JP2897861B2 - Nonlinear optical silica glass and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate-like, flake-like or fiber-like silica glass having a non-linear optical effect and a method for producing the same, and more particularly to a harmonic laser of an input laser, particularly a second harmonic (hereinafter, SHG). ) And a method for producing the same.

[0002]

2. Description of the Related Art In recent years, high-power ultraviolet lasers have been used for laser lithography, laser medical treatment, laser processing, and the like, and lasers in the visible to ultraviolet range of short wavelengths for optical information processing and optical measurement of optical disks and the like. It has become In addition to such applications, lasers are also used for photochemical reactions and isotope separation, and for that purpose, it has become necessary to shorten the wavelength of laser light and freely control the wavelength, that is, tunability.

Conventional lasers have been used as lasers for the above purpose.
Lasers and dye lasers have been used,
Due to the high cost of the mold, the solid-state laser can be shortened with a nonlinear optical material.
Technology for converting to wavelength lasers has attracted attention, and
Nonlinear optical materials have been proposed. Such inorganic nonlinear optics
As a material, for example, KTP (KTiOPO_Four), KDP
(KH_TwoPO_Four), BBO (BaB_TwoO_Four), LN (LiN
bO_Three) Etc. and single crystal CdS_xSe _1-xParticle dope gas
Glass, CdS particle-doped glass, CuCl particle-doped glass
There is an optical glass such as a lath. However, the inorganic non-
Linear optical materials, for example, have high power in optical single crystals
It is hard to be damaged even by laser irradiation,
Although it has the advantage of excellent damageability, it has few structural defects.
It is difficult to synthesize large single crystals of high quality
But also has the disadvantage of being expensive. In addition, optical glass
In other words, large and homogeneous materials
Is easy to obtain, but the SHG generation efficiency is low.
In addition, light absorption in the converted wavelength range is large,
There was a drawback that cannot be enlarged. In this way,
With the nonlinear optical material of the above, a satisfactory wavelength conversion element can be made.
Awaiting the emergence of difficult, higher-performance nonlinear optical materials
Was.

[0004]

In view of the above situation, the present inventors have conducted intensive studies and found that a specific amount of a transition metal element, a specific amount of aluminum or phosphorus, and a specific amount of an OH group were contained in silica glass. Containing a non-linear optical silica glass free of the above-mentioned disadvantages by conducting a polling treatment or a seeding treatment.
The present invention has been completed. Ie

It is an object of the present invention to provide a nonlinear optical silica glass having a high nonlinear optical effect, especially a high SHG generation efficiency.

According to the present invention, damage caused by an input laser or a wavelength-converted output laser is hardly caused even after long-time use, and furthermore, generation, coloring and transmittance of a color center by laser irradiation are reduced. It is an object of the present invention to provide a non-linear optical silica glass that is unlikely to cause a decrease or the like.

An object of the present invention is to provide a nonlinear optical silica glass for wavelength conversion which is large and easy to machine.

An object of the present invention is to provide a method for producing the above-mentioned nonlinear optical silica glass at low cost.

[0009]

According to the present invention, which achieves the above object, at least one kind of transition metal element is used in the present invention.
5,000 wt. ppm, at least one of aluminum or phosphorus is from 10 to 5,000 wt. ppm and an OH group concentration of 10 to 5,000 wt. ppm silica glass or silica glass fiber.
The present invention relates to a nonlinear optical silica glass obtained by a ring or seeding process and a method for producing the same.

The transition metal element includes an atomic number 21
~ 29 (Sc, Ti, V, Cr, Mn, Fe, Co, N
i, Cu), 39-47 (Y, Zr, Nb, Mo, T
c, Ru, Rh, Pd, Ag) or 57-71 (L
a, Ce, Pr, Nd, Pm, Sm, Eu, Gd, T
b, Dy, Ho, Er, Tm, Yb, Lu), and at least one of them is selected. Especially Ti, Cr,
Fe, Cu, Zr, Ce, Nd, Eu, Dy, or E
The transition metal element of r is preferably used. When the content of the transition metal element is 10 to 5,000 wt. The non-linear optical effect increases by being ppm. When the content of the transition metal element is 10 wt. If less than ppm, the nonlinear optical effect does not occur,
5,000 wt. If it exceeds ppm, a homogeneous silica glass exhibiting high transmittance cannot be obtained.

