Abstract

A behavior is reported where the index change process used for UV writing of integrated optical waveguides in deuterium loaded Ge:SiO2 glass can become unstable and suddenly switch off or on. It is shown that such discontinuities are associated with abrupt changes in the amount of absorbed UV power. We suggest that these events are controlled by a coupling between UV absorption, local heating and the D2-GeO2 reaction rate. From our findings we predict, and confirm experimentally, that strong waveguides can not be fabricated under normal UV writing conditions in thin core layers with a low initial UV absorption. Our findings show that an improved understanding of the waveguide formation process and future process development requires that thermal effects are taken into account.

© 2005 Optical Society of America

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References

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  1. M. Svalgaard, C.V. Poulsen, A. Bjarklev, O. Poulsen, 'Direct UV-writing of buried single-mode channel waveguides in Ge-doped silica films,' Electron. Lett. 30, 1401-1402 (1994).
    [CrossRef]
  2. M.Y. Park, W. Yoon, S. Han, G. H. Song, "Fabrication of low-cost planar wavelength-selective optical add-drop multiplexer by employing UV photosensitivity," Electron. Lett. 38, 1532-1533 (2002).
    [CrossRef]
  3. G.D. Emmerson, S.P. Watts, C.B.E. Gawith, V. Albanis, M. Ibsen, R.B. Williams, P.G.R. Smith, "Fabrication of directly UV written channel waveguides with simultaneously defined integral gratings," Electron. Lett. 38, 1531�??1532 (2002).
    [CrossRef]
  4. M. Svalgaard, K. Faerch, L.-U. Andersen, "Variable optical attenuator fabricated by direct UV writing," J. Lightwave Technol. 21, 2097-2103 (2003).
    [CrossRef]
  5. C. Peucheret, Y. Geng, M. Svalgaard, B. Zsigri, H.R. Sørensen, N. Chi, H.-J. Deyerl, M. Kristensen, P. Jeppesen, "Direct UV written Michelson Interferometer for RZ signal generation using phase-to-intensity modulation conversion," Phot. Tech. Lett. 17, 1674-1676 (2005).
    [CrossRef]
  6. P.J. Lemaire, R.M. Atkins, V. Mizrahi, W.A. Reed, "High Pressure H2 loading as a technique for achieving ultrahigh UV photosensitivity and thermal sensitivity in GeO2 doped optical fibres," Electron. Lett. 29, 1191-1193 (1993).
    [CrossRef]
  7. G.D. Maxwell, B.J. Ainslie, "Demonstration of a directly written directional coupler using UV induced photosensitivity in a planar silica waveguide," Electron. Lett. 31, 95-96 (1995).
    [CrossRef]
  8. D. Zauner, K. Kulstad, J. Rathje, M. Svalgaard, "Directly UV-written silica-on-silicon planar waveguides with low insertion loss," Electron. Lett. 34, 1582-1584 (1998).
    [CrossRef]
  9. M.J. Yuen, "Ultraviolet absorption studies of germanium silicate glasses," App. Opt. 21, 136-140 (1982).
    [CrossRef]
  10. M. Svalgaard, "Effect of D2 outdiffusion on direct UV writing of optical waveguides," Electron. Lett. 35, 1840-1842 (1999).
    [CrossRef]
  11. T.W. Whitbread, R.A. Betts, F. Lui, �??Non destructive two-dimensional refractive index profiling of integrated optical waveguides by an interferometric method,�?? Appl. Opt. 30, 4384-4389, (1991).
    [CrossRef] [PubMed]
  12. M. Svalgaard, A. Harpøth, T. Rosbirk, "Characterization of UV-written waveguides with luminescence microscopy," Opt. Express 13, 5170-5178 (2005), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-13-5170.">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-13-5170</a>
    [CrossRef] [PubMed]
  13. L.N. Skuja, A.N. Trukhin, A.E. Plaudis, "Luminescence in germanium-doped glassy SiO2," Phys. Status Solidi. A 84, K153-157 (1984).
    [CrossRef]
  14. M. Svalgaard, A. Harpøth, M. Andersen, "Discontinuities during UV writing of waveguides," in Proceedings of OSA Topical Meeting on Bragg Gratings, Poling and Photosensitivity, B.J. Eggleton, ed., (Technical Digest Series, Optical Society of America, Washington, D.C., 2005), 121-123.
  15. S. Adachi, "Model dielectric constants of Si and Ge," Phys. Rev. B 38, 12966-12976 (1988).
    [CrossRef]
  16. A. Iino, M. Kuwabara, K. Kokura, "Mechanisms of hydrogen-induced losses in silica-based optical fibers," J. Lightwave Technol. 8, 1675-1679 (1990).
    [CrossRef]
  17. P.J. Lemaire, A.M. Vengsarkar, W.A. Reed, D.J. DiGiovanni, "Thermally enhanced ultraviolet photosensitivity in GeO2 and P2O5 doped optical fibers," Appl. Phys. Lett. 66, 2034-2036 (1995).
    [CrossRef]
  18. M. Kristensen, "Ultraviolet-light-induced processes in germanium-doped silica," Phys. Rev. B 64, 144201 (2001).
    [CrossRef]
  19. P.J. Lemaire, "Reliability of optical fibers exposed to hydrogen: Prediction of long-term loss increases," Opt. Eng. 30, 780-789 (1991).
    [CrossRef]
  20. K. Færch, M. Svalgaard, "Symmetrical waveguide device fabricated by direct UV writing," Phot.. Tech. Lett. 14, 173-175, (2002).
    [CrossRef]

