JP4977119B2 - Wavelength conversion element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a wavelength conversion element and a manufacturing method thereof, and more particularly to a structure required for ensuring long-term reliability of a wavelength conversion element and a manufacturing method thereof.

  A wavelength conversion element that generates sum frequency light, difference frequency light, and second-order or higher-order harmonic light by irradiating a dielectric material having nonlinearity with single or plural excitation laser beams is used. (See, for example, Non-Patent Document 1).

  FIG. 6 is a schematic configuration diagram illustrating an example of a wavelength conversion laser light source. The wavelength conversion laser light source 111 includes a wavelength conversion module 112, a fiber coupler 116, and two semiconductor lasers 114 and 115. The light of wavelength λ1 output from the first semiconductor laser 114 and the light of wavelength λ2 output from the second semiconductor laser 115 are coupled by the fiber coupler 116, and the wavelength conversion incorporated in the wavelength conversion module 112 The light enters the element 113 as input light 117. In the wavelength conversion element 113, light having a wavelength λ 3 corresponding to the sum frequency of light having a wavelength λ 1 and light having a wavelength λ 2 is generated and emitted as output light 118. Note that the relationship 1 / λ3 = 1 / λ1 + 1 / λ2 is established between λ1, λ2, and λ3. For example, when λ1 is 976 nm and λ2 is 1307 nm, λ3 is 559 nm, and yellow laser light can be generated from two infrared laser beams.

Next, a wavelength conversion element 113 and its surrounding structure particularly related to the present invention will be described with reference to FIG. 7 (see, for example, Patent Document 1). In FIG. 7, an example of AA 'sectional drawing of the conventional wavelength conversion element is shown.
A wavelength converter 12 having a ridge-type waveguide structure in which a domain-inverted structure (quasi-phase matching structure, QPM structure) is formed on zinc-doped lithium niobate (LiNbO ₃ : Zn) is formed on a substrate 14 made of lithium tantalate (LiTaO ₃ ). It is directly bonded to the top and bonded onto the metal carrier plate 11. Furthermore, the carrier plate 11 is bonded onto the temperature adjustment element 120 for setting the entire wavelength conversion element 113 to a desired temperature.

In the conventional wavelength conversion element 113, as shown in FIG. 7, the wavelength conversion body 12 is exposed to the air surface and is electrically insulated from the carrier plate 11.
JP 2003-140214 A International Conference Proceeding Paper: Yube et al., "Laser Diode Pumped 560-590nm Light Source Using Sum Frequency Generation in Direct Junction Quasi-Phase Matched LiNbO3 Waveguide" 2005 International Conference on Lasers and Optoelectronics (CLEO2005, American Optical Society) (OSA) sponsored), lecture number CML3))

  However, the wavelength conversion element 113 having the above-described structure has a problem that a part of the dielectric crystal constituting the wavelength conversion body 12 is damaged and the wavelength conversion efficiency is remarkably lowered.

  FIG. 8 shows an example of a result of an on / off test of a conventional wavelength conversion laser light source. The vertical axis represents the intensity of output light having a wavelength of 559 nm, and the horizontal axis represents time. This is an observation of how the intensity of the output light changes over time when the power of the entire wavelength conversion laser light source is turned on and off three times per hour. It can be seen that the intensity of the output light suddenly decreases after about 40 hours, that is, 120 on / off cycles, and the wavelength conversion laser light source is broken. When the wavelength conversion element 113 after the output reduction was observed in the on state, bright spots due to crystal defects of the dielectric material constituting the wavelength converter 12 were observed.

  The inventors have discovered that when the electric charge accumulated in the wavelength converter 12 is instantaneously discharged, a part of the dielectric crystal is damaged and the wavelength conversion efficiency is significantly reduced. did. The charge accumulated in the wavelength converter 12 is charged due to the dielectric material itself of the wavelength converter 12 or pyroelectricity when the temperature adjustment element 120 changes the temperature from room temperature to a set temperature. It has been discovered that the charge resulting from the stress effect due to the deflection of the carrier plate 11 due to temperature change is generated in the wavelength converter 12.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a wavelength conversion element that prevents charge accumulation in a wavelength converter, and a method for manufacturing the same.

