JPH04320220A - Second higher harmonic generation device - Google Patents

Abstract

PURPOSE:To save expensive nonlinear optical crystal, to eliminate the need for curved surface polishing, and to reduce the manufacture cost of the 2nd higher harmonic generation device which has a monolithic resonator. CONSTITUTION:Both the end surfaces of a nonlinear optical crystal 19 are made plane and glass blocks 21 and 23 are joined with both the end surfaces. The end surfaces of the glass blocks 21 and 23 are formed into curved surface mirrors 25 and 27 to constitute the monolithic resonator 17. A fundamental wave 35 emitted by an LD 13 passes through lenses 15 and 16 and is made incident on the monolithic resonator 17, and the wave resonates in a ring shape between the curved surface mirrors 25 and 27 and a plane mirror 29 and is converted into a 2nd higher harmonic 37, which is outputted from the curved surface mirror 27. The curved surface mirrors 25 and 27 are formed of the glass blocks 21 and 23, so a nonlinear optical crystal 19 is made small and the need for the curved surface polishing is eliminated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a second harmonic generator that converts a fundamental wave emitted from a laser light source into a second harmonic within a monolithic resonator.

0002

2. Description of the Related Art In recent years, research has been carried out to pass a fundamental wave emitted from a semiconductor laser or the like through a nonlinear optical material to obtain a second harmonic wave having half the wavelength. In order to efficiently generate the second harmonic, various conditions such as phase matching are required, but in general, the stronger the fundamental wave is, the more the second harmonic is generated.
Harmonics can be generated efficiently. For this reason,
Various devices have been proposed that efficiently generate second harmonics by constructing a resonator using mirrors, arranging nonlinear optical materials inside the resonator, and confining the fundamental wave inside the resonator and amplifying it. has been done.

Recently, in order to reduce the size of the device and improve the conversion efficiency to second harmonics, from an external resonator type that uses individual mirrors to a device that resonates the fundamental wave inside a nonlinear optical material. The mainstream is shifting to a monolithic type.

FIG. 6 shows an example of a second harmonic generator using such a monolithic resonator.

The second harmonic generator 1 is composed of a semiconductor laser (hereinafter referred to as LD) 2, a collimator lens 3, a mode matching lens 10, and a nonlinear optical material 4 made of KNbO3 crystal or the like. LD2 is
For example, a fundamental wave 7 having a wavelength of 860 nm is emitted.

The two surfaces of the nonlinear optical material 4, on the left and right sides in the figure, are polished into curved (usually spherical) shapes. The surface on the left side of the figure serves as an incident surface for the fundamental wave 7, and a curved mirror 5 is formed on this surface to partially transmit the fundamental wave 7 and reflect the second harmonic 8. In addition, the surface on the right side of the figure forms the output surface of the second harmonic wave 8, and the fundamental wave 7 is reflected on this surface.
A curved mirror 6 that transmits the second harmonic 8 is formed. Furthermore, the bottom surface of the nonlinear optical material 4 in the figure has a fundamental wave 7.
A plane mirror 9 reflects both the second harmonic wave 8 and the second harmonic wave 8.

A fundamental wave 7 having a wavelength of 860 nm emitted from the LD 2 passes through a collimating lens 3 and a mode matching lens 10, and enters a curved mirror 5 made of a nonlinear optical material 4. This fundamental wave 7 is transmitted to the curved mirror 6 and the flat mirror 9.
It is reflected within a ring resonator constituted by a curved mirror 5, resonates, and is amplified. When the fundamental wave 7 passes through the nonlinear optical material 4 in a predetermined direction, a part of it is converted into a second harmonic wave 8 having a wavelength of 430 nm, which is transmitted through the curved mirror 6 and output. If such a monolithic resonator is used, conversion to the second harmonic can be performed efficiently, and the second harmonic generator can be downsized.

[0008]

[Problems to be Solved by the Invention] However, in conventional monolithic resonators, the end face of a nonlinear optical material is polished into a spherical shape with a radius of curvature of several mm, and a dielectric material or the like is deposited on this face to form a mirror. It had to be formed, and productivity was poor. Furthermore, since polishing must be performed with high precision, polishing often fails and expensive nonlinear optical materials are wasted. For this reason, the product cost has been high.

