Abstract

We report the presence of a curious and highly reproducible effect in multimode lithium niobate waveguides fabricated by proton exchange (PE) in molten benzoic acid at temperatures ranging from 160°C to ~250°C. The spectral lines in the mode spectra of these guides (measured using a prism coupler) are anomalously side-shifted out of the expected geometrical plane. Transforming these measurements back into the plane of the waveguide, we find that the direction of scattering (relative to the crystal axis) is extremely precise (<1% deviation about a mean), and that the effect can be explained by postulating the existence of precisely oriented, stress-induced gratinglike structures (with irregular periods in the 10–70-μm range) in the guides.

© 1986 Optical Society of America

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References

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  1. C. E. Rice, J. L. Jackel, “Structural Changes with Composition and Temperature in Rhombohedral LiNbO3,” Mater. Res. Bull. 19, 915 (1984).
    [CrossRef]
  2. J. L. Jackel, C. E. Rice, J. J. Veselka, “Proton Exchange for High Index Waveguides in LiNbO3,” J. Appl. Phys. 41, 607 (1982).
  3. D. F. Clark, A. C. G. Nutt, K. K. Wong, P. J. R. Laybourn, R. M. De La Rue, “Characterization of Proton-Exchanged Slab Optical Waveguides in X-cut LiNbO3,” J. Appl. Phys. 54, 6218 (1983).
    [CrossRef]
  4. M. De Micheli, J. Botineau, P. Sibillot, D. B. Ostrowsky, M. Papuchon, “Fabrication and Characterisation of Titanium-Indiffused Proton Exchanged Waveguides in Lithium Niobate,” Opt. Commun. 42, 101 (1982).
    [CrossRef]
  5. M. De Micheli et al., “Crystalline and Optical Quality of Proton Exchanged Waveguides,” in Technical Digest, Fifth International Conference on Integrated Optics and Optical Fiber Communication–Eleventh European Conference on Optical Communication, Venice (1985), p. 55.
  6. M. De Micheli, J. Vollmer, J. P. Barety, S. Neveu, “Postdead-line paper n∘9/A3 “Proton Exchange in LiNbO3: Temperature and Water Influence during the Process,” IEE Conf. Publ. London 227, (1983).
  7. M. De Micheli, “Nonlinear Interaction in LiNbO3 Guides,” in New Direction in Guided Waves and Coherent Optics, Vol. 2 (Martinus Nijhoff Publishers, The Hague1982), p. 495.

1984 (1)

C. E. Rice, J. L. Jackel, “Structural Changes with Composition and Temperature in Rhombohedral LiNbO3,” Mater. Res. Bull. 19, 915 (1984).
[CrossRef]

1983 (2)

D. F. Clark, A. C. G. Nutt, K. K. Wong, P. J. R. Laybourn, R. M. De La Rue, “Characterization of Proton-Exchanged Slab Optical Waveguides in X-cut LiNbO3,” J. Appl. Phys. 54, 6218 (1983).
[CrossRef]

M. De Micheli, J. Vollmer, J. P. Barety, S. Neveu, “Postdead-line paper n∘9/A3 “Proton Exchange in LiNbO3: Temperature and Water Influence during the Process,” IEE Conf. Publ. London 227, (1983).

1982 (2)

M. De Micheli, J. Botineau, P. Sibillot, D. B. Ostrowsky, M. Papuchon, “Fabrication and Characterisation of Titanium-Indiffused Proton Exchanged Waveguides in Lithium Niobate,” Opt. Commun. 42, 101 (1982).
[CrossRef]

J. L. Jackel, C. E. Rice, J. J. Veselka, “Proton Exchange for High Index Waveguides in LiNbO3,” J. Appl. Phys. 41, 607 (1982).

Barety, J. P.

M. De Micheli, J. Vollmer, J. P. Barety, S. Neveu, “Postdead-line paper n∘9/A3 “Proton Exchange in LiNbO3: Temperature and Water Influence during the Process,” IEE Conf. Publ. London 227, (1983).

Botineau, J.

M. De Micheli, J. Botineau, P. Sibillot, D. B. Ostrowsky, M. Papuchon, “Fabrication and Characterisation of Titanium-Indiffused Proton Exchanged Waveguides in Lithium Niobate,” Opt. Commun. 42, 101 (1982).
[CrossRef]

Clark, D. F.

D. F. Clark, A. C. G. Nutt, K. K. Wong, P. J. R. Laybourn, R. M. De La Rue, “Characterization of Proton-Exchanged Slab Optical Waveguides in X-cut LiNbO3,” J. Appl. Phys. 54, 6218 (1983).
[CrossRef]

De La Rue, R. M.