The transition metal element contains at least one of aluminum and phosphorus in an amount of 10 to 5,000 wt. ppm
When coexisting within the range, it is uniformly dispersed and dissolved in the silica glass. If the content of aluminum or phosphorus deviates from the above range, uniform dispersion and dissolution of the transition metal element cannot be achieved, resulting in a decrease in transmittance.

In addition to the above components, an OH group concentration of 1
0 to 5,000 wt. In the range of ppm, the nonlinear optical effect is further increased and the laser damage resistance is improved. When the OH group concentration is 10 wt. If it is less than ppm, the nonlinear optical effect is weak and 5,000 wt. It is industrially difficult to make the silica glass contain OH groups exceeding ppm.

The silica glass containing each of the above components exhibits a nonlinear optical effect when subjected to a poling treatment or a seeding treatment.

The poling process is a process of applying a DC voltage to the silica glass at a high temperature to rearrange and polarize the dipole of the isotropic silica glass having the central symmetry. For example, in the case of plate-like silica glass having a length of 20 × 20 × width (0.5 to 5) mm, a DC voltage of 1 to 10 KV / mm (glass thickness) is maintained at a processing temperature of 200 to 500 ° C.
By taking 60 minutes, the nonlinear optical effect appears.

The seeding process is a process of transmitting seed light to an optical fiber. For example, outer diameter 200
When an SHG seed light separately generated at the same time as the pump light before the light wavelength conversion is transmitted to an optical fiber-like silica glass of μmφ, a core diameter of 50 μm, and a length of 1 m, a nonlinear optical effect is exhibited.

The processing temperature in the polling process is 200
At temperatures below 500C, there is no poling effect, and at temperatures above 500C, the poling effect decreases. If the DC voltage is less than 1 KV / mm (glass thickness), there is no polling effect, and the DC voltage is 10 KV / mm (glass thickness).
If it exceeds, the polling effect is reduced and the glass is broken by dielectric breakdown. When the poling treatment or the seeding treatment is performed in a hydrogen-containing atmosphere, hydrogen dissolves in the silica glass, and the nonlinear optical effect is dramatically improved. The amount of dissolved hydrogen is 1 × 10 ¹⁶ to 1 × 10
^It is preferably ¹⁹ molecules / cm ³ , and if it is out of this range, no improvement in the nonlinear optical effect is observed.

Irradiation with γ-rays before the poling or seeding treatment of the above-mentioned plate-like or fiber-like silica glass facilitates the development of the nonlinear optical effect in a short time. It is preferable that the γ-ray irradiation uses cobalt 60 as a radiation source and the total irradiation dose is set within a range of 1 × 10 ⁵ to 1 × 10 ⁸ R (X-ray).

The nonlinear optical silica glass of the present invention is manufactured by the following manufacturing method. (I) Method for producing plate-like nonlinear optical silica glass Synthetic silica glass powder obtained by decomposing a silicon compound such as highly purified quartz powder or silicon tetrachloride by a flame hydrolysis method or a sol-gel method. Cristobalite powder is used as a silica raw material, and its OH group concentration is 10 wt. ppm or more, preferably 100 wt. Adjust to more than ppm. The adjustment of the OH group concentration is performed by adjusting the water content by drying the mixed raw material powder, or with respect to the input amount of the mixed raw material powder.
How to adjust the thermal power of oxyhydrogen flame (Berny oxyhydrogen method)
And so on.

The OH group-adjusted silica raw material powder has a transition metal element.
Element compounds. As transition metal compound to be mixed
Is an oxide, iodide, chloride, nitrate or carbonate
Suitable, these compounds are soluble in alcohol and water
In the case of, mixed as a solution,
If it is insoluble in water, it is mixed as fine particles. Alcow
Compounds soluble in water and water include cerium chloride (II
I) CeCl_Three, Chromium (II) chloride, CrCl_Two, Chloride
Luminium hydrate AlCl_Three・ 6H_TwoO, etc.
As the soluble compound, titanium oxide (IV) TiO_Two,acid
Cerium (IV) Ce O_Two, Cerium carbonate (III)
Hydrate Ce_Two(CO_Three) ・ 5H_TwoO and the like.

