Abstract

Waveguide modulators incorporating paralle-plate electrodes are investigated by computer modeling. Metal-electrode structures differ from severe optical losses that are due to surface plasmons. Silicon-electrode structures exhibit lower losses. Bandwidth is limited by the resistivity and the proximity of the electrodes. Doping the silicon improves conductivity but increases optical absorption. Device optimization involves a trade-off between bandwidth and optical loss. Devices are fabricated by the use of substrates of silicon on sapphire, with rf sputtered lithium niobate films and plasma-enhanced chemical vapor-deposited hydrogenated amorphous silicon for the upper electrodes. The electro-optic coefficient of these lithium niobate films is ∼50% of the value for bulk material. The results indicate the possibility of using these devices for combining silicon integrated circuits with waveguide modulators on a common substrate.

© 1993 Optical Society of America

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References

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  1. D. H. Hartman, “Digital high speed interconnects: a study of the optical alternative,” Opt. Eng. 25, 1086–1102 (1986).
  2. P. R. Haugen, S. Rychnovsky, A. Husain, L. D. Hutcheson, “Optical interconnects for high speed computing,” Opt. Eng. 25, 1076–1085 (1986).
  3. D. Erasme, M. G. F. Wilson, “Analysis and optimization of integrated-optic travelling-wave modulators using periodic and non-periodic phase reversals,” Opt. Quantum Electron. 18, 203–211 (1986).
    [Crossref]
  4. L. M. Walpita, “Solutions for planar optical waveguide equations by selecting zero elements in a characteristic matrix,” J. Opt. Soc. Am. A 2, 595–602 (1985).
    [Crossref]
  5. A. Reisinger, “Characteristics of optical guided modes in lossy waveguides,” Appl. Opt. 12, 1015–1025 (1973).
    [Crossref] [PubMed]
  6. I. P. Kaminow, W. L. Mammel, H. P. Weber, “Metal-clad optical waveguides: analytical and experimental study,” Appl. Opt. 13, 396–405 (1974).
    [Crossref] [PubMed]
  7. F. Zernike, “Fabrication and measurement of passive components,” in Integrated Optics,T. Tamir, ed. (Springer-Verlag, New York, 1979), pp. 201–241.
  8. J. M. Hammer, “Modulation and switching of light in dielectric waveguides,” in Integrated Optics, T. Tamir, ed. (Springer-Verlag, New York, 1979), pp. 139–200.
  9. H. Kogelnik, “Theory of dielectric waveguides,” in Integrated Optics, T. Tamir, ed. (Springer-Verlag, New York, 1979), pp. 13–81.
  10. P. Lorrain, D. Corson, “Maxwell's equations,” in Electromagnetic Fields and Waves (Freeman, San Francisco, Calif., 1970), Chap. 10, pp. 422–458.
  11. C-C. Shih, A. Yariv, “A theoretical model of the linear electro-optic effect,” J. Phys. C 15, 825–846 (1982).
    [Crossref]
  12. This figure for refractive index is based on crystalline silicon. Test structures, described in the next section, employed hydrogenated amorphous silicon for the upper electrodes. This exhibits a slightly higher refractive index, ∼3.67; the results presented here are not substantially altered by this difference.
  13. S. M. Sze, Physics of Semiconductor Devices, (Wiley, New York, 1981), Chap. 1, pp. 27–38.
  14. P. E. Schmidt, “Optical absorption in heavily doped silicon,” Phys. Rev. B 23, 5531–5536 (1981).
    [Crossref]
  15. T. Cholapranee, L. Fabiny, “Properties of lithium niobate thin polycrystalline films deposited on silicon substrates,” in Proceedings of the Sixth International Symposium on Applications of Ferroelectrics, (Institute of Electrical and Electronics Engineers, New York, 1986), pp. 585–588.
    [Crossref]
  16. P. R. Meek, L. Holland, P. D. Townsend, “Sputter deposition of LiNbO3 films,” Thin Solid Films 141, 251–259 (1986).
    [Crossref]
  17. H. Robinson, C. W. Pitt, “RF Sputtered films of z-oriented lithium niobate on silicon,” in Proceedings of the 8th International Conference on Ion and Plasma Assisted Techniques.
  18. R. Betts, C. W. Pitt, “Growth of thin-film lithium niobate films by molecular beam epitaxy,” Electron. Lett. 21, 960–962 (1985).
    [Crossref]
  19. H. Robinson, “Electro-optic waveguide modulators using the parallel-plate configuration,” Ph.D. dissertation (University College London, London, 1991), Chap. 6, pp. 154–183.
  20. P. G. LeComber, W. E Spear, “Doped amorphous semiconductors,” in Amorphous Semiconductors, M. H. Brodsky, ed. (Butterworth, London, 1959), pp. 251–285.