D. F. Clark, A. C. G. Nutt, K. K. Wong, P. J. R. Laybourn, R. M. De La Rue, “Characterization of Proton-Exchanged Slab Optical Waveguides in X-cut LiNbO3,” J. Appl. Phys. 54, 6218 (1983).
[CrossRef]

De Micheli, M.

M. De Micheli, J. Vollmer, J. P. Barety, S. Neveu, “Postdead-line paper n∘9/A3 “Proton Exchange in LiNbO3: Temperature and Water Influence during the Process,” IEE Conf. Publ. London 227, (1983).

M. De Micheli, J. Botineau, P. Sibillot, D. B. Ostrowsky, M. Papuchon, “Fabrication and Characterisation of Titanium-Indiffused Proton Exchanged Waveguides in Lithium Niobate,” Opt. Commun. 42, 101 (1982).
[CrossRef]

M. De Micheli et al., “Crystalline and Optical Quality of Proton Exchanged Waveguides,” in Technical Digest, Fifth International Conference on Integrated Optics and Optical Fiber Communication–Eleventh European Conference on Optical Communication, Venice (1985), p. 55.

M. De Micheli, “Nonlinear Interaction in LiNbO3 Guides,” in New Direction in Guided Waves and Coherent Optics, Vol. 2 (Martinus Nijhoff Publishers, The Hague1982), p. 495.

Jackel, J. L.

C. E. Rice, J. L. Jackel, “Structural Changes with Composition and Temperature in Rhombohedral LiNbO3,” Mater. Res. Bull. 19, 915 (1984).
[CrossRef]

J. L. Jackel, C. E. Rice, J. J. Veselka, “Proton Exchange for High Index Waveguides in LiNbO3,” J. Appl. Phys. 41, 607 (1982).

Laybourn, P. J. R.

D. F. Clark, A. C. G. Nutt, K. K. Wong, P. J. R. Laybourn, R. M. De La Rue, “Characterization of Proton-Exchanged Slab Optical Waveguides in X-cut LiNbO3,” J. Appl. Phys. 54, 6218 (1983).
[CrossRef]

Neveu, S.

M. De Micheli, J. Vollmer, J. P. Barety, S. Neveu, “Postdead-line paper n∘9/A3 “Proton Exchange in LiNbO3: Temperature and Water Influence during the Process,” IEE Conf. Publ. London 227, (1983).

Nutt, A. C. G.

D. F. Clark, A. C. G. Nutt, K. K. Wong, P. J. R. Laybourn, R. M. De La Rue, “Characterization of Proton-Exchanged Slab Optical Waveguides in X-cut LiNbO3,” J. Appl. Phys. 54, 6218 (1983).
[CrossRef]

Ostrowsky, D. B.

M. De Micheli, J. Botineau, P. Sibillot, D. B. Ostrowsky, M. Papuchon, “Fabrication and Characterisation of Titanium-Indiffused Proton Exchanged Waveguides in Lithium Niobate,” Opt. Commun. 42, 101 (1982).
[CrossRef]

Papuchon, M.

M. De Micheli, J. Botineau, P. Sibillot, D. B. Ostrowsky, M. Papuchon, “Fabrication and Characterisation of Titanium-Indiffused Proton Exchanged Waveguides in Lithium Niobate,” Opt. Commun. 42, 101 (1982).
[CrossRef]

Rice, C. E.

C. E. Rice, J. L. Jackel, “Structural Changes with Composition and Temperature in Rhombohedral LiNbO3,” Mater. Res. Bull. 19, 915 (1984).
[CrossRef]

J. L. Jackel, C. E. Rice, J. J. Veselka, “Proton Exchange for High Index Waveguides in LiNbO3,” J. Appl. Phys. 41, 607 (1982).

Sibillot, P.

M. De Micheli, J. Botineau, P. Sibillot, D. B. Ostrowsky, M. Papuchon, “Fabrication and Characterisation of Titanium-Indiffused Proton Exchanged Waveguides in Lithium Niobate,” Opt. Commun. 42, 101 (1982).
[CrossRef]

Veselka, J. J.

J. L. Jackel, C. E. Rice, J. J. Veselka, “Proton Exchange for High Index Waveguides in LiNbO3,” J. Appl. Phys. 41, 607 (1982).

Vollmer, J.