Following the mixing of the transition metal element compound, a compound of aluminum or phosphorus is blended. Such compounds can include oxides, iodides, chlorides, nitrates, or carbonates.

The raw material of the powdered glass in which the transition metal element compound and the compound of aluminum or phosphorus are mixed is then vitrified by the oxyhydrogen flame Bernoulli method, the vacuum electric heating melting method, and the electric heating zone melting method. In the case of a volatile liquid raw material, a transparent vitrification is performed by a soot method, a direct method, or a plasma method of oxyhydrogen flame hydrolysis. The obtained silica glass is converted into a plate-like body, for example, 10 × 10 × 0.1-1.
It is formed into a plate having dimensions of 0 mm to 50 × 50 × 0.1 to 1 mm in thickness, and both surfaces are mirror-polished. The polished plate-shaped silica glass is sandwiched between the negative electrode and the positive electrode in the electric furnace, the temperature in the furnace is raised to a predetermined temperature in the range of 200 to 500 ° C., and the silica glass is kept at this temperature. DC voltage of 1-10 KV / mm per thickness of 10-10
The non-linear optical effect is obtained by performing a poling process in the range of 00 minutes. An atmosphere heating furnace is used as the electric furnace. In particular, when the poling treatment is performed in an atmosphere containing hydrogen gas, hydrogen molecules are dissolved in the silica glass, and the nonlinear optical effect is improved.

(Ii) Method for Manufacturing Nonlinear Optical Optical Fiber A transition metal element, aluminum or phosphorus, O
After preparing a fiber preform doped with an H group and drawing the fiber, an optical fiber is manufactured.
SHG generated separately while transmitting 064 nm light
A seeding process for transmitting light (532 nm) at the same time is performed to develop a nonlinear optical effect. The seeding process significantly increases the generation efficiency of SHG.

The fiber preform is prepared by (i) using a silicon compound such as high-purity silicon tetrachloride SiCl ₄ , chlorotrimethylsilane SiCl (CH ₃ ) ₃ , trichloromethylsilane SiCl ₃ (CH ₃ ) in an oxyhydrogen flame; A soot body that is decomposed by a hydrolysis method to form a core portion is prepared, and a transition metal element, aluminum or phosphorus compound, preferably a chloride thereof, is used to dope the transition metal element, aluminum or phosphorus. Then, a method of forming a fluorine-doped cladding part on the outer periphery thereof and vitrifying it in a vacuum furnace. Or (ii) a method in which a core rod co-doped with a transition metal element and aluminum or phosphorus is prepared, and the core rod is heat-melted and integrated with a separately prepared fluorine-doped clad cylinder by a rod-in-tube method.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

[0025]

【Example】

Examples 1 to 5 A high-purity quartz powder having a purity of 99.999% by weight and a particle diameter of 50 to
It was adjusted to 200 μm, and this was mixed with titanium oxide powder having a purity of 99.9 wt% and a particle size of 0.5 to 5 μm, or titanium oxide powder and cesium oxide powder, or titanium oxide powder and europium oxide powder in proportions shown in Table 1. The mixture was placed in a high-purity silica glass ball mill container and mixed uniformly. This mixture is further mixed with an aqueous solution of an aluminum compound having a predetermined concentration, and
Drying was performed at 00 ° C. for 100 hours and further at 200 ° C. for 10 hours. Next, transparent vitrification was performed by an oxyhydrogen flame Bernoulli method, processed into a plate-shaped body having a width of 20 × length 20 × 1 mm, and both surfaces thereof were mirror-polished to prepare a thin plate-shaped sample. After sandwiching the thin plate sample between the negative electrode and the positive electrode, the sample was placed in an electric furnace, a DC voltage of 5 KV / mm was applied, and the temperature in the furnace was raised to 300 ° C.
After holding for a minute, the electrical source was turned off and cooled. The voltage of the glass sample was kept at 5 KV / mm until it cooled to room temperature, and when it reached room temperature, the switch was turned off.

The atmosphere in the electric furnace was hydrogen 100 of Example 5.
% Atmosphere was in the air.

