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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 22 — Oct. 29, 2007
  • pp: 14414–14421
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Long, low loss etched As2S3 chalcogenide waveguides for all-optical signal regeneration

S. J. Madden, D-Y. Choi, D. A. Bulla, A. V. Rode, B. Luther-Davies, V.G. Ta’eed, M.D. Pelusi, and B.J. Eggleton  »View Author Affiliations


Optics Express, Vol. 15, Issue 22, pp. 14414-14421 (2007)
http://dx.doi.org/10.1364/OE.15.014414


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Abstract

We report on the fabrication and optical properties of etched highly nonlinear As2S3 chalcogenide planar rib waveguides with lengths up to 22.5 cm and optical losses as low as 0.05 dB/cm at 1550 nm - the lowest ever reported. We demonstrate strong spectral broadening of 1.2 ps pulses, in good agreement with simulations, and find that the ratio of nonlinearity and dispersion linearizes the pulse chirp, reducing the spectral oscillations caused by self-phase modulation alone. When combined with a spectrally offset band-pass filter, this gives rise to a nonlinear transfer function suitable for all-optical regeneration of high data rate signals.

© 2007 Optical Society of America

1. Introduction

Chalcogenide glasses are promising candidates for planar non-linear optical (NLO) waveguide devices due to their large NLO coefficients, high refractive index, and low linear and non-linear optical losses [e.g. 1]. A surge in planar activity over the last 10 years has seen a diverse range of fabrication techniques yield reasonably low loss planar waveguides in the As2S3, As2Se3, As-S-Se, Ga-La-S, Ge-As-Se and Ge-As-S-Se systems, amongst others, with losses down to 0.2dB/cm at 1550nm at best in any system [2–7

2. R. G. DeCorby, N. Ponnampalam, M. M. Pai, H. T. Nguyen, P. K. Dwivedi, T. J. Clement, C. J. Haugen, J. N. McMullin, and S. O. Kasap, “High index contrast waveguides in chalcogenide glass and polymer,” IEEE J. Sel. Top. Quantum Electron. 11, 539–546 (2005). [CrossRef]

].

However, to attain sub-Watt thresholds for all-optical processing of high data rate (160Gb/s) telecommunications signals in chalcogenide glass waveguides, advances are required that lead to a simultaneous reduction in the mode area of the waveguide and an increase in waveguide length. In chalcogenide glasses it is not practical to simply follow the route used, for example, with silicon nanowire waveguides of shrinking to very small sizes [8

8. Y. A. Vlasov and S. J. McNab, “Losses in single-mode silicon-on-insulator strip waveguides and bends,” Opt. Express 12, 1622–1631 (2004). [CrossRef] [PubMed]

]. Firstly, chalcogenide glass films have damage mechanisms that limit the short term maximum fluence in the waveguide to ≈1 GW/cm2 [9

9. N. Ho, J. M. Laniel, R. Vallee, and A. Villeneuve, “Photosensitivity of As2S3 chalcogenide thin films at 1.5 μm,” Opt. Lett. 28, 965–967 (2003). [CrossRef] [PubMed]

]. Secondly their ultra-fast Kerr response leads to relatively small index changes (10-5 to 10-4) compared with materials such as silicon, whose index change is resonantly enhanced by the generation of free carriers. Hence device lengths of several tens of centimeters are mandatory.

At present the usable length of chalcogenide planar waveguides is loss-limited, and reduction of the mode area is challenging since waveguide loss often increases as the waveguide cross-section decreases due to scattering induced by surface roughness [10

10. 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, 1617–1619 (2000). [CrossRef]

]. These problems can be overcome using improved process technology as well as waveguide designs that suppress field enhancement at the etched sidewall surfaces as the waveguide is shrunk to smaller dimensions.

In this paper we report significant advances on both of these aspects of NLO waveguides resulting in As2S3 chalcogenide planar rib waveguides with lengths up to 22.5 cm and optical losses as low as 0.05 dB/cm at 1550 nm. We demonstrate strong nonlinear spectral broadening of 1.2 ps optical pulses in excellent agreement with simulations by the split-step Fourier method. The simulations show that the chromatic dispersion of these waveguides enhances their performance when used for self-phase modulation based signal regeneration [11

11. P. V. Mamyshev, “All-optical data regeneration based on self-phase modulation effect,” in Proceedings of European Conference on Optical Communication (ECOC)(Madrid, Spain, 1998), pp. 475–476.

