JP2005266703A - Wavelength conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make production stages efficient by preventing a variation in refractive index of a QPM element with temperature, instability of the output of an optical resonator, peeling of the QPM element from a holder, and characteristic deterioration. <P>SOLUTION: A polarization inversion type nonlinear optical element uses lithium tantalate crystal with magnesium-oxide doped stoichiometric composition after polarization inversion, and is bonded to an SL holder 21 using lithium tantalate crystal (SLT) with a stoichiometric composition very similar in coefficient of linear expansion to the converting SL element with ultraviolet-ray setting resin 22. This structure prevents the QPM element from deforming owing to temperature variation and the refractive index does not vary, so the output is stabilized. Further, neither peeling of the converting SL element 20 from the SL holder 21 due to strain nor characteristic deterioration is caused. Further, an efficient production stage is enabled that dicing is carried out after the holder material is bonded to a QPM element material wafer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laser diode-pumped solid-state laser device that generates harmonic light from fundamental light using a wavelength conversion element and extracts the harmonic light to the outside. Hereinafter, the laser diode pumped solid-state laser device is referred to as a wavelength converter.

  Conventionally, a quasi-phase-matching wavelength conversion element (hereinafter referred to as a QPM element) used in a wavelength conversion device has a thickness of 0.3 to 0.5 mm in order to obtain uniform polarization inversion. When placed in the optical resonator provided inside the wavelength conversion device, it is bonded to a thick holder having the same area as the QPM element for easy handling. . A metal is generally used as the material of the holder. Hereinafter, the structure and operation of an optical resonator and a conventional QPM element disposed in the optical resonator will be described with reference to FIGS. 3A, 3B, and 3C (see, for example, Patent Document 1). .

  FIG. 3A shows a schematic structure of the optical resonator. In the drawing, 1 is a laser diode that generates excitation light, 2 is a lens that collects the excitation light, and 3 is a laser medium that emits fundamental light including harmonic light by the excitation light. Reference numeral 4 denotes a conversion element for generating second harmonic light having a wavelength of ½ from the fundamental light, and the QPM element is used. Reference numeral 6 denotes an output mirror that reflects part of the light from the conversion element 4 (fundamental wave light) in the direction of the conversion element 4 and transmits part of the light (second harmonic light) outward.

  The laser diode 1 is fixed to the laser base 7 and the lens 2 is fixed to the lens base 8. The conversion element 4 is bonded to the holder 5 to constitute a polarization inversion type nonlinear optical element. Hereinafter, the polarization inversion type nonlinear optical element is referred to as a QPM block.

  The laser medium 3, the holder 5, and the output mirror 6 are fixed on the holder base 9. The holder base 9 is fixed on the Peltier element 10, and the Peltier element 10 is fixed on the base 11 together with the laser base 7. The Peltier element 10 is inserted for cooling the generated heat accompanying the operation of the apparatus. On the left surface of the laser medium 3, that is, the surface on which the excitation light from the lens 2 is incident, a reflection layer (not shown) that efficiently transmits the excitation light and reflects the fundamental wave light and the second harmonic light with high reflectivity. Is formed.

  The excitation light generated by the laser diode 1 is converged by the lens 2 and irradiates the laser medium 3. The laser medium 3 is excited by excitation light to stimulate and emit laser light including fundamental wave light. The stimulated emission laser light is incident on the conversion element 4, and the conversion element 4 generates second harmonic light (hereinafter referred to as harmonic light) from the fundamental light. The harmonic light passes through the output mirror 6 and is output outward to the right, but the fundamental light is reflected leftward by the output mirror 6 and further reflected rightward by the laser medium 3. The output mirror 6 constitutes an optical resonator, and the fundamental wave light is amplified and oscillated during this period, and is continuously converted into harmonic light by the conversion element 4. The harmonic light passes through the output mirror 6 and is extracted outward. FIG. 3B shows a QPM block. As described above, the material of the holder 5 is conventionally a metal. An adhesive is usually used for fixing.

