JP2010039317A - Optical element and method for manufacturing optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of peeling and to obtain stable optical characteristics and satisfactory yield. <P>SOLUTION: Groove groups 1g and 2g are formed on sticking surfaces of laser crystal 1 and wavelength conversion crystal 2 of an optical element 10 so that a fundamental wave of laser oscillation by the laser crystal 1 has such action that reflectance to light polarized in a desired polarization direction is made lower than that to light polarized in a direction orthogonal to the desired polarization direction. Thereby, reflection of light polarized in the desired polarization direction by the sticking surfaces can be neglected and laser oscillation is stabilized. The laser oscillation is stabilized due to the definite polarization direction. Since an anchor effect is obtained by adding an adhesive 4 to the groove groups 1g and 2g and strong unification can be attained, peeling is hardly caused and yield can be enhanced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical element and a method for manufacturing the optical element, and more particularly to an optical element having excellent stability and a method for manufacturing the optical element.

An optical element having a structure in which a laser crystal and a wavelength conversion crystal are bonded together and a manufacturing method thereof are known (for example, see Patent Documents 1 and 2).
On the other hand, a technique for reducing the reflectance with respect to light in a desired polarization direction by a structure having structural birefringence is known (see, for example, Patent Document 3 and Non-Patent Document 1).
JP 2005-57043 A JP 2007-225786 A JP 2008-145457 A Daniel H. Raguin and G. Michael Morris "Antirefrection structure d surfaces for the infrared spectral region" Applied Optics, Vol.32, No.7 (1 March 1993)

In a conventional optical element having a structure in which a laser crystal and a wavelength conversion crystal are bonded, the bonded surfaces of the laser crystal and the wavelength conversion crystal are polished and bonded to a flat surface.
However, reflection that cannot be ignored occurs on the bonding surface, and a composite resonator is formed, which may adversely affect the stability of laser oscillation.
In addition, when the laser crystal does not have polarization dependency (ceramic or the like), the polarization is not fixed and may become unstable.
Therefore, an object of the present invention is to provide an optical element having excellent stability and a method for manufacturing the optical element.

In a first aspect, the present invention provides at least one of the laser crystal (1) and the wavelength conversion crystal (2) in the optical element (10) in which the wavelength conversion crystal (2) is bonded to the laser crystal (1). Provided is an optical element (10) characterized in that a structure (1g, 2g) having structural birefringence is provided on the bonding surface.
In the optical element (10) according to the first aspect, structures (1g, 2g) having structural birefringence are provided on the bonding surfaces of the laser crystal (1) and the wavelength conversion crystal (2). For this reason, the reflectance with respect to the light of a desired polarization direction can be made small. As a result, a complex resonator is not formed for light having a desired polarization direction, and laser oscillation becomes stable. Even when the laser crystal does not have polarization dependence, the polarization is determined and the laser oscillation becomes stable.

In a second aspect, the present invention provides the optical element (10) according to the first aspect, wherein the structure (1g, 2g) having the structural birefringence is a fundamental wave that causes the laser crystal (1) to oscillate. The groove group (1g, 2g) is formed so that the reflectance with respect to light polarized in a desired polarization direction is smaller than the reflectance with respect to light polarized in a direction orthogonal to the desired polarization direction. An optical element (10) is provided.
In the optical element (10) according to the second aspect, since the structure (1g, 2g) having structural birefringence is realized by the groove group (1g, 2g), it is more than the other structure (for example, moth-eye structure). Easy to manufacture. Further, when the adhesive (4) enters the groove group (1g, 2g), an anchor effect can be obtained, which can be firmly integrated and hardly peeled off.