].

2. Planar waveguide fabrication

Fig. 1. “Snake” pattern layout schematic, inner bend radius was 2.5mm, outer radius was 3.2mm

The final plasma conditions were 25 sccm CHF3, 2 sccm O2, 5 mT process pressure, 40 W substrate bias power, 400 W ICP power (Oxford Instruments 100 series ICP etcher). The etched surface roughness was better than halved compared to the CF4 + O2 process as shown in Fig. 2 from AFM scans.

Fig 2. AFM scans of a) as deposited film surface, (b) surface after optimized CF4 + O2 etch, (c) optimized CHF3 etch. Scan size is 1×1μm, vertical scale is 10 nm/div. RMS roughnesses are (a) 0.3 nm, (b) 3.3 nm, (c) 1.5 nm.

After resist removal with standard wet stripping, the waveguides were clad with a 15 μm thick film of UV cured inorganic polymer glass (RPO Pty Ltd, IPG™) which has a refractive index of 1.53 at 1550 nm. End facets were then prepared on the waveguides by hand cleaving the silicon substrate with a diamond scriber. The resulting waveguide chips were approximately 4 cm wide and 7.2 cm long. Figure 3 shows the end facet of a finished waveguide.

Fig. 3. Optical micrograph of cleaved finished waveguide in the 2.6 μm thick As2S3 film

3. Linear characterization

Insertion loss data was then gathered for all waveguides in the two snake designs and the 7.2 cm long straights between them. Fiber coupling was accomplished using lensed fibers with a 3.3 μm 1/e2 mode field diameter to suppress the Fabry-Perot cavity between the waveguide and fiber end faces. To avoid the Fabry-Perot effects within the waveguide chip itself, an external cavity tunable laser with linewidth broadened to greater than 7 times the minimum free spectral range of the waveguide chip was used as a source for the measurements at 1550 nm. Polarization dependent loss (PDL) data was gathered using a scanning polarisation controller.

Figure 4 shows insertion loss data for the 4 μm wide waveguides, including data for an additional 6 cm long straight waveguide chip from the wafer with 2.6 μm of As2S3. Five waveguides of each length were measured, and the measurement was repeated one week later using new lens coupling and zero offsets for the 1550nm data. The propagation loss at 1550 nm was estimated from a least squares linear fit to the data at 0.05dB/cm for the TE mode for the 2.6 μm film and 0.17 dB/cm for the 0.9 μm film. The very low losses were also obtained from a second measurement method that is not dependent on the repeatability of coupling between the fiber and the waveguide, namely the Fabry-Perot method. Here, by measuring the waveguide chip Fabry-Perot fringe contrast for the 7, 15, and 22cm waveguides within a single waveguide chip and then least squares fitting the facet reflectivity and propagation loss [14

14. H. Takeuchi and K. Oe, “Low-Loss Single-Mode Gaas Algaas Miniature Optical Wave-Guides with Straight and Bending Structures,” J. Lightwave Technol. 7, 1044–1054 (1989). [CrossRef]

], we also obtained a value of 0.05dB/cm for the TE mode of waveguides in the 2.6 μm film. PDL averaged 0.35 dB for each of the 6, 7.1 and 15.5 cm long waveguides in the 2.6 μm film, including measurement system PDL of 0.15 dB and input coupling PDL of 0.12 dB. For reasons not yet clear to us, the PDL of the 22.5 cm waveguides rose to an average value of 2.4 dB (range 1.3 to 3.5dB). For the 0.9 μm film the PDL was at most 1 dB for all waveguide lengths. At 1310 nm the loss for the 2.6 μm film was slightly higher, 0.08±0.05 dB/cm, but the PDL was lower, 0.32 dB even for the 22.5 cm waveguides. These are the lowest optical losses ever reported for chalcogenide planar waveguides by up to a factor of four.