1986 (4)

D. H. Hartman, “Digital high speed interconnects: a study of the optical alternative,” Opt. Eng. 25, 1086–1102 (1986).

P. R. Haugen, S. Rychnovsky, A. Husain, L. D. Hutcheson, “Optical interconnects for high speed computing,” Opt. Eng. 25, 1076–1085 (1986).

D. Erasme, M. G. F. Wilson, “Analysis and optimization of integrated-optic travelling-wave modulators using periodic and non-periodic phase reversals,” Opt. Quantum Electron. 18, 203–211 (1986).
[Crossref]

P. R. Meek, L. Holland, P. D. Townsend, “Sputter deposition of LiNbO3 films,” Thin Solid Films 141, 251–259 (1986).
[Crossref]

1985 (2)

R. Betts, C. W. Pitt, “Growth of thin-film lithium niobate films by molecular beam epitaxy,” Electron. Lett. 21, 960–962 (1985).
[Crossref]

L. M. Walpita, “Solutions for planar optical waveguide equations by selecting zero elements in a characteristic matrix,” J. Opt. Soc. Am. A 2, 595–602 (1985).
[Crossref]

1982 (1)

C-C. Shih, A. Yariv, “A theoretical model of the linear electro-optic effect,” J. Phys. C 15, 825–846 (1982).
[Crossref]

1981 (1)

P. E. Schmidt, “Optical absorption in heavily doped silicon,” Phys. Rev. B 23, 5531–5536 (1981).
[Crossref]

1974 (1)

1973 (1)

Betts, R.

R. Betts, C. W. Pitt, “Growth of thin-film lithium niobate films by molecular beam epitaxy,” Electron. Lett. 21, 960–962 (1985).
[Crossref]

Cholapranee, T.

T. Cholapranee, L. Fabiny, “Properties of lithium niobate thin polycrystalline films deposited on silicon substrates,” in Proceedings of the Sixth International Symposium on Applications of Ferroelectrics, (Institute of Electrical and Electronics Engineers, New York, 1986), pp. 585–588.
[Crossref]

Corson, D.

P. Lorrain, D. Corson, “Maxwell's equations,” in Electromagnetic Fields and Waves (Freeman, San Francisco, Calif., 1970), Chap. 10, pp. 422–458.

Erasme, D.

D. Erasme, M. G. F. Wilson, “Analysis and optimization of integrated-optic travelling-wave modulators using periodic and non-periodic phase reversals,” Opt. Quantum Electron. 18, 203–211 (1986).
[Crossref]

Fabiny, L.

T. Cholapranee, L. Fabiny, “Properties of lithium niobate thin polycrystalline films deposited on silicon substrates,” in Proceedings of the Sixth International Symposium on Applications of Ferroelectrics, (Institute of Electrical and Electronics Engineers, New York, 1986), pp. 585–588.
[Crossref]

Hammer, J. M.

J. M. Hammer, “Modulation and switching of light in dielectric waveguides,” in Integrated Optics, T. Tamir, ed. (Springer-Verlag, New York, 1979), pp. 139–200.

Hartman, D. H.

D. H. Hartman, “Digital high speed interconnects: a study of the optical alternative,” Opt. Eng. 25, 1086–1102 (1986).

Haugen, P. R.

P. R. Haugen, S. Rychnovsky, A. Husain, L. D. Hutcheson, “Optical interconnects for high speed computing,” Opt. Eng. 25, 1076–1085 (1986).

Holland, L.

P. R. Meek, L. Holland, P. D. Townsend, “Sputter deposition of LiNbO3 films,” Thin Solid Films 141, 251–259 (1986).
[Crossref]

Husain, A.

P. R. Haugen, S. Rychnovsky, A. Husain, L. D. Hutcheson, “Optical interconnects for high speed computing,” Opt. Eng. 25, 1076–1085 (1986).

Hutcheson, L. D.

P. R. Haugen, S. Rychnovsky, A. Husain, L. D. Hutcheson, “Optical interconnects for high speed computing,” Opt. Eng. 25, 1076–1085 (1986).

Kaminow, I. P.

Kogelnik, H.

H. Kogelnik, “Theory of dielectric waveguides,” in Integrated Optics, T. Tamir, ed. (Springer-Verlag, New York, 1979), pp. 13–81.

LeComber, P. G.