In a third aspect, the present invention relates to the optical axis direction side and the width direction side of the wavelength conversion crystal large substrate (32) which is a plate-like body having an optical axis direction side, a width direction side, and a thickness direction side. A large dummy substrate (13) of a plate-like body is attached to at least one surface partitioned by (1) to form a first composite large substrate (21 ′), and the optical axis direction side of the first composite large substrate (21 ′) A plurality of first composite substrates are prepared by cutting at a working length (L), and a laser beam incident surface and a plate-like body partitioned by the width direction side and the thickness direction side of the first composite substrate. An optical element in which a plurality of optical elements (10) are obtained by bonding together the laser light emitting surface of a laser crystal substrate whose one surface is a laser light emitting surface to form a second composite substrate. Before the first composite substrate and the laser crystal substrate are bonded to each other. Light having a reflectivity with respect to light polarized in a desired polarization direction with respect to the fundamental wave to be laser-oscillated by the laser crystal on at least one bonding surface of the composite substrate and the laser crystal substrate is polarized in a direction orthogonal to the desired polarization direction A groove group (1g, 2g) is made to be smaller than the reflectance with respect to, and the first composite substrate and the laser crystal substrate are bonded with an adhesive (4). Provide a method.
In the optical element manufacturing method according to the third aspect, the optical element (10) according to the second aspect can be preferably manufactured. Further, when the adhesive (4) enters the groove group (1g, 2g), an anchor effect can be obtained and it can be firmly integrated. Therefore, when the second composite substrate is cut to obtain a plurality of optical elements (10). In addition, it is difficult to cause peeling, and the yield can be improved.

According to the optical element of the present invention, stable optical characteristics can be obtained.
According to the method for manufacturing an optical element of the present invention, the yield can be improved.

  Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited thereby.

FIG. 1 is a perspective view illustrating an optical element 10 according to the first embodiment. FIG. 2 is an exploded perspective view of the optical element 10.
The optical element 10 is excited by excitation laser light Li from a semiconductor laser to emit fundamental laser light from a laser light emission surface 1o, and harmonics of fundamental laser light incident from a laser light incidence surface 2i. A wavelength conversion crystal 2 for emitting the wavelength conversion laser light Lo, and a dummy material 3 for sandwiching the wavelength conversion crystal 2 in a sandwich shape.
The laser crystal 1, the wavelength conversion crystal 2, and the dummy material 3 are attached with an adhesive 4.
Groove groups 1g and 2g are engraved on the attachment surface of the laser crystal 1, the wavelength conversion crystal 2 and the dummy material 3 by, for example, ion milling.

The laser crystal 1 is, for example, a YAG crystal or YVO4 crystal doped with Nd.
The wavelength conversion crystal 2 is, for example, a ferroelectric crystal (an LN or LT substrate, an LN or LT substrate doped with MgO) having a domain-inverted periodic structure, or a KPT substrate.
The dummy material 3 is preferably made of a material having a thermal conductivity larger than that of glass so as to function suitably as a heat sink. Further, in order to suppress adverse effects when thermally expanded, it is preferable to use a material having a thermal expansion coefficient comparable to that of the laser crystal 1 and the wavelength conversion crystal 2. For example, the same material as the wavelength conversion crystal 2 (periodic polarization inversion structure is not required), quartz glass, or BK-7.

  In the groove groups 1g and 2g, the reflectance with respect to light polarized in a desired polarization direction with respect to a fundamental wave (for example, wavelength 1.064 μm) laser-oscillated by the laser crystal 1 is orthogonal to the desired polarization direction in a state after bonding. It is formed to have an effect of being smaller than the reflectance with respect to light polarized in the direction.

  On the surface of the laser crystal 1 facing the bonding surface and the surface of the wavelength conversion crystal 2 facing the bonding surface, a highly reflective film for the fundamental wave (for example, wavelength 1.064 μm) is formed.

FIG. 3 is a flowchart showing the manufacturing procedure of the optical element 10.
In step S1, as shown in FIG. 4, the length L ′ of the side in the optical axis direction of the polarization inversion direction Dr, the width G in the width direction intersecting the polarization inversion direction Dr and the polarization direction Dp, and the thickness direction of the polarization direction Dp. The wavelength conversion crystal large substrate 32 which is a plate-like body having a thickness d is prepared. The length L ′ is, for example, 6 mm, the width G is, for example, 6 mm, and the thickness d is, for example, 0.4 mm. Then, the process proceeds to step S3.