App. Opt. (1)

M.J. Yuen, "Ultraviolet absorption studies of germanium silicate glasses," App. Opt. 21, 136-140 (1982).
[CrossRef]

Appl. Opt. (1)

Appl. Phys. Lett. (1)

P.J. Lemaire, A.M. Vengsarkar, W.A. Reed, D.J. DiGiovanni, "Thermally enhanced ultraviolet photosensitivity in GeO2 and P2O5 doped optical fibers," Appl. Phys. Lett. 66, 2034-2036 (1995).
[CrossRef]

Electon. Lett. (1)

D. Zauner, K. Kulstad, J. Rathje, M. Svalgaard, "Directly UV-written silica-on-silicon planar waveguides with low insertion loss," Electron. Lett. 34, 1582-1584 (1998).
[CrossRef]

Electron. Lett. (6)

P.J. Lemaire, R.M. Atkins, V. Mizrahi, W.A. Reed, "High Pressure H2 loading as a technique for achieving ultrahigh UV photosensitivity and thermal sensitivity in GeO2 doped optical fibres," Electron. Lett. 29, 1191-1193 (1993).
[CrossRef]

G.D. Maxwell, B.J. Ainslie, "Demonstration of a directly written directional coupler using UV induced photosensitivity in a planar silica waveguide," Electron. Lett. 31, 95-96 (1995).
[CrossRef]

M. Svalgaard, "Effect of D2 outdiffusion on direct UV writing of optical waveguides," Electron. Lett. 35, 1840-1842 (1999).
[CrossRef]

M. Svalgaard, C.V. Poulsen, A. Bjarklev, O. Poulsen, 'Direct UV-writing of buried single-mode channel waveguides in Ge-doped silica films,' Electron. Lett. 30, 1401-1402 (1994).
[CrossRef]

M.Y. Park, W. Yoon, S. Han, G. H. Song, "Fabrication of low-cost planar wavelength-selective optical add-drop multiplexer by employing UV photosensitivity," Electron. Lett. 38, 1532-1533 (2002).
[CrossRef]

G.D. Emmerson, S.P. Watts, C.B.E. Gawith, V. Albanis, M. Ibsen, R.B. Williams, P.G.R. Smith, "Fabrication of directly UV written channel waveguides with simultaneously defined integral gratings," Electron. Lett. 38, 1531�??1532 (2002).
[CrossRef]

J. Lightwave Technol. (2)

M. Svalgaard, K. Faerch, L.-U. Andersen, "Variable optical attenuator fabricated by direct UV writing," J. Lightwave Technol. 21, 2097-2103 (2003).
[CrossRef]

A. Iino, M. Kuwabara, K. Kokura, "Mechanisms of hydrogen-induced losses in silica-based optical fibers," J. Lightwave Technol. 8, 1675-1679 (1990).
[CrossRef]