Using the mode-locked Q-switch Nd-doped YAG laser at 1064 nm, the sample after the above treatment was used to measure the second-order nonlinear optical constant d ₃₃ (pm / V) by the mecha-fringe method of detecting the converted light at 532 nm. Table 1 shows the results. The oscillation frequency of the YAG laser is 1 KHz, the life of one pulse is about 700 nsec, the half width of the pulse life is 2.0 nsec, and the output per pulse of 700 nsec is 1
It was KW.

The maker fringe method is described in D. Mak
er, et. al, Physical Review
Letters. Vol. 8, No. 1, 1962,
pp. 21 to 22, and the nonlinear optical constant d
The measurement of ₃₃ (pm / V) is described in J. Jerphagnon,
S. K. Kurtz (1970), Journal o
fApplied Physics, Vol. 41, N
o. 4, 1970 pp. 1667-1681.

Comparative Example 1 The quartz powder of Examples 1 to 5 had a purity of 99.9% by weight and a particle diameter of 0.1%.
5-5 μm titanium oxide 500 wt. ppm and aluminum 250 wt. ppm, and the mixture was sufficiently dried. The OH group concentration was 3 wt. ppm. The obtained silica glasses were as shown in Table 1. Measurement of the nonlinear optical constant d _33.

Comparative Example 2 The quartz powders of Examples 1 to 5 were transparently vitrified by an oxyhydrogen flame Bernoulli method. The OH group concentration is 300 wt. ppm. The resulting silica glass were shown in Table 1 was measured nonlinear optical constant d _33.

Comparative Example 3 The quartz powder of Examples 1 to 5 had a purity of 99.9% by weight and a particle size of 0.1%.
5-5 μm titanium oxide 500 and aluminum 25
0 wt. ppm, and vitrified by the oxyhydrogen flame Bernoulli method. The OH group concentration is 300 wt. ppm.
The obtained silica glasses were measured the nonlinear optical constant d ₃₃ without a polling process. Table 1 shows the results.

Comparative Example 4 The quartz powder of Examples 1 to 5 had a purity of 99.9% by weight and a particle size of 0.1%.
5 to 5 μm of titanium oxide 500 was mixed and vitrified. The OH group concentration is 300 wt. ppm. The obtained silica glass subjected to the same polling treatment as in Example 1-4, was measured nonlinear optical constant d _33. The results are as shown in Table 1.

Examples 6 and 7 Using silicon tetrachloride SiCl ₄ as a raw material, high-purity white silica glass soot was prepared by an oxyhydrogen flame hydrolysis method. Separately, using titanium (III) chloride, cesium (III) chloride, aluminum chloride hexahydrate (AlCl ₃ .6H ₂ O) or phosphoric acid, a solution having a predetermined concentration of a transition metal element, aluminum or phosphorus is prepared. The white soot body was added thereto and impregnated with the solution. The soot body was placed in a dryer and dried at 100 ° C. for 10 hours and further at 200 ° C. for 10 hours. The dried soot body was band-melted by a cylindrical graphite heater electric melting furnace to form a transparent glass. The obtained silica glass was subjected to processing and poling treatment in the same manner as in Examples 1 to 5, and the physical properties thereof were measured.
Table 1 shows the results.

Example 8 Silicon tetrachloride SiCl ₄ , titanium (IV) chloride TiC
l ₄ , phosphoryl chloride (POCl ₃ ) was used as a raw material, a white soot body was prepared by a CVD soot method of oxyhydrogen flame pyrolysis, and this soot body was inserted from the top of a cylindrical electric heating furnace and gradually melted. Then, a transparent core rod was prepared. Its dimensions were 5 × 200 mm in diameter. Separate outer diameter 5
0mm x inner diameter 5.5mm x length 200mm and outer diameter 1
A fluorine-doped jacket glass cylinder having a size of 00 x an inner diameter of 51 x a length of 200 mm was prepared, the core rod was inserted into the jacket glass cylinder, and heated and fused in a vacuum furnace to produce an optical fiber preform. Next, the optical fiber preform was drawn to obtain a core diameter of 5.0 μm and a refractive index difference Δ between the core and the clad.
A single mode optical fiber with n = 0.003 was made. From one end of this optical fiber, a YAG laser 1064
At the same time, a harmonic laser of 532 nm of a YAG laser was supplied and transmitted, and a seeding process was performed for 10 minutes.

