, B. Esembeson, I. Biaggio, T. Michinobu, F. Diederich, W. Freude, and J. Leuthold, “All-optical high-speed signal processing with silicon-organic hybrid slot waveguides,” Nat. Photonics 3, 216 (2009). [CrossRef]

9.

C. G. Poulton, C. Koos, M. Fujii, A. Pfrang, T. Schimmel, J. Leuthold, and W. Freude, “Radiation modes and roughness loss in high index-contrast waveguides,” IEEE J. Sel. Top. Quantum Electron. 12, 1306–1321 (2006). [CrossRef]

10.

F. P. Payne and J. P. R. Lacey, “A theoretical analysis of scattering loss from planar optical waveguides,” Opt. Quantum Electron. 26, 977–986 (1994). [CrossRef]

11.

K. K. Lee, D. R. Lim, H.-C. Luan, A. Agarwal, J. Foresi, and L. C. Kimerling, “Effect of size and roughness on light transmission in a Si/SiO2 waveguide: Experiments and model,” Appl. Phys. Lett. 77, 1617 (2000). [CrossRef]

12.

K. K. Lee, D. R. Lim, L. C. Kimerling, J. Shin, and F. Cerrina, “Fabrication of ultralow-loss Si/SiO2 waveguides by roughness reduction,” Opt. Lett. 26, 1888–1890 (2001). [CrossRef]

13.

D. Sparacin, S. Spector, and L. Kimerling, “Silicon waveguide sidewall smoothing by wet chemical oxidation,” J. Lightwave Technol. 23, 2455–2461 (2005). [CrossRef]

14.

K. P. Yap, A. Delâge, J. Lapointe, B. Lamontagne, J. H. Schmid, P. Waldron, B. A. Syrett, and S. Janz, “Correlation of scattering loss, sidewall roughness and waveguide width in silicon-on-insulator (SOI) ridge waveguides,” J. Lightwave Technol. 27, 3999–4008 (2009). [CrossRef]

15.

F. Grillot, L. Vivien, S. Laval, and E. Cassan, “Propagation loss in single-mode ultrasmall square silicon-on-insulator optical waveguides,” J. Lightwave Technol. 24, 891–896 (2006). [CrossRef]

16.

J. Schrauwen, J. V. Lysebettens, T. Claes, K. D. Vos, P. Bienstman, D. V. Thourhout, and R. Baets, “Focused-ion-beam fabrication of slots in silicon waveguides and ring resonators,” IEEE Photon. Technol. Lett. 20, 2004–2006 (2008). [CrossRef]

17.

F. Grillot, L. Vivien, S. Laval, D. Pascal, and E. Cassan, “Size influence on the propagation loss induced by sidewall roughness in ultrasmall SOI waveguides,” IEEE Photon. Technol. Lett. 16, 1661–1663 (2004). [CrossRef]

18.

ePIXfab silicon photonics shuttle service, http://www.epixfab.eu/.

19.

FIMMWAVE by Photon Design, http://www.photond.com/.

20.

C. Koos, L. Jacome, C. Poulton, J. Leuthold, and W. Freude, “Nonlinear silicon-on-insulator waveguides for all-optical signal processing,” Opt. Express 15, 5976–5990 (2007). [CrossRef] [PubMed]

OCIS Codes
(130.3130) Integrated optics : Integrated optics materials
(230.7370) Optical devices : Waveguides
(240.5770) Optics at surfaces : Roughness
(310.2785) Thin films : Guided wave applications
(220.4241) Optical design and fabrication : Nanostructure fabrication

ToC Category:
Integrated Optics

History
Original Manuscript: March 22, 2011
Revised Manuscript: May 14, 2011
Manuscript Accepted: May 25, 2011
Published: May 31, 2011

Citation
T. Alasaarela, D. Korn, L. Alloatti, A. Säynätjoki, A. Tervonen, R. Palmer, J. Leuthold, W. Freude, and S. Honkanen, "Reduced propagation loss in silicon strip and slot waveguides coated by atomic layer deposition," Opt. Express 19, 11529-11538 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-12-11529


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References

  1. V. R. Almeida, Q. Xu, C. A. Barrios, and M. Lipson, “Guiding and confining light in void nanostructure,” Opt. Lett. 29, 1209–1211 (2004). [CrossRef] [PubMed]
  2. Q. Xu, V. R. Almeida, R. R. Panepucci, and M. Lipson, “Experimental demonstration of guiding and confining light in nanometer-size low-refractive-index material,” Opt. Lett. 29, 1626–1628 (2004). [CrossRef] [PubMed]
  3. C. A. Barrios, K. B. Gylfason, B. Sánchez, A. Griol, H. Sohlström, M. Holgado, and R. Casquel, “Slot-waveguide biochemical sensor,” Opt. Lett. 32, 3080–3082 (2007). [CrossRef] [PubMed]
  4. P. Bienstman, “Label-free biosensing with a slot-waveguide-based ring resonator in silicon on insulator,” IEEE Photon. J. 1, 197–204 (2009). [CrossRef]
  5. T. Alasaarela, A. Säynätjoki, T. Hakkarainen, and S. Honkanen, “Feature size reduction of silicon slot waveguides by partial filling using atomic layer deposition,” Opt. Eng. 48, 080502 (2009). [CrossRef]
  6. T. Alasaarela, T. Saastamoinen, J. Hiltunen, A. Saynatjoki, A. Tervonen, P. Stenberg, M. Kuittinen, and S. Honkanen, “Atomic layer deposited titanium dioxide and its application in resonant waveguide grating,” Appl. Opt. 49, 4321–4325 (2010). [CrossRef] [PubMed]
  7. J. Leuthold, W. Freude, J.-M. Brosi, R. Baets, P. Dumon, I. Biaggio, M. L. Scimeca, F. Diederich, B. Frank, and C. Koos, “Silicon organic hybrid technology - a platform for practical nonlinear optics,” Proc. IEEE 97, 1304–1316 (2009). [CrossRef]
  8. C. Koos, P. Vorreau, T. Vallaitis, P. Dumon, W. Bogaerts, R. Baets, B. Esembeson, I. Biaggio, T. Michinobu, F. Diederich, W. Freude, and J. Leuthold, “All-optical high-speed signal processing with silicon-organic hybrid slot waveguides,” Nat. Photonics 3, 216 (2009). [CrossRef]
  9. C. G. Poulton, C. Koos, M. Fujii, A. Pfrang, T. Schimmel, J. Leuthold, and W. Freude, “Radiation modes and roughness loss in high index-contrast waveguides,” IEEE J. Sel. Top. Quantum Electron. 12, 1306–1321 (2006). [CrossRef]
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  11. K. K. Lee, D. R. Lim, H.-C. Luan, A. Agarwal, J. Foresi, and L. C. Kimerling, “Effect of size and roughness on light transmission in a Si/SiO2 waveguide: Experiments and model,” Appl. Phys. Lett. 77, 1617 (2000). [CrossRef]
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