JPH05173215A - Manufacture of optical second harmonic generating device - Google Patents

Abstract

PURPOSE:To obtain a stable and compact device necessary for an optical recording device by securing the temperature stability of the laser crystal and resonator structure, and providing the fabrication method in a secure and simplified manner. CONSTITUTION:A heat radiation means is provided by brazing the laser crystal 3 to a laser crystal holder 6 comprised of copper. An angular cutting is applied to both holders 6, 7 of the laser crystal 3 and the nonlinear optical crystal 5 and a groove machining is applied to a cylindrical holder fixing body 8 respectively, to suppress the rotation of both the holders. The nonlinear optical crystal holder 7 is of double construction, and a screw is provided on the outer circumferential holder to adjust the inner circumferential holder. A spherical machining is applied to the part where an output mirror holder 5 is brought into contact with the cylindrical holder fixing body 8, providing no aperture between the output mirror holder and the holder fixing body 8 even when adjustment is made by inclining the output mirror relative to the optical axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of optoelectronics, particularly SHG (Second Harmonic) used for optical recording and the like.
Generation) device.

[0002]

2. Description of the Related Art In order to easily process a large amount of information with a small device, it is necessary to increase the recording density of a recording device. In the case of an optical disc device, a technique for shortening the wavelength of a light source is required to increase the recording density. This is because the recording areal density of the optical disk device depends on the wavelength of the light source.
For example, if the wavelength of the light source is halved, the recording density can be increased by 4 times at once. The SHG technique is a technique for converting the wavelength of a laser beam (hereinafter simply referred to as a fundamental wave) incident on a nonlinear optical element into 1/2, and is therefore a technique expected for optical disk devices in the future.

In order to promote the practical use of this SHG device, it was necessary to reduce the power consumption to the level of the LD currently used as the light source of the optical disk device and to simplify the assembling method. A conventional technique for the above two problems is shown below.

First, efficiency will be described. It is generally known that the optical second harmonic output (hereinafter simply referred to as SH output) is proportional to the square of the power of the fundamental wave. Nd: YAG (Nd-doped yttrium aluminum garnet), which has been used as a conventional laser crystal in an SHG device in which a nonlinear optical crystal is placed inside a resonator including a laser crystal and whose oscillation is the fundamental wave of a solid-state laser, replaces it. With smaller oscillation threshold and higher efficiency YVO (Nd: YV
O ₄ and neodymium added yttrium vanadate) have begun to be used. However, since the YVO crystal has good absorption of the excitation input, the phenomenon that the crystal temperature rises up to about 100 ° C was observed. Furthermore, the phenomenon that the power of the fundamental wave decreases due to the temperature rise of the crystal has been reported (Tetsuo Kojima, Takatomo Sasaki et al. "Semiconductor laser pumped Nd: YVO ₄ microchip laser" Applied Physics Vol. 59, No. 9, 1235. -1238, (1990)). In the above-mentioned document, two types of holders having different thermal conductivities, that is, copper and acrylic are used to compare the fundamental wave power, and when the temperature rise of the crystal can be further reduced, that is, a copper holder having a large thermal conductivity is used. It was reported that the power of the fundamental wave was higher when it was present.

When the laser crystal exhibits anisotropy in the plane of the optical axis, the effective value of the nonlinear optical constant d differs depending on the angle formed by the crystal axes of the laser crystal and the nonlinear optical crystal. Therefore, in order to maximize the SH output, it is necessary to control the angle formed by both crystal axes. Second, the simplification of assembly will be described. Since it is easy to secure the optical axis when assembling an element composed of a plurality of optical components, a method of attaching each optical component to a cylindrical holder and inserting it into various circular optical component holders has been conventionally used in many cases. An example is an optical isolator. Further, when a condensing optical system is provided in the subsequent stage of the SHG device and is condensed to a submicron beam diameter and applied to an optical disc device or the like, the SHG device has means for adjusting the transverse mode to the single mode easily and surely. There is a need. Since the SHG device has recently been commercialized, detailed information on the assembling method is not disclosed and there are many unclear points about the conventional technology.