The above seeding process is performed according to R. H. Sto
lenn and H.L. W. K. Tom, Optic
s Letters, Vol. 12, No. 8, 198
7, pp. 585-257.

The YAG laser is a mode-locked Q-switch Nd-doped YAG laser having an oscillation frequency of 2 KHz,
The total life of one pulse was about 500 nsec, the pulse life half width was 1.2 nsec, and the output per 500 nsec pulse was 3 KW. The output of the YAG second harmonic laser was 30 W.

Thereafter, the Nd-doped YAG laser 106
The output of 532 nm converted light when only 4 nm was transmitted was measured. Its SHG conversion efficiency was 8%.

Comparative Example 5 An optical fiber was prepared in the same manner as in Example 8, except that the titanium element and phosphorus were not doped. OH of this optical fiber
The group was freed and doped with germanium. When the SHG conversion efficiency of this optical fiber was measured in the same manner as in Example 8, it was less than 0.01%.

[0039]

[Table 1]

As is clear from Table 1, when the silica glass containing the transition metal element, aluminum or phosphorus, and the OH group concentration within the range specified in the present invention is subjected to poling treatment or seeding treatment, the nonlinear optical effect becomes remarkable. appear. Particularly, it is excellent when the processing atmosphere is performed in the presence of hydrogen.

[0041]

The nonlinear optical silica glass of the present invention is a silica glass having a large nonlinear optical constant and a high SHG generation intensity. Moreover, since it has excellent optical homogeneity and excellent resistance to laser damage, it is effective as a wavelength conversion element material, particularly a laser-wavelength conversion element material. Furthermore, the nonlinear optical silica glass of the present invention has a simple manufacturing method, is excellent in machinability, and can manufacture a large-sized wavelength conversion element at low cost.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-6-265946 (JP, A) Jpn. J. Appl. Phys. , Vol. 32, Part 2, No. 3B, (1993) pp. L406-L407 Opt. Lett. , Vol. 16, No. 21, (1991) pp. 1650-1652 Proceedings of the Annual Meeting of the Chemical Society of Japan, p. 167 1 B2 26 (58) Field surveyed (Int. Cl. ⁶ , DB name) G02F 1/35 505 G02F 1/37 JICST file (JOIS)

Claims (8)

(57) [Claims] (1) at least one kind of transition metal element
0 to 5,000 wt. ppm, at least one of aluminum or phosphorus is from 10 to 5,000 wt. ppm and an OH group concentration of 10 to 5,000 wt. ppm
A nonlinear optical silica glass obtained by subjecting a silica glass to a polling treatment. 2. The method of claim 1, wherein at least one of the transition metal elements is
0 to 5,000 wt. ppm, at least one of aluminum or phosphorus is from 10 to 5,000 wt. ppm and an OH group concentration of 10 to 5,000 wt. ppm
A nonlinear optical silica glass obtained by subjecting a silica glass fiber as described above to a seeding treatment. 3. It contains at least one kind of transition metal element and at least one kind of aluminum or phosphorus, and has an OH group concentration of 10 to 5,000 wt. A method for producing a nonlinear optical silica glass, comprising: preparing a plate-like silica glass having a concentration of 1 ppm and subjecting it to a poling treatment at a DC voltage of 1 to 10 KV / mm in a temperature range of 200 to 500 ° C. 4. It contains at least one kind of transition metal element, at least one kind of aluminum or phosphorus, and has an OH group concentration of 10 to 5,000 wt. A method for producing a non-linear optical silica glass, comprising: preparing a fiber preform having a silica glass core portion of ppm, drawing the fiber, and performing seeding treatment. 5. The method for producing a nonlinear optical silica glass according to claim 3, wherein the silica glass is irradiated with gamma rays before the poling treatment. 6. The method for producing nonlinear optical silica glass according to claim 4, wherein gamma rays are irradiated to the silica glass fiber before the seeding treatment. 7. The method for producing a nonlinear optical silica glass according to claim 3, wherein the poling treatment is performed in a hydrogen-containing atmosphere. 8. The method for producing a nonlinear optical silica glass according to claim 4, wherein the seeding treatment is performed in a hydrogen-containing atmosphere.