  In order to solve the above-described problems, the wavelength conversion element according to the present invention is characterized in that the charge accumulated in the wavelength converter is always discharged to the carrier plate.

Specifically, the wavelength conversion element according to the present invention includes a carrier plate having conductivity and a dielectric material mounted on the carrier plate and having a pyroelectric property, and converts the wavelength of light passing therethrough. A charge transfer film electrically connected to the carrier plate and the wavelength converter, made of a conductive material or a semi-insulating material, and moving the charge accumulated in the wavelength converter to the carrier plate; The carrier plate is grounded .

Since the charge transfer film is provided, the charge accumulated in the wavelength converter can always be discharged to the carrier plate. Therefore, it is possible to prevent charge accumulation in the wavelength converter.
In addition, since the carrier plate is grounded, the charges accumulated in the wavelength converter can be discharged at all times.

In the wavelength conversion element according to the present invention, it is preferable that the wavelength converter has a domain-inverted structure.
A wavelength conversion characteristic with high light efficiency can be obtained.

In the wavelength conversion element according to the present invention, it is preferable that the wavelength converter has a waveguide optical structure for guiding the light for converting the wavelength. The waveguide structure is preferably a ridge type or a slab type.
It can be used for a wavelength conversion module.

In the wavelength conversion element according to the present invention, it is preferable that the surface resistance of the charge transfer film is low enough not to generate an electric field due to charges generated by a pyroelectric effect in the wavelength converter.
Generation of an electric field in the wavelength converter can be prevented. Therefore, damage to the wavelength conversion element due to rapid discharge can be avoided.

In the wavelength conversion element according to the present invention, the dielectric material constituting the wavelength converter includes LiNbO ₃ or LiTaO ₃ .

  In the wavelength conversion element according to the present invention, the conductive material includes a conductive polymer, a surfactant, a metal oxide dispersion material, and a carbon nanotube. A semi-insulating material is a metal oxide-based material in which an insulating material is made semi-insulating by imparting crystal imperfection to the insulating material or by doping a conductive oxide into the insulating material. Including.

A method for manufacturing a wavelength conversion element according to the present invention is a method for manufacturing a wavelength conversion element according to the present invention, wherein the wavelength converter is mounted on the carrier plate, and a conductive material or a semi-insulating material. And a coating step of coating the carrier plate and the wavelength converter so as to form the charge transfer film.
Since the charge transfer film is applied, the charge accumulated in the wavelength converter can be discharged to the carrier plate at all times. Therefore, it is possible to prevent charge accumulation in the wavelength converter.

  ADVANTAGE OF THE INVENTION According to this invention, the wavelength conversion element which prevents accumulation | storage of the electric charge to a wavelength converter, and its manufacturing method can be provided.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiment described below is an example of the configuration of the present invention, and the present invention is not limited to the following embodiment.

(Embodiment 1)
FIG. 1 is a cross-sectional view taken along the line AA ′ showing an example of the wavelength conversion element according to the present embodiment. The wavelength conversion element 91 according to this embodiment includes a carrier plate 11, a wavelength conversion body 12, and a charge transfer film 13.

  The carrier plate 11 has conductivity. For example, a metal carrier. The wavelength converter 12 is mounted on the carrier plate 11 and converts the wavelength of light passing therethrough. The charge transfer film 13 is electrically connected to the carrier plate 11 and the wavelength converter 12 and moves the charges accumulated in the wavelength converter to the carrier plate. In this way, the charge transfer film 13 is provided with the charge transfer film 13 so as to straddle the wavelength converter 12 and the carrier plate 11 on which the wavelength converter 12 is mounted. Can be discharged to the carrier plate 11 at all times. Thereby, accumulation of electric charges in the wavelength converter can be prevented. Therefore, the carrier plate 11 is preferably grounded.

  Here, the charge transfer film 13 is preferably electrically connected to both at least part of the surface of the wavelength converter 12 and at least part of the carrier plate 11. Thereby, the electric charge accumulated in the wavelength converter 12 can be removed. The charge transfer film 13 preferably covers the entire surface of the wavelength converter 12. Thereby, the charge remaining in the wavelength converter 12 can be reduced.