M. De Micheli, J. Vollmer, J. P. Barety, S. Neveu, “Postdead-line paper n∘9/A3 “Proton Exchange in LiNbO3: Temperature and Water Influence during the Process,” IEE Conf. Publ. London 227, (1983).

Wong, K. K.

D. F. Clark, A. C. G. Nutt, K. K. Wong, P. J. R. Laybourn, R. M. De La Rue, “Characterization of Proton-Exchanged Slab Optical Waveguides in X-cut LiNbO3,” J. Appl. Phys. 54, 6218 (1983).
[CrossRef]

IEE Conf. Publ. London (1)

M. De Micheli, J. Vollmer, J. P. Barety, S. Neveu, “Postdead-line paper n∘9/A3 “Proton Exchange in LiNbO3: Temperature and Water Influence during the Process,” IEE Conf. Publ. London 227, (1983).

J. Appl. Phys. (2)

J. L. Jackel, C. E. Rice, J. J. Veselka, “Proton Exchange for High Index Waveguides in LiNbO3,” J. Appl. Phys. 41, 607 (1982).

D. F. Clark, A. C. G. Nutt, K. K. Wong, P. J. R. Laybourn, R. M. De La Rue, “Characterization of Proton-Exchanged Slab Optical Waveguides in X-cut LiNbO3,” J. Appl. Phys. 54, 6218 (1983).
[CrossRef]

Mater. Res. Bull. (1)

C. E. Rice, J. L. Jackel, “Structural Changes with Composition and Temperature in Rhombohedral LiNbO3,” Mater. Res. Bull. 19, 915 (1984).
[CrossRef]

Opt. Commun. (1)

M. De Micheli, J. Botineau, P. Sibillot, D. B. Ostrowsky, M. Papuchon, “Fabrication and Characterisation of Titanium-Indiffused Proton Exchanged Waveguides in Lithium Niobate,” Opt. Commun. 42, 101 (1982).
[CrossRef]

Other (2)

M. De Micheli et al., “Crystalline and Optical Quality of Proton Exchanged Waveguides,” in Technical Digest, Fifth International Conference on Integrated Optics and Optical Fiber Communication–Eleventh European Conference on Optical Communication, Venice (1985), p. 55.

M. De Micheli, “Nonlinear Interaction in LiNbO3 Guides,” in New Direction in Guided Waves and Coherent Optics, Vol. 2 (Martinus Nijhoff Publishers, The Hague1982), p. 495.

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Figures (3)

Fig. 1
Fig. 1

Sketch in perspective of the experimental setup (schematic only). Light is coupled into the planar X-cut PE waveguide(crystal axis C) using a prism, it travels a distance of ~2 cm in the guide, and is then coupled out by a second prism. The mode spectrum, imaged onto a screen oriented parallel to the prism hypotenuse, is shifted laterally in an anomalous manner. The prism angle is β and its height is L. The heavy dashed line is normal to the prism face and joins the output coupling point to the origin of the (X, Y) coordinate system, itself fixed in the plane of the screen. The (x,y,z) coordinate system is fixed as shown with its origin at the output coupling point.

Fig. 2
Fig. 2

Experimentally determined wave vector diagram (plotted in terms of the effective refractive indices) for three different samples. Nx and Ny are the effective indices of the modes resolved parallel to the x and y axes, respectively. The primary mode numbers in the three cases are 2 (□), 3 (○), and 3 (△). In each case a straight line can be fitted to the experimental points to an accuracy of better than 1%. The grading lines that would cause Bragg scattering of this kind are oriented normal to these fitted lines.

Fig. 3
Fig. 3

Wave vector diagram for the □ case in Fig. 2, including the grating vectors needed to cause the observed scattering. Note that the scales on the Ny and Nx axes are different. The deflection angles of the five modes (measured from the Ny axis) are −2.514°, −1.148°, 0°, 0.750°, and 1.294° for m = 4, 3, 2, 1, and 0, respectively, and the grating periods needed to create the measured wave vectors gij range in this case from 10 to 23 μm. The grating vectors are oriented at an angle θ = 38° to the crystal axis C (see text).

Tables (2)

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Table I Fabrication Parameters

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Table II Typical Fabrication Parameters of Samples Presenting the Reported Effect

Equations (3)

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ϕ m = arctan { Z / [ ( χ 2 - R 2 ) cos β - X sin β ] } ,
N eff = n p [ 1 - ( R / χ ) 2 cos β - ( X / χ ) sin β ] 2 - ( Z / χ ) 2 ,
χ = n p D 2 + R 2 and R = X 2 + Z 2 .

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