P. G. LeComber, W. E Spear, “Doped amorphous semiconductors,” in Amorphous Semiconductors, M. H. Brodsky, ed. (Butterworth, London, 1959), pp. 251–285.

Lorrain, P.

P. Lorrain, D. Corson, “Maxwell's equations,” in Electromagnetic Fields and Waves (Freeman, San Francisco, Calif., 1970), Chap. 10, pp. 422–458.

Mammel, W. L.

Meek, P. R.

P. R. Meek, L. Holland, P. D. Townsend, “Sputter deposition of LiNbO3 films,” Thin Solid Films 141, 251–259 (1986).
[Crossref]

Pitt, C. W.

R. Betts, C. W. Pitt, “Growth of thin-film lithium niobate films by molecular beam epitaxy,” Electron. Lett. 21, 960–962 (1985).
[Crossref]

H. Robinson, C. W. Pitt, “RF Sputtered films of z-oriented lithium niobate on silicon,” in Proceedings of the 8th International Conference on Ion and Plasma Assisted Techniques.

Reisinger, A.

Robinson, H.

H. Robinson, “Electro-optic waveguide modulators using the parallel-plate configuration,” Ph.D. dissertation (University College London, London, 1991), Chap. 6, pp. 154–183.

H. Robinson, C. W. Pitt, “RF Sputtered films of z-oriented lithium niobate on silicon,” in Proceedings of the 8th International Conference on Ion and Plasma Assisted Techniques.

Rychnovsky, S.

P. R. Haugen, S. Rychnovsky, A. Husain, L. D. Hutcheson, “Optical interconnects for high speed computing,” Opt. Eng. 25, 1076–1085 (1986).

Schmidt, P. E.

P. E. Schmidt, “Optical absorption in heavily doped silicon,” Phys. Rev. B 23, 5531–5536 (1981).
[Crossref]

Shih, C-C.

C-C. Shih, A. Yariv, “A theoretical model of the linear electro-optic effect,” J. Phys. C 15, 825–846 (1982).
[Crossref]

Spear, W. E

P. G. LeComber, W. E Spear, “Doped amorphous semiconductors,” in Amorphous Semiconductors, M. H. Brodsky, ed. (Butterworth, London, 1959), pp. 251–285.

Sze, S. M.

S. M. Sze, Physics of Semiconductor Devices, (Wiley, New York, 1981), Chap. 1, pp. 27–38.

Townsend, P. D.

P. R. Meek, L. Holland, P. D. Townsend, “Sputter deposition of LiNbO3 films,” Thin Solid Films 141, 251–259 (1986).
[Crossref]

Walpita, L. M.

Weber, H. P.

Wilson, M. G. F.

D. Erasme, M. G. F. Wilson, “Analysis and optimization of integrated-optic travelling-wave modulators using periodic and non-periodic phase reversals,” Opt. Quantum Electron. 18, 203–211 (1986).
[Crossref]

Yariv, A.

C-C. Shih, A. Yariv, “A theoretical model of the linear electro-optic effect,” J. Phys. C 15, 825–846 (1982).
[Crossref]

Zernike, F.

F. Zernike, “Fabrication and measurement of passive components,” in Integrated Optics,T. Tamir, ed. (Springer-Verlag, New York, 1979), pp. 201–241.

Appl. Opt. (2)

Electron. Lett. (1)

R. Betts, C. W. Pitt, “Growth of thin-film lithium niobate films by molecular beam epitaxy,” Electron. Lett. 21, 960–962 (1985).
[Crossref]

J. Opt. Soc. Am. A (1)

J. Phys. C (1)

C-C. Shih, A. Yariv, “A theoretical model of the linear electro-optic effect,” J. Phys. C 15, 825–846 (1982).
[Crossref]

Opt. Eng. (2)

D. H. Hartman, “Digital high speed interconnects: a study of the optical alternative,” Opt. Eng. 25, 1086–1102 (1986).

P. R. Haugen, S. Rychnovsky, A. Husain, L. D. Hutcheson, “Optical interconnects for high speed computing,” Opt. Eng. 25, 1076–1085 (1986).

Opt. Quantum Electron. (1)

D. Erasme, M. G. F. Wilson, “Analysis and optimization of integrated-optic travelling-wave modulators using periodic and non-periodic phase reversals,” Opt. Quantum Electron. 18, 203–211 (1986).
[Crossref]

Phys. Rev. B (1)

P. E. Schmidt, “Optical absorption in heavily doped silicon,” Phys. Rev. B 23, 5531–5536 (1981).
[Crossref]

Thin Solid Films (1)

P. R. Meek, L. Holland, P. D. Townsend, “Sputter deposition of LiNbO3 films,” Thin Solid Films 141, 251–259 (1986).
[Crossref]

Other (10)

H. Robinson, C. W. Pitt, “RF Sputtered films of z-oriented lithium niobate on silicon,” in Proceedings of the 8th International Conference on Ion and Plasma Assisted Techniques.