JP 2003-304019 A (first page, FIG. 1)

The structure of the conventional QPM block is as described above. In this structure, the performance of the optical resonator changes due to temperature change, and the life of the QPM block is shortened. Furthermore, the processing method is also limited. That is, the material of the holder 5 is, for example, aluminum having a linear expansion coefficient of 2.31 × 10 ⁻⁵ , and the material of the conversion element 4 is, for example, 1.61 × 10 ^{−5 in the} X-axis direction, Y Since it is a lithium tantalate crystal having a numerical value of 1.54 × 10 ^{−5 in} the axial direction and 0.22 × 10 ^{−5 in} the Z-axis direction, the conversion element 4 and the holder 5 have different linear expansion coefficients. When the temperature when the block is used is different from the temperature when the conversion element 4 is fixed to the holder 5, the fixing interface between the conversion element 4 and the holder 5 receives a force similar to that of the bimetal, and is shown in FIG. Thus, the QPM block is deformed. If the deformation shown in FIG. 3C occurs when the temperature is higher than that at the time of fixing, the deformation in the opposite direction occurs when the temperature is low. When the deformation occurs, even if the deformation is extremely small, the refractive index of the conversion element 4 changes and the output to be taken out becomes unstable. Moreover, peeling of the conversion element 4 from the holder 5 and deterioration of the characteristics of the conversion element 4 occur due to distortion. Even if an alloy having the same linear expansion coefficient as that of the conversion element 4 is manufactured and used in the holder 5 at a certain temperature, an alloy that conforms to the anisotropy of the thermal expansion coefficient in each crystal axis direction of the conversion element 4 is manufactured. It is difficult. In general, the numerical value of the thermal expansion coefficient of a metal increases as the temperature rises, but it is impossible to match the temperature dependency tendency with the temperature dependency tendency of the conversion element 4 in each crystal axis direction.

  Further, the conversion element 4 and the holder 5 are different in hardness. The Mohs hardness of aluminum used for the holder 5 is 2.9, for example, while the Mohs hardness of the lithium tantalate crystal used for the conversion element 4 is 5.5 to 6. For this reason, it is difficult in terms of production technology to perform end face polishing in a state where the conversion element 4 and the holder 5 are fixed, and the holder material is first bonded to the QPM element material wafer which is the initial state of the conversion element 4. Efficient production processes such as dicing (chip formation) and end face polishing cannot be performed. An object of this invention is to provide the wavelength conversion element and wavelength converter which solve such a problem.

  In order to solve the above problems, the wavelength conversion device provided by the present invention uses a material having a linear expansion coefficient and hardness equal to or very close to those of the QPM element as a holder.

  In the wavelength conversion device of the present invention, since the linear expansion coefficient of the holder is the same as or very close to the linear expansion coefficient of the QPM element, the QPM element is hardly deformed or distorted even if the temperature of the QPM element changes, and its refractive index. Since does not change, the output becomes stable. Further, peeling of the QPM element from the holder and deterioration of the characteristics of the QPM element due to strain do not occur. Furthermore, since the holder uses a material whose hardness is the same as or very close to that of the QPM element, the holder material is first bonded to the QPM element material wafer, and then dicing (chip formation) is performed, and then end face polishing is performed efficiently. It becomes possible to take a simple production process.

  A material having the same or very similar linear expansion coefficient as that of the QPM element is used for the holder.

  FIGS. 1A and 1B show an embodiment of a QPM block according to the present invention. FIG. 1A shows a top view and FIG. 1B shows a side view. In the figure, the conversion SL element 20 is a QPM element comprising a lithium tantalate crystal (hereinafter referred to as MgO-SLT) having a magnesium oxide-doped stoichiometric composition (stoichiometric composition) subjected to polarization reversal. It is adhered to an SL holder 21 having a lithium tantalate crystal (hereinafter referred to as SLT) having a stoichiometric composition (stoichiometric composition) to constitute a QPM block. In bonding, the crystal axis directions of the crystals of the conversion SL element 20 and the SL holder 21 are the same as the three-dimensional directions (X-axis, Y-axis, and Z-axis directions in the figure).

  The present invention is not limited to the above-described embodiments, and various modified embodiments can be given. For example, instead of the MgO-SLT, the material of the conversion SL element 20 is a magnesium oxide-doped lithium tantalate crystal (hereinafter referred to as MgO-LT) that has undergone polarization inversion, or a magnesium oxide-doped lithium niobate crystal that has undergone polarization inversion. (Hereinafter referred to as MgO-LN), magnesium oxide-doped lithium niobate crystal (hereinafter referred to as MgO-SLN) having a stoichiometric composition (stoichiometric composition) subjected to polarization inversion can be used.