Fig. 4. Measured insertion loss for 2.5×4 μm and 0.9×4 μm waveguides. Data for the 1310 nm measurement and the 0.9 μm thick film have been offset for clarity.

The probable cause for the increase in loss at 1310 nm relative to 1550 nm is material absorption. Chalcogenide glasses display a characteristic exponentially-decaying absorption tail (Ate /Et) due to the presence of defects within their band gap [15

15. see e.g. D. L. Wood and J. Tauc, “Weak Absorption Tails in Amorphous Semiconductors,” Phys. Rev. B5, 3144–& (1972). [CrossRef]

]. Films contain larger numbers of defects compared with bulk glasses (as indicated by their different refractive index) and this results in losses in the 0.01-0.05 dB/cm range [16

16. A. Zakery, Y. Ruan, A. V. Rode, M. Samoc, and B. Luther-Davies, “Low-loss waveguides in ultrafast laser-deposited As2S3 chalcogenide films”, J. Opt. Soc. Am. B , 20, 1844–1852 (2003). [CrossRef]

].

At present the reason for the higher loss for 0.9 μm thick films is not completely understood. However we observed that these waveguides supported the propagation of three modes and in the case of the 0.9 μm films this resulted in mode-beating at the output between the lowest order and first symmetric high order mode as the 1550 nm source was tuned. Compared with the thicker film, this mode is very close to cut-off and this could increase the losses to radiation for the higher order mode particularly at the bends.

Fig. 5. Computed quasi-TE mode field of fabricated waveguides

An interesting point to note from the mode profiles is that there is little field concentration at the etched rib sidewalls, in contrast to typical nanowire devices [8

8. Y. A. Vlasov and S. J. McNab, “Losses in single-mode silicon-on-insulator strip waveguides and bends,” Opt. Express 12, 1622–1631 (2004). [CrossRef] [PubMed]

]. This suggests even smaller mode areas may be obtainable whilst suffering only a moderate increase in losses from sidewall scattering.

Numerical modeling showed, for example, that for a 2 μm wide rib (undemanding lithography and the upper width limit of single mode operation of the waveguide) and film thicknesses down to 0.5 μm, the smallest mode area attainable for a 30-40% etch depth is 0.95 μm2. For comparison, for the best nanowire design for this materials system (0.55×0.55 μm), the mode area is 0.35μm2 but then field enhancement at the waveguide sidewalls is significant for the TE mode. For the rib design, and 1 μm film thickness (corresponding to a geometry where the total waveguide dispersion is expected to be ≈0) the mode area increases to 1.5 μm2 but there is still little enhancement of the field at the etched sidewalls. Using the full vector two dimensional generic finite difference bent waveguide mode of Olympios (Bend2D) with >300 grid points in the in plane bend direction, we also established this design is single mode, capable of being bent with radii down to 1 mm with bend losses of below 0.01 dB/radian, and that both TE and TM modes propagate at 1550 nm with similar mode field dimensions.

4. Nonlinear pulse propagation and optical regeneration

To characterize the nonlinear properties of the waveguides we observed the nonlinear spectral broadening of pulses propagating through a 4 μm wide, 2.6 μm tall serpentine waveguide of length 22.5 cm. The setup, as shown in Fig. 6, was based on optical pulses of 1.2 ps duration generated from a passively mode-locked, figure-eight, fiber laser operating at a repetition rate of 4.0 MHz. The pulses were launched into the rib waveguide by direct butt-coupling via an intermediate section of high numerical aperture fiber (NA = 0.35) and index-matching oil to improve mode matching and remove fiber-waveguide Fabry-Perot effects, resulting in a total fiber-to-fiber insertion loss of 6.0 dB (≈1.1 dB due to propagation loss). A 1% fiber coupler and variable optical attenuator facilitated power control and a fiber based polarization controller was used to set the input to the lower loss TE polarization mode.

Fig. 6 Experimental setup for demonstration of spectral broadening. F8: figure eight fiber laser; VOA: variable optical attenuator; OSA: Optical spectrum analyzer.