  The wavelength conversion crystal large substrate 32 is formed, for example, by forming a periodic electrode 32b and a solid electrode 32c on opposite surfaces of a ferroelectric crystal large substrate 32a of a predetermined size, and applying a voltage between the electrodes to form the ferroelectric crystal large substrate 32a. It can be created by forming a periodically poled structure inside. The opposing direction of the electrodes is the polarization direction Dp, and the periodic pattern direction of the shape of the periodic electrode 32b is the polarization inversion direction Dr. The electrode may be left as it is or may be removed. When using an optical contact for bonding to the dummy material, it is preferable to remove it.

  The ferroelectric crystal large substrate 32a is, for example, a MgO-doped, stoichiometric composition or stoichiometric lithium tantalate substrate (MgO doped stoichiometric lithium tantalate j substrate), The molar fraction Li2O / (Ta2O5 + Li2O) is 0.49 or more and less than 0.5.

  On the other hand, in step S2, a dummy material large substrate 13 which is a plate-like body having a length L ', a width G, and a thickness W is formed as shown in FIG. The thickness W is 1 mm, for example. Then, the process proceeds to step S3.

In step S3, as shown in FIG. 6, the wavelength conversion crystal large substrate 32 and the dummy material large substrate 13 are alternately bonded to form a first composite large substrate 21 ′. The width Z of the first composite large substrate 21 ′ in the bonded direction is, for example, 8 mm.
As the bonding method, an adhesive may be used, or an optical contact may be used.

  In step S4, as shown in FIG. 7, the wavelength conversion crystal large substrate 32 is cut with a dicing apparatus for each predetermined action length L in the polarization inversion direction Dr (= optical axis direction), and the first composite substrate as shown in FIG. A plurality of 21 are obtained. C 'is a cutting line. The action length L is, for example, 2 mm.

  In step S5, optical polishing is performed on two surfaces of the first composite substrate 21 facing the polarization inversion direction Dr, and an HR film for the fundamental wave to be used is formed on one surface. Further, a groove group 2g in the direction perpendicular to the polarization reversal direction Dr and the polarization direction Dp is formed on the other surface by using an ion milling device, and the first composite substrate 21 ″ (with grooves) as shown in FIG. Then, the process proceeds to step S11.

On the other hand, in step S8, a large laser crystal substrate having a thickness h between two surfaces perpendicular to the optical axis is formed. The thickness h is 1 mm, for example.
In step S9, two surfaces perpendicular to the optical axis of the laser crystal large substrate are optically polished, and an HR film for the fundamental wave to be used is formed on one surface. Further, a groove group 1g corresponding to the groove group 2g of the first composite substrate 21 ″ is engraved on the other surface using an ion milling device.
In step S10, the large laser crystal substrate is cut to a size matching the length G and width Z of the first composite substrate 21 ″ to obtain the laser crystal substrate 11 as shown in FIG. 10. Then, the process proceeds to step S11.

  In step S11, as shown in FIG. 11, the surface on which the groove group 2g of the first composite substrate 21 ″ is formed and the surface on which the groove group 1g of the laser crystal substrate 11 is formed are bonded together by the adhesive 4, and the second composite substrate 22 is created.

  In step S12, the second composite substrate 22 is cut along the cutting line C as shown in FIG. 12, and a plurality of optical elements 10 as shown in FIG. 1 are obtained simultaneously.