T. Cholapranee, L. Fabiny, “Properties of lithium niobate thin polycrystalline films deposited on silicon substrates,” in Proceedings of the Sixth International Symposium on Applications of Ferroelectrics, (Institute of Electrical and Electronics Engineers, New York, 1986), pp. 585–588.
[Crossref]

H. Robinson, “Electro-optic waveguide modulators using the parallel-plate configuration,” Ph.D. dissertation (University College London, London, 1991), Chap. 6, pp. 154–183.

P. G. LeComber, W. E Spear, “Doped amorphous semiconductors,” in Amorphous Semiconductors, M. H. Brodsky, ed. (Butterworth, London, 1959), pp. 251–285.

This figure for refractive index is based on crystalline silicon. Test structures, described in the next section, employed hydrogenated amorphous silicon for the upper electrodes. This exhibits a slightly higher refractive index, ∼3.67; the results presented here are not substantially altered by this difference.

S. M. Sze, Physics of Semiconductor Devices, (Wiley, New York, 1981), Chap. 1, pp. 27–38.

F. Zernike, “Fabrication and measurement of passive components,” in Integrated Optics,T. Tamir, ed. (Springer-Verlag, New York, 1979), pp. 201–241.

J. M. Hammer, “Modulation and switching of light in dielectric waveguides,” in Integrated Optics, T. Tamir, ed. (Springer-Verlag, New York, 1979), pp. 139–200.

H. Kogelnik, “Theory of dielectric waveguides,” in Integrated Optics, T. Tamir, ed. (Springer-Verlag, New York, 1979), pp. 13–81.

P. Lorrain, D. Corson, “Maxwell's equations,” in Electromagnetic Fields and Waves (Freeman, San Francisco, Calif., 1970), Chap. 10, pp. 422–458.

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Figures (13)

Fig. 1
Fig. 1

Effective indices of silicon nitride waveguides vs. silicon nitride thickness. The curves were calculated with the computer model: the upper curve of each pair illustrates the effect of an uncertainty of 0.01 in the refractive index of the silicon nitride. The points represent measurements.

Fig. 2
Fig. 2

Measured and calculated waveguide losses. The dashed horizontal lines indicate the range of measurement, and the dashed diagonal line represents perfect agreement. The arrows indicate measurements for which only an upper or a lower bound could be specified (see text).

Fig. 3
Fig. 3

Modal profiles (transverse magnetic field versus depth through waveguide) of silver/lithium niobate/silver for two values of the lithium niobate thickness.

Fig. 4
Fig. 4

Characteristics of silver/lithium niobate/silver structure (TM modes, λ = 0.6328 μm).

Fig. 5
Fig. 5

Characteristics of silver/lithium niobate/silver structure (TE modes, λ = 0.6328 μm).

Fig. 6
Fig. 6

Silicon-electrode modulator structure, with corresponding modal profile.

Fig. 7
Fig. 7

π modulation length of the silicon/lithium niobate/silicon structure as a function of lithium niobate thickness (λ = 1.53 μm).

Fig. 8
Fig. 8

Modeled modulator structure.

Fig. 9
Fig. 9

Device bandwidth and optical attenuation as functions of electrode resistivity. (Data on single crystal silicon from Sze13 and Schmidt14: see text.)

Fig. 10
Fig. 10

Optical micrograph of a finished device. Bond wires and pads are to the left. The active region is visible between the two metal bus bars that extend as far as the cleaved end on the right.

Fig. 11
Fig. 11

Scanning electron micrograph and schematic diagram of the cleaved end of a completed modulator.

Fig. 12
Fig. 12

Experimental arrangement for waveguide modulation measurements (reference beam omitted). The bright flash to the right of the video image is light scattered from the cleaved end of the modulator. The guided signal is visible as a small bright spot at the left-hand end of the device.

Fig. 13
Fig. 13

Modulated signal versus applied voltage. Crosses, from measurements (see text); curve, sinusoid fitted to the negative-bias portion of the data.

Equations (6)

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L π Δ n eff = π .
Δ n eff = γ Δ n = ½ γ n 3 r V / d ,
2 P Δ β = 0 ω Δ EE * d x ,
H = [ ( 0 μ 0 ) n k 0 β E ] 1 / 2 ,
γ = β / k 0 n S d x
P = S d x = 1 ,

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