Figure 7 (a) shows the experimentally observed self phase modulation (SPM) spectral broadening of the pulses resulting in 3 spectral lobes for an average power of 0.25 mW in fiber, corresponding to a calculated peak power of 23.7 W inside the waveguide. No nonlinear absorption (i.e. two photon absorption) was observed, in agreement with earlier measurements [4

4. Y. L. Ruan, B. Luther-Davies, W. T. Li, A. Rode, V. Kolev, and S. Madden, “Large phase shifts in AS2S3 waveguides for all-optical processing devices,” Opt. Lett. 30, 2605–2607 (2005). [CrossRef] [PubMed]

, 18

18. V. G. Ta´eed, M. Shokooh-Saremi, L B. Fu, D. J. Moss, M. Rochette, I. C. M. Littler, B. J. Eggleton, Y. L. Ruan, and B. Luther-Davies, “Integrated all-optical pulse egenerator in chalcogenide waveguides,” Opt. Lett. 30, 2900–2902 (2005). [CrossRef]

]. Also plotted, in good agreement with the experimental data, are the results of simulations solving the nonlinear Schrödinger equation by the split-step Fourier method using parameters based on the experimental setup described above, with n 2 = 2.92 × 10-18 m2W-1 [18

18. V. G. Ta´eed, M. Shokooh-Saremi, L B. Fu, D. J. Moss, M. Rochette, I. C. M. Littler, B. J. Eggleton, Y. L. Ruan, and B. Luther-Davies, “Integrated all-optical pulse egenerator in chalcogenide waveguides,” Opt. Lett. 30, 2900–2902 (2005). [CrossRef]

]. The weak spectral oscillations on the pulses are due to the presence of strong normal dispersion within the waveguides which results in linear pulse chirp [19

19. G. P. Agrawal, Nonlinear Fiber Optics (Academic Press, San Diego, 2001).

].

Fig. 7. (a) Spectral broadening of 1.2 ps pulses with peak power specified inside waveguide (experiment:solid and simulation:dashed). (b) Resulting regenerator power transfer function for a 2.8 nm spectrally offset Gaussian filter immediately after the waveguide. Inset shows filter spectrum and simulated broadening with and without dispersion at 23.7 W peak power.

The nonlinear spectral response of the waveguide makes it suitable for SPM based optical signal regeneration [11

11. P. V. Mamyshev, “All-optical data regeneration based on self-phase modulation effect,” in Proceedings of European Conference on Optical Communication (ECOC)(Madrid, Spain, 1998), pp. 475–476.

]. Such regenerators operate using a combination of SPM and a bandpass filter offset from the signal wavelength by more than the signal optical bandwidth so that at low intensities, the optical signal is blocked by the filter. At high intensities, (representing logical “1’s”) the pulses undergo sufficient spectral broadening so that a portion is transmitted through the pass band. At still higher intensities, the signal experiences significant broadening and the power within the transmission band pass saturates. The resulting “S-shaped” nonlinear power transfer curve is a hallmark of optical regenerators (for reshaping), and has the effect of reducing noise on both the signal “0’s” and “1’s”.

Figure 7 (b) shows the resulting transfer function using the experimental and simulated spectra derived by adding a spectrally offset, Gaussian band-pass filter to the output of the waveguide. The 1.96 nm filter bandwidth was set to match the laser FWHM and offset to longer wavelengths by 2.8 nm (the inset overlays the band-pass filter spectrum onto the simulated spectra for a peak coupled power of 23.7 W). At lower peak powers the pulses are completely blocked by the offset filter, while high powers result in spectral slicing of the SPM induced spectral broadened pulses, generating a nonlinear transfer function. Also shown in Fig. 7 (b) is the simulated transfer function in the absence of normal dispersion. Comparing simulations shows that normal dispersion in the long serpentine waveguides improves the saturation effect and reduces the modulation of the transfer function while only marginally increasing power requirements, enhancing the waveguide’s potential regenerative performance [11

11. P. V. Mamyshev, “All-optical data regeneration based on self-phase modulation effect,” in Proceedings of European Conference on Optical Communication (ECOC)(Madrid, Spain, 1998), pp. 475–476.