According to the first embodiment, the groove group 1g, 2g provided on the bonding surface of the laser crystal 1 and the wavelength conversion crystal 2 can reduce the reflectance with respect to the light in the desired polarization direction, and thus the desired polarization direction. For this light, a composite resonator is not formed, and laser oscillation becomes stable. Even when the laser crystal 1 does not have polarization dependency, the polarization is determined and the laser oscillation becomes stable.
Further, the groove groups 1g and 2g are easier to manufacture than other structures (for example, a moth-eye structure) for realizing a structure having structural birefringence.
Furthermore, since the anchor effect is obtained when the adhesive 4 enters the groove groups 1g and 2g and can be firmly integrated, peeling occurs when the second composite substrate 22 is cut to obtain the plurality of optical elements 10. It becomes difficult and yield can be improved.

  Only one of the groove groups 1g and 2g may be formed.

  The dummy substrate 3 may be bonded to only one side of the wavelength conversion crystal 2.

  After the laser crystal 1, the wavelength conversion crystal 2 and the dummy material 3 are bonded together, the HR film may be formed.

  The optical element and the optical element manufacturing method of the present invention can be used for, for example, a semiconductor-excited solid-state laser using SHG wavelength conversion technology.

1 is a perspective view showing an optical element according to Example 1. FIG. 1 is an exploded perspective view showing an optical element according to Example 1. FIG. FIG. 3 is a flowchart showing a manufacturing procedure of the optical element according to Example 1. It is a perspective view which shows a wavelength conversion crystal large substrate. It is a perspective view which shows a dummy material large board | substrate. It is a perspective view which shows a 1st composite large board | substrate. It is a perspective view which shows the cutting | disconnection of a 1st composite large board | substrate. It is a perspective view which shows a 1st composite substrate. It is a perspective view which shows the 1st composite substrate which engraved the groove group. It is a perspective view which shows the laser crystal substrate which engraved the groove group. It is a perspective view which shows a 2nd composite substrate. It is a perspective view which shows the cutting | disconnection of a 2nd composite substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser crystal 1g Groove group 2 Wavelength conversion crystal 2g Groove group 3 Dummy material 4 Adhesive 10 Optical element 11 Laser crystal substrate 12 Wavelength conversion crystal substrate 13 Dummy material large substrate 21 1st composite substrate 21 '1st composite large substrate 22 1st 2 Composite substrate 32 Wavelength conversion crystal large substrate C, C 'cutting line

Claims (3)

In the optical element (10) in which the wavelength conversion crystal (2) is bonded to the laser crystal (1), structural birefringence is applied to at least one bonded surface of the laser crystal (1) and the wavelength conversion crystal (2). An optical element (10), characterized in that the structure (1g, 2g) is provided. 2. The optical element (10) according to claim 1, wherein the structure (1g, 2g) having structural birefringence is for light polarized in a desired polarization direction with respect to a fundamental wave to be oscillated by the laser crystal (1). An optical element (10), wherein the optical element (10) is a groove group (1g, 2g) formed so that a reflectance is smaller than a reflectance with respect to light polarized in a direction orthogonal to the desired polarization direction. Plate-shaped on at least one surface defined by the optical axis direction side and the width direction side of the wavelength conversion crystal large substrate (32), which is a plate-like body having an optical axis direction side, a width direction side, and a thickness direction side. A large dummy substrate (13) is attached to form a first composite large substrate (21 ′), and the side of the first composite large substrate (21 ′) in the optical axis direction is cut by an action length (L). A plurality of first composite substrates are formed, and a laser light incident surface and a plate-like body defined by the width direction side and the thickness direction side of the first composite substrate, one surface of which is a laser light emission surface. A method of manufacturing an optical element, wherein the laser crystal substrate is bonded to the laser light emitting surface to form a second composite substrate, and the second composite substrate is cut to obtain a plurality of optical elements (10). Before laminating the composite substrate and the laser crystal substrate, the first composite substrate and the laser crystal The reflectance for light polarized in a desired polarization direction with respect to the fundamental wave to be laser-oscillated by the laser crystal is smaller than the reflectance for light polarized in a direction orthogonal to the desired polarization direction on at least one bonding surface of the plate. A groove group (1g, 2g) to be made is formed, and the first composite substrate and the laser crystal substrate are bonded with an adhesive (4).

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