  In place of the SLT, the SL holder 21 is made of lithium tantalate crystal (hereinafter LT), stoichiometric composition (stoichiometric composition) lithium niobate crystal (hereinafter SLN), lithium niobate crystal (hereinafter LN). ), MgO-SLT, MgO-LT, MgO-SLN, MgO-LN, and the like can be used. Further, as shown in FIG. 2B, due to the structure in which the SL holder 21 is bonded to both surfaces of the conversion SL element 20, the force acting on the interface between the SL holder 21 and the conversion SL element 20 due to temperature change is the both surfaces of the conversion SL element 20. Since both are in the same direction, the bending force is eliminated and the deformation is in principle only extended or shortened. Therefore, the structure of FIG. 2B further reduces the deformation of the QPM block with respect to the temperature change as compared with the structure of FIG.

  Furthermore, in the present invention, the hardness of the conversion SL element 20 and the SL holder 21 is the same or almost the same, so that it is possible in production technology to perform end face polishing with the conversion SL element 20 and the SL holder 21 fixed. First, the holder material is first bonded to the QPM element material wafer, which is the initial state of the conversion SL element 20, and then dicing (chip formation) is performed, and end face polishing, antireflection coating, and dicing are performed. After that, a QPM element can be manufactured. In the embodiment shown in FIGS. 1A and 1B, the crystal axis directions are matched at the time of bonding, but the thermal strain of the QPM block is less than that of the conventional structure even if the matching is not performed completely. It is natural that it will decrease dramatically. The present invention includes all of these.

(A) is a top view of the Example of this invention, (b) is a side view. (A) is a side view of the Example of this invention, (b) is a side view of a modification Example. (A) is a schematic structure diagram of a conventional optical resonator, and (b) is a side view of a conventional QPM block.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser diode 2 Lens 3 Laser medium 4 Conversion element 5 Holder 6 Output mirror 7 Laser stand 8 Lens stand 9 Holder stand 10 Peltier element 11 Base 20 Conversion SL element 21 SL holder 22 UV curable resin

Claims (4)

  A quasi-phase-matched wavelength conversion element comprising a domain-inverted magnesium oxide-doped lithium tantalate crystal or magnesium oxide-doped lithium niobate crystal is converted into a lithium tantalate crystal, lithium niobate crystal, or magnesium oxide-doped lithium tantalate. A domain-inverted nonlinear optical element comprising a crystal or a magnesium-doped lithium niobate crystal bonded as a holder.   A lithium tantalate crystal, a lithium niobate crystal, a magnesium oxide-doped lithium tantalate crystal, or a magnesium oxide-doped lithium niobate crystal is bonded to both sides of the quasi-phase matching wavelength conversion element according to claim 1. A domain-inverted nonlinear optical element.   A quasi-phase-matched wavelength conversion element material comprising a magnesium oxide-doped lithium tantalate crystal or magnesium oxide-doped lithium niobate crystal having a domain-inverted state, doped with lithium tantalate crystal, lithium niobate crystal or magnesium oxide It is bonded to a wafer-shaped holder material made of lithium tantalate crystal or magnesium oxide doped lithium niobate crystal, and then it is fabricated through the steps of dicing → end face polishing → antireflection coating → dicing Type nonlinear optical element.   In a laser diode-pumped solid-state laser device that pumps a solid-state laser medium with output light from a laser diode, a lithium niobate crystal, a lithium tantalate crystal, or a magnesium oxide-doped tantalum is placed inside an optical resonator including the solid-state laser medium A polarization-reversed nonlinear optical element bonded to a quasi-phase matched wavelength conversion element with a lithium oxide crystal or magnesium oxide-doped lithium niobate crystal as a holder is placed, and the fundamental wave stimulated and emitted from the solid-state laser medium is polarized. A laser diode-excited solid-state laser device, wherein the wavelength is converted into a second harmonic by a non-linear optical element, and the second harmonic is output to the outside through an output mirror.

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