Therefore, an object of the present invention is to provide a second harmonic generator having a monolithic resonator that can be manufactured with high productivity and at low cost.

0010

Means for Solving the Problems In order to achieve the above object, the present invention provides a second harmonic generation device having a monolithic resonator using a nonlinear optical material, wherein the monolithic resonator has a flat end face. a nonlinear optical material cut into a shape, and a transparent base material bonded to at least one end face of the nonlinear optical material, and characterized in that at least one outer circumferential surface of the transparent base material forms a curved mirror. shall be.

In a preferred embodiment of the present invention, the transparent substrate is made of glass or plastic. This transparent base material can be formed into a curved surface by polishing the end face of a block formed into an appropriate shape, but it can also be easily formed into a curved shape by injection molding, cast molding, press molding, etc. can.

[0012] The nonlinear optical material and the transparent substrate can be bonded, for example, by adhesion using an optical adhesive. In this case, in order to suppress reflection between the transparent base material and the adhesive, it is preferable to use an adhesive having the same refractive index as the transparent base material. Further, in order to prevent reflection between the nonlinear optical material and the adhesive, it is preferable to provide an antireflection film on the bonding surface of the nonlinear optical material.

Furthermore, the structure of the monolithic resonator may be of various types, such as a triangular ring type or a standing wave type, as shown in the embodiments described later. In these resonators, the transparent base material is arranged at least in a portion constituting the curved mirror.

According to a preferred embodiment of the present invention, the transparent base material is bonded to both end surfaces of the nonlinear optical material, and the respective outer peripheral surfaces constitute curved mirrors on the incident side and the output side. According to another preferred embodiment of the present invention, the transparent base material is bonded to the curved mirror portions on both end faces of the nonlinear optical material and the flat mirror portion between them, and according to this embodiment, the transparent base material The usage amount can be further reduced.

[0015]

[Function] In the present invention, a transparent base material is bonded to the end face of the nonlinear optical material to construct a monolithic resonator, so the amount of nonlinear optical material used can be reduced compared to a construction made of only nonlinear optical material. , production costs can be lowered.

[0016] Furthermore, since the end face of the nonlinear optical material can be cut into a flat surface, operations such as polishing are facilitated. Furthermore, since the transparent base material constituting the curved mirror etc. can be manufactured by injection molding or casting molding of glass, plastic, etc., productivity can be improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a second harmonic generator according to the present invention.

The second harmonic generation device 11 is constructed by sequentially arranging an LD 13 as a laser light source, a collimating lens 15, a mode matching lens 16, and a monolithic resonator 17.

In this embodiment, the LD 13 has a wavelength of 860 nm.
nm, single longitudinal mode, single transverse mode, and emits a fundamental wave 35 with little astigmatism. However, as the laser light source, a solid laser such as YAG, Ti:Al2O3, etc. can also be used.

The collimating lens 15 and the mode matching lens 16 are used to convert the fundamental wave 35 into a predetermined beam and irradiate the monolithic resonator 17 with the same mode. In this example, collimating lens 1
5 is f=4.2mm, mode matching lens 16 is f
= 150mm.

[0021] The monolithic resonator 17 has a size of 3×3 mm.
Nonlinear optical material 1 consisting of a KNbO3 crystal with a size of
9, and glass blocks 21 and 23 with a size of 3 x 2 mm bonded to the left and right end faces in the figure via optical adhesives 31 and 33, respectively. The overall size of the monolithic resonator 17 is 3 mm in length and 7 mm in width.
mm, and the thickness is 3 mm.

In this embodiment, the nonlinear optical material 19 has a rectangular parallelepiped shape, and its entire surface is cut flat. In addition to KNbO3 crystal, as the nonlinear optical material 19,
KTiOPO4, KH2PO4, LiNbO3
Various nonlinear optical crystals and organic nonlinear optical materials can be used.

The glass blocks 21 and 23 have outer surfaces facing the bonding surface with the nonlinear optical material 19 having a radius of curvature of 5 m.
It has a spherical surface of m, and both are made by press working. However, instead of the glass blocks 21 and 23, other transparent substrates such as plastic can also be used.