, 20

20. L B. Fu, M. Rochette, V. G. Ta´eed, D. J. Moss, and B. J. Eggleton, “Investigation of self-phase modulation based optical regeneration in single mode As2Se3 chalcogenide glass fiber,” Opt. Express 13, 7637–7644 (2005). [CrossRef] [PubMed]

]. This is in contrast with our earlier report based on a shorter 5 cm waveguide where the effects of dispersion were negligible [18

18. V. G. Ta´eed, M. Shokooh-Saremi, L B. Fu, D. J. Moss, M. Rochette, I. C. M. Littler, B. J. Eggleton, Y. L. Ruan, and B. Luther-Davies, “Integrated all-optical pulse egenerator in chalcogenide waveguides,” Opt. Lett. 30, 2900–2902 (2005). [CrossRef]

]. In assessing the serpentine chalcogenide glass waveguides for SPM based optical regeneration we find that both the large nonlinearity and high dispersion, which result in weak SPM spectral oscillations, contribute to device performance.

5. Summary

In conclusion, we have demonstrated As2S3 waveguides up to 22.5 cm long with losses down to 0.05 dB/cm at 1550 nm, the lowest ever reported by a factor of 4×. It appears there is a realistic prospect of achieving similar losses in waveguides with mode areas as low as 1 μm2. Furthermore using chalcogenide glasses with higher nonlinearity (e.g. ×4 is possible using Ge-As-Se glasses, [1

1. J. T. Gopinath, M. Soljacic, E. P. Ippen, V. N. Fuflyigin, W. A. King, and M. Shurgalin, “Third order nonlinearities in Ge-As-Se-based glasses for telecommunications applications,” J. Appl. Phys. 96, 6931–6933 (2004). [CrossRef]

]), a peak power for all-optical signal processing below 1 W will be achieved. We show the suitability of these waveguides for all-optical signal processing by demonstrating spectral broadening of picosecond duration pulses, in excellent agreement with theory. Furthermore, simulations show that the group velocity dispersion of these waveguides results in a near optimal nonlinear transfer function for all-optical signal regeneration of high data rate signals.

Acknowledgement

The support of the Australian Research Council through its Centres of Excellence, Federation Fellow and Discovery grant programs is gratefully acknowledged.

References and links

1.

J. T. Gopinath, M. Soljacic, E. P. Ippen, V. N. Fuflyigin, W. A. King, and M. Shurgalin, “Third order nonlinearities in Ge-As-Se-based glasses for telecommunications applications,” J. Appl. Phys. 96, 6931–6933 (2004). [CrossRef]

2.

R. G. DeCorby, N. Ponnampalam, M. M. Pai, H. T. Nguyen, P. K. Dwivedi, T. J. Clement, C. J. Haugen, J. N. McMullin, and S. O. Kasap, “High index contrast waveguides in chalcogenide glass and polymer,” IEEE J. Sel. Top. Quantum Electron. 11, 539–546 (2005). [CrossRef]

3.

S. Ramachandran and S. G. Bishop, “Photoinduced integrated-optic devices in rapid thermally annealed chalcogenide glasses,” IEEE J. Sel. Top. Quantum Electron. 11, 260–270 (2005). [CrossRef]

4.

Y. L. Ruan, B. Luther-Davies, W. T. Li, A. Rode, V. Kolev, and S. Madden, “Large phase shifts in AS2S3 waveguides for all-optical processing devices,” Opt. Lett. 30, 2605–2607 (2005). [CrossRef] [PubMed]

5.

A. V. Rode, A. Zakery, M. Samoc, R. B. Charters, E. G. Gamaly, and B. Luther-Davies, “Laser-deposited As2S3 chalcogenide films for waveguide applications,” Appl. Surf. Sci. 197, 481–485 (2002). [CrossRef]

6.

A. K. Mairaj, P. Hua, H. N. Rutt, and D. W. Hewak, “Fabrication and characterization of continuous wave direct UV (λ=244 nm) written channel waveguides in chalcogenide (Ga : La : S) glass,” J. Lightwave Technol. 20, 1578–1584 (2002). [CrossRef]

7.

N. Ponnampalam, P. Dwivedi, T. Allen, T. Clement, R. DeCorby, and Y Tsui, Conference on Laser Ablation COLA’05, Banf Canada, 11–16 September 2005.

8.

