Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Patent
1991-05-17
1993-05-11
Kunemund, Robert
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
423641, 423593, 156621, 156624, 156DIG71, 156DIG87, C30B 2930, C30B 1902
Patent
active
052099172
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a lithium niobate single crystal thin film having a film thickness suited for use in various optical materials including thin film guided wave SHG devices, and to production method thereof.
BACKGROUND TECHNOLOGY
With recent advance in optical applications technology, shorter wavelengths of laser sources are increasing in demand.
This is because a shorter wavelength laser can improve the recording density and photosensitivity, and such a shorter wavelength laser is expected to be applied to optical devices such as optical discs, laser printers, and the like.
Therefore, there have been intensively conducted studies on second harmonic wave generating (SHG) devices which are capable of converting wavelengths of incident laser light to 1/2.
Heretofore, bulk single crystals of nonlinear optical crystals have been used as such second harmonic wave generating (SHG) devices, using high-output gas lasers as light sources. However, since there has been a strong demand for compact optical disc devices, laser printers, and the like, and gas lasers, which use optical modulation, require external modulators, semiconductor have been increasingly and predominantly used in place of gas lasers, for their capability of direct modulation and low costs. For this purpose, thin film waveguide SHG device has become in demand in order to obtain high conversion outputs with low light source outputs of several mW to several tens of mW.
Heretofore, as nonlinear optical materials for use in such thin film waveguide SHG devices, there have been known a lithium niobate bulk single crystal which is diffused with Ti or the like to form a waveguide layer having a different refractive index, and a lithium tantalate substrate on which a lithium niobate single crystal thin film is formed as a waveguide by radio-frequency sputtering or the like, these methods have been difficult to obtain lithium niobate single crystal thin films of good crystallinity, and it has thus been impossible to obtain high conversion efficiency.
Liquid phase epitaxy method is considered to be advantageous as a method to fabricate single crystal thin films with good crystallinity.
Liquid phase epitaxial methods to obtain lithium niobate single crystal thin films are described, for example, in
1) Japanese Patent Publication 51-9720/1976, and Applied Physics Letters, Vol. 26, No. 1, January 1975 p8-10, in which a lithium niobate thin film for optical waveguide is formed on a lithium tantalate substrate by a liquid phase epitaxial method, using Li.sub.2 O or V.sub.2 O.sub.5 as a flux.
2) Japanese Patent Publication 56-47160/1981, in which a lithium niobate/lithium tantalate solid solution thin film containing Mg is formed by an epitaxial technique on a substrate using Li.sub.2 O or V.sub.2 O.sub.5 as a flux.
However, with liquid phase epitaxial methods which have heretofore been known, it is impossible to obtain a lithium niobate single crystal thin film with good crystallinity on a lithium tantalate substrate, and, it is particularly difficult to obtain a lithium niobate single crystal thin film having a thickness required for fabrication of SHG devices and having low propagation losses. There have been known no thin film waveguide SHG devices which have been practically applied.
The film thickness required to fabricate the thin film guided wave SHG devices means a thickness which is capable of coinciding the effective index of a basic wavelength light of wavelength .lambda. with that of the second harmonic wave of wavelength .lambda./2, to enable phase matching of incident laser light to the second harmonic wave, and, in particular, when a SHG device for semiconductor laser is fabricated using a lithium niobate thin film formed on a lithium tantalate substrate, it is considered that a lithium niobate single crystal thin film with a thickness of over 5 .mu.m is required to coincide the effective indices.
Furthermore, in order to obtain high-output thin film guided wave SHG devices, it is necessary to increase the difference be
REFERENCES:
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patent: 4953931 (1990-09-01), Miyazaki et al.
Ballman et al (III), "The Growth of LiNbO.sub.3 Thin Films by Liquid Phase Epitaxial Techniques", Journal of Crystal Growth, 29 (1975) pp. 289-295.
Tien et al, "Light Beam Scanning and Deflection In Epitaxial LiNb.sub.3 O.sub.3 Electro-Optic Waveguides", Applied Physics Letters, vol. 25, No. 10, Nov. 15, 1974, pp. 563-565.
Neurgaonkar et al, "Epitaxial Growth of Ferroelectric Films for Optoelectronic (SAW) Applications", Journal of Crystal Growth, vol. 84 (1987) pp. 409-412.
Voronov et al, "Production of Single Crystal Films of Lithium Niobate by Liquid Phase Epitaxy", Deposited Doc. SPSTL 1 khp-D81, 148-55 1981 (abstract only).
Enomoto Ryo
Ohno Satoshi
Yamada Masaya
Ibiden Co. Ltd.
Kunemund Robert
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