Opt. Eng. (1)

P.J. Lemaire, "Reliability of optical fibers exposed to hydrogen: Prediction of long-term loss increases," Opt. Eng. 30, 780-789 (1991).
[CrossRef]

Opt. Express (1)

OSA Bragg Gratings, Poling, and Phot. 05 (1)

M. Svalgaard, A. Harpøth, M. Andersen, "Discontinuities during UV writing of waveguides," in Proceedings of OSA Topical Meeting on Bragg Gratings, Poling and Photosensitivity, B.J. Eggleton, ed., (Technical Digest Series, Optical Society of America, Washington, D.C., 2005), 121-123.

Phot. Tech. Lett. (2)

C. Peucheret, Y. Geng, M. Svalgaard, B. Zsigri, H.R. Sørensen, N. Chi, H.-J. Deyerl, M. Kristensen, P. Jeppesen, "Direct UV written Michelson Interferometer for RZ signal generation using phase-to-intensity modulation conversion," Phot. Tech. Lett. 17, 1674-1676 (2005).
[CrossRef]

K. Færch, M. Svalgaard, "Symmetrical waveguide device fabricated by direct UV writing," Phot.. Tech. Lett. 14, 173-175, (2002).
[CrossRef]

Phys. Rev. B (2)

M. Kristensen, "Ultraviolet-light-induced processes in germanium-doped silica," Phys. Rev. B 64, 144201 (2001).
[CrossRef]

S. Adachi, "Model dielectric constants of Si and Ge," Phys. Rev. B 38, 12966-12976 (1988).
[CrossRef]

Phys. Status Solidi. A (1)

L.N. Skuja, A.N. Trukhin, A.E. Plaudis, "Luminescence in germanium-doped glassy SiO2," Phys. Status Solidi. A 84, K153-157 (1984).
[CrossRef]

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Figures (7)

Fig 1.
Fig 1.

Waveguide width (red squares) and index step (blue circles) versus scan velocity. A sudden ‘shut-down’ behavior occurs at 220 μm/s, after which the waveguide becomes very weak.

Fig 2.
Fig 2.

Close-up view (40×30 μm2) of a Δn discontinuity. Image a) is a brightfield micrograph sensitive to index contrast while image b) shows blue luminescence from GODC’s upon excitation with a weak UV field. The transition occurs over a length of just 2-3 μm, which is comparable in size to the UV spot. In these images it is evident that an oscillation in the scanning stages was present, this has since been removed and we have verified that it is unrelated to the topics discussed in this paper.

Fig. 3.
Fig. 3.

Setup used for measuring the power absorbed in the core layer during UV writing.

Fig. 4.
Fig. 4.

The UV power absorbed in the core vs. time during a discontinuity event. The transition between ‘low’ and ‘high’ absorption occurs over a time interval of just 6×10-4 sec. An illustration of the corresponding index structure is shown in the inset.

Fig. 5.
Fig. 5.

Calculated 2D steady state temperature change profile for the ‘high’ UV absorption state (β=1.3×105 m-1). The top/bottom of the plot corresponds to the glass boundaries, while the layer boundaries and incident/reflected UV beam are indicted with white lines. The peak temperature increase is ~600 K.

Fig. 6.
Fig. 6.

Calculated vertical temperature profile corresponding to the measured ‘low’ and ‘high’ UV absorption state (β=1.8×104 m-1, β=1.3×105 m-1). The peak temperature increase is ~130 K for the low absorption state and ~600 K for the high absorption state. The temperature profile due to substrate absorption is also plotted, showing only a modest heating due to the large thermal conductivity of silicon.

Fig. 7.
Fig. 7.

Calculated ‘low’ UV absorption state vertical temperature profile for a thick (5.5 μm) and a thin (2.8 μm) core layer. The peak temperature increase is ~130 K for the thick core and ~80 K for the thin core. Experiments show that strong waveguides can not be written in the thin core.

Equations (2)

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D 1 = c 1 e 2 P in
c p ρ T t = k ( 2 T z 2 + 2 T r 2 + 1 r T r ) + I down ( r ) β e β ( L 2 z ) + I up ( r ) β e β ( z L 1 )

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