The optical adhesives 31 and 33 used have the same refractive index as the glass blocks 21 and 23 in order to prevent reflection at the interface with the glass blocks 21 and 23. Further, in order to prevent reflection at the interface with the nonlinear optical material 19, an antireflection film (not shown) is provided on the nonlinear optical material 19.

The surface of the glass block 21 on which the fundamental wave 35 is incident has a reflectance of 92% for the fundamental wave 35 of 860 nm and 99.5% for the second harmonic wave 37 of 430 nm.
A curved mirror 25 having a reflectance of . Further, on the surface of the glass block 23 from which the second harmonic wave 37 is emitted, there is a curved mirror 2 having a reflectance of 99.8% for the fundamental wave 35 and a reflectance of 10% for the second harmonic wave 37.
7 is formed. Furthermore, a plane mirror 29 for total reflection of the fundamental wave 35 and the second harmonic 37 is formed on the lower surface of the nonlinear optical material 19 in the drawing.

Using this second harmonic generator 11, the LD
A fundamental wave 35 with a wavelength of 860 nm is emitted from the resonator 13, and is irradiated onto the curved mirror 25 of the monolithic resonator 17 through the collimating lens 15 and the mode matching lens 16. The fundamental wave 37 enters the monolithic resonator 17 through the curved mirror 25 and is amplified by the triangular ring-shaped resonator composed of the curved mirrors 25 and 27 and the plane mirror 29. When the fundamental wave 37 passes through the nonlinear optical material 19 in a predetermined direction, the second harmonic 37 with a wavelength of 430 nm
This second harmonic wave 37 is emitted from the curved mirror 27 on the output side.

As described above, by constructing the monolithic resonator 19 using the nonlinear optical material 19 and the glass blocks 21 and 23, it is possible to reduce the amount of the nonlinear optical material 19 used and reduce the material cost. . In addition, curved mirrors 25 and 2 are provided on the glass blocks 21 and 23.
7, it is no longer necessary to polish the nonlinear optical material 19 into a curved surface, and processing costs can also be reduced.

FIG. 2 shows another embodiment of the second harmonic generator of the present invention. In the following embodiments, parts that are substantially the same as those in the apparatus of the embodiment shown in FIG.

In this embodiment, a monolithic resonator 39 is composed of a rectangular parallelepiped nonlinear optical material 19 and glass blocks 41, 43, and 45. That is, glass blocks 41 and 43 are bonded to the left and right end surfaces of the nonlinear optical material 19 in the figure via optical adhesives 31 and 33, and the nonlinear optical material 19 and the glass blocks 41 and 4
A glass block 45 is arranged on the lower surface of 3.

The end surfaces of the glass blocks 41 and 45 on the left side in the figure are formed into a spherical shape, and a curved mirror 25 on the incident side of the fundamental wave 35 is formed on this surface. Further, the end surfaces of the glass blocks 43 and 45 on the right side in the figure are also formed in a spherical shape, and a curved mirror 27 on the output side of the second harmonic 37 is formed on this surface.
is formed. Furthermore, the lower surface of the glass block 45 forms a plane mirror 29.

In this second harmonic generator as well, a triangular ring-shaped resonator is constituted by the curved mirrors 25 and 27 and the plane mirror 29, and the fundamental wave 35 incident on the monolithic resonator 39 is transmitted through these mirrors 25. , 27, 29
It is reflected, resonates, and is amplified. When the fundamental wave 35 passes through the nonlinear optical material 19 in a predetermined direction, a part of it is converted into a second harmonic wave 37 and outputted from the curved mirror 27 on the output side.

Since the fundamental wave 35 is converted into a second harmonic wave 37 only when it passes in a predetermined direction within the nonlinear optical material 19, the portion where the fundamental wave 35 passes in a direction other than the above-mentioned direction is converted into a second harmonic wave 37. Therefore, it will not contribute to the occurrence of 37. In this embodiment, the nonlinear optical material 19 is formed by forming the portion that does not contribute to the generation of the second harmonic 37 with a glass block.
It is possible to further reduce costs by making it even smaller.