The surface resistance of the charge transfer film 13 is preferably low enough not to generate an electric field due to charges generated by the pyroelectric effect in the wavelength converter 12. For example, compared to the constant tau _c when determined by the capacitance _{C c} and bulk resistance _{R b} of the wavelength converter 12, and the capacitance _{C c} and bulk resistance _{R b} of the wavelength converter 12, determined by the resistance _{R s} of the charge transfer film 13 The time constant τ _d is preferably shorter by one digit or more. Thereby, generation | occurrence | production of the electric field in the wavelength converter 12 can be prevented. Therefore, damage to the wavelength conversion element due to rapid discharge can be avoided. The time constants τ _c and τ _d are expressed by the following equations.
τ _c = C _c · R _b (1)
τ _d = C _c / (1 / R _b + 1 / R _s ) (2)

The wavelength converter 12 is made of a dielectric material having pyroelectricity. Such dielectric material is, for example, LiNbO ₃ , LiTaO ₃ , LiNb _x Ta _(1-x) O ₃ (0 ≦ x ≦ 1), KNbO ₃ or KTiOPO ₄ . The wavelength converter 12 preferably has a domain-inverted structure. For example, the domain-inverted structure is formed by zinc-doped lithium niobate (LiNbO ₃ : Zn), Mg-doped LiNbO ₃ , Sc-doped LiNbO _3, or In-doped LiNbO ₃ . The wavelength converter 12 has a waveguide optical structure that guides light that converts a wavelength, such as a ridge type, a slab type, or a bulk type. In addition, a proton injection waveguide or a buried waveguide may be used.

For example, the wavelength converter 12 is made of zinc-doped lithium niobate (LiNbO ₃ : Zn) on which a domain-inverted structure (quasi phase matching structure, QPM structure) is formed. And it has a bulk-type waveguide structure and is bonded on the carrier plate 11.

The charge transfer film 13 is made of a conductive material or a semi-insulating material. The conductive material is, for example, a conductive polymer, a surfactant, a metal oxide dispersion material, or a material containing carbon nanotubes. The conductive polymer is, for example, a polythiophene conductive polymer or a polyethylenedioxythiophene conductive polymer. The metal oxide dispersion material is, for example, a conductive oxide dispersion material such as SnO ₂ or In ₂ O ₃ . The semi-insulating material is, for example, a crystal imperfection in an insulating material such as a metal oxide material, or a conductive oxide such as Sn or In in an insulating material such as a metal oxide material. Is a metal oxide-based material in which an insulating material such as TiO ₂ or SiO ₂ is made semi-insulating.

The electrical conductivity of the charge transfer film 13 is not more than a value that makes the resistance R _s of the charge transfer film 13 and the bulk constant R _b of the wavelength converter 12, and is a time constant τ _{d that} is sufficiently smaller than the charge accumulation rate. Is preferably equal to or less than the value obtained. For example, the sheet resistance of the charge transfer film 13 is preferably 1 Ω / □ or more and 1 × 10 ¹³ Ω / □ or less. As a result, the amount of accumulated charge can be reduced.

The method for manufacturing a wavelength conversion element according to the present embodiment is characterized by having a mounting step and a coating step in this order.
In the mounting process, the wavelength converter 12 is mounted on the carrier plate 11. For example, the wavelength converter 12 is directly bonded on the carrier plate 11. Moreover, both, adhesive, or it may be bonded with the SiO ₂ layer. In particular, the present invention is not limited to the case of bonding different types of substrates, and can also be applied to the case where the wavelength converter 12 and the substrate are formed of the same dielectric material.
In the application step, a conductive material or a semi-insulating material is applied so as to straddle the carrier plate 11 and the wavelength converter 12 to form the charge transfer film 13.

(Embodiment 2)
FIG. 2 is a cross-sectional view taken along the line AA ′ showing an example of the wavelength conversion element according to the present embodiment. The wavelength conversion element 92 further includes the substrate 14 in addition to the wavelength conversion element described in the first embodiment, and is laminated in the order of the carrier plate 11, the substrate 14, and the wavelength converter 12. Thereby, a slab type waveguide structure is formed.

The refractive index of the substrate 14 is smaller than the refractive index of the wavelength converter 12 and forms a waveguide in the wavelength converter 12. The substrate 14 is made of, for example, lithium tantalate (LiTaO ₃ ), Si, or SiO ₂ .

