Compositions – Light transmission modifying compositions – Inorganic crystalline solid
Reexamination Certificate
2000-02-01
2001-03-20
Utech, Benjamin L. (Department: 1765)
Compositions
Light transmission modifying compositions
Inorganic crystalline solid
Reexamination Certificate
active
06203728
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical single crystal film, a process for producing the same and an optical element comprising the same.
1. Description of Related Art
It is well-known to develop blue laser light sources for optical recording and reading-out with a high density, for example, second-harmonic generation (SHG) devices using a lithium niobate or lithium tantalate single crystal.
For example, according to “Journal of Applied Physics” Vol.70, No.5, p.2536-2541, (September 1991), there is disclosed the formation of a lithium niobate film on a MgO doped lithium niobate substrate by means of a liquid phase epitaxial process using Li
2
O-V
2
O
5
flux. The optical propagation loss of this film, however, is extremely large, for example, as large as 25 dB/cm at a green light of 514.5 nm wavelength. This defect is attributable to optical absorption caused by a V ion introduced into the film from the flux. It further describes that in order to decrease the optical absorption caused by the V ion, it is necessary to change the valence number of V ion from +3 to +5. To accomplish this an ozone annealing treatment is employed. Especially, it reports that the optical propagation loss at the green light of 514.5 nm wavelength can be improved to 1.6 dB/cm, by annealing a once produced lithium niobate film at 600° C. for an hour in an ozonic atmosphere. However, it also discloses that even with the ozone annealing treatment, the optical propagation loss is at least 10 dB/cm, for example, in the case of a blue beam of 450 nm wavelength.
According to, the “Journal of Crystal Growth” 132 (1993), p.48-60, a lithium niobate film is formed by means of a liquid phase epitaxial process using Li
2
O-V
2
O
5
flux and subjected to an ozone annealing treatment. Although this process highly improves an optical absorption in a green light range, the effect is not sufficient in a blue light range with shorter wavelengths. Accordingly, in order to use the film in a blue light range, it is effective to form a lithium niobate film by using, for example, a Li
2
O-B
2
O
3
flux that is free from transition metal elements such as V and the like causing the absorption.
According to “Journal of Applied Physics” Vol.67, No.2, 15, (January 1990) p.949-954, a Bi-substituted magnetic garnet is formed by means of a liquid phase epitaxial process using a Bi
2
O
3
flux. The Bi-substituted magnetic garnet is then subjected to an ozone annealing treatment, for example, at 700° C. for three hours and thereafter to an oxygen annealing treatment at 500° C. to decrease the optical propagation loss at a 1.3 &mgr;m wavelength to 1 dB/cm or less.
As mentioned above, in either “Journal of Applied Physics” Vol.70, No.5 (September 1991) or “Journal of Crystal Growth” 132 (1993) p.48-60, they failed to sufficiently decrease the optical absorption in the blue light range.
Additionally, the description of “Journal of Applied Physics” Vol.67, No.2, p.15 relates to the decrease of the optical absorption in an infrared range of, for example, 1.3-1.5 &mgr;m wavelengths and not to the decrease of the optical absorption in the blue light range of 400-500 nm wavelengths.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to decrease an absorption coefficient for a light in a blue light range of, for example, 400-500 nm wavelengths, when an optical single crystal film is manufactured by means of a liquid phase epitaxial process from a melt containing a transition metal.
According to the first aspect of the invention there is a provision of a process for manufacturing an optical single crystal film on a single crystal substrate which comprises the steps of:
liquid phase epitaxial growing for forming an optical single crystal epitaxial film from a melt containing a transition metal on a single crystal substrate;
increasing a temperature of the epitaxial film up to a predetermined temperature;
annealing said epitaxial film at said predetermined temperature in an atmosphere which contains ozone; and
decreasing the temperature of the epitaxial film from said predetermined temperature;
which process is characterized by exposing said epitaxial film to an atmosphere substantially free from ozone in at least one step of increasing and decreasing the temperature.
The present inventors have conceived that in forming an epitaxial film by means of an liquid phase epitaxial process and subjecting the epitaxial film to an ozone annealing treatment, an atmosphere substantially free from ozone is run around the epitaxial film in at least one step of increasing the temperature to an annealing temperature and decreasing the temperature from the annealing temperature. As the result, they have found that an absorption coefficient for a light in blue light range of 400-500 nm wavelengths is extremely decreased and have reached the present invention.
It has been found that the effect in decreasing the optical absorption coefficient by ozone annealing unexpectedly occurs only when the annealing temperature is within a predetermined temperature range, and if an ozone annealing time is prolonged, the optical absorption coefficient is unexpectedly increased as crystallinity deteriorates. In the temperature-increasing step and temperature-decreasing step before and after the ozone annealing step within the predetermined temperature range, the effect in decreasing the optical absorption coefficient is poor and rather it is likely that the optical absorption coefficient will increase as the crystallinity deteriorates. In the present invention, a substantially ozone-free atmosphere is used during a temperature-increasing step or temperature-decreasing step, such that an ozone annealing treatment which most improves the optical absorption coefficient can be realized.
It is conjectured that this is because the annealing temperature in an ozonic atmosphere can be increased and at the same time the ozone annealing time can be decreased.
Ozone has a property of self-decomposition. The degree of the self-decomposition of ozone extremely changes with changes of temperature, pressure, structure of apparatuses and the like. Therefore, since an ozone concentration in the actual annealing atmosphere surrounding the epitaxial film extremely changes, it is difficult to define the ozone concentration. Accordingly, in the present invention, the ozone concentration in the ozonic atmosphere just before being supplied around the epitaxial film will be mentioned.
The ozone concentration in the ozonic atmosphere is preferably at least 0.1% and maximally 100%, by volume. However, since actually an atmosphere containing both the ozone and oxygen is easily available, the ratio of the ozone in the ozone/oxygen-containing atmosphere is preferable to be 0.1-50% by volume. Moreover, it is possible to mix the ozone/oxygen-containing atmosphere with an inert gas carrier. In this case, the mix ratio of the ozone/oxygen-containing atmosphere with the inert gas is preferably 100:1~1:10. As the inert gas, nitrogen, argon, etc., are preferred.
In the present invention, the ozone concentration in “substantially ozone-free atmosphere” is defined to be not more than 0.1 ppm by volume. This atmosphere is preferably an inert gas atmosphere such as nitrogen, argon and the like.
Furthermore, in each of the temperature-increasing, temperature-decreasing and ozone annealing steps, the water vapor in the atmosphere is desired to be in a concentration of not less than 0.01% by volume. When the water vapor concentration is less than 0.01% by volume, it is not practical, because the degradation of the substrate is increased owing to, for example, the drawing out of Li from lithium niobate. From this point of view, the water vapor is more preferably in a concentration of not less than 0.1% by volume.
In the ozone annealing step, the water vapor in the atmosphere is particularly preferable to be in a concentration of not more than 5% by volume. When the water vapor concentration is more than 5% by volume, the degradation rate of ozone is so
Imaeda Minoru
Kawaguchi Tatsuo
Anderson Matthew
Burr & Brown
NGK Insulators Ltd.
Utech Benjamin L.
LandOfFree
Optical single crystal film process for producing the same... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical single crystal film process for producing the same..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical single crystal film process for producing the same... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2515223