In the above embodiment, the glass block 41
, 43, and 45 may be integrally molded.

FIGS. 3 and 4 show still another embodiment of the present invention. Note that FIG. 3 is a plan view, and FIG. 4 is a side view.

This embodiment is basically the same as the embodiment shown in FIG. Brewster) angle, and the difference is that an antireflection film is not provided on the end face of the nonlinear optical material 19.

When a KNbO3 single crystal is used as the nonlinear optical material 19, when the wavelength of the LD 13 (not shown) is around 860 nm, the Brewster angle is about 66.3°, so the incident direction of the fundamental wave 35 is Both end faces of the nonlinear optical material 19 are cut with a taper of 23.7° relative to the nonlinear optical material 19. And this nonlinear optical material 1
Glass blocks 21 and 23, whose end surfaces are similarly shaped into a tapered shape, are bonded to both end surfaces of the glass block 9 via an optical adhesive in the same manner as in the previous embodiment.

In this way, by setting both end faces of the nonlinear optical material 19 at the Brewster angle, p of the incident light is
Since the transmission of polarized light is 100%, there is no need to provide an antireflection film on the surface of the nonlinear optical material 19. KNbO3 crystal, etc., which is the material of the nonlinear optical material 19, is
Since it is sensitive to high heat, eliminating the need to provide an antireflection film has the advantage that its quality can be maintained well.

FIG. 5 shows yet another embodiment of the invention.

In this embodiment, the present invention is applied to a standing wave type resonator. As shown in the figure, this standing wave type resonator 53 is constructed by bonding glass blocks 55 and 57 to both end surfaces of a rectangular parallelepiped nonlinear optical material 19 via optical adhesives 31 and 33. ing. The outer end surfaces of the glass blocks 55 and 57 are curved mirrors 25 on the incident side of the fundamental wave 35;
It forms the curved mirror 27 on the output side of the second harmonic 37.

The fundamental wave 35 emitted from the LD 13 (not shown) enters the standing wave type resonator 53 through the curved mirror 25 on the incident side, and the curved mirror 25,
27, it passes through a figure-eight optical path connecting points A, B, C, and D, and is reflected and amplified. When the fundamental wave 35 passes through the nonlinear optical material 19 in a predetermined direction, a part of it is converted into a second harmonic wave 37 and output from the curved mirror 27 on the output side.

[0041]

[Effects of the Invention] As explained above, according to the present invention,
Production costs can be reduced by reducing the amount of nonlinear optical material that constitutes the monolithic resonator. Further, since it is no longer necessary to polish the nonlinear optical material into a curved surface, workability and productivity can be improved.

[Brief explanation of drawings]

FIG. 1 is a side view showing an embodiment of the second harmonic generator of the present invention.

FIG. 2 is a side view showing another embodiment of the second harmonic generator of the present invention.

FIG. 3 is a plan view showing still another embodiment of the second harmonic generator of the present invention.

[Figure 4] Side view of the second harmonic generator

FIG. 5 is a plan view showing still another embodiment of the second harmonic generator of the present invention.

[Fig. 6] Side view showing a conventional second harmonic generator

[Explanation of symbols]

11 Second harmonic generator 13 Semiconductor laser (LD) 15 Collimating lens 16 Mode matching lens 17 Monolithic resonator 19 Nonlinear optical materials 21 Glass block 23 Glass block 25 Curved mirror 27 Curved mirror 29 Plane mirror 35 Fundamental wave 37 Second harmonic 39 Monolithic resonator 45 Glass block 47 Monolithic resonator 53 Monolithic resonator 55 Glass block 57 Glass block

Claims (2)

[Claims] 1. A second harmonic generation device having a monolithic resonator using a nonlinear optical material, wherein the monolithic resonator includes a nonlinear optical material whose end face is cut into a flat surface, and at least one of the nonlinear optical material. 1. A second harmonic generation device comprising: a transparent base material joined to one end surface; at least one outer peripheral surface of the transparent base material forms a curved mirror. 2. The second harmonic generator according to claim 1, wherein the transparent base material is glass or plastic.