[0006]

The first point of high efficiency will be described. In mounting, for example, when fixing the laser crystal semi-permanently to a copper holder, the thermal conductivity is not much different from that of acrylic even if an adhesive having relatively good thermal conductivity is used,
There was a problem that the thermal resistance with the copper holder increased and the effect of the copper holder could not be fully utilized.

Further, heat is also transferred from the copper holder to various optical component holders and holder fixed bodies which form the resonator, and the resonator length becomes thermally unstable, which similarly causes a problem that SH output decreases.

In many adhesives, there is a possibility that the resonator structure may be deformed due to softening of the adhesive due to heat conduction and moisture absorption from the laser crystal, and the outgas of the adhesive due to aging may cause contamination of the crystal and corrosion of the holder. There is a problem such as having a possibility of causing.

When inserting a nonlinear optical crystal holder into a cylindrical holder fixed body in which it is easy to secure an optical axis, the angle formed by the crystal axes of the laser crystal and the nonlinear optical crystal is rotated in the holder fixed body. There has been a problem that the SH output is reduced by deviating from the angle at which the effective nonlinear optical constant is maximized.

The point of simplifying the second assembling method will be described.

When controlling the transverse mode in the SHG device, for example, when the optical surface of the laser crystal is used as the reference surface, it is necessary to adjust the nonlinear optical crystal and the output mirror by inclining with respect to the optical axis. Therefore, there is a problem in that a fixed state becomes unstable due to a gap between the holder fixed body and the nonlinear optical crystal holder or the output mirror holder.

[0012]

[Means for Solving the Problems] First, the point of high efficiency will be described. In the present invention, the thermal resistance of the laser crystal and the laser crystal holder is reduced by brazing the laser crystal holder and the laser crystal. Moreover, since brazing is adopted, there is no possibility of generating corrosive gas, and highly reliable joining is possible.

Next, the heat radiation path was improved. The SHG device needs to have some attachment means when it is applied to a light source of an optical disk. Therefore, heat was radiated from the contact surface with the laser crystal holder as the mounting portion. By making the thermal conductivity of each holder and holder fixed body smaller than that of the metal to which it is attached, the heat conduction to various optical component holders and holder fixed bodies was reduced.

Further, by using Invar material (Ni; 36%, Fe; 64%) for various holders and holder fixed bodies, the coefficient of thermal expansion is remarkably reduced, and the reliability of the resonator structure due to thermal fluctuation is enhanced. I was able to do it. Furthermore, by assembling the entire SHG device such as the various holders and the holder fixing body on the surface of the electronic cooling element on the cooling side, it was possible to maintain the entire device at a constant temperature and remove the factor of thermal fluctuation.

Next, a groove structure is adopted so that the crystal axis does not rotate when the circular laser crystal holder or the nonlinear optical crystal holder is inserted into the cylindrical holder fixed body.

Second, the simplification of the assembling method will be described.

The nonlinear optical crystal holder has a first cylindrical holder for holding the nonlinear optical crystal and a double structure for holding the first holder and inserting it in a second cylindrical holder for adjusting the angle. did. The outer diameter of the first holder and the second
There is enough clearance between the inner diameters of the holders to tilt the first holder to adjust the transverse mode,
It can be adjusted by a total of 6 screws formed in the second holder in three rotation directions. The output mirror holder has a spherical surface processed at the contact portion with the cylindrical holder. Therefore, even if the output mirror is tilted with respect to the optical axis, the cylindrical holder and the output mirror holder are always in stable circular contact with the cylindrical holder. Further, the adjustment is performed by adjusting the triaxial screws formed on both the holders.

[0018]

According to the present invention, the thermal resistance of the laser crystal and the holder can be reduced, and the temperature rise of the laser crystal and the reduction of SH output due to the shift of the crystal axes of the laser crystal and the nonlinear optical crystal can be avoided. Also, by brazing, high reliability in the fixed state can be secured as compared with the adhesive. Furthermore, by adjusting the structure of the nonlinear optical crystal holder and the output mirror holder, the lateral mode of SH output can be easily adjusted.