Y. A. Vlasov and S. J. McNab, “Losses in single-mode silicon-on-insulator strip waveguides and bends,” Opt. Express 12, 1622–1631 (2004). [CrossRef] [PubMed]

9.

N. Ho, J. M. Laniel, R. Vallee, and A. Villeneuve, “Photosensitivity of As2S3 chalcogenide thin films at 1.5 μm,” Opt. Lett. 28, 965–967 (2003). [CrossRef] [PubMed]

10.

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, 1617–1619 (2000). [CrossRef]

11.

P. V. Mamyshev, “All-optical data regeneration based on self-phase modulation effect,” in Proceedings of European Conference on Optical Communication (ECOC)(Madrid, Spain, 1998), pp. 475–476.

12.

W. T. Li, Y. L. Ruan, B. Luther-Davies, A. Rode, and R. Boswell, “Dry-etch of As2S3 thin films for optical waveguide fabrication,” J. Vac. Sci. Technol. A 23, 1626–1632 (2005). [CrossRef]

13.

D. G. Georgiev, P. Boolchand, and K. A. Jackson, “Intrinsic nanoscale phase separation of bulk As2S3 glass,” Philosophical Magazine 83, 2941–2953 (2003). [CrossRef]

14.

H. Takeuchi and K. Oe, “Low-Loss Single-Mode Gaas Algaas Miniature Optical Wave-Guides with Straight and Bending Structures,” J. Lightwave Technol. 7, 1044–1054 (1989). [CrossRef]

15.

see e.g. D. L. Wood and J. Tauc, “Weak Absorption Tails in Amorphous Semiconductors,” Phys. Rev. B5, 3144–& (1972). [CrossRef]

16.

A. Zakery, Y. Ruan, A. V. Rode, M. Samoc, and B. Luther-Davies, “Low-loss waveguides in ultrafast laser-deposited As2S3 chalcogenide films”, J. Opt. Soc. Am. B , 20, 1844–1852 (2003). [CrossRef]

17.

M. Lamont, CM. de Sterke, and B. Eggleton, “Dispersion engineering of highly nonlinear As2S3 waveguides for parametric gain and wavelength conversion,” Opt. Express 15, 9458–9463 (2007). [CrossRef] [PubMed]

18.

V. G. Ta´eed, M. Shokooh-Saremi, L B. Fu, D. J. Moss, M. Rochette, I. C. M. Littler, B. J. Eggleton, Y. L. Ruan, and B. Luther-Davies, “Integrated all-optical pulse egenerator in chalcogenide waveguides,” Opt. Lett. 30, 2900–2902 (2005). [CrossRef]

19.

G. P. Agrawal, Nonlinear Fiber Optics (Academic Press, San Diego, 2001).

20.

L B. Fu, M. Rochette, V. G. Ta´eed, D. J. Moss, and B. J. Eggleton, “Investigation of self-phase modulation based optical regeneration in single mode As2Se3 chalcogenide glass fiber,” Opt. Express 13, 7637–7644 (2005). [CrossRef] [PubMed]

OCIS Codes
(060.4510) Fiber optics and optical communications : Optical communications
(070.4340) Fourier optics and signal processing : Nonlinear optical signal processing
(130.3120) Integrated optics : Integrated optics devices

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: September 7, 2007
Revised Manuscript: October 14, 2007
Manuscript Accepted: October 15, 2007
Published: October 18, 2007

Citation
S. J. Madden, D-Y. Choi, D. A. Bulla, A. V. Rode, B. Luther-Davies, V. G. Ta'eed, M. D. Pelusi, and B. J. Eggleton, "Long, low loss etched As2S3 chalcogenide waveguides for all-optical signal regeneration," Opt. Express 15, 14414-14421 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-22-14414


