Production of waveguides made of materials from the KTP family

Abstract

The invention relates to a method for producing waveguides (201) from a material (202) of the KTP family comprising the following method steps: b) treating the material (202) in such a way that a periodic poling of the material (202) is achieved, c) treating the material (202) in a molten salt bath (309c), which contains rubidium ions, characterized in that the molten salt bath (309c) which contains rubidium ions in step c) satisfies the following boundary conditions: the mole fraction of rubidium nitrate (RbNO.sub.3) in the melt lies in the range of 86-90 mol % at the beginning of the treatment, the mole fraction of potassium nitrate (KNO.sub.3) in the melt lies in the range of 10-12 mol % at the beginning of the treatment, the mole fraction of barium nitrate (Ba(NO.sub.3).sub.2) in the melt lies in the range of 0.5-1 mol % at the beginning of the treatment, the temperature of the melt lies in the range of 357-363° C. during the treatment. Thus the problem is solved, when reversing the known method steps, of achieving substantially identical diffusion depths of the ions during the ion exchange in order to produce periodically poled waveguides as free of corrugation as possible.

Claims

1. Method for producing waveguides from a material of the KTP family comprising: b) treating the material in such a way that a periodic poling of the material is achieved, c) treating the material in a molten salt bath, which contains rubidium ions, characterized in that the molten salt bath which contains rubidium ions in c) satisfies the following boundary conditions: the mole fraction of rubidium nitrate (RbNO3) in the melt lies in the range of 86-90 mol % at the beginning of the treatment, the mole fraction of potassium nitrate (KNO3) in the melt lies in the range of 10-12 mol % at the beginning of the treatment, the mole fraction of barium nitrate (Ba(NO3)2) in the melt lies in the range of 0.5-1 mol % at the beginning of the treatment, the temperature of the melt lies in the range of 357-363° C. during the treatment.

2. Method according to claim 1, characterized in that the method is carried out in the sequence b), c).

3. Method according to claim 1, characterized in that the method has an upstream a) preparatory treating the material, in order to homogenize or to reduce the conductivity of the material.

4. Method according to claim 3, characterized in that the preparatory treatment includes a treatment of the material in a KNO3 melt.

5. Method according to claim 1, characterized in that the treatment, which leads to a periodic poling, includes a use of a pulsed electric field between two electrodes, which are applied on mutually opposite sides of the material sample.

6. Method according to claim 5, characterized in that a periodically-shaped electrode is thereby used on one side of the material sample.

7. Method according to claim 1, characterized in that the treatment in the molten salt bath, which contains the rubidium ions, in c) is used only on one side of the material sample, and this is carried out with respect to the surface in a strip-like way.

8. Method according to claim 7, characterized in that a strip-shaped mask is thereby used on one side of the material sample.

Description

(1) The invention is described below in greater detail on the basis of a preferred embodiment with reference to the drawings.

(2) As shown in the drawing,

(3) FIG. 1 a conventional, corrugated, periodically poled waveguide,

(4) FIG. 2 a periodically poled waveguide free of corrugation according to one preferred embodiment of the invention,

(5) FIG. 3 a structure for the treatment in steps a and c according to one preferred embodiment of the invention,

(6) FIG. 4 the electrodes which are used for the step of the periodic poling, and

(7) FIG. 5 the effect of step c on the material sample in a schematic depiction.

(8) FIG. 1 shows a longitudinal section through a conventional, corrugated periodically poled waveguide 100 in a schematic representation. A production of the waveguide made from a KTP material sample 102 through ion exchange after the periodic poling generally leads to a corrugated waveguide 100. The differently poled (−c, +c) areas 103 have differently large diffusion coefficients (D.sub.+≠D.sub.−). Due to this, the ions diffuse into the material at different depths during the ion exchange, depicted by means of diffusion depth 104. A corrugation of waveguide 100 leads to impairment in the efficiency of the conversion process.

(9) FIG. 2 schematically shows a perspective depiction and a longitudinal section through a periodically poled waveguide 201 without corrugation made from a KTP material sample 202 by producing the waveguide through an ion exchange after the periodic poling according to a method according to one preferred embodiment of the invention. The diffusion coefficient depends on the temperature and on which material is diffused into which other material. The selection of the exchange parameters in the ion exchange leads to substantially identically large diffusion coefficients and thus to substantially identically deep diffusion depths 204 for differently poled areas 203 of material 202.

(10) The presently described preferred embodiment of the method provides three method steps. In the first step a), a preparatory treatment is carried out with the goal of homogenizing and/or reducing the conductivity of the material. A treatment of the material thereby takes place in a KNO.sub.3 melt 309a. FIG. 3 schematically shows the structure for this step. The temperature of KNO.sub.3 melt 309a thereby lies at 375° C. in the present embodiment. The residence time of material sample 202 in the melt is thereby 24 h.

(11) In the second step b), a periodic poling of the material occurs. FIG. 4 shows electrodes 406, which are used for the step of periodic poling, in a schematic depiction. A periodically-shaped electrode 407, which is manufactured according to known techniques, is located on one side of material sample 202. An area of insulating material 408 delimits in each case the area of periodically-shaped electrode 407, which directly contacts the material. By generating a pulsed electric field, the domains are able to be inverted, which leads to a periodic poling.

(12) The structure for third step c) is analogous to that of step a) and is schematically shown in FIG. 3. In third step c), a treatment of material 202 takes place in a molten salt bath 309c, which contains rubidium ions. This leads to an ion exchange between the rubidium ions in the melt and the potassium ions in the material, due to which the refractive index changes.

(13) FIG. 5 shows the effect of third step c) on material sample 202 in a schematic representation. Waveguides 201 are produced only in certain areas 510 of material 202. For this purpose, a strip-shaped mask 505, which was manufactured according to known techniques, is used on one side of material sample 202. Mask 505 ensures that only selected strip-like areas 510 of material 202 come into contact with the molten salt bath. The other side is completely shielded from the molten salt bath. Only in areas 510, which are not covered by the mask, does an ion exchange with the melt take place.

(14) Melt 309c, which contains rubidium ions, comprises, according to the previously described preferred embodiment of the invention, a mixture of rubidium nitrate, potassium nitrate, and barium nitrate, and is composed as follows: the mole fraction of rubidium nitrate (RbNO.sub.3) in the melt lies at 88 mol % at the beginning of the treatment, the mole fraction of potassium nitrate (KNO.sub.3) in the melt lies at 11 mol % at the beginning of the treatment, and the mole fraction of barium nitrate (Ba(NO.sub.3).sub.2) in the melt lies at 1 mol % at the beginning of the treatment. The temperature of the melt during the treatment is 360° C.

(15) Periodically poled waveguides 201 substantially free of corrugation are thus collectively achieved.

LIST OF REFERENCE NUMERALS

(16) 100 Corrugated, periodically poled waveguide 102 KTP material sample 103 Areas of poling 104 Diffusion depth 201 Periodically poled waveguide free of corrugation 202 KTP material sample 203 Areas of poling 204 Diffusion depth 309a Molten salt bath KNO.sub.3 309c Molten salt bath and its mixture made from RbNO.sub.3, KNO.sub.3 and Ba(NO.sub.3).sub.2 406 Electrodes 407 Periodically-shaped electrode 408 Area made from insulating material 505 Strip-shaped mask 510 Strip-shaped areas