[0019]

【Example】

(Embodiment 1) FIG. 1 is a diagram for explaining one embodiment of the present invention. In FIG. 1, excitation light emitted from a semiconductor laser (hereinafter referred to as LD) 1 is focused on a laser crystal 3 by a focusing optical system 2. The excited laser crystal 3 oscillates a fundamental wave on the incident surface of the laser crystal 3 and the concave surface portion of the output mirror 4. The fundamental wave passing through the nonlinear optical crystal 5 is S
It is converted into H output and emitted from the output mirror 4.

FIG. 2 is a diagram for explaining a method of fixing the laser crystal to the laser crystal holder. Laser crystal 3
In the above, the excitation light incident side optical surface is subjected to a solder undercoat treatment, and the laser crystal holder 6 plated with gold is soldered without using flux. The thermal conductivity of solder is 2 / of copper
As high as about 3, no temperature rise of the laser crystal 3 was observed,
No reduction in SH output was observed. Here, silver solder or the like may be used instead of solder.

FIG. 3 is a diagram for explaining the structure and mounting method of the laser crystal holder 6. As shown in FIG. 3, a laser crystal holder 6 made of copper having a circular hole in the center of the optical axis is fitted and fixed in a cylindrical holder fixing body 8 having a notch structure. The mounting surface provided on the laser crystal holder 6 is mounted on a reference surface such as an optical head housing. The aluminum that composes the optical head housing is made of a holder holder 8
Since the thermal conductivity of the laser crystal 3 is remarkably higher than that of the Invar material used for the components forming the resonator, the heat of the laser crystal 3 is radiated to the optical head casing. Therefore, the change in the resonator length due to heat can be greatly reduced, and a stable SH output can be obtained.

FIG. 4 is a diagram for explaining a processing method for controlling the angle formed by the crystal axes of the laser crystal and the nonlinear optical crystal. In FIG. 4, the nonlinear optical crystal holder 7 is mountain-cut and the cylindrical holder fixing body 8 is grooved. The angle between the crystal axis of the nonlinear optical crystal 5 and the groove notch formed in the holder fixed body and the straight line connecting the optical axis centers is set to have a constant value α. The laser crystal holder 6 is inserted into the notch provided in the holder fixing body 8. At this time, the angle formed by the crystal axis of the laser crystal 3 and the groove cut processing of the holder fixing body 8 and the straight line connecting the optical axis centers is set to have a constant value β. As a result, the angle formed by the crystal axes of the laser crystal and the nonlinear optical crystal 5 takes a set value (α-β), and the maximum SH output 8 is obtained without changing.

FIG. 5 is a diagram for explaining the structure of the nonlinear optical crystal holder 7. The nonlinear optical crystal holder 7 has a double structure, and has a first cylindrical holder for holding the nonlinear optical crystal 5 inside and a second holder for adjusting the angle of the first holder outside. An ellipse or a hole similar to an ellipse is formed in the second holder in three axes of rotation, and the angle of the first holder is adjusted by adjusting a screw from the outside. That is, the angle is adjusted by rotating the screw and pushing or pulling the first holder to adjust the lateral mode of SH output. This screw adjustment can be performed using a hole (not shown) of the crystal holder 7 even after inserting the second holder into the crystal holder 7. There is no gap between the second holder and the holder fixing body 8 which is equal to or more than the gap.

FIG. 6 is a diagram for explaining the structure of the output mirror holder. The output mirror holder 5 has a spherical surface processed in a portion in contact with the cylindrical holder fixing body 8. Even if the output mirror 4 is tilted with respect to the optical axis for adjustment, a gap is left between the output mirror holder 5 and the holder fixing body 8. The structure does not occur. The angle adjustment can be performed by using triaxial screws provided on the output mirror 4 and the holder fixing body 8.

When the SHG device is incorporated into an optical disk device, the heat dissipation of the electronic cooling element used for controlling the wavelength of the LD is achieved by bringing the heat dissipation plate into thermal contact with the optical head casing to secure the heat dissipation path.