For example, the wavelength converter 12 has a slab waveguide structure in which a domain-inverted structure (pseudo phase matching structure, QPM structure) is formed in zinc-doped lithium niobate (LiNbO ₃ : Zn). When the wavelength converter 12 is zinc-doped lithium niobate (LiNbO ₃ : Zn), the substrate 14 is preferably made of lithium tantalate (LiTaO ₃ ). The substrate 14 is bonded onto the carrier plate 11.

Further, a charge transfer film 13 is applied over the carrier plate 11 so as to cover the wavelength converter 12 and the substrate 14. The carrier plate 11 is grounded. In this embodiment, a conductive polymer is used for the conductive material of the charge transfer film 13. In addition, a TiO ₂ film having crystal imperfection or doped with a conductive oxide, a surfactant, a metal oxide dispersion material, or a carbon nanotube material can be used.

(Embodiment 3)
3 and 4 are AA ′ cross-sectional views showing a first example and a second example of the wavelength conversion element according to the present embodiment. The wavelength conversion elements 93 and 94 according to the present embodiment have a ridge-type waveguide structure instead of the slab-type waveguide structure of the second embodiment.

The wavelength converter 12 has a ridge-type waveguide structure in which a domain-inverted structure (pseudo phase matching structure, QPM structure) is formed in zinc-doped lithium niobate (LiNbO ₃ : Zn). The substrate 14 is lithium tantalate (LiTaO ₃ ). The wavelength converter 12 is directly bonded on the substrate 14. The substrate 14 is bonded onto the carrier plate 11.

Further, a charge transfer film 13 is applied over the carrier plate 11 so as to cover the wavelength converter 12 and the substrate 14. The carrier plate 11 is grounded. A conductive polymer is used as the electric material of the charge transfer film 13. In addition, a TiO ₂ film having crystal imperfection or doped with a conductive oxide, a surfactant, a metal oxide dispersion material, or a carbon nanotube material can be used.

  An embodiment of the wavelength conversion element shown in FIG. 4 will be described. The wavelength conversion element 94 shown in FIG. 4 is mounted on the wavelength conversion laser light source 111 shown in FIG. 6 to constitute a 559 nm wavelength conversion laser light source. Then, it was observed how the intensity of the output light changed with time when the power of the entire light source was turned on and off 7.5 times per hour at intervals of 8 minutes.

FIG. 5 shows an example of the result of an on / off test of the wavelength conversion laser light source. The vertical axis represents the intensity of output light having a wavelength of 559 nm, and the horizontal axis represents time.
Even after 1300 hours, that is, 9750 times of on / off, the output did not decrease and no failure was observed. That is, by applying the charge transfer film 13 over the carrier plate 11 so as to cover the wavelength converter 12 and the substrate 14, the wavelength conversion caused by the crystal breakage due to the rapid discharge of the charge accumulated in the wavelength converter 12. It was found that a wavelength conversion laser light source capable of avoiding a sudden deterioration of the conversion efficiency of the element and operating stably for a long period of time can be realized.

Here, the surface resistance of the charge transfer film 13 will be described.
Unit cell of poled structure in the wavelength converter 12, length 4 [mu] m, a width 8 [mu] m, if the height 7 [mu] m, the capacity of the wavelength converter 12 _{C c} is 1.2 × ^{10 -12} F, bulk wavelength converter 12 The resistance is estimated to be 1.5 × 10 ²² Ω. In this state, the discharge time constant is 1.8 × 10 ⁷ sec. Assuming a temperature cycle in which the temperature is increased from 25 ° C. to 50 ° C. over 1 minute, held for 2 minutes, and lowered to the original 25 ° C. over 1 minute, the maximum electric field reaches 4.2 kV / mm. In this case, crystal loss of the dielectric material constituting the wavelength converter 12 due to rapid discharge may occur.

On the other hand, when the surface resistance of the applied charge transfer film 13 is 1 × 10 ¹⁶ Ωm, the discharge time constant is 10.3 sec, and the maximum electric field reaches only 0.75 kV / mm. In such a case, crystal loss of the dielectric material constituting the wavelength converter 12 due to rapid discharge can be avoided.