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References

  1. J. T. Gopinath, M. Soljacic, E. P. Ippen, V. N. Fuflyigin, W. A. King, and M. Shurgalin, "Third order nonlinearities in Ge-As-Se-based glasses for telecommunications applications," J. Appl. Phys. 96, 6931-6933 (2004). [CrossRef]
  2. R. G. DeCorby, N. Ponnampalam, M. M. Pai, H. T. Nguyen, P. K. Dwivedi, T. J. Clement, C. J. Haugen, J. N. McMullin, and S. O. Kasap, "High index contrast waveguides in chalcogenide glass and polymer," IEEE J. Sel. Top. Quantum Electron. 11, 539-546 (2005). [CrossRef]
  3. S. Ramachandran and S. G. Bishop, "Photoinduced integrated-optic devices in rapid thermally annealed chalcogenide glasses," IEEE J. Sel. Top. Quantum Electron. 11, 260-270 (2005). [CrossRef]
  4. Y. L. Ruan, B. Luther-Davies, W. T. Li, A. Rode, V. Kolev, and S. Madden, "Large phase shifts in AS2S3 waveguides for all-optical processing devices," Opt. Lett. 30, 2605-2607 (2005). [CrossRef] [PubMed]
  5. A. V. Rode, A. Zakery, M. Samoc, R. B. Charters, E. G. Gamaly, and B. Luther-Davies, "Laser-deposited As2S3 chalcogenide films for waveguide applications," Appl. Surf. Sci. 197, 481-485 (2002). [CrossRef]
  6. A. K. Mairaj, P. Hua, H. N. Rutt, and D. W. Hewak, "Fabrication and characterization of continuous wave direct UV (λ=244 nm) written channel waveguides in chalcogenide (Ga : La : S) glass," J. Lightwave Technol. 20, 1578-1584 (2002). [CrossRef]
  7. N. Ponnampalam, P. Dwivedi, T. Allen, T. Clement, R. DeCorby, and Y Tsui, Conference on Laser Ablation COLA’05, Banf, Canada, 11-16 September 2005.
  8. Y. A. Vlasov and S. J. McNab, "Losses in single-mode silicon-on-insulator strip waveguides and bends," Opt. Express 12, 1622-1631 (2004). [CrossRef] [PubMed]
  9. N. Ho, J. M. Laniel, R. Vallee, and A. Villeneuve, "Photosensitivity of As2S3 chalcogenide thin films at 1.5 µm," Opt. Lett. 28, 965-967 (2003). [CrossRef] [PubMed]
  10. 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, 1617-1619 (2000). [CrossRef]
  11. P. V. Mamyshev, "All-optical data regeneration based on self-phase modulation effect," in Proceedings of European Conference on Optical Communication (ECOC)(Madrid, Spain, 1998), pp. 475-476.
  12. W. T. Li, Y. L. Ruan, B. Luther-Davies, A. Rode, and R. Boswell, "Dry-etch of As2S3 thin films for optical waveguide fabrication," J. Vac. Sci. Technol. A 23, 1626-1632 (2005). [CrossRef]
  13. D. G. Georgiev, P. Boolchand, and K. A. Jackson, "Intrinsic nanoscale phase separation of bulk As2S3 glass," Philosophical Magazine 83, 2941-2953 (2003). [CrossRef]
  14. H. Takeuchi and K. Oe, "Low-Loss Single-Mode Gaas Algaas Miniature Optical Wave-Guides with Straight and Bending Structures," J. Lightwave Technol. 7, 1044-1054 (1989). [CrossRef]
  15. see e.g. D. L. Wood and J. Tauc, "Weak Absorption Tails in Amorphous Semiconductors," Phys. Rev. B 5, 3144-(1972). [CrossRef]
  16. A. Zakery, Y. Ruan, A. V. Rode, M. Samoc, and B. Luther-Davies, "Low-loss waveguides in ultrafast laser-deposited As2S3 chalcogenide films", J. Opt. Soc. Am. B,  20, 1844-1852 (2003). [CrossRef]
  17. M. Lamont, C. M. de Sterke, and B. Eggleton, "Dispersion engineering of highly nonlinear As2S3 waveguides for parametric gain and wavelength conversion," Opt. Express 15, 9458-9463 (2007). [CrossRef] [PubMed]
  18. V. G. Ta'eed, M. Shokooh-Saremi, L. B. Fu, D. J. Moss, M. Rochette, I. C. M. Littler, B. J. Eggleton, Y. L. Ruan, and B. Luther-Davies, "Integrated all-optical pulse regenerator in chalcogenide waveguides," Opt. Lett. 30, 2900-2902 (2005). [CrossRef]
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