(Embodiment 2) FIG. 7 is a diagram for explaining one embodiment of the present invention. A plate-shaped holder fixing body 8 is arranged on the surface of the electronic cooling element on the cooling side, and an SHG device such as a resonator structure including the LD 1, the condensing optical system 2 and the laser crystal 3 on the surface of the holder fixing body 8. Can be arranged to control the wavelength of the LD and the resonator length at the same time.

[0027]

According to the present invention, it is possible to obtain an SHG device which is thermally stable and has a high output and a simple assembling method, and an optical recording device to which the SHG device is applied.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention.

FIG. 2 is a diagram for explaining a method of fixing a laser crystal to a laser crystal holder.

FIG. 3 is a diagram for explaining a structure and a mounting method of a laser crystal holder.

FIG. 4 is a diagram for explaining a processing method for controlling the angle formed by the crystal axes of the laser crystal and the nonlinear optical crystal.

FIG. 5 is a diagram for explaining the structure of a nonlinear optical crystal holder.

FIG. 6 is a diagram for explaining the structure of an output mirror holder.

FIG. 7 is a diagram for explaining an example of the present invention.

[Explanation of symbols]

1; LD, 2; focusing optical system, 3; laser crystal, 4; output mirror, 5; nonlinear optical crystal, 6; laser crystal holder,
7: Non-linear optical crystal holder, 8: Holder fixed body.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Koji Muraoka 1-280, Higashi Koikeku, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor Tetsuo Ando 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central research institute

Claims (12)

[Claims] 1. A laser crystal, a resonator structure including a nonlinear optical crystal, optical components such as an output mirror, a holder for fixing the laser crystal, and various optical components for fixing other optical components. In a SHG device including a holder, a laser crystal holder, a holder fixing body that fixes the various holders to an outer frame of the SHG device, and a means for exciting the laser crystal, the laser crystal is used as the laser crystal holder. A method for manufacturing an SHG device, which is characterized by being attached. 2. The method of manufacturing an SHG device according to claim 1, wherein a metallized film is formed on one of the two optical surfaces of the laser crystal on the excitation light incident side optical surface. 3. The method for manufacturing an SHG device according to claim 1, wherein the laser crystal holder has a heat radiating means other than the various optical component holders and the holder fixing body. 4. The SH according to claim 1, wherein the laser crystal is Nd: YVO _4.
G device manufacturing method. 5. A laser crystal holder or various optical component holders for fixing an optical material exhibiting anisotropy and an isotropic optical material in a plane perpendicular to the optical axis, and a hollow cylinder as a holder fixing body. A method for manufacturing an SHG device, wherein the various optical component holders and the holder fixing body are made of Invar material. 6. A method of manufacturing an SHG device, characterized in that a grooved structure or a mountain cutting structure is formed in an optical component holder for fixing an anisotropic material and a hollow cylindrical holder fixing body. 7. A double structure comprising a non-linear optical crystal holder and a cylindrical part for holding the non-linear optical crystal, and a hollow cylindrical part for holding the non-linear optical crystal and for adjusting the angle. A method of manufacturing an SHG device, comprising: 8. The method of manufacturing an SHG device according to claim 7, wherein the nonlinear optical crystal holder has an adjusting mechanism of at least three axes. 9. A method of manufacturing an SHG device, characterized in that a holder for fixing an output mirror is subjected to spherical processing. 10. A semiconductor laser and the LD as an excitation light source.
In an SHG device comprising an electronic cooling element for controlling the temperature of a laser, a laser crystal, various optical parts, various holders for holding the laser crystal and various optical parts, and a holder fixing body holding the various holders, the holder fixing body is A method for manufacturing an SHG device, comprising fixing to the electronic cooling element. 11. An optical disk device using the SHG device according to any one of claims 1 to 10 as a light source of an optical head. 12. An S having an electronic cooling element for controlling the temperature of the LD and a radiator plate for radiating heat from the electronic cooling element.
An optical disk device having an HG device and a housing for fixing the SHG device, wherein the heat dissipation plate is fixed to the housing.