Assuming the above unit cell shape and temperature cycle, the maximum electric field (0.75 kV / mm) when the surface resistance is 1 × 10 ¹⁰ to 1 × 10 ¹⁶ Ωm is 1 × 10 ¹⁸ to 1 × 10 ²⁴ Ωm. It becomes 20% or less of the maximum electric field (4.2 kV / mm) at (up to infinity), and charging due to the pyroelectric effect can be avoided. In other words, if the surface resistance of the charge transfer film 13 is low enough not to generate an electric field due to the charge generated by the pyroelectric effect, charging of the wavelength converter 12 can be prevented.

  For the wavelength conversion elements 91 and 92 shown in FIGS. 1 and 2, the temperature change history was observed using a conductive polymer for the charge transfer film 13. Also in this case, as in FIG. 5, even if a temperature change history of about 10,000 times was added, crystal loss of the dielectric material constituting the wavelength converter 12 did not occur.

  The above embodiments are not limited to the 559 nm sum frequency generation light source in the domain-inverted structure, but the 589 nm and 547 nm sum frequency generation light sources, the 532 and 488 nm second harmonic generation light sources, the 3 μm band and the 4 μm band. It can also be applied to a difference frequency generating light source.

  Since the present invention is used for a wavelength conversion laser light source, it can be used in the telecommunications industry.

4 is a cross-sectional view taken along line A-A ′ showing an example of a wavelength conversion element according to Embodiment 1. FIG. 6 is a cross-sectional view taken along line A-A ′ showing an example of a wavelength conversion element according to Embodiment 2. FIG. 10 is a cross-sectional view taken along line A-A ′ showing a first example of a wavelength conversion element according to Embodiment 3. FIG. FIG. 10 is a cross-sectional view taken along the line A-A ′ showing a second example of the wavelength conversion element according to the third embodiment. It is an example of the result of the on-off test of the wavelength conversion laser light source which concerns on a present Example. It is a composition schematic diagram showing an example of a wavelength conversion laser light source. It is an example of A-A 'sectional view of the conventional wavelength conversion element. It is an example of the result of the on-off test of the conventional wavelength conversion laser light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Carrier plate 12 Wavelength converter 13 Charge transfer film 14 Substrate 91, 92, 93, 94 Wavelength conversion element 111 Wavelength conversion laser light source 112 Wavelength conversion module 113 Wavelength conversion element 114, 115 Semiconductor laser 116 Fiber coupler 117 Input light 118 Output light 120 Temperature control element

Claims (8)

A conductive carrier plate;
A wavelength converter that is mounted on the carrier plate, is made of a dielectric material having pyroelectricity, and converts the wavelength of light passing therethrough,
A charge transfer film electrically connected to the carrier plate and the wavelength converter, made of a conductive material or a semi-insulating material, and moving charges accumulated in the wavelength converter to the carrier plate;
Equipped with a,
The wavelength conversion element , wherein the carrier plate is grounded .   The wavelength conversion element according to claim 1, wherein the wavelength converter has a polarization inversion structure.   The wavelength conversion element according to claim 1, wherein the wavelength converter has a waveguide optical structure that guides the light for converting the wavelength.   The wavelength conversion element according to claim 3, wherein the waveguide structure is a ridge type or a slab type.   5. The wavelength conversion element according to claim 1, wherein a surface resistance of the charge transfer film is low enough not to generate an electric field caused by a charge generated by a pyroelectric effect in the wavelength converter. . 6. The wavelength conversion element according to claim 1, wherein the dielectric material constituting the wavelength converter is LiNbO ₃ or LiTaO ₃ .   The conductive material or semi-insulating material constituting the charge transfer film includes a conductive polymer, a surfactant, a metal oxide dispersed material, a carbon nanotube, or a metal oxide-based material. The wavelength conversion element according to any one of 6. It is a manufacturing method of the wavelength conversion element according to any one of claims 1 to 7 ,
A mounting step of mounting the wavelength converter on the carrier plate;
An application step of applying a conductive material or a semi-insulating material so as to straddle the carrier plate and the wavelength converter, and forming the charge transfer film;
In order, the manufacturing method of the wavelength conversion element characterized by the above-mentioned.

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