Abstract

LiTaO3 optical modulators have been developed using the technique of self-compensation for therma stability. By using two crystals in cascade, with optic axes 180° apart, and a half-wave plate between them with axis at 45°, the birefringence of each crystal is equal but opposite and there is no net change in birefringence with temperature. Aside from thermal stability, the optical modulator described damps out mechanical resonances caused by the piezoelectric properties of the crystals, and its thin-film substrate mounting is applicable to wideband modulation. Experimental measurements show that 95% modulation depth can be attained over a 25° C temperature range with virtually no change in the amplitude or phase of the modulated signal.

© 1971 Optical Society of America

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References

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  1. R. T. Denton, F. S. Chen, A. A. Ballman, J. Appl. Phys. 38, 1611 (1967).
    [CrossRef]
  2. E. G. Spencer, P. V. Lenzo, A. A. Ballman, Proc. IEEE 55, 2074 (1967).
    [CrossRef]
  3. C. J. Peters, Proc. IEEE 53, 455 (1965).
    [CrossRef]
  4. R. P. Reisz, M. R. Biazzo, Appl. Opt. 8, 1393 (1969).
    [CrossRef]
  5. G. White, “Optical Modulation at Gigahertz Rates,” presented at the IEEE International Conference on Communications, San Francisco, 8–10 June 1970 (Digest of Technical Papers, Session 22).
  6. G. White, Proc. IEEE (Lett.) 58, 1779 (1970).
    [CrossRef]

1970 (1)

G. White, Proc. IEEE (Lett.) 58, 1779 (1970).
[CrossRef]

1969 (1)

1967 (2)

R. T. Denton, F. S. Chen, A. A. Ballman, J. Appl. Phys. 38, 1611 (1967).
[CrossRef]

E. G. Spencer, P. V. Lenzo, A. A. Ballman, Proc. IEEE 55, 2074 (1967).
[CrossRef]

1965 (1)

C. J. Peters, Proc. IEEE 53, 455 (1965).
[CrossRef]

Ballman, A. A.

R. T. Denton, F. S. Chen, A. A. Ballman, J. Appl. Phys. 38, 1611 (1967).
[CrossRef]

E. G. Spencer, P. V. Lenzo, A. A. Ballman, Proc. IEEE 55, 2074 (1967).
[CrossRef]

Biazzo, M. R.

Chen, F. S.

R. T. Denton, F. S. Chen, A. A. Ballman, J. Appl. Phys. 38, 1611 (1967).
[CrossRef]

Denton, R. T.

R. T. Denton, F. S. Chen, A. A. Ballman, J. Appl. Phys. 38, 1611 (1967).
[CrossRef]

Lenzo, P. V.

E. G. Spencer, P. V. Lenzo, A. A. Ballman, Proc. IEEE 55, 2074 (1967).
[CrossRef]

Peters, C. J.

C. J. Peters, Proc. IEEE 53, 455 (1965).
[CrossRef]

Reisz, R. P.

Spencer, E. G.

E. G. Spencer, P. V. Lenzo, A. A. Ballman, Proc. IEEE 55, 2074 (1967).
[CrossRef]

White, G.

G. White, Proc. IEEE (Lett.) 58, 1779 (1970).
[CrossRef]

G. White, “Optical Modulation at Gigahertz Rates,” presented at the IEEE International Conference on Communications, San Francisco, 8–10 June 1970 (Digest of Technical Papers, Session 22).

Appl. Opt. (1)

J. Appl. Phys. (1)

R. T. Denton, F. S. Chen, A. A. Ballman, J. Appl. Phys. 38, 1611 (1967).
[CrossRef]

Proc. IEEE (2)

E. G. Spencer, P. V. Lenzo, A. A. Ballman, Proc. IEEE 55, 2074 (1967).
[CrossRef]

C. J. Peters, Proc. IEEE 53, 455 (1965).
[CrossRef]

Proc. IEEE (Lett.) (1)

G. White, Proc. IEEE (Lett.) 58, 1779 (1970).
[CrossRef]

Other (1)

G. White, “Optical Modulation at Gigahertz Rates,” presented at the IEEE International Conference on Communications, San Francisco, 8–10 June 1970 (Digest of Technical Papers, Session 22).

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Figures (7)

Fig. 1
Fig. 1

Complete assembly of lithium tantalate thermal compensating optical modulator.

Fig. 2
Fig. 2

Lithium tantalate modulator crystal orientation.

Fig. 3
Fig. 3

Two lithium tantalate crystals positioned on substrate.

Fig. 4
Fig. 4

Optical modulator assembly jig.

Fig. 5
Fig. 5

The well-defined laser beam spot above shows the exit beam as it appears on the target after passing through two lithium tantalate rods 0.25 mm square by 9.5 mm long and a half-wave plate. The spot shows no trace of distortion due to the light striking the walls of the modulator rods. The spot shape is round. The apparent ellipticity was caused by the camera angle necessary to take the photograph.

Fig. 6
Fig. 6

(A) Starting temperature 37°C. The modulation output shows the vertical center line of the oscilloscope passing through the negative peak of the 60-Hz modulation. The straight sweep line in each photograph indicates zero dc bias. (B) Temperature increased to 37.5°C. The temperature increase of 0.5°C results in a phase shift of 90°. 60-Hz modulation has doubled in frequency to 120 Hz. (C) Temperature increased to 38°C. Another 0.50° C increase in temperature produces another 90° phase shift in the modulation. (A) and (C) are now 180° out of phase for a total temperature change of 1°C.

Fig. 7
Fig. 7

(A) This photograph shows the half-wave voltage of a single lithium tantalate modulator rod. The voltage is along the horizontal scale, whose sensitivity is 16 V cm−1. The total halfwave voltage is shown as 5 cm, or 80 V peak to peak. (B) Photograph of the modulated output after passing through the same rod and then the half-wave retardation plate oriented at 45°. The half-wave voltage is still 80 V peak to peak, but its phase has shifted 180° due to the half-wave plate. (C) In this photograph the light has passed through all three components of the modulator. After passing through the half-wave plate, the light passes through the second modulator rod, so the half-wave voltage has been reduced to 2.5 cm or